Pilato, S. A. | Search bioRxiv

bioRxiv2025

Responses to taste and eating in the parabrachial nucleus of the pons in awake, unrestrained rats

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.

neuroscience↗

bioRxiv2024

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in this structure respond when an animal is eating solid food. Here, single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm). Results showed that most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms. The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion. Significance StatementThe rostral part of the NTS has traditionally, but perhaps narrowly, been thought of as a "taste relay". While it is true that this structure receives and transmits information about tastants in the mouth to higher order structures in the central gustatory pathway, data presented here show that its function is more diverse. Specifically, in addition to the responses to liquid tastants in the mouth, its responses to approach and exploration of solid food define a significant role for the rNTS in the appetitive phase of eating. Moreover, responses to food consumption, albeit weaker than those during appetitive behavior, buttress the idea that the rNTS is part of the larger hindbrain circuit guiding energy regulation.

neuroscience↗