Thyrotropin-releasing hormone effects in the central nervous system: dependence on arousal state

Thyrotropin-releasing hormone was microinjected into the dorsal hippocampus of ground squirrels (Citellus lateralis) when they were at different levels of arousal, as assessed by electrophysiological and behavioral criteria. When administered to the awake animal, thyrotropin-releasing hormone produced dose-dependent decreases in body temperature accompanied by behavioral quieting and reductions in metabolic rate and electromyographic activity. The magnitude of these effects was greater when the peptide was microinjected during a period of behavioral activation. In contrast, administration of the peptide during slow wave sleep produced increased thermogenesis, an increase in electromyographic activity, and an increase in the amount of electroencephalographic desynchronization.