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Spinal cord-mediated cross-organ sensitization between the uterus and the lower urinary tract may underlie the high concurrence of obstetrical/gynecological inflammation and chronic pelvic pain syndrome characterized by urogenital pain. However, the neural pathway and the neurotransmitters involved are still unknown. We tested the hypothesis that the excitation of capsaicin-sensitive primary afferent fibers arising from the uterus through the stimulation of transient receptor potential vanilloid 1 (TRPV1) induces cross-organ sensitization on the pelvic-urethra reflex activity. Capsaicin (1-1,000 microM, 0.05 ml) was instilled into the uterus to induce cross-organ reflex sensitization. Activation of capsaicin-sensitive primary afferent fibers by capsaicin instillation into the uterine horn sensitized the pelvic-urethra reflex activity that was reversed by an intrauterine pretreatment with capsaizepine, a TRPV1-selective antagonist. Intrathecal injection of AP5, a glutamatergic N-methyl-D-aspartate (NMDA) antagonist, and Co-101244, an NMDA NR2B-selective antagonist, both abolished the cross-organ reflex sensitization caused by capsaicin instillation. These results demonstrated that TRPV1 plays a crucial role in contributing to the capsaicin-sensitive primary afferent fibers mediating the glutamatergic NMDA-dependent cross-organ sensitization between the uterus and the lower urinary tract when there is a tissue injury.

Central nervous system neurons process information converging from the uterus, colon, and bladder, partly via the hypogastric nerve. This processing is influenced by the estrous cycle, suggesting the existence of an estrous-modifiable central nervous system substrate by which input from one pelvic organ can influence functioning of other pelvic organs. Here, we tested predictions from this hypothesis that acute inflammation of colon, uterine horn, or bladder would produce signs of inflammation in the other uninflamed organs (increase vascular permeability) and that cross-organ effects would vary with estrous and be eliminated by hypogastric neurectomy (HYPX). Under urethane anesthesia, the colon, uterine horn, or bladder of rats in proestrus or metestrus, with or without prior HYPX, was treated with mustard oil or saline. Two hours later, Evans Blue dye extravasation was measured to assess vascular permeability. Extravasation was increased in all inflamed organs, regardless of estrous stage. For rats in proestrus, but not metestrus, either colon or uterine horn inflammation significantly increased extravasation in the uninflamed bladder. Much smaller cross-organ effects were seen in colon and uterine horn. HYPX reduced extravasation in the inflamed colon and inflamed uterine horn, but not the inflamed bladder. HYPX eliminated the colon-to-bladder and uterine horn-to-bladder effects. These results demonstrate that inflaming one pelvic organ can produce estrous-modifiable signs of inflammation in other pelvic organs, particularly bladder, and suggest that the cross-organ effects involve the hypogastric nerve and are at least partly centrally mediated. Such effects could contribute to co-occurrence and cyclicity of distressing pelvic disorders in women.

1. The uterus, cervix, and vaginal canal are innervated by afferent fibers in the hypogastric and pelvic nerves. Four studies compared the innervation territory and sensitivity to peripheral stimuli of the two sets of fibers in adult virgin rats. 2. Innervation territory was studied anatomically by injecting different fluorescent dyes into different parts of the reproductive, lower urinary, and lower digestive tracts and examining retrogradely labeled neurons in dorsal root ganglia. It was also studied electrophysiologically in anesthetized rats by summing potentials evoked in branches of the two nerves by electrical stimulation of different parts of the reproductive tract. 3. In both studies sensory innervation of the reproductive tract shifted from the pelvic to the hypogastric nerve (i.e., shifted entry into the spinal cord from the L6-S1 to the T13-L3 dorsal root ganglia, respectively) as the dye or stimulating electrode shifted from the vaginal entrance to the uterine horns, with fibers from both nerves densely innervating the cervix region (i.e., entering the spinal cord through both sets of ganglia). The anatomic results suggested that the regions innervated by fibers in one nerve might also be innervated by a small component of normally quiescent fibers in the other nerve. 4. Response sensitivity was studied electrophysiologically by simultaneously recording multiunit activity in branches of the hypogastric and pelvic nerves in two ways. First, in intact, anesthetized rats, activity was recorded during mechanical stimulation of the reproductive tract (distension of the vagina and uterus, probing the cervix). Second, in an in vitro organ preparation of the uterus and vagina, activity was recorded during chemical stimulation through the uterine artery with bradykinin, serotonin, NaCN, CO2, and KCl. 5. Pelvic nerve fibers were markedly more sensitive than hypogastric nerve fibers to uterine and cervical mechanostimulation. Similarly, pelvic nerve fibers were more likely to respond or responded more vigorously than hypogastric nerve fibers to all chemical stimuli (except KCl). 6. These results provide strong evidence that afferent fibers in the pelvic and hypogastric nerves of nulliparous adult rats subserve different functions in reproduction and sensation. Pelvic nerve fibers seem closely tied to sensory and behavioral processes associated with mating and conception, whereas hypogastric fibers seem closely tied to pregnancy and nociception, with fibers in both nerves serving functions during parturition.

1. Previous studies in the rat have shown that the hypogastric nerve conveys input from the cervix and uterus mainly to the T13-L3 segments of the spinal cord, whereas the pelvic nerve conveys input from the cervix and vaginal canal mainly to the L6-S2 segments. 2. To study the effects of this input, the dorsal horns of the T13-L1, L6-S2, and L4-L5 segments in 13 decerebrate, T10-spinalized, unanesthetized, and paralyzed adult female rats in estrus were searched for neurons responsive to gentle mechanical stimulation of the cervix. The 87 neurons found were then further tested for their responses to gentle mechanical stimulation of the skin and to distension of both uterine horns, distension of the colon, and shearing stimulation of the colon and vaginal canal. 3. Neurons responsive to cervix stimulation, primarily by excitation, were readily found in the ventral part of the dorsal horn in T13-L1 and throughout the dorsal horn in L6-S2. Cervix-responsive neurons were less readily found throughout the dorsal horn in L4-L5, where 25% were inhibited by the stimulation. All but one neuron had cutaneous receptive fields. 4. The 30 cervix-responsive neurons in T13-L1 had large bilateral cutaneous receptive fields covering the perineum and hind-limbs. Most (76%) also responded, primarily by excitation, to uterine distension, as well as to colonic stimulation (59%). More than half were activated by both types of stimulation. 5. The 33 cervix-responsive neurons in L6-S2 had cutaneous receptive fields in the same regions as those in T13-L1, but generally smaller, particularly for neurons in the dorsal part of the dorsal horn, many of whose receptive fields were confined to the perineum. The L6-S2 neurons also exhibited less convergent input from other visceral structures, particularly the uterus. Fewer neurons (42%) responded to uterine distension, mostly by being inhibited, whereas about the same proportion (51%) responded with excitation to colonic stimulation. Only 24% responded to both uterus and colon. 6. All 24 cervix-responsive neurons in medial L4-L5 had small cutaneous receptive fields on the toes, and the neurons received less convergent input from other visceral structures (25% from the uterus, 33% from the colon, 13% from both). 7. These results indicate the presence of an extensive system of neurons throughout the caudal spinal cord of the rat, concentrated in separated thoracolumbar and lumbosacral segments, that is concerned with input from the reproductive tract.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Previous studies in the rat and other species have shown that neurons in and near the ventrobasal complex (VB) can be activated by various visceral as well as somatic stimuli. 2. This study examined the responses of 84 single neurons in and near the rostral 2/3 of VB in 19 adult female rats in estrus to mechanical stimulation of the skin (brush, pressure, noxious pinch) and 4 different visceral stimuli, as follows: distension of both uterine horns, mechanical probing of the vagina, gentle pressure against the cervix, and distension of the colon. The rats were studied while under moderate gaseous anesthesia (33% O2-67% N2O + 0.5% halothane) and paralyzed (pancuronium bromide). 3. Of 77 neurons tested with both somatic and visceral stimuli, 70 were responsive to one type and/or the other. Responses to somatic stimuli were immediate with brief afterdischarges to the pinch stimuli. In contrast, responses to visceral stimuli were delayed an average of 9 s with long afterdischarges averaging 2 min. Most viscerally responsive neurons (74%) had somatic receptive fields, often (44%) to noxious pinch. 4. Of the 70 responsive neurons, 43 (61%) responded to 1 or more of the 4 visceral stimuli, primarily with excitation. Most of these 43 neurons (71%) were responsive to uterine distension, whereas fewer responded to stimulation of the cervix (45%), vagina (29%), or colon (34%). 5. Viscerally responsive neurons were preferentially located in regions bordering or near VB. Only 6 of 22 neurons within the core of VB (27%) responded to visceral stimuli, in contrast with 37 of 48 neurons bordering or near VB (77%). 6. The six viscerally responsive neurons within VB all had somatic receptive fields located primarily on the caudal part of the body and were responsive to only one or two of the four visceral stimuli, usually the uterus. The 37 viscerally responsive neurons bordering or near VB were of 3 types. Neurons of the first type (n = 15) were scattered throughout the areas bordering VB and responded to both somatic and visceral stimuli much like VB neurons, except that they showed more visceral convergence. Neurons of the second type (n = 11) were concentrated at the rostral and dorsal borders of VB and responded only to visceral stimuli, mainly the uterus. Neurons of the third type (n = 11) were concentrated ventrally and had very complex, long-lasting and history-dependent response characteristics to both visceral and somatic stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Electrophysiological techniques were used to characterize responses of afferent fibers in pelvic nerve of adult, virgin female rats to mechanical or chemical stimulation of internal reproductive organs and to mechanical stimulation of other pelvic organs. 2. In an in vivo barbiturate-anesthetized preparation, pelvic nerve afferent fibers responded to a wide variety of mechanical stimulation applied to restricted regions of the vaginal canal, caudal uterus (body and cervix), bladder, ureter, colon, or anus. 3. Single-fiber mechanoreceptive fields were invariably confined to a single organ. Notably, responses could be evoked not only by gentle stimulation of the unit's receptive field directly on the organ itself, but also by stimulating the field indirectly with intense stimulation through the appropriate part of a contiguous organ. This innervation feature is consistent with the separability of pelvic organ functions under innocuous conditions but their confusion under noxious ones. 4. Receptive fields on the reproductive organs extended from the caudal edge of the vagina to the uterine body (including the cervix) but were most often located in the fornix (vaginocervical junction). Most units had no or low levels of spontaneous activity. Their responses to mechanical stimuli were usually slowly or moderately adapting and time-locked to the stimulus. 5. Fibers with vaginal receptive fields (including the fornix) responded best either to vaginal distension with a balloon or, more often, to a probe moving along the internal vaginal surface in a direction toward the cervix. They were observed most frequently during the proestrus stage of the rat's estrous cycle. These fibers, therefore, seem particularly suited for relaying information about stimuli that occur during mating. 6. Fibers with receptive fields on the uterine cervix and body responded best to static pressure and were observed less frequently than those with vaginal fields, regardless of estrous stage. They were, however, sensitized by hypoxia. In addition, irritation of the uterus increased the probability of observing them. These fibers, therefore, may exert their primary function during reproductive conditions different from those of virgin rats, such as parturition. 7. Response activity of most of the mechanoreceptive afferent fibers supplying reproductive organs increased as the stimulus intensity increased into the noxious range; i.e., into a range in which the stimulus momentarily produced ischemia at the stimulus site. In addition, in an in vitro preparation, pelvic nerve fibers responded in a dose-dependent manner to injections through the uterine artery of bradykinin (BRAD) as well as to other algesic chemicals, 5-hydroxytryptamine (5-HT) and KCl.(ABSTRACT TRUNCATED AT 400 WORDS)

The relative contribution of the ovarian nerves and hypogastric plexus in the innervation of the guinea pig uterus and ovary was assessed. Chronic section of the hypogastric nerve did not reduce norepinephrine (NE) concentration in either organ. Localization of the hypogastric plexus in female guinea pigs was unsuccessful. Crushing the ovarian nerves 1) lowered the NE concentration in the ovary (70%) and in all portions of the uterus (86%), 2) decreased by 80-90% the uterine retention of [3H]NE, and 3) decreased the intensity of fluorescent adrenergic fibers in the uterus. However, the denervated uterus failed to exhibit supersensitivity to NE. In conclusion, sympathetic innervation of the guinea pig uterus and ovary is predominantly via the ovarian nerves, and a minor pathway of innervation may come from hypogastric plexus.

The distribution and concentration of vasoactive intestinal polypeptide (VIP) in different parts of the female genital organs from various species (cat, goat, pig, rabbit, rat, and guinea pig) were studied by means of immunohistochemistry and immunochemistry. In addition, the effect of VIP on the mechanical activity of uterine muscle was investigated in vitro. VIP immunoreactive nerve fibers innervating vessels and smooth muscle cells were fairly numerous in the genital organs of the cat and goat and less numerous in the pig, rabbit, rat, and guinea pig. In all species studied, VIP-containing nerves were most numerous in the cervix. The tissue concentration of VIP measured by immunochemistry was in agreement with the immunohistochemical findings. VIP inhibited the mechanical uterine activity in the cat, goat, pig, and rabbit, whereas only minimal effects were obtained in the rat and guinea pig. This difference between the species corresponded to the number of VIP-containing nerves in the uterine muscle. The data support the hypothesis that VIP may play a physiological role in the local nervous control of the uterine mechanical activity.

1. In the present three-part study electrophysiological techniques were used to characterize responses of afferent fibers in the rat hypogastric nerve to mechanical or chemical stimulation of the uterus, and anatomical techniques were used to identify the spinal segments through which uterine afferent fibers enter the spinal cord. 2. In an in vivo barbiturate-anesthetized preparation, hypogastric afferent fibers responded in a time-locked manner to mechanical stimulation confined to restricted regions of the uterus and adjacent ligament. Receptive fields were most often located on the uterine body, particularly over the cervix. The few located on the uterine horn were usually near regions irritated during preparative surgery. Effective mechanical stimuli (pressure, stretching, squeezing, probing, rarely contractions) were typically greater than 5 g and simultaneously accompanied by transient ischemia around the probe or contracted area. Distension, unless extreme, was not an effective stimulus. Retrospective analysis of the data indicated that fibers may be more sensitive to uterine stimulation when rats are in vaginal estrus/proestrus than in diestrus/metestrus. 3. In an in vitro preparation, hypogastric afferent fibers responded in a dose-dependent fashion to injections into the uterine artery of the algesic chemicals bradykinin, 5-hydroxytryptamine, and KCl. They also responded to high doses of CO2 (in saline) and NaCN, but rarely to lower doses. Nearly all fibers responded to more than one chemical with response characteristics unique to each chemical (e.g., latency, duration, peak rate). 4. Injections of horseradish peroxidase into the uterine body and small portions of the adjacent horns in rats in vaginal estrus consistently labeled a small number of cells in the L1-S1 dorsal root ganglia, with peaks at L2 and L6. Virtually no cells were labeled in rats whose estrous cycle had been disrupted (by inadvertently keeping them in constant light conditions for several weeks). 5. These results indicate that uterine afferent fibers travel to the central nervous system through both the hypogastric (e.g., L1-L4 ganglia) and pelvic (e.g., L5-S1 ganglia) nerves in the rat, and that hypogastric fibers are capable of conveying fairly precise information about temporal and spatial aspects of uterine mechanical and chemical stimulation. The results also encourage future research into the possibility that the responses of these fibers vary as a function of estrous stage or other aspects of the condition of the uterus (e.g., its irritation).(ABSTRACT TRUNCATED AT 400 WORDS)

Myometrial tissue slices from virgin, pregnant (uni- or bilateral pregnancy), and puerperal animals were incubated in media containing [3H]norepinephrine ([3H]NE), and the neuronal and extraneuronal uptake was estimated. The metabolic fate of [3H]NE was elucidated by the chromatographic separation of [3H]NE, [3H]normetanephrine and 3H-labeled acid metabolites. An early and extensive reduction in both total and neuronal uptakes occurred in the myometrial regions surrounding the fetuses, and at term pregnancy no neuronal [3H]NE uptake at all was found in tissue slices from the fetus-containing horns. Concomitantly, the fraction of unchanged [3H]NE decreased with a corresponding increment in its metabolites. Similar changes, though less extensive, also occurred in the empty horn in unilateral pregnancy. The total amount of neuronal uptake in the cervix seemed unchanged compared to virgin animals. Earlier and present data support the following suggestion that in uterine horns harboring fetuses, an extensive axonal degeneration occurs; in those devoid of fetuses (unilateral pregnancy), the nerve terminals are to a great extent structurally intact, but functionally damaged. Recovery of the pregnancy-induced impairment of the adrenergic nerve plexus is slow and incomplete.

Uterine adrenergic and cholinergic nerves were examined histochemically and chemically in combination with surgical denervation. There was a clear regional variation with a greater number of axon terminals in the tubal end of the uterine horn and in the cervix compared to the remainder (major part) of the uterine horn. No cholinergic nerves were found in the uterus but were abundant around the uterine artery and its primary ramifications. Clusters of ganglion cells were located near the cervix: the majority were acetylcholinesterase positive, whereas the remainder stored catecholamines. Unexpectedly, the suspensory ligament (connecting the tubal end of the uterine horn with the two lower ribs) was found to contain an extensive number of adrenergic nerves. The major part of the uterine horns, as well as the cervix, was innervated mainly from two sources contributing almost equally: the paracervical ganglia (short adrenergic neurons) and postganglionic fibers running in the hypogastric nerves. A restricted area at the tubal end of the uterus received most of its via the suspensory ligament.

This review concerns the influence of ovarian steroids and of pregnancy on norepinephrine (NE) metabolism in the adrenergic neurons of the female reproductive tract and speculates on the physiological consequences of this influence. Estrogen and progesterone affect not only the NE content of these nerves but also the turnover of NE, the activity of its synthetic enzyme, and releases of NE from nerve terminals. During pregnancy additional factors including stretch-induced hypertrophy come into play and cause degeneration of the nerves in the uterine corpus. This degeneration makes the muscle supersensitive to NE and may also induce morphological changes in the muscle cell membrane. As a result there may be a withdrawal of neural inhibitory influences on the corpus, allowing spontaneous myogenic contractions to intensify. Although the physiological significance of the steroid-transmitter interactions are still unclear, these nerves per se are of interest because they represent a model system for the study of neuroendocrine regulation in the peripheral nervous system.

Whole-mount preparations of the uterus and mesentery from nonpregnant rats were examined after staining with glyoxylic acid or acetylcholinesterase to demonstrate the innervation. Some uterine tissues were also evaluated by electron microscopy. Glyoxylic acid fluorescent nerves were present in the mesentery, mesometrium, and uterine wall exclusively around blood vessels. Acetylcholinesterase positive nerve fibers from Frankenhäuser's plexus (cervical ganglia) were associated with blood vessels and muscle in the uterine wall but not in the mesentery. Electron microscopy revealed nerve varicosities with granular vesicles associated with blood vessels and varicosities with agranular vesicles located near blood vessels and muscle cells. Treatment of animals for 3 days with 5- and 6-hydroxydopamine, respectively, increased granular size and damaged the varicosities with granular vesicles but did not change nerves with agranular vesicles or induce the presence of gap junctions. The results of this study suggest that blood vessels in the uterus are highly innervated by both adrenergic and other types of nerves that probably control blood flow. Nonadrenergic but not adrenergic nerves may also directly control myometrial contractility.