The sense of taste plays a critical role in making a decision on what will or will not be ingested. Such accurate but fast decision making occurs based on analyses of quality and intensity of chemicals which are operated by the central nervous system. According to current models, the parvicellular division of the ventroposteromedial nucleus of the thalamus (VPMpc) serves as an obligatory taste relay nucleus between the pontine parabrachial nucleus and the gustatory insular cortex in rodents. In spite of the possibility that the VPMpc may process taste information cooperatively with other taste centers such as the insular gustatory cortex or the central nucleus of the amygdala, the VPMpc has often been considered as a passive relay station. Consequently less attention has been paid to the VPMpc relative to peripheral structures, brainstem relays, or even gustatory cortex. To understand how the sense of taste effectively guides feeding behavior, it is necessary to reveal the exact roles of VPMpc in the central gustatory system. The current proposal aims to elucidate the basic characteristics of the VPMpc functions by using complementary anatomical, physiological and behavioral approaches in the C57BL/6J and GAD1-EGFP transgenic mice. We propose the following specific aims:
Aim 1 : To determine the efferent and afferent connection patterns of the mouse VPMpc. We will inject anterograde and retrograde tracers into the VPMpc to collect comprehensive anatomical data which enable the VPMpc to engage in higher-order taste information processing.
Aim 2 : To determine the properties of single-unit responses of the VPMpc neurons to various taste stimuli in anesthetized mouse. We will carry out in vivo electrophysiological experiments to show 1) the basic characteristics of the mouse VPMpc taste-responsive units with traditional and novel analyses and 2) functional evidence of existence of corticofugal influence on the VPMpc taste activities by using cortical spreading depression.
Aim 3 : To characterize deficits in conditioned taste aversion behavior following excitotoxic lesions of the VPMpc using licking microstructural analyses. In this aim we will collect licking microstructure data by using Davis rig to assess the function of the mouse VPMpc in innate and learned taste preference and aversion behaviors. Conditioned taste aversion will be used to test the hypothesis that VPMpc lesions disrupt fine but not gross taste discrimination.
Feeding behavior in animals, including humans, is critically governed by the guidance of taste sensations. Taste recognition behavior involves analyses of both quality and intensity of chemical stimuli, and this rapid decision making takes place in the brain. To understand the neural basis of taste recognition and ingestive decisions is a critical step for promoting healthy diet selection, and precluding pathologies in eating behavior.