Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter muscle in the rat

Effects of lateral funiculus sparing, spinal lesion level, and gender on recovery of bladder voiding reflexes and hematuria in rats

Deficits in bladder function are complications following spinal cord injury (SCI), severely affecting quality of life. Normal voiding function requires coordinated contraction of bladder and urethral sphincter muscles dependent upon intact lumbosacral reflex arcs and integration of descending and ascending spinal pathways. We previously reported, in electrophysiological recordings, that segmental reflex circuit neurons in anesthetized male rats were modulated by a bilateral spino-bulbo-spinal pathway in the mid-thoracic lateral funiculus. In the present study, behavioral measures of bladder voiding reflexes and hematuria (hemorrhagic cystitis) were obtained to assess the correlation of plasticity-dependent recovery to the degree of lateral funiculus sparing and mid-thoracic lesion level. Adult rats received mid-thoracic-level lesions at one of the following severities: complete spinal transection; bilateral dorsal column lesion; unilateral hemisection; bilateral dorsal hemisection; a bilateral lesion of the lateral funiculi and dorsal columns; or a severe contusion. Voiding function and hematuria were evaluated by determining whether the bladder was areflexic (requiring manual expression, i.e., "crede maneuver"), reflexive (voiding initiated by perineal stroking), or "automatic" (spontaneous voiding without caretaker assistance). Rats with one or both lateral funiculi spared (i.e., bilateral dorsal column lesion or unilateral hemisection) recovered significantly faster than animals with bilateral lateral funiculus lesions, severe contusion, or complete transection. Bladder reflex recovery time was significantly slower the closer a transection lesion was to T10, suggesting that proximity to the segmental sensory and sympathetic innervation of the upper urinary tract (kidney, ureter) should be avoided in the choice of lesion level for SCI studies of micturition pathways. In addition, hematuria duration was significantly longer in males, compared to females, despite similar bladder reflex onset times. We conclude that the sparing of the mid-thoracic lateral funiculus on one side is required for early recovery of bladder reflex voiding function and resolution of hematuria.

Spinal projections of the A5, A6 (locus coeruleus), and A7 noradrenergic cell groups in rats

The pontine noradrenergic cell groups, A5, A6 (locus coeruleus), and A7, provide the only noradrenergic innervation of the spinal cord, but the individual contribution of each of these populations to the regional innervation of the spinal cord remains controversial. We used an adeno-associated viral (AAV) vector encoding green fluorescent protein under an artificial dopamine beta-hydroxylase (PRSx8) promoter to trace the spinal projections from the A5, A6, and A7 groups. Projections from all three groups travel through the spinal cord in both the lateral and ventral funiculi and in the dorsal surface of the dorsal horn, but A6 axons take predominantly the dorsal and ventral routes, whereas A5 axons take mainly a lateral and A7 axons a ventral route. The A6 group provides the densest innervation at all levels, and includes all parts of the spinal gray matter, but it is particularly dense in the dorsal horn. The A7 group provides the next most dense innervation, again including all parts of the spinal cord, but is it denser in the ventral horn. The A5 group supplies only sparse innervation to the dorsal and ventral horns and to the cervical and lumbosacral levels, but provides the densest innervation to the thoracic intermediolateral cell column, and in particular to the sympathetic preganglionic neurons. Thus, the pontine noradrenergic cell groups project in a roughly topographic and complementary fashion onto the spinal cord. The pattern of spinal projections observed suggests that the locus coeruleus might have the greatest effect on somatosensory transmission, the A7 group on motor function, and the A5 group on sympathetic function.

Acute administration of AMPA/Kainate blocker combined with delayed transplantation of neural precursors improves lower urinary tract function in spinal injured rats

To evaluate bladder function recovery after spinal cord injury (SCI) in response to a combination treatment of an acutely administered AMPA/kainate receptor antagonist and delayed transplantation of neuronal precursors. Female rats received a contusion injury at T8/9. The AMPA/kainate receptor antagonist NBQX was directly administered into the lesion site immediately after injury. Nine days post-injury, NRP/GRP were delivered into the lesion site. Controls received NRP/GRP grafts only or no treatment (OP-Controls). Animals underwent bladder function testing during the course of the experiment and at the endpoint. Motor function was evaluated as well. After sacrifice, histological analysis of lesion site and lumbosacral spinal cord regions was performed. Rats receiving the combined treatment (NBQX&NRP/GRP) had voided volumes/micturition resembling that of normal animals and showed greater improvement of urodynamic parameters, compared to NRP/GRP alone or OP-Controls. Similarly, NBQX&NRP/GRP induced more spouting, regeneration or sparing of descending projections to the lumbosacral cord. The density of primary afferent projections at the lumbosacral spinal cord in rats with combined treatments was similar to that of NRP/GRP alone with decreased sprouting of primary afferents in lumbosacral cord, compared to OP-Control. Immunohistochemical evaluation revealed that the combined treatment reduced the size of the lesion to a greater extent than NRP/GRP alone or OP-Controls. NRP/GRP with and without NBQX produced a significant recovery of hindlimb compared to OP-Controls. In conclusion, transplants of NRP/GRP combined with NBQX promote recovery of micturition function following spinal cord injury, likely through increased neuroprotection.

Micturition-suppressing region in the periaqueductal gray of the mesencephalon of the cat

The periaqueductal gray (PAG) of the mesencephalon has been implicated to be involved in the control of micturition. We investigated the micturition-suppressing region in the PAG of the cat. Decerebrated 27 adult cats were used. A microelectrode was inserted stereotaxically into the PAG, and a region was searched where electrical stimulation suppressed isovolumetric bladder contractions. Simultaneous stimulation of the pontine micturition center (PMC) and micturition-suppressing region in the PAG was performed before and after an injection of bicuculline (GABAA blocker) into the PMC. The micturition-suppressing region was found at the dorsolateral margin of the rostral PAG. Bladder contractions were not provoked by simultaneous stimulation of the PMC and micturition-suppressing region in the PAG. However, after bicuculline injection into the PMC, partial bladder contractions were provoked by simultaneous stimulation of the PMC and the micturition-suppressing region in the PAG. These results suggest that the dorsolateral margin of the rostral PAG includes the micturition-suppressing region that seems to have neural connections with the PMC. GABA is assumed to be one of the neurotransmitters that are involved in the PMC inhibition from the micturition-suppressing region in the PAG.

Barrington's nucleus in the guinea pig (Cavia porcellus): location in relation to noradrenergic cell groups and connections to the lumbosacral spinal cord

Micturition is largely controlled by Barrington's nucleus in the dorsolateral tegmentum of the pons. This nucleus coordinates simultaneous bladder contraction and external urethral sphincter relaxation, by means of a specific pattern of projections to the lumbosacral spinal cord. The most widely used small animal model in neurourological research is the rat. However, urodynamic studies suggest that, in sharp comparison to rat, guinea pig micturition is very similar to human micturition. Therefore, the present study, using retrograde and anterograde tracing and double immunofluorescence, was designed to investigate the location of Barrington's nucleus in the guinea pig, to identify Barrington's nucleus projections to the spinal cord and to clarify the relationship of Barrington's nucleus to pontine noradrenergic cell groups. Results show that Barrington's nucleus is located in the dorsolateral pons, projects to the intermediolateral and intermediomedial cell groups of the lumbosacral spinal cord and is clearly distinct from the pontine noradrenergic cell groups. These results show that the neuroanatomical circuitry in the spinal cord and brainstem that controls micturition in the guinea pig is similar to that in rat. This means that the differences between rat and guinea pig micturition on a behavioral level are not the result of different neuroanatomical connections in these parts of the central nervous system. These results provide a neuroanatomical basis for further neurourological studies in guinea pig.

Serotonin 5-HT2A and 5-HT5A receptors are expressed by different motoneuron populations in rat Onuf's nucleus

Motoneurons of Onuf's nucleus innervate the pelvic striated muscles, which play a crucial role in erection, ejaculation, and urinary continence. Serotonergic descending projections from the brain are involved in the modulation of Onuf's motoneuron activity. However, conflicting results regarding the effects of spinal serotonin (5-HT) on pelvi-perineal functions have been reported. They may be partly accounted for by the multiplicity of neuronal targets and receptor subtypes on which 5-HT is acting. In order to provide comparative data regarding 5-HT receptor expression in various groups of Onuf's motoneurons, we used retrograde tracing techniques from different pelvic muscles combined with immunocytochemistry of 5-HT2A and 5-HT5A receptors in male and female rats. In males, 5-HT2A receptor immunolabeling was very dense in motoneurons innervating the ischiocavernosus muscle. By contrast, in female rats, 5-HT2A receptor expression in Onuf's nucleus was very weak. In both genders, 5-HT5A receptor immunoreactivity was found in motoneurons innervating the external urethral sphincter. In males, a moderate or low 5-HT5A immunolabeling was observed in motoneurons innervating the bulbospongiosus and ischiocavernosus muscles, respectively. These data show a preferential localization of 5-HT2A and 5-HT5A receptors to motoneurons controlling the striated muscles located at the penile crus and sphincter muscles, respectively, suggesting a specific serotoninergic control on different pelvic functions. In addition, the subcellular distribution of receptors suggests a different mode of action of 5-HT, paracrine at 5-HT2A receptors and synaptic at 5-HT5A receptors. This might have implications for pharmacological research targeting different pelvic functions e.g., micturition and ejaculation.

Transplantation of neuronal and glial restricted precursors into contused spinal cord improves bladder and motor functions, decreases thermal hypersensitivity, and modifies intraspinal circuitry

Transplanting neuronal and glial restricted precursors (NRP/GRP) into a midthoracic injury 9 d after contusion improved bladder and motor function, diminished thermal hypersensitivity, and modified lumbosacral circuitry compared with operated controls (OP-controls). Histological analysis showed that NRP/GRP survived, filled the lesion site, differentiated into neurons and glia, and migrated selectively. Volume of spinal cord spared was increased in NRP/GRP recipients, suggesting local protection. Bladder areflexia developed in both operated groups, but NRP/GRP recipients exhibited an accelerated recovery, with decreased micturition pressure and fewer episodes of detrusor hyperreflexia. Because noradrenergic receptors proliferate after spinal injury and descending noradrenergic pathways contribute to regulation of bladder control, we examined the effects of administering an alpha-1A-adrenergic antagonist, Tamsulosin, on urodynamics. This improved all cystometric parameters in both operated groups, and micturition pressure in NRP/GRP rats recovered to normal levels. Both operated groups initially showed increased sensitivity to a thermal stimulus applied to the tail; the NRP/GRP rats showed significant improvement over time. NRP/GRP grafts also produced greater recovery of hindlimb function in several tests, although both groups showed persistent and similar deficits in locomotion on a grid. Because bladder, hindlimb, and tail sensory and motor functions are organized through lumbosacral cord, we examined descending and primary afferent projections at L6-S1. The density of serotonergic, noradrenergic, and corticotrophin releasing factor-positive fibers increased in the NRP/GRP group compared with OP-controls, suggesting some sparing and/or sprouting of these modulatory pathways. Immunocytochemical staining density of dorsal root axons in the dorsal horn increased in the OP-controls but appeared normal in the NRP/GRP group. Synaptophysin immunoreactivity in the lumbosacral dorsal horn was similar among groups, consistent with restoration of synaptic density in both groups of operated animals but by different pathways. We suggest that local protection provided by NRP/GRP resulted in increased sparing/sprouting of descending pathways, which prevented sprouting by dorsal root axons, and that this modification in lumbosacral circuitry contributes to the recovery of function.

Alterations in eliminative and sexual reflexes after spinal cord injury: defecatory function and development of spasticity in pelvic floor musculature

Spinal cord injury often results in loss of normal eliminative and sexual functions. This chapter is focused on defecatory function, although aspects of micturition and erectile function will be covered as well due to the overlap in anatomical organization and response to injury. These systems have both autonomic and somatic components, and are organized in the thoracolumbar (sympathetic), lumbosacral (somatic), and sacral (parasympathetic) spinal cord. Loss of supraspinal descending control and plasticity-mediated alterations at the level of the spinal cord, result in loss of voluntary control and in abnormal functioning of these systems including the development of dyssynergies and spasticity. There are several useful models of spinal cord injury in rodents that exhibit many of the autonomic dysfunctions observed after spinal cord injury in humans. Numerous studies involving these animal models have demonstrated development of abnormalities in bladder, external anal sphincter, and erectile function, such as detrusor-sphincter-dyssynergia and external anal sphincter hyperreflexia. Here we review many of these studies and show some of the anatomical alterations that develop within the spinal cord during the development of these hyperreflexias. Furthermore, we show that spasticity develops in other pelvic floor musculature as well, such as the bulbospongiosus muscle, which results in increased duration and magnitude of pressures developed during erectile events and increased duration of micturition. Advances and continued improvement in the use of current animal models of spinal cord injury should encourage and increase the laboratory work devoted to this relatively neglected area of experimental spinal cord injury.

Effect of injury severity on lower urinary tract function after experimental spinal cord injury

Lower urinary tract dysfunction is a serious burden for patients following spinal cord injury. Patients are usually limited to treatment with urinary drainage catheters, which can lead to repeated urinary tract infections and lower quality of life. Most of the information previously obtained regarding lower urinary tract function after spinal cord injury has been in completely transected animals. After thoracic transection in the rat, plasticity of local lumbosacral spinal circuitry establishes a "reflex bladder," which results in partial recovery of micturition, albeit with reduced voiding efficiency. Since at least half of cord-injured patients exhibit neurologically incomplete injury, rat models of clinically relevant incomplete contusion injury have been developed. With respect to lower urinary tract function, recent anatomical and physiological studies have been performed after incomplete thoracic contusion injury. The results show greater recovery of lower urinary tract function that varies inversely with the severity of the initial trauma and is positively correlated with time after injury. Recovery, as measured by coordination of the bladder with the external urethral sphincter, occurs between 1 and 4 weeks after spinal cord injury. It is associated with normalization of: serotonin immunoreactivity and glutamate receptor subunit mRNA expression in the dorsolateral nucleus that innervates the external urethral sphincter muscle, the response to glutamatergic pharmacological probes administered at the lumbosacral spinal cord level, and c-Fos activation patterns in the lumbar spinal cord. Understanding the mechanisms involved in this recovery will provide a basis for enhancing lower urinary tract function in patients after incomplete spinal cord injury.

Influence of the paraventricular nucleus and oxytocin on the retrograde stain of pubococcygeus muscle motoneurons in male rats

Lumbosacral cord motoneurons innervating the pubococcygeus muscle (Pcm) at the pelvic floor of male rats were analyzed. We showed previously that these motoneurons participate in sexual functions and are sensitive to fluctuations of systemic androgen and estrogen. Though estrogen receptors have not been identified in Lamina IX at these spinal areas, the release of oxytocin from the paraventricular nucleus of the hypothalamus (PvN) has been found to control pelvic sexual physiology. We therefore worked on the hypothesis that steroid hormones in the PvN induce the release of oxytocin at the lumbosacral level to modulate the function of Pcm motoneurons. Four experiments were developed, and results were observed with the retrograde staining of motoneurons with horseradish peroxidase. Data indicated that morphometric parameters of Pcm motoneurons were significantly reduced after castration or blocking of the steroids at the PvN site, or following complete transection of the spinal cord at the T8 level. In each case, the reduction of the stain was recovered after intrathecal treatment with oxytocin. Thus, present results show that Pcm motoneurons respond to spinal oxytocin. The conclusive model that we propose is that steroids stimulate the PvN, causing the nucleus to release oxytocin at the level of the lumbosacral spinal cord, and the release of the peptide regulates the spread of the stain of Pcm motoneurons. This work also shows that motoneurons distal to a transected area in the spinal cord could respond to exogenous oxytocin, an important finding for the research of spinal cord lesioned subjects.

Projections from bed nuclei of the stria terminalis, posterior division: implications for cerebral hemisphere regulation of defensive and reproductive behaviors

The posterior division of the bed nuclei of the stria terminalis has three major nuclei: principal, interfascicular, and transverse, which receive topographically ordered inputs from the medial amygdalar nucleus. The overall pattern of axonal projections from each nucleus was determined in male rats with the Phaseolus vulgaris-leucoagglutinin method. Together, these nuclei project topographically back to the medial amygdalar nucleus, to the adjacent lateral septal nucleus, to the nucleus accumbens and substantia innominata, to hypothalamic parts of the behavior control column, and to the hypothalamic periventricular region, which controls patterned neuroendocrine and autonomic responses. The principal nucleus preferentially innervates septal and hypothalamic regions that control reproductive behavior and visceromotor responses, confirming a similar analysis by Gu et al. (J Comp Neurol [2003] 460:542-562). In contrast, the interfascicular and transverse nuclei differentially innervate septal and hypothalamic regions that control defensive as well as reproductive behaviors. In addition, the transverse nucleus projects significantly to midbrain parts of the behavior control column concerned with foraging/exploratory behavior. All three posterior division nuclei also project to thalamocortical feedback loops (by means of the nucleus reuniens and paraventricular nucleus). These structural data may be interpreted to suggest that the bed nuclei posterior division forms part (pallidal) of a corticostriatopallidal system involved in controlling two major classes of social (defensive and reproductive) behavior.

Firing of micturition center neurons in the rat mesopontine tegmentum during urinary bladder contraction

Micturition is controlled by a network of brainstem neurons involving the Barrington's nucleus. To depict clearly the brainstem system for micturition control, the present study was designed to record single neuronal activity in the mesopontine tegmentum including the Barrington's nucleus, and to observe its precise timing in relation to bladder contraction recorded simultaneously. About 1/5 of neurons encountered had firing modulated in relation to bladder contraction. Three types of neurons were distinguished; those which fired only prior to the start of contraction (type E1), those whose firing started shortly prior to and was maintained during contraction (type E2), and those whose firing was strongly suppressed during contraction (type I). Type E2 neurons were most frequently observed in the Barrington's nucleus and its close vicinity, while the neurons of the other two types were scattered widely in the mesopontine tegmentum. The results show clearly that direct neural signals to induce bladder contraction may arise from the Barrington's nucleus, and that the nucleus may receive regulatory inputs from wide areas of the mesopontine tegmentum. In addition, the present study clarified that the noradrenergic and cholinergic neurons, which are located in nuclei adjoining the Barrington's nucleus and function to control sleep/wakefulness, may not be concerned in controlling micturition directly.

Descending spinal projections from the rostral gigantocellular reticular nuclei complex

Electrophysiological and physiological studies have suggested that the ventral medullary gigantocellular reticular nuclei (composed of the gigantocellular ventralis and pars alpha nuclei as well as the adjacent lateral paragigantocellular nucleus; abbreviated Gi-LPGi complex) provide descending control of pelvic floor organs (Mackel [1979] J. Physiol. (Lond.) 294:105-122; Hubscher and Johnson [1996] J. Neurophysiol. 76:2474-2482; Hubscher and Johnson [1999] J. Neurophysiol. 82:1381-1389; Johnson and Hubscher [1998] Neuroreport 9:341-345). Specifically, this complex of paramedian reticular nuclei has been implicated in the inhibition of sexual reflexes. In the present study, an anterograde fluorescent tracer was used to investigate direct descending projections from the Gi-LPGi complex to retrogradely labeled pudendal motoneurons (MN) in the male rat. Our results demonstrated that, although a high density of arborizations from Gi-LPGi fibers appears to be in close apposition to pudendal MNs, this relationship also applies to other MNs throughout the entire spinal cord. The Gi-LPGi also projects to spinal autonomic regions, i.e., both the intermediolateral cell column and the sacral parasympathetic nucleus, as well as to regions of the intermediate gray, which contain interneurons involved in the organization of pelvic floor reflexes. Lastly, throughout the length of the spinal cord, numerous neurons located primarily in laminae VII-X, were retrogradely labeled with Fluoro-Ruby after injections into the Gi-LPGi. The diffuse descending projections and arborizations of this pathway throughout the spinal cord suggest that this brainstem area is involved in the direct, descending control of a variety of spinal activities. These results are in contrast with our observations of the discrete projections of the caudal nucleus raphe obscurus, which target the autonomic and somatic MNs involved specifically in sexual and eliminative functions (Hermann et al. [1998] J. Comp. Neurol. 397:458-474).

Motor pudendal nerve characterization in the female rat

The aim of our study was to provide quantitative data on pudendal motor neuron cell bodies and axons in the female rat. To confirm earlier studies, fluorescent retrograde tracers were used to label the motor neurons for correlation with myelinated axon counts along the length of the motor pudendal nerve. The external urethral sphincter of female rats was injected with diamidino yellow and the external anal sphincter with fast blue. The L(6) spinal cord revealed labeled motor neurons. Those in the dorsolateral column (60.8 +/- 10.6) had nuclei labeled yellow from the external urethral sphincter and those in the dorsomedial column (31.7 +/- 8.5) had cytoplasm labeled blue from the external anal sphincter. Double labeling was not present, suggesting that pudendal motor neurons in each column innervate separate sphincters. The motor pudendal nerve in the ischiorectal fossa was also characterized by light microscopy. The mean myelinated axon count (151.4 +/- 17.0) was highly correlated (r = 0.995) in the proximal fascicles and the sum of distal fascicles. This indicated that myelinated axons do not branch at the point where the main motor pudendal nerve branches into separate fascicles. Axon counts between sides were not as well correlated (r = 0.883). The ratio of motor neurons to myelinated axons is 56%, suggesting that some myelinated axons either innervate other muscles or are sensory. This reproducible characterization of the normal pudendal nerve anatomy provides an excellent basis for experimental studies associated with pudendal nerve denervation as a model for neurogenic incontinence.

Discrete regions in the laterodorsal tegmental area of the rat regulating the urinary bladder and external urethral sphincter

In urethane anesthetized rats, the laterodorsal tegmental area was stimulated systematically with a carbon fiber electrode to clarify regions regulating the urinary bladder and/or the external urethral sphincter. Contraction of the former was monitored by bladder pressure and that of the latter by electromyogram. Stimulation of a small area around the ventrolateral edge of the central gray in a plane at the junction of the mesencephalon and pons, where cholinergic neurons in the laterodorsal tegmental nucleus formed the largest mass, induced contraction only of the bladder. Arranged in tandem rostrocaudally with this bladder site, a very small area whose stimulation induced contraction only of the sphincter was found also at the ventrolateral edge of the central gray in a plane slightly caudal to the above. Slightly lateral and caudal to this sphincter site, there were sites the stimulation of which induced contraction of both the bladder and sphincter. It was thus shown physiologically that there were discrete sites in the laterodorsal tegmental area regulating the bladder and sphincter independently.

Coordination of the bladder detrusor and the external urethral sphincter in a rat model of spinal cord injury: effect of injury severity

Recovery of urinary tract function after spinal cord injury (SCI) is important in its own right and may also serve as a model for studying mechanisms of functional recovery after injury in the CNS. Normal micturition requires coordinated activation of smooth muscle of the bladder (detrusor) and striated muscle of the external urethral sphincter (EUS) that is controlled by spinal and supraspinal circuitry. We used a clinically relevant rat model of thoracic spinal cord contusion injury to examine the effect of varying the degree of residual supraspinal connections on chronic detrusor-EUS coordination. Urodynamic evaluation at 8 weeks after SCI showed that detrusor contractions of the bladder recovered similarly in groups of rats injured with a 10 gm weight dropped 12.5, 25, or 50 mm onto the spinal cord. In contrast, the degree of coordinated activation of the EUS varied with the severity of initial injury and the degree of preservation of white matter at the injury site. The 12.5 mm SCI resulted in the sparing of 20% of the white matter at the injury site and complete recovery of detrusor-EUS coordination. In more severely injured rats, the chronic recovery of detrusor-EUS coordination was very incomplete and correlated to decreased innervation of lower motoneurons by descending control pathways and their increased levels of mRNA for glutamate receptor subunits NR2A and GluR2. These results show that the extent of recovery of detrusor-EUS coordination depends on injury severity and the degree of residual connections with brainstem control centers.

Micturition evoked by glutamate microinjection in the ventrolateral periaqueductal gray is mediated through Barrington's nucleus in the rat

Neural tracing experiments have demonstrated a direct spinal projection to Barrington's nucleus and a possible indirect pathway to Barrington's nucleus via the periaqueductal gray. We sought to identify the role of the periaqueductal gray matter in micturition in urethane-anesthetized rats. Blockade of micturition by focal injection of cobalt chloride was used to identify sites critical to micturition. These sites were located near the ventral margin of the caudal ventrolateral periaqueductal gray and in Barrington's nucleus. L-Glutamate injections into caudal regions of the periaqueductal gray evoked bladder contraction with coordinated sphincter activation. Additional L-glutamate sites with a similar pattern of response and sites where sphincter activation was produced without bladder contraction were found more rostrally and dorsally in the periaqueductal gray. Activation of bladder contractions by L-glutamate injection in the ventrolateral periaqueductal gray was blocked by prior injection of cobalt chloride into Barrington's nucleus. From these data we propose that ventrolateral periaqueductal gray is functionally important to micturition in the urethane-anesthetized rat. Further, we have shown that a periaqueductal gray to Barrington's nucleus pathway is functionally relevant to central mediation of bladder contraction.

A computer model of the neural control of the lower urinary tract

Better understanding of the underlying working mechanism of the neural control of the lower urinary tract will facilitate the treatment of dysfunction with a neurogenic cause. We developed a computer model to study the effect of a neural control system on lower urinary tract behavior. To model the mechanical properties and neural control, assumptions had to be made. These assumptions were based, as much as possible, on knowledge and hypotheses taken from the literature. With valid assumptions, it should be possible to simulate normal as well as pathological behavior. To test the computer model, first, normal behavior of the lower urinary tract was simulated, and secondly, the known features of bladder outlet obstruction were simulated after the properties of the urethra were changed. The simulation results are comparable with measured data, so the assumptions on which the model is based could be valid. If the assumptions are valid, the feedback loops used in the model are also important feedback loops in vivo, and the model can be used to gain insight into the underlying mechanism of neural control.

Comparison of different computer models of the neural control system of the lower urinary tract

This paper presents a series of five models that were formulated for describing the neural control of the lower urinary tract in humans. A parsimonious formulation of the effect of the sympathetic system, the pre-optic area, and urethral afferents on the simulated behavior are included. In spite of the relative simplicity of the five models studied, behavior that resembles normal lower urinary tract behavior as seen during an urodynamic investigation could be simulated. The models were tested by studying their response to disturbances of the afferent signal from the bladder. It was found that the inhibiting reflex that results from including the sympathetic system or the pre-optic area (PrOA) only counteracts the disturbance in the storage phase. Once micturition has started, these inhibiting reflexes are suppressed. A detrusor contraction that does not result in complete micturition similar to an unstable detrusor contraction could be simulated in a model including urethral afferents. Owing to the number of uncertainties in these models, so far no unambiguous explanation of normal and pathological lower urinary tract behavior can be given. However, these models can be used as an additional tool in studies of the mechanisms of the involved neural control.

Firing of putative cholinergic neurons and micturition center neurons in the rat laterodorsal tegmentum during distention and contraction of urinary bladder

The relation between unit activity in the laterodorsal tegmental (LDT) area and the state of the urinary bladder was examined in urethane-anesthetized rats. Neurons in the LDT area can be classified into two populations: broad-spike (possibly cholinergic) and brief-spike (non-cholinergic). When the rats showed cortical electroencephalographic activity with large amplitude lower frequency, indicative of deep anesthesia, more than 40% of the broad-spike neurons was excited and about 10% was inhibited by infusion of saline into the bladder. The response was followed by decrease in amplitude and slight increase in frequency of the cortical activity, i.e., lightening of anesthesia. During light anesthesia, excitation was observed only in less than 10% of the units, while 17% was inhibited. In the brief-spike neurons, a similar proportion (about 20%) was excited and less than 10% was inhibited by the distention during either state of anesthesia. About 10% of the broad-spike neurons in the LDT area and 30% of the brief-spike neurons examined were discharged prior to the bladder contraction. Such neurons of the brief-spike category were encountered frequently outside of the central gray; lateral, caudal and ventral to the main mass of cholinergic neurons in the LDT area. These results suggest the possible involvement of the broad-spike (cholinergic) neurons in the elevation of vigilance level caused by bladder distention. The brief-spike (non-cholinergic) neurons firing with relation to bladder contraction may be part of the micturition reflex center.

Direct projections from the medial preoptic area to spinally-projecting neurons in Barrington's nucleus: an electron microscope study in the rat

Direct projections from the medial preoptic area (MPO) to the pontine micturition center neurons directly projecting to the lumbosacral spinal cord were revealed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the MPO and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. At light microscopic level, BDA-labeled presumptive axon terminals completely overlapped with HRP-labeled neurons in Barrington's nucleus. Electron microscopic observation showed that some BDA-labeled axon terminals made synaptic contacts with dendrites of HRP-labeled neurons in Barrington's nucleus. The present results indicated that the MPO may be involved in the modulation of the pontine micturition reflex in the rat.

Regional patterning of reticulospinal and vestibulospinal neurons in the hindbrain of mouse and rat embryos

The dispositions and axonal trajectories of bulbospinal neurons in the pons and medulla of mouse and rat embryos is described from the earliest times these projections can be labelled retrogradely from the cervical spinal cord. Reticulospinal and vestibulospinal neurons are clustered into identifiable groups, each with a characteristic combination of spatial domain and axon trajectory. The various groups can be labelled retrogradely in a specific developmental sequence. The position of some groups shifts from medial to lateral with development, apparently through cell migration. These observations show that the basic regional organization of the reticulospinal and vestibulospinal projections is similar in mouse and rat and is already established during early stages of axon outgrowth.

A computer model for describing the effect of urethral afferents on simulated lower urinary tract function

A computer model of mechanical properties of the bladder, the urethra and the rhabdosphincter, as well as their neural control is presented in this paper. The model has a rather simple design and processes sensory information from both the bladder wall tension and urethral stretch. It is assumed that afferent signals from the urethra are involved in a sacral excitatory reflex and a supraspinal inhibitory reflex. Pressure and flow signals that resemble experimentally measured normal human behaviour could be simulated with this model. From these simulations the relation between the neural control mechanisms used in the model and the neural control mechanism in vivo cannot be judged entirely because similar behaviour could be simulated with models that are bas ed on different neural control mechanisms. Also behaviour that resembles detrusor overactivity was simulated with our model after an externally induced rise in detrusor pressure was added. Detrusor overactivity, sometimes in combination with urethral relaxation, can occur during a urodynamic investigation. A possible explanation for this detrusor overactivity might be that the micturition reflex is triggered by unknown disturbances and is inhibited immediately after by the same mechanism that normally ceases voiding. The described model provides such a mechanism. Based on these simulations, therefore, it is concluded that urethral afferent signals might be important in lower urinary tract control.

Volume-evoked micturition reflex is mediated by the ventrolateral periaqueductal gray in anesthetized rats

The central pathway of the micturition reflex in the rat was investigated functionally by acute blockade of synaptic neurotransmission using microinjection of cobalt chloride into the periaqueductal gray or pontine tegmental region. In 27 urethan-anesthetized (1.2 g/kg ip) rats, the bladder pressure response to continuous infusion of the bladder with saline (0.1-0.25 ml/min) was assessed. Electromyographic activity of external urethral sphincter and arterial blood pressure were also monitored. Bladder contractions and external urethral sphincter activity were reversibly attenuated after unilateral or bilateral stereotaxic injections of 10 mM cobalt chloride into the caudal (bregma -7.80 to -8.80) ventrolateral periaqueductal gray as well as into Barrington's nucleus. Blood pressure was not affected by injection into either area. The results demonstrate that the caudal ventrolateral periaqueductal gray, in addition to Barrington's nucleus, is a critical part of the long-routed micturition reflex circuitry in the anesthetized rat.

Retrograde and transganglionic transport of horseradish peroxidase-conjugated cholera toxin B subunit, wheatgerm agglutinin and isolectin B4 from Griffonia simplicifolia I in primary afferent neurons innervating the rat urinary bladder

In the present study, we investigated and compared the ability of the cholera toxin B subunit, wheat germ agglutinin and isolectin B4 from Griffonia simplicifolia I conjugated to horseradish peroxidase, to retrogradely and transganglionically label visceral primary afferents after unilateral injections into the rat urinary bladder wall. Horseradish peroxidase histochemical or lectin-immunofluorescence histochemical labelling of bladder afferents was seen in the L6-S1 spinal cord segments and in the T13-L2 and L6-S1 dorsal root ganglia. In the lumbosacral spinal cord, the most intense and extensive labelling of bladder afferents was seen when cholera toxin B subunit-horseradish peroxidase was injected. Cholera toxin B subunit-horseradish peroxidase-labelled fibres were found in Lissauer's tract, its lateral and medial collateral projections, and laminae I and IV-VI of the spinal gray matter. Labelled fibres were numerous in the lateral collateral projection and extended into the spinal parasympathetic nucleus. Labelling from both the lateral and medial projections extended into the dorsal grey commissural region. Wheat germ agglutinin-horseradish peroxidase labelling produced a similar pattern but was not as dense and extensive as that of cholera toxin B subunit-horseradish peroxidase. The isolectin B4 from Griffonia simplicifolia I-horseradish peroxidase-labelled fibres, on the other hand, were fewer and only observed in the lateral collateral projection and occasionally in lamina I. Cell profile counts showed that a larger number of dorsal root ganglion cells were labelled with cholera toxin B subunit-horseradish peroxidase than with wheat germ agglutinin- or isolectin B4-horseradish peroxidase. In the L6-S1 dorsal root ganglia, the majority (81%) of the cholera toxin B subunit-, and almost all of the wheat germ agglutinin- and isolectin B4-immunoreactive cells were RT97-negative (an anti-neurofilament antibody that labels dorsal root ganglion neurons with myelinated fibres). Double labelling with other neuronal markers showed that 71%, 43% and 36% of the cholera toxin B subunit-immunoreactive cells were calcitonin gene-related peptide-, isolectin B4-binding- and substance P-positive, respectively. A few cholera toxin B subunit cells showed galanin-immunoreactivity, but none were somatostatin-, vasoactive intestinal polypeptide-, or neuropeptide Y-immunoreactive or contained fluoride-resistant acid phosphatase. The results show that cholera toxin B subunit-horseradish peroxidase is a more effective retrograde and transganglionic tracer for pelvic primary afferents from the urinary bladder than wheat germ agglutinin-horseradish peroxidase and isolectin B4-horseradish peroxidase, but in contrast to somatic nerves, it is transported mainly by unmyelinated fibres in the visceral afferents.

Bilateral projections of the pontine micturition center to the sacral parasympathetic nucleus in the rat

Previous work has revealed that pontine micturition center (PMC) neurons send projections to the sacral parasympathetic nucleus (SPN) of the intermediolateral (IML) regions of L6-S1 spinal cord segments in rats. Although unilateral SPN injections will retrogradely label PMC neurons bilaterally, it is not known whether single PMC neurons project bilaterally to the SPN. There may be two different populations of PMC neurons on each side of the brainstem, with both groups independently connecting to the SPNs on opposite sides of the spinal cord. To verify one of these alternatives, a small injection of either rhodamine-labeled latex microspheres or a red fluorescent emulsion was made into the SPN on one side of the cord; a similar injection of either fluorescein-tagged microspheres or a green fluorescent emulsion was made into the other. After at least seven days, the rats were perfused. Inspection of 40 micron cord sections confirmed the similar placement of these injections along the rostrocaudal axis of the cord and that no tracer had spread across midline. Thirty-micron brain sections were examined for filled neurons. Red, green and double labeled neurons were found bilaterally in the PMC, subcoeruleus, and A5 regions. Although some red nucleus cells were also filled, they were only singly labeled and always located contralateral to the injection. Finally, immunohistochemical staining of dopamine-beta-hydroxylase (DBH) containing cells confirmed that some labeled cells were also noradrenergic. We therefore conclude that some PMC, subcoeruleus, and A5 neurons send axons to the SPN on both sides of the lumbosacral cord.

Direct projections from the periaqueductal gray to pontine micturition center neurons projecting to the lumbosacral cord segments: an electron microscopic study in the rat

Direct projections from the periaqueductal gray (PAG) to the pontine micturition center neurons directly projecting to the lumbosacral cord segments were observed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the PAG and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. After injection of BDA into the ventrolateral part of the PAG, many BDA-labeled axons were seen light microscopically in Barrington's nucleus; a moderate number of them were found in the pontine tegmental region just ventral to Barrington's nucleus (D-region [Ding, Y-Q., Takada, M., Tokuno, H. and Mizuno, N., J. Comp. Neurol., 357 (1996) 318-330]). On the other hand, after injection of BDA into the dorsolateral part of the PAG, only a few BDA-labeled axons were seen in Barrington's nucleus or the D-region. BDA-labeled axon terminals were electron microscopically confirmed to be in synaptic contact with HRP-labeled dendrites and somata in Barrington's nucleus and the D-region. The results indicate that the ventrolateral part of the PAG is implicated in regulation of the micturition reflex.

Direct projections from the lumbosacral spinal cord to Barrington's nucleus in the rat: a special reference to micturition reflex

In the present study, direct projections from the lumbosacral cord to Barrington's nucleus in the rat were investigated by using retrograde and anterograde tracing techniques. After injection of cholera toxin B subunit (CTb) into Barrington's nucleus, a number of moderately CTb-labeled neurons were observed in the lumbosacral cord, with a slight ipsilateral dominance; most were located in the spinal parasympathetic and dorsal commissural nuclei of the lumbosacral cord. In addition, some retrogradely labeled neurons were found in the periaqueductal gray (PAG). These findings were confirmed by an anterograde labeling experiment. After biotinylated dextran amine (BDA) was injected into the lumbosacral cord, dense BDA-labeled axon terminals were found in Barrington's nucleus as well as in the PAG. Injection of BDA into the PAG resulted in many BDA-labeled terminals in Barrington's nucleus. The present results provided clear evidence for a direct projection from the spinal parasympathetic and dorsal commissural nuclei to Barrington's nucleus that could subserve conveying bladder-filling information from the lumbosacral cord to Barrington's nucleus in the micturition reflex of the rat.

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.

Neurons in the rat brain and spinal cord labeled after pseudorabies virus injected into the external urethral sphincter

Male Sprague-Dawley rats, with their pelvic and hypogastric nerves transected, were infected with pseudorabies virus (PRV) injected into the external urethral sphincter. Animals were sacrificed at 2, 2.5, 3, and 4 days postinfection. Spinal cord and brain tissue were sectioned and processed by immunohistochemical techniques with antisera against PRV and choline acetyl transferase (CAT). At 2 days postinfection, virus-labeled neurons were found in the ventrolateral divisions of Onuf's nucleus and in the dorsal gray commissure (DGC). At progressively later incubation times, labeled neurons were found in the intermediolateral regions, the superficial layer of the dorsal horn, and the brainstem, in particular, the pontine micturition center. PRV/CAT-positive neurons were only found in Onuf's nucleus. Preganglionic neurons in the L6-S1 intermediolateral regions were CAT positive but PRV negative, thus suggesting that they are interneurons, not sacral parasympathetic preganglionic neurons. After 4 days, virus had spread to neurons in the paraventricular, preoptic, and even cortical regions. The distribution of these PRV-labeled brain neurons strongly resembled that obtained after the injection of PRV into the urinary bladder (Nadelhaft et al. [1992] Neurosci. Lett. 143:271-274). In both cases, neurons were labeled in the DGC in the spinal cord. The data therefore suggest that neurons in the DGC may be involved in the integrated control of the bladder and the external urethral sphincter.

Single neurons in Barrington's nucleus projecting to both the paraventricular thalamic nucleus and the spinal cord by way of axon collaterals: a double labeling study in the rat

Barrington's nucleus, a center for the micturition reflex in the pontine tegmentum, was recently reported to send projection fibers to the paraventricular thalamic nucleus (PVT). In the present study, we examined whether or not Barrington's nucleus neurons projecting to the PVT issue axon collaterals to the lowest lumbar cord segment (L6) containing the spinal micturition center. Our retrograde double-labeling study revealed that a subset of Barrington's nucleus neurons send projection fibers to both the L6 and the thalamic midline including the PVT via axon collaterals. Such neurons projecting directly to the thalamic midline and L6 by way of axon collaterals were additionally scattered in the locus coeruleus, subcoeruleus nucleus and sublaterodorsal nucleus.