PCB126 is the most potent agonist of the aryl hydrocarbon receptor (AhR) in the whole family of chlorinated biphenyls (PCBs), a class of persistent organic pollutants that are classified as probable human carcinogens. It exerts systematic toxicities in animals mainly through the AhR pathway and generates cellular oxidative stress which might damage cellular macromolecules. The goal of this thesis is to elucidate the mechanisms of PCB126 toxicity in the aspect of AhR-related oxidative stress. Reactive superoxide radicals could be generated as the result of electron leakage in the catalytic cycles of cytochrome P450 (CYP) enzymes which are super-induced by sustained AhR activation in response to PCB126. In addition, the disruption of mitochondrial electron transport chain caused by AhR ligands also contributes to the production of superoxide radicals. Correspondingly in this thesis, the impact of PCB126 on the expression of the recently-discovered, TCDD-inducible microsomal CYP2S1 enzyme was studied. Then the regulation of mitochondrial antioxidant enzyme MnSOD in response to PCB126 was investigated. Lastly, a microarray study on classic AhR ligands of β-naphthoflavone and 3-methylcholanthrene was conducted to explore possible mechanisms of AhR-associated toxicities and to find explanations for the regulation of CYP2S1 as well as MnSOD after PCB126 exposure. It was found that CYP2S1 was only weakly or not at all regulated by PCB126 in rats. As for MnSOD, although its messenger and protein levels were induced by PCB126, its enzymatic activity was significantly reduced in the liver, probably through post-translational mechanisms. Although dietary manganese supplementation did not reverse the loss of MnSOD activity due to PCB126 exposure, it significantly protected against liver hypertrophy caused by PCB126. Microarray study results were consistent with previous findings and indicated that in addition to changed expression of a number of CYPs, metal homeostasis as well as mitochondria functions were also affected by AhR ligands. Overall, both CYP enzymes and the mitochondria contribute to the AhR-mediated toxicities of PCB126 that are associated with a disturbance of cellular redox homeostasis.

Metabolic Syndrome (MetS) is a collective term for a cluster of disorders, including dysglycemia, central obesity, dyslipidemia, hypertension, and eventual end organ damage. The combination of these disorders increases the risk of many kinds of end organ damages, including coronary heart disease, kidney failure, and cirrhosis. MetS is highly prevalent in the United States, affecting one third of the U.S. population in a 2009 estimate. The Lyon strains are three rat strains selectively inbred from the same colony of outbred rats for different blood pressure levels. The Lyon Hypertensive (LH) strain, in addition to its essential hypertension phenotype, also harbors many disorders found in MetS. The Lyon Normotensive (LN) rat strain is completely devoid of these symptoms, while Lyon Low-pressure (LL) is obese but is resistant to other traits of MetS. Rat chromosome 17 (RNO17) has previously been linked with many of MetS' phenotypes in Lyon Hypertensive (LH). In this project, we are using a mixture of genetical genomics and systems biology methods to identify genetic elements that may cause the LH phenotype. Divergent haplotype blocks between the Lyon strains were first identified by the analysis of the distribution of observed strain differences (OSD) calculated from the result of genome resequencing. Divergent haplotype regions totaling less than 16% of the rat genome that contain more than 95% of the identified SNPs in each of the three pairwise comparisons between the Lyon strains have been identified; in particular, there are 14 divergent haplotype blocks between LH and LN spanning 7.7% of RNO17 that harbor more than 97% of SNPs identified on RNO17. Twenty-five genes in these regions were thus identified as potential genetic determinants for MetS. Phenotypic QTLs (pQTL) and expression QTLs (eQTL) mapping from a cohort of male LH × LN F2 rats were performed by putting the cohort on a 15-week phenotyping protocol and genome-wide genotyping. Total liver RNA from 36 individuals from the cohort were sequenced to provide expression data for eQTL mapping. We have mapped 22 pQTLs that are statistically linked to 15 traits, with RNO17 linked to 15 traits associated with blood pressure, leptin and body weight. We have also identified 1,200 eQTLs from this cohort, including 11 eQTLs with cis-linkage with one or more genes. On RNO17, we have identified two SNPs between 29-39 Mb which are significantly linked to the expression of 85 genes; the only gene with cis-linkage with these SNPs, RGD1562963, was hence identified as a putative master regulator. Transcriptome analyses were then performed on the Lyon parental animals; the total liver and kidney of RNA from 6 each of LH, LL and LN strains that were subjected to the same 15-week phenotyping protocol were sequenced for differential expression analysis, gene coexpression network analysis and quantitative trait transcript analysis. Differential expression analysis identified 4 genes on RNO17's divergent haplotype regions: Cul2 and the aforementioned RGD1562963 for liver, Amph and Bambi for kidney. Quantitative trait transcript analyses have shown significant correlations between the expressions of these four genes with one or more of the traits of the animals treated, validating their status as potential genetic determinants for MetS. However, out of the 84 genes that RGD1562963 potentially regulates, only two other genes (Cul2 and Supt4h1) have significant correlations with one or more traits. Gene coexpression network analyses have shown a relationship between genes on the TGF-β pathway and the differentially expressed genes in the kidney, supporting our speculation on the hyperactivity of the TGF-β system in the etiology of the LH phenotypes. An LH-17LN consomic strain was also generated by introgressing an LN copy of RNO17 onto the LH genomic background to validate in vivo the role of RNO17 in the etiology of MetS symptoms in LH. We have observed that the consomic strain has significantly decreased body weight, adiposity, blood pressure, and inter-week blood pressure differences that may be a surrogate for salt sensitivity. Thus, the role of RNO17 on the LH genotype is validated. In summary, we have been able to identify, by in vivo and in silico methods, that RNO17 is related to the MetS traits in LH; that 4 genes, Amph, Bambi, Cul2, and RGD1562963, are potential genetic contributors to RNO17's effects; and that their effects may include, but are not limited to, the activation of TGF-Β signals.

Resurgence refers to the reappearance of an extinguished operant behavior when reinforcement for an alternative behavior is also discontinued. It is especially relevant to the reappearance of problem behavior because many behavioral interventions discontinue reinforcement for aberrant behavior while simultaneously reinforcing an appropriate response. Existing information about the neuropharmacology of resurgence is scarce, but suggests overlap between drug seeking observed in the resurgence model and drug seeking observed in the more widely studied reinstatement and renewal models. The aim of this dissertation was to explore additional neural systems relevant to reinstatement and renewal preparations within a resurgence paradigm to assess further overlap. The neuropharmacology of resurgence was examined in two studies via administration of two drugs that have proven effective in blocking drug seeking in reinstatement and renewal preparations. In two experiments, rats earned food pellets for pressing a target lever in Phase I. In Phase II, lever pressing no longer produced food, but food was delivered contingent on an alterative nose poke response. Finally in Phase III, neither response produced food deliveries. Prior to these Phase III sessions, separate groups of rats were injected with 0, 50, or 100 mcg/kg of the dopamine D-2 receptor antagonist raclopride in Experiment 1 or 0, 20, or 40 mcg/kg of alpha-2 agonist clonidine in Experiment 2. Both doses of raclopride were effective in blocking resurgence, but there was strong evidence that the higher dose did so via motor rather than motivational impairment. Furthermore, the lower dose significantly suppressed the alternative nose poke, which suggests motor impairment, as well. Only the higher dose of clonidine blocked resurgence, but did so with no evidence of motor impairment. Raclopride significantly impacted extinction of the alternative poke at both doses tested, whereas clonidine had no effect at either dose. The results of the present studies provide additional information about the neuropharmacology of resurgence, as well as additional evidence of overlap between resurgence, reinstatement, and renewal. The present results may also have implications regarding underlying neural mechanisms and for pharmacotherapies to attenuate relapse when alternative sources of reinforcement are thinned or discontinued.

The effect of Mg status on the behavior of rats, as determined by nonspecific excitability level and audio genic seizure susceptibility, was investigated. Also, selected biochemical and neurological mechanisms mediating the chain of events from dietary magnesium deficit to the hyper excitability symptoms were examined. Weanling rats fed a low magnesium (10 ppm) diet for 14 days had reduced serum, cerebrospinal fluid and brain magnesium concentrations, and increased brain (Na+ K+)-ATPase activity. They exhibited increased NEL and became highly susceptible to audio genic seizures. Through dietary manipulation and intraperitoneal and cerebral intraventricular injections, it was possible selectively to alter either serum or cerebrospinal fluid magnesium concentrations. Both nonspecific excitability level and audio genic seizure susceptibility responded inversely to cerebrospinal fluid magnesium concentration, but not to serum magnesium, unless the latter was very high. In this instance, nonspecific excitability level but not seizure activity was depressed. Brain serotonin concentration was elevated in 150- 200 g rats fed a low magnesium diet for 21 days, compared with rats fed a control diet (0.73 μg/g fresh brain cf. 0.56 μg/g) . The magnesium deficient rat may serve as an excellent model for epilepsy research. The animal can often be revived following seizure, thus enabling the study of drug interactions while using a small number of subjects. Preliminary findings indicate that the most promising subjects are female rats between 3 and 5 weeks old at the start of feeding and who are fed a low magnesium diet 17 to 21 days. A procedure for determining (Na+ K+)-ATPase activity in rat brain homogenates, without requiring isolation or purification, is described. Computer modeling techniques have yielded expressions for equating enzyme activity to sodium, potassium, magnesium or calcium concentrations in the reaction media. A thorough statistical treatment of the data is presented.

A series of in vitro trials have been conducted to determine what relationship exists between zinc and the insulin mechanism. There were no significant differences of the zinc contents in total pancreases excised from the rats thirty minutes after the intraperitoneal glucose dose or from the non-dosed controls. When pancreases were cut into three pieces, and treated in three ways: Incubated without glucose (IWG) followed by isolation of the islets; incubated with glucose (IWG) followed by isolation of the islets; islets were isolated, then incubated with glucose (IWG). The zinc content in the islets was significantly higher (p < 0.01) in the first group than the others. The insulin release and zinc movement were studied in zinc-deficient status. In both Experiment 3 and 5 each pancreas was divided into two, one was treated IWG, one was treated IWOG. There were significant (p < 0.01) differences of zinc content in the islets between lWG and IWOG groups in zinc-supplemented pair-fed and ad lib. controls but not in zinc-deficient rats. In Experiment 5 the zinc contents in the islets of IWOG group were significantly (p < 0.01) lower in zinc-deficient rats than in zinc-supplemented pair-fed rats. Insulin release from the islets incubated with glucose was significantly (p < 0.01) less in zinc-deficient group than in zinc-supplemented pair-fed group. Glutathione contents of the pancreases were measured in Experiment 3, no significant difference was found between zinc-deficient group and both zinc-supplemented groups. Rats were intraperitoneally dosed with glucose or with saline in Experiment 6. After 30 minutes pancreases were excised and the isolated islets were treated with IWG or IWOG. There was no significant difference of zinc content in the islets treated IWOG in glucose-dosed and saline0dosed groups, but significant (p < 0.01) difference was found in the islets treated IWG. Insulin release from the islets treated IWG was significantly (p < 0.01) less in glucose-dosed group than in saline-dosed group. It is concluded that zinc is released from the islets as a component of insulin on glucose stimulation, zinc-deficiency results in an impairment of insulin release or synthesis, and insulin secretion was reduced in the isolated islets taken from animals prestimulated with glucose in vivo.

Angiostrongylus cantonensis is a parasitic nematode endemic to tropical and subtropical regions and is the leading cause of human eosinophilic meningitis. The parasite is commonly known as rat lungworm because the primary host in its lifecycle is the rat. A clinical overview of rat lungworm infection is presented, followed by a literature review of rat lungworm epidemiology, risk factors, and surveillance projects. Data collected from previous snail surveys in Florida was considered alongside elevation, population per square kilometer, median household income by zip code territory, and normalized difference vegetation index specific to the geographic coordinates from which the snail samples were retrieved. The parameters of interest were incorporated as possible predictor variables in a Poisson probability regression model and a negative binomial regression model. NDVI and population density were determined to be positively associated with number of snail samples positive for A. cantonensis in a given Miami-based location. A surveillance project was conducted in Hillsborough County, Florida, U.S.A.. Snail samples were collected and tested for A. cantonensis DNA via polymerase chain reaction (PCR) and gel electrophoresis. None of the samples tested positive for A. cantonensis.

Doctor of Philosophy (PhD) / Abstract Olfactory tasks are used very often with laboratory animals in studies of the neurobiology of learning and memory. Rats and mice are extremely sensitive in their detection and discrimination of odours, learn olfactory tasks rapidly, and can display higher order cognitive functions in olfactory tasks. This cognitive capacity may rival the ability of primates to learn analogous tasks with visual cues and most likely reflects strong anatomical connections between the olfactory bulbs and higher brain regions such as the piriform cortex, orbitofrontal cortex and hippocampus. The current thesis explored olfactory discrimination learning and performance in rats and had two principal aims. The first part of the thesis was oriented around odour masking phenomena in rats: the ability of one odour in a mixture to suppress detection of a second odour in that mixture. A specialized behavioural paradigm was developed to allow the study of odour masking in the rat. The second part of the thesis was pharmacological and determined whether the acquisition, reversal and performance of olfactory discriminations, and analogous auditory discriminations, are affected by two commonly used classes of drugs (benzodiazepines and cannabinoids). Together, these studies attempt to gain a better understanding of the nature of olfactory discrimination learning in rats, by using both psychophysical and pharmacological approaches, and to develop behavioural paradigms which may be used in future psychophysical and pharmacological studies. Following an introduction and review of olfactory and auditory studies in rat (Chapter 1), odour masking phenomena were studied in Chapter 2. The aliphatic aldehydes butanal (C4) and heptanal (C7) were used in the study. Aldehydes were of interest as this class of odorants abound in nature and may be important for rodents’ species-specific communication. Thirsty rats were initially trained to discriminate C4 and C7 in the olfactometer, using a go/no-go olfactory discrimination task. This involved rats learning to nose poke in an odour port and to lick a tube for a water reward on presentation of the rewarded component S+, while withholding licking at the tube when the other, unrewarded, aldehyde (S-) was presented. Odour mixtures (C4C7 or C7C4) were then introduced into the task as an additional non-rewarded condition (mixture S-). The concentration of the non-rewarded aldehyde in the mixture was then systematically decreased, while the concentration of the rewarded aldehyde was kept constant. When the non-rewarded aldehyde reached a critical low level in the mixture, rats started to make responses to the non-rewarded mixture (false alarms) showing that the S+ odour was suppressing the S- odour in the mixture, so the mixture was being responded to in the same manner as the S+ odour presented alone. Results also showed asymmetric suppression in the mixture condition, such that butanal suppressed detection of heptanal at a much lower concentration than vice versa. A second experiment demonstrated that when both butanal and heptanal were present in a binary mixture at the same concentration (10-6 volume %), rats responded to the mixture as if only butanal was present. Our findings are in agreement with human studies showing component interactions in binary mixtures of aldehydes. The molecular feature of carbon chain length appears to be a critical factor in determining the outcome of interactions between aldehydes at peripheral olfactory receptors, with smaller chain aldehydes better able to compete for receptor occupancy. Subsequent chapters explored the effects of two classes of commonly used drugs - benzodiazepines and cannabinoids - on olfactory and auditory discrimination in rats. Animal models such as the radial arm maze, Morris water maze and object recognition test are routinely used to test adverse and facilitatory effects of drugs on cognition in rodents. However, comparatively few pharmacological studies employ olfactory or auditory go/no-go paradigms. Thus, an important part of the present thesis was to assess the viability of using such paradigms in detecting pharmacological effects, and to identify whether such effects may be modality specific (i.e. whether a drug has a greater effect on olfactory or auditory tasks). In Chapter 3, the effects of benzodiazepines on olfactory discrimination tasks were explored. Rats were injected with the benzodiazepine drugs midazolam or diazepam and tested on discrimination tasks involving either the auditory and olfactory modality. Results showed that midazolam (0.5–2 mg/kg sc) did not affect the performance of a well-learned two-odour olfactory discrimination task, and moderately facilitated the performance of a go/no-go auditory discrimination task. On the contrary, midazolam (1 mg/kg) impaired the acquisition of a novel go/no-go olfactory discrimination task, as well as the reversal of a previously well-learned olfactory discrimination. However, midazolam did not affect the acquisition or reversal of an equivalent auditory discrimination task. The olfactory bulb and the piriform cortex are intimately involved in associative learning and behavioural aspects of olfactory performance, and have high concentrations of benzodiazepine receptors. These may therefore be possible neural substrates for the disruptive effects of benzodiazepines on olfactory learning. Findings from Chapter 4 indicated that the prototypical cannabinoid agonist delta-9-tetrahydrocanabinol (Δ9 THC) (0.3, 1 and 3 mg/kg) impairs auditory discrimination performance, but had no effect on equivalent olfactory discriminations. This is in marked contrast to the effects of benzodiazepines. Residual effects were observed, such that auditory discrimination performance was still impaired on the day following Δ9 THC administration. Delta-9-tetrahydrocanabinol effects were prevented by co-administration of the cannabinoid antagonist rimonabant (3 mg/kg). In addition, the anandamide hydrolysis inhibitor URB597 (0.1 and 0.3 mg/kg), which boosts levels of endogenous cannabinoids in the synapse, also impaired auditory discrimination performance, and this effect was also reversed by rimonabant. This study also assessed the effects of Δ9 THC (0.3, 1 and 3 mg/kg) and URB597 (0.1 and 0.3 mg/kg) on acquisition and reversal of novel olfactory discriminations. Results showed that Δ9 THC impairs olfactory reversal learning without affecting acquisition of the original discrimination. It is argued that this reversal deficit may be part of a wider capacity for cannabinoids to impair cognitive flexibility. The final Chapter (General Discussion) discusses the relevance and implications of the combined findings. The results add significantly to our current understanding of perceptual, learning and memory processes involving the olfactory modality in rats. With respect to olfactory perception, this thesis introduced a new behavioural paradigm, which can be used to assess component suppression in mixtures, and may be of use in future psychophysical studies involving rodents or other species. With respect to learning and memory, the thesis provides novel information on the disruptive effects of benzodiazepines and cannabinoids on olfactory and auditory tasks. It is concluded that go/no-go olfactory and auditory discrimination tasks in rats can provide a useful platform for assessing the disruptive and modality-specific effects of drugs on learning, performance and cognitive flexibility. Future studies might expand the range of drugs tested on these paradigms and might consider chronic as well as acute drug effects.

This project aimed to reanalyse two large historical data sets from two different locations in New Zealand (Fiordland in the South Island and Pureora Forest Park in the North Island). The data describe populations of mice (Mus musculus), rats (Rattus rattus and R. norvegicus), and stoats (Mustela erminea) collected using standard monitoring techniques from five distinct types of forest habitat. The new analysis methods selected were an index of patchiness and Site Occupancy analysis. The objectives of the analysis were (1) to evaluate whether the patchiness index and Site Occupancy analysis methods might contribute to improved protocols for monitoring small mammal populations in the future, and (2) to use formal tests of five hypotheses to evaluate two of the assumptions made by the conventional density index often used in small mammal studies. I describe the results of the analyses for each species, including any problems encountered (such as the inability of the Site Occupancy method to analyse very sparse data sets). I also describe the results pooled from each of the two study locations and potential consequences for small mammal monitoring and control. This analysis has suggested that in most cases the density index is not a rigorous measure of small mammal populations. However, both the index of patchiness and Site Occupancy analysis provided useful, new information about these populations of rodents and stoats, despite the fact that these historical data sets were not designed for use with modern methods of analysis. Please note: some figures and tables were printed separately and added to the thesis as unnumbered pages. These can be found in the file 03Plates_and_Tables.pdf.

The experiments reported in this thesis studied the contributions of opioid and NMDA receptors to predictive fear learning, as measured by freezing in the rat. The first series of experiments (Chapter 2) used a within-subject one-trial blocking design to study whether opioid receptors mediate a direct action of predictive error on Pavlovian association formation. Systemic administrations of the opioid receptor antagonist naloxone or intra-vlPAG administrations of the selective μ-opioid receptor antagonist CTAP prior to Stage II training prevented one-trial blocking. These results show for the first time that opioid receptors mediate the direct actions of predictive error on Pavlovian association formation. The second series of experiments (Chapter 3) then studied temporal-difference prediction errors during Pavlovian fear conditioning. In Stage I rats received CSA ?? shock pairings. In Stage II they received CSA/CSB ?? shock pairings that blocked learning to CSB. In Stage III, a serial overlapping compound, CSB → CSA, was followed by shock. The change in intra-trial durations supported fear learning to CSB but reduced fear of CSA, revealing the selective operation of temporal-difference prediction errors. This bi-directional change in responding was prevented by systemic NMDA receptor antagonism prior to Stage III training. In contrast opioid receptor antagonism differentially affected the learning taking place during Stage III, enhancing learning to CSB while impairing the loss of fear to CSA. The final series of experiments (Chapter 4) then examined potential neuroanatomical loci for the systemic effects reported in Chapter 3. It was observed that intra-BLA infusion of ifenprodil, an antagonist of NMDA receptors containing the NR2B subunit, prevented all learning during Stage III, whereas intra-vlPAG infusion of the μ-opioid receptor antagonist CTAP facilitated learning to CSB but impaired learning to CSA. These results are consistent with the suggestion that opioid receptors in the vlPAG provide an important contribution to learning. Importantly, this contribution of the vlPAG is over and above its role in producing the freezing conditioned response. Furthermore, the findings of this thesis identify complementary but dissociable roles for amygdala NMDA receptors and vlPAG μ-opioid receptors in predictive fear learning.

Exercise has been shown to cause an increase in the concentration of brain serotonin (5-hydroxytryptamine, 5-HT) in humans and experimental animals. The increase in brain serotonin coincides with the onset of fatigue and is referred to as "central fatigue". Experiments in humans and animals involving serotonin receptor agonists have demonstrated reductions in exercise performance by simulating the exercise-induced increase in endogenous serotonin. Conversely, the administration of serotonin receptor antagonists has been shown to extend exercise performance in experimental animals, but not in humans. Although the relationship between the concentration of brain serotonin and exercise performance is well described in the literature, the precise effect of central fatigue on muscle function per se is unclear. Furthermore, there appear to be differences in serotonergic function between trained and untrained cohorts. However, it is not clear whether the differences are due to a training adaptation or if the differences are inherent in the individual. In addition, the time course of these adaptations and the mechanisms of adaptation are not known. The initial purpose of this thesis was to determine whether six weeks of endurance exercise training had any effect on central serotonin receptor sensitivity in Wistar rats. The rats ran on a treadmill 4 times per week with 2 exercise tests of endurance performance per week. Receptor sensitivity was determined indirectly, at the end of each training week, by the reduction in endurance performance, under the influence of a 5-HT1a agonist, (m-Chlorophenylpiperazine, m-CPP). Improved tolerance to the fatiguing effects of the serotonin agonist would suggest desensitisation of central serotonin receptors, probably 5-HT1a receptors. Two groups of controls were used to examine, i) the effect of the injection per se on exercise performance and ii) changes in serotonin receptor sensitivity associated with maturation, in the absence of any exercise training. In the training group, undrugged exercise performance significantly improved by 47% after 6 weeks of training (mean ± SEM, 4518 ± 729 s vs. 6640 ± 903 s, p=0.01). Drugged exercise performance also increased significantly from week 1 to week 6 (306 ± 69 s to 712 ± 192 s, p=0.004). Control group results indicated that the dose of m-CPP alone caused fatigue during exercise tests and that maturation was not responsible for any decrease in receptor sensitivity. Endurance training appears to stimulate an adaptive response to the fatiguing effects of increased brain serotonin, which may enhance endurance exercise performance. The purpose of the second set of experiments described in this thesis was to investigate changes in serotonin receptor sensitivity in response to exercise training in human subjects. Twelve male volunteers completed 30 minutes of stationary cycling at 70% of VO2peak, on 3 days per week, for 9 weeks. Serotonin receptor sensitivity was assessed indirectly by measuring the prolactin response to a serotonin receptor agonist (buspirone hydrochloride), using a placebo controlled, blind cross-over design. A sedentary group of control subjects were also recruited to control for possible seasonal variations in serotonin receptor sensitivity. Endurance capacity was also assessed as time to exhaustion while cycling at 60% of VO2peak. The exercise training caused a significant increase in aerobic power (VO2peak, 3.1±0.16 to 3.6±0.15 L.m-1, p< 0.05) and endurance capacity (93±8 to 168±11 min, p<0.05), but there was no change (p>0.05) in the prolactin response to a serotonin agonist. However, 25% of the subjects in the training group demonstrated a decrease in receptor sensitivity, as indicated by a decrease in prolactin response. These results suggest that while the exercise training caused an increase in aerobic power and endurance capacity, there was no measurable change in 5-HT receptor sensitivity. In addition, it is possible that changes in receptor sensitivity may take longer to occur, the training stimulus used in the present investigation was inadequate or that changes occurred in other 5-HT receptor subtypes that were not assessed by the present methodology. The third set of experiments described here, investigated the changes in neuromuscular function under the influence of a serotonin receptor agonist (buspirone hydrochloride). Subjects were administered the agonist or a placebo in a blind cross over design. Measures of neuromuscular function included reaction time (RT), hand eye coordination (HEC), isometric neuromuscular control (INC), maximal voluntary isometric contractile force (MVIC-F), isometric muscular endurance capacity (IMEC) and various electromyographic (EMG) indices of fatigue in biceps brachii. A preliminary experiment was conducted to determine a drug dose that did not cause sedation of the research subjects. The agonist caused a significant (p<0.05) decrease in MVIC-F, INC and IMEC. There was a non significant (p = 0.08) decrease in EMG amplitude during the MVIC-F trial with the agonist, compared to the effect of the placebo. The median EMG frequency during the IMEC test was also significantly less with the agonist, when compared to the placebo effect. There was a decline in RT and HEC, although this was not significant. These findings indicate that a serotonin receptor agonist causes a decrease in neuromuscular function during isometric muscle contractions. The decrements in muscle function reported in this study may help to explain previous reports of an association between increased brain serotonin concentration and a reduction in endurance performance. Although the present study does not exclude the possibility that an increase in brain serotonin does cause fatigue by affecting organs peripheral to the brain, it provides evidence of fatigue within the central nervous system. Further examination of the effect of a serotonin agonist on muscle function during non-isometric muscle contractions is warranted.