Non-NMDA and NMDA receptors in the synaptic pathway between area postrema and nucleus tractus solitarius

Area postrema (AP) modulates cardiovascular function through excitatory projections to neurons in nucleus tractus solitarius (NTS), which also process primary sensory (including cardiovascular-related) input via the solitary tract (TS). The neurotransmitter(s) and their receptors in the AP-NTS pathway have not been fully characterized. We used whole cell recordings in voltage- and current-clamp modes in the rat brain stem slice to examine the role of ionotropic glutamatergic receptors and alpha(2)-adrenergic receptors in the pathway from AP to NTS neurons receiving visceral afferent information via the TS. In neurons voltage clamped at potentials from -100 to +80 mV,AP stimulation (0.2 Hz) evoked excitatory postsynaptic currents having a fast component blocked by the non-N-methyl-D-aspartate (NMDA) receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo- quinoxaline-7-sulfonamide (NBQX; 3 mu M, n = 7) and a slow component blocked by the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV; 50 mu M, n = 8). Although NBQX (3 mu M, n = 14) abolished AP-evoked action potentials, APV (50 mu M, n = 9 or 500 mu M, n = 6) or yohimbine, (200 nM, n = 5 or 2 mu M, n = 10) did not. Thus, although AP stimulation activates both non-NMDA and NMDA receptors on NTS neurons receiving TS input, only non-NMDA receptors are required for synaptic transmission.