Cyclo (His-Pro): mapping hypothalamic sites for its hypothermic action.

Hypothalamic loci of Sprague-Dawley rats were individually injected with cyclo (His-Pro) to determine the sites where that metabolite of thyrotropin-releasing hormone acts to produce hypothermia. There was almost always a positive hypothermic response in the preoptic-anterior hypothalamic area (POA/AHA); injection into the posterior or middle hypothalamic areas or into the hippocampus caused no significant decrease in core temperature. The fact that only injection into the POA/AHA evoked hypothermia suggests that this area is a major hypothalamic site of action of cyclo (His-Pro) in modulating thermoregulation in the rat.