RAPIDLY DEACTIVATING AMPA RECEPTORS DETERMINE EXCITATORY SYNAPTIC TRANSMISSION TO INTERNEURONS IN THE NUCLEUS TRACTUS SOLITARIUS FROM RAT

Excitatory synaptic transmission was investigated in interneurons of t he parvocellular nucleus tractus solitarius (pNTS) by performing patch -clamp experiments in thin slice preparations from rat brain stem. Sti mulation of single afferent fibers evoked excitatory postsynaptic curr ents (EPSCs) mediated by glutamate receptors of the L-alpha-amino-3-hy droxy-5-methylisoxazoIepropionic acid (AMPA) and N-methyl-D-aspartate types. AMPA-receptor-mediated EPSCs displayed decay time constants of 3.5 +/- 1.2 (SD) ms (13 cells), which were slow compared with EPSC dec ay time constants in neurons of the cerebellum or hippocampus. Slow EP SC decay was not explained by dendritic filtering, because the passive membrane properties of pNTS interneurons provided favorable voltage-c lamp conditions. Also, the slowness of EPSC decay did not result from slow deactivation of AMPA receptors (0.7 +/- 0.2 ms, 5 cells), which w as investigated during rapid application of agonist to outside-out pat ches. Comparison of AMPA receptor kinetics with EPSC decay time consta nts suggested that the slow time course of EPSCs resulted from the pro longed presence of glutamate in the synaptic cleft.