Seasonal variation in vasopressin innervation in the brain of the European hamster (Cricetus cricetus).

Using immunocytochemistry, vasopressin innervation was determined in the brain of the European hamster (Cricetus cricetus) during different seasons. It was found that the spring period coincides with a dense vasopressin innervation in many brain regions in the male hamster, and lower vasopressin fibre density in some brain regions in the female hamster. In autumn just before hibernation an almost complete disappearance of vasopressin innervation is noted in those brain regions that are sexually dimorphically innervated in spring. These results suggest that vasopressin activity in certain areas of the brain might be required for some seasonal functions to find expression.