Aromatase is the only enzyme that converts androgens into estrogens, which is found in the brain, testes and ovaries. In teleosts, brain aromatase is exclusively expressed in radial glial cells, which are the abundant stem-like non-neuronal progenitors involved in neuroendocrine functions and neurogenesis in the central nervous system. With little information about radial glial cell regulation by neurotransmitters and neurohormones available, the overall goal of this thesis is to investigate the interactions between dopamine neurons and radial glial cells in the adult goldfish (Carassius auratus) forebrain. Immunocytochemistry and confocal imaging revealed a close anatomical relationship between dopamine neurons and radial glial cells along the ventricular surface in the telencephalon. Transcriptional regulation of brain aromatase by dopamine indicated a brain region-specific pattern and suggested the involvement of other regulators in the goldfish forebrain. A novel goldfish primary radial glial cell culture model was established and characterized for brain aromatase regulation studies. Pharmacological studies demonstrated that specific activation of dopamine D1 receptors up-regulates brain aromatase through a cAMP-dependent molecular mechanism, which can be enhanced or attenuated by the product of aromatase action, 17β-estradiol. Proteome profiling and the response following treatment with the specific dopamine D1 receptor agonist SKF 38393 revealed that proteins involved in cell proliferation and growth are regulated through small molecules- and transcription factors-mediated signaling pathways. Analysis of genes related to radial glial cell and dopamine neuron functions demonstrated that glial activation and dopamine neuron recovery are estrogen-dependent in a neurotoxin MPTP-induced goldfish model of Parkinson’s disease. This thesis illustrates novel molecular mechanisms underlying brain aromatase regulation as well as radial glial cell function regulation and provides a framework for future investigation of existing endocrine disruptors modulating neurosteroid levels in the teleost brain.

In the teleost brain, radial glial cells (RGCs) are the main macroglia and are stem- like progenitors that express key steroidogenic enzymes, including the estrogen- synthesizing enzyme, aromatase B (cyp19a1b). As a result, RGCs are integral to neurogenesis and neurosteroidogenesis in the brain, however little is known about the permissive factors and signaling mechanisms that control these functions. The aim of this thesis is to investigate if the secretogranin-derived neuropeptide secretoneurin (SN) can exert regulatory control over goldfish (Carassius auratus) RGCs. Immunohistochemistry revealed a close neuroanatomical relationship between RGCs and soma of SNa- immunoreactive magnocellular and parvocellular neurons in the preoptic nucleus in both goldfish and zebrafish (Danio rerio) models. Both intracerebroventricular injections of SNa into the third brain ventricle and SNa exposures of cultured goldfish RGCs in vitro show that SNa can reduce cyp19a1b expression, thus implicating SNa in the control of neuroestrogen production. RNA-sequencing was used to characterize the in vitro transcriptomic responses elicited by 1000 nM SNa in RGCs. These data revealed that gene networks related to central nervous system function (neurogenesis, glial cell development, synaptic plasticity) and immune function (immune system activation, leukocyte function, macrophage response) were increased by SNa. A dose-response study using quantitative proteomics indicates a low 10 nM dose of SNa increased expression of proteins involved in cell growth, proliferation, and migration whereas higher doses down- regulated proteins involved in these processes, indicating SNa has dose-dependent regulatory effects. Together, through these altered gene and protein networks, this thesis proposes SNa exerts trophic and immunogenic effects in RGCs. These datasets identified a total of 12,180 and 1,363 unique transcripts and proteins, respectively, and demonstrated that RGCs express a diverse receptor and signaling molecule profile. Therefore, RGCs can respond to and synthesize an array of hormones, peptides, cytokines, and growth factors, revealing a multiplicity of new functions critical to neuronal-glial interactions.