The involvement of the pre-optic region of the anterior hypothalamus in the hypothermic response to hemorrhage

This dissertation characterized the thermoregulatory response of male rats to a controlled hemorrhage in order to identify the mechanisms underlying hypothermic response to hemorrhage. My overall hypothesis was that the hypothermic response to hemorrhage is due to a regulated decrease in the thermoregulatory set point, and is mediated at the level of the pre-optic area of the anterior hypothalamus (POAH).; Experiments in specific aim one demonstrated a decrease in thermoregulatory set point follows hemorrhage. Rats housed in a thermal gradient consistently moved to colder ambient temperatures following hemorrhage, even though body core temperature was also decreased. The significant decrease in selected ambient temperature associated with the hypothermic response illustrates both behavioral and autonomic pathways favoring heat loss are activated after hemorrhage. These data are consistent with a decreased thermoregulatory set point.; Experiments in specific aim two showed that the pre-optic anterior hypothalamus is partially responsible for the hemorrhagic hypothermic response. Microinjection of the neuronal blocker lidocaine significantly attenuated hemorrhagic hypothermia suggesting that this response is partially mediated by the POAH.; Experiments in specific aim three determined that temperature sensitive neurons in the POAH mediate the hemorrhagic hypothermic response. Local tissue heating of the POAH significant exacerbated the hypothermic response to hemorrhage suggesting that the POAH acts as the comparator of the thermoregulatory system. This confirms that a functional POAH is necessary for a normal hemorrhagic hypothermic response.; Together, the data in this dissertation suggest that the hypothermic response to hemorrhage is due to a regulated decrease in the thermoregulatory set point, and it is mediated at the level of the pre-optic area of the anterior hypothalamus.