title: Thyrotropin-releasing hormone action in the preoptic/anterior hypothalamus decreases thermoregulatory set point in ground squirrels.
abstract: Earlier work has shown that thyrotropin releasing hormone (TRH) produces dose-dependent decreases in body temperature (Tb) and metabolic rate when microinjected into the dorsal hippocampus (HPC) or preoptic/anterior hypothalamus (PO/AH) of awake ground squirrels. This study employed a behavioral paradigm to investigate the possibility that TRH-induced hypothermia is associated with a decrease in thermoregulatory set point. Six animals were successfully trained to press a bar for radiant heat escape and cool air reinforcement in order to obtain a cooler ambient temperature (Ta). During experimental testing, the animals were microinjected remotely with TRH (10-1000 ng/microliters) or a control solution (sterile saline or TRH-OH) into the PO/AH. The micro-injections were delivered via bilateral injection cannulae inserted through chronic bilateral cannula guides that had been stereotaxically implanted under pentobarbital anesthesia. Cumulative and time-integrated bar presses were obtained on a computer generated display. Tb, measured in the brain via a bead-type thermistor, and chamber Ta were recorded continuously. Following TRH administration, a significant increase in mean bar-press rate was observed during the period in which Tb was falling, when compared to a comparable time period just prior to the microinjection. These findings complement results obtained from four animals that were trained to press a bar for heat reinforcement in a cold (- 10 degrees C) environment. In this alternative behavioral paradigm, microinjection of TRH into the PO/AH or HPC induced a decrease in mean bar-press rate as Tb was falling. The results support the hypothesis that TRH-induced hypothermia in golden-mantled ground squirrels is achieved by lowering thermoregulatory set point.
authors.affiliation: Department of Physiology, California State University, Long Beach 90840-3701.
authors.forename: J H
authors.initials: JH
authors.lastname: Hendriksen
authors.forename: P A
authors.initials: PA
authors.lastname: Bachelor
authors.forename: R J
authors.initials: RJ
authors.lastname: Newman
authors.forename: T L
authors.initials: TL
authors.lastname: Stanton
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D005260:Female; D007031:Hypothalamus / Q000378:metabolism*; D008297:Male; D008845:Microinjections; D012589:Sciuridae; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology*
chemical_list: D013973:Thyrotropin-Releasing Hormone