Lateral hypothalamic modulation of oral sensory afferent activity in nucleus tractus solitarius neurons of rats.

This study was designed to examine whether the sensory afferents from the anterior part of the tongue are modulated by activity of the lateral hypothalamic area (LHA) at the level of the nucleus tractus solitarius (NTS) in rats. The electrical activity of the NTS neurons was recorded extracellularly, and they were classified as gustatory, thermal, or mechanical neurons in accordance with their responsiveness to tongue stimulation by taste solutions, by warm and cool water, and by stroking the tongue surface. Sixty-two percent of the neurons were polysynaptically activated by electrical stimulation of the LHA. When a single conditioning stimulus of the LHA was applied prior to the test electrical stimulation of the tongue at various conditioning-test intervals, the activity of the gustatory neurons was facilitated by 30 to 80% of their control level for a period of approximately 20 to 150 msec. The activity of the mechanical and thermal neurons was suppressed for a 50- to 300-msec period. These results demonstrate the existence of modulatory effects from the LHA on the NTS neurons, which receive sensory information from the tongue.