Time-course analysis of changes in calcitonin gene-related peptide-and methionine-enkephalin-immunoreactivity in the female rat preoptic area after estrogen treatment.

The time-course effects of one month of estrogen upon calcitonin gene-related peptide - and methionine-enkephalin-immunoreactivity in the periventricular preoptic nucleus and medial preoptic nucleus were semi-quantitatively investigated with a computer-based image analysis system. Female Wistar rats were ovariectomized and implanted subcutaneously with a 10-mm-long silastic capsule containing estradiol-17 beta, or with a blank capsule, as a control. Estradiol-17 beta-treated rats were killed at days 1, 4, 7, 10, 14 and 28 after the implantation of estradiol-17 beta. To investigate the details of changes in calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers in the periventricular preoptic nucleus and medial preoptic nucleus, a grid, made up of 8 x 16 squares (one square corresponding to 50 x 50 microns in the true section), was set on the wall of the third ventricle, and immunoreactivity within each square was measured with an image analyser. In the control rats, calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers were distributed in the periventricular preoptic nucleus and medial preoptic nucleus. In the estradiol-17 beta-treated rats, calcitonin gene-related peptide-immunoreactive fibers increased prominently at day 1, day 7 and day 10 in the periventricular preoptic nucleus, whereas methionine-enkephalin-immunoreactive fibers increased at day 1, day 14 and day 28 in the periventricular preoptic nucleus and medial preoptic nucleus. These findings suggest that the mechanism underlying the increases in these calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers after estrogen treatment might be different.