Effects of halothane on membrane potential and discharge activity in pairs of bulbar respiratory neurons of decerebrate cats.

In aiming to test the possibility of synaptic interactions, the effect of inhalation of halothane (2% for 90 sec) was studied on 45 out of 88 pairs of respiratory neurons, simultaneously recorded with intracellular and extracellular microelectrodes, in both sides of the ventral respiratory group of decerebrate cats. Halothane produced various effects on these respiratory neurons; namely, depolarization (n = 30) or hyperpolarization (n = 15) of intracellularly recorded neurons, an increase (n = 7) or decrease (n = 38) in the firing of extracellularly recorded neurons. However, with repeated application, the agent produced a consistent effect in a given cell. Spike-triggered averaging of synaptic noise, using spikes of non-antidromically-activated respiratory units, did not reveal any unitary postsynaptic potential but a symmetric synaptic wave of medium-frequency-oscillation (35-50 Hz) in 7 pairs. In addition, power spectral analysis of the membrane potential and spike-interval histogram of the paired neuron, displayed no correlated activity suggestive of synaptic interactions. For all the neuronal pairs examined, halothane produced random effects on their patterns of firing and synaptic waves. The present results suggest that halothane exerts a selective effect on each respiratory neuron and that the lack of a correlated response to application of halothane reflects the lack of synaptic interaction between pairs of bilaterally sampled neurons of the ventral respiratory group.