[The mechanism of taste quality discrimination in rat pontine parabrachial nucleus].

Abstract

1. Cross-correlation analysis was made in the taste-sensitive neuron pairs recorded simultaneously from the parabrachial nucleus (PBN) of rats. Three indices were adopted to evaluate the activities of the taste neurons: 1) the spike response density (RD value), which is the net spike density with the 4 basic tastes. 2) the frequency of correlated discharges (FC value), which was determined by measuring the area of the peak appearing in the cross-correlogram (CC) during application of the test fluids. 3) the weight of correlated discharge (WC = FC/RD), which shows the relative importance of correlated discharges in the taste signals delivered by a component neuron of a given pair. 2. In 11 of the 23 pairs, the CCs exhibited peaks during stimulation with tastants. These 11 pairs, which were recorded in the pontine taste area, were composed of 18 NaCl-best (most sensitive to NaCl) and 4 HCl-best neurons. In 8 pairs, the best-taste of both of the component neurons was NaCl, and it was HCl in 1 pair (homo-type pairs). The remaining two pairs consisted of an NaCl-best and an HCl best neuron (hetero-type pairs). 3. In 8 homo-type pairs (7 NaCl-best and 1 HCl-best pair), each pair exhibited the maximal FC value during stimulation with the best-taste of the component neurons (2.3 less than or equal to maximal FC less than or equal to 26.6 Hz). In the remaining three pairs, the maximal FC values were low (0.8-1.9 Hz). Two of these pairs were hetero-type, and, in their cases, the maximal FC value was obtains during stimulation with a tastant which was different from the best-taste of the component neurons. 4. The peaks in the CCs usually straddled the origin, and their highest point was located at the origin or very close to it. The width of the peaks appearing in the CCs was broad (3-8 ms) in 7 pairs and narrow (0.5-2 ms) in 4 pairs. In all of the broad-peak pairs, the best-taste of both of the component neurons was identical (homo-type), NaCl or HCl. In six broad-peak pairs peaks also appeared during the application of distilled water. In the narrow-peak pairs, two were of homo-type (NaCl-best) and their maximal FC value was obtained during NaCl stimulation. Their maximal FC value was higher than that of the other two narrow-peak pairs, which were hetero-type and exhibited no peaks during water application.(ABSTRACT TRUNCATED AT 400 WORDS)