Effects of peripheral nerve lesions during pregnancy on parturition in rats

Anatomical distribution of CGRP-containing lumbosacral spinal afferent neurons in the mouse uterine horn

Sensory stimuli from the uterus are detected by spinal afferent neurons whose cell bodies arise from thoracolumbar and lumbosacral dorsal root ganglia (DRG). Using an in vivo survival surgical technique developed in our laboratory to remove select DRG from live mice, we recently quantified the topographical distribution of thoracolumbar spinal afferents innervating the mouse uterine horn, revealed by loss of immunoreactivity to calcitonin gene-related peptide (CGRP). Here, we used the same technique to investigate the distribution of lumbosacral uterine spinal afferents, in which L5-S1 DRG were unilaterally removed from adult female C57BL/6J mice (N = 6). Following 10–12 days recovery, CGRP immunoreactivity was quantified along the length of uterine horns using fluorescence immunohistochemistry. Relative to myometrial thickness, overall CGRP density in uterine tissues ipsilateral to L5-S1 DRG removal was reduced compared to the DRG-intact, contralateral side (P = 0.0265). Regionally, however, myometrial CGRP density was unchanged in the cranial, mid, and caudal portions. Similarly, CGRP-expressing nerve fiber counts, network lengths, junctions, and the proportion of area occupied by CGRP immunoreactivity were unaffected by DRG removal (P ≥ 0.2438). Retrograde neuronal tracing from the caudal uterine horn revealed fewer spinal afferents here arise from lumbosacral than thoracolumbar DRG (P = 0.0442) (N = 4). These data indicate that, unlike thoracolumbar DRG, lumbosacral spinal afferent nerves supply relatively modest sensory innervation across the mouse uterine horn, with no regional specificity. We conclude most sensory information between the mouse uterine horn and central nervous system is likely relayed via thoracolumbar spinal afferents.

Dystocia and cesarean section in a free-ranging ocelot (Leopardus pardalis) after traumatic spinal cord injury resulting from dog (Canis familiaris) attack

Background:

Ex situ breeding programs are essential to establish genetic resource banks and produce offspring to strengthen the in situ conservation of endangered species. However, many programs fail to maintain viable ex situ populations due to reproductive problems, including dystocia in pregnant females. Dystocia encompasses different emergency obstetric situations for the lives of dams and fetuses that require urgent intervention. This condition has been studied in domesticated species but published records in wildlife, specifically in felines species, are scarce.

Case Description:

An adult female ocelot (Leopardus pardalis) was referred to the wildlife hospital of the Universidad San Francisco de Quito after being attacked by dogs (Canis familiaris). Neurological tests revealed traumatic spinal cord injury at a thoracolumbar level. Complementary tests (laboratory exams, radiographs, and ultrasound) revealed a full-term pregnancy, failure in the labor progress, and critical fetal stress. A cesarean section was performed, and the newborns received resuscitation care after assessing their viability using the Apgar score system. The neonate with the lowest Apgar score died within the first hour after birth, while the second one showed an increase in Apgar score after resuscitation care and survived the procedure.

Conclusion:

We provide new obstetric data that could be relevant to save the lives of dams and newborns in related cases for ocelots and other species of wild felids. Furthermore, this study confirms the adverse effects that domestic dogs have on wildlife species.

Ultrasound-guided bilateral pudendal nerve blocks of nulliparous women with epidural labour analgesia in the second stage of labour: a randomised, double-blind, controlled trial

OBJECTIVE

To explore whether an ultrasound-guided pudendal nerve block (PNB) could decrease anaesthetic use, thereby shortening the length of the second stage of labour in women undergoing epidural analgesia.

DESIGN

Prospective, single-centre, randomised, double-blind, controlled trial.

SETTING

An obstetric centre in a general hospital in China.

PARTICIPANTS

72 nulliparous women were randomised, and 71 women completed the study.

INTERVENTION

An ultrasound-guided bilateral PNB was administered to all study participants; the PNB group were given 0.25% ropivacaine 10 mL, while the control group were given 10 mL saline.

MAIN OUTCOME MEASURE

The primary outcome measure was the duration of the second stage of labour. Secondary outcomes included additional bolus administration, total hourly bupivacaine consumption, difference in thickness between the contracted and relaxed rectus abdominis muscle before (DRAM1) and 30 min after (DRAM2) PNB, urge to defecate, maternal cooperation, preservation of the lower limb motor function, tightness of the perineum, and Numeric Rating Scale (NRS) score for pain.

RESULTS

The duration of the second stage of labour was shorter in the PNB group than in the control group (difference of 33.8 min (95% CI 15.6 to 52.0), p<0.001). Additional bolus administration and total hourly bupivacaine consumption were lower in the PNB group than in the control group (p<0.001). DRAM2 was greater (p<0.001), rate of parturient women with the urge to defecate was higher (p=0.014), maternal cooperation was superior (p=0.002), and lower limb motor function preservation was greater (p=0.004) in the PNB group relative to the control group. Tightness of the perineum was eliminated from the results due to the inconsistent application of the criteria by the nursing staff. There was no significant difference in NRS scores between the groups.

CONCLUSIONS

Nulliparous women with epidural analgesia who received an ultrasound-guided bilateral PNB may reduce their need for bupivacaine and consequently shorten the length of the second stage of labour, therein indicating that a bilateral PNB may serve as an additional effective adjunct method of labour analgesia.

TRIAL REGISTRATION NUMBER

ChiCTR-IOR-16009121.

Characterization of Vascular Endothelial Growth Factor (VEGF) in the Uterine Cervix over Pregnancy: Effects of Denervation and Implications for Cervical Ripening

Bilateral neurectomy of the pelvic nerve (BLPN) that carries uterine cervix-related sensory nerves induces dystocia, and administration of its vasoactive neuropeptides induces changes in the cervical microvasculature, resembling those that occur in the ripening cervix. This study was designed to test the hypothesis that (a) the cervix of pregnant rats expresses vascular endothelial growth factor (VEGF) and components of the angiogenic signaling pathway [VEGF receptors (Flt-1, KDR), activity of protein kinase B, Akt (phosphorylated Akt), and endothelial nitric oxide synthase (eNOS)] and von Willebrand Factor (vWF) and that these molecules undergo changes with pregnancy, and (b) bilateral pelvic neurectomy (BLPN) alters levels of VEGF concentration in the cervix. Using RT-PCR and sequencing, two VEGF isoforms, 120 and 164, were identified in the rat cervix. VEGF, VEGF receptor-1 (Flt-1), eNOS, and vWF immunoreactivities (ir) were localized in the microvasculature of cervical stroma. Their protein levels increased during pregnancy but decreased to control levels by 2 days postpartum. VEGF receptor-2 (KDR)-ir was confined to the epithelium of the endocervix. BLPN downregulated levels of VEGF by a third. Therefore, the components of the angiogenic signaling pathway are expressed in the cervix and change over pregnancy. Furthermore, angiogenic and sensory neuronal factors may be important in regulating the dynamic microvasculature in the ripening cervix and may subsequently play a role in cervical ripening and the birth process.

The Role of Sensory Neurons in Cervical Ripening: Effects of Estrogen and Neuropeptides

Central nervous system nuclei and circuits, such as the medial preoptic, ventromedial and paraventricular nuclei of the hypothalamus, play important roles in reproduction and parturition, and are influenced by estrogen. Peripheral autonomic and sensory neurons also play important roles in pregnancy and parturition. Moreover, the steroid hormone estrogen acts directly, not only on the reproductive tract organs (uterus and cervix), but also on the central and peripheral nerves by regulating expression of various neuronal genes. The peripheral primary afferent neurons innervating the uterine cervix relay mechanical and biochemical sensory information induced by local cervical events and by passage of fetuses, to the spinal cord and supraspinal centers. Consequently, the birth process in mammals is influenced by the combined action of neurons and hormones. Peripheral sensory stimuli, induced physiologically by fetal expulsion or mechanically by vaginocervical stimulation, alter behavior, as well as autonomic and neuroendocrine systems. Recent evidence indicates that primary afferent neurons innervating the cervix, in addition to their sensory effects, likely exert local “efferent” actions on the ripening cervix near term. These efferent effects may involve estrogen-regulated production of such neuropeptides as substance P and calcitonin gene-related peptide in lumbosacral dorsal root ganglia, and their release in the cervix. Collectively, these findings suggest an interrelationship among estrogen, cervix-related sensory neurons, and local cervical events near term.

Transection of the pelvic or vagus nerve forestalls ripening of the cervix and delays birth in rats

Innervation of the cervix is important for normal timing of birth because transection of the pelvic nerve forestalls birth and causes dystocia. To discover whether transection of the parasympathetic innervation of the cervix affects cervical ripening in the process of parturition was the objective of the present study. Rats on Day 16 of pregnancy had the pelvic nerve (PnX) or the vagus nerve (VnX) or both pathways (PnX+VnX) transected, sham-operated (Sham) or nonpregnant rats served as controls. Sections of fixed peripartum cervix were stained for collagen or processed by immunohistochemistry to identify macrophages and nerve fibers. All Sham controls delivered by the morning of Day 22 postbreeding, while births were delayed in more than 75% of neurectomized rats by more than 12 h. Dystocia was evident in more than 25% of the PnX and PnX+VnX rats. Moreover, on prepartum Day 21, serum progesterone was increased severalfold in neurectomized versus Sham rats. Assessments of cell nuclei counts indicated that the cervix of neurectomized rats and Sham controls had become equally hypertrophied compared to the unripe cervix in nonpregnant rats. Collagen content and structure were reduced in the cervix of all pregnant rats, whether neurectomized or Shams, versus that in nonpregnant rats. Stereological analysis of cervix sections found reduced numbers of resident macrophages in prepartum PnX and PnX+VnX rats on Day 21 postbreeding, as well as in VnX rats on Day 22 postbreeding compared to that in Sham controls. Finally, nerve transections blocked the prepartum increase in innervation that occurred in Sham rats on Day 21 postbreeding. These findings indicate that parasympathetic innervation of the cervix mediates local inflammatory processes, withdrawal of progesterone in circulation, and the normal timing of birth. Therefore, pelvic and vagal nerves regulate macrophage immigration and nerve fiber density but may not be involved in final remodeling of the extracellular matrix in the prepartum cervix. These findings support the contention that immigration of immune cells and enhanced innervation are involved in processes that remodel the cervix and time parturition.

The effect of bilateral pelvic neurectomy on cervical ripening in pregnant rats

AIMS

To determine the effect of bilateral pelvic neurectomy (BPN) on cervical ripening in pregnant rats by measuring cervical extensibility and changes in collagen cross-linkages.

METHODS

Timed-pregnant rats were randomly laparotomized on days 9 or 10 of gestation and the pelvic nerves were exposed and either bilaterally transected, or left intact in sham control animals. The rats were sacrificed on day 18 and the uterine cervices obtained. Cervical ripening was assessed by cervical resistance-to-stretch, light-induced autofluorescence (LIF) of cross-linked collagen, and collagen changes analyzed by picrosirius polarization microscopy.

RESULTS

Measurements of extensibility and collagen cross-linkages indicated that after BPN the cervix was significantly more ripened than the cervix from sham control animals.

CONCLUSION

BPN stimulates cervical ripening instead of inhibiting this event as previously proposed. Further studies in this area could be critical for developing treatments for dystocia, preterm labor, and cervical insufficiency.

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.

Progesterone withdrawal promotes remodeling processes in the nonpregnant mouse cervix

Prepartum cervical ripening is associated with remodeling of collagen structure and with inflammation. Progesterone withdrawal is critical for parturition, but the effects of progesterone decline on cervical morphology are unknown. The present study tested the hypothesis that progesterone withdrawal promotes processes associated with remodeling of the cervix. Adult, virgin, female C57BL/6 mice received silastic capsules with oil vehicle or estradiol plus progesterone to parallel concentrations in circulation during pregnancy. After 17 days of estradiol and progesterone treatment, the progesterone implant was removed from one group. Mice in each group were killed 15, 18, or 19 days after placement of capsules. Sections of cervix were stained for collagen, and the densities of macrophages, neutrophils, and area with nerve fibers were assessed. Treatment with gonadal steroids promoted hypertrophy of the cervix, as well as reduced collagen and increased area with nerve fibers compared with vehicle-treated controls. Removal of the progesterone capsule did not affect hypertrophy or innervation, but it did reduce collagen. By contrast, significantly more macrophages and neutrophils were present in the cervix on Days 18 and 19 (i.e., by 24 and 48 h after withdrawal of the progesterone capsule); the immune cell census was equivalent to that in vehicle controls. Findings indicate that gonadal steroids, comparable to those during pregnancy, promote hypertrophy and suppress immigration of immune cells in the cervix. Therefore, in a nonpregnant murine model for parturition, progesterone withdrawal is suggested to recruit immune cells and processes that remodel the cervix.

Pregnancy increases excitability of mechanosensitive afferents innervating the uterine cervix

BACKGROUND

Labor pain derives primarily from stimulation of afferents innervating the uterine cervix and lower uterine segment. The authors have previously shown that the excitability of these afferents is regulated by sex hormones and test in this study whether pregnancy also alters their excitability.

METHODS

After animal care committee approval, Sprague-Dawley rats (nonpregnant, pregnant days 17 and 21) were anesthetized, and two metal rods were placed through the cervix for distension. The right hypogastric nerve was dissected and carefully teased until recording from a single unit was obtained. Spontaneous activity and the response to a graded distension (20-80 g) were recorded for off-line analysis.

RESULTS

A total of 151 fiber units were recorded. Pregnancy was associated with an increase in spontaneous nerve activity in the absence of a mechanical stimulus (median of 0.98 and 1.56 Hz from pregnant days 17 and 21, respectively, compared with 0.45 Hz in nonpregnant; P < 0.01). The proportion of fibers responding to the weakest stimulus (20 g) was significantly greater in pregnant than in nonpregnant animals. The response to graded distension differed significantly among groups, with day 21 > day 17 > nonpregnant.

CONCLUSIONS

Afferents that innervate the uterine cervix sprout into this tissue during late pregnancy, and estrogen increases excitability of these mechanosensitive afferents. Here, the authors show that excitability also increases during pregnancy. These data suggest that, close to the onset of labor, there is an increased input to the spinal cord from cervical distension and an increased depolarization of afferent terminals in the cervix, effects that could influence pain and the progress of labor.

Time course of neuroanatomical and functional recovery after bilateral pudendal nerve injury in female rats

The pudendal nerve innervates the external urethral sphincter (EUS) and is among the tissues injured during childbirth, which may lead to symptoms of stress urinary incontinence (SUI). To understand the mechanisms of injury and repair, urethral leak-point pressure (LPP) was measured 4 days, 2 wk, or 6 wk after bilateral pudendal nerve crush. Morphometric changes in the distal nerve and EUS were examined by light and electron microscopy. To determine whether recovery resulted from pudendal neuroregeneration, LPP was measured before and after pudendal nerve transection 2 wk after nerve crush. LPP was significantly decreased 4 days after pudendal nerve crush compared with sham-injured animals as well as 2 or 6 wk after nerve crush. LPP was not significantly different 2 or 6 wk after nerve crush compared with sham-injured animals, suggesting that urethral function had returned to normal. Four days after pudendal nerve crush, the EUS branch of the pudendal nerve distal to the injury site showed evidence of nerve degeneration and the EUS appeared disrupted. Two weeks after nerve crush, the distal nerve and EUS both showed evidence of both nerve degeneration and recovery. Two weeks after nerve crush, LPP was significantly decreased after nerve transection. Six weeks after nerve injury, evidence of neuroregeneration was observed in the pudendal nerve and the EUS. This study has demonstrated that functional recovery and neuroregeneration are significant 2 wk after nerve crush, although by anatomical assessment, recovery appears incomplete, suggesting that 2 wk represents an early time point of initial neuroregeneration.

Increased innervation and ripening of the prepartum murine cervix

OBJECTIVE

Ripening of the cervix before birth is coincident with reduced collagen content and leukocyte immigration, characteristics that are analogous to a neurogenic inflammatory-like process. We sought to assess the morphologic relationship between innervation and remodeling of the peripartum cervix.

METHODS

Cervix was obtained from C3H/HeN mice on days 15 and 18 of pregnancy, 1 day postpartum, and from non-pregnant controls. Tissues were immersion-fixed, paraffin-embedded, and some sections stained with Picrosirius red to assess collagen content and complexity of organization. By image analysis of optical density, collagen content and structure were significantly decreased by the day before birth. Other sections were processed to visualize nerve fibers by immunohistochemistry with antibodies against neuron-specific epitopes, PGP9.5, peripherin, as well as brain nitric oxide synthase (bNOS), calcitonin gene-related peptide (CGRP), and other neuropeptides. Fiber density was assessed stereologically and normalized to cell density in non-pregnant cervix to correct for tissue hypertrophy due to reproductive status.

RESULTS

In groups of non-pregnant, day 15 pregnant, and postpartum mice, cervix contained nerve fibers that were immunoreactive for the pan-neural markers PGP9.5 and peripherin. Punctate and beaded varicosities were sparsely distributed in stroma, subepithelium, and in proximity to vascular structures. By day 18 of pregnancy, 1 day before birth, fiber density was increased fourfold or more compared to other groups. bNOS fibers and, to a lesser extent, CGRP accounted for most of the increased innervation of the murine cervix by the day before birth, a period when macrophage numbers are enhanced.

CONCLUSIONS

The findings suggest that increased bNOS and CGRP innervation contribute to early inflammatory-like processes that ripen the cervix before birth.

Expression of pituitary adenylate cyclase activating peptide in the uterine cervix, lumbosacral dorsal root ganglia and spinal cord of rats during pregnancy

The uterine cervix is highly innervated by the sensory nerves containing neuropeptides which change during pregnancy and are regulated, in part, by estrogen. These neuropeptides act as transmitters both in the spinal cord and cervix. The present study was undertaken to determine the expression pattern of the neuropeptide pituitary adenylate cyclase activating peptide (PACAP) in the cervix and its nerves during pregnancy and the influence of estrogen on this expression using immunohistochemistry, radioimmunoassay and RT-PCR. PACAP immunoreactivity was detected in nerves in the cervix, lumbosacral (L6-S1) dorsal root ganglia (DRG) and spinal cord. PACAP immunoreactivity was highest at day 15 of pregnancy in the cervix and dorsal spinal cord, but then decreased over the last trimester of pregnancy. However, levels of PACAP mRNA increased in the L6-S1 DRG at late pregnancy relative to early pregnancy. DRG of ovariectomized rats treated with estrogen showed increased PACAP mRNA synthesis in a dose-related manner, an effect partially blocked by the estrogen receptor (ER) antagonist ICI 182,780. We postulate that synthesis of PACAP in L6-S1 DRG and utilization in the cervix and spinal cord increase over pregnancy and this synthesis is the under influence of the estrogen-ER system. Since PACAP is expressed by sensory nerves and may have roles in nociception and vascular function, collectively, these data are consistent with the hypothesis that sensory nerve-derived neuronal factors innervate the cervix and play a role in cervical ripening.

Ascending spinal pathways from sexual organs: effects of chronic spinal lesions

A recent survey of paraplegics indicates that regaining sexual function is of the highest priority for both males and females (Anderson, K.D. (2004) Targeting recovery: priorities of the spinal cord-injured population J. Newrotrauma, 21: 1371-1383). Our understanding of the neural pathways and mechanisms underlying sexual behavior and function is limited at the present time. More studies are obviously needed to direct experiments geared toward developing effective therapeutic interventions. In this chapter, a review of studies on the processing of sensory inputs from the male and female reproductive organs is presented with a review of what is known about the location of ascending spinal pathways conveying this information. The effect of spinal cord injury on sexual function and the problems that ensue are discussed.

Activation and circuitry of uterine-cervix-related neurons in the lumbosacral dorsal root ganglia and spinal cord at parturition

Stimulation of the uterine cervix at parturition activates neural circuits involving primary sensory nerves and supraspinally projecting neurons of the lumbosacral spinal cord, resulting in output of hypothalamic neurohormones. Dorsal root ganglia (DRG) and spinal neurons of these circuits are not well-characterized. The objectives of this study were to detail the activation of DRG and spinal neurons of the L6/S1 levels that are stimulated at late pregnancy, verify hypothalamic projections of activated spinal neurons, and determine whether activated neurons express estrogen receptor-alpha (ERalpha). Expression of phosphorylated cyclic-AMP response element-binding protein (PCREB) and Fos immunohistochemistry were used to "mark" activated DRG and spinal neurons, respectively. Retrograde tracing identified uterine-cervix-related and spinohypothalamic neurons. Baseline PCREB expression in the DRG increased during pregnancy and peaked during the last trimester. Some PCREB-expressing neurons contained retrograde tracer identifying them as cervix-related neurons. Fos-expressing neurons were few in spinal cords of nonpregnant and day 22 pregnant rats but were numerous in parturient animals. Some Fos-expressing neurons located in the dorsal half of the spinal cord contained retrograde tracer identifying them as spinohypothalamic neurons. Some DRG neurons expressing PCREB also expressed ERalpha, and some spinal neurons activated at parturition projected axons to the hypothalamus and expressed ERalpha. These results indicate that DRG and spinal cord neurons are activated at parturition; that those in the spinal cord are present in areas involved in autonomic and sensory processing; that some spinal neurons project axons to the hypothalamus, ostensibly part of a neuroendocrine reflex; and that sensory and spinal neurons can respond to estrogens. Moreover, some activated sensory neurons may be involved in the animal's perception of labor pain.

Comparaison de l’activité réflexe de l’utérus au cours de l’insémination artificielle et de l’accouplement chez la brebis

AIM

To identify and to compare the reflex mechanisms involved in the activation of the uterine motility following artificial insemination (AI) and mating in the ewe.

MATERIALS AND METHODS

The contractile activity of the uterus was monitored in presence and absence of adrenergic (phentolamine) and cholinergic (atropine) antagonists, using an implantable telemetric device equipped with a sensor catheter inserted into the uterine lumen, and connected to a radio-telemetric transmitter.

RESULTS

During AI, a uterine contraction (UC) of short duration (<20 seconds) appeared in direct response to animal restraint, to the speculum introduction, then when the speculum was opened. Both the UC evoked by restraint of the ewe and insertion of the speculum were abolished in presence of phentolamine, while atropine inhibited the UC in response to opening of the speculum only. After AI, the uterine activity increased sharply and was all the more intense and extended with higher vaginal wall pressure. Phentolamine or atropine did not inhibit this motor response, whereas a similar pattern of uterine hyperactivity occurred following i.v. injection of oxytocin (100 and 200 mIU; Syntocinon). After mating, an increase in uterine activity was never observed. Only penis intromission evoked a UC of short duration (about 20 seconds), abolished in presence of phentolamine only.

CONCLUSION

Artificial insemination in the ewe increases uterine motility, resulting from the reflex activation of adrenergic and cholinergic nerve fibres of the autonomic nervous system, following by a reflex release of oxytocin from the pituitary gland (also called "Ferguson reflex"). This secretion of OT was elicited by the excessive dilation of the vaginal wall with the speculum. By comparison, mating did not evoke a period of uterine hyperactivity and respects the physiological post-coital resting period.

The effects of pregnancy and estrogen on the expression of calcitonin gene-related peptide (CGRP) in the uterine cervix, dorsal root ganglia and spinal cord

Before parturition the uterine cervix undergoes a ripening process ("softens" and dilates) to allow passage of the fetus at term. The exact mechanism(s) responsible for cervical ripening are unknown, though a role for peptidergic sensory neurons is emerging. Previous work demonstrated that administration of substance P (SP) to ovariectomized rats caused events associated with cervical ripening, that production of SP in cervix-related dorsal root ganglion (DRG) is estrogen responsive, and that release of SP from neurons terminating in the cervix and spinal cord peaks prior to parturition. The present study was designed to test the hypothesis that calcitonin gene-related peptide (CGRP), a neuropeptide co-stored with SP in many sensory neurons, undergoes changes with pregnancy and hormonal environment. Immunohistochemistry, in situ hybridization, reverse transcriptase-polymerase chain reaction (RT-PCR) and radioimmunoassay (RIA) were used to investigate CGRP in L6-S1 DRG, spinal cord and cervix during pregnancy and the role of estrogen in CGRP synthesis. CGRP-immunoreactive primary sensory neurons expressed estrogen receptors (ER-alpha and ER-beta). In the cervix, CGRP concentrations decreased, but in the L6-S1 DRG and the spinal cord segments, CGRP levels increased, with peak effects observed at day 20 of gestation. CGRP mRNA synthesis increased in DRG over pregnancy. Sensory neurons of ovariectomized rats treated with estrogen showed increased CGRP mRNA synthesis in a dose-related manner, an effect blocked by the ER antagonist ICI 182 780. From these results, we postulate that synthesis of CGRP in L6-S1 DRG and utilization in the cervix increase over pregnancy and this synthesis is the under influence of the estrogen-ER system. Collectively, these data are consistent with the hypothesis that CGRP plays a role in cervical ripening and, consequently in the birth process.

Do sensory calcitonin gene-related peptide nerve fibres in the rat pelvic plexus supply autonomic neurons projecting to the uterus and cervix?

Sensory nerve fibres containing calcitonin gene-related peptide (CGRP) innervate neurons of the paracervical ganglion (PCG) in the female rat pelvic plexus. We have combined retrograde tracing with immunocytochemistry to investigate whether CGRP-immunoreactive (-IR) fibres supply neurons targeting the genital tract. Of the total neurons projecting to either the uterine horns or the cervix, 38 and 41% received CGRP-IR innervation, respectively. All these neurons displayed choline acetyltransferase-IR, thus are cholinergic. They were found throughout the PCG and other pelvic plexus ganglia, namely accessory ganglia (AG) and hypogastric plexus (HP). Pelvic nerve section showed that afferent fibres in these nerves provided most of the CGRP-IR fibres supplying uterine- or cervical-related neurons in the PCG/AG, none in HP. It is suggested that such sensory-motor network may provide a local pathway for reflex control of genital tract activity, acting through cholinergic nerve projections.

Sensory nerves and neuropeptides in uterine cervical ripening

At the time of parturition (fetal delivery) the uterine cervix must "ripen," becoming soft, pliable, and dilated to accommodate the fetus' delivery. The fundamental processes underlying cervical ripening remain poorly understood. Knowledge that abundant autonomic and sensory nerves supply the uterine cervix, that transection of afferent nerves supplying the cervix blocks parturition, and that some of the changes in the cervix resemble those seen in inflammatory reactions suggests nerves may have a role in the cervical ripening changes. The present study utilized immunohistochemistry, plasma extravasation, and solution hybridization-nuclease protection assay to elucidate the complement of primary afferent nerves and some receptors in the rat cervix during pregnancy, and to determine if they may have roles in the ripening process at term. This study revealed an abundance of nerves associated with the cervical vasculature and myometrial smooth muscle containing immunoreactivity for substance P, calcitonin gene-related peptide, secretoneurin, and nitric oxide synthase throughout pregnancy. Many of these are small unmyelinated capsaicin-sensitive C-fibers. Substance P- (NK1-) and calcitonin gene-related peptide receptors were apparent on uterine cervix vasculature from pregnant, parturient, and postpartum rats. NK1 receptor mRNA was maximal at 20 days of pregnancy. Plasma extravasation of i.v. administered Evans Blue or Monastral Blue was most pronounced at parturition (shortly after NK1 mRNA is maximal); this was similar to plasma extravasation evoked by i.v. administration of substance P or capsaicin-treatment. This study revealed new data about the nervous system of the rat uterine cervix and that these nerves and their transmitters could very well be part of a neurogenic inflammatory process involved in cervical ripening.

Fertility ratio in male rats: effects after denervation of two pelvic floor muscles

Fertility ratio is defined here as the proportion of females that a male can impregnate after a constant period of in-polygyny living. This ratio was investigated in male rats after denervation of two pelvic floor muscles, the pubococcygeus and iliococcygeus. Denervation was carried out by transecting the somatomotor branch of the pelvic nerve. The lesion did not modify the sexual behavior of males or their overall fertility, but decreased the weight of the ejaculated seminal plug. Consequently, the number of days living in cohabitation to induce pregnancy was increased in lesioned males (approximately 13 days) compared with intact and sham animals (approximately 5 days). These results showed that the fertility ratio was optimal when intact/sham males cohabited with females for two consecutive estrous cycles, but that lesioned males needed up to four cycles to induce most pregnancies. Two hypotheses are raised by our results. The first is that pelvic floor denervation decreases the forceful tension required to expel the semen from the prostatic urethra to the vagina, then an incomplete seminal plug is expelled. The second is that denervation cut afferent fibers that reflexively promote the continence of the semen deposited in the prostatic urethra during seminal emission, allowing some to leak out before ejaculation. The latter hypothesis can also explain the recovery of the fertility ratio in lesioned males. It could be a compensatory mechanism mediated by the pudendal nerve supply to the coccygeus muscle, the other pelvic floor muscle.

Distribution and origin of secretoneurin-immunoreactive nerves in the female rat uterus

Secretoneurin is a 33-amino acid peptide derived from secretogranin II. Secretoneurin immunoreactivity has been localized in the peripheral nervous system where it exerts potent chemotactic activity for monocytes and may play a role in inflammation. Secretoneurin could play a role in this process, although the presence and distribution of secretoneurin-immunoreactive neurons in the female reproductive system has not been documented. Thus, this study was undertaken to examine secretoneurin immunoreactivity in nerves of the rat uterus and uterine cervix. A moderate plexus of secretoneurin-immunoreactive nerve fibers was present in the myometrium and endometrium of the uterus as well as in the smooth muscle and endocervix of the cervix. Many of these fibers were associated with the vasculature as well as the myometrium. Secretoneurin immunoreactivity was present in small- to medium-sized neurons of dorsal root and nodose ganglia. Retrograde tracing with FluoroGold indicated that some of these sensory neurons project axons to the cervix and uterine horns. Secretoneurin-immunoreactive terminal-like structures were associated with neurons in the sacral parasympathetic nucleus of the lumbosacral spinal cord. In addition, some secretoneurin terminals were apposed to pelvic parasympathetic neurons in the paracervical ganglia that projected axons to the uterus and cervix. Double-immunostaining indicated co-existence of calcitonin gene-related peptide or substance P with secretoneurin in some sensory neurons, in some terminals of the pelvic ganglia, as well as nerve fibers in the uterine horn and cervix. Finally, fibers in the uterus and cervix were depleted of secretoneurin by capsaicin treatment. This study indicates that secretoneurin is present in the uterus in C-afferent nerve fibers whose cell bodies are located in sensory ganglia. Some of these fibers contain both secretoneurin and calcitonin gene-related peptide or substance P. These substances have functions in inflammatory reactions. Further, secretoneurin could influence postganglionic parasympathetic "uterine-related" neurons in the pelvic ganglia and preganglionic parasympathetic neurons in the lumbosacral spinal cord.

Effects of pudendal nerve injury in the female rat

To test a neurogenic hypothesis for external urethral sphincter (EUS) dysfunction associated with urinary incontinence, the proximal pudendal nerve was crushed in anesthetized retired breeder female rats (n = 5) and compared with a sham lesion group (n = 4). Outcome measures included concentric needle electromyograms (EMGs) from the target EUS, voiding patterns during a 2-hour dark period, and micturition data over a 24-hour period. Fast Blue (FB) was introduced to the crush site at the time of injury and Diamidino Yellow (DY) to the EUS at the time the rats were killed (3 months post-operative), when histological analysis of the nerve and urethra was also performed. EMG records indicated the EUS motor units undergo typical denervation changes followed by regeneration and recovery. Voiding patterns from the crush group show a significant increase of small urine marks in the front third of the cage. At 1-2 weeks post-op, the frequency of voids was significantly increased in the crush group compared to pre-op and late post-op time periods. The mean volume voided in the light phase at the early post-op time was significantly increased in the sham group. Light and electron microscopic patterns seen in nerve and muscle suggest the regenerating motor units maintain a structural integrity. Motoneurons in the lower lumbar cord were labeled with either DY (14. 5 +/- 6.8), FB (31.7 +/- 23.7), or both (35.0 +/- 17.5) tracers, indicating approximately 54% of the crushed pudendal neurons regenerated to the EUS. In conclusion, several measures suggest this reversible crush lesion induces mild urinary incontinence. This animal model is promising for further development of hypotheses regarding neural injury, the pathogenesis of incontinence, and strategies aimed at prevention and treatment. Neurourol. Urodynam. 19:53-69, 2000.

Temporal and behavioral patterning of parturition in rabbits and rats

Although the rabbit (Oryctolagus cuniculus) continues to play an important role in the study of parturitional processes, a detailed behavioral description of birth in this species, necessary for accurately assessing the effects of experimental manipulation, is lacking. It is the aim of this report to provide such a description and to compare it with corresponding behavior in the better-studied rat. Ten pregnant chinchilla-breed rabbits and 10 pregnant Wistar rats were placed in glass-bottomed observation cages 2 days before term, and their behavior recorded on closed-circuit video, viewing the animals from below. All aspects of parturition were accomplished much faster in rabbits than rats; latency to birth of first pup, rate of delivery, duration of vaginal retention, time spent by mothers eating placentas, and in licking and nursing pups. In contrast to rat pups, rabbits were usually born separated from the placenta and already free from membranes. They were much more active, and well able to cast off any remaining membranes, suckle, and survive, whether directly attended to by the mother or not. We conclude that the tight temporal organization of events in the rabbit provides an unusually sensitive assay for investigating mechanisms underlying mammalian parturition.

The sensory but not muscular pelvic nerve branch is necessary for parturition in the rat

In the rat the pelvic nerve consists of a viscerocutaneous (sensory) branch which receives information from pelvic viscera and the midline perineal region, and a somatomotor (muscular) branch which innervates the ilio- and pubococcygeous muscles. To investigate the contribution of these branches to the parturition process, the length of gestation and course of delivery were closely monitored in 43 pregnant, Wistar-strain rats randomly assigned to five groups: untreated control animals, animals in which the somatomotor branch of the pelvic nerve was bilaterally sectioned on Day 14 of gestation, animals in which the viscerocutaneous branch of the pelvic nerve was bilaterally sectioned on Day 14 of gestation, animals treated similarly to the previous group but with young delivered by C-section at term, and sham-operated controls. Sectioning the viscerocutaneous branch seriously disrupted parturition and resulted in major dystocia and a high percentage of stillbirths in all females. In contrast, sectioning the somatomotor branch had no apparent effect on parturition and no significant differences were found between females of this group and sham or control dams on any of the measures recorded. It is concluded that the viscerocutaneous branch of the pelvic nerve is vital for the normal course of parturition in the rat but that the somatomotor branch plays little role, if any.

Electrophysiological evidence for the nomenclature of the pudendal nerve and sacral plexus in the male rat

Surgical microscopy and electrophysiological techniques were used to standardize the nomenclature for the pudendal nerve and sacral plexus according to their somatic axonal composition in the male rat. We conclude that the pudendal nerve is the segment running from the L6-S1 trunk to the sacral plexus, carrying efferent fibers to the coccygeus, internal obturator, ventral and dorsal bulbospongiosus, ischiocavernosus, external anal sphincter, and external urethral sphincter muscles, and afferent fibers from the penis, prepuce, scrotum, and ventral-proximal tail. The sacral plexus is the complex formed by the bridge-like structure connecting the pudendal nerve with the lumbosacral trunk, and two nerve branches emerging from it, one innervating the proximal half of the scrotal skin, and the other innervating the muscles at the base of the penis known as the motor branch. These branches are only considered as a part of the sacral plexus because they integrate axons from both the lumbosacral trunk and pudendal nerve. The gross anatomy of the pudendal nerve and sacral plexus has a main organization that was observed in 70% of cases, whereas the remaining 30% occurred in two variants. This nomenclature is appropriate to describe the pudendal nerve and sacral plexus in studies that involve them being lesioned or electrophysiologically analysed. A main additional finding was that two large afferent branches innervate the scrotum, one the proximal half and the other the distal half. As mentioned above, the proximal branch belongs to the sacral plexus, whereas the distal branch belongs to the pudendal nerve because all its axons travel to the cord via this nerve. Since stimulation or even manipulation of the scrotal branches resulted in the secretion of semen containing spermatozoa, it is suggested that scrotal afferents are involved in some way in the ejaculatory process, a topic that deserves further research.

Uterine electromyography: a critical review

On the basis of a literature review, this work summarizes uterine animal and human electromyographic information obtained at cellular, myometrial, and abdominal levels during gestation and parturition. We show that both internal and external electromyograms occur in phase with intrauterine pressure increase and exhibit similar spectra, including a slow wave (0.01 < frequency < 0.03 Hz) probably because of mechanical artifacts and a fast wave whose frequency content can be subdivided into a low-frequency band always present in every contraction and a high-frequency band related to efficient parturition contractions. Application of classic spectral techniques to electromyogram envelopes has identified group propagation but not pacemaker areas. However, no time delay or classic propagation has been demonstrated by applying the same spectral techniques to the electromyogram itself, probably because of the nonlinearity and three-dimensional nature of the propagating process.