MORPHINE-INDUCED CHANGES IN CEREBRAL AND CEREBELLAR NITRIC-OXIDE SYNTHASE ACTIVITY

The effect of acute and chronic morphine treatment on nitric oxide (NO ) synthase activity (determined by the rate of conversion of [C-14]arg inine into [C-14]citrulline) on mouse brain was studied. Acute morphin e treatment induced an increase in Ca2+-dependent NO synthase in cereb ellum. This effect was blocked by coadministration with naloxone. Chro nic morphine treatment (by s.c. pellet) also produced an increase in c erebellar NO synthase, with a maximum on the second day of implantatio n. No significant changes were found in frontal cortex and forebrain d uring acute or chronic morphine treatment. The relationship between op iate effects and the L-arginine:NO pathway is discussed.