[Activation of locus coeruleus inhibits vagal inputs in nucleus tractus solitarius]

On pentobarbital anesthetized rabbits, a three-wavelet compound potential to cervical vagal afferent stimulation was recorded in ipsilateral nucleus tractus solitarius (NTS). The latency of the three wavelets (P1, P2 and P3) was 6.8 +/- 0.6 ms (P1), 25.8 +/- 4.2 ms (P2) and 89.1 +/- 2.7 ms (P3) respectively, which might represent postsynaptic activity of different kinds of vagal afferent fibers. Microinjection of glutamate into ipsilateral locus coeruleus (LC) decreased the amplitude of P2 and P3 significantly. Electrical stimulation of LC could activate 111 units in ipsilateral NTS with a mean latency of 6.3 +/- 1.4 ms. Of the 169 units in the NTS to vagal afferent stimulation, 90 units also responded to LC stimulation. 39 (43.3%) of the ninety, units shows similar response to both stimuli, while the rest show different response. Of the 25 units which showed excitatory response to both LC and vagal stimulation, but when LC stimulation was followed by vagus stimulation, the latter's response was either markedly suppressed (14 units) or completely inhibited (11 units). These results showed that activation of LC exerts an inhibitory effect on the responses of the NTS to vagal afferent stimulation.