[Gustatory information processing in rat medullary solitary tract nucleus]

1. The present experiment aimed at examining the possibility that the taste-sensitive neurons with similar taste-sensitivity are preferentially innervated by common driving neurons whose taste-selectivity is also similar. 2. A pair of glued electrodes was inserted into the unilateral solitary tract nucleus (NTS) of the rat, and simultaneous recordings were made in neuron pairs responding to the four basic taste stimuli. The spike response density (RD) of each neuron during tastant stimulation was determined. Correlation coefficients of spike occurrence were calculated for each neuron pair during application of tastants and distilled water, and also during spontaneous background activity. The frequency of correlated discharge (FC) of a neuron pair was measured as the area of the peak appearing on the cross-correlogram (CC). The FC value was divided by the RD value to calculate the weight of the correlated discharges in the output of each neuron (WC value). 3. Eleven pairs showed peak formation on the CC constructed during tastant stimulation, while in other 11 pairs no peak formation was found. The cross-correlation-positive group with peak formation was composed of 18 NaCl-best (responding most vigorously to NaCl) and 4 HCl-best neurons, while the negative group without peak formation included 9 NaCl-best, 9 HCl-best, and 4 sucrose-best neurons. From the cross-correlation negative group without peak formation the probability to pick up by chance two neurons responding most strongly to the same taste quality was calculated to be 0.367. 4. In 7 cross-correlation-positive pairs out of 11, both of the component neurons were NaCl-best, giving 7/11 = 0.636. 5. In the cross-correlation-positive pairs the best taste of one of the component neurons was often (13 NaCl-best and 2 HCl-best, 15/22 = 0.681) identical to the taste quality giving the highest probability of correlated discharge, i.e., the highest FC value, in the neuron pair. 6. There were 5 cross-correlation-positive pairs (5/11 = 0.455) in which both of the component neurons were NaCl-best and the FC value was highest during NaCl stimulation. 7. The CCs constructed during water application showed peak formation in all the pairs which gave positive cross-correlation following stimulation with tastants, while all the pairs with negative cross-correlation during tastant stimulation never gave a detectable peak during water application. 8. In 3 pairs of the cross-correlation-positive group, the CCs constructed during spontaneous background activity without application of any liquid showed a small peak.(ABSTRACT TRUNCATED AT 400 WORDS)