Learning disorders in thymectomized mice: a new screening model for cognitive enhancer.

Although the close relationship between the thymus and neuroendocrine system during the aging process has been well documented, influence of the thymus on the cognitive function of the central nervous system remains unknown. Male ddY mice were thymectomized 3-4 weeks after birth. Learning behavior, tested in a step-down test and in a spatial memory task, was significantly impaired in thymectomized mice at 10 months, but not before 5 months, after thymectomy. Reduced immune response was also not obvious before 10 months. These results suggested that thymectomy in young adult life in mice not only impaired the immune response, but also deteriorated the learning and memory ability, and that learning disorders in thymectomized mice could be utilized as a new screening model for cognitive enhancer.