Responses of thermosensitive preoptic and septal neurons to hippocampal and brain stem stimulation

Abstract

In anesthetized rabbits, preoptic and septal single units were tested for their response to changes in preoptic temperature and low-frequency electrical stimulation in the hippocampus, midbrain reticular formation, lateral lemniscus and lateral spinothalamic tract. Forty-two percent of the units were affected by at least 1 of the stimulation sites, and most of these were excited. Prolonged stimulation altered the thermosensitivity of some neurons. Brain stem stimulation affected 64% of the cold-sensitive neurons, 60% of the warm-sensitive neurons and 17% of the temperature-insensitive neurons. Hippocampal stimulation affected 47% of the cold-sensitive neurons, 34% of the warm-sensitive neurons and only 4% of the temperature-insensitive neurons. For the warm-sensitive neurons, brain stem stimulation had its greatest effect on those units firing between 15-25 impulses/s, while hippocampal stimulation had its predominant effect on those units firing between 10-15 impulses/s. These differences in firing rate correlate with different temperature ranges of preoptic thermosensitivity.