SYNAPTIC-INDUCED AND AGONIST-INDUCED CHLORIDE CURRENTS IN NEONATAL RAT SYMPATHETIC PREGANGLIONIC NEURONS IN-VITRO

1. By using the whole-cell recording configuration of the patch-clamp technique in a spinal cord slice preparation, we have made recordings from visually identified neurones in the lateral horn of the thoracic and lumbar spinal cord of neonatal rats (newborn to 14 days postnatal) . 2. Some of the recorded neurones were labelled with the fluorescent dye Lucifer Yellow (n = 27). Their morphology was typical for sympathe tic preganglionic neurones (SPNs). Based on the size of the cell soma and the electrophysiological properties, unlabelled neurones were also regarded as SPNs. 3. Spontaneous synaptic activity of different patte rns could be observed in 73 % of the recorded neurones (n = 106). It r eversed at the chloride equilibrium potential (E(Cl)) and could be rev ersibly blocked by strychnine (1-10 muM), but not by bicuculline (10 m uM) or SR95531 (5-10 muM). 4. Synaptic activity could be elicited by f ocal electrical stimulation in the vicinity of the recorded neurone. T hese evoked synaptic events exhibited features similar to the spontane ous synaptic activity. 5. Application of glycine (100 muM-1 mM) by a f ast microperfusion system induced a chloride current in twenty-seven o ut of thirty cells tested. The currents were reversibly blocked by str ychnine (1-10 muM), but were only weakly sensitive to bicuculline (10 muM). Stability of current responses to glycine was increased by inclu sion of ATP (4 mM) in the intracellular medium. 6. Application of gamm a-aminobutyric acid (GABA; 100 muM-1 mM) by the fast microperfusion sy stem induced a chloride current in all twenty neurones tested. These c urrents were reversibly blocked by bicuculline (10 muM). Strychnine (1 -10 muM) blocked this current only weakly. Run-down of GABA-induced cu rrents was prevented to a great extent by inclusion of ATP (4 mM) in t he pipette. 7. These results suggest that the inhibitory synaptic acti vity recorded from SPNs in thin, transverse slices of neonatal rat spi nal cord is mediated by glycine receptor-gated Cl- channels. GABA(A) r eceptor-gated Cl- channels might be activated by inputs from other spi nal segments and/or descending pathways from higher brain regions.