Noradrenergic and acetylcholinesterase-positive nerve fibres of the uterus in sexually immature and cycling rats

Adrenergic and Cholinergic Uterine Innervation and the Impact on Reproduction in Aged Women

In recent years, the development of Assisted Reproductive Technique, the egg and embryo donation changed substantially the role of the uterus in recent years. It provided a higher chance for a pregnancy even in women over 45 years or post-menopause. In fact, the number of aged patients and in peri/post-menopause in pregnancy is nowadays increasing, but it increases obstetrical and neonatal related problems. The human uterus is richly innervated and modified especially during pregnancy and labor, and it is endowed with different sensory, parasympathetic, sympathetic and peptidergic neurofibers. They are differently distributed in uterine fundus, body and cervix, and they are mainly observed in the stroma and around arterial vessel walls in the myometrial and endometrial layers. Many neurotransmitters playing important roles in reproductive physiology are released after stimulation by adrenergic or cholinergic nerve fibers (the so called sympathetic/parasympathetic co-transmission). Immunohistochemical study demonstrated the localization and quantitative distribution of neurofibers in the fundus, the body and cervix of young women of childbearing age. Adrenergic and cholinergic effects of the autonomous nervous system are the most implicated in the uterine functionality. In such aged women, the Adrenergic and AChE neurofibers distribution in the fundus, body and cervix is progressively reduced by increasing age. Adrenergic and AChE neurotransmitters were closely associated with the uterine arteries and myometrial smooth muscles, and they reduced markedly by ageing. The Adrenergic and AChE neurofibers decreasing has a dramatical and negative impact on uterine physiology, as the reduction of pregnancy chance and uterine growth, and the increase of abortion risk and prematurity.

Estrogen and female reproductive tract innervation: cellular and molecular mechanisms of autonomic neuroplasticity

The female reproductive tract undergoes remarkable functional and structural changes associated with cycling, conception and pregnancy, and it is likely advantageous to both individual and species to alter relationships between reproductive tissues and innervation. For several decades, it has been appreciated that the mammalian uterus undergoes massive sympathetic axon depletion in late pregnancy, possibly representing an adaptation to promote smooth muscle quiescence and sustained blood flow. Innervation to other structures such as cervix and vagina also undergo pregnancy-related changes in innervation that may facilitate parturition. These tissues provide highly tractable models for examining cellular and molecular mechanisms underlying peripheral nervous system plasticity. Studies show that estrogen elicits rapid degeneration of sympathetic terminal axons in myometrium, which regenerate under low-estrogen conditions. Degeneration is mediated by the target tissue: under estrogen's influence, the myometrium produces proteins repulsive to sympathetic axons including BDNF, neurotrimin, semaphorins, and pro-NGF, and extracellular matrix components are remodeled. Interestingly, nerve depletion does not involve diminished levels of classical sympathetic neurotrophins that promote axon growth. Estrogen also affects sympathetic neuron neurotrophin receptor expression in ways that appear to favor pro-degenerative effects of the target tissue. In contrast to the uterus, estrogen depletes vaginal autonomic and nociceptive axons, with the latter driven in part by estrogen-induced suppression of BMP4 synthesis. These findings illustrate that hormonally mediated physiological plasticity is a highly complex phenomenon involving multiple, predominantly repulsive target-derived factors acting in concert to achieve rapid and selective reductions in innervation.

Cervix remodeling and parturition in the rat: lack of a role for hypogastric innervation

The hypogastric nerve is a major pathway innervating the uterine cervix, yet its contribution to the processes of cervical ripening and parturition is not known. The main objective of this study was to determine the effect of hypogastric nerve transection on remodeling of the cervix and timing of birth. As an initial goal, processes associated with remodeling of the peripartum cervix were studied. The cervix was obtained from time-dated pregnant rats on days 15, 19, 21, and 21.5 of pregnancy, and post partum on the day of birth (day 22). The cervix was excised, post-fixed overnight, and sections stained to evaluate collagen content and structure or processed by immunohistochemistry to identify macrophages or nerve fibers. The census of macrophages and density of nerve fibers in the cervix peaked on day 21, the day before birth, and then declined post partum. These results replicate in time course and magnitude previous studies in mice. To address the main objective, the hypogastric nerve was bilaterally transected on day 15 post-breeding; sham-operated rats served as controls. Pups were born in both groups at normal term. Transection of the hypogastric nerves did not affect remodeling of collagen or the census of macrophages or the density of nerve fibers in the cervix. These findings support the contention that enhanced innervation and immigration of immune cells are associated with remodeling of the cervix and parturition, but that a neural pathway other than the hypogastric nerve may participate in the process of cervical ripening.

A quantitative study of rat uterine sympathetic innervation during pregnancy and post partum

In mammals, pregnancy induces a transient and extensive degeneration of uterine sympathetic innervation. We used the models of unilateral oviduct ligation and in oculo myometrium transplant in pregnant rats to address the role of stretching forces and/or hormone milieu in the loss of sympathetic innervation. The sympathetic fibres of the uterine horn and in oculo myometrial transplants were quantified on tissue sections processed by the glyoxylic acid technique. In normal pregnant rats, the density of uterine horn innervation was significantly reduced at late pregnancy and recovery took place during post partum. The empty horn of pregnant rats showed no significant changes in density of myometrial innervation during pregnancy or post partum. In oculo myometrial transplants were organotypically reinnervated in virgin animals. When the transplants were exposed to gestational hormonal milieu, few or no fibres were observed to the end of pregnancy; however, a significant increase at post partum was observed. Results showed that both the effects of stretching and the hormone milieu derived from the fetus–placenta complex play a role as inductors of changes on sympathetic myometrial innervation during pregnancy and support the idea that immature muscular uterine fibres are more susceptible to the effects of pregnancy than those originating from adult animals.

Plasticity of pelvic autonomic ganglia and urogenital innervation

Pelvic ganglia contain a mixture of sympathetic and parasympathetic neurons and provide most of the motor innervation of the urogenital organs. They show a remarkable sensitivity to androgens and estrogens, which impacts on their development into sexually dimorphic structures and provide an array of mechanisms by which plasticity of these neurons can occur during puberty and adulthood. The structure of pelvic ganglia varies widely among species, ranging from rodents, which have a pair of large ganglia, to humans, in whom pelvic ganglion neurons are distributed in a large, complex plexus. This plexus is frequently injured during pelvic surgical procedures, yet strategies for its repair have yet to be developed. Advances in this area will come from a better understanding of the effects of injury on the cellular signaling process in pelvic neurons and also the role of neurotrophic factors during development, maintenance, and repair of these axons.

Plasticity in rat uterine sympathetic nerves: the role of TrkA and p75 nerve growth factor receptors

Uterine sympathetic innervation undergoes profound remodelling in response to physiological and experimental changes in the circulating levels of sex hormones. It is not known, however, whether this plasticity results from changes in the innervating neurons, the neuritogenic properties of the target tissue or both. Using densitometric immunohistochemistry, we analysed the effects of prepubertal chronic oestrogen treatment (three subcutaneous injections of 20 microg of beta-oestradiol 17-cypionate on days 25, 27 and 29 after birth), natural peripubertal transition and late pregnancy (19-20 days post coitum) on the levels of TrkA and p75 nerve growth factor receptors in uterine-projecting sympathetic neurons of the thoraco-lumbar paravertebral sympathetic chain (T7-L2) identified using the retrograde tracer Fluorogold. For comparative purposes, levels of TrkA and p75 were assessed in the superior cervical ganglion (SCG) following prepubertal chronic oestrogen treatment. These studies showed that the vast majority of uterine-projecting neurons expressed both TrkA and p75. Both prepubertal chronic oestrogen treatment and the peripubertal transition increased the ratio p75 to TrkA in uterine-projecting neurons, whereas pregnancy elicited the opposite effect. Prepubertal chronic oestrogen treatment had no effects on levels of TrkA or p75 in sympathetic neurons of the SCG. Taken together, our data suggest that neurotrophin receptor-mediated events may contribute to regulate sex hormone-induced plasticity in uterine sympathetic nerves, and are in line with the idea that, in vivo, plasticity in uterine nerves involves changes in both the target and the innervating neurons.

Supraspinal connections of the reproductive organs: structural and functional aspects

Gonadal functions are governed by the hypothalamo-hypophyseal system. Other organs of the reproduction tract are under the regulatory action of gonadal steroids. In the past two decades several data have been accumulated on the involvement of fine-tuning control mechanisms which include autocrine and paracrine effects of biologically active substances produced locally and the regulatory action of nerves innervating the organs of the system. Recent studies using the viral transsynaptic technique have revealed cell groups in the central nervous system that are transneuronally connected with the male and female reproductive organs. This review summarizes neuromorphological data on the supraspinal innervation of reproductive organs and the functional significance of these brain areas in the control of reproduction.

Regional and muscle layer variations in cholinergic nerve control of the rat myometrium during the oestrous cycle

To determine regional and muscle layer differences in the cholinergic nerve control of uterine activity, functional and immunohistochemical experiments were carried out on the cervix, and circular and longitudinal muscle from the caudal and rostral uterine horn in cyclic rats. During oestrus, in vitro electrical field stimulation evoked contractions in the cervix and myometrium of the caudal horn, predominantly in circular muscle layer. All evoked responses were tetrodotoxin-sensitive and completely abolished by atropine, thus were cholinergic nerve-mediated. In contrast, no electrical field stimulation-induced contraction occurred in either the circular or longitudinal muscle from the rostral uterus. Concentration-response curves for carbachol showed that muscarinic receptor-mediated contractions occurred in all uterine regions and muscle layers during oestrus. Immunohistochemistry for the cholinergic nerve marker, vesicular acetylcholine transporter showed that the predominance of the acetylcholine-dependent contractions in circular muscle preparations were related to a layer-specific distribution of cholinergic nerve fibres, abundant in the circular muscle but scarce in the longitudinal muscle layer. In addition, the absence of electrical field stimulation-evoked acetylcholine-dependent contractions in the rostral uterus was correlated to a marked decrease in the density of cholinergic fibres along the caudo-rostral axis of the organ. In the uterus from diestrus rats, contractions were not elicited in response to electrical field stimulation in the cervix and circular or longitudinal muscle from the caudal as well as rostral uterine horn. Addition of cumulative doses of carbachol failed to increase in a concentration-dependent manner the frequency and amplitude of contractions in the cervix and myometrial layers from either the caudal and rostral uterine horn. The distribution and density of cholinergic nerve fibres along the uterus and between the muscle layers did not differ from the oestrus stage. We conclude that the cholinergic nerve control of uterine activity is layer-specific and predominant in the caudal uterine horn and the cervix. Impairment of this nerve control from oestrus to diestrus stages occurred in relation to a decrease in the myometrial sensitivity to muscarinic stimulation, not to a decrease in the density of cholinergic innervation.

The oestrogenized rat myometrium inhibits organotypic sympathetic reinnervation

Chronic administration of oestrogen to rats during the infantile/prepubertal period provokes, at 28 days of age, complete loss of noradrenaline-labelled intrauterine sympathetic nerves. It is not known whether oestrogen inhibits the growth or causes the degeneration of developing uterine sympathetic nerves, or whether the uterus recovers its innervation following cessation of infantile/prepubertal oestrogen treatment. In the present study, we analysed the time-course of the effects of oestrogen on the development of uterine sympathetic nerves in the rat, using histochemical methods. In addition, the pattern of sympathetic reinnervation of the uterus of intact and ovariectomised females was assessed 3 and 6 months after cessation of chronic oestrogen treatment. The ability of sympathetic nerves to reinnervate the oestrogenized uterine tissue was assessed in intraocular transplants of uterine myometrium into ovariectomised host rats. Early exposure to oestrogen did not inhibit the approach of sympathetic nerves to the uterus, but prevented the normal growth and maturation of intrauterine sympathetic fibres and abolished the innervation that reached the organ before initiation of treatment. Three or six months following cessation of oestrogen treatment, most of the sympathetic nerves were restricted to the mesometrium and mesometrial entrance, whereas intrauterine innervation remained persistently depressed as a consequence of a sustained oestrous-like state provoked by ovarian dysfunction (polycystic ovary). An organotypic regrowth of uterine sympathetic nerves was observed in ovariectomised infantile/prepubertal oestrogen-treated animals. After 5 weeks in oculo, the innervation of oestrogenized myometrial transplants was reduced by 50%, and substantial changes in the pattern of reinnervation were observed. In control transplants, 86% of the nerves were terminal varicose myometrial and perivascular nerve fibres, whereas 14% were preterminal nerve bundles. In oestrogenized myometrial transplants, 83% of the noradrenaline-labelled intercepting nerves were enlarged preterminal bundles and only 17% were terminal fibres. These results indicate that the oestrogenized myometrium is unattractive for sympathetic nerves and inhibits organotypic sympathetic reinnervation.

Effects of infantile/prepubertal chronic estrogen treatment and chemical sympathectomy with guanethidine on developing cholinergic nerves of the rat uterus

The innervation of the uterus is remarkable in that it exhibits physiological changes in response to altered levels in the circulating levels of sex hormones. Previous studies by our group showed that chronic administration of estrogen to rats during the infantile/prepubertal period provoked, at 28 days of age, an almost complete loss of norepinephrine-labeled sympathetic nerves, similar to that observed in late pregnancy. It is not known, however, whether early exposure to estrogen affects uterine cholinergic nerves. Similarly, it is not known to what extent development and estrogen-induced responses in the uterine cholinergic innervation are affected by the absence of sympathetic nerves. To address this question, in this study we analyzed the effects of infantile/prepubertal chronic estrogen treatment, chronic chemical sympathectomy with guanethidine, and combined sympathectomy and chronic estrogen treatment on developing cholinergic nerves of the rat uterus. Cholinergic nerves were visualized using a combination of acetylcholinesterase histochemistry and the immunohistochemical demonstration of the vesicular acetylcholine transporter (VAChT). After chronic estrogen treatment, a well-developed plexus of cholinergic nerves was observed in the uterus. Quantitative studies showed that chronic exposure to estrogen induced contrasting responses in uterine cholinergic nerves, increasing the density of large and medium-sized nerve bundles and reducing the intercept density of fine fibers providing myometrial and perivascular innervation. Estrogen-induced changes in the uterine cholinergic innervation did not appear to result from the absence/impairment of sympathetic nerves, because sympathectomy did not mimic the effects produced by estrogen. Estrogen-induced responses in parasympathetic nerves are discussed, considering the direct effects of estrogen on neurons and on changes in neuron-target interactions.

Noradrenergic and cholinergic nerves in the uterus of the Japanese long-fingered bat, Miniopterus schreibersii fuliginosus, change with reproductive cycle

The pattern of uterine innervation by noradrenergic (NA) and acetylcholinesterase-positive (AChE) nerves in different reproductive stages of the adult Japanese long-fingered bats were investigated histochemically and immunohistochemically. In the non-pregnant bat, the uterine horn was supplied with abundant NA and AChE nerves. These two types of nerves were closely associated with the uterine arteries and myometrial smooth muscles. In the pregnant bat, NA and AChE nerves supplying the uterus did not degenerate much during hibernating period, but reduced markedly after arousal. In the postpartum bat, the density of nerves recovered progressively. The significant change in the innervation pattern of uterine NA and AChE nerves in the pregnant bats under and after hibernation, and in the postpartum bat must be considered in relation to the adrenergic and cholinergic controlling mechanisms on the uterine function that is matched for the unique reproductive cycle of this bat.

Unusual autonomic ganglia: connections, chemistry, and plasticity of pelvic ganglia

The pelvic ganglia provide the majority of the autonomic nerve supply to reproductive organs, urinary bladder, and lower bowel. Of all autonomic ganglia, they are probably the least understood because in many species their anatomy is particularly complex. Furthermore, they are unusual autonomic ganglia in many ways, including their connections, structure, chemistry, and hormone sensitivity. This review will compare and contrast the normal structure and function of pelvic ganglia with other types of autonomic ganglia (sympathetic, parasympathetic, and enteric). Two aspects of plasticity in the pelvic pathways will also be discussed. First, the influence of gonadal steroids on the maturation and maintenance of pelvic reflex circuits will be considered. Second, the consequences of nerve injury will be discussed, particularly in the context of the pelvic ganglia receiving distributed spinal inputs. The review demonstrates that in many ways the pelvic ganglia differ substantially from other autonomic ganglia. Pelvic ganglia may also provide a useful system in which to study many fundamental neurobiological questions of broader relevance.

Differential effects of prepubertal chronic oestrogen treatment on the synthesis of noradrenaline in uterine myometrial and perivascular sympathetic nerves

Previous studies have shown that chronic administration of oestrogen to prepubertal rats reduces the total content of noradrenaline in the uterine horn, abolishes myometrial noradrenergic innervation and reduces noradrenaline-fluorescence intensity of intrauterine perivascular nerve fibres. The mechanisms underlying these changes are not known. In the present study we have analysed the effects of prepubertal chronic oestrogen treatment on the synthesis of noradrenaline in the rat uterine sympathetic nerves using biochemical and immunohistochemical approaches. Tyrosine hydroxylase activity was evaluated biochemically, by measuring the in vivo accumulation of dihydroxyphenylalanine (DOPA) in the presence of a DOPA-decarboxylase inhibitor. In addition, nerve fibres were visualised immunohistochemically using antibodies against tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DbetaH) and the general marker protein gene product 9.5 (PGP 9.5). After chronic oestrogen treatment, the total content of noradrenaline of the uterine horn was reduced, whereas the total content of DOPA was increased. In controls, TH-immunoreactive, DbetaH-immunoreactive and PGP 9.5-immunoreactive nerve fibres were distributed in both the circular and longitudinal myometrial layers and in the blood vessels of the intran-myometrial region. After chronic oestrogen treatment the only fibres recognised by the three antibodies were those associated with the blood vessels, but no myometrial-associated fibres could be recognised. These results suggest that noradrenaline synthesis is selectively reduced in myometrial-associated uterine sympathetic nerves, but is preserved in perivascular sympathetic nerves. The increased DOPA levels measured after chronic exposure to oestrogen was interpreted as the consequence of the substantial increase in size and number of blood vessels observed in the uterus of oestrogen-treated animals. A possible neurodegenerative effect of oestrogen on myometrial sympathetic fibres is discussed.

Origins of the sympathetic innervation of the cervical end of the uterus in the rat

A retrograde neuronal tracer (Fast Blue) was injected in the cervical end of the uterine horn of virgin rats. The majority of the retrogradely labeled post-ganglionic sympathetic neurons were found in the sympathetic chain (74%). The superior mesenteric ganglia, inferior mesenteric ganglia and suprarenal ganglia accounted for 22, 3 and < 1%, respectively. The distribution of neurons in the sympathetic chain labeled from the uterus resembles that described for other pelvic organs.

Distribution of noradrenergic neurons in the female rat pelvic plexus and involvement in the genital tract innervation

The involvement of the pelvic plexus noradrenergic neurons in the innervation of the genital tract was studied in the female rat. Several small ganglia were observed in addition to the paracervical ganglion and immunocytochemistry for tyrosine hydroxylase was performed to examine the distribution and number of the noradrenergic neurons. 5069 +/- 1525 nerve cell bodies were counted in the paracervical ganglion and 9.0 +/- 0.8% of them were noradrenergic, displaying a clear somatotopic distribution in the ventro-medial part of the ganglion. Some accessory ganglia were located ventral to the main paracervical ganglion. 414 +/- 149 nerve cell bodies were found in the accessory ganglia, of which 20.4 +/- 3.1% were noradrenergic. Ganglia along the vesical branch of the hypogastric nerve, referred to as an hypogastric plexus, contained 233 +/- 83 neurons among which 12.7 +/- 7.2% were noradrenergic. Bilateral removal of the pelvic plexus produced degeneration of all the tyrosine hydroxylase-immunoreactive nerve fibres in the lower part of the uterus and in the cervix. In contrast, excision of the paracervical ganglia and the accessory ganglia caused no significant change in this innervation pattern. Combined retrograde tracing study and immunocytochemistry for tyrosine hydroxylase revealed a very small number of noradrenergic neurons also labelled with fluoro-Gold. Both findings suggest a limited involvement of the pelvic plexus noradrenergic neurons in the innervation of the lower genital tract.