Clorgyline effect on pineal melatonin biosynthesis in rats with lesioned suprachiasmatic nuclei.

We have reported that clorgyline-induced stimulation of pineal melatonin biosynthesis could be augmented by the exposure to 24h of constant light in young but not in aged rats. Aging is associated with the declined integrity of the suprachiasmatic nuclei (SCN), the major station of the light signal passage from the retina to the pineal gland. The present study aimed to investigate whether SCN integrity is essential for clorgyline effects on pineal melatonin biosynthesis in light-primed rats. Clorgyline (2.5 mg/kg, s.c.) was administered to sham-operated and SCN-lesioned Sprague-Dawley rats kept under regular light/dark cycle or exposed to 24h of constant light. Pineal melatonin and related indoles were evaluated by HPLC-fluorimetric procedure. Clorgyline stimulated pineal melatonin biosynthesis in both SCN-lesioned and sham-operated rats kept under regular light/dark cycle. Exposure to constant light (for 24h) augmented clorgyline-induced stimulation of melatonin biosynthesis in sham-operated rats, but not in SCN-lesioned animals. The obtained results suggest that decline in SCN activity (e.g., age-associated) might contribute to previously reported attenuation of clorgyline-induced stimulation of melatonin biosynthesis in light-primed aged rats.