This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Rajaratnam, S.M.W. Articles by Redman, J.R. Search for Related Content PubMed PubMed Citation Articles by Rajaratnam, S.M.W. Articles by Redman, J.R. Social Bookmarking                         What's this?

Effects of Daily Melatonin Administration on Circadian Activity Rhythms in the Diurnal Indian Palm Squirrel (Funambulus pennanti

Department of Psychology, Monash University, Clayton, Victoria 3168, Australia

J.R. Redman

Department of Psychology, Monash University, Clayton, Victoria 3168, Australia

Exogenous melatonin induces phase shifts in circadian rhythms ac cording to a phase response curve in nocturnal rodents, several nonmammalian diurnal species, and humans. Daily administration of melatonin entrains rhythms within a narrow circadian window of sensitivity in these species. Entrainment to exogenous melatonin has not previously been demonstrated in a (nonhuman) diurnal mammal. The authors examined the effects of daily melatonin administration (via food) in the diurnal Indian palm squirrel, Funam bulus pennanti. The effects of melatonin or vehicle were examined at two times of day: zeitgeber time 0 (ZT 0: light onset time) and ZT 12 (dark onset time). In addition to melatonin- and vehicle-treated squirrels, there was a third group of squirrels that received no treatment. Squirrels were held initially under 12:12 light-dark (LD) cycles, and melatonin (1 mg/kg) or vehicle was administered in food (a raisin) at either ZT 0 or ZT 12 for a total of 17 days. On the third day of treatment, constant lighting (LL) was imposed. Treatment continued at the same ZTs for a further 14 days. The number of days before free-running commenced under constant conditions was assessed for squirrels in each treatment group. Results showed that regardless of the ZT of administration, the number of days before free-running commenced was significantly greater in melatonin-treated squirrels than in vehicle-treated and untreated squirrels, and there was no difference between vehicle-treated and untreated squirrels. Although there was not a significant difference in the number of days before free-running com menced between the two times of administration, the results showed a trend for greater sensitivity to melatonin at ZT 12. This study has therefore demonstrated that the palm squirrel circadian system is entrainable to melatonin at both times of day tested, ZTs 0 and 12. This finding is in contrast to previous melatonin entrainment studies in other species, where entrainment generally occured at only one phase, around circadian times 10 to 12. Interspecies differences in response to melatonin were discussed.

Key Words: circadian • activity rhythm • melatonin • diurnal • Indian palm squirrel

Journal of Biological Rhythms, Vol. 12, No. 4, 339-347 (1997)
DOI: 10.1177/074873049701200406


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				C. M. Novak and H. E. Albers Novel phase-shifting effects of GABAA receptor activation in the suprachiasmatic nucleus of a diurnal rodent Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2004; 286(5): R820 - R825. [Abstract] [Full Text] [PDF]

				J. R. Redman and A. J. P. Francis Entrainment of Rat Circadian Rhythms by the Melatonin Agonist S-20098 Requires Intact Suprachiasmatic Nuclei But Not the Pineal J Biol Rhythms, February 1, 1998; 13(1): 39 - 51. [Abstract] [PDF]

				J. R. Redman Circadian Entrainment and Phase Shifting in Mammals with Melatonin J Biol Rhythms, December 1, 1997; 12(6): 581 - 587. [Abstract] [PDF]