Orexins and Animal BehaviorBiology 342 Fall 06 |
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PhylogenyOrexin is produced by vertebrate animals including reptiles, birds, mammals, and amphibians. The presence of orexin in so many distantly related genera suggests that it evolved early in the vertebrate lineage and has been highly conserved. Much of the gene sequence that encodes the receptors as well as the orexins has been conserved. Although in all animals that have been studied, orexin is produced in the hypothalamus, the specific area of the hypothalamus differs among species. The behavioral effects of orexin have not been extensively studied in non-mammals, so it is not known if it performs the same functions in all animals. Mammals![]() top Birds
Fish![]() In goldfish, orexin-like immunoreactivity and orexin mRNA expression in the brain increases in fasted fish and decreases in fish injected with glucose. An orexin injection caused an increase in both food consumption and locomotor activity, while an injection of anti-orexin serum or glucose decreased food consumption and activity. These results suggest that orexin may have a similar role in feeding and arousal in fish as in mammals. top AmphibiansOrexin has been identified in the green tree frog (4) as well as at least one other kind of frog. I was unable to find any studies on how orexin impacts their behavior.ReptilesNot many studies have been done on orexin in reptiles. I was able to find two meeting abstracts: one about orexin distribution in the brain of the green anole lizard (5) and one about orexin cell distribution in Pseudemys turtles (6). No mention was made of how (or whether) orexin affects behavior in these animals.top photos from http://en.wikipedia.org/wiki/Wikipedia:List_of_images/Nature/Animals |