Induction of thymic hyperplasia and suppression of splenic T cells by lesioning of the anterior hypothalamus in aging Wistar rats.

The effect of destruction of the anterior hypothalamus (AHT) on the immune system was examined in rats 4-50 weeks after the treatment. The thymic weight significantly increased in the experimental group regardless of age, while a significant decrease was observed in the percentage of splenic T cells as well as their proliferative response to phytohemagglutinin (PHA). The increase of thymic weight was observed as long as 24 weeks and the decrease of splenic T cell number was observed as long as 50 weeks after the operation. Hypophysectomy gave rise to atrophy of both thymus and spleen, while either adrenalectomy or gonadectomy resulted in hypertrophy of both thymus and spleen. The results taken together suggest that development and aging of the immune system are under the balance of positive and negative signals from AHT.