Whole cell patch recordings were made from sympathetic preganglionic neurons (SPNs), the majority of which contain brain nitric oxide synthase (bNOS), in transverse spinal cord slices of 12- to 16-day-old rats. 2. Repetitive discharge of SPNs induced by a train of depolarizing current pulses (40 Hz. 10 s) was followed by a long-lasting increase (140 +/- 22%, mean +/- SD) of the amplitude of excitatory postsynaptic potentials (EPSPs) evoked by stimulation of lateral funiculus in 50 of 75 SPNs. 3. In slices pretreated with the nitric oxide synthase inhibitors, NG-monomethyl-L-arginine (L-NMA: 100 microM) or Nw-nitro-L-arginine (L-NARG; 30 microM) or with bovine hemoglobin (100 microM), repetitive discharge of SPNs was not followed by a significant increase of EPSPs. 4. Superfusing the slices with L-arginine (L-Arg, 300 microM) but not D-Arg reversibly increased the EPSPs by an average of 140 +/- 19%. 5. Inclusion of the Ca2+ chelator 1.2-bis(2-aminophenoxy)- ethane-N,N,N',N'-tetraacetic acid (BAPTA, 1 mM) in the patch electrodes resulted in no significant increase of EPSPs after repetitive discharge in all cells studied. 6. It is concluded that during repetitive discharge of SPNs, Ca2+ influx via voltage-gated channels activates bNOS, resulting in a release of nitric oxide and potentiation of EPSPs.
