INTERCHANGEABLE DISCHARGE PATTERNS OF NEURONS IN CAUDAL NUCLEUS-TRACTUS-SOLITARII IN RAT SLICES - ROLE OF GABA AND NMDA

1. We characterized in rat brain slices the discharge patterns of spon taneously active neurons in the caudal region of the nucleus tractus s olitarii (cNTS) and the neuromodulatory role of G-ABA and glutamate, v ia GABA, and NMDA receptors. 2. Spontaneous action potentials recorded intracellularly from cNTS neurons manifested either a regular or an i rregular discharge pattern, alongside characteristic waveforms of the action potentials. These discharge patterns were interchangeable, and were highly sensitive to fluctuations in membrane potentials. In addit ion, the repolarizing rate of the after-hyperpolarization (AHP) in cNT S neurons that exhibited a regular discharge pattern was significantly higher than that of neurons that displayed irregular discharges. 3. c NTS neurons that manifested a regular discharge pattern were converted to irregular discharges upon superfusion with GABA (200 mu M). This w as accompanied by a reduction in the repolarizing rate of the AHP of b oth spontaneous and evoked action potentials. Conversion of discharge patterns in the opposite direction was elicited by superfusion with NM DA (6.8 mu m). 4. The irregular discharges of spontaneous or evoked cN TS neurons were converted to a regular discharge pattern by bicucullin e (200 mu M). Subsequent application of D(-)-2-amino-5-phosphonopentan oic acid (250 mu M) essentially led the neuronal discharges to revert to an irregular pattern. 5. Our results support the presence of two in terchangeable modes of electrophysiological manifestations from the sa me cNTS neuronal population. They also showed that GABA and glutamate, via GABA(A) and NMDA receptors, may provide a novel form of neuromodu lation at tile cNTS by switching the patterns of neuronal discharges.