Convergence onto hamster medullary taste neurons.

Research has shown that gustatory afferents innervating different areas of the oral cavity converge onto single neurons in the nucleus tractus solitarii (NTS). However, most studies of gustatory physiology have only stimulated the receptors on the anterior tongue. No information exists on the responses of hamster NTS neurons to stimulation of receptors located in other areas of the oral cavity. The present investigation compared responses of hamster NTS neurons to stimulation of receptors on the anterior tongue and posterior oral cavity, and to stimulation of both receptor populations together. Of the neurons, 64% responded to both anterior tongue and posterior oral cavity stimulation. The remaining neurons responded exclusively to stimulation of one area. Cells responsive to both fields of stimulation were found throughout the rostral NTS. Cells responding to stimulation of only one field were anatomically separate. Most neurons (69%) were more responsive to anterior tongue than posterior oral cavity stimulation. The neural responses to stimulation of both fields simultaneously were complex. Frequently, a cell's response was intermediate between those produced by stimulation of either receptor population alone. In other cases the response was the same as the larger of the two individual responses. The breadth of responsiveness to the 4 basic taste stimuli (sucrose, NaCl, HCl and quinine-HCl) was similar for both receptor populations, but the breadth of tuning of an individual cell for one field of stimulation was not correlated with its breadth of responsiveness for the other. In contrast, the breadth of tuning following stimulation of the entire oral cavity was correlated with that following stimulation of the anterior tongue.