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The preoptic anterior hypothalamus (POAH) is considered the thermointegrative center of the mammalian brain. Studies on anesthetized and unanesthetized animals have demonstrated neurons in the POAH that respond to changes in both POAH temperature (TPOAH) and skin temperature (Ts). 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 arousal state to create the appearance that cells are thermosensitive or thermoresponsive when in fact they may not be responding directly to temperature or to thermoafferent input. It is therefore necessary to reexamine the influence of central and peripheral temperature on POAH cells. In the present study, 66 POAH cells were recorded from urethan-anesthetized rats while EEG, TPOAH, and Ts were monitored. Seventy-five percent (41 of 55) of the cells were EEG state responsive; 22% (6 of 27) were TPOAH sensitive; and 33% (19 of 58) appeared to be Tsresponsive. However, when EEG state changes were taken into account, none of the cells that appeared to be Ts responsive were responding to Ts within any uniform EEG state. All changes in their firing rates were associated with EEG state changes. This study raises a question as to whether or not peripheral temperature information is integrated in the POAH. Consideration should be given to the possibility that Ts information is integrated lower in the neuroaxis. Monitoring EEG is essential in studies attempting to characterize the integrative properties of POAH neurons of anesthetized or unanesthetized animals. This caveat applies not just to thermoregulatory studies but to investigations of other integrative functions of the hypothalamus and many other brain regions as well.

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Eastern red-spotted newts are ectotherms, aquatic as adults, and active year-round, breeding even during winter under ice. Earlier research, with field-captured newts, showed a correlation between seasonal changes in the activity of some muscle metabolic enzymes and in the behavior of the newts in a thermal gradient. This study was undertaken to further characterize acclimatory responses in the newts in a more controlled laboratory environment. Newts were obtained during fall, and maintained at 15 degrees C with 12:12 LD for 4 weeks for SMR (at 8 and 26 degrees C) and temperature preference experiments. Subsequently, half the newts were exposed to summer conditions (26 degrees C, 14:10 LD) and half to winter conditions (8 degrees C, 10:14 LD). After 12 weeks, SMR and temperature preference experiments were repeated, and enzyme assays for cytochrome c oxidase (CCO), citrate synthase (CS), and lactate dehydrogenase (LDH) were performed on muscle tissue homogenates, also at 8 and 26 degrees C. Newts changed all three parameters in the laboratory. SMRs were highest in winter-acclimated newts and lowest in summer-acclimated newts, whereas temperature preference was lowest in winter-acclimated newts and highest in summer-acclimated newts. Finally, CCO activity was completely compensated in winter-acclimated newts, CS activity was partially compensated, and LDH activity was not seasonally sensitive. These results indicate a connection or relationship between changes in seasonal environmental conditions, and some aspects of the muscle biochemistry, SMR, and thermoregulatory behavior of these ectotherms.