In embryonic neurons, the intracellular chloride concentration is elevated, making GABA and glycine depolarizing. Later in development, coincident with neuronal maturation, the extruding potassium-chloride co-transporter KCC2 is expressed. It reverses the chloride gradient, rendering it hyperpolarizing. Early depolarization is assumed to play trophic roles during nervous system development. I thus decided to investigate the effects of the depolarizing chloride gradient on development in vivo in the zebrafish embryo. I first determined the temporal pattern of KCC2 expression in zebrafish and found it was absent in the embryo. I then over-expressed wild-type, gain-of-function and loss-of-function variants of human KCC2, using GFP-tagged constructs for detection purposes. Over-expression of functional hKCC2 perturbed the morphology and motor behaviours of the embryos. At the cellular level, KCC2 impaired axonal growth and affected the neuronal populations in the brain, hindbrain and spinal cord. This suggests the depolarizing effects of glycine are critical for neurogenesis.

Two groups of neuropeptides (secretin and gonadotropin-releasing hormone groups, GnRH) and their receptors are of considerable interest because they are highly conserved in structure during evolution and have important physiological effects. To study the role of these neuropeptides during development, the zebrafish was selected initially as a model because the embryo is transparent and accessible for genetic manipulation. Later, a mouse model was added to evaluate the effects of permanent gene loss. The purpose of this thesis was to 1) characterize the structure and function of several peptides and receptors within the secretin group that had not been previously identified for zebrafish, 2) examine brain development in zebrafish after gene knock down of an important peptide in each of the secretin and GnRH groups, 3) identify the pattern and location of expression of the GnRH receptors in zebrafish embryos, and 4) study the functional importance of the GnRH receptor in a mouse line deficient in the receptor. The secretin superfamily of hormones includes 10 structure-related polypeptides in mammals, but fewer in zebrafish. In this thesis it was discovered that within the secretin group, zebrafish have two peptides, peptide histidine-isoleucine (PHI) and vasoactive intestinal polypeptide (VIP), in addition to two receptors, PHI receptor and growth hormone-releasing hormone-like peptide (GHRH-LP) receptor that were not previously identified. After isolation of the cDNA for each, the signaling pathways were characterized in vitro by transfection of the receptors into COS cells. The PHI-R was activated by PHI but not by VIP or pituitary adenylate cyclase-activating polypeptide (PACAP). The GHRH-LP receptor was activated by GHRH-LP 1 and GHRH but not by GHRH-LP2. A novel observation was that the PAC, receptor is activated by both PACAP and VIP, whereas the PAC, receptor is usually specific to PACAP. Also novel was evidence that a VPAC2 receptor in zebrafish was structurally and functionally a PHI receptor. In examining the role of PACAP in early brain development in zebrafish, morpholinos were used to knockdown PACAP1 and PACAP2 in the zygote. The study revealed that loss of PACAP leads to change in the expression of brain markers. GnRH and its receptors (GnRH-R) are key regulators of reproduction and sexual behaviour. In zebrafish, morpholino-induced knock down of GnRH revealed that GnRH is critical in eye and brain development by affecting transcription factors and/or secreted factors: pax2.1, fgf8, pax6.1 and mab. Further, the GnRH receptor was expressed at 24h post fertilization showing that GnRH and its receptor could influence early development. To determine whether the GnRH receptor is critical at all stages of reproduction, a mouse line was created in which the GnRH receptor was disrupted using the gene trap method. This model has a similar phenotype to the clinical syndrome of hypogonadotropic hypogonadism. In mice, GnRH receptor disruption results in small sexual organs, low gonadotropin and steroid hormone levels, failure of sexual maturation, and lack of reproduction. Also, the GnRH receptor may be important in the fetal testis. This thesis provides evidence that 1) in evolution the PAC, receptor may have responded to both PACAP and VIP in fish, 2) zebrafish have a PHI receptor rather than a VPAC2 receptor, 3) PACAP and GnRH peptides have a fundamental role in early brain development, 4) the GnRH receptor is not only important in reproduction but unexpectedly, in zebrafish embryos is localized in hindbrain motor neurons and fibers, which are involved normally in movement and escape, and 5) GnRH receptor-disrupted mice should be a valuable model for understanding reproduction and clinical approaches to hypogonadotropic hypogonadism.

Zebrafish (Brachydanio rerio) are small, freshwater teleost fishes in the family Cyprinidae, the true minnows. They are native to the tropical latitudes of India, but have become widespread through their use as aquarium fish and as models for several branches of biological research. Their ease of rearing, short generation time, year-around egg laying potential, brief developmental period, and embryo transparency have made them especially desirable as models for developmental biology, genetics, and neurobiology. Because of their popularity, they were also the first small aquarium fish to be used as test organisms for carcinogenesis in the early 1960's. For reasons that have never been stated, their use as a model for carcinogenesis research did not continue. Due to the number of positive characteristics that this species has, the goal of this research effort was to systematically evaluate the potential of zebrafish for use as an environmental monitor, to evaluate the toxicology and carcinogenesis of surface and/or ground waters. The overall project was multidisciplinary in nature, but the focus of this thesis research was on the whole animal, dose-response to a number of well-known carcinogens, administered by multiple exposure routes, and the pathological description of the resulting lesions. Exposure to N-nitrosodiethylamine (DEN) and N-nitrosodimethylamine (DMN) in the diet was ineffective, but static water bath exposure of fry and embryos to these nitrosamines resulted in neoplasms, primarily in the liver. Embryo exposure to DEN resulted in a low response of neoplasms in several other organs as well. Dietary exposure of zebrafish to aflatoxin B₁ resulted in few hepatic neoplasms, revealing a marked resistance to this carcinogen. Dietary exposure to methylazoxymethanol acetate (MAM-Ac) produced mostly liver tumors, as did both fry and embryo water bath exposures. Each water bath exposure also produced neoplasms at other tissue and organ sites, but the embryo stage produced the greatest variety. These results demonstrate a relative resistance to neoplastic development compared to the well-known rainbow trout model. But in one comparative trial, zebrafish were similar to Japanese medaka in their response to dietary MAM-Ac. The major limitation of this species, that will prevent its use as a model for environmental monitoring, however, is its narrow range of temperature tolerance. Temperatures below 15°C produce marked sluggishness, and below 10-12°C cause anesthesia and death. Therefore, this research indicates that this species is not as versatile as some other small fish species for laboratory and especially field monitoring of environmental carcinogenic hazards. / Graduation date: 1997

Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 70-82). Also available for download via the World Wide Web; free to University of Oregon users.

Honors Project--Smith College, Northampton, Mass., 2009. / Includes bibliographical references (p. 111-118).

Thesis supervisor: Robert A. Cornell. Includes bibliographical references (p. 121-142).

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 156-169) Also available in print.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / On t.p. "2+" is superscript. Includes bibliographical references (leaves 126-133). Also available in electronic version.

Honors Project--Smith College, Northampton, Mass., 2010. / Includes bibliographical references (p. 91-96).

Thesis (Ph.D.)--Kent State University, 2006. / Title from PDF t.p. (viewed Sept. 19, 2006). Advisor: Eric Glasgow. Keywords: oxytocin; isotocin; vasopressin; vasotocin; hypothalamo-neurohypophysial system; hypothalamus; development; autism; Prader-Willi Syndrome; single-minded; orthopedia; arylhydrocarbon nuclear translocator; Brn2; POU; zebrafish; behavior; paraventricular nucleus; supraoptic nucleus; preoptic nucleus; diencephalon; suprachiasmatic nucleus; thyroid transcription factor; sonic hedgehog; NK 2 transcription factor related; distal-less homeobox gene; homeobox; homeodomain; morpholino Includes bibliographical references (p. 230-266).