Slow IPSP and the noradrenaline-induced inhibition of the cat sympathetic preganglionic neuron in vitro.

Focal electrical stimulation of the slice of the cat thoracic cord evoked in sympathetic preganglionic neurons a slow inhibitory postsynaptic potential (IPSP) associated with decreased neuronal input resistance. The slow IPSP decreased in amplitude with membrane hyperpolarization and reversed at about -90 mV. It increased in amplitude in low potassium and decreased in high potassium. Noradrenaline (NA) at doses of 10-50 microM caused in some of these cells a hyperpolarization with properties similar to those of the slow IPSP. Both the slow IPSP and the NA-evoked hyperpolarization were abolished by yohimbine, but not by prazosin or propranolol. These data suggest that both responses are due to an increase in potassium conductance and that NA may be the mediator of the slow IPSP evoked by focal stimulation.