Diazepam potentiates postsynaptic inhibition in bulbar respiratory neurons of cats

The purpose of this study was to assess the effect of benzodiazepine on inhibitory postsynaptic potentials (IPSPs) of medullary respiratory neurons in decerebrate, paralyzed cats. Diazepam (0.05 and 0.1 mg/kg i.v.) reversibly increased the IPSP waves occurring during the inactive phase of the respiratory cycle in all inspiratory and postinspiratory neurons examined. Input resistances of these neurons were reduced at that phase. The reversal potential for the IPSP wave was unaltered. Intracellular injection of chloride ions reversed the IPSP to depolarization, and diazepam produced a purely depolarizing effect. The drug effects observed during the active phase of each neuron include a decrease in the firing rate and a shortening of the burst activity. The firing threshold and shape of these spikes, however, remained unaltered. These results suggest that diazepam depresses the bulbar respiratory neuronal activities specifically by potentiating the periodic postsynaptic inhibition.