Effects of photoperiod history on immune responses to intermediate day lengths in Siberian hamsters (Phodopus sungorus).

Seasonal changes in day length enhance or suppress immune function in individuals of several mammalian species. Siberian hamsters (Phodopus sungorus) are long-day breeders that adjust reproductive physiology and behavior, body mass, and immune function following exposure to short photoperiods. Photoperiods of intermediate-duration, encountered in nature by juvenile hamsters born in early-spring and by those born in mid-summer, trigger gonadal development in the former cohort and inhibit the onset of puberty in the latter. Divergent reproductive responses to the same intermediate photoperiod depend on a photoperiod history, communicated during gestation. These experiments assessed whether photoperiod history during gestation likewise impacts immunological responses to intermediate photoperiods. Male hamsters were gestated in long photoperiods and remained in long photoperiods postnatally, or were transferred to an intermediate-duration or a short-duration photoperiod; other males were gestated in short days and transferred to an intermediate-duration photoperiod at birth. Long days stimulated, and short days inhibited, somatic and reproductive development; intermediate day lengths either accelerated or inhibited somatic and reproductive development, depending on whether hamsters were gestated in short days or long days, respectively. By contrast, photoperiod during gestation did not affect most immune endpoints. The data suggest that photoperiodic mechanisms that enhance and suppress several aspects of immunity in young-adult hamsters are not responsive to prenatally communicated photoperiod history information.