Search

Global opioid use and misuse remains high, despite efforts to decrease rates of prescribing and diversion. Chronic exposure to opioids, particularly during critical periods of development, can lead to long-lasting effects, including effects that may extend to future generations. Using a rodent model, we have demonstrated significant transgenerational effects of female adolescent morphine exposure, despite the absence of in utero drug exposure. While these effects have been observed in both sexes, effects on anxiety-like behavior were only observed in F1 females. The current study was designed to examine both inter- and transgenerational effects of adolescent morphine exposure on anxiety-like behavior. Female Sprague Dawley rats were administered increasing doses of morphine (5-25 mg/kg s.c.) or saline for 10 days during adolescence (PND30-39). Adult diestrous female offspring (MORF1 or SALF1) and grand offspring (F2) were tested for anxiety-like behavior using the elevated plus maze (EPM). F1 females cross-fostered to donor mothers were also examined. The results show that MORF1 and MORF2 females spend significantly more time on the open arms of the EPM compared to SALF1 controls, an effect that persisted in cross-fostered females. Additional studies demonstrate that this effect is estrous cycle dependent, as decreased anxiety-like behavior was observed in diestrus, while increased anxiety-like behavior was observed in estrus. These behavioral effects were not associated with any differences in circulating corticosterone either at baseline or following EPM testing. Thus, female adolescent morphine exposure alters the regulation of anxiety-like behavior in an estrous-dependent manner and this effect persists in the F2 generation.

Opioid use and abuse remain a significant public health problem, particularly in the United States. Indeed, it is estimated that up to 10% of youths (age 12–18) have taken opioids illicitly. A growing body of evidence suggests that this level of widespread opioid exposure can have effects that extend to subsequent generations. Utilizing a well-established rodent model of preconception adolescent opioid exposure in females, we found decreased opioid self-administration coupled with increased cocaine self-administration in adult offspring. This bidirectional effect may be related to negative affect associated with opioid withdrawal, including enhanced stress reactivity. In this study, we tested the hypothesis that the adult offspring of females exposed to morphine during adolescence will demonstrate increased signs of opioid withdrawal when compared to offspring of saline controls. Females were administered increasing doses of morphine (5–25 mg/kg s.c.) or saline (1 ml/kg) from postnatal day 30 (PND30)-PND39. They were then maintained drug free for a minimum of 4 weeks and mated with drug-naïve males on or after PND70. As adults, their male and female offspring (referred to as Mor-F1 or Sal-F1) were administered morphine (10 mg/kg s.c.) twice a day for 5 days. They were then tested for spontaneous withdrawal behaviors for the next 4 days (~PND70). Levels of corticotropin releasing hormone (Crh) and urocortin 3 (Ucn3) were examined in the amygdala at 48 hours and 96 hours of withdrawal. Circulating corticosterone was measured at 48 hours. Results indicate that Mor-F1 males are heavier than Sal-F1 males with no baseline differences in females. However, Mor-F1 females did not gain weight at the same rate as Sal-F1 females during withdrawal. While there were no differences in somatic withdrawal signs, gene expression data revealed a sex-specific and time-dependent effect on Crh as well as increased Ucn3 and corticosterone in females at 48hrs withdrawal. Overall, these data point to differences in withdrawal and stress reactivity in Mor-F1 animals that may contribute to observed differences in addiction-like behaviors.

A growing body of evidence demonstrates that environmental exposures can impact the physiology and behavior of subsequent generations. We have previously demonstrated reduced morphine self-administration in the F1 and F2 offspring of female rats exposed to morphine during adolescence. The current study was designed to determine whether attenuated self-administration for a substance not in the opioid class is also observed in the F1 progeny of adolescent morphine exposed females. Female adolescent rats were administered morphine at increasing doses for 10 days (P30–39). Females then remained drug free for at least 3 weeks prior to mating with drug-naive males. As adults, male and female offspring (F1 animals) were tested for cocaine self-administration acquisition, progressive ratio, extinction, and reinstatement. In addition, β-endorphin peptide levels were measured in the nucleus accumbens (NAc) of behaviorally experienced animals following reinstatement and in behaviorally naive littermates after acute cocaine (0 or 10 mg/kg, i.p.). Proopiomelanocortin, the polypeptide that is cleaved to produce β-endorphin, as well as β-endorphin, was examined in the arcuate nucleus of the hypothalamus and the nucleus accumbens, respectively. Finally, corticosterone was measured following acute cocaine. While no differences were observed during the cocaine acquisition phase (FR-1 and FR-5 schedules), under a PR schedule, Mor-F1 animals (both males and females) had increased motivated responding for cocaine. In addition, Mor-F1 males demonstrated enhanced reinstatement compared to Sal-F1 males. In Mor-F1 males, an acute injection of cocaine (10 mg/kg, i.p.) decreased β-endorphin levels in the NAc compared to a saline injection while acute cocaine increased β-endorphin in the NAc in Sal-F1 males compared to saline injection. Following acute cocaine, Mor-F1 males had significantly lower levels of β-endorphin in the Nac compared to Sal-F1 males. Additionally, β-endorphin levels in the nucleus accumbens were negatively correlated with reinstatement behavior only in Mor-F1 males. Levels of POMC in the arcuate nucleus were elevated in Mor-F1 males compared to Sal-F1 males, a main effect driven primarily by POMC levels in the acute cocaine condition. These changes were not observed in Mor-F1 females. Finally, plasma corticosterone was increased in Mor-F1 males regardless of acute injection while Mor-F1 females displayed increased corticosterone in response to acute cocaine. These data indicate that morphine prior to conception increases the rewarding effects of cocaine in male and female offspring. In addition, sex-specific alterations in endogenous opioids and hypothalamic physiology were observed.

The past decade has seen a drastic rise in the number of infants exposed to opioids in utero. It is unclear what lasting effect this exposure may have on these children. Animal models of prenatal opioid exposure may provide insight into potential areas of vulnerability. The present review summarizes the findings across animal models of prenatal opioid exposure, including exposure to morphine, methadone, buprenorphine, and oxycodone. Details regarding the drug, doses, and duration of treatment, as well as key findings, are summarized in tables with associated references. Finally, significant gaps in the current preclinical literature and future directions are discussed.

The use of oxycodone in the past two decades has dramatically risen, yet the amount of research regarding how it impacts neuronal health is lacking. As prescription use and misuse in women of reproductive age increases there has been a corresponding increase in the number of infants who have been exposed to oxycodone in utero. Given the critical role of the striatum in motor control and reward regulation, the aim of the current study was to examine the effects of oxycodone on developing rat striatal neurons. Sex-specific effects of oxycodone on neuronal cytoarchitecture were examined in cultured rat striatal neurons with a primary focus on dendritic arborization. Neurons were extracted from either male or female embryonic day 18 rat striata and cultured and exposed to varying concentrations of oxycodone over a ten-day period. Dendritic complexity of the neurons was measured using Sholl analysis. Results indicate that oxycodone inhibits dendritic complexity in a dose-dependent manner in female but not male striatal neurons. Additional analysis indicated the number of non-primary dendrites in female striatal neurons significantly decreased with increasing concentrations of oxycodone, while the number of primary dendrites as well as the length of primary and non-primary dendrites was unaffected by oxycodone treatment in both sexes. These in vitro findings demonstrate sex-specific effects of oxycodone on the development of striatal dendritic architecture which may be important for understanding the effects of oxycodone exposure in utero.

A number of parental experiences, even when occurring prior to conception, have been shown to induce transgenerational effects beyond the first generation. In the case of exposure to drugs of abuse, studies in rodents suggest that offspring demonstrate significant differences in how they respond to the drug to which their parent was exposed. We have previously observed significant alterations in morphine analgesia, conditioned place preference and self-administration in the offspring of females exposed to morphine during adolescent development. In addition to effects on pain perception and reward, morphine also modulates the hypothalamic pituitary adrenal (HPA) axis. The purpose of the current study was to determine whether female adolescent morphine exposure results in transgenerational effects on regulation of the HPA axis by morphine in future generations. Adolescent morphine was administered to female Sprague Dawley rats using a 10 day, escalating dose regimen of morphine (5–25 mg/kg; from 30 to 39 days of age). Control animals received saline. Both saline and morphine exposed females (SAL-F0 and MOR-F0, respectively) were mated with drug naive males beginning at least 3 weeks after the final injection. Plasma corticosterone levels were measured in male and female offspring (F1) during adulthood following 0, 0.1, or 10 mg/kg morphine. In addition, expression of corticotropin releasing hormone (Crh) and mu opioid receptor (Oprm1) in the paraventricular nucleus (PVN) were measured using quantitative PCR. MOR-F1 males, but not females, had blunted morphine-induced corticosterone secretion. This effect was specific to offspring from females exposed to morphine during adolescence as those exposed during adulthood produced offspring in which the effect was absent. In addition, MOR-F1 males had significantly lower levels of PVN Crh following saline. These effects were not driven by PVN oprm1 in the F1 males as there were no differences based on maternal adolescent exposure. To determine the persistence of the blunted morphine-induced corticosterone effect, SAL-F2 and MOR-F2 males were examined. Blunted morphine-induced corticosterone secretion extended into the MOR-F2 generation, as well as effects on Crh. In addition, there was additional dysregulation ofOprm1 expression in the PVN in MOR-F2 compared with SAL-F2 males. These findings suggest that sex-specific alterations in opioid-mediated regulation of the HPA axis are transgenerationally transmitted for at least two generations following female adolescent morphine exposure. These effects may play a role in the previously observed changes in morphine analgesia and reward-related behaviors observed in this phenotype. In addition, alterations in HPA functioning such as these may play a broad role in transgenerational epigenetic transmission.

The United States is in the midst of an opiate epidemic, with abuse of prescription and illegal opioids increasing steadily over the past decade. While it is clear that there is a genetic component to opioid addiction, there is a significant portion of heritability that cannot be explained by genetics alone. The current study was designed to test the hypothesis that maternal exposure to opioids prior to pregnancy alters abuse liability in subsequent generations. Female adolescent Sprague Dawley rats were administered morphine at increasing doses (5-25 mg/kg, s.c.) or saline for 10 days (P30-39). During adulthood, animals were bred with drug-naïve colony males. Male and female adult offspring (F1 animals) were tested for morphine self-administration acquisition, progressive ratio, extinction, and reinstatement at three doses of morphine (0.25, 0.75, 1.25 mg/kg/infusion). Grandoffspring (F2 animals, from the maternal line) were also examined. Additionally, gene expression changes within the nucleus accumbens were examined with RNA deep sequencing (PacBio) and qPCR. There were dose- and sex-dependent effects on all phases of the self-administration paradigm that indicate decreased morphine reinforcement and attenuated relapse-like behavior. Additionally, genes related to synaptic plasticity, as well as myelin basic protein (MBP), were dysregulated. Some, but not all, effects persisted into the subsequent (F2) generation. The results demonstrate that even limited opioid exposure during adolescence can have lasting effects across multiple generations, which has implications for mechanisms of the transmission of drug abuse liability in humans.

Transgenerational epigenetic inheritance is a burgeoning field that has recently garnered much attention. A growing body of evidence identifies behavioral phenotypes associated with inter-, multi-, and transgenerational studies following a wide variety of parental exposures. This chapter in current topics in behavioral neurogenomics examines the evidence for the presence of behavioral phenotypes and, in particular, the varied and often opposite behavioral responses observed with protocol shifts. Effects following parental exposure to drugs of abuse are used as an example of the wide range of behavioral outcomes and the variability associated with these multiple generation studies. The behavioral phenotypes associated with drug exposure are reviewed in depth.

© 2019 Society for the Study of Addiction Worldwide consumption of opioids remains at historic levels. Preclinical studies report intergenerational effects on the endogenous opioid system of future progeny following preconception morphine exposure. Given the role of endogenous opioids in energy homeostasis, such effects could impact metabolism in the next generation. Thus, we examined diet-induced modifications in F1 male progeny of morphine-exposed female rats (MORF1). When fed a high fat-sugar diet (FSD) for 6 weeks, MORF1 males display features of emerging metabolic syndrome; they consume more food, gain more weight, and develop fasting-induced hyperglycemia and hyperinsulinemia. In the hypothalamus, proteins involved in energy homeostasis are modified and RNA sequencing revealed down-regulation of genes associated with neuronal plasticity, coupled with up-regulation of genes associated with immune, inflammatory, and metabolic processes that are specific to FSD-maintained MORF1 males. Thus, limited preconception morphine exposure in female rats increases the risk of metabolic syndrome/type 2 diabetes in the next generation.

The United States is in the midst of an opioid epidemic and is thus experiencing unprecedented levels of opioid exposure. A growing body of evidence has demonstrated that this may have consequences on multiple generations. The current set of experiments examined the effect of male adolescent opioid exposure on cocaine and opioid self-administration in the F1 generation. Male Sprague Dawley rats were administered increasing doses of morphine (5–25 mg/kg, s.c.) for 10 days during adolescence (P30-39). Rats were then maintained drug free until adulthood (P70-80) at which point they were mated with drug-naive females. Male and female F1 offspring were first examined for cocaine self-administration during adulthood. Naive littermates were tested for morphine self-administration acquisition followed by a within subjects design progressive ratio test for morphine, oxycodone, and cocaine. Results show that male and female F1 rats have delayed acquisition and decreased intake of cocaine. In addition, they have blunted PR levels compared to Sal-F1 control rats. Female Mor-F1 rats also demonstrate increased levels of morphine intake during acquisition and increased PR responding for oxycodone. Surprisingly, even following acquisition of morphine self-administration, Mor-F1 males and females still demonstrate blunted effort for cocaine. There were no differences in sucrose self-administration in naive littermates. MorF0 seminiferous tubules demonstrated increased levels of acetylated histone H3 and there were increased levels of BDNF mRNA in the mPFC in male and female F1 offspring. Together, these data identify systems that are vulnerable to the impact of opioids in the F0 generation.

Transgenerational epigenetic inheritance is a burgeoning field that has recently garnered much attention. A growing body of evidence identifies behavioral phenotypes associated with inter-, multi-, and transgenerational studies following a wide variety of parental exposures. This chapter in current topics in behavioral neurogenomics examines the evidence for the presence of behavioral phenotypes and, in particular, the varied and often opposite behavioral responses observed with protocol shifts. Effects following parental exposure to drugs of abuse are used as an example of the wide range of behavioral outcomes and the variability associated with these multiple generation studies. The behavioral phenotypes associated with drug exposure are reviewed in depth.

The present study measured postnatal ultrasonic vocalization (USV) and gene expression to examine potential changes in communication and/or attachment in the offspring of mothers exposed to morphine during adolescence. Offspring of morphine-exposed (Mor-F1), saline-exposed (Sal-F1), or non-handled control (Con-F1) female Sprague-Dawley rats were tested for separation-induced distress calls and maternal potentiation of distress calls during early postnatal development. We also examined relative expression of dopamine D2 receptor and mu opioid receptor (oprm1) mRNA in the nucleus accumbens and hypothalamus in these offspring, as their activity has been implicated in the regulation of postnatal USV in response to maternal separation. The findings indicate that adolescent experiences of future mothers, including their 10 daily saline or morphine injections, can result in significant region-specific differences in gene expression. In addition, these experiences resulted in fewer numbers of separation-induced distress calls produced by offspring. In contrast, augmented maternal potentiation was only observed in Mor-F1 offspring. © 2016 Wiley Periodicals, Inc. Dev Psychobiol 58:714-723, 2016.

Extending from research documenting adaptive parental responses in nonthreatening contexts, the influences of various neuroethological and physiological challenges on effective parenting responses are considered in the current review. In natural habitats, rodent family units are exposed to predators, compromised resources, and other environmental stressors that disrupt HPA axis functions. With the additional physiological demands associated with caring for offspring, alterations in stress-related neuroendocrine responsiveness contribute to adaptive responses in many challenging contexts. Some environmental contexts, however, such as restricted nesting resources, result in disrupted maternal responses that have a negative impact on offspring wellbeing. Additionally, parental dysregulation associated with exposure to environmental chemicals or pharmacological substances, also compromise maternal responses with effects that often extend to future generations. Continued preclinical and clinical research elucidating parental responses to various stressors and physiological disruptors is necessary to provide valuable translational information identifying threats to effective parenting outcomes.

Opioid use and abuse has reached epidemic levels in the United States. As these drugs are frequently used by women of reproductive age, there has been a significant increase in the number of infants born to opioid dependent women. Few preclinical studies have examined voluntary opioid intake during pregnancy, and none have used intravenous self-administration. Thus, the purpose of the current set of studies was to utilize a translational model of oxycodone self-administration in rats to determine the effects of oxycodone intake during pregnancy on early postnatal outcomes. Females were trained to intravenously self-administer oxycodone several weeks prior to mating and then continuously throughout pregnancy followed by withdrawal around the time of parturition. Offspring were monitored for weight gain and separation-induced ultrasonic vocalizations (i.e. number of calls) while dams were examined for motivated maternal responding. Neural expression of the mu opioid receptor gene OPRM1 was examined in offspring on postnatal day 1 (PND1). Results indicate that females self-administer oxycodone during pregnancy at levels similar to those observed in cycling females. Postpartum, oxycodone withdrawn females demonstrate impaired maternal responding. In offspring, while no significant group effects were observed on body weight or call number, age-dependent alterations in weight gain and call number correlated with the dams cumulative oxycodone dose during pregnancy. In addition, offspring demonstrated region specific effects of oxycodone exposure on OPRM1 on PND1. Overall, these findings demonstrate that pregnant females will voluntarily self-administer oxycodone at levels similar to cycling females when using a short access model. Further, maternal oxycodone self-administration alters the maternal-offspring dyad in a manner that is dose-dependent and results in sex-and region-specific effects on early measures of neurodevelopment.

Environmental enrichment can modulate mild and chronic stress, responses to anxiogenic stimuli as well as drug vulnerability in a number of animal models. The current study was designed to examine the impact of postnatal environmental enrichment on selectively bred 4th generation high- (HAn) and low-anxiety (LAn) male rats. After weaning, animals were placed in isolated (IE), social (SE) and enriched environments (EE) (e.g., toys, wheels, ropes, changed weekly). We measured anxiety-like behavior (ALB) on the elevated plus maze (EPM; trial 1 at postnatal day (PND) 46, trial 2 at PND 63), amphetamine (AMPH) (0.5mg/kg, IP)-induced locomotor behavior, basal and post anxiogenic stimuli changes in (1) plasma corticosterone, (2) blood pressure and (3) core body temperature. Initially, animals showed consistent trait differences on EPM with HAn showing more ALB but after 40 days in select housing, HAn rats reared in an EE showed less ALB and diminished AMPH-induced activity compared to HAn animals housed in IE and SE. In the physiological tests, animals housed in EE showed elevated adrenocortical responses to forced novel object exposure but decreased body temperature and blood pressure changes after an air puff stressor. All animals reared in EE and SE had elevated brain-derived neurotrophic factor (BDNF)-positive cells in the central amygdala (CeA), CA1 and CA2 hippocampal regions and the caudate putamen, but these differences were most pronounced in HAn rats for CeA, CA1 and CA2. Overall, these findings suggest that environmental enrichment offers benefits for trait anxiety rats including a reduction in behavioral and physiological responses to anxiogenic stimuli and AMPH sensitivity, and these responses correlate with changes in BDNF expression in the central amygdala, hippocampus and the caudate putamen.

It is clear that both genetic and environmental factors contribute to drug addiction. Recent evidence indicating trans-generational influences of drug abuse highlight potential epigenetic factors as well. Specifically, mounting evidence suggests that parental ingestion of abused drugs influence the physiology and behavior of future generations even in the absence of prenatal exposure. The goal of this review is to describe the trans-generational consequences of preconception exposure to drugs of abuse for five major classes of drugs: alcohol, nicotine, marijuana, opioids, and cocaine. The potential epigenetic mechanisms underlying the transmission of these phenotypes across generations also are detailed. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Reproductive experience (i.e. parturition and lactation) leads to persistent alterations in anxietylike behaviour that are influenced by the oestrous cycle. We recently found that repeated administration of the selective oestrogen receptors (ER)α agonist propyl-pyrazole triol (PPT) results in anxiolytic-like behaviours on the elevated plus maze (EPM) in primiparous (but not nulliparous) female rats. The present study examined the effects of the acute administration of PPT on EPM behaviour in primiparous and aged-matched, nulliparous female rats. In addition, corticosterone secretion, corticotrophin-releasing hormone (CRH) gene expression and expression of the immediate early gene product Fos in the paraventricular nucleus (PVN) and amygdala were measured either after EPM testing or in home cage controls. Acute PPT administration significantly modified EPM behaviour as a function of reproductive experience, with nulliparous females tending toward increased anxiety-like behaviours and primiparous females tending toward decreased anxiety-like behaviours. In home cage controls, PPT increased corticosterone secretion in all females; however, both vehicle- and PPT-treated, primiparous females had reduced corticosterone levels compared to their nulliparous counterparts. Significant effects of PPT on CRH mRNA within the PVN were observed after the administration of PPT but only in primiparous females tested on the EPM. PPT also increased Fos expression within the PVN of EPM-exposed females; however, both vehicle- and PPT-treated primiparous females had reduced Fos expression compared to nulliparous females. In the amygdala, PPT increased Fos immunore-activity in the central but not the medial or basolateral amygdala, although these effects were only observed in home cage females. Additionally, both vehicle- and PPT-treated home cage, primiparous females had increased Fos in the central nucleus of the amygdala compared to nullip-arous controls. Overall, these data demonstrate that reproductive experience alters the behavioural response to acute ERα activation. Moreover, the findings suggest that central regulation of the hypothalamic-adrenal-pituitary axis is modified as a consequence of reproductive experience.

Female adolescent marijuana use is increasing, yet the effect on future offspring is unknown. Here, adolescent female Sprague Dawley rats (postnatal-day 30; PN30) were given subcutaneous (s.c.) injections with the cannabinoid agonist WIN-55,212 (WIN) or its vehicle (VEH) for three consecutive days using a twice-daily, increasing dosage regimen (1 mg/kg day 1; 2 mg/kg day 2; 4 mg/kg day 3). As adults (PN60), females were mated with drug-naïve males. Their adult female offspring (VEH-F1 or WIN-F1) were tested for behavioral sensitization by administering morphine (0 or 7.5 mg/kg s.c.) every other day for a total of five administrations. Following five days of abstinence, all animals received a morphine challenge (7.5 mg/kg s.c.) and locomotor activity was monitored. At completion of behavioral testing, mu opioid receptor (OPRM1), FosB, cFos, and dopamine receptor mRNA expression was measured in the nucleus accumbens as well as OPRM1 and corticotropin-releasing hormone mRNA in the paraventricular nucleus. In addition, plasma corticosterone levels were examined. On the day of challenge, morphine-pretreated WIN-F1 animals demonstrated a significantly enhanced response to morphine compared to morphine-pretreated VEH-F1 animals. Also following the morphine challenge, significantly higher levels of OPRM1 in the nucleus accumbens were observed in WIN-F1 animals. Together, these findings demonstrate transgenerational effects of adolescent exposure to cannabinoids in the absence of any in utero exposure.

The use and misuse of prescription opiates in adolescent populations, and in particular, adolescent female populations, has increased dramatically in the past two decades. Given the significant role that opioids play in neuroendocrine function, exposure to opiates during this critical developmental period could have significant consequences for the female, as well as her offspring.In the current set of studies, we utilized the female rat to model the transgenerational impact of adolescent opiate exposure.We examined locomotor sensitization in response to the dopamine D2/D3 receptor agonist quinpirole in the adult male progeny (F1 and F2 generations) of females exposed to morphine during adolescence. All females were drug-free for at least 3 weeks prior to conception, eliminating the possibility of direct fetal exposure to morphine.Both F1 and F2 progeny of morphine-exposed females demonstrated attenuated locomotor sensitization following repeated quinpirole administration. These behavioral effects were coupled with increased quinpirole-induced corticosterone secretion and upregulated kappa opioid receptor and dopamine D2 receptor (D2R) gene expression within the nucleus accumbens.These results suggest significant modifications in response to repeated D2R activation in the progeny of females exposed to opiates during adolescence. Given the significant role that the D2R plays in psychopathology, adolescent opiate exposure could shift the vulnerability of future offspring to psychological disorders, including addiction. Moreover, that effects are also observed in the F2 generation suggests that adolescent opiate exposure can trigger transgenerational epigenetic modifications impacting systems critical for motivated behavior.

Visual Abstract, Estrogens and leptins act in the hypothalamus to maintain reproduction and energy homeostasis. Neurogenesis in the adult mammalian hypothalamus has been implicated in the regulation of energy homeostasis. Recently, high-fat diet (HFD) and estradiol (E2) have been shown to alter cell proliferation and the number of newborn leptin-responsive neurons in the hypothalamus of adult female mice. The current study tested the hypothesis that new cells expressing estrogen receptor α (ERα) are generated in the arcuate nucleus (ARC) and the ventromedial nucleus of the hypothalamus (VMH) of the adult female mouse, hypothalamic regions that are critical in energy homeostasis. Adult mice were ovariectomized and implanted with capsules containing E2 or oil. Within each hormone group, mice were fed an HFD or standard chow for 6 weeks and treated with BrdU to label new cells. Newborn cells that respond to estrogens were identified in the ARC and VMH, of which a subpopulation was leptin sensitive, indicating that the subpopulation consists of neurons. Moreover, there was an interaction between diet and hormone with an effect on the number of these newborn ERα-expressing neurons that respond to leptin. Regardless of hormone treatment, HFD increased the number of ERα-expressing cells in the ARC and VMH. E2 decreased hypothalamic fibroblast growth factor 10 (Fgf10) gene expression in HFD mice, suggesting a role for Fgf10 in E2 effects on neurogenesis. These findings of newly created estrogen-responsive neurons in the adult brain provide a novel mechanism by which estrogens can act in the hypothalamus to regulate energy homeostasis in females.

In the United States, marijuana is one of the drugs most abused by adolescents, with females representing a growing number of users. In previous studies, treatment of adolescent female rats with morphine significantly altered brain reward systems in future offspring. As both cannabinoid and opioid systems develop during adolescence, it was hypothesized that early exposure to cannabinoids would induce similar transgenerational effects. In the current study, female rats were treated with the cannabinoid receptor (CB1/CB2) agonist WIN 55,212-2 or its vehicle for three consecutive days during adolescent development (30 days of age), and were subsequently mated in adulthood (60 days of age). The adolescent and adult male offspring of these WIN 55,212-2 (WIN-F1)- or vehicle (VEH-F1)-treated females were tested for their response to morphine using the conditioned place preference (CPP) paradigm. Both adolescent and adult WIN-F1offspring exhibited greater sensitivity to morphine CPP than their VEH-F1 counterparts. Collectively, the findings provide additional evidence of transgenerational effects of adolescent drug use.

Previous studies have demonstrated that prior reproductive experience can influence anxiety-like behaviors, although neural mechanisms underlying this shift remain unknown. Studies in virgin females suggest that activation of the two estrogen receptor subtypes, ERα and ERβ, have differing effects on anxiety. Specifically, ERβ activation has been shown to reduce anxiety-like behaviors, while ERα activation has no significant effect. The purpose of the present study was to examine the possible roles of ERα and ERβ subtypes in parity-induced alterations in anxiety-like behavior, as tested on the elevated plus maze (EPM). Groups of ovariectomized, age-matched, nulliparous and primiparous females were tested on the EPM following administration of the ERα agonist 4,4',4''-(4-Propyl-{1H}-pyrazole-1,3,5-tryl)trisphenol (PPT; 1 mg/kg), the ERβ agonist Diarylpropionitrile (DPN; 1 mg/kg) or vehicle (DMSO). All drugs were administered once daily for 4 days prior to testing as this dosing paradigm has previously been used to demonstrate anxiolytic effects of DPN in virgin rats. In addition, as exposure to the EPM is a psychological stressor, physiological markers of the stress response were measured in both plasma (corticosterone) and brain (corticotropin releasing hormone; CRH) post-EPM testing. Unexpectedly, the ERα agonist PPT selectively increased the time spent exploring the open arms of the EPM in non-lactating, primiparous females, with no significant effects of DPN observed in either nulliparous or primiparous subjects. All females administered PPT and tested on the EPM demonstrated significantly reduced corticosterone secretion when compared to vehicle-treated controls. In addition, significant effects of both reproductive experience and PPT administration on CRH mRNA expression were observed in both the paraventricular nucleus and amygdala using qPCR. These findings indicate that reproductive experience modulates the effects of ERα activation on both EPM behavior related to anxiety and CRH gene expression.

Recent studies have supported the hypothesis that pregnancy and parturition are associated with altered sensitivity of brain dopamine systems. An increased behavioral sensitivity to a direct-acting D1/D2 receptor agonist (apomorphine) has also been observed several weeks after lactation, suggesting that these adaptations are long-lasting. To further characterize this phenomenon, the effects of reproductive experience on behavioral sensitization to an indirect-acting dopamine agonist (amphetamine) in female rats were studied. In two separate experiments, nulliparous and primiparous (12–16 weeks post-weaning) female rats were pretreated with amphetamine (1.0 or 5.0 mg/kg) or vehicle (saline) once daily for 5 consecutive days. After 10 days of withdrawal, all animals were challenged with a low dose of amphetamine (25% of pretreatment dose). Locomotor activity was measured following each drug or vehicle administration. Locomotor sensitization to amphetamine challenge was observed in all animals pretreated with 1 mg/kg, regardless of reproductive experience. In contrast, primiparous animals pretreated with 5 mg/kg amphetamine displayed a significantly larger locomotor response to the challenge compared to nulliparous controls. The findings indicate enhanced behavioral sensitization to amphetamine in reproductively experienced rats, and confirm previous reports of lasting adaptations of dopamine systems following pregnancy and lactation.

Recent studies have reported that reproductive experience in female rats alters prolactin (PRL) receptor gene expression in the brain as well as neural sensitivity to PRL. Given PRL's actions in nonneural tissues, that is, mammary tissue and liver, it was asked whether reproductive experience may also alter prolactin receptor (Prlr) gene expression in these tissues. Groups of age-matched female rats were generated with varying reproductive histories. Separate groups of primiparous (first lactation) and multiparous (second lactation) had mammary tissue and liver samples collected on Day 3 or 10 of lactation. A fifth group raised one litter to weaning and then resumed estrous cyclicity. This group and a final group of age-matched, virgin controls were killed on diestrus. Tissue was processed by quantitative PCR for expression rates of the long and short forms of Prlr mRNA as well as casein beta mRNA (mammary tissue only). Western blots were performed to quantify receptor protein content. Multiple lactations as well as lactation itself resulted in alterations in Prlr expression. Prlr gene expression in mammary tissue was increased in primiparous mothers compared with that in multiparous dams, whereas in the liver, Prlr expression was reduced during an initial lactation. In contrast, PRLR protein levels declined during lactation in mammary, but not hepatic, tissues. Overall, the results demonstrate that the prolactin receptor system is altered in nonneural tissues as a result of the female's reproductive history. The findings are discussed in the context of milk and bile production and PRL's possible role in breast cancer.

Reproductive experience (i.e. pregnancy and lactation) alters a number of physiological and behavioral endpoints, many of which are related to reproductive function and are regulated by oestrogen. For example, reproductive experience significantly attenuates the oestradiol-induced prolactin surge on the afternoon of proestrous and circulating oestradiol levels are reduced at this time. While parity-related effects on oestrogen receptor alpha (ERα) have been observed within the anterior pituitary, there are currently no data regarding possible parity-induced alterations in ERα in the brain. Thus, the purpose of the current study was to examine the effect of parity on the expression of ERα in reproductively relevant brain regions. Moreover, because previous findings have demonstrated that the long-term effects of reproductive experience are often oestrous cycle dependent, ERα was examined at two stages of the oestrous cycle (diestrous and proestrous). Finally, as the expression of ERα is significantly influenced by age, both young and middle-aged females were included in the present study. ERα status was determined using immunohistochemistry in select brain regions involved in the regulation of reproductive behavior in age-matched, cycling primiparous (one pregnancy and lactation) and nulliparous females as well as in age-matched, non-cycling (persistent estrus) 12 month-old primiparous and nulliparous females. Significant shifts in ERα cell numbers were observed in the medial preoptic area and medial amygdala as a consequence of reproductive experience in an oestrous-dependent manner. These findings indicate that significant changes in ERα activity occur in the brain as a function of reproductive experience.

Reproductive experience (i.e. pregnancy and lactation) leads to reduced levels of circulating prolactin in both women and rats. Stimulation of prolactin secretion by dopamine antagonists is also blunted following reproductive experience in both species. Whereas a parity-induced reduction in haloperidol-stimulated prolactin secretion is evident in ovariectomised rats, it is unknown whether a similar attenuation of prolactin secretion is present in reproductively experienced, cycling pro-oestrous rats. The present study examined this possibility. Moreover, to determine possible mechanisms involved in parity-mediated changes in prolactin secretion, both dopamine utilisation within the arcuate nucleus/median eminence and expression of dopamine D 2 receptor mRNA (short and long forms) in the anterior pituitary were measured across the afternoon of pro-oestrous in reproductively experience and inexperienced females. Prolactin secretion was lower on the afternoon of pro-oestrous in primiparous females compared to age-matched, nulliparous controls. In addition, haloperidol-stimulated prolactin secretion was reduced in ovariectomised, reproductively experienced females. Although no differences in dopamine utilisation were observed as a function of reproductive experience, parity did affect the expression of both forms of D 2 receptor mRNA in the anterior pituitary. Compared with nulliparous controls, primiparous females had increased D 2 long mRNA expression at 12.00 h on pro-oestrous as well as increased D 2 short mRNA expression at 14.00 h. Because the ratio of D 2 long /D2 short can significantly effect lactotroph proliferation and prolactin secretion, a shift in relative expression of the two D 2 receptor isoforms within the anterior pituitary of parous females may help account for the reduction in prolactin secretion that occurs following reproductive experience.

Background/Aim: Reproductive experience (i.e., pregnancy and lactation) alters anxiety-like behavior. One neurotransmitter system that may mediate the effects of reproductive experience on anxiety-like behavior is γ-aminobutyric acid (GABA). The purpose of the current study was to determine whether reproductive experience alters the mRNA expression of selective GABAA receptor subunits in brain regions associated with anxiety-like behaviors. Methods: Brains were collected from age-matched nulliparous and primiparous female rats in either diestrus or proestrus, and the subunit mRNA expression was determined using real-time reverse transcription-polymerase chain reaction with Taqman®. Results: Increased α1 mRNA expression was found in proestrus within both medial preoptic area (MPOA) and medial amygdala (MeA) in nulliparous and primiparous females. The expression of α2 mRNA was also increased within the MPOA in proestrus in both nulliparous and primiparous females; however, within the MeA, an increased α2 mRNA expression in proestrus was only observed in nulliparous females, with primiparous females having a significantly reduced expression when compared to nulliparous controls. In addition, a significant increase in the expression of α2 mRNA expression was observed within the periaqueductal gray of reproductively experienced female rats. Conclusion: These results indicate that reproductive experience results in significant shifts in the expression of GABAA α2 mRNA expression in the MeA.

The present study measured postnatal ultrasonic vocalization (USV) and gene expression to examine potential changes in communication and/or attachment in the offspring of mothers exposed to morphine during adolescence. Offspring of morphine-exposed (Mor-F1), saline-exposed (Sal-F1), or non-handled control (Con-F1) female Sprague-Dawley rats were tested for separation-induced distress calls and maternal potentiation of distress calls during early postnatal development. We also examined relative expression of dopamine D2 receptor and mu opioid receptor (oprm1) mRNA in the nucleus accumbens and hypothalamus in these offspring, as their activity has been implicated in the regulation of postnatal USV in response to maternal separation. The findings indicate that adolescent experiences of future mothers, including their 10 daily saline or morphine injections, can result in significant region-specific differences in gene expression. In addition, these experiences resulted in fewer numbers of separation-induced distress calls produced by offspring. In contrast, augmented maternal potentiation was only observed in Mor-F1 offspring. © 2016 Wiley Periodicals, Inc. Dev Psychobiol 58:714-723, 2016.

Prescription opiate use and abuse has increased dramatically over the past two decades, including increased use in adolescent populations. Recently, it has been proposed that use during this critical period may affect future offspring even when use is discontinued prior to conception. Here, we utilize a rodent model to examine the effects of adolescent morphine exposure on the reward functioning of the offspring. Female Sprague Dawley rats were administered morphine for 10 days during early adolescence (post-natal day 30-39) using an escalating dosing regimen. Animals then remained drug free until adulthood at which point they were mated with naive males. Adult offspring (F1 animals) were tested for their response to morphine-induced (0, 1, 2.5, 5, and 10 mg/kg, s.c.) conditioned place preference (CPP) and context-independent morphine-induced sensitization. Naive littermates were used to examine mu opiate receptor expression in the nucleus accumbens and ventral tegmental area. Results indicate that F1 females whose mothers were exposed to morphine during adolescence (Mor-F1) demonstrate significantly enhanced CPP to the lowest doses of morphine compared with Sal-F1 females. There were no differences in context-independent sensitization between maternal treatment groups. Protein expression analysis showed significantly increased levels of accumbal mu opiate receptor in Mor-F1 offspring and decreased levels in the VTA. Taken together, these findings demonstrate a shift in the dose response curve with regard to the rewarding effects of morphine in Mor-F1 females which may in part be due to altered mu opiate receptor expression in the nucleus accumbens and VTA.

There is much speculation regarding the effects of estrogen withdrawal at the end of pregnancy on forebrain dopamine, however, few studies have directly examine changes in this system postpartum. The present work sought to determine what changes in forebrain dopamine function occur in the postpartum rat. Specifically, prepulse inhibition of the acoustic startle response (PPI) was measured in primiparous female rats on postpartum day 2 (PPD2) or 14 (PPD14) following treatment with saline or the dopamine D2 agonist, quinpirole. Diestrus (DI) females served as controls. Dopamine content and turnover as well as cyclic AMP (cAMP) accumulation were determined within the nucleus accumbens and dorsal striatum in these same females. In addition, circulating levels of plasma corticosterone, estradiol and progesterone were measured. PPI was significantly disrupted in both postpartum groups. This effect was associated with decreased cAMP content within the nucleus accumbens. Quinpirole treatment (0.1 and 0.5 mg/kg) dose-dependently disrupted PPI in DI controls while PPD2 and PPD14 animals demonstrated reduced sensitivity to the D2 agonist. PPD14 animals demonstrated increased startle amplitude, an effect that was attenuated by quinpirole treatment. PPD14 females were also less sensitive to quinpirole-mediated reductions in DA turnover within the nucleus accumbens and both PPD2 and PPD14 females had an attenuated response to the stimulatory effects of quinpirole on corticosterone secretion. Collectively these findings suggest that the postpartum period is associated with reduced sensorimotor gating and altered forebrain DA systems, which may be related to shifts in circulating hormones.

Reproductive experience (i.e. pregnancy and lactation) results in significant alterations in subsequent hormone levels in female rats. Several studies have demonstrated that circulating hormones can significantly affect anxiety-like behavior. Thus, the purpose of the present study was to determine whether reproductive experience induces alterations in anxiety-like behaviors in cycling female rats and in older, reproductively senescent rats. In Experiment 1, the elevated plus maze (EPM) was used to test young cycling (6-8 weeks post-weaning) and middle-aged (32-36 weeks post-weaning) primiparous rats and their age-matched nulliparous counterparts for anxiety-like responses. In Experiment 2, activity in the open field was used as an additional measure of anxiety-like behavior in young (proestrus) and middle-aged (constant estrus) primiparous and nulliparous rats. For Experiment 3, EPM testing was conducted in separate groups of young and middle-aged animals tested two weeks after ovariectomy. The results revealed that during proestrus, primiparous animals exhibited fewer anxiety-like behaviors on the EPM compared to nulliparous controls. In middle-aged animals, however, parity was associated with increased anxiety-like behavior. In the open field, young, non-lactating primiparous animals again exhibited fewer anxiety-like behaviors compared to nulliparous controls, an effect that was reversed in middle-aged animals. Effects of reproductive experience on the EPM in both age groups were eliminated by ovariectomy. Overall, the findings indicate that reproductive experience significantly alters anxiety-like behavior, effects that are influenced by the endocrine status and/or age of the female.

Opiate abuse in adolescent girls has increased in the past decade; however, few animal studies have examined the potential consequences of opiate use occurring at this time. The purpose of the present study was to determine whether exposing female rats to morphine during the peripubertal period can alter the adult behavior of their offspring.Beginning at 30 days of age, female rats were injected subcutaneously (s.c.) twice daily with either morphine sulfate or saline. The initial morphine dose of 2.5 mg/kg was increased by 2.5 mg/kg daily for a total of 20 days. Ten days after the final drug treatment, all subjects were mated. Their subsequent offspring were then tested as adults on the elevated plus maze, in a novel environment or were examined in a morphine locomotor sensitization paradigm.Adult female offspring of dams exposed to morphine during puberty spent less time in the open arms of the elevated plus maze and displayed decreased exploration in a novel environment. Female offspring also demonstrated a more rapid induction of morphine sensitization. Finally, male offspring demonstrated a significant enhancement in the expression of morphine sensitization.Chronic morphine exposure during adolescence can have significant transgenerational effects on adult offspring. Future studies will be needed to determine how these changes are transferred to the offspring and whether these effects are specific to drug exposure that occurs during the peripubertal period.

Brief contact with pups at parturition enables the female rat to establish and retain the full repertoire of maternal behaviors, allowing her to respond rapidly to pups in the future. To determine whether the dopamine system is involved in the retention of maternal behavior, females were continuously infused with dopamine antagonists during the periparturitional period and then allowed either a brief interaction period with pups (3 h) or no interaction with pups (pups removed as they were born). Females were exposed to either the D1-like antagonist SCH 23390 (0.1 or 1.0 mg/kg/day) or the D2-like antagonist clebopride (0.5 or 1.0 mg/kg/day). The high dose of either DA antagonist resulted in significant attenuation of maternal care immediately postpartum. When tested for the retention of maternal behavior 7 days later, however, only the females exposed to the D2 antagonist displayed a delayed response to shown full maternal behavior (FMB) towards donor pups. Thus, while both dopamine receptor subtypes appear necessary for the full and rapid expression of maternal behavior during the early postpartum period, only the D2 receptor subtype appears to be involved in the retention of this behavior.

Relaxin is an essential pregnancy-related hormone with broad peripheral effects mediated by activation of relaxin-like family peptide 1 receptors (RXFP1). More recent studies suggest an additional role for relaxin as a neuropeptide, with RXFP1 receptors expressed in numerous brain regions. Neurons in an area of the brainstem known as the nucleus incertus (NI) produce relaxin 3 (RLN3), the most recently identified neuropeptide in the relaxin family. RLN3 has been shown to activate both RXFP1 and relaxin-like family peptide receptor 3 (RXFP3) receptor subtypes. Studies suggest wide-ranging neuromodulatory effects of both RXFP1 and RXFP3 activation, although to date the majority of studies have been conducted in young males. In the current study, we examined potential sex- and age-related changes in RLN3 gene expression in the NI as well as RXFP1 and RXFP3 gene expression in the dorsal hippocampus (HI), ventral hippocampus (vHI) and amygdala (AMYG) using young adult (9-12weeks) and middle-aged (9-12months) male and female rats. In addition, regional changes in RXFP1 and RXFP3 protein expression were examined in the CA1, CA2/CA3 and dentate gyrus (DG) as well as within basolateral (BLA), central (CeA), and medial (MeA) amygdaloid nuclei. In the NI, RLN3 showed an age-related decrease in males. In the HI, only the RXFP3 receptor showed an age-related change in gene expression, however, both receptor subtypes showed age-related changes in protein expression that were region specific. Additionally, while gene and protein expression of both receptors increased with age in AMYG, these effects were both region- and sex-specific. Finally, overall males displayed a greater number of cells that express the RXFP3 protein in all of the amygdaloid nuclei examined. Cognitive and emotional processes regulated by activity within the HI and AMYG are modulated by both sex and age. The vast majority of studies exploring the influence of sex on age-related changes in the HI and AMYG have focused on sex hormones, with few studies examining the role of neuropeptides. The current findings suggest that changes in relaxin family peptides may contribute to the significant sex differences observed in these brain regions as a function of aging.

Prescription opiate use by adolescent girls has increased significantly in the past decade. Preclinical studies using rats report alterations in morphine sensitivity in the adult offspring of adolescent morphine-exposed females (MOR-F1) when compared with the offspring of adolescent saline-exposed females (SAL-F1). To begin to elucidate the development of these next generation modifications, the present study examined the effects of acute morphine administration on sedation and corticosterone secretion in prepubescent SAL-F1 and MOR-F1 male and female rats. In addition, alterations in proopiomelanocortin (POMC) gene expression in the arcuate nucleus, as well as in tyrosine hydroxylase (TH) and μ-opioid receptor (OPRM1) gene expressions in the ventral tegmental area, were analyzed using quantitative PCR, to determine whether differential regulation of these genes was correlated with the observed behavioral and/or endocrine effects. Increased morphine-induced sedation, coupled with an attenuation of morphine-induced corticosterone secretion, was observed in MOR-F1 males. Significant alterations in both POMC and OPRM1 gene expressions were also observed in MOR-F1 males, with no change in TH mRNA expression. Overall, these data suggest that the transgenerational effects of adolescent morphine exposure can be discerned before pubertal development and are more pronounced in males, and suggest dysregulation of the hypothalamic-pituitary-adrenal axis in the offspring of adolescent morphine-exposed females.

Several studies have suggested that alterations in forebrain dopamine activity during the postpartum period may result in the onset of postpartum psychosis in women [J. Psychosom. Obstet. Gynecol. 19 (1998) 104; Prog. Neuro-Psychopharmacol. Biol. Psychiatry 17 (1993) 571; J. Clin. Psychiatry 51 (1990) 365.]. The present study investigated whether increased dopamine activity in these forebrain regions is a normal consequence of reproductive experience in rodents. Both intact and ovariectomized parous and nulliparous females were tested for their responses to the dopamine agonist apomorphine using two behavioral measures, prepulse inhibition (PPI) and oral stereotypy. In addition, dopamine and DOPAC levels were measured in tissue from the striatum and nucleus accumbens together with circulating plasma prolactin levels. The results of the behavioral studies demonstrate an increased response to apomorphine in parous females. Parous subjects also had increased levels of dopamine and DOPAC in striatal tissue and lower levels of circulating prolactin. Ovariectomy in nulliparous females resulted in a potentiated response to apomorphine with regard to the disruption of PPI, as well as a significant decrease in the plasma prolactin levels, as compared with intact nulliparous females. These data suggest that increased dopamine activity in forebrain regions occurs as a consequence of parity, which persists for a minimum of several weeks postpartum. These findings support the hypothesis that increased dopamine sensitivity in forebrain dopamine regions may be one potential mechanism underlying the development of postpartum psychosis in women.

The expression of maternal behavior in the newly parturient rat is under endocrine regulation. Blocking endogenous PRL secretion with bromocriptine delays the normal rapid expression of maternal care shown toward foster young in steroid-primed virgin female rats. The recent development of the PRL receptor antagonist S179D-PRL, a mutant of human PRL in which the serine residue at the 179 position is replaced with aspartate, provides a potentially useful tool to examine the role of PRL in neural processing. In the present report, three experiments were conducted that examined the effects of this PRL antagonist on the induction of maternal behavior. In each experiment, ovariectomized, nulliparous rats were treated sequentially with SILASTIC capsules implanted sc with progesterone (days 1–11) and estradiol (days 11–17), a treatment that stimulates a rapid onset of maternal behavior in virgin rats. On day 11, females were implanted with Alzet miniosmotic pumps connected to cannulae directed unilaterally at the...

High levels of μ opioid receptor activation during the postpartum period result in the disruption of ongoing maternal behavior. The role of physiological levels of endogenous opioids on the mediation of maternal behavior in postpartum females, however, has not been closely examined. The purpose of the present experiments was to examine the function of endogenous opioids during early and mid-lactation by treating postpartum females with the opioid antagonist naloxone and monitoring their behavioral interactions with pups. Although this treatment did not lead to any qualitative differences in the maternal behaviors measured (pup retrieval and grooming, nest building, grouping of pups, or crouching over pups), there was a quantitative difference in the amount of time the females spent with pups on the nest and actively nursing pups. Naloxone, given either systemically or centrally (intracerebroventricularly), resulted in prolonged nursing and nesting bouts. This effect, however, was only observed during the early lactation time point (postpartum days 5–7). Females tested later in lactation (postpartum days 10–12 or 12–14) did not display the increased nursing or nesting bouts in response to the antagonist. These data indicate that central opioids play a role in the duration of nursing bouts during early lactation.

Environmental enrichment attenuates the response to psychostimulants and has been shown to reduce both anxiety and stress-related behaviors. Since stress is a major vulnerability factor for addiction, we investigated whether enrichment could reverse stress profiles in high anxious rats as well as reduce their amphetamine sensitivity. Using selectively-bred high and low anxiety males (filial 3) from enriched, social or isolated environments, we tested elevated plus maze exploration, novelty place preference and amphetamine (AMPH; 0.5 mg/kg, IP)-induced hyperactivity. We measured plasma corticosterone (CORT) response after forced novel object exposure, phosphorylation of the tropomyosin-related kinase B receptor (pTrkB) in the hippocampus and striatum, and dopamine (D2) receptor mRNA levels in the striatum and nucleus accumbens. Results indicate that high anxiety animals reared in social or enriched environments spent more time on open arms of the EPM while low anxiety animals raised in enriched environments spent more time on open arms when compared to either isolated or social groups. There were no group differences or interactions found for novelty place preference. Enriched environments decreased the response to AMPH and stress-induced CORT regardless of trait but selectively decreased pTrkB and increased D2 mRNA levels in high anxiety animals. The results suggest that selectively-bred trait anxiety rats show state anxiety that is influenced by rearing environments, and D2 protein levels and BDNF/TrkB signaling may differentially contribute to integrating these effects.

Prior studies have supported a role for mesolimbic dopaminergic mechanisms in the regulation of maternal behavior. Accordingly, the ventral tegmental area (VTA) and its dopaminergic projections to the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) have been implicated in both the onset and maintenance of normal maternal behavior. To date, studies of direct manipulation of VTA neurochemistry at the onset of maternal behavior have been limited. The current study was undertaken to directly test the hypothesis that enhancement of dopaminergic transmission in the mesolimbic dopamine system can stimulate maternal activity using a pup-induced virgin model. Nulliparous female rats were stereotaxically infused with pertussis toxin (PTX 0, 0.1, or 0.3 μg/hemisphere) into the VTA to chronically stimulate the activity of dopaminergic projection neurons. After 3 days of recovery, maternal responding to donor pups was tested daily, and latency (in days) to full maternal behavior was recorded. Intra-VTA PTX treatment produced a robust dose-dependent decrease in maternal behavior latency, and a long-lasting increase in locomotor activity. These effects were associated with significantly decreased dopamine D1 receptor mRNA expression in the NAc. No effects of PTX treatment on mesolimbic dopamine utilization or mPFC receptor expression were observed. The findings indicate that chronic neural activation in the VTA accelerates the onset of maternal behavior in virgin female rats via modification of the NAc dopamine D1 receptor.

The use of narcotics by adolescent females is a growing problem, yet very little is known about the long-term consequences for either the user or her future offspring. In the current study, we utilized an animal model to examine the transgenerational consequences of opiate exposure occurring during this sensitive period. Female rats were exposed to increasing doses of morphine or its saline vehicle twice daily during adolescent development (postnatal days 30–40), after which they remained drug free. At 60 days of age, all females were mated and their adult offspring were tested for anxiety-like behavior and sensitivity to morphine. Specifically, offspring of adolescent morphine (MOR-F1)- or saline (SAL-F1)-exposed mothers were tested for acute locomotor responses in an open field, followed by testing of acute or chronic morphine analgesia on the hot plate. Open field testing indicated alterations in anxiety-like behavior in MOR-F1 female offspring, with effects dependent upon the stage of the estrus cycle. Hot plate testing revealed sex differences in baseline pain threshold and morphine sensitivity in all offspring, regardless of maternal exposure. However, when compared to their SAL-F1 counterparts, MOR-F1 male offspring demonstrated significantly increased sensitivity to the analgesic effects of acute morphine, and developed analgesic tolerance more rapidly following chronic morphine treatment. The findings indicate that prior opiate exposure during early adolescence in females produces sex-specific alterations of both emotionality and morphine sensitivity in their progeny.

Maternal aggression is highly expressed during lactation and serves to protect the developing young from intruders that may injure the offspring. One neurochemical modulator of maternal aggression appears to be arginine vasopressin (AVP). Earlier research supports a role for AVP in maternal aggression in rats as treatment with an AVP antagonist in lactating, primiparous rats stimulates the mother’s aggression towards intruders the second half of lactation, but that AVP itself was without major effects during early lactation. Recent behavioral findings indicate that during a second lactation (multiparous) mothers display higher levels of maternal aggression than do first time mothers (primiparous). The present study was designed to assess the involvement of AVP as mothers acquire reproductive experience. Therefore, the involvement of AVP in maternal aggression in multiparous mothers was measured after intracerebroventricular (ICV) treatment with both AVP and a V1a receptor antagonist. Behavior was assessed during early lactation when aggression levels are very high in multiparous mothers as well as during late lactation when aggression levels are lower. The results demonstrated that ICV infusions of AVP significantly reduced maternal aggression in multiparous females on day 5 of lactation, whereas V1a antagonist infusions increased aggression on day 15 of lactation. These findings suggest that the role of AVP in maternal aggression may be amplified as reproductive/lactational experiences increase, and support the involvement of the central AVP system as a key modulator of maternal protection of the young.

This chapter presents clinical data regarding the long-term psychological effects of prior reproductive experience. Researchers used the female rat to explore the neural and endocrine consequences of parity. The use of this animal model has provided insights into the influence of reproductive experience on both hormones and behavior. Overall, the current findings indicate that reproductive experience can significantly alter behavioral expression. Moreover, these behavioral adaptations are often conditional, depending on the females' reproductive status. Pregnancy and mothering both appear to play a role in the manifestation of these parity effects. Long-term alterations in hormone secretion and a shift in the sensitivity of neuroendocrine parameters following reproductive experience likely underlie the behavioral adaptations. Finally, the medial and cortical nuclei of the amygdala may be critical for the integration of endocrine and sensory stimuli in modifying the behavior of parous females. The chapter proposes that these changes enhance the reproductive competency of the female and increase her chances of future reproductive success.

Substance abuse in developing females may have significant long-term effects on reproductive competency. Chronic morphine exposure during puberty has been shown to reduce prolactin secretion in lactating rats. Opioid activity within the mediobasal hypothalamus (MBH) regulates suckling-induced prolactin secretion. Thus, the current study was conducted to determine whether chronic pubertal morphine exposure alters the expression of mu- and/or kappa-opioid receptor mRNA or pro-opioimelanocortin (POMC) mRNA within the MBH. Using an increasing dose regimen, female Sprague-Dawley rats were injected twice daily for a total of 20 days with morphine sulfate or saline beginning at 30 days of age. Several weeks later, quantitative RT-PCR was used to determine mRNA expression within the MBH in diestrus, never pregnant (nulliparous) controls, postpartum day 5 (PPD5), PPD10, PPD18, and diestrus, reproductively experienced (primiparous) females. Pubertal morphine exposed females had increased mu- and kappa-receptor mRNA expression as well as decreased POMC mRNA expression on diestrus. During lactation, mu- and kappa-receptor mRNA expression in the MBH decreased while POMC mRNA expression increased in similarly treated females. No changes in mRNA expression were observed during lactation in pubertal saline-treated females; however, increased mu- and kappa-receptor mRNA expression as well as decreased POMC mRNA expression was observed in primiparous, pubertal saline-treated females when compared to nulliparous controls. Thus, chronic morphine exposure during puberty results in long-term alterations in mu- and kappa-receptor as well as POMC mRNA expression in the MBH which are similar to the changes observed following reproductive experience. These changes do not correlate with the decreased prolactin secretion observed during early lactation; however, they do demonstrate the enduring nature of the effects of chronic opiate exposure during puberty on hypothalamic opioid systems in adulthood.

Reproductive experience (i.e., pregnancy and lactation) alters anxiety-like behavior. One neurotransmitter system that may mediate the effects of reproductive experience on anxiety-like behavior is gamma-aminobutyric acid (GABA). The purpose of the current study was to determine whether reproductive experience alters the mRNA expression of selective GABA(A) receptor subunits in brain regions associated with anxiety-like behaviors.Brains were collected from age-matched nulliparous and primiparous female rats in either diestrus or proestrus, and the subunit mRNA expression was determined using real-time reverse transcription-polymerase chain reaction with Taqman.Increased alpha1 mRNA expression was found in proestrus within both medial preoptic area (MPOA) and medial amygdala (MeA) in nulliparous and primiparous females. The expression of alpha2 mRNA was also increased within the MPOA in proestrus in both nulliparous and primiparous females; however, within the MeA, an increased alpha2 mRNA expression in proestrus was only observed in nulliparous females, with primiparous females having a significantly reduced expression when compared to nulliparous controls. In addition, a significant increase in the expression of alpha2 mRNA expression was observed within the periaqueductal gray of reproductively experienced female rats.These results indicate that reproductive experience results in significant shifts in the expression of GABA(A) alpha2 mRNA expression in the MeA.

The maternal and neurobiological responses of biological mothers and pup-induced maternal virgin rats were compared 55 and 80 days after an initial 2-day maternal experience. When tested for home cage responsiveness after prolonged isolation from young, the biological, primiparous rats displayed shorter maternal latencies. Primiparous females tested in the presence of pups on the elevated plus-maze displayed increased exploration of the open arms and increased c-Fos expression in the cortical nucleus of the amygdala. Pup exposure and parity also enhanced activation of the nucleus accumbens shell and medial nucleus of the amygdala, respectively. Therefore, although both nulliparous and primiparous rats retain a maternal memory for a prolonged time, the memory and neurochemical response appear stronger in primiparous mothers.