PHOTOPERIODIC AND PINEAL INFLUENCES ON ESTROGEN-STIMULATED BEHAVIORS IN FEMALE SYRIAN-HAMSTERS

Three experiments investigated the effects of short photoperiod exposu re on the estrogenic facilitation of locomotor activity and lordosis. In Experiment 1, ovariectomized female hamsters were administered exog enous estrogen to stimulate locomotor activity in running wheels. Estr ogen was effective in the long photoperiod group but did not stimulate running-wheel activity in the short photoperiod group. In Experiment 2, the role of the pineal gland in mediating photoperiodic influences on female hamster behavior was examined. Both estrogen-induced locomot or activity and estrogen + progesterone-stimulated lordosis behavior w ere significantly reduced in short photoperiod females. Both these pho toperiodic effects were absent in pinealectomized hamsters. Sham-pinea lectomized, short photoperiod females expressed behavioral deficits; p inealectomized hamsters in the short photoperiod did not. Experiment 3 investigated lordosis only and used hormone injections rather than si lastic implants to administer estrogen. The photoperiodic and pineal e ffects observed in Experiment 2 were replicated in Experiment 3. Addit ionally, the suppression of lordosis responsiveness by short photoperi od exposure was estrogen dose dependent. Photoperiodic effects were pr esent when 2 mug estradiol cypionate was used but absent when higher e strogen doses were used. These findings are discussed in the context o f other results that suggested photoperiodic effects on hamster lordos is were pineal independent.