Post-coital ultrastructural changes in neurons of the suprachiasmatic nucleus of the rabbit.

Abstract

The effects of coitus on the ultrastructure of neurons in the suprachiasmatic nucleus of the rabbit were studied. Changes first became apparent 1/2 h after coitum in neurons located near capillaries. More pronounced ultrastructural changes were observed in large neurons removed at 1 h post-coitus. These changes, characterized by well developed Golgi systems and rough endoplasmic reticulum, the presence of large dense-core vesicles and a significant increase in both neuronal and nuclear size, were also evident in neurons observed at 2 to 10 h post coitum. Similar ultrastructural features were not observed in the neurons of the control animals. The post-coital ultrastructural changes observed within these neurons suggest high synthetic activity which may concern the production sites of the neurohormone LH-RF. Two populations of dense-core vesicles were observed: a) those with a mean diameter of 849 A, and b) those with a mean diameter of 1542 A. The small dense-core vesicle is probably monoamine in nature; the larger vesicle may contain the neurohormone LH-RF. A third vesicle type with a mean diameter of 1836 A and characterized by a granular content of low electron density was also observed. That this vesicle represents the immature form of the large (1542 A) dense-core vesicle is suggested; however, morphological evidence supporting this hypothesis is inconclusive. There is also no evidence for the storage of secreted materials within the soma of these neurons. Immediate transport toward the median eminence is suggested.