Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaves 31-35). Also available via the World Wide Web.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains viii, 71 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 61-70).

Thesis (Ph. D.)--Washington State University, December 2009. / Title from PDF title page (viewed on Dec. 16, 2009). "School of Molecular Biosciences." Includes bibliographical references.

Thesis (Ph. D.)--University of California, San Diego, San Diego State University, 2003. / Vita. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1989.

published_or_final_version / abstract / toc / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

Sexual selection and the maintenance of species diversity in Lake Malawi cichlid fishes are greatly dependent on optical communication, which is influenced by environmental, physiological and endocrinological factors. The diversity in spectral sensitivity of cichlids has been partially attributed to differences in opsin gene expression, with each species preferentially expressing a subset of seven possible genes. Hormones such as gonadotropin releasing hormone (GnRH) can mediate changes in gene expression and the presence of GnRH immunoreactive fibers and GnRH receptors throughout the retinal layers make it an excellent candidate for mediating changes in visual processes. Effects of exogenous GnRH administration on the visual system of zebra cichlids (Metriaclima zebra) via prolonged release cholesterol implants and intubation was investigated using electroretinogram (ERG) recordings, quantitative real-time RT-PCR and in situ hybridization. Three week and ten week sampling periods were used in the intubation study. No obvious differences in spectral sensitivity were evident when looking at a-wave, b-wave and d-wave components of the ERG waveform in any of the treatment groups. A multiple mechanism model was used to describe the cone mechanisms mediating spectral sensitivity and this analysis showed that the activity of cones was shaped by opponent and non opponent cone interactions based on subsets of five opsin genes previously described in cichlids (SWS1, SWS2b, RH2b, RH2aβ, and RH2aα). Although differences in the spectral sensitivity between control and GnRH-treated fish were not evident on a functional level, there were changes in the gonadosomatic index in the intubation group. Quantitative real-time RT-PCR (qRT-PCR) and in situ hybridization demonstrated that treatment with a synthetic GnRH3 analogue using the oral intubation delivery system resulted in statistically significant changes in opsin gene expression in both three week and ten week treatment groups, specifically the upregulation of RH2b and the downregulation of RH2a opsin genes. Moreover, in situ hybridization analysis showed that the pattern of labeling for the RH2a and RH2b riboprobes corroborated the changes in opsin gene expression found in the qRT-PCR data. In contrast, GnRH treatment using the cholesterol implant delivery system did not result in significant changes in spectral sensitivity or opsin gene expression. / Thesis (Master, Biology) -- Queen's University, 2011-01-05 22:57:11.308

The gonadotropin-releasing hormone (GnRH) neurons of the hypothalamus are the principal regulators of reproductive function and are strongly modulated by estrogen (E₂). Several studies indicate that E₂ is able to influence GnRH neurons, both with "classical" long-term transcriptional effects, and with rapid non-transcriptional effects. One most interesting action of E₂ is that of modulating intracellular calcium concentration [Ca�⁺]I: this has been shown to happen in many different cell types, including embryonic models of GnRH neurons. The aim of this project was to evaluate if these rapid effects of E₂ on [Ca�⁺]I also happen at the level of adult GnRH neurons. In order to study the acute effects of E₂ on calcium dynamics, a novel transgenic mouse line was generated, that allows real-time measurement of [Ca�⁺]I selectively in GnRH neurons in an acute brain slice preparation. Using this mouse line, our group has previously shown that these cells show spontaneous activity in the form of Ca�⁺ transients. A first set of experiments was designed to define the effects of E₂ on spontaneous activity. E₂ was found to modulate [Ca�⁺]I in a activity-dependent manner: it increased the frequency of [Ca�⁺]I transients in about 50% of GnRH neurons with low spontaneous activity, whereas it decreased the frequency of the transients in more than 80% spontaneously active GnRH neurons. Different experiments were then performed in order to determine the molecular pathways that generates these opposite effects. The inhibitory effect was reproduced by the membrane-impermeable compound E2-6-BSA, indicating that it happens through a membrane receptor. The E₂ isomer l7α-estradiol was also able to reproduce the inhibitory effect of E₂, suggesting the involvement of some non-classical receptor. This is also confirmed by the presence of this effect in estrogen-receptor β (ER-β) knock-out mice, which exclude the involvement of this receptor. The stimulatory effect was found to be generated through a novel, indirect mechanism. It cannot be reproduced by E2-6-BSA nor by l7α-estradiol, and it is still present in the ER-β knock-out mice. The stimulation, though, can be reproduced in about 50% of cells with an ER-α selective agonist. As this receptor is not present in GnRH neurons, an indirect mechanism must be generating the stimulatory effect. Blockage of action potential mediated synaptic transmission with tetrodotoxin (TTX) did not block E₂ effects, but blockage of non-action potential mediated GABAergic transmission using the GABA[A] selective blocker gabazine completely abolished them. Our hypothesis is therefore that E₂ stimulates the generation of [Ca�⁺]I transients through estrogen-receptor a (ER-α) located in the terminals of GABAergic afferents. This modulation, in turn, is able to determine release of Ca�⁺ from IP₃-sensitive intracellular stores. To confirm this, we applied exogenous GABA to the neurons and found that it was able to initiate [Ca�⁺]I transients. Furthermore, removal of tonic GABAergic tone with gabazine was able to block spontaneous activity. To further analyse the effects of E₂, Ca�⁺ imaging experiments were performed together with cell-attached patch clamp electrophysiological recordings in order to correlate the electrical activity with the calcium activity. Simultaneous recordings revealed a strong correlation between [Ca�⁺]I transients and bursts of action currents in adult GnRH neurons. E₂ was able to increase the electrical activity of GnRH neurons with low spontaneous activity, and inhibit that of highly active ones. Application of GABA to GnRH neurons resulted in increased firing, accompanied by an increase in [Ca�⁺]I. These observations provide evidence for a complex mechanism of E₂ action on adult GnRH neurons, that may be important for the generation of the pulsatile release of this hormone.