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PubMed1983

Attenuation of pregnancy-induced analgesia by hypogastric neurectomy in rats.

This study confirms previous observations of an increase in pain threshold prepartum followed by a decrease postpartum. Moreover hypogastric nerve transection significantly attenuated the analgesia of pregnancy by a factor of 5 but did not abolish it. Thus, the hypogastric nerve plays a major, but not exclusive, role in the analgesia of pregnancy.

Animals↗
PubMed1989

Organizational role of testosterone on the biochemical and morphological development of the hypogastric ganglion.

Previous reports have demonstrated that after postnatal day 10 testosterone influences hypogastric ganglion (HG) development by 'activating' morphological and biochemical indices. We now report an 'organizational' influence on the developing HG during the first 10 postnatal days. To investigate the organizational effects of testosterone, male rats were castrated within 12 h of birth. Testosterone replacement therapy initiated following castration maintained the normal number of neurons in the HG. Conversely, delayed replacement therapy starting at day 10 or vehicle treatment only, resulted in a significant decrease in neuron number. Castration also produced a significant decrease in somal and nuclear cross-sectional areas. Testosterone replacement, whether initiated immediately or if delayed until day 10, restored somal and nuclear cross-sectional areas to normal. Tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) activities were sensitive to both testosterone dosage and the time of administration. Testosterone decanoate administered subsequent to castration was not able to completely reverse the enzyme activity deficits, while delayed replacement therapy was even less effective in restoring enzyme activities. In contrast, higher doses of testosterone completely reversed enzyme activity deficits, and in fact produced a significant increase in TH activity. Again, delayed testosterone replacement did not fully restore deficits in enzyme activity. In summary, the hormonal environment during the first 10 days of life is critical for the organization of HG cell number; in contrast, nuclear and cell size appear to be dependent on testosterone for activation. TH and ChAT activities also appear to be organized during this dose- and time-dependent developmental period.

Adrenergic Fibers↗
PubMed1989

Hypogastric ganglion perinatal development: evidence for androgen specificity via androgen receptors.

The hypogastric ganglion (HG) has previously been shown to be sensitive to both the organizational and activational influences of testosterone. The current investigations examined whether testosterone exerts similar effects prenatally, whether these events are specifically controlled by androgen, and whether androgens might directly masculinize the HG. Prenatal treatment with an anti-androgen, flutamide, resulted in significant decreases in the adult levels of tyrosine hydroxylase (TH) activity, an index of postsynaptic noradrenergic ontogeny, and choline acetyltransferase (ChAT) activity, a marker for presynaptic terminal formation. In addition, testosterone propionate and dihydrotestosterone benzoate reversed the effects of neonatal castration on the development of TH and ChAT activities. In contrast estradiol benzoate was unable to restore enzyme activities. To determine whether the above observations might be produced by direct effects on the HG, androgen cytosol receptor characteristics were studied. Competition and saturation analyses demonstrate that the affinity and specificity of the androgen cytosol receptor in the HG are similar to that displayed in the pituitary, which has previously been shown to contain androgen receptors. These results suggest that the adult levels of TH and ChAT activities are organized during prenatal and early postnatal development. In addition, the organization of the HG appears to be androgen specific. The presence of cytosol androgen receptors suggests that the organizational effects of androgens are possibly induced by a direct mechanism.

Adrenergic Fibers↗
PubMed1989

Responses of neurons in nucleus ventralis posterolateralis of the cat thalamus' to hypogastric inputs.

Recordings were made from 68 units in the nucleus ventralis posterolateralis (VPL) of the cat thalamus, which responded to stimulation of hypogastric afferents. These units also received nociceptive inputs from the contralateral integument. Units which responded exclusively to hypogastric afferent inputs were not found. Thirty seven of the units were nociceptive specific (NS), and the remaining 31 were wide dynamic range (WDR) units. All of these units were located in the shell region of the lateral subdivision of the caudal VPL. NS units responding to hypogastric afferent inputs had a circumscribed cutaneous receptive field on the contralateral abdomen, gluteal region, tail or hind limb. These areas corresponded to tactile dermatomes T13-S2. Similarly, the cutaneous receptive fields of WDR units receiving hypogastric afferent inputs were distributed in the contralateral abdomen, gluteal region, tail and hind limb, with the sole exception of one unit, whose receptive field also included a part of the lower thorax. These findings extend the previous findings that the shell region of the caudal VPL of the cat thalamus constitutes a thalamic link in a visceral pain pathway, and that the visceral and cutaneous pathways share a common projection locus in the VPL.

Afferent Pathways↗
PubMed1991

Differential roles of hypogastric and pelvic nerves in the analgesic and motoric effects of vaginocervical stimulation in rats.

Bilateral transection of the pelvic and/or hypogastric nerves, which convey afferent activity from the reproductive tract, was performed to ascertain the role of these nerves in the analgesic and motoric effects of vaginocervical mechanostimulation (VS) in rats. Two indices of analgesia were used: tail flick latency to radiant heat (TFL) and vocalization threshold to electrical shock of the tail (Voc-T). Nerve cuts were performed at least one week prior to behavioral testing. Bilateral transection of both the pelvic and hypogastric nerves eliminated the analgesic effects of VS on the TFL and Voc-T tests. Bilateral transection of only the pelvic nerves reduced the number of rats showing maximal VS-induced elevation in TFL, without altering the effect of VS on Voc-T. By contrast, bilateral transection of only the hypogastric nerves attenuated the Voc-T-elevating effect of VS, without reducing the effect of VS on elevating TFL. The effects of VS on producing immobility, hindlimb extension and blockage of hindlimb withdrawal to foot pinch were eliminated by combined bilateral pelvic and hypogastric neurectomy. However, bilateral transection of either nerve alone did not significantly alter the efficacy of VS in producing these effects. These findings indicate that the pelvic and hypogastric nerves contribute to the immobility- and extensor-inducing, and flexor-inhibiting effects of VS, and differentially mediate the analgesia-producing effects of VS.

Analgesia↗
PubMed1991

Electrophysiological analysis of the ascending and descending components of the micturition reflex pathway in the rat.

Electrophysiological techniques were used to examine the organization of the spinobulbospinal micturition reflex pathway in the rat. Electrical stimulation of afferent axons in the pelvic nerve evoked a long latency (136 +/- 41 ms) response on bladder postganglionic nerves, whereas stimulation in the dorsal pontine tegmentum elicited shorter latency firing (72 +/- 25 ms) on these nerves. Transection of the pelvic nerve eliminated these responses. Firing on the bladder postganglionic nerves was evoked by stimulation in a relatively limited area of the pons within and close to the laterodorsal tegmental nucleus (LDT) and adjacent ventral periaqueductal gray. Stimulation at sites ventral to this excitatory area inhibited at latencies of 107 +/- 11 ms the asynchronous firing on the bladder postganglionic nerves elicited by bladder distension. Electrical stimulation of afferents in the pelvic nerve evoked short latency (13 +/- 3 ms) negative field potentials in the dorsal part of the periaqueductal gray as well as long latency (42 +/- 7 ms) field potentials in and adjacent to the LDT. The responses were not altered by neuromuscular blockade. Similar responses were elicited by stimulation of afferent axons in the bladder nerves. The sum of the latencies of the ascending and descending pathways between the LDT and the pelvic nerve (i.e. 72 ms plus 42 ms = 114 ms) is comparable although somewhat shorter (22 ms) than the latency of the entire micturition reflex. These results provide further evidence that the micturition reflex in the rat is mediated by a spinobulbospinal pathway which passes through the dorsal pontine tegmentum, and that neurons in the periaqueductal gray as well as the LDT may play as important role in the regulation of the micturition.

Afferent Pathways↗
PubMed1991

Conduction velocity distribution of afferent fibers in the female rat hypogastric nerve.

Conduction velocities of single afferent fibers in the female rat hypogastric nerve were measured by stimulating dorsal rootlets and recording from the hypogastric nerve. A total of 344 units were identified and measured. They were distributed among dorsal roots T13 to L3 ipsilaterally (75%) and between L1 and L2 contralaterally (25%). Over 95% were found in the L1 plus L2 dorsal roots. Ninety-six percent of the units had conduction velocities less than 2 m/s; the average conduction velocity was 0.98 m/s. By way of contrast, afferents in the postganglionic nerves innervating the urinary bladder with conduction velocities less than 2 m/s constituted 65% of the afferents. We conclude that the overwhelming majority of afferents in the female rat hypogastric nerve are unmyelinated C-fibers.

Animals↗
PubMed1992

Histochemical study of the lumbar colonic nerve supply to the internal anal sphincter and its physiological role in dogs.

The sympathetic innervation of the internal and sphincter (IAS) and its physiological role in maintaining sphincter tone were histochemically and mechanically studied in dogs anesthetized with pentobarbital sodium. Numerous catecholamine-fluorescent nerve fibers with varicosities were identified in the IAS of normal dogs. Such fibers were markedly reduced at one week and one month after resection of the hypogastric nerves (HGNs) or the lumbar colonic nerve (LCN), and disappeared after combined HGN and LCN resection. IAS tone decreased to 37.2% of baseline at 1 h after LCN resection and to 69.9% after HGN resection. It returned to the preoperative level at one week and one month after resection. The restored IAS tone was decreased again by acute transection of the previously intact HGNs or LCN. Combined LCN and HGN resection also caused a marked reduction of IAS tone (36.9%) at 1 h after the procedure, and was then restored to the preoperative level with time. The restored tone was not decreased by phentolamine administration. These findings confirmed that both the LCN and the HGN innervate the IAS and play a physiological role in the development of resting tone. The restoration of IAS tone after denervation may be due to intrinsic myogenic properties of the sphincter.

Acetylcholine↗
PubMed1992

The segmental distribution of afferent fibers from the vaginal cervix and hypogastric nerve in rats.

Injections of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) into the walls of the vagina and cervix (vaginocervical injections) of rats resulted in labeling of dorsal root ganglia (DRG) cells located at T11-L4 and L6-S2. In a second group of animals, exposure of the hypogastric nerve to HRP-WGA resulted in a similar bimodal distribution of labeled cells as compared to vaginocervical injections. In a third group, unilateral hypogastric nerve transection prior to injection of HRP-WGA into the vaginocervical walls resulted in a significant reduction in DRG cells labeled at T13, L1, L2, L6 and S1. Bilateral transection of the hypogastric nerves prior to vaginocervical injections eliminated labeled DRG cells at thoracolumbar levels but not at L6 and S1. Bilateral pelvic neurectomy reduced, but did not eliminate labeled DRG cells at L6 and S1 following vaginocervical injections. These results indicate that the hypogastric nerve constitutes a major sensory pathway from the vaginocervical walls to thoracic, lumbar and sacral levels of the spinal cord. The hypogastric nerve may subserve the transmission of noxious input from the vaginocervical walls as well as the activation of ascending spinal pathways involved in neuroendocrine reflexes during parturition.

Afferent Pathways↗
PubMed1992

Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat.

Multi-unit afferent nerve activity was recorded from branches of the hypogastric and pelvic nerves in virgin female rats on different days of the estrous cycle. In each rat, the response of hypogastric nerve fibers to uterine distension and the response of pelvic nerve fibers to vaginal distension was tested. The minimal pressure necessary to evoke a response was highest in diestrus for both the hypogastric and pelvic nerve fibers. For the hypogastric nerve, the minimal necessary pressures were significantly lower during both proestrus and estrus, whereas for the pelvic nerve, the pressure was significantly lower only on the day of proestrus. These results suggest that the overall response sensitivity of afferent fibers in the pelvic and hypogastric nerves are differentially affected by hormonal variations occurring across the estrous cycle in a manner that would enhance reproduction.

Afferent Pathways↗
PubMed1993

Intraspinal modulation of neuronal responses to uterine and cervix stimulation in rat L1 and L6 dorsal horn.

This two-part study examined intraspinal processing of input from the uterus, cervix and skin within the caudal spinal cord of virgin rats in estrus. The first part examined the effects of removing either pelvic or hypogastric nerve input (by appropriate dorsal rhizotomies) on neuronal responses to stimulation of uterus, cervix and skin in either the L1 or L6 dorsal horn of decerebrate, spinalized unanesthetized rats. Bilateral section of the T13-L2 roots (through which most hypogastric afferents travel) eliminated almost all responses to uterine distension in L1 and L6. Such rhizotomies also decreased the inhibitory effects of cervix input on neurons in L6. Bilateral section of the L6-S2 roots (through which most pelvic afferents travel) had no effect on responses to uterus, but decreased the inhibitory effects of cervix input on neurons in L1. Sections of both sets of roots eliminated responses to cervix stimulation in L6. The second part examined neuronal responses in T13/L1 of urethane-anesthetized rats before and after a T10 spinal transection. Transection increased the probability of observing neurons excited by uterine stimulation. Transection also increased excitatory responses and decreased inhibitory responses to cervix stimulation. These results confirm previous findings that input from the uterus to the spinal cord is mainly by way of the hypogastric nerve, while that from the cervix is by way of both the pelvic and hypogastric nerves. The results also demonstrate that descending influences in the estrous rat mainly increase the ability of cervix stimulation to inhibit spinal neuronal activity and reduce the effectiveness of uterine stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Inhibition of withdrawal responses by pelvic nerve electrical stimulation.

In urethane-anesthetized rats, the compound action potential of the pelvic nerve was found to consist of three different waves, two in the A delta fiber and one in the C-fiber range of conduction velocity. Electrical stimulation of the pelvic nerve produced a complete inhibition of the withdrawal response to noxious foot pinch or foot compression. The electromyographic (EMG) activity of the contralateral posterior biceps muscle was used to record the withdrawal response. The withdrawal response inhibition was related to the duration and the frequency of electrical stimulation. Low (5-10 Hz) and high (100-300 Hz) frequencies were ineffective in inhibiting the withdrawal response, whereas intermediate frequencies (20-80 Hz) produced a complete inhibition of the withdrawal response. Short (300 ms) trains of stimulation inhibited the withdrawal response only during the stimulation period. Longer trains of stimulation (500 ms-10 s) produced long-lasting inhibition of the response to noxious stimulation. The inhibition persisted for up to 20 s after the end of electrical stimulation of the pelvic nerve. A delta fiber stimulation was adequate to inhibit the withdrawal response in most (15 out of 17) of the animals. However, A delta plus C-fiber stimulation was needed to inhibit the response to noxious stimulation in two animals. In addition to inhibiting the response to noxious stimulation, pelvic nerve electrical stimulation reflexively activated abdominal muscles. On the basis of present findings using electrical stimulation, it can be suggested that, in the rat, A delta and C-visceral afferents of the pelvic nerve mediate the analgesic effect of vaginocervical probing pelvic and A delta afferents the contraction of abdominal muscles in the fetus-expulsion reflex.

Abdominal Muscles↗