| Abstract
|
:
|
The orexins are a family of hypothalamic peptides implicated in the modulation of feeding, arousal state, and somatomotor functions. The first part of this dissertation examines the distribution of cell bodies and fibers expressing immunoreactivity for orexin A (OXA) or orexin B (OXB) in two nocturnal rodents, the Long-Evans rat ( Rattus norvegicus ) and Syrian hamster (Mesocricetus auratus ), and two diurnal rodents, the Nile grass rat (Arvicanthis niloticus ) and the degu ( Octodon degus ). I show that although the overall distribution of orexin is very similar in these species, there are significant species differences in the distribution of orexin cell bodies as well as in the density of orexin-IR fibers in some regions. Specifically, I show species differences in the organization of the main body of orexin neurons in the lateral hypothalamus, and provide evidence for a previously undescribed population of OXA neurons in the magnocellular neurosecretory nuclei of the hypothalamus. With respect to orexin fiber density, the differences observed were few, but dramatic. The majority of the differences were observed in the degu, suggesting that this species is an outlier. The second series of experiments investigated the functional and anatomical relationships between the orexins and patterns of activity in the grass rat. Some individuals of this species switch to a more nocturnal pattern of activity when given access to a running wheel, while others continue to be most active during the day. In both day- and night-active grass rats, the percentages of orexin A (OXA) and orexin B (OXB) cells expressing Fos were highest when animals were actively running in wheels. In night-active animals, removal of the running wheel significantly decreased Fos expression in OXA and OXB cells. Additionally, in night-active animals, clear regional differences were apparent, such that the presence of a wheel induced Fos in a higher percentage of orexin cells in medial regions of the lateral hypothalamus (LH) than in lateral regions. No regional differences were observed in day-active animals. (Abstract shortened by UMI.)
|