EFFECTS OF L-ARGININE-DERIVED NITRIC-OXIDE SYNTHESIS ON NEURONAL-ACTIVITY IN NUCLEUS-TRACTUS-SOLITARIUS

The purpose of these studies was to determine the effects of L-arginin e-derived nitric oxide (NO) synthesis on neuronal activity in solitary tract nucleus (NTS) neurons. Single unit activity was recorded extrac ellularly from medial NTS neurons in Fischer-344 rats in vivo and in v itro. In anesthetized rats with arterial pressure maintained constant, N-G-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg iv), an inhibitor of NO synthesis, decreased the discharge rate in 12 of 14 neurons and increased the discharge rate in two. After injection of L-NAME, the s lowing of neuronal activity began within 2-5 min, and maximal response s were observed 12-15 min after injection. The decreases in activity w ere reversed within 12-15 min with L-arginine (30 mg/kg iv) or immedia tely with nitroglycerin (NTG, 10-30 mu g/kg iv). In superfused rat bra in slices, the discharge rate was reduced by 1 mM L-NAME in seven neur ons, increased in two, and unchanged in one. The decreases in discharg e rate were reversed by 2 mM L-arginine (4 of 6 neurons) and by 10-30 mu M NTG (6 of 7 neurons). The results show that L-arginine-derived NO can affect the spontaneous discharge rate of NTS neurons. We conclude that NO may influence the excitability of NTS neurons involved in cen tral autonomic control.