Nitric Oxide in the biological clock: NO news is good news

S.A. PLANO, P.V. AGOSTINO AND D.A. GOLOMBEK

Córdoba (Argentina)

Simposio; VIII Latin American Symposium of Chronobiology; 2005

Light reaches the suprachiasmatic nucleus (SCN) through the retinohypothalamic tract. In mammals, the administration of a light pulse during the late night induces a phase advance in the activity rhythm and activates the immediate early gene cfos. The ventral subdivision of the SCN receives the glutamatergic signal, and re-transmits it through the dorsal area. Nitric oxide (NO) is a common messenger that might be involved in the intercellular communication within the SCN. In this work we studied the role of NO in the intercellular communication within the ventral and dorsal portions of the SCN. We analyzed the wheel-running activity of hamsters in constant darkness, and their behavior after a light pulse (7 min, 600 lux) at circadian time (CT) 18 (late night) with or without the previous i.c.v. administration of the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) (100 mM, 1 ml during 1 min). Our results indicate that PTIO injection blocked light-induced phase advances. We also observed a complete inhibition of light induced cFOS-ir in animals treated with PTIO. Preliminary results at CT 14 (early night), when a light pulse induces a phase delay, showed no significant changes in behavioral rhythms of animals treated with PTIO. Thus, the communication within the SCN at CT 14 might be NO-independent. Together, these results suggest that NO may act as an intercellular messenger in the SCN, mediating light-induced phase advances but not phase delays.