Introduction show tail-flick responses to radiant heat [20]. Vaginocervi-
Brain Research 880 2000 109–117 www.elsevier.com locate bres
Research report
Influence of estrous cycle on vaginocervical sensitivity: a fos- immunohistochemical study of lumbosacral spinal cord
a a ,
b b
A. Ghanima , M. Bennis , O. Rampin , J.P. Rousseau
a
´ ´
Laboratoire de Neuroscience du Comportement , Faculte des Sciences Semlalia, Departement de Biologie, Bd. Prince My Abdallah, 40 000,
Marrakech , Maroc
b
´ ´ Laboratoire de Neurobiologie des Fonctions Vegetatives
, INRA, Jouy-en-Josas, France Accepted 2 August 2000
Abstract
Expression of c-fos in L –S spinal segments in response to mechanical vaginocervical stimulation was investigated in both cycling
5 1
and ovariectomized females. The aim of this paper was to verify the influence of estrous cycle on females genital tract sensitivity using immunodetection of a neural activity endogenous marker. The results indicate that lumbosacral spinal Fos-labeling was highly increased
in vaginocervical stimulated rats relative to control, and labeled neurons were present more intensively in the dorsal horn in comparison to other spinal areas. Significant differences in Fos-labeling were observed according to the estrous cycle stage at which the stimulation was
applied. In estrous females, the response was greater than that obtained at diestrous and much greater than the response of proestrous females. The spinal Fos-labeling of ovariectomized females is equivalent to that of diestrous females. These results give evidence that the
vaginocervical 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.
2000 Elsevier
Science B.V. All rights reserved.
Theme : Sensory system
Topic : Spinal cord
Keywords : Female rat; Vaginocervical stimulation; Fos; Lumbosacral spinal cord; Estrous cycle
1. Introduction show tail-flick responses to radiant heat [20]. Vaginocervi-
cal afferent activity enters the spinal cord via the pelvic Vaginocervical stimulation VCS elicits a variety of
and hypogastric nerves, two nerves which innervate struc- neuroendocrine, behavioral and neural changes in female
tures of the female reproductive tract, including the vagina, rats [32,45]. VCS potentiates both the lordosis reflex, and
cervix and the uterine [3,19,20,46], as shown by elec- proceptive pacing behaviors [13,27,45]. It regulates neuro-
tophysiological recording [5] and horseradish peroxydase endocrine reflexes associated with luteinizing hormone
neural tracings [5,36,37,48]. The input of the pelvic nerve, release [47] and induces prolactin surges during the first
which occurs at lumbosacral spinal cord, is critical for days of pseudo-pregnancy or early pregnancy [14,21]. It is
VCS-induced changes, since transection of the pelvic involved in sperm transport, and fertility [1,33] and
nerve blocks or attenuates the behavioral, autonomic and pregnancy [2,15]. In addition, VCS attenuates neural and
neuroendocrine effects of VCS [14,25]. behavioral responses to noxious stimulation [13,26,40].
Recent studies have demonstrated that the expression of The analgesic effect of VCS has been measured for
immediate-early genes such as c-fos can be used as example, by the increased vocalization thresholds in
endogenous markers of neural activity in response to response to tail shock [13,20] or increased latencies to
sensory stimulation [24]. Populations of neurons that respond to VCS were successively identified in several
brain areas [42,49] using immunodetection of Fos, the
Corresponding author. Tel.: 1212-4-4346-4649; fax: 1212-4-437-
protein product of c-fos gene. Nevertheless, most of the
412. E-mail address
: mbennisucam.ac.ma M. Bennis.
available data have been developed in castrated or hor-
0006-8993 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 2 7 8 0 - 3
110 A
mone primed female rats and rarely in cycling females. Sections were then rinsed with PBS, mounted onto gelatin-
The present study was conducted in cycling and ovariec- coated slides, dehydrated in graded alcohol and cover-
tomized rats, in order to identify the spinal distribution of slipped with Eukitt. Five sections of each spinal segment
neurons responding to VCS and to verify whether the were randomly selected and examined under a light
estrous cycle modulates c-fos expression in lumbosacral microscope. Fos-immunoreactive neurons characterized by
spinal segments that receive sensory afferents from the the presence of a brown reaction product in their nuclei
vaginocervical area. were counted. The mean number of Fos-positive neurons
was calculated for each labeled area in each studied spinal segment. Comparison between areas within a segment,