The Role of Glutamate and CCK in the PBN in Taste Reactivity

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DESCRIPTION (provided by applicant): The long-term goal of this research is to elucidate the central neural mechanisms underlying feeding-related behaviors initiated by taste input in the rat. Recent studies have focused on the neurochemistry of two brainstem areas that receive gustatory sensory information, the rostral nucleus of the solitary tract and the parabrachial nucleus (PBN). The role of the PBN in the processing of sensory information and the initiation of oromotor responses is particularly intriguing since neurons in the PBN process taste-related sensory information and project to the network of motor neurons in the medulla that controls oromotor behaviors. Suggesting a role for glutamatergic neurotransmission within the PBN in the initiation of oromotor behaviors, microinjection of glutamate directly into the taste regions of the PBN in conscious rats elicits ingestive behaviors like mouth movements and tongue protrusions. Therefore, the first specific aim of the proposed study is to determine the role of glutamate receptors within the PBN in oromotor behaviors elicited by taste stimulation. It is hypothesized that the activitation of glutamate receptors is necessary for normal behavioral responses. Cholecystokinin (CCK) is a gut peptide that has satiety effects. There is some evidence that CCK modulates ingestive behaviors but a specific functional role for CCK and its receptors within the PBN has not been addressed. Therefore, the second specific aim of the proposed study is to determine the role of CCK in the PBN in oromotor behaviors elicited by intra-oral infusion of taste solutions in conscious rats. The hypothesis is that, consistent with its role in satiety, CCK will reduce ingestive oromotor responses to taste input. Both specific aims will be addressed by implanting cannula into the PBN as well as into the oral cavity so that glutamate or CCK receptor blockers can be injected into the PBN immediately prior to infusing taste solutions into the oral cavity in conscious rats. The proposed research is relevant to public health because it will improve the understanding of the neural circuits within the brainstem that control behavioral responses to taste input. These behavioral responses are critical to survival since they result in the acceptance of appropriate foods and rejection of potential toxins. Specifically, data collected during the proposed investigation will determine if glutamate and CCK in the PBN play a critical role in the assessment of ingested substances and subsequent behavioral responses.