Effect of calcium removal on thermosensitivity of preoptic neurons in hypothalamic slices.

Extracellular single-unit activities of thermosensitive neurons were recorded from the medial preoptic area in rat's hypothalamic slices in vitro. Of 256 preoptic units, 74 were warm-units which increased firing rates in response to a rise in slice temperature and 16 units were cold-units having the opposite type of thermosensitivity. Eighteen of 23 warm-units and 3 of 4 cold-units retained their thermosensitivities during perfusion with Ca2+-free/high Mg2+ salt solution. The thermosensitivities of the remaining 5 warm-units were reversibly abolished in the Ca2+ deficient medium. The results suggest that some warm- and cold-sensitive neurons in the medial preoptic area have an inherent thermosensitivity.