Social status influences reproductive physiology in many species, and sex change in marine teleost fishes provides an excellent model to understand how an organism can modulate its reproductive system in response to social stimuli. The series of experiments presented in this dissertation has focused on the proximate mechanisms underlying sex change and, in particular, the neuroendocrine factors that might translate social information into physiological changes. The bluebanded goby (Lythrypnus dalli) is a sexually plastic fish, and the dominant female typically changes sex when the male is removed from the social group. The direct physical interactions between the male and the females were found to be the main sensory cues that inhibit sex change. Sex steroids can both modulate and be modulated by behavior, and as a result they have been the most obvious candidates for a key role in the regulation of sex change. Males and females showed similar diurnal patterns for steroid hormones, but females had significantly higher water-borne estrogen levels. Concentrations of estradiol, testosterone and 11-ketotestosterone presented sex and tissue differences in brain, gonad and muscle, and they varied in complex ways in different tissues during sex change. The neurotransmitter serotonin (5-HT) has been suggested to be involved in the inhibition of socially regulated sex change because of its role in the modulation of both reproductive and aggressive behavior. None of the pharmacological manipulations performed in L. dalli to alter serotonergic activity was able to overcome the input from the social environment and affect sex change. Neither monoamine levels nor the area or number of 5-HT immunoreactive neurons were different between males, females and sex changers or between dominant and subordinate females. The results do not support the hypothesis of a serotonergic inhibition on sex change in L. dalli, but show that rapid changes in brain androgen levels might be implicated in inducing behavioral or morphological changes associated with sex reversal. Also, steroids respond to changes in the social environment in different ways in different tissues so local steroid synthesis should receive greater attention, and caution is required when using circulating levels to understand behavioral regulation.

Serotonin stimulates reproduction and inhibits feeding/growth in the neuroendocrine brain of goldfish. The objective of this thesis is to study the effects of selective serotonin reuptake inhibitor pharmaceuticals (SSRIs) on these systems, as SSRIs, such as fluoxetine, are detected in effluent and bioconcentrate in the brain of wild fish. Genes of the serotonin system were cloned to identify molecular conservation, seasonal expression, and tissue distribution. The serotonin transporter, the target molecule of fluoxetine, was highly conserved and ubiquitously expressed in goldfish. Seasonal changes of hypothalamic gene expression of the serotonin transporter support a role in the seasonal modulation of both processes. Fluoxetine injection experiments were used to assess effects on reproductive endpoints and to identify molecular mechanisms in the neuroendocrine brain. Fluoxetine inhibited serum estradiol concentrations in female goldfish and decreased isotocin mRNA abundance in the hypothalamus and telencephalon. Isotocin injections stimulated circulating estradiol concentrations, providing a causal link. Evidence for an involvement of serotonin in isotocin regulation was investigated using immunocytochemistry and 5-HT1A receptor agonists and antagonists. A close proximity of serotonin fibers and isotocin cell bodies and fibers was found in the telencephalon and pituitary,respectively. Injection of a 5-HT1A receptor antagonist inhibited isotocin mRNA expression in the telencephalon. Identified gene targets were investigated in waterborne fluoxetine exposures,including environmental concentrations. Waterborne fluoxetine led to a reduction in basal and pheromone-stimulated milt volume in male goldfish. Gene expression evidence indicated a central inhibitory effect of fluoxetine through the decrease in mRNA abundance of follicle-stimulating hormone in the pituitary and isotocin in the telencephalon. Feeding rate and weight decreased in fluoxetine-injected goldfish, indicating an anorexigenic effect. Fluoxetine induced changes in the gene expression of the feeding peptides neuropeptide Y, corticotropin-releasing factor, and cocaine- and amphetamine-regulated transcript-I in the hypothalamus and telencephalon. Waterborne exposure to fluoxetine validated the anorexigenic effect in goldfish and was correlated with increased expression of corticotropin-releasing factor mRNA, an anorectic peptide. The thesis provides evidence for disrupting effects of fluoxetine on neuroendocrine control of reproductive function and feeding/growth in goldfish, partially at environmental concentrations. The thesis provides the framework for the investigation of existing aquatic contaminants which modulate the serotonin system.

Electroconvulsive therapy (ECT) effectively treats depression by administration of repeated seizure-inducing electrical stimuli. Sprague-Dawley rats were administered 6 electroconvulsive shocks (ECS) over 2 weeks, and in vivo single unit extracellular electrophysiological activity was recorded after 48 hours. Overall firing activity in the locus coeruleus and ventral tegmental area was unchanged, suggesting the therapeutic efficacy of ECT may not be attributed to increased norepinephrine and dopamine release. There were more spontaneously active neurons in the substantia nigra pars compacta (SNc), indicating greater dopamine tone in the nigrostriatal motor pathway, which may contribute to alleviation of psychomotor retardation. In the facial motor nucleus (FMN), locally administered norepinephrine, but not serotonin, facilitated greater glutamate-induced firing, which may contribute to improved facial motricity. Current results indicate that repeated ECS enhances postsynaptic norepinephrine neurotransmission in the FMN and SNc dopamine neurotransmission, which could represent the mechanism behind the alleviation of depressive symptoms including psychomotor retardation.

In zebrafish, the ventilatory response to hypoxia first develops at 3 days post-fertilization (d.p.f.) before O2-chemoreceptive neuroepithelial cells (NECs) of the gill appear at 7 d.p.f. This indicates the presence of extrabranchial chemoreceptors in embryos and a developmental transition to primarily gill O2 sensing. This thesis examined the skin NECs, which reach peak density in embryos but decline as gill NECs appear. Exposure of embryos and larvae to chronic hypoxia prevented the loss of skin NECs, shifted peak basal ventilation to a later developmental stage, and induced a hypoventilatory response to acute hypoxia. Chronic exposure to hyperoxia rapidly diminished skin NECs, shifted peak ventilation to earlier stages and eliminated the response to acute hypoxia. Administration of the neurotoxin 6-hydroxydopamine degraded nerve terminals that contact skin NECs and reduced both basal ventilation frequency and the hypoxic ventilatory response. Thus, skin NECs are candidates for extrabranchial O2 chemoreceptors in developing zebrafish.

Fluoxetine (FLX), the active ingredient of Prozac™, is a member of the selective serotonin reuptake inhibitor (SSRI) class of anti-depressant drugs and is present in aquatic environments worldwide. Previous studies reported that FLX is an endocrine disruptor in fish, bioconcentrating in tissues including the brain. Evidence implicates that serotonin influences the activity of the hypothalamo-pituitary-interrenal (HPI) stress axis, thus exposure to FLX may disrupt the teleost stress response. This study examined in vitro cortisol production in rainbow trout (Oncorhynchus mykiss) head kidney/interrenal cells exposed to FLX and 14C-pregnenolone metabolism in head kidney microsome preparations of FLX-exposed trout. Results indicated that cells exposed in vitro to increasing concentrations of FLX had lower cortisol production and cell viability (versus control) and microsomes isolated from trout exposed to 54 μg/L FLX had higher pregnenolone metabolism versus those of control and low FLX-exposed (0.54 μg/L) trout.

Animals show a great variety in physiological and behavioural responses to stressors. These responses are often bimodally distributed within populations and show consistency on an individual level over time and across situations, which in terrestrial vertebrates have been identified as proactive and reactive stress coping strategies. Proactive animals show lower cortisol responses, higher sympathetic activation and brain serotonergic activity compared to reactive animals. Behaviourally, proactive animals are more aggressive, more active in avoiding stressors, they form routines and show fewer cases of conditioned immobility compared to reactive animals. Our aim has been to reveal if such stress coping strategies exist in fish. Our results show that rainbow trout with high (HR) or low (LR) cortisol responses to stressors differs in sympathetic activation and brain serotonin turnover in the same manner as proactive and reactive mammals. HR fish showed less locomotor activity when reared in large groups (30 individuals) compared to LR fish. When reared in isolation there were no differences between HR and LR fish when exposed to stressors within a familiar environment. The adaption of a proactive coping style among reactive coping individuals when they are challenged within a familiar environment has previously been shown to be distinction between proactive and reactive coping mammals. However, when they were transferred to unfamiliar environments a behavioural difference between the two lines was observed indicating different stress coping strategies akin to those described in mammals. Finally, we observed a consistency over time in the cortisol response of an unselected line of rainbow trout. Fish from this line also demonstrated a correlation between behavioural responses to different stressors. However, there was no apparent connection between these behavioural responses and the cortisol response. Overall, the results of this thesis have strengthened the hypothesis that different stress coping strategies exist in teleost fish.

The synthesis of 2,4-disubstituted pyrimidine derivatives is described. The synthetic route involved the addition reaction of lithiated intermediates, mostly heterocycles, to position 4 of 2-chloropyrimidine to give a dihydropyrimidine intermediate which was oxidized back to a pyrimidine. This was followed by nucleophilic aromatic substitution with various amines of the chlorine in the position 2. A number of compounds were prepared which showed binding towards various serotonin receptors in preliminary biological evaluation.

<p>Activation of monoaminergic receptors is essential to the mechanism by which psychostimulants and antidepressants induce changes in behavior. Although these drugs rapidly increase monoaminergic transmission, they need to be administered for several weeks or months in order to produce long-lasting alterations in behavior. This observation suggests that it is likely that molecular mechanisms downstream of receptor activation contribute to the effects of psychostimulants and antidepressants on behavior. </p><p>Recently, we and others have demonstrated that the methyl-CpG-binding protein 2 (MeCP2) contributes to both neural and behavioral adaptations induced by repeated psychostimulant exposure (Deng et al, 2010, Im et al, 2010). Psychostimulants induce rapid and robust phosphorylation of MeCP2 at Ser421 (pMeCP2), a site that is thought to modulate MeCP2-dependent chromatin regulation (Cohen et al, 2011), and this phosphorylation event is selectively induced in the GABAergic interneurons of the nucleus accumbens (NAc). In order to understand the signaling pathways that contribute to the pattern of pMeCP2 we observe, I characterized the monoaminergic signaling pathways that regulate pMeCP2. I found that activation of dopamine (DA) and serotonin (5-HT) transmission is sufficient to induce pMeCP2. The novel finding that drugs that activate serotonergic signaling induce pMeCP2 suggests that pMeCP2 may be involved in serotonergic mediated behaviors.</p><p>To determine the requirement of pMeCP2 in serotonergic mediated behaviors, I utilized mice that bear a knockin (KI) mutation that converts serine to alanine at 421 (S421A) (Cohen et al, 2011). After characterizing the behavioral phenotype of these mice, I conducted tests to assess anxiety- and depression-like behavior. I found that the KI mice do not display heightened anxiety in several assays. However, the KI mice exhibit depression-like behavior in the forced swim and tail suspension but show no differences compared to wild-type (WT) littermates in the sucrose preference test, suggesting that pMeCP2 may be implicated in the behavioral response to stressful stimuli. </p><p>Because we are interested in examining the role of pMeCP2 in the behavioral adaptations to chronic monoaminergic signaling, I then put the KI mice and their WT littermates through chronic social defeat stress, a behavioral paradigm in which repeated exposure to aggressive mice causes social avoidance that is reversed by chronic but not acute antidepressant treatment. Although the WT mice show an increase in social interaction following chronic imipramine treatment, the KI mice fail to show a behavioral response to chronic treatment. These data suggest that pMeCP2 may be implicated in the antidepressant action of chronic imipramine. Finally, investigation of the brain regions in which pMeCP2 may be contributing to the behavioral response to chronic imipramine treatment revealed that chronic but not acute imipramine treatment induces pMeCP2 in the lateral habenula (LHb), a brain region involved in the behavioral response to stress and reward. Together, these data implicate a novel role for pMeCP2 in depression-like behavior and the behavioral response to chronic antidepressant treatment.</p> / Dissertation

Neurotransmitters are widely distributed in the central nervous system of tilapia during development. In the present study, the effects of gonadal steroids, temperature, and neurotransmitters on the development of central neurotransmitter systems in tilapia, Oreochromis mossambicus, were investigated. Exogenous E2 before 10 days posthatching resulted in an inhibitory effect on the activity of central 5-HT system via decreasing TPH activity and increasing MAO activity, a decrease of the gene expression of brain aromatase and ERa, which is involved in the feminization. The masculinizing actions of 17a-methyltestosterone (MT) are most potent later at up to day 20 of age, and may depend on MT-induction of aromatase activity, aromatase mRNA gene expression and estrogen receptor-b mRNA gene expression. The development of central neurotransmitter systems is influenced by aquatic temperature during its respective restricted period. The influence of both lower and elevated temperatures on the neurotransmitter activity, either increasing or suppressing, is dependent on its developing stage. Neurotransmitters have an effect to influence the development of central neurotransmitter and this effect may mediated by the neural proliferation.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2004. / Includes bibliographical references.