The effects of leucine-enkephalin on the membrane potential and activity of rat respiratory center neurons in vitro.

Studies of transverse slices of Wistar rat brainstem using a patch clamp technique addressed the effects of the opioid peptide leucine-enkephalin (10 nM-1 microM) on the membrane potential and pattern of spontaneous activity of neurons in two parts of the respiratory center: the ventrolateral area of the solitary tract nucleus and the pre-Bötzinger complex. Leucine-enkephalin induced membrane hyperpolarization of respiratory center neurons and decreased the level of spike activity in spontaneously active cells. In pre-Bötzinger complex neurons showing a burst pattern of activity, leucine-enkephalin decreased the burst frequency, and two cells showed a transition from burst activity to tonic activity. These results provide evidence that the mechanism of the central respiratory activity of leucine-enkephalin results from its direct action on the membranes of respiratory center neurons.