VIGILANCE AND EEG POWER IN RATS - EFFECTS OF POTENT INHIBITORS OF THENEURONAL NITRIC-OXIDE SYNTHASE

We examined the effects of potent neuronal nitric oxide synthase inhib itors, 3-bromo-7-nitro indazole (3-Br-7-NI) and S-methyl-L-thiocitrull ine (S-Me-TC) on general behaviour, vigilance stages and electroenceph alographic (EEG) power spectra in rats. In addition, we studied the ef fect of 7-nitro indazole (7-NI) on EEG power spectra in rats during da rk and light periods. 3-Br-7-NI induced ptosis and decrease of slow wa ve sleep and rapid eye movement sleep in the rat. 7-NI and 3-Br-7-NI r educed the EEG power density in all frequency bands in the rat, sugges ting a depression of central neuronal activity. This effect of 7-NI wa s more prominent during the day than during the night, indicating a ci rcadian variation the nitric oxide synthase (NOS) response to NOS inhi bitor. EEG power was the most reduced in the 7-9 Hz range of the rhyth mic slow activity (theta rhythm), which is in accordance with decrease d locomotion observed following administration of NOS inhibitors. Alth ough S-Me-TC is the most potent NOS inhibitor in vitro experiments, it had less effect on vigilance and EEG power in the rat than other NOS inhibitors used in this study, probably due to its short lasting and b lood pressure raising effect. The present results indicate that nitric oxide exerts an excitatory and circadian dependent effect in the cent ral neuronal structures involved in the regulation of vigilance.