Accession Number : ADA268200


Title :   Melatonin, the Pineal Gland, and Circadian Rhythms


Descriptive Note : Annual rept. 1 Jun 92-31 May 93,


Corporate Author : TEXAS A AND M UNIV COLLEGE STATION DEPT OF BIOLOGY


Personal Author(s) : Cassone, Vincent M ; Warren, Wade S ; Brooks, David S ; Lu, Jun


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a268200.pdf


Report Date : 31 May 1993


Pagination or Media Count : 74


Abstract : Previous work has shown that daily injections of the pineal hormone melatonin (N- acetyl, 5 methoxytryptamine) entrain the free-running locomotor rhythms of rats held in constant darkness (DD) (with a median effective dose [ED50 of 5.45 plus or minus 1.33 microgram/kg) and in constant bright light (LL). The present experiments determined the dose-response characteristics of entrainment and phase-shifting to daily and single melatonin injections in both sham operated (SHAM) and pinealectomized (PINX) rats. The data indicated an ED50 of 332 plus or minus 53 ng/kg and 121 plus or minus 22 ng/kg for SHAM and PINX rats respectively during the entrainment experiment. The ED50's for the entrainment experiment were considerably lower than doses previously employed and much lower than doses employed in reproductive and metabolic studies in rats and hamsters. The data indicated that no partial entrainment - occurred, nor were there differences in phase angle, length of activity or period among all effective doses. Next, a single injection of 1 microgram/kg melatonin has previously been shown to cause a phase-advance of approximately 45 minutes when administered around circadian time (CT) 10. We found that both SHAM and PINX animals phase-advanced to a single melatonin injection given at CT10 in a dose-dependent manner. The data for the phase- shifting experiment indicated a median effective dose of 8.19 plus or minus 0.572 microgram/kg and 2.16 plus or minus .326 microgram/kg for SHAM and PINX animals respectively with an average phase advance of 40 minutes for both groups. Together, the data suggest that the presence of the pineal gland is not necessary for the effects of melatonin on the rat circadian system and that PINX animals are marginally more sensitive to melatonin than their SHAM operated controls.


Descriptors :   *CIRCADIAN RHYTHMS , *PHOTORECEPTORS , HORMONES , MAMMALS , RATS , INTERACTIONS , LIGHT , DARKNESS , FEEDBACK , WAKE , NERVOUS SYSTEM , TEMPERATURE CONTROL , EYE , SYMPATHETIC NERVOUS SYSTEM , SECRETION , SLEEP , GLANDS , MELATONIN , PINEAL GLAND , HYPOTHALAMUS , LOCOMOTION


Subject Categories : Anatomy and Physiology


Distribution Statement : APPROVED FOR PUBLIC RELEASE