Loss during aging of beta-endorphinergic neurons in the hypothalamus of female C57BL/6J mice

Beta-endorphin (B-EP) content is often reduced in hypothalami of aging rodents. The objective of this study was to determine whether reduced B-EP content is associated with a reduced number of B-EP immunoreactive neurons. Serial coronal sections extending from the caudal hypothalamus through the retrochiasmatic area were examined by quantitative light microscopy in mature (5-6 month) and senescent (24-28 month) mice that had been ovariectomized 1 week earlier and injected with colchicine 24-48 h before sacrifice. Old mice were acyclic. As expected, B-EP immunoreactive cell bodies were restricted to the region of the arcuate nucleus. There was a 35% loss of B-EP immunopositive neurons in old, macroscopically disease-free animals. By contrast, some old animals with pituitary tumors had no loss of B-EP neurons. These results suggest that a subpopulation of B-EP neurons either die or stop synthesizing detectable concentrations of B-EP in aged mice. The basis for the absence of reduced B-EP neurons in some mice with pituitary tumors is unclear, but this observation underscores the importance of distinguishing age-related changes associated with diseases of aging from those that are independent of such diseases.