Sensory Coding in Taste

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DESCRIPTION (provided by applicant): The gustatory system provides sensory information that is necessary for decisions about food intake, which plays a critical role in human health through its impact on such conditions as obesity, diabetes, heart disease, hypertension, and stroke. Little is known about the differential roles played by central taste- responsive neurons in coding stimulus quality vs. palatability, which ultimately guides ingestion. The studies proposed here test the hypothesis that neurons in the parabrachial nuclei (PbN) that project to the ventral posterior medial nucleus of the thalamus (VPMpc) are more important for coding taste quality, whereas those neurons projecting to the limbic forebrain, specifically to the central nucleus of the amygdala (CeA), are critical for coding palatability. Three specific aims address the hypothesis that taste-responsive neurons comprise parallel functional pathways. Aim 1: To determine the gustatory response properties of PbN neurons projecting to the thalamus or amygdala. These studies use extracellular recording to examine how PbN neurons respond to stimuli that vary in quality and palatability (concentration series of sucrose, NaCI, HCI and quinine hydrochloride); neurons projecting to the VPMpc and the CeA are identified in vivo using antidromic activation from electrodes implanted in these target nuclei. Since palatability, but not quality, is altered following conditioned taste aversion (CTA), the responses of VPMpc- and CeA-projecting neurons are examined following an aversion to 0.5 M sucrose, which should alter responses in CeA-projecting cells. Aim 2: To determine the distribution of gustatory-activated Fos expression in PbN neurons retrogradely labeled from the thalamus or amygdala. These studies examine the distribution of neurons activated by stimuli differing in taste quality and palatability and use CTA to sucrose to alter palatability and determine whether cells projecting to the CeA are differentially activated after this manipulation. Aim 3: To determine the intrinsic properties of PbN neurons projecting to the thalamus or amygdala. These studies employ patch-clamp recording from neurons in the PbN that have been retrogradely labeled with fluorescent tracers prior to recording to identify them as projecting to the VPMpc or the CeA, combined with biocytin fills to examine neuronal morphology. These experiments test the hypothesis that there are differences in voltage- activated conductances and cell morphology between neurons projecting to the VPMpc and the CeA.