Electrophysiological characterization of excitatory amino acid responses in rat lateral parabrachial neurons in vitro.

The pontine parabrachial nucleus (PBN) is a major recipient of a diverse array of autonomic-related information from the caudal brainstem. Recent data indicate the presence of glutamate-like immunoreactivity within this nucleus. The effect of specific excitatory amino acid (EAA) receptor agonists and antagonists were studied in the lateral PBN (LPBN) by the use of whole-cell patch recordings in an in vitro brainstem slice preparation. Under current and voltage clamp conditions, independent bath applications of N-methyl-D-aspartate (NMDA; 10 microM), quisqualic acid (QUIS; 10 microM) and kainic acid (kainate; 10 microM) evoked membrane depolarization and an inward current in 28 of 31 LPBN neurons. In voltage clamp mode, the NMDA current (INMDA) was undetectable at potentials negative to -70 mV and a small inward current was observed at more depolarized potentials. However, in the absence of external Mg2+, the voltage dependence of INMDA was similar to that observed for QUIS and kainate. The allosteric modulation of the NMDA receptor by the strychnine-insensitive glycine binding site was examined by the application of the amino acid D-serine (0.5 mM). A marked and sustained potentiation of the steady-state INMDA (-60 mV holding potential) was observed. The selective NMDA-antagonist DL-2-amino-5-phosphonovaleric acid (APV; 10 microM) completely and reversibly blocked the NMDA-induced current, that was maximized in the absence of external Mg2+. Furthermore, this dose of APV was found to reversibly reduce the firing frequency of spontaneously active LPBN neurons.(ABSTRACT TRUNCATED AT 250 WORDS)