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Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can produce seizures that rapidly progress to life-threatening status epilepticus. Significant research effort has been focused on investigating the involvement of muscarinic acetylcholine receptors (mAChRs) in OP-induced seizure activity. In contrast, there has been far less attention on nicotinic AChRs (nAChRs) in this context. Here, we address this data gap using a combination of in vitro and in vivo models. Pharmacological antagonism and genetic deletion of α4, but not α7, nAChR subunits prevented or significantly attenuated OP-induced electrical spike activity in acute hippocampal slices and seizure activity in mice, indicating that α4 nAChR activation is necessary for neuronal hyperexcitability triggered by acute OP exposures. These findings not only suggest that therapeutic strategies for inhibiting the α4 nAChR subunit warrant further investigation as prophylactic and immediate treatments for acute OP-induced seizures, but also provide mechanistic insight into the role of the nicotinic cholinergic system in seizure generation.

Acetylcholine (ACh) is a major excitatory neurotransmitter in the insect central nervous system, and insect neurons express several types of ACh receptors (AChRs). AChRs are classified into two subgroups, muscarinic AChRs and nicotinic AChRs (nAChRs). nAChRs are also divided into two subgroups by sensitivity to α-bungarotoxin (α-BGT). The cricket Gryllus bimaculatus is one of the useful insects for studying the molecular mechanisms in olfactory learning and memory. However, the roles of nAChRs in olfactory learning and memory of the cricket are still unknown. In the present study, to investigate whether nAChRs are involved in cricket olfactory learning and memory, we tested the effects of two different AChR antagonists on long-term memory (LTM) formation and retrieval in a behavioral assay. The two AChR antagonists that we used are mecamylamine (MEC), an α-BGT-insensitive nAChR antagonist, and methyllycaconitine (MLA), an α-BGT-sensitive nAChR antagonist. In crickets, multiple-trial olfactory conditioning induced 1-day memory (LTM), whereas single-trial olfactory conditioning induced 1-h memory (mid-term memory, MTM) but not 1-day memory. Crickets injected with MEC 20 min before the retention test at 1 day after the multiple-trial conditioning exhibited no memory retrieval. This indicates that α-BGT-insensitive nAChRs participate in memory retrieval. In addition, crickets injected with MLA before the multiple-trial conditioning exhibited MTM but not LTM, indicating that α-BGT-sensitive nAChRs participate in the formation of LTM. Moreover, injection of nicotine (an nAChR agonist) before the single-trial conditioning induced LTM. Finally, the nitric oxide (NO)-cGMP signaling pathway is known to participate in the formation of LTM in crickets, and we conducted co-injection experiments with an agonist or inhibitor of the nAChR and an activator or inhibitor of the NO-cGMP signaling pathway. The results suggest that nAChR works upstream of the NO-cGMP signaling system in the LTM formation process. [ABSTRACT FROM AUTHOR]

In the retrosplenial cortex (RSC), the role of cholinergic modulation via α7 nicotinic receptors and their involvement in memory is unknown. In recent years, the RSC has been shown to deteriorate in the early stages of Alzheimer's disease (AD). Likewise, the cholinergic system has been postulated as one of those responsible for cognitive impairment in patients with AD. Great interest has arisen in the study of α7 nicotinic receptors as more specific targets for the treatment of this disease. For this reason, we aim to study the role of α7 receptors of the RSC in memory processing. We infused a selective α7 receptor antagonist into the anterior part of the RSC (aRSC) to assess its role in different phases of aversive memory processing using an inhibitory avoidance task. We found that α7 nicotinic receptors are involved in memory acquisition and expression, but not in its consolidation. These results identify aRSC α7 nicotinic receptors as key players in aversive memory processing and highlight their significant potential as therapeutic targets for Alzheimer's disease. [ABSTRACT FROM AUTHOR]

In the retrosplenial cortex (RSC), the role of cholinergic modulation via α7 nicotinic receptors and their involvement in memory is unknown. In recent years, the RSC has been shown to deteriorate in the early stages of Alzheimer’s disease (AD). Likewise, the cholinergic system has been postulated as one of those responsible for cognitive impairment in patients with AD. Great interest has arisen in the study of α7 nicotinic receptors as more specific targets for the treatment of this disease. For this reason, we aim to study the role of α7 receptors of the RSC in memory processing. We infused a selective α7 receptor antagonist into the anterior part of the RSC (aRSC) to assess its role in different phases of aversive memory processing using an inhibitory avoidance task. We found that α7 nicotinic receptors are involved in memory acquisition and expression, but not in its consolidation. These results identify aRSC α7 nicotinic receptors as key players in aversive memory processing and highlight their significant potential as therapeutic targets for Alzheimer’s disease.

Therapeutic intervention for spinal cord injury is limited, with many approaches relying on strengthening the remaining substrate and driving recovery through rehabilitative training. As compared with learning novel compensatory strategies, rehabilitation focuses on restoring movements lost to injury. Whether rehabilitation of previously learned movements after spinal cord injury requires the molecular mechanisms of motor learning, or if it engages previously trained motor circuits without requiring novel learning remains an open question. In this study, mice were randomly assigned to receive intraperitoneal injection with the pan-nicotinic, non-competitive antagonist mecamylamine and the nicotinic α7 subunit selective antagonist methyllycaconitine citrate salt or vehicle (normal saline) prior to motor learning assays, then randomly reassigned after motor learning for rehabilitation study post-injury. Cervical spinal cord dorsal column lesion was used as a model of incomplete injury. Results of this study showed that nicotinic acetylcholine signaling was required for motor learning of the single pellet-reaching task but it was dispensable for the rehabilitation of the same task after injury. Our findings indicate that critical differences exist between the molecular mechanisms supporting compensatory motor learning strategies and the restoration of behavior lost to spinal cord injury.

Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can produce seizures that rapidly progress to life-threatening status epilepticus. Significant research effort has been focused on investigating the involvement of muscarinic acetylcholine receptors (mAChRs) in OP-induced seizure activity. In contrast, there has been far less attention on nicotinic AChRs (nAChRs) in this context. Here, we address this data gap using a combination of in vitro and in vivo models. Pharmacological antagonism and genetic deletion of α4, but not α7, nAChR subunits prevented or significantly attenuated OP-induced electrical spike activity in acute hippocampal slices and seizure activity in mice, indicating that α4 nAChR activation is necessary for neuronal hyperexcitability triggered by acute OP exposures. These findings not only suggest that therapeutic strategies for inhibiting the α4 nAChR subunit warrant further investigation as prophylactic and immediate treatments for acute OP-induced seizures, but also provide mechanistic insight into the role of the nicotinic cholinergic system in seizure generation.

Larkspurs (Delphinium spp.) are native forbs that are poisonous to cattle and cost livestock producers millions of dollars in losses each year. Macro and micro minerals are required for normal functioning of essentially all metabolic processes in ruminants. The role that mineral status may play in larkspur poisoning in cattle is not clear. In this study, we seek to determine the effects a mineral-salt supplement, commonly used by cattle producers, to potentially reduce cattle losses to larkspur. The ability of mineral-salt supplementation to alter susceptibility to larkspur toxicosis was evaluated in a pen study. Animals supplemented with mineral-salt were found to be less susceptible to larkspur poisoning than the non-supplemented animals. A separate group of animals were then grazed on larkspur infested rangelands. One group was supplemented with a mineral-salt mix and the other group did not receive any mineral-salt. Supplementing cattle with the mineral-salt mix did not alter larkspur consumption (P > 0.05). However, overall larkspur consumption was low and averaged 3 ± 1.0% and 2 ± 1.1% for cattle supplemented with mineral and non-supplemented, respectively. Serum was collected from animals once a week during the grazing study. Average and maximum serum concentrations of toxic larkspur alkaloids were numerically higher in mineral-salt supplemented cattle compared with the non-supplemented animals. Results from the pen study suggest that a good mineral supplementation program will provide a protective effect for animals grazing in larkspur-infested ranges. The mineral-salt supplemented steers, in the grazing study, were not observed to consume less larkspur than the non-supplemented animals; however, the mineral-salt supplemented animals had higher concentrations of larkspur alkaloids in their serum indicating they may be able to tolerate higher larkspur consumption. The data also indicate that mineral-salt supplementation must be continuous throughout the time the animals are grazing these rangelands as the positive effects can be lost within 30 d post supplementation. [ABSTRACT FROM AUTHOR]

The α7-nicotinic acetylcholine receptor (α7-nAChR) is a recognized target for the treatment of dementia associated with aging and certain developmental disorders. This study evaluates memory improvement in a rat model by the effects of polyunsaturated fatty acids EPA and DHA mediated by α7-nAChR, as well as identifying the minimum dose of EPA/DHA required to generate an effect in the improvement of cognition through α7-nAChR in rats. The modified Y-maze and object recognition behavioral tests were performed in scopolamine-induced amnesic rats, in order to study the effects of long-term supplementation (10, 15, 30, and 60 mg/kg) of the two polyunsaturated fatty acids in improving cognitive impairment. Cognitive enhancement by EPA and DHA is mediated through α7-nAChRs, as evidenced by memory recovery after treatment with a selective α7-nAChR antagonist, methyllycaconitine (MLA). Tacrine, a centrally active acetylcholinesterase inhibitor, and PNU282987, an α7-nAChR agonist, are employed as reference standards. Our data demonstrate that 15 mg/kg EPA and DHA can affect cholinergic neurotransmission positively through memory and cognition and, thus, can exert a beneficial action on learning and memory deficits. [ABSTRACT FROM AUTHOR]

Large-conductance cation channels (LCC-channels) were found in both (inner and outer) nuclear membranes of cerebellar Purkinje neurons. They are the most common type of intracellular spontaneously active ion channels among other identified. Their structure and physiological functions are still unknown, but the previous findings confirmed their sensitivity to a number of agonists/antagonists of nicotinic acetylcholine receptors. The purpose of the investigation was to estimate the effect of other regulators of the N-cholinoreceptors functioning – neostigmine, hexamethonium, and methyllycaconitine (MLA) on the LCC-channels in the nuclear membrane of cerebellar Purkinje neurons of rats. The effect of the agents was estimated based on changes in the following biophysical parameters: current amplitude, Po, channel flickering effect. Ion currents through single channels were registered using the patch-clamp technique in a nucleus-attached mode in voltage-clamp configuration. Among the studied substances, only MLA and hexamethonium influenced the LCC-channels functioning. Hexamethonium at a concentration of 2 mM reduced the Po of the LCC-channels by 46%. Under the influence of MLA, a slight effect of channel flickering was observed ("Poisson surprise" was 2.14 in the control and 3.81 under the influence of 200 μM of the substance respectively). No significant change of the biophysical characteristics of the LCC-channels under the influence of neostigmine was detected. Despite the low efficiency as LCC-channels blockers, the lack or only slight effect is a strong argument in favor of the substance usage in medicine due to their wide therapeutic potential. The severity of their effects is necessary for a comprehensive analysis of the effect patterns of the abovementioned substances on the molecular dynamics of the studied channels. The results will also be important for the identification or synthesis of new and more effective inhibitors of the LCC-channels. [ABSTRACT FROM AUTHOR]

Huntington's disease (HD) is an inheritable autosomal-dominant disorder that targets mainly the striatum. 3-Nitropropionic acid (3-NP) induces obvious deleterious behavioral, neurochemical, and histological effects similar to the symptoms of HD. Our study aimed to examine the neuroprotective activity of tropisetron, an alpha-7 neuronal nicotinic acetylcholine receptor (α-7nAChR) agonist, against neurotoxic events associated with 3-NP-induced HD in rats. Forty-eight rats were randomly allocated into four groups. Group I received normal saline, while Groups II, III and IV received 3-NP for 2 weeks. In addition, Group III and IV were treated with tropisetron 1 h after 3-NP administration. Meanwhile, Group IV received methyllycaconitine (MLA), an α-7nAChR antagonist, 30 min before tropisetron administration. Treatment with tropisetron improved motor deficits as confirmed by the behavioral tests and restored normal histopathological features of the striatum. Moreover, tropisetron showed an anti-oxidant activity via increasing the activities of SDH and HO-1 as well as Nrf2 expression along with reducing MDA level. Tropisetron also markedly upregulated the protein expression of p-PI3K and p -Akt which in turn hampered JAK2/NF-κB inflammatory cascade. In addition, tropisetron showed an anti-apoptotic activity through boosting the expression of Bcl-2 and reducing Bax expression and caspase-3 level. Interestingly, all the aforementioned effects of tropisetron were blocked by pre-administration of MLA, which confirms that such neuroprotective effects are mediated via activating of α-7nAChR. In conclusion, tropisetron showed a neuroprotective activity against 3-NP-induced HD via activating PI3K/Akt signaling and suppressing JAK2/NF-κB inflammatory axis. Thus, repositioning of tropisetron could represent a promising therapeutic strategy in management of HD. [Display omitted] • Tropisetron attenuated 3-NP-induced neurotoxicity and motor deficits. • Tropisetron enhanced neuro-survival signaling and stimulated PI3K/Akt axis. • Tropisetron mitigated neuro-inflammatory status and inhibited JAK/NF-κB p65 cascade. • Tropisetron increased SDH and OH activities as well as Nrf2 and decreased MDA. • Tropisetron boosted Bcl2 and reduced Bax and Caspase-3. [ABSTRACT FROM AUTHOR]

Acetylcholine (ACh) is a major excitatory neurotransmitter in the insect central nervous system, and insect neurons express several types of ACh receptors (AChRs). AChRs are classified into two subgroups, muscarinic AChRs and nicotinic AChRs (nAChRs). nAChRs are also divided into two subgroups by sensitivity to α-bungarotoxin (α-BGT). The cricket Gryllus bimaculatus is one of the useful insects for studying the molecular mechanisms in olfactory learning and memory. However, the roles of nAChRs in olfactory learning and memory of the cricket are still unknown. In the present study, to investigate whether nAChRs are involved in cricket olfactory learning and memory, we tested the effects of two different AChR antagonists on long-term memory (LTM) formation and retrieval in a behavioral assay. The two AChR antagonists that we used are mecamylamine (MEC), an α-BGT-insensitive nAChR antagonist, and methyllycaconitine (MLA), an α-BGT-sensitive nAChR antagonist. In crickets, multiple-trial olfactory conditioning induced 1-day memory (LTM), whereas single-trial olfactory conditioning induced 1-h memory (mid-term memory, MTM) but not 1-day memory. Crickets injected with MEC 20 min before the retention test at 1 day after the multiple-trial conditioning exhibited no memory retrieval. This indicates that α-BGT-insensitive nAChRs participate in memory retrieval. In addition, crickets injected with MLA before the multiple-trial conditioning exhibited MTM but not LTM, indicating that α-BGT-sensitive nAChRs participate in the formation of LTM. Moreover, injection of nicotine (an nAChR agonist) before the single-trial conditioning induced LTM. Finally, the nitric oxide (NO)-cGMP signaling pathway is known to participate in the formation of LTM in crickets, and we conducted co-injection experiments with an agonist or inhibitor of the nAChR and an activator or inhibitor of the NO-cGMP signaling pathway. The results suggest that nAChR works upstream of the NO-cGMP signaling system in the LTM formation process., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Matsumoto, Matsumoto and Mizunami.)

Escitalopram, a drug of choice in the treatment of depression, was recently shown to possess an anti-inflammatory activity. The aim of the present study was to elucidate the effect of escitalopram on peripheral inflammatory cascades in iodoacetamide-induced colitis associated with depressive behavior in ovariectomized rats. Moreover, the role of α-7 nicotinic acetylcholine receptor in mediating the anti-colitic effect of escitalopram was examined using a nicotinic receptor antagonist methyllycaconitine citrate. Colitis was induced by intracolonic injection of 4% iodoacetamide in ovariectomized rats. Escitalopram (10 mg/kg/day, i.p.) was then injected for 1 week and several parameters including macroscopic (colon mass index and ulcerative area), microscopic (histopathology and scoring), and biochemical (myeloperoxidase and tumor necrosis factor-α) were determined. Colitis induction in ovariectomized rats resulted in a marked increase in colon mass index, ulcerative area, histopathological scoring, myeloperoxidase activity and tumor necrosis factor-α levels. These effects were ameliorated by escitalopram, even in the presence of methyllycaconitine indicating that α-7 nicotinic acetylcholine receptor does not mediate the anti-inflammatory effect of escitalopram. The present study revealed the beneficial effect of escitalopram in iodoacetamide induced colitis in ovariectomized rats and suggests that it may represent a new therapeutic agent for the treatment of inflammatory bowel disease, especially in patients with or at high risk of depressive behavior. [ABSTRACT FROM AUTHOR]

Recurrent relapse is a major problem in treating opiate addiction. Pavlovian conditioning plays a role in recurrent relapse whereby exposure to cues learned during drug intake can precipitate relapse to drug taking. α7 nicotinic acetylcholine receptors (nAChRs) have been implicated in attentional aspects of cognition and mechanisms of learning and memory. In this study we have investigated the role of α7 nAChRs in morphine-conditioned place preference (morphine-CPP). CPP provides a model of associative learning that is pertinent to associative aspects of drug dependence. The α7 nAChR antagonist methyllycaconitine (MLA; 4 mg/kg s.c.) had no effect on the acquisition, maintenance, reconsolidation or extinction of morphine-CPP but selectively attenuated morphine-primed reinstatement of CPP, in both mice and rats. Reinstatement of morphine-CPP in mice was accompanied by a selective increase in [3 H]-AMPA binding (but not in [3 H]-MK801 binding) in the ventral hippocampus that was prevented by prior treatment with MLA. Administration of MLA (6.7 μg) directly into the ventral hippocampus of rats prior to a systemic priming dose of morphine abolished reinstatement of morphine-CPP, whereas MLA delivered into the dorsal hippocampus or prefrontal cortex was without effect. These results suggest that α7 nAChRs in the ventral hippocampus play a specific role in the retrieval of associative drug memories following a period of extinction, making them potential targets for the prevention of relapse. [ABSTRACT FROM AUTHOR]

Larkspur (Delphinium spp.) poisoning is a long-term problem for cattle grazing on rangelands of western North America. Recent research has shown that both plant and animal-based factors are critical in understanding and mitigating larkspur poisoning in cattle. Non-toxicological factors including sex, age, cattle breed, and plant chemotype affect cattle responses to larkspur. For example, Angus heifers are more susceptible to larkspur intoxication than are steers or bulls. Young cattle appear to be more susceptible to larkspur poisoning than mature animals. Beef breeds of cattle are more susceptible to larkspur intoxication than dairy breeds. In addition to animal factors, plant alkaloid composition (chemotype) affects the potential toxicity for cattle because of differences in the ratios and concentrations of highly toxic N -(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids compared to less lethal non-MSAL-type alkaloids. Animal- and plant-based factors can provide substantial information to inform livestock producers on management to reduce risk and cattle losses to various larkspur species in western North America. • Larkspurs (Delphinium spp.) are a significant problem for cattle grazing on rangelands of western North America. • Cattle age, breed, and sex are important factors in the physiological response to larkspur toxins. • Larkspur plant alkaloid composition (chemotype) also affects the intoxication of cattle. [ABSTRACT FROM AUTHOR]

Abstract Larkspurs (Delphinium spp.) are native perennial plants that have a serious toxic potential to cattle on foothill and mountain rangelands in the western United States. Livestock death due to larkspur toxicity is attributed to norditerpenoid alkaloids. Diagnosing plant poisonings in livestock is often challenging. The objective of this study was to evaluate the use of three matrices; earwax, oral fluid, and nasal mucus, as noninvasive specimens to determine livestock exposure to larkspurs. Reversed phase high performance liquid chromatography – high resolution mass spectrometry was used to analyze for norditerpene alkaloids, in all three matrices, in cattle administered a single dose of larkspur. Earwax, oral fluid, and nasal mucus were collected over 6 days post-dosing. Methyllycaconitine (MLA) and deltaline concentrations in earwax ranged from 0.4 ± 0.1 to 0.2 ± 0.06 and 0.6 ± 0.5 to 0.11 ± 0.08 ng/mg, respectively. MLA and deltaline concentrations in oral fluid ranged from 0.08 ± 0.03 to 0.01 ± 0.002 ng/mg and 0.07 ± 0.03 ng/mg to not detected (ND), respectively. MLA and deltaline concentrations in nasal mucus ranged from 0.2 ± 0.13 to 0.03 ± 0.01 ng/mg and 0.2 ± 0.12 ng/mg to ND, respectively. The ability to detect differing norditerpene alkaloid chemotypes from two different Delphinium spp. was also possible in the three matrices. This study demonstrates the potential of earwax, oral fluid, and nasal mucus as noninvasive specimens for chemical analyses to aid in the diagnosis of livestock that may have been exposed to and poisoned by larkspur plants. Highlights • Diagnosing plant poisonings in livestock is often challenging. • Earwax, oral fluid, and nasal mucus can aid in the diagnosis of livestock exposure to plant toxins. • Alkaloid profiles from larkspur consisting of diverse chemotypes were differentiated in earwax, oral fluid, and nasal mucus. • Earwax, oral fluid, and nasal mucus can be used for analyses to aid in the diagnosis of livestock exposure to larkspur. [ABSTRACT FROM AUTHOR]

Larkspur (Delphinium spp.) poisoning is a long-term problem for cattle grazing on rangelands of western North America. Results from preliminary experiments have suggested that differences in larkspur toxicity may exist between heifers and bulls. The objective of this study was to compare the physiological responses of yearling Angus heifers, steers, and bulls with a standardized dose of Delphinium barbeyi and to test the hypothesis that the response is sex dependent. Clinical signs of intoxication, including muscle coordination and function, were measured 24 h after oral dosing with larkspur by walking the cattle at a pace of 5 to 6 km h−1 for up to 40 min on an oval dirt track. Due to the experimental methods used, the variation in susceptibility to larkspur was not quantifiable for walking times of 0 or 40 min or more. Larkspur susceptible animals that were not able to walk (0 min; 36% of the animals) or larkspur resistant animals that walked the entire test period of 40 min (9% of the animals) resulted in censored or truncated data. The statistical methods (censReg and lmec) were used to adjust for data truncation or censoring. The heifers were only able to walk −8.9 ± 3.9 min (65.5% censored on the left) compared with 13.2 ± 3.7 min for bulls and 15.9 ± 2.7 min for steers. When heifers were compared with bulls and steers together, heifers walked 23.4 ± 4.5 min less (P < 0.0001). Serum alkaloid concentrations were measured immediately before walking, and deltaline concentrations averaged 266 ± 28, 131 ± 20, and 219 ± 28 ng mL−1 for all heifers, steers, and bulls, respectively, and serum methyllycaconitine concentrations averaged 660 ± 46, 397 ± 32, and 612 ± 34 ng mL−1 for all heifers, steers, and bulls, respectively. The relative risk of a zero walk time for yearling heifers is 330% that of yearling bulls (P = 0.0008). These results suggest that yearling Angus heifers are more susceptible to larkspur intoxication and, when possible, heifers should be kept from grazing larkspur-infested rangelands as a simple management tool to reduce the risk of fatal poisoning. [ABSTRACT FROM AUTHOR]

Cattle losses from larkspur (Delphinium spp.) toxicity are a long-term challenge on the rangelands of western North America. In addition to animal factors that affect livestock poisonings, plant alkaloid composition (chemotype) affects the intoxication of cattle because some chemotypes are significantly more toxic. Differences in larkspur chemotype toxicity are due to the ratios of N -(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids to non-MSAL-type alkaloids and the concentrations of those alkaloids in the plant material. The objective of this study was to compare the responses of 6 Angus heifers to 6 chemotypes of larkspur using a Latin square study design. These Angus heifers from the USDA-ARS, Meat Animal Research Center in Clay Center, NE, were chosen for this research because they are the most larkspur-susceptible cattle observed to date. The 6 heifers were given an oral dose of dried ground larkspur and tested for muscle weakness with an exercise test (i.e. walk time). The 6 chemotypes of larkspur had non-MSAL to MSAL-type alkaloid ratios ranging from 1.4:1 to 6:1 and were administered at an oral dose of 7.5 mg/kg MSAL-type alkaloids BW. There was a treatment effect due to larkspur chemotype (P < 0.0001), and period effects were not significant (P = 0.6). There were also significant correlations between the length of time walking on a dirt track at 5 to 6 km/h, and total alkaloid dose (r = −0.92, P = 0.0045) and alkaloid ratio (r = −0.81, P = 0.0258). Serum alkaloid concentrations at 24 h after dosing were representative of the relative abundance of the alkaloid in the plant material. Results from this work suggest that total alkaloid concentrations in combination with alkaloid ratios can be used together to accurately predict the plant risk component of larkspur poisoning to grazing cattle. Animal factors such as cattle age, breed, and sex must also be considered to comprehensively manage larkspur risk. [ABSTRACT FROM AUTHOR]

There are numerous species of larkspur (Delphinium spp.) in North America. Larkspurs are a major cause of cattle losses on western ranges in the USA, especially on foothill and mountain rangelands. The toxicity of larkspur species is due to various norditerpenoid alkaloids. In this article, we review the current knowledge regarding larkspur ecology and distribution, analytical technologies to study and quantify the toxins in larkspur, the toxicology of the larkspur plants and their individual toxins, known genetic variations in larkspur susceptibility, and current management recommendations to mitigate losses from larkspur poisoning.

Aims: Studies have shown that stellate ganglion nerve activity has association with atrial electrical remodelling and atrial fibrillation (AF) inducibility, while median nerve stimulation (MNS) decreases cardiac sympathetic drive. In this study, we tested the hypothesis that MNS suppresses atrial electrical remodelling and AF vulnerability.Methods and results: The atrial effective refractory period (AERP) and AF inducibility at baseline and after 3 h of rapid atrial pacing were determined in dogs undergoing MNS (n = 7), MNS+ application of methyllycaconitine (n = 7) or sham procedure (n = 6). Then, the levels of tumour necrosis factor-alpha (TNF-a), interleukin-6 (IL-6), and acetylcholine (Ach) in the plasma and atrial tissues were measured. The control dogs (n = 4) were assigned to measure atrial inflammation cytokines. Short-term rapid atrial pacing induced shortening of the AERP, an increase in AERP dispersion, and an increase AF vulnerability in the sham dogs, which were all suppressed by MNS. Levels of TNF-a and IL-6 were higher, and Ach levels were lower in the left and the right atrium in the sham dogs than in the MNS dogs. Methyllycaconitine blunted the effects of MNS on the AERP, AERP dispersion, the AF vulnerability, and TNF-a and IL-6 levels in the atrium, but had no impact on the levels of Ach.Conclusions: The effects of MNS on atrial electrical remodelling and AF inducibility might be associated with the cholinergic anti-inflammatory pathway. [ABSTRACT FROM AUTHOR]

The aim of the present study was to identify in vivo electrophysiological correlates of the interaction between cholinergic and glutamatergic neurotransmission underlying memory. Extracellular spike recordings were performed in the hippocampal CA1 region of anesthetized rats in combination with local microiontophoretic administration of N-methyl-D-aspartate (NMDA) and acetylcholine (ACh). Both NMDA and ACh increased the firing rate of the neurons. Furthermore, the simultaneous delivery of NMDA and ACh resulted in a more pronounced excitatory effect that was superadditive over the sum of the two mono-treatment effects and that was explained by cholinergic potentiation of glutamatergic neurotransmission. Next, animals were systemically treated with scopolamine or methyllycaconitine (MLA) to assess the contribution of muscarinic ACh receptor (mAChR) or α7 nicotinic ACh receptor (nAChR) receptor-mediated mechanisms to the observed effects. Scopolamine totally inhibited ACh-evoked firing, and attenuated the firing rate increase evoked by simultaneous application of NMDA and ACh. However, the superadditive nature of the combined effect was preserved. The α7 nAChR antagonist MLA robustly decreased the firing response to simultaneous application of NMDA and ACh, suspending their superadditive effect, without modifying the tonic firing rate increasing effect of ACh. These results provide the first in vivo electrophysiological evidence that, in the hippocampal CA1 region, α7 nAChRs contribute to pyramidal cell activity mainly through potentiation of glutamatergic signaling, while the direct cholinergic modulation of tonic firing is notably mediated by mAChRs. Furthermore, the present findings also reveal cellular physiological correlates of the interplay between cholinergic and glutamatergic agents in behavioral pharmacological models of cognitive decline.

The aim of the present study was to identify in vivo electrophysiological correlates of the interaction between cholinergic and glutamatergic neurotransmission underlying memory. Extracellular spike recordings were performed in the hippocampal CA1 region of anesthetized rats in combination with local microiontophoretic administration of N-methyl-D-aspartate (NMDA) and acetylcholine (ACh). Both NMDA and ACh increased the firing rate of the neurons. Furthermore, the simultaneous delivery of NMDA and ACh resulted in a more pronounced excitatory effect that was superadditive over the sum of the two mono-treatment effects and that was explained by cholinergic potentiation of glutamatergic neurotransmission. Next, animals were systemically treated with scopolamine or methyllycaconitine (MLA) to assess the contribution of muscarinic ACh receptor (mAChR) or α7 nicotinic ACh receptor (nAChR) receptor-mediated mechanisms to the observed effects. Scopolamine totally inhibited ACh-evoked firing, and attenuated the firing rate increase evoked by simultaneous application of NMDA and ACh. However, the superadditive nature of the combined effect was preserved. The α7 nAChR antagonist MLA robustly decreased the firing response to simultaneous application of NMDA and ACh, suspending their superadditive effect, without modifying the tonic firing rate increasing effect of ACh. These results provide the first in vivo electrophysiological evidence that, in the hippocampal CA1 region, α7 nAChRs contribute to pyramidal cell activity mainly through potentiation of glutamatergic signaling, while the direct cholinergic modulation of tonic firing is notably mediated by mAChRs. Furthermore, the present findings also reveal cellular physiological correlates of the interplay between cholinergic and glutamatergic agents in behavioral pharmacological models of cognitive decline. [ABSTRACT FROM AUTHOR]

Poisoning of cattle by larkspur plants ( Delphinium spp.) is a concern for cattle ranchers in western North America. Previous research studies have evaluated the toxicokinetic profile of multiple larkspur toxins in several livestock species. However, those studies were all performed by orally dosing plant material. Consequently some toxicokinetic parameters could not be definitively determined. In this study, we compared the serum toxicokinetic profile of the larkspur alkaloids methyllycaconitine (MLA) and deltaline in goats dosed both IV and via oral gavage. The results from this study indicate that the toxic alkaloids in larkspurs undergo flip-flop kinetics, meaning the rate of absorption of the alkaloids is slower than the rate of elimination. The implications of flip-flop kinetics in treating animals poisoned by larkspur is discussed. [ABSTRACT FROM AUTHOR]

Quantitative analysis of antagonism is infrequently used to identify nAChRs mediating behavioral effects. Here, nicotine (0.032 mg/kg i.v.) was established as a discriminative stimulus in rhesus monkeys responding under a fixed ratio 5 schedule; pharmacokinetics and underlying nAChR mechanism(s) were examined. When measured up to 4 h in venous blood, the training dose resulted in the following mean pharmacokinetic parameters: nicotine C max = 71.7 ng/ml, t 1/2 = 116 min, and clearance = 6.25 ml/min/kg; cotinine C max = 191 ng/ml; and 3OH-cotinine C max = 63 ng/ml. The ED 50 value of nicotine to produce discriminative stimulus effects was 0.013 mg/kg. Epibatidine and varenicline increased drug-lever responding to 97% and 95%, respectively (ED 50 values = 0.00015 and 0.031 mg/kg, respectively), whereas cocaine, midazolam, and morphine produced no more than 28% drug-appropriate responding. Mecamylamine and dihydro-β-erythroidine (DHβE) dose-dependently attenuated the discriminative stimulus effects of the nicotine training dose, whereas methyllycaconitine (MLA) did not. DHβE (0.1 and 0.32) produced rightward shifts of the nicotine and varenicline dose-response functions; Schild plots fitted through individual data resulted in slopes that were not different from unity; the apparent pA 2 calculated for DHβE did not significantly differ in the presence of nicotine (6.58) or varenicline (6.45). Compared to human cigarette smoking, nicotine blood levels after 0.032 mg/kg nicotine i.v. took a similar time to reach maximal concentration, levels at Cmax were similar to smoking 2–3 cigarettes, while average nicotine levels were comparable to smoking 5–6 cigarettes. Apparent pA 2 analysis with DHβE under these conditions is consistent with nicotine and varenicline acting through the same nAChRs to produce discriminative stimulus effects. [ABSTRACT FROM AUTHOR]

Methyllycaconitine and the new C-diterpene alkaloid flexiosine were isolated from roots of Delphinium flexuosum M. Bieb. The structure of the latter was elucidated using PMR, C NMR, and IR spectroscopy and mass spectrometry. [ABSTRACT FROM AUTHOR]

Larkspurs ( Delphinium spp.) are a major cause of cattle losses in western North America, whereas sheep are thought to be resistant to larkspur toxicosis. Goats are often used as a small ruminant model to study poisonous plants. In this study, we compared the serum toxicokinetic profile of toxic larkspur alkaloids from Delphinium barbeyi in cattle, goats, and sheep. The results from this study indicate that kinetic differences could partially explain species differences in susceptibility to larkspur toxicosis. [ABSTRACT FROM AUTHOR]

Cholinergic transmission in both the medial vestibular nucleus (MVN) and prepositus hypoglossi nucleus (PHN) plays an important role in horizontal eye movements. We previously demonstrated that the current responses mediated via nicotinic acetylcholine receptors (nAChRs) were larger than those mediated via muscarinic acetylcholine receptors (mAChRs) in cholinergic MVN and PHN neurons that project to the cerebellum. In this study, to clarify the predominant nAChR responses and the expression patterns of nAChRs in MVN and PHN neurons that exhibit distinct neurotransmitter phenotypes, we identified cholinergic, inhibitory, and glutamatergic neurons using specific transgenic rats and investigated current responses to the application of acetylcholine (ACh) using whole cell recordings in brain stem slices. ACh application induced larger nAChR-mediated currents than mAChR-mediated currents in every neuronal phenotype. In the presence of an mAChR antagonist, we found three types of nAChR-mediated currents that exhibited different rise and decay times and designated these as fast (F)-, slow (S)-, and fast and slow (FS)-type currents. F-type currents were the predominant response in inhibitory MVN neurons, whereas S-type currents were observed in the majority of glutamatergic MVN and PHN neurons. No dominant response type was observed in cholinergic neurons. Pharmacological analyses revealed that the F-, S-, and FS-type currents were mainly mediated by α7, non-α7, and both α7 and non-α7 nAChRs, respectively. These findings suggest that cholinergic responses in the major neuronal populations of the MVN and PHN are predominantly mediated by nAChRs and that the expression of α7 and non-α7 nAChRs differ among the neuronal phenotypes. [ABSTRACT FROM AUTHOR]

Abstract The effect of age on larkspur poisoning of cattle is unknown. An experiment consisting of oral dosing of dried, ground, Delphinium barbeyi to ten Angus steers as yearlings, and again at two years was performed. There was a significant difference between the responses of yearling and two year old steers (P = 0.0015), with yearling steers being more susceptible. These results suggest that the adverse response of Angus cattle to larkspur is age-dependent. Highlights • Larkspurs ( Delphinium spp. ) are a significant problem for cattle grazing on rangelands of the western North America. • Oral dosing of dried, ground, Delphinium barbeyi to ten Angus steers as yearlings, and again at two years was performed. • There was a significant difference between the responses of yearling and two year old steers (P = 0.0015). [ABSTRACT FROM AUTHOR]