SYNAPTIC CONNECTIONS AND INTERACTIONS BETWEEN AREA POSTREMA AND NUCLEUS-TRACTUS-SOLITARIUS

The purpose of this study was to examine whether there are separate ex citatory and inhibitory pathways from the area postrema (AP) to the nu cleus tractus solitarius (NTS) and to examine the synaptic interaction s between inputs from the AP and solitary tract (ST) on the NTS neuron s. The following observations were made: (1) the predominant projectio ns from the AP to the NTS were excitatory. Among the cells that had AP input, 90% of the cells (43/48) were excited by AP stimulation while 10% (5/48) of the cells were inhibited; (2) inputs from the AP and ST mainly summated occlusively on the NTS neurons, but at near threshold of discharge, the input from one source could facilitate the generatio n of action potentials induced by the other; and (3) single conditioni ng stimulation of the AP did not significantly inhibit the NTS neurona l response to ST stimulation, but stimulation of the AP with a train o f high frequency stimuli inhibited the response of NTS neurons to ST s timulation and inhibited the evoked response to AP stimulation. The re sults of this study may help in the understanding of the modulatory ro le of the AP in the baroreflex and the integration process in the NTS.