Electrophysiological analysis of neuronal thermosensitivity in rat preoptic and hypothalamic tissue cultures.

1. Ninety-six neurones in forty-six explant tissue cultures of rat medial basal hypothalamus (m.b.h.) and preoptic area (p.o.a.h.) were subjected to thermal stimulation. 2. Neuronal response to temperature was determined on the basis of an extrapolated Q10 calculated from the regression line relating mean spontaneous activity to bath temperature. 3. Thermal stimulation (28-41 degrees C) of p.o.a.h. cultures resulted in the identification of three distinct groups of neurones: (1) temperature-insensitive (0.5 less than or equal to Q10 less than or equal to 2), (2) warm-sensitive (Q10 greater than 2), and (3) cold-sensitive (Q10 less than 0.5). 4. No temperature-sensitive neurones were identified in m.b.h. cultures. 5. In the presence of a medium which effectively blocks synaptic transmission (12 mM-Mg2+ and 0.25 mM-Ca+) the sensitivity of both warm- and cold-sensitive neurones was preserved. 6. These data indicate that thermosensitivity is a characteristic not only of the preoptic neuronal network in vitro but also is an intrinsic characteristic of individual neurones.