DOES THE PREOPTIC-ANTERIOR HYPOTHALAMUS RECEIVE THERMOAFFERENT INFORMATION

The preoptic anterior hypothalamus (POAH) is considered the thermointe grative center of the mammalian brain. Studies on anesthetized and una nesthetized animals have demonstrated neurons in the POAH that respond to changes in both POAH temperature (T-POAH) and skin temperature (T- s). In these studies, however, electroencephalographic (EEG) activity was not monitored. Recent work has revealed the potential for arousal state selectivity of neurons combined with thermal influences on arous al state to create the appearance that cells are thermosensitive or th ermoresponsive when in fact they may not be responding directly to tem perature or to thermoafferent input. It is therefore necessary to reex amine the influence of central and peripheral temperature on POAH cell s. In the present study, 66 POAH cells were recorded from urethan-anes thetized rats while EEG, T-POAH, and T-s were monitored. Seventy-five percent (41 of 55) of the cells were EEG state responsive; 22% (6 of 2 7) were T-POAH sensitive; and 33% (19 of 58) appeared to be T-s respon sive. However, when EEG state changes mere taken into account, none of the cells that appeared to be T-s responsive were responding to T-s w ithin any uniform EEG state. All changes in their firing rates were as sociated with EEG state changes. This study raises a question as to wh ether or not peripheral temperature information is integrated in the P OAH. Consideration should be given to the possibility that T-s informa tion is integrated lower in the neuroaxis. Monitoring EEG is essential in studies attempting to characterize the integrative properties of P OAH neurons of anesthetized or unanesthetized animals. This caveat app lies not just to thermoregulatory studies but to investigations of oth er integrative functions of the hypothalamus and many other brain regi ons as well.