The solitary nucleus (nucleus tractus solitarii) the first central relay for taste in mammals, is being studied anatomically and physiologically in the hamster (Mesocricetus auratus) . The objective is to understand how the neurons in the solitary nucleus process taste quality information from taste buds on the anterior tongue by studying structural and functional properties of single solitary nucleus neurons. One approach is determining whether extracellularly recorded physiological responses of solitary nucleus neurons are arranged in a chemotopic pattern within the anatomical dimensions of the gustatory region of the solitary nucleus. Taste-responsive cells with a wide range of chemical sensitivities that could form the basis for a chemotopic organization are found within the solitary nucleus. Using an optimal mapping strategy, representations of taste quality will be defined by reconstructing recording sites from histological sections within the context of known cytoarchitectonic subdivisions of the solitary nucleus. A second approach is establishing the morphologies of cells within the solitary nucleus that are processing taste information by intracellularly recording responses to taste stimuli and filling cells with a dye. The rostral-central subdivision of the solitary nucleus, where many neural units responsive to anterior tongue taste stimulation are located, contains varieties of elongate, stellate and tufted cells, which may play different roles in taste processing. Signalling and synaptic properties of cells will be recorded. Morphological properties of cells will be determined by reconstructing soma and dendritic and axonal processes from histological sections. Locations and varieties of synaptic endings will be determined from electron micrographs for selected filled neurons. These studies will be a basis for hypotheses about the role of cellular and synaptic organization in signal coding in the solitary nucleus. Diet plays a role in many common diseases and the sweet and salty tastes influence dietary choices; understanding the way that the brain codes taste information could lead to control of sugar and sodium intake.
