Meeting Abstract

P1.227  Friday, Jan. 4  Effects of Photoperiod, Melatonin, and Gonadal Steroids on Gastrointestinal Development in the Male Marsh Rice Rat (Oryzomys palustris) EDMONDS, K.E.*; Indiana University Southeast kedmonds@ius.edu

Environmental factors can regulate the development of various physiological systems in many species. Photoperiod and melatonin are known to inhibit significantly the reproductive system in seasonal breeders, but effects on the GI tract have not been as extensively studied. The present study examined whether photoperiod, melatonin, and gonadal steroids affect reproductive and gastrointestinal (GI) development in juvenile male rice rats. Rice rats were subjected to long (14L:10D) or short (12L:12D) photoperiods, the presence of control or melatonin implants (20 mm total), or the presence of empty or testosterone implants (10 mm total) in separate experiments from 21-56 days of age. The following masses were examined: body, testes, seminal vesicles (SV), Harderian glands (HG), and wet (W) and dry (D) masses of the stomach (St), small intestine (SI), cecum (Ce), and colon (Co). In addition, small intestine and colon lengths were measured. Short photoperiods reduced body, testes, SV, HG, WSt, WCo, and DCo masses and the lengths of the SI and Co. Melatonin implants reduced body, testes, SV, HG, WSt, WCe, WCo, DSt, DCe, and DCo masses and the lengths of the SI and Co. Testosterone implants had no effect on any end point measured except for a significant increase in SV mass. These data show that photoperiod and melatonin affect growth, reproduction, and GI development in males, but that testosterone supplementation is without effect on any GI end points. The effects of castration on GI development are currently being examined. It is hypothesized that changes in gut capacity may be a necessary mechanism for coping with likely seasonal changes in metabolic requirements. (Supported by funds from IU Southeast.)