INHIBITION BY N-OMEGA-NITRO-L-ARGININE METHYL-ESTER OF THE ELECTROCORTICAL AROUSAL RESPONSE IN RATS

In rats chronically implanted with cannulae into one lateral cerebral ventricle and recording electrodes onto the fronto-parietal cortex, the effects of systemic or intraventricular administration of the nitric oxide (NO) synthesis inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on electrocortical (ECoG) arousal response evoked by sound stimulation were studied. In control animals, a single acoustic stimulation (80 dB for 15 s) produced a significant decrease in ECoG total voltage power lasting approximately 25 s. No tolerance developed after repeating the same sound stimulation at 15, 30, 60 min and 24 h intervals. Under these experimental conditions, pretreatment with L-NAME, given systemically (10 mg kg-1, i.p.) or intracerebroventricularly (300 mug), significantly reduced the sound-evoked arousal response 1 h and 15 min later, respectively. In conclusion, the present data are in favour of a physiological role of NO in the control of arousal mechanisms.