Electrophysiology of taste-mediated functions in parabrachial nuclei of behaving rabbit.

A single-unit analysis of parabrachial (PBN) neuronal activity associated with orolingual response to auditory-cued intraoral injections of basic type tastants and water revealed 7 major functional types of neurons. Several types dealt with mechanoreceptive orosensory input from superficial and/or deep receptors and from proprioceptors (possibly joint receptors). Some were multimodal in sensitivity. In one type, thermal or gustatory input acted to inhibit movement-related excitation in activity. Three types of taste-sensitive elements were distinguished. "Movement-taste sensitive" elements showed relations to orolingual movement and hedonic properties of fluid input. These cells may contribute to motivational control of licking activity. A tentative distinction was drawn between "taste-hedonic" and "taste" elements. One type responded to water and showed a bias toward hedonic properties of tastants. The other type exhibited no response to water and smaller responses to tastants that had no hedonic relationship. Both, however, had common properties, including inhibitory modulation of activity in apparent anticipation of fluid delivery. In addition to serving as a gustatory relay, PBN act to integrate orolingual response to taste and other orosensory input, and may operate as an output mechanism in the ventral forebrain control of ingestive behavior.