Potentiation of IPSCs by nitric oxide in immature rat sympathetic preganglionic neurones in vitro.

1. Whole-cell patch-clamp recording techniques were applied to sympathetic preganglionic neurones (SPNs), the majority of which contain neuronal nitric oxide synthase (NOS), in transverse thoracolumbar spinal cord slices from 8- to 12-day-old rats, and the role of nitric oxide (NO) in modulating the inhibitory postsynaptic current (IPSC) evoked by focal stimulation was examined. 2. Superfusing the slices with the NO precursor L-arginine (L-Arg, 300 microM) and the NO donor sodium nitroprusside (SNP, 100 microM) potentiated IPSCs from several minutes to more than 1 h; the increase was prevented by pretreating the slices with bovine haemoglobin (100 microM), the nitric oxide synthase inhibitor N omega-nor-L-arginine (NO-Arg, 100 microM) or the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM). Haemoglobin, NO-Arg and ODQ slightly reduced the IPSCs evoked in some of the SPNs. 3. Superfusion of the slices with N2,2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate (dbcGMP, 300 microM) in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX, 750 microM) reversibly increased the IPSCs as well. 4. While enhancing the IPSCs, L-Arg or SNP had no significant effects on outward currents induced by pressure application of the putative inhibitory transmitter glycine in the same cells. 5. A train of suprathreshold depolarizing current pulses (30 Hz for 10 s) injected into the recording SPNs caused, after a delay of several minutes, a long-lasting increase of IPSCs; this effect was nullified by superfusing the slices with haemoglobin or NO-Arg. 6. The result suggests that NO released endogenously from SPNs may act as a retrograde messenger molecule to enhance the release of glycine or a related substance, possibly via a cGMP-dependent mechanism.