Effects of synaptic blockade on thermosensitive neurons in rat diencephalon in vitro.

To identify the distribution of inherently thermosensitive and conditionally (i.e., synaptically dependent) thermosensitive neurons in the rat diencephalon, single-unit recordings (n = 88) were made in horizontal tissue slices during localized thermal stimulation before, during, and after reversible synaptic blockade. Inherently warm-sensitive neurons (n = 17) were found in 10 nuclei, the largest number occurring in the preoptic area-anterior hypothalamus (POAH). Inherently cold-sensitive neurons (n = 5) were encountered in three nuclei, with the highest number in the posterior hypothalamus (PH) and mammillary body (MB). Fifty-nine percent of the inherently thermosensitive neurons showed a change in spontaneous activity and/or thermosensitivity during synaptic blockade, indicating that these neurons undergo synaptic modulation. Conditionally warm-sensitive neurons (n = 14) were found in six nuclei with the majority of these neurons located in the accumbens nucleus, diagonal band of Broca, and PH-MB. Two conditionally cold-sensitive neurons were found in the POAH and one in the MB. Temperature-insensitive neurons (n = 49) were rarely affected by synaptic blockade. Thus inherently and conditionally thermosensitive neurons are found in many locations in the diencephalon. These thermosensitive neurons may belong to the neuronal networks responsible for thermo-regulation and the other homeostatic systems that are influenced by temperature.