c-Fos expression as endogenous marker of lumbosacral spinal neuron activity in response to vaginocervical-stimulation

The focus of this paper is to describe a method for the simultaneous stimulation of the vagina and uterine cervix and recording of vaginal contractions in the female rat. The influence of the estrous cycle on vaginocervical sensitivity was also investigated. The use of a latex balloon, inflated with water via a syringe and connected to a pressure transducer allowed us to record vaginal contractions, the intensity of which is an index of vaginal sensitivity, and to stimulate those spinal neurons involved in the reflex arc; at the end of the stimulation the deflated balloon was used as a probe to perform a vaginal smear in order to determine the stage of the estrous cycle at the moment of the experiment. Activated neurons were identified by Fos-immunocytochemistry. Light microscope counting of Fos-immunoreactive neurons at different stages of the estrous cycle permitted us to quantify the response to vaginocervical stimulation and to demonstrate that vaginocervical sensitivity changes significantly throughout the estrous cycle. This finding confirms the important role of sex hormones in the modulation and control of the sensitivity of the vagina and cervix, a part of the female genital tract which is implicated in a variety of neuroendocrine, behavioral and neural changes.