Fos Expression in the Rat Brain Following Vaginal‐Cervical Stimulation by Mating and Manual Probing

Abstract

Vaginal-cervical stimulation (VCS), provided by mating or manual probing, induces many reproductive behavioral and endocrine changes in female rats. These changes include an increase in lordosis duration, heat termination and pseudopregnancy. Electrophysiological and [14C]2-deoxy-D-glucose studies collectively show that neurons in the medial preoptic area, ventromedial hypothalamus and midbrain central gray respond to manual VCS. In the present study we immunocytochemically labeled brain sections for Fos, the protein product of the immediate early gene c-fos, to detect VCS-responsive neurons in hormone-primed animals receiving VCS by mating or manual probing. In Experiment 1, females receiving mounts and intromissions were compared to: 1) vaginally-masked females receiving mounts but no VCS, 2) females exposed to an intact anesthetized male or 3) females not exposed to males or the testing arena. Those animals receiving VCS showed a dramatic increase in the number of Fos-immunoreactive cells in the medial preoptic area, posterodorsal portion of the medial amygdala and bed nucleus of the stria terminalis, as well as the dorsomedial hypothalamus, ventromedial hypothalamus and midbrain central gray. These effects of VCS were confirmed in Experiment 2 in animals receiving manual vaginal-cervical probing. These findings extend previous electrophysiological and [14C]2-deoxy-D-glucose studies by providing evidence that additional brain areas respond to VCS by mating, as well as manual probing.

Fos immunoreactivity in the rat brain following consummatory elements of sexual behavior: a sex comparison

“…This finding is supported by other studies, since Tetel et al [42] reported no increase of Fos-IR in the MEApd following exposure of females to anesthetized males. Furthermore, Rajendren and Moss [35] showed that removal of the vomeronasal organ did not significantly reduce Fos-IR in the MEApd follow ing mating in female rats.…”

“…This contrast can be explained by the differences in the amount or intensity of vaginocervical stimulation used to induce Fos-IR in the different studies. The amount of vaginocervical stimulation by eight intro missions in our study is low compared to the stimulation used in other studies, which consisted of high numbers of manual stimulations (30 [42,43] to 50 [33]), high numbers of intromissions (30-36 [42]), or by intromissions includ ing ejaculations [10,38].…”

“…Several investiga tors have reported that Fos-IR is induced following mating in female rodents in the MPOA, BNST, MEA, central Male rats were allowed to copulate during four or live pre-test mating sessions and were included after displaying ejaculation within the first 10 min of the last two mating sessions. The female rats were bilaterally ovariectomized tegmental field, ventromedial hypothalamic nucleus (VMH), and periaquaductal gray (PAG) [10,21,33,34,38,42,46]. It was also reported that vaginocervical stimulation, by intromissions and ejaculations of the male partner or by manual probing, was followed by a three weeks prior to testing.…”

“…Sexual receptivity was in duced using a standard regimen of exogenous estrogen and progesterone. This includes administration of 50 fig estra diol benzoate (EB)/0.1 ml arachidis-oil 48 h before test ing, and 500 /¿g progesterone (P)/0.1 ml arachidis oil 4 h much stronger induction of Fos-IR than the Fos-IR after lordosis behavior induced by flank stimulation [33,38,42]. Since vaginocervical stimulation seems to be essential for the induction of Fos-IR in the female brain, we were interested to know which phases of sexual behavior induce Fos-IR in specific parts of the brain.…”

Effects of Chronic Lesions in Mesencephalic Raphe Nuclei on Induction of Pseudopregnancy.

“…The existence of nerve terminals of the fibers from the dorsal raphe nucleus had also been verified in the preoptic area [17,26,27]. The vaginal stimulation is reported to facilitate metabolic activity in the dorsal raphe nucleus [28] and FOS protein expression in the preoptic area [29,30]. These findings suggest the possibility that the serotonergic neurons in the dorsal raphe nucleus play an important role as the relay station in sending signals for the induction of PSP from the vagina to the preoptic area.…”