The Siberian hamster as a model for study of the mammalian photoperiodic mechanism.

The Siberian hamster has been a useful model for studies of mammalian photoperiodism for a number of reasons: 1) Siberian hamsters are hardy animals that are easily maintained and bred in the laboratory. 2) The species exhibits a large number of seasonal, photoperiod-driven, pineal-dependent responses. Thus, the Siberian hamster is an excellent species in which to examine whether several different types of photoperiod responses share similar mechanistic features with respect to their control by MEL. Are all the responses cued to the duration of the nocturnal MEL peak? Does MEL act at a single site to influence all the types of responses, or are there separate MEL target sites for different responses? 3) Juvenile Siberian hamsters exhibit an unusually rapid (for mammals) response to photoperiod change or to MEL treatments, making them ideal subjects for certain types of photoperiod-related studies. 4) Populations of Siberian hamsters show individual variations in photoperiod responsiveness, and the differences are at least partly heritable. These hamsters also exhibit strong influences of environmental history on short day responsiveness. Thus, the species may be a valuable model for the investigation of both genetic and environmental influences on the photoperiodic mechanism. 5) Siberian hamsters have proved to be useful animals in which to study maternal influences on the developing photoperiodic mechanism of the fetus.