ROLE OF PROLACTIN AND THE GONADS IN SEASONAL PHYSIOLOGICAL-CHANGES INTHE COLLARED LEMMING (DICROSTONYX-GROENLANDICUS)

On a seasonal basis, collared lemmings undergo a number of physiologic al and morphological changes. Short photoperiod exposure results in a molt to a white pelage, an increase in body weight, a reduction in rel ative body fat content, an increase in relative water content, and the development of a bifid claw. Treatment with the dopamine agonist, CB- 154, resulted in a reduction in serum prolactin and the development of the white pelage in lemmings housed under 16L:8D, while treatment wit h the dopamine antagonist, sulpiride, prevented the winter molt in ani mals transferred to 8L:16D. Castration under 16L:8D resulted in an inc rease in body weight and an enlargement of the bifid claw. Castrated a nimals also molted more readily when treated with CB-154 and developed a relatively greater carcass water content. Treatment with CB-154 inc reased relative carcass fat content. These findings suggest that, in t he collared lemming, seasonal changes in pelage parameters are regulat ed by prolactin, with gonadal hormones playing a modulating role. Body weight, water content, and bifid claw size appear to be influenced by gonadal hormones.