Experiments were performed on in vitro brainstem slice preparations from neonatal rats that retain respiratory network activity. Extracellular recordings were made from 99 neuronal units, respiratory-related or non-respiratory related with rhythmical activity, out of which there were 7 biphasic expiratory and 11 inspiratory ones. Possible roles of non-NMDA receptors in reciprocal excitation among the biphasic expiratory neurons and in excitatory synaptic inputs to inspiratory neurons were investigated by administration of non-NMDA receptor agonist KA and its antagonist DNQX in the perfusion solution. Bath application of non-NMDA receptor agonist KA increased the peak frequency of both biphasic expiratory and inspiratory neuronal discharges, and increased the discharge frequency of the biphasic expiratory neurons and the inspiratory neurons in the middle phase, while the frequency of discharge in the early and late phases were less affected. All of these effects were blocked by addition of the non-NMDA receptor antagonist DNQX, suggesting the involvement of non-NMDA receptors.