Previous studies have shown that the calcitonin gene-related peptide (CGRP) immunoreactivity in the central nervous system (CNS) of adult rats is sexually dimorphic and regulated by sex steroid. In the present study
we used immunocytochemistry to investigate the sex difference in CGRP-immunoreactive (IR) neurons in rat dorsal root ganglia (DRG). The numbers of CGRP-IR neurons at the cervical
lumbar and sacral levels in the female rats were significantly lower than those of the male rats. We also found that the number of CGRP-IR neurons at the lumbar level was increased in ovariectomized (OVX) rats
but was decreased in estradiol (E-2)-treated rats (OVX + E-2). A large number of estrogen receptor (ER)-IR neurons at the lumbar level were found in the female rats
and its number was greater than that in the male rats. We also investigated the change in the number of ER-IR neurons of OVX rats after estrogen treatment. The number of ER-IR neurons in the OVX + E-2 rats was consistent with that of the intact female rats
but was significantly increased in the OVX rats. As shown by a double-labeling immunocytochemical method
over 80% of the CGRP-IR neurons at the lumbar level showed ER immunoreactivity in the female
OVX and OVX + E-2 rats
compared to only about 46% in the male rats. These results indicate that there is a gender difference in CGRP expression in the rat DRG
and that this CGRP expression might be downregulated by estrogen (at least in part) through its receptor. (C) 1998 Elsevier Science B.V.
