N-METHYL-D-ASPARTATE-INDUCED OSCILLATIONS IN WHOLE CELL CLAMPED NEURONS FROM THE ISOLATED SPINAL CORD OF XENOPUS LAEVIS EMBRYOS

The patch-clamp technique was used to measure the effect ofN-methyl-d-aspartate (NMDA) onXenopus embryonic neurons in an isolated, but intact spinal cord. Whole cell recordings were done at external calcium concentrations of 1 mM. NMDA alone (50–200 μM) or in association with 10 μM serotonin or glycine induced oscillatory activity in most presumed motoneurons, which were therefore considered part of rhythm generating networks. In the presence of TTX, one-half of these neurons maintained this activity. The oscillations fell into two main categories: voltage-dependent, low-frequency (0.3–0.5 Hz) and voltage-independent, high-frequency (3–8 Hz) oscillations. NMDA alone induced TTX-insensitive oscillations in one-third of the neurons; however, the percentage of neurons showing oscillations was greater in the presence of exogenous 5-hydroxytryptamine (5-HT) or glycine. Because these observations were made at embryonic stages where little or no serotonergic innervation exists, it is likely that NMDA-induced int...