Aging changes in the beta-endorphin neuronal system in the preoptic area of the C57BL/6J mouse: ultrastructural...

In hypothalami of aging rodents, beta-endorphin (beta-EP) neuron number and content are reduced. The objectives of this study were: first, to analyze ultrastructurally the population of neuronal elements in a selected region of the preoptic area (POA) in young and old mice; second, to study the beta-EP neuronal system in the same region to determine whether or not this population remains stable with age. Vibratome sections from the most caudal POA through the diagonal band of Broca were examined by light microscopy and immunocytochemistry in mature, cycling (5-6 months old) and old, acyclic, disease-free (24-26 months old) mice. A subset of beta-EP-like perikarya and associated structures was observed in the periventricular POA. When this subregion was examined at the ultrastructural level, there was a significant decrease in the number of recipient dendrites [3.78 +/- 0.04 SEM/micron 2 young vs. 0.82 +/- 0.03/micron 2 old; p < 0.007, analysis of variance (ANOVA)], but a significant increase in the number of nonmyelinated axons (20.0 +/- 2.6/micron 2 young vs. 26.8 +/- 0.7/micron 2 old; p < 0.05). Immunolabeled terminals that contained a synapse comprised 2.56 +/- 0.08% of all terminals with synapses in young mice but only 0.34 +/- 0.04% in old ones when corrected for surface area examined (p < 0.03). A significant age-related loss was also observed in the nonmyelinated beta-EP-labeled axon population (1.50 +/- 0.10% young vs. 0.40 +/- 0.01% old; p < 0.009, ANOVA). We conclude that there are critical changes in the microenvironment of the POA in old, noncycling female mice that are likely to affect neuron function.