ELECTROPHYSIOLOGICAL EVIDENCE FOR MULTIPLE GLYCINERGIC INPUTS TO NEONATAL RAT SYMPATHETIC PREGANGLIONIC NEURONS IN-VITRO

The time pattern of glycinergic inhibitory postsynaptic currents (IPSC s) in sympathetic preganglionic neurons was studied in thin transverse spinal cord slices of neonatal (1-10 days postnatal) rats by means of the patch-clamp technique. Three time patterns could be distinguished : (i) large events [mostly > 400 pA (30-36 degrees C)] occurring at re gular intervals, (ii) small events occurring at irregular intervals, a nd (iii) small events occurring in transient (1.5-10 s), high-frequenc y (> 15 Hz) bursts of synaptic activity. The large regular events had uniform kinetics which was consistent with the idea of a proximal site of origin for all of these events. They were reversibly inhibited in amplitude and frequency by extracellular application of a high concent ration of acetylcholine (200 mu M) or the specific nicotinic acetylcho line receptor agonist dimethylphenylpiperazinium iodide (DMPP; 1 mM), but unaffected by glutamate (100 mu M). IPSCs occurring in bursts had slower and less uniform kinetics, suggesting a more diverse site of or igin, The frequency of events decreased during a burst. Similar bursts could be induced by extracellular application of glutamate receptor a gonists. These results indicate that sympathetic preganglionic neurons in a thin, transverse spinal cord slice receive at least two differen t glycinergic inputs.