EFFECTS OF NMDA ON RESPIRATORY NEURONS IN NEWBORN RAT MEDULLA INVITRO

In 30 brain stem-spinal cord preparations isolated from newborn rats, we examined effects of 10 muM N-methyl-D-asparate (NMDA) on 21 pre-ins piratory (Pre-I) and 26 inspiratory (1) neurons during perfusion in a synaptic blockade (low Ca2+, high Me2+) bath, referred to here as low Ca. Application of NMDA to 9 Pre-I neurons that burst rhythmically in low Ca significantly increased the burst rates of 6. The activity of t wo Pre-I neurons out of four that fired tonically in low Ca, was chang ed to rhythmic bursts by NMDA. One of eight Pre-I neurons that were si lent in low Ca was caused to burst rhythmically by NMDA. Application o f NMDA had no effect on 20 1 neurons out of 26 tested. NMDA made one I neuron that was otherwise silent burst rhythmically in low Ca. The re sults suggest that, in this preparation, activation of NMDA receptors could contribute to induction or facilitation of burst activity by res piratory neurons, especially Pre-I neurons.