Responses to taste and eating in the parabrachial nucleus of the pons in awake, unrestrained rats
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Background/Objectives.
The parabrachial nucleus of the pons (PbN) is a hub in the central pathway for taste in non-primate mammals. Recent evidence has identified a role for the PbN in regulating ingestion; however, little is known about how the PbN responds to solid food. Here, we recorded PbN responses to liquid taste stimuli over days/weeks, and tested whether these responses are good predictors of responses to solid foods consumed in a naturalistic way.
Methods.
Rats were prepared for one-photon calcium imaging by surgical implantation of a GRIN lens. PbN activity was imaged during multiple sessions spanning up to 112 days while animals licked various tastants in an experimental chamber (Lick phase). In some sessions, following the Lick phase, rats were presented with Granny Smith apples, milk chocolate and/or salted peanuts (Food phase). In one session, chocolate or peanut odor was presented during the Lick phase along with the tastants.
Results.
PbN cells responded to more than one taste quality with tastant-specific spatiotemporal patterns of response. While response profiles of individual PbN cells shifted over days/weeks, across-unit patterns differentiating taste quality remained relatively stable. Population responses to liquid tastants and solid foods were segregated according to the different motor patterns required for ingestion. Responses to liquid tastants were not good predictors of responses to solid foods. Importantly, PbN cells also responded to food-related odorants.
Conclusions.
Collectively, these results challenge the traditional view of the PbN as a simple relay for taste and instead position it as an integrative hub involved in processing gustatory, olfactory, and somatosensory information. Moreover, the findings emphasize the importance of population coding in maintaining perceptual stability.
