Hypothalamic input to brain stem neurons responsive to oropharyngeal stimulation.

The aim of this study was to determine if electrical stimulation of diencephalic sites previously implicated in feeding behavior and metabolic homeostasis could influence the unit activity of caudal brain stem neurons receiving oropharyngeal input. Electrical stimulation of the chorda tympani nerve (CT) was used to first identify brain stem units. A significant number of these CT-responsive neurons could also be driven by lateral hypothalamic area (LHA) stimulation. Medially placed diencephalic stimulating electrodes were not effective in altering unit activity of CT-responsive brain stem neurons. Tests of temporal summation showed that LHA conditioning pulses could significantly alter brain stem unit responses to CT test pulses at short interpulse intervals. These results demonstrate the presence of descending input from the LHA-medial forebrain bundle (MFB) to brain stem neurons possibly involved in oropharyngeal sensation and gustatory-evoked phenomena.