Thermal response patterns of septal and preoptic neurons in cats

Abstract

The thermosensitivities of preoptic and septal neurons were studied in Urethan-anesthetized or decerebrated cats. Local brain temperature was varied over an 8 C range using water-perfused thermodes while single unit activity was recorded with steel microelectrodes. The thermosensitivities of neurons showing a smooth, continuous relationship of firing rate to temperature were characterized by their Q 10. The slopes of the thermal response curves for all such units were positive. The Q 101 and Q 102 units were distributed widely through the septum and preoptic area, and are assumed to be unspecialized in their thermosensitivity. Units with Q 10 > 2 were localized in the dorsal preoptic area and ventral septum, and are considered to be the central thermosensors responsible for monitoring brain or core temperature. The Q 101 units showed a marked decrease in firing rate or a change in response pattern following injection of barbiturate (Methohexital Sodium, “Brevital”), while units of Q 102 or greater were relatively insensitive to anesthetic depression. Another class of responses was characterized by a sharp change in slope of the thermal response curve at some set temperature. Both units which fired at higher rates when cooled and units with higher firing rates when warm were found. These were distributed through the septum and rostral preoptic area. Units with this type of response were very sensitive to barbiturate anesthetic. Based on their thermoresponsiveness, distribution, and anesthetic sensitivity they are considered to be interneurons in the thermoregulatory pathways. In a given preparation, whether anesthetized or decerebrated, several of these classes of response could be recorded, although all were not obtained from any one animal.