Influence of estrous cycle on vaginocervical sensitivity: a fos-immunohistochemical study of lumbosacral spinal cord

Expression of c-fos in L-5-S-1 spinal segments in response to mechanical va ginocervical stimulation was investigated in both cycling and ovariectomize d females. The aim of this paper was to verify the influence of estrous cyc le on females genital tract sensitivity using immunodetection of a neural a ctivity endogenous marker. The results indicate that lumbosacral spinal Fos -labeling was highly increased in vaginocervical stimulated rats relative t o control, and labeled neurons were present more intensively in the dorsal horn in comparison to other spinal areas. Significant differences in Fos-la beling were observed according to the estrous cycle stage at which the stim ulation was applied. In estrous females, the response was greater than that obtained at diestrous and much greater than the response of proestrous fem ales. The spinal Fos-labeling of ovariectomized females is equivalent to th at of diestrous females. These results give evidence that the vaginocervica l induced expression of c-fos is modulated by cyclic changes in circulating sex hormones, whereas results observed in ovariectomized females indicate the likely involvement of other mechanisms independent of ovarian hormones. (C) 2000 Elsevier Science B.V. All rights reserved.