Roles of the cholinergic system and vagal innervation in the regulation of GnRH secretion and ovulation: Experimental evidence.

Reproduction is the biological process that sustains life. It is regulated by a neuro-hormonal mechanism that is synchronized by the interaction among the hypothalamus, hypophysis, and ovaries. Ovulation is regulated by the secretion of the gonadotropin-releasing hormone (GnRH), which stimulates the release of the luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In addition to these neuroendocrine signals, other signals originating from the central nervous system, hypophysis, thyroid, adrenal glands, and the ovary itself are also involved. One of the neurotransmission systems involved in the regulation of ovulation is the cholinergic system, which not only participates in the regulation of reproductive functions but also modulates motor coordination, thermoregulation, and cognitive function. In mammals, the vagus nerve is one of the pathways through which acetylcholine reaches the ovary, and this pathway also participates in the regulation of ovulation. However, this regulation depends on the age of the animal (prepubertal or adult) and its endocrine status. The present review analyzes evidence of the roles of the central and peripheral cholinergic system and vagal innervation in the regulation of GnRH secretion and ovulation as well as their roles in the development and persistence of polycystic ovary syndrome (PCOS).

Role of the superior ovarian nerve in the regulation of follicular development and steroidogenesis in the morning of diestrus 1.

PURPOSE: Little is known about the role of the superior ovarian nerve (SON) in follicular development during the estrus cycle. The aim of the present study was to analyze the role of neural signals arriving through the SON at the ovaries in the regulation of follicular development and ovarian steroid secretion in diestrus 1 of cyclic rats. METHODS: Cyclic rats were subjected to left, right, or bilateral SON sectioning or to unilateral or bilateral laparotomy at diestrus 1 at 11:00 h. Animals were sacrificed 24 h after surgery. RESULTS: Compared to laparotomized animals, unilateral SON sectioning decreased the number of preovulatory follicles, while bilateral SON sectioning resulted in a decreased number of atretic preantral follicles. An important observation was the presence of invaginations in the follicular wall of large antral and preovulatory follicles in animals with denervation. Furthermore, left SON sectioning increased progesterone levels but decreased testosterone levels, which are effects that were not observed in animals that were subjected to right denervation. CONCLUSIONS: At 11:00 h of diestrus 1, the SON was found to stimulate follicle development, possibly via neural signals, such as noradrenaline and/or vasoactive intestinal peptide, and this stimulation induced the formation of follicle-stimulating hormone receptors. The role of the SON in the regulation of ovarian steroid secretion is asymmetric: the left SON inhibits the regulation of progesterone and stimulates testosterone secretion, and the right nerve does not participate in these processes.

Unilateral or bilateral vagotomy performed on prepubertal rats at puberty onset of female rat deregulates ovarian function.

BACKGROUND: Injecting a neurotoxin virus into ovary of adult rats has provided morphologic evidence of a multisynaptic neural pathway between ovary and central nervous system (CNS). Vagus nerve is one of the pathways used by CNS to send and receive information to and from the ovary. METHODS: The present study analyzed whether or not vagal innervation of ovaries in prepubertal rats modulated, in a stimulatory fashion, functions of the ovary and whether the modulating function of these nerves was asymmetric. RESULTS: Animals vagotomized at 24 and 28 days of age showed delay in age of onset of puberty. Unilateral or bilateral vagotomy performed at 24 days of age did not modify ovulation rates or number of ova shed. In turn, bilateral vagotomy performed at 28 days of age resulted in a significant increase in number of ova shed by ovulating animals. Unilateral and bilateral vagotomy performed on day 24 or 28 resulted in a decrease in estradiol serum levels. Unilateral vagotomy performed on 24-day-old rats did not modify progesterone levels, while bilateral vagotomy on the same age group resulted in a significant increase of progesterone levels. In turn, unilateral and bilateral vagotomy performed on rats aged 28 days resulted in lower progesterone levels. CONCLUSIONS: Present results confirmed results of previous studies, indicating that interrupting ovarian innervation had an effect on regulation of ovarian functions by CNS and that these effects varied according to age at which denervation was performed.