Responses of preoptic thermosensitive neurons to mediobasal hypothalamic stimulation

Single-unit responses of preoptic-anterior hypothalamic (PO/AH) thermosensitive neurons to electrical stimulation of the mediobasal hypothalamus (MBH: ventromedial and arcuate nuclei) have been studied in urethane-anesthetized male rats. About half of thermosensitive neurons (46.4% of 69 warm-units and 50% of 28 cold-units) were initially inhibited following MBH stimulation with latencies up to 51.2 msec, while only 29.7% of 91 thermally insensitive units showed the inhibitory response. Orthodromic excitation of spontaneous activity was observed in 17.6% of the units (13.0% of warm-units, 14.3% of cold-units and 21.9% of insensitive units) with the onset latencies between 1.0 and 41.3 msec. A small proportion of neurons (5.3%) were antidromically activated by MBH stimulation, and the estimated conduction velocities of these neurons ranged from 0.11 to 0.67 m/sec. The results suggest reciprocal connections between PO/AH thermosensitive neurons and MBH, which may play some roles in thermoregulation and, also, in functional interactions between thermoregulation and other vital functions controlled in the hypothalamus.