Pineal cross-transplantation (old-to-young and vice versa) as evidence for an endogenous "aging clock".

Circadian (night), chronic administration of melatonin and young-to-old pineal grafting into the thymus have provided evidence for the existence of an endogenous, primary and central "aging clock" in the pineal gland. The new model described here serves to definitely demonstrate that the replacement of the pineal gland of an old mouse with the pineal from a young, syngeneic donor mouse remarkably prolongs its life and, conversely, the "old" pineal transplanted into a younger mouse will considerably shorten its life span. Pineal cross-transplantation thus provides clear-cut evidence for the central role of the pineal gland in the initiation and progression of senescence. It offers a novel basis for interventions in the aging process.