SEMIQUANTITATIVE ANALYSIS OF THE EFFECTS OF ESTROGEN ON CGRP-ENKEPHALIN-IMMUNOREACTIVITY AND METHIONINE-ENKEPHALIN-IMMUNOREACTIVITY IN THE PERIVENTRICULAR PREOPTIC NUCLEUS AND THE MEDIAL PREOPTIC AREA OF FEMALE RATS

The effects of 17-beta-estradiol (E2) on calcitonin gene-related peptide (CGRP)- and methionine-enkephalin (Met-Enk)-immunoreactive (IR) nerve fibers in the periventricular preoptic nucleus (Pe) and the medial preoptic area, including the medial preoptic nucleus (MPN), of the female rat were studied semi-quantitatively by using a computer-based image analysis system. The area occupied by CGRP- and Met-Enk-IR fibers was significantly increased in the Pe and the MPN after 28-day exposure to E2. Computer-based analysis of CGRP- and Met-Enk-IR fibers in an area of 50-mu-m intervals from the wall of the third ventricle showed a low flat histogram pattern in ovariectomized rats, but E2 treatment caused a diphasic pattern, corresponding to the Pe and the MPN, respectively. Since the Pe and the MPN contain a high population of estrogen receptors, it is suggested that E2 may have an influence on the neuronal configuration of afferent fibers to these areas.