Search

A lack of effective treatment and sex-based disparities in psychostimulant addiction and overdose warrant further investigation into mechanisms underlying the abuse-related effects of amphetamine-like stimulants. Uptake-2 transporters such as organic cation transporter 3 (OCT3) and plasma membrane monoamine transporter (PMAT), lesser studied potential targets for the actions of stimulant drugs, are known to play a role in monoaminergic neurotransmission. Our goal was to examine the roles of OCT3 and PMAT in mediating amphetamine (1 mg/kg)-induced conditioned place preference (CPP) and sensitization to its locomotor stimulant effects, in males and females, using pharmacological, decynium-22 (D22; 0.1 mg/kg, a blocker of OCT3 and PMAT) and genetic (constitutive OCT3 and PMAT knockout (−/−) mice) approaches. Our results show that OCT3 is necessary for the development of CPP to amphetamine in males, whereas in females, PMAT is necessary for the ability of D22 to prevent the development of CPP to amphetamine. Both OCT3 and PMAT appear to be important for development of sensitization to the locomotor stimulant effect of amphetamine in females, and PMAT in males. Taken together, these findings support an important, sex-dependent role of OCT3 and PMAT in the rewarding and locomotor stimulant effects of amphetamine.

Organic cation transporters 1-3 (OCT1-3, SLC22A1-3) and the plasma membrane monoamine transporter (PMAT, SLC29A4) play a major role in maintaining monoaminergic equilibrium in the central nervous system. With many psychoactive substances interacting with OCT1-3 and PMAT, a growing literature focuses on characterizing their properties via in vitro and in vivo studies. In vitro studies mainly aim at characterizing compounds as inhibitors or substrates of murine, rat, and human isoforms. The preponderance of studies has put emphasis on phenylalkylamine derivatives, but ketamine and opioids have also been investigated. Studies employing in vivo (knockout) models mostly concentrate on the interaction of psychoactive substances and OCT3, with an emphasis on stress and addiction, pharmacokinetics, and sensitization to psychoactive drugs. The results highlight the importance of OCT3 in the mechanism of action of psychoactive compounds. Concerning in vivo studies, a veritable research gap concerning OCT1, 2, and PMAT exists. This review provides an overview and summary of research conducted in this field of research.

Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed medications for psychiatric disorders, yet they leave the majority of patients without full symptom relief. Therefore, a major research challenge is to identify novel targets for the improved treatment of these disorders. SSRIs act by blocking the serotonin transporter (SERT), the high-affinity, low-capacity, uptake-1 transporter for serotonin. Other classes of antidepressant work by blocking the norepinephrine or dopamine transporters (NET and DAT), the high-affinity, low-capacity uptake-1 transporters for norepinephrine and dopamine, or by blocking combinations of SERT, NET, and DAT. It has been proposed that uptake-2 transporters, which include organic cation transporters (OCTs) and the plasma membrane monoamine transporter (PMAT), undermine the therapeutic utility of uptake-1 acting antidepressants. Uptake-2 transporters for monoamines have low affinity for these neurotransmitters, but a high capacity to transport them. Thus, activity of these transporters may limit the increase of extracellular monoamines thought to be essential for ultimate therapeutic benefit. Here preclinical evidence supporting a role for OCT2, OCT3, and PMAT in behaviors relevant to psychiatric disorders is presented. Importantly, preclinical evidence revealing these transporters as targets for the development of novel therapeutics for psychiatric disorders is discussed.

Organic cation transporters 1-3 (OCT1-3, SLC22A1-3) and the plasma membrane monoamine transporter (PMAT, SLC29A4) play a major role in maintaining monoaminergic equilibrium in the central nervous system. With many psychoactive substances interacting with OCT1-3 and PMAT, a growing literature focuses on characterizing their properties via in vitro and in vivo studies. In vitro studies mainly aim at characterizing compounds as inhibitors or substrates of murine, rat, and human isoforms. The preponderance of studies has put emphasis on phenylalkylamine derivatives, but ketamine and opioids have also been investigated. Studies employing in vivo (knockout) models mostly concentrate on the interaction of psychoactive substances and OCT3, with an emphasis on stress and addiction, pharmacokinetics, and sensitization to psychoactive drugs. The results highlight the importance of OCT3 in the mechanism of action of psychoactive compounds. Concerning in vivo studies, a veritable research gap concerning OCT1, 2, and PMAT exists. This review provides an overview and summary of research conducted in this field of research.

Major depressive disorder is typically treated with selective serotonin reuptake inhibitors (SSRIs), however, SSRIs take approximately six weeks to produce therapeutic effects, if any. Not surprisingly, there has been great interest in findings that low doses of ketamine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, produce rapid and long-lasting antidepressant effects. Preclinical studies show that the antidepressant-like effects of ketamine are dependent upon availability of serotonin, and that ketamine increases extracellular serotonin, yet the mechanism by which this occurs is unknown. Here we examined the role of the high-affinity, low-capacity serotonin transporter (SERT), and the plasma membrane monoamine transporter (PMAT), a low-affinity, high-capacity transporter for serotonin, as mechanisms contributing to ketamine&rsquo, s ability to increase extracellular serotonin and produce antidepressant-like effects. Using high-speed chronoamperometry to measure real-time clearance of serotonin from CA3 region of hippocampus in vivo, we found ketamine robustly inhibited serotonin clearance in wild-type mice, an effect that was lost in mice constitutively lacking SERT or PMAT. As expected, in wild-type mice, ketamine produced antidepressant-like effects in the forced swim test. Mapping onto our neurochemical findings, the antidepressant-like effects of ketamine were lost in mice lacking SERT or PMAT. Future research is needed to understand how constitutive loss of either SERT or PMAT, and compensation that occurs in other systems, is sufficient to void ketamine of its ability to inhibit serotonin clearance and produce antidepressant-like effects. Taken together with existing literature, a critical role for serotonin, and its inhibition of uptake via SERT and PMAT, cannot be ruled out as important contributing factors to ketamine&rsquo, s antidepressant mechanism of action. Combined with what is already known about ketamine&rsquo, s action at NMDA receptors, these studies help lead the way to the development of drugs that lack ketamine&rsquo, s abuse potential but have superior efficacy in treating depression.

A variety of human and animal studies support the hypothesis that serotonin (5-hydroxytryptamine or 5-HT) system dysfunction is a contributing factor to the development of autism in some patients. However, many questions remain about how developmental manipulation of various components that influence 5-HT signaling (5-HT synthesis, transport, metabolism) persistently impair social behaviors. This review will summarize key aspects of central 5-HT function important for normal brain development, and review evidence implicating perinatal disruptions in 5-HT signaling in the pathophysiology of autism spectrum disorder. We discuss the importance, and relative dearth, of studies that explore the possible correlation to autism in the interactions between important intrinsic and extrinsic factors that may disrupt 5-HT homeostasis during development. In particular, we focus on exposure to 5-HT transport altering mechanisms such as selective serotonin-reuptake inhibitors or genetic polymorphisms in primary or auxiliary transporters of 5-HT, and how they relate to neurological stores of serotonin and its precursors. A deeper understanding of the many mechanisms by which 5-HT signaling can be disrupted, alone and in concert, may contribute to an improved understanding of the etiologies and heterogeneous nature of this disorder. We postulate that extreme bidirectional perturbations of these factors during development likely compound or synergize to facilitate enduring neurochemical changes resulting in insufficient or excessive 5-HT signaling, that could underlie the persistent behavioral characteristics of autism spectrum disorder.

Growing evidence supports involvement of low-affinity/high-capacity organic cation transporters (OCTs) and plasma membrane monoamine transporter (PMAT) in regulating clearance of monoamines. Currently decynium-22 (D22) is the best pharmacological tool to study these transporters, however it does not readily discriminate among them, underscoring a need to develop compounds with greater selectivity for each of these transporters. We developed seven D22 analogs, and previously reported that some have lower affinity for α1-adrenoceptors than D22 and showed antidepressant-like activity in mice. Here, we extend these findings to determine the affinity of these analogs for OCT2, OCT3 and PMAT, as well as serotonin, norepinephrine and dopamine transporters (SERT, NET and DAT) using a combination of uptake competition with [(3)H]methyl-4-phenylpyridinium acetate in overexpressed HEK cells and [(3)H]citalopram, [(3)H]nisoxetine and [(3)H]WIN 35428 displacement binding in mouse hippocampal and striatal preparations. Like D22, all analogs showed greater binding affinities for OCT3 than OCT2 and PMAT. However, unlike D22, some analogs also showed modest affinity for SERT and DAT. Dual OCT3/SERT and/or OCT3/DAT actions of certain analogs may help explain their ability to produce antidepressant-like effects in mice and help account for our previous findings that D22 lacks antidepressant-like effects unless SERT function is either genetically or pharmacologically compromised. Though these analogs are not superior than D22 in discriminating among OCTs/PMAT, our findings point to development of compounds with combined ability to inhibit both low-affinity/high-capacity transporters, such as OCT3, and high-affinity/low-capacity transporters, such as SERT, as therapeutics with potentially improved efficacy for treatment of psychiatric disorders.

High dietary salt intake increases risk of stress-related neuropsychiatric disorders. Here, we explored the contribution of high dietary salt intake-induced neuroinflammation in key stress-responsive brain regions, the hypothalamic paraventricular nucleus and basolateral amygdala, in promoting exaggerated neuronal activation and coping behaviors in response to acute psychogenic stress. Mice that underwent high dietary salt intake exhibited increased active stress coping behaviors during and after an acute swim stress, and these were reduced by concurrent administration of minocycline, an inhibitor of microglial activation, without affecting body fluid hyperosmolality caused by high dietary salt intake. Moreover, minocycline attenuated high dietary salt intake-induced increases of paraventricular nucleus tumor necrosis factor-α, activated microglia (ionized calcium-binding adaptor molecule 1), and acute swim stress-induced neuronal activation (c-Fos). In the basolateral amygdala, similar effects were observed on ionized calcium-binding adaptor molecule 1+ and c-Fos+ counts, but not tumor necrosis factor-α levels. These data indicate that high dietary salt intake promotes neuroinflammation, increasing recruitment of neurons in key stress-associated brain regions and augmenting behavioral hyper-responsivity to acute psychological stress.

Originally, uptake-mediated termination of monoamine (e.g., serotonin and dopamine) signalling was believed to only occur via high-affinity, low-capacity transporters ("uptake1 ") such as the serotonin or dopamine transporters, respectively. Now, the important contribution of a second low-affinity, high-capacity class of biogenic amine transporters has been recognised, particularly in circumstances when uptake1 transporter function is reduced (e.g., antidepressant treatment). Pharmacologic or genetic reductions in uptake1 function can change locomotor, anxiety-like or stress-coping behaviours. Comparable behavioural investigations into reduced low-affinity, high-capacity transporter function are lacking, in part, due to a current dearth of drugs that selectively target particular low-affinity, high-capacity transporters, such as the plasma membrane monoamine transporter. Therefore, the most direct approach involves constitutive genetic knockout of these transporters. Other groups have reported that knockout of the low-affinity, high-capacity organic cation transporters 2 or 3 alters anxiety-like and stress-coping behaviours, but none have assessed behaviours in plasma membrane monoamine transporter knockout mice. Here, we evaluated adult male and female plasma membrane monoamine transporter wild-type, heterozygous and knockout mice in locomotor, anxiety-like and stress-coping behavioural tests. A mild enhancement of anxiety-related behaviour was noted in heterozygous mice. Active-coping behaviour was modestly and selectively increased in female knockout mice. These subtle behavioural changes support a supplemental role of plasma membrane monoamine transporter in serotonin and dopamine uptake, and suggest sex differences in transporter function should be examined more closely in future investigations.

Amphetamine abuse is a major public health concern for which there is currently no effective treatment. To develop effective treatments, the mechanisms by which amphetamine produces its abuse-related effects need to be fully understood. It is well known that amphetamine exerts its actions by targeting high-affinity transporters for monoamines, in particular the cocaine-sensitive dopamine transporter. Organic cation transporter 3 (OCT3) has recently been found to play an important role in regulating monoamine signaling. However, whether OCT3 contributes to the actions of amphetamine is unclear. We found that OCT3 is expressed in dopamine neurons. Then, applying a combination of in vivo, ex vivo, and in vitro approaches, we revealed that a substantial component of amphetamine's actions is OCT3-dependent and cocaine insensitive. Our findings support OCT3 as a new player in the actions of amphetamine and encourage investigation of this transporter as a potential new target for the treatment of psychostimulant abuse.

The antidepressant-sensitive norepinephrine (NE) transporter (NET) inactivates NE released during central and peripheral neuronal activity by transport into presynaptic cells. Altered NE clearance due to dysfunction of NET has been associated with the development of mental illness and cardiovascular diseases. NET activity in vivo is influenced by stress, neuronal activity, hormones and drugs. We investigated the mechanisms of Ca2+ regulation of NET and found that Ca2+ influenced both Vmax and Km for NE transport into cortical synaptosomes. Changes in extracellular Ca2+ triggered rapid and bidirectional surface trafficking of NET expressed in cultured cells. Deletion of residues 28-47 in the NET NH2-terminus abolished the Ca2+ effect on surface trafficking. Mutagenesis studies identified Thr30 in this region as the essential residue for both Ca2+- dependent phosphorylation and trafficking of NET. Depolarization of excitable cells increased surface NET in a Thr30 dependent manner. A proteomic analysis, RNA interference, and pharmacological inhibition supported roles of CaMKI and CaMKII in Ca2+-modulated NE transport and NET trafficking. Depolarization of primary noradrenergic neurons in culture with elevated K+ increased NET surface expression in a process that required external Ca2+ and depended on CaMK activity. Hippocampal NE clearance in vivo was also stimulated by depolarization, and inhibitors of CaMK signaling prevented this stimulation. In summary, Ca2+ signaling influenced surface trafficking of NET through a CaMK-dependent mechanism requiring Thr30.

Herein we describe the synthesis and evaluation of antidepressant properties of seven analogues ( 1–7 ) of the low affinity/high capacity transporter blocker decynium-22 (D-22). All analogues ( 1–7 ) were synthesized via base promoted coupling reactions between N -alkylated-2-methylquinolinium iodides or N -alkylated-4-methylquinolinium iodides and electrophilic N -alkylated-2-iodoquinolinium iodides. All final compounds were purified by re-crystallization or preparative HPLC and initial evaluation studies included; 1) screening for in vitro α1-adrenoceptor activity (a property that can lead to unwanted side-effects), 2) measuring antidepressant-like activity in a mouse tail suspension test (TST), and 3) measuring effects upon mouse locomotion. The results showed some analogues have lower affinities at α1-adrenoceptors compared to D-22 and showed antidepressant-like activity without the need for co-administration of SSRIs. Additionally, many analogues did not affect mouse locomotion to the same extent as D-22. Plans for additional evaluations of these promising analogues, including measurement of antidepressant-like activity with co-administration of selective serotonin re-uptake inhibitors (SSRIs), are outlined.

Depression is a major public health concern with symptoms that are often poorly controlled by treatment with common antidepressants. This problem is compounded in juveniles and adolescents, because therapeutic options are limited to selective serotonin reuptake inhibitors (SSRIs). Moreover, therapeutic benefits of SSRIs are often especially limited in certain subpopulations of depressed patients, including children and carriers of low-expressing serotonin transporter (SERT) gene variants. Tricyclic antidepressants (TCAs) offer an alternative to SSRIs; however, how age and SERT expression influence antidepressant response to TCAs is not understood. We investigated the relation between antidepressant-like response to the TCA desipramine using the tail suspension test and saturation binding of [3H]nisoxetine to the norepinephrine transporter (NET), the primary target of desipramine, in juvenile (21 days postnatal [P21]), adolescent (P28), and adult (P90) wild-type (SERT+/+) mice. To model carriers of low-expressing SERT gene variants, we used mice with reduced SERT expression (SERT+/−) or lacking SERT (SERT−/−). The potency and maximal antidepressant-like effect of desipramine was greater in P21 mice than in P90 mice and was SERT genotype independent. NET expression decreased with age in the locus coeruleus and increased with age in several terminal regions (e.g., the cornu ammonis CA1 and CA3 regions of the hippocampus). Binding affinity of [3H]nisoxetine did not vary as a function of age or SERT genotype. These data show age-dependent shifts for desipramine to produce antidepressant-like effects that correlate with NET expression in the locus coeruleus and suggest that drugs with NET-blocking activity may be an effective alternative to SSRIs in juveniles.

Depression is a disabling affective disorder for which the majority of patients are not effectively treated. This problem is exacerbated in children and adolescents for whom only two antidepressants are approved, both of which are selective serotonin reuptake inhibitor (SSRIs). Unfortunately SSRIs are often less effective in juveniles than in adults; however, the mechanism(s) underlying age-dependent responses to SSRIs is unknown. To this end, we compared the antidepressant-like response to the SSRI escitalopram using the tail suspension test and saturation binding of [(3)H]citalopram to the serotonin transporter (SERT), the primary target of SSRIs, in juvenile [postnatal day (P)21], adolescent (P28), and adult (P90) wild-type (SERT+/+) mice. In addition, to model individuals carrying low-expressing SERT variants, we studied mice with reduced SERT expression (SERT+/-) or lacking SERT (SERT-/-). Maximal antidepressant-like effects were less in P21 mice relative to P90 mice. This was especially apparent in SERT+/- mice. However, the potency for escitalopram to produce antidepressant-like effects in SERT+/+ and SERT+/- mice was greater in P21 and P28 mice than in adults. SERT expression increased with age in terminal regions and decreased with age in cell body regions. Binding affinity values did not change as a function of age or genotype. As expected, in SERT-/- mice escitalopram produced no behavioral effects, and there was no specific [(3)H]citalopram binding. These data reveal age- and genotype-dependent shifts in the dose-response for escitalopram to produce antidepressant-like effects, which vary with SERT expression, and may contribute to the limited therapeutic response to SSRIs in juveniles and adolescents.

Introduction A solid body of preclinical evidence shows that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate the effects of substance use disorder related behaviors. The mechanisms underlying these effects remain elusive. In the present study, we hypothesized that GLP-1R activation modulates dopaminetransporter (DAT) and thus dopamine (DA) homeostasis in striatum. This was evaluated in three different experiments: two preclinical and one clinical. Methods Rat striatal DA uptake, DA clearance and DAT cell surface expression was assessed following GLP-1 (7-36)-amide exposure in vitro. DA uptake in mice was assesed ex vivo following systemic treatment with the GLP-1R agonist exenatide. In addition, DA uptake was measured in GLP-1R knockout mice and compared with DA-uptake in wild type mice. In healthy humans, changes in DAT availability was assessed during infusion of exenatide measured by single-photon emission computed tomography imaging. Results In rats, GLP-1 (7-36)-amide increased DA uptake, DA clearance and DAT cell surface expression in striatum. In mice, exenatide did not change striatal DA uptake. In GLP-1R knockout mice, DA uptake was similar to what was measured in wildtype mice. In humans, systemic infusion of exenatide did not result in acute changes in striatal DAT availability. Conclusions The GLP-1R agonist-induced modulation of striatal DAT activity in vitro in rats could not be replicated ex vivo in mice and in vivo in humans. Therefore, the underlying mechanisms of action for the GLP-1R agonists-induced efficacy in varios addiction-like behavioural models still remain.

Poorly managed gestational diabetes can lead to severe complications for mother and child including fetal overgrowth, neonatal hypoglycemia and increased autism risk. Use of metformin to control it is relatively new and promising. Yet safety concerns regarding gestational metformin use remain, as its long-term effects in offspring are unclear. In light of beneficial findings with metformin for adult mouse social behavior, we hypothesized gestational metformin treatment might also promote offspring sociability. To test this, metformin was administered to non-diabetic, lean C57BL/6 J female mice at mating, with treatment discontinued at birth or wean. Male offspring exposed to metformin through birth lost social interaction preference relative to controls by time in chambers, but not by sniffing measures. Further, prenatal metformin exposure appeared to enhance social novelty preference only in females. However due to unbalanced litters and lack of statistical power, firm establishment of any sex-dependency of metformin’s effects on sociability was not possible. Since organic cation transporter 3 (OCT3) transports metformin and is dense in placenta, social preferences of OCT3 knock-out males were measured. Relative to wild-type, OCT3 knock-outs had reduced interaction preference. Our data indicate gestational metformin exposure under non-diabetic conditions, or lack of OCT3, can impair social behavior in male C57BL6/J mice. Since OCT3 transports serotonin and tryptophan, impaired placental OCT3 function is one common mechanism that could persistently impact central serotonin systems and social behavior. Yet no gross alterations in serotonergic function were evident by measure of serotonin transporter density in OCT3, or serotonin turnover in metformin-exposed offspring brains. Mechanisms underlying the behavioral outcomes, and if with gestational diabetes the same would occur, remain unclear. Metformin’s impacts on placental transporters and serotonin metabolism or AMPK activity in fetal brain need further investigation to clarify benefits and risks to offspring sociability from use of metformin to treat gestational diabetes.

Depression is a serious public health concern. Many patients are not effectively treated, but in children and adolescents this problem is compounded by limited pharmaceutical options. Currently, the Food and Drug Administration approves only two antidepressants for use in these young populations. Both are selective serotonin reuptake inhibitors (SSRIs). Compounding matters further, they are therapeutically less efficacious in children and adolescents than in adults. Here, we review clinical and preclinical literature describing the antidepressant efficacy of SSRIs in juveniles and adolescents. Since the high-affinity serotonin transporter (SERT) is the primary target of SSRIs, we then synthesize these reports with studies of SERT expression/function during juvenile and adolescent periods. Preclinical literature reveals some striking parallels with clinical studies, primary among them is that, like humans, juvenile and adolescent rodents show reduced antidepressant-like responses to SSRIs. These findings underscore the utility of preclinical assays designed to screen drugs for antidepressant efficacy across ages. There is general agreement that SERT expression/function is lower in juveniles and adolescents than in adults. It is well established that chronic SSRI treatment decreases SERT expression/function in adults, but strikingly, SERT expression/function in adolescents is increased following chronic treatment with SSRIs. Finally, we discuss a putative role for organic cation transporters and/or plasma membrane monoamine transporter in serotonergic homeostasis in juveniles and adolescents. Taken together, fundamental differences in SERT, and putatively in other transporters capable of serotonin clearance, may provide a mechanistic basis for the relative inefficiency of SSRIs to treat pediatric depression, relative to adults.

Synthetic cathinone derivatives are a new class of psychoactive substances (NPS), also known as "bath salts", designed to exert psychostimulant effects resembling those of well-known psychostimulants, such as cocaine and 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"). As major constituents of bath salts, the cathinone derivatives 3,4-methylenedioxypyrovalerone (MDPV) and 4-methylmethcathinone (mephedrone), have received considerable media attention. MDPV and mephedrone interfere with the function of the high affinity transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT), resulting in increased extracellular levels of these monoamines, though their mechanism of action differs. MDPV acts as a non-transported inhibitor of DAT, NET and SERT, whereas mephedrone promotes transporter-mediated release in an amphetamine-like fashion. MDPV and mephedrone are often taken together, creating a conundrum in as much as non-transported inhibitors, like MDPV, prevent mephedrone-induced reverse transport via DAT, NET and SERT. Here we provide evidence supporting a role for organic cation transporter 3 (OCT3) in the actions of mephedrone, which may account for its ability to enhance effects of MDPV. We show that mephedrone can induce substrate efflux via OCT3 in the presence of MDPV. Real-time recordings of the fluorescent OCT3 substrate (4-(4-dimethylamino)styryl)-N-methylpyridinium (ASP+) and radiotracer-flux studies using [3H]1-methyl-4-phenyl-pyridinium (MPP+), demonstrated that OCT3 is MDPV-insensitive when expressed in human embryonic kidney (HEK293) cells. Ex vivo experiments performed in cultured superior cervical ganglia (SCG) cells, rich in NET and OCT3, revealed that mephedrone induces [3H]MPP+ release in an OCT3-dependent manner when NET is fully occupied with MDPV. These results extend our recent findings that OCT3 is key in the mechanism of action of amphetamine-induced substrate release. OCT3 likewise appears to be a mechanism through which mephedrone can induce release of monoamines, thereby accounting for the paradoxically more potent psychostimulant effects of MDPV taken together with mephedrone, and greater risk for deleterious side effects.

PURPOSE: Stress contributes to many psychiatric disorders; however, responsivity to stressors can vary depending on previous or current stress exposure. Relatively innocuous heterotypic (differing in type) stressors can summate to result in exaggerated neuronal and behavioral responses. Here we investigated the ability of prior high dietary sodium chloride (salt) intake, a dehydrating osmotic stressor, to enhance neuronal and behavioral responses of mice to an acute psychogenic swim stress (SS). Further, we evaluated the contribution of the osmo-regulatory stress-related neuropeptide arginine vasopressin (VP) in the hypothalamic paraventricular nucleus (PVN), one of only a few brain regions that synthesize VP. The purpose of this study was to determine the impact of high dietary salt intake on responsivity to heterotypic stress and the potential contribution of VPergic-mediated neuronal activity on high salt-induced stress modulation, thereby providing insight into how dietary (homeostatic) and environmental (psychogenic) stressors might interact to facilitate psychiatric disorder vulnerability. APPROACH: Salt loading (SL) with 4% saline for 7 days was used to dehydrate and osmotically stress mice prior to exposure to an acute SS. Fluid intake and hematological measurements were taken to quantify osmotic dehydration, and serum corticosterone levels were measured to index stress axis activation. Immunohistochemistry (IHC) was used to stain for the immediate early gene product c-Fos to quantify effects of SL on SS-induced activation of neurons in the PVN and extended amygdala – brain regions that are synaptically connected and implicated in responding to osmotic stress and in modulation of SS behavior, respectively. Lastly, the role of VPergic PVN neurons and VP type 1 receptor (V1R) activity in the amygdala in mediating effects of SL on SS behavior was evaluated by quantifying c-Fos activation of VPergic PVN neurons and, in functional experiments, by nano-injecting the V1R selective antagonist dGly[Phaa1,d-tyr(et), Lys, Arg]-VP bilaterally into the amygdala prior to the SS. FINDINGS: SL increased serum osmolality (P < 0.01), which positively correlated with time spent mobile during, and time spent grooming after a SS (P < 0.01, P < 0.01), and SL increased serum corticosterone levels (P < 0.01). SL alone increased c-Fos immunoreactivity among PVN neurons (P = 0.02), including VP positive neurons (P < 0.01). SL increased SS-induced c-Fos activation of PVN neurons as well (P

Clinical evidence indicates brain serotonin (5-HT) stores and neurotransmission may be inadequate in subpopulations of individuals with autism, and this may contribute to characteristically impaired social behaviors. Findings that depletion of the 5-HT precursor tryptophan (TRP) worsens autism symptoms support this hypothesis. Yet dietetic studies show and parents report that many children with autism consume less TRP than peers. To measure the impact of dietary TRP content on social behavior, we administered either diets devoid of TRP, with standard TRP (0.2 gm%), or with 1% added TRP (1.2 gm%) overnight to three mouse strains. Of these, BTBRT+Itpr3tf/J and 129S1/SvImJ consistently exhibit low preference for social interaction relative to C57BL/6. We found that TRP depletion reduced C57BL/6 and 129S social interaction preference, while TRP enhancement improved BTBR sociability (p < 0.05; N= 8–10). Subsequent marble burying was similar regardless of grouping. After behavior tests, brain TRP levels and plasma corticosterone were higher in TRP enhanced C57BL/6 and BTBR, while 5-HT levels were reduced in all strains by TRP depletion (p