Orexins and Animal Behavior
Biology 342 Fall 06
Since orexin has been so highly conserved among vertebrates, it likely serves an adaptive function for these animals.
Orexin is important in coordination of sleep with eating behavior.
Orexin may help animals coordinate their sleep cycles and alertness with anticipated food availability. This would give an advantage in foraging behavior. When an animal has been fasting for some time, it should become more alert such that it can find the food it desperately needs. When the animal has eaten enough, it may be in its best interest to rest rather than continue being active and burn up all its hard-earned calories.
Orexin helps separate sleep from waking states.
Orexin also could be adaptive in separating REM sleep from the rest of the animal's states. The advantage can be seen by looking at when the system fails: in narcolepsy. Narcoleptic animals fall asleep in the midst of normal activities, which reduces their ability to function during these episodes.
Orexin may help sustain muscle function.
Narcoleptics also can have attacks of cataplexy-- during high excitement their muscles suddenly atrophy. It could be that orexin plays a role in stimulating muscles during times when they would otherwise lose function, allowing an animal to sustain its normal activity even during times of intense fear or other excitement, when an animal needs to be able to efficiently move.Although orexin may seem redundant considering the many other neural systems involved in each of the behaviors it affects, it likely has adaptive value in its ability to coordinate all of these systems such that they support one another.