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

Anatomical and physiological properties of pelvic ganglion neurons in female mice

Most neurons that regulate motility and blood flow in female pelvic organs are located within pelvic (paracervical) ganglia. In this study we investigated the anatomical and physiological properties of neurons within mouse (C57/Bl/6) paracervical ganglia. Most neurons showed immunoreactivity for choline acetyl transferase (CHAT) and were presumably cholinergic. Few neurons (approximately 5%) were tyrosine hydroxylase (TH) positive. Immunohistochemical labelling for microtubule associated protein 2 showed most neurons had small somata (cross sectional area approximately 300 microm(2)) and lacked dendrites. Action potential (AP) discharge characteristics, determined by depolarising current step injection, revealed most neurons (70%) adapted rapidly to depolarising current injection and were classified as "phasic". The remaining neurons discharged APs throughout the current step and were classified as "tonic". Membrane properties and current-voltage relationships were similar in phasic and tonic neurons, however the afterhyperpolarisation was significantly smaller in tonic neurons. Stimulation of preganglionic axons usually evoked a single strong preganglionic input (21/27 and 9/10 for pelvic and hypogastric nerves, respectively). In 19 preparations where we tested for inputs from both nerves pelvic inputs predominated (23/45 neurons) and inputs via the hypogastric nerve were rarely observed (3/45 neurons). Together, our data indicate that most neurons within mouse paracervical ganglia are cholinergic and parasympathetic. As there is little anatomical or functional evidence for integration of preganglionic inputs we propose that the role of paracervical neurons is restricted to one of spatial amplification or filtering of preganglionic inputs.

Herpes simplex virus vector-mediated delivery of glial cell line-derived neurotrophic factor rescues erectile dysfunction following cavernous nerve injury

Erectile dysfunction (ED) is frequently associated with injury to the cavernous nerve sustained during pelvic surgery. Functional recovery from cavernous nerve injury is generally incomplete and occurs over an extended time frame. We employed a therapeutic gene transfer approach with herpes simplex virus (HSV) vector expressing glial cell line-derived neurotrophic factor (GDNF). Rat cavernous nerve was injured bilaterally using a clamp and dry ice. For HSV-treated groups, 20 microl of purified vector stock was administered directly to and around the damaged nerve. Delivery of an HSV vector expressing both green fluorescent protein (GFP) and lacZ (HSV-LacZ) was used as a control. Intracavernous pressure along with systemic arterial pressure (ICP/AP) was measured 2 and 4 weeks after the nerve injury. Fluorogold (FG) was injected into the penile crus 7 days before killing to assess nerve survival. Approximately 60% of major pelvic ganglion (MPG) cells were GFP positive after viral administration. At 4 weeks after nerve injury, rats treated with HSV-GDNF exhibited significant recovery of ICP/AP compared with control vector or untreated groups. The HSV-GDNF group also yielded more FG-positive MPG cells than the control vector group. HSV vector-mediated delivery of GDNF presents a viable approach for the treatment of ED following cavernous nerve injury.

Electrical properties of neurons in the intact rat major pelvic ganglion

The aim of this investigation was to characterize the electrical properties of neurons in the rat major pelvic ganglia (MPG) using intracellular recording techniques. MPG were dissected from male rats euthanized by isoflurane and thoracotomy. Neurons were classified as "phasic" or "tonic" according to their rate of accommodation during a 500-ms depolarizing current pulse. Phasic cells were further subdivided into rapidly or slowly adapting. The firing pattern of tonic cells was divided into regular high frequency, low frequency or irregular firing. In tonic cells, onset spikes showed TTX-resistant discharges; whereas sustained spikes were TTX sensitive. Changing the current pulse amplitude or the stimulation interval could alter the firing pattern in both types of neurons. Subthreshold membrane potential oscillations (SMPOs) were primarily observed when neurons were depolarized. SMPOs were Na(+) dependent and TTX sensitive. The majority of tonic and phasic neurons generated rebound spikes, most of which were partially Na(+) dependent. A small percentage (<6%) of neurons exhibited spontaneous activity. Taken together these findings are consistent with the concept that neurons in the MPG exhibit heterogeneous electrical properties.

Transient suppression of the vesicular acetylcholine transporter in urinary bladder pathways following spinal cord injury

The aim of this study was to examine the expression profile of the vesicular acetylcholine transporter (VAChT), which is a cholinergic pre-synaptic marker, in the lower neural tract following spinal cord injury (SCI) and its effect on coordination of micturition. In adult female Sprague-Dawley rats, SCI was induced by complete transection of the spinal cord at T9. At various time points, 3, 7, 14 and 28 days, after SCI, cystometry was performed on conscious rats. Bladder areflexia was observed during the first week. Twenty-eight days after SCI the rats showed reflex contractions and voiding. The expression of VAChT was examined with immunohistochemistry. The number of VAChT-positive nerve terminals, which were surrounding neuronal soma, was transiently decreased in pelvic ganglion and spinal cord (L1, L2, L6 and S1). In particular VAChT terminals surrounding motor neurons in the ventral horn and autonomic pre-ganglion cells were dramatically decreased from 3 to 14 days after SCI. Similarly, and the number of VAChT-positive fibers in the bladder wall was also decreased. The intensity of VAChT terminals recovered in all above regions in conjunction with recovery of bladder function. These observations indicate that the transient decrease of the VAChT-positive nerve might cause a failure of cholinergic neuronal transmission along the urinary bladder tract after SCI. As the cholinergic system was recovered at least in rat, the functional recovery of neurogenic bladder syndrome in SCI patients may become possible by further understanding the mechanism underlying the recovery of cholinergic system in rat.

Sensory, motor somatic, and autonomic neurons projecting to the porcine cremaster muscle

The location of sensory, somatic, and autonomic neurons projecting to the pig cremaster muscle (CM) was studied by means of the retrograde neuronal tracer Fast Blue (FB) technique. FB was randomly injected in the left CM of four impuberal pigs and serial sections of sensory and autonomic ganglia and spinal cord were examined under a fluorescence microscope. Additionally, some indications about the number and size of labeled neurons were given. Sensory pseudounipolar somata were located ipsilaterally in the L2-L6 and S1-S2 dorsal root ganglia, their total number ranging between 125 and 194, their mean diameter between 24 and 89 microm. Somatic multipolar motoneurons were located ipsilaterally in the L2-L4 neuromeres of the spinal cord, their total number ranging between 53 and 169, their mean diameter between 29 and 53 microm. Autonomic multipolar paravertebral ganglia neurons were located ipsilaterally from L1 to S4 and contralaterally from L2 to S2. Their total number ranged from 2,015 to 3,067 and their mean diameter between 25 and 55 microm. The multipolar caudal mesenteric ganglia neurons were located bilaterally, their total number ranging between 14 and 1,408 and their diameter from 22 to 39 microm. In two subjects only, multipolar neurons were also found ipsilaterally in the microganglia of pelvic plexus (2 and 13 neurons). Their mean diameter ranged between 28 and 54 microm. Our study documented that the CM-projecting neurons were located at different neural levels, with a predominance in the autonomic ganglia.

Comparison of extrinsic efferent innervation of guinea pig distal colon and rectum

The extrinsic efferent innervation of the distal colon and rectum of the guinea pig was compared, by using retrograde tracing combined with immunohistochemistry. Application of the carbocyanine tracer DiI to the rectum filled significantly greater numbers of extrinsic neurons than similar injections into the distal colon. Approximately three-fourths of all filled neurons from either location were either sympathetic or parasympathetic; the rest were spinal sensory neurons. Nerve cell bodies in sympathetic prevertebral ganglia labelled from the two regions were similar in number. Both regions were innervated by sympathetic neurons in paravertebral ganglia; however, the rectum received much more input from this source than the colon. The rectum received significantly more input from pelvic ganglia than the colon. The rectum also received direct innervation from two groups of neurons in the spinal cord. Neurons located in the spinal parasympathetic nucleus in segment S2 and S3 were labelled by DiI injected into the rectal wall. Similar numbers of neurons, located in intermediolateral cell column and dorsal commissural nucleus of lumbar segments, also projected directly to rectum, but not colon. The great majority (>80%) of retrogradely labelled nerve cell bodies in sympathetic ganglia were immunoreactive for tyrosine hydroxylase. In pelvic ganglia, retrogradely labelled neurons contained choline acetyltransferase and/or nitric oxide synthase or tyrosine hydroxylase. Although the rectum and colon in this species are continuous and macroscopically indistinguishable, they have significantly different patterns of extrinsic efferent innervation, presumably reflecting their different functions.

Structural effects and potential changes in growth factor signalling in penis-projecting autonomic neurons after axotomy

Background

The responses of adult parasympathetic ganglion neurons to injury and the neurotrophic mechanisms underlying their axonal regeneration are poorly understood. This is especially relevant to penis-projecting parasympathetic neurons, which are vulnerable to injury during pelvic surgery such as prostatectomy. We investigated the changes in pelvic ganglia of adult male rats in the first week after unilateral cavernous (penile) nerve axotomy (cut or crush lesions). In some experiments FluoroGold was injected into the penis seven days prior to injury to allow later identification of penis-projecting neurons. Neurturin and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors for penile parasympathetic neurons, so we also examined expression of relevant receptors, GFRα1 and GFRα2, in injured pelvic ganglion neurons.

Results

Axotomy caused prolific growth of axon collaterals (sprouting) in pelvic ganglia ipsilateral to the injury. These collaterals were most prevalent in the region near the exit of the penile nerve. This region contained the majority of FluoroGold-labelled neurons. Many sprouting fibres formed close associations with sympathetic and parasympathetic pelvic neurons, including many FluoroGold neurons. However immunoreactivity for synaptic proteins could not be demonstrated in these collaterals. Preganglionic terminals showed a marked loss of synaptic proteins, suggesting a retrograde effect of the injury beyond the injured neurons. GFRα2 immunofluorescence intensity was decreased in the cytoplasm of parasympathetic neurons, but GFRα1 immunofluorescence was unaffected in these neurons.

Conclusion

These studies show that there are profound changes within the pelvic ganglion after penile nerve injury. Sprouting of injured postganglionic axons occurs concurrently with structural or chemical changes in preganglionic terminals. New growth of postganglionic axon collaterals within the ganglion raises the possibility of the formation of aberrant synaptic connections between injured and un-injured ganglion neurons. Together these changes demonstrate a broader effect on the pelvic autonomic circuitry than simply loss of neuroeffector connections. These structural changes are accompanied by potential changes in neurotrophic factor signalling due to altered expression of receptors for members of the GDNF family. Together our results advance understanding of the responses of pelvic autonomic nerve circuits to injury and may assist in designing strategies for promoting regeneration.

An α3β4 subunit combination acts as a major functional nicotinic acetylcholine receptor in male rat pelvic ganglion neurons

We identified major subunits of the nicotinic acetylcholine receptor (nAChR) involved in excitatory postsynaptic potential and intracellular Ca(2+) ([Ca(2+)]i) increase in the major pelvic ganglion (MPG) neurons of the male rat. ACh elicited fast inward currents in both sympathetic and parasympathetic MPG neurons. Mecamylamine, a selective antagonist for alpha3beta4 nAChR, potently inhibited the ACh-induced currents in sympathetic and parasympathetic neurons (IC(50); 0.53 and 0.22 microM, respectively). Furthermore, alpha-conotoxin AuIB (10 microM), a new selective antagonist for alpha3beta4 nAChR, blocked more than 80% of the ACh-induced currents in MPG neurons. Conversely, alpha-bungarotoxin, alpha-methyllycaconitine, and dihydro-beta-erythroidine, known as blockers of the alpha7 or alpha4beta2, did not show selective blocking effects on MPG neurons. ACh transiently increased [Ca(2+)]i which was subsequently abolished in the extracellular Ca(2+)-free environment. Simultaneous recording of [Ca(2+)]i and ionic currents revealed that ACh increased [Ca(2+)]i under the conditions of the voltage-clamped (at -80 mV) state, and this resulted from the influx through nAChR itself. ACh-induced [Ca(2+)]i increase was blocked by mecamylamine (10 microM), but was not affected by atropine (1 microM). RT-PCR analysis showed that, among subunits of nAChR, alpha3 and beta4 were predominantly expressed in MPG. We suggest that activation of alpha3 and beta4 nAChR subunits in MPG neurons induce fast inward currents and [Ca(2+)]i increase, possibly mediating a major role in pelvic autonomic synaptic transmission.

Plasticity of pelvic autonomic ganglia and urogenital innervation

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

Neurturin has multiple neurotrophic effects on adult rat sacral parasympathetic ganglion neurons

Neurturin (NTN) is an important neurotrophic factor for parasympathetic neurons; however, no studies to date have investigated the signalling mechanisms downstream of GFRalpha2 and Ret activation underlying this neurotrophic support. This is particularly important for pelvic parasympathetic neurons, which are prone to injury during surgical procedures such as prostatectomy, and where there are no current therapies for axonal regeneration. To address this issue we have cultured dissociated adult rat pelvic ganglion neurons and also examined the structural changes in pelvic ganglion neurons after axotomy. Axotomised penile neurons deprived of target-derived support had smaller somata than intact neurons. Studies of cultured adult pelvic ganglion neurons also demonstrated that NTN stimulated soma growth. Further experiments showed that NTN reduced the up-regulation of tyrosine hydroxylase expression in cultured pelvic parasympathetic neurons. NTN stimulated the extension of neurites in cultured parasympathetic, but not sympathetic, pelvic ganglion neurons. Inhibition of phosphatidylinositol 3-kinase prevented initiation of neurite outgrowth, whereas inhibition of the mitogen-activated protein kinase and the Src family kinase pathways disrupted NTN-stimulated microtubule assembly. Surprisingly, NTN did not activate the transcription factor cAMP-response element binding protein (CREB), which is typically involved in neurotrophic signalling in sympathetic neurons. This is the first study to identify signalling pathways activated by NTN in adult parasympathetic neurons. Our results may lead to a better understanding of regenerative mechanisms in parasympathetic neurons, especially for those innervating urogenital organs. Our results also indicate that neurotrophic signalling in parasympathetic neurons is different from that in other types of peripheral neurons.

Neurotrophin-3 is a target-derived neurotrophic factor for penile erection-inducing neurons

The aim of this study was to determine whether the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3 could act as endogenous target-derived trophic factors for erection-inducing, i.e. penis-projecting major pelvic ganglion (MPG) neurons, and/or penile sensory neurons in adult rat. This was accomplished by studying the expression of NT mRNAs in the penis and their cognate receptors in the MPG and dorsal root ganglia (DRGs), and the retrograde axonal transport of radioiodinated NTs injected into the corpora cavernosa. Northern hybridization showed that NGF, BDNF, and NT-3 mRNAs are expressed in the shaft of the penis. In situ hybridization combined with usage of the retrograde tracer Fluoro-Gold showed that TrkC and p75 receptors are expressed in penis-projecting neurons of the MPG whereas the mRNAs for TrkA and TrkB receptors were undetectable. However, all the NT receptor mRNAs were expressed in penile sensory neurons of sacral level 1 (S1) DRG. (125)I-NT-3 injected into the shaft of the penis was retrogradely transported into the MPG and S1 DRG, whereas radioiodinated NGF and BDNF were transported specifically into the S1 DRG, thus confirming the existence of functional NT receptors in these penile neurons. In conclusion, these data suggest that NT-3 may act as a target-derived neurotrophic factor for both erection-inducing and penile sensory neurons, whereas NGF and BDNF may be more important for the sensory innervation of the penis.

Post-stimulus potentiation of transmission in pelvic ganglia enhances sympathetic dilatation of guinea-pig uterine artery in vitro

Vasodilatation produced by stimulation of preganglionic neurones in lumbar and sacral pathways to pelvic ganglia was studied using an in vitro preparation of guinea-pig uterine artery and associated nerves in a partitioned bath allowing selective drug application to the ganglia or artery. Arterial diameter was monitored using real time video imaging. Vasodilatations produced by hypogastric nerve stimulation (HN; 300 pulses, 10 Hz) were significantly larger and longer in duration than with pelvic nerve stimulation (N = 18). Stimulation of ipsilateral lumbar splanchnic nerves or ipsilateral third lumbar ventral roots also produced prolonged vasodilatations. Blockade of ganglionic nicotinic receptors (0.1-1 mM hexamethonium) delayed the onset and sometimes reduced the peak amplitude of dilatations, but slow dilatations persisted in 16 of 18 preparations. These dilatations were not reduced further by 3 microM capsaicin applied to the artery and ganglia, or ganglionic application of 1 microM hyoscine, 30-100 microM suramin or 10 microM CNQX. Dilatations were reduced slightly by ganglionic application of NK1 and NK3 receptor antagonists (SR140333, SR142801; 1 microM), but were reduced significantly by bathing the ganglia in 0.5 mM Ca2+ and 10 mM Mg2+. Intracellular recordings of paracervical ganglion neurones revealed fast excitatory postsynaptic potentials (EPSPs) in all neurones on HN stimulation (300 pulses, 10 Hz), and slow EPSPs (3-12 mV amplitude) in 25 of 37 neurones. Post-stimulus action potential discharge associated with slow EPSPs occurred in 16 of 37 neurones (firing rate 9.4 +/- 1.5 Hz). Hexamethonium (0.1-1 mM) abolished fast EPSPs. Hexamethonium and hyoscine (1 microM) did not reduce slow EPSPs and associated post-stimulus firing in identified vasodilator neurones (with VIP immunoreactivity) or non-vasodilator paracervical neurones. These results demonstrate a predominantly sympathetic origin of autonomic pathways producing pelvic vasodilatation in females. Non-cholinergic mediators of slow transmission in pelvic ganglia produce prolonged firing of postganglionic neurones and long-lasting dilatations of the uterine artery. This mechanism would facilitate maintenance of pelvic vasodilatation on stimulation of preganglionic neurones during sexual activity.

Remodelling of connections in pelvic ganglia after hypogastric nerve crush

Pelvic ganglia innervate the urogenital organs and contain both sympathetic and parasympathetic neurons. Previous studies have shown that within days of cutting either the lumbar or sacral preganglionic axons that innervate pelvic ganglia, many axon collaterals grow and appear to form specific connections with denervated pelvic neurons. Here we have examined the longer term consequences of partial deafferentation by studying pelvic ganglia up to 7 weeks after hypogastric nerve (HGN) crush, a lesion which also allows faster regeneration of spinal axons. Noradrenergic neurons were denervated by HGN crush, as demonstrated by loss of varicosities immunostained for the synaptic proteins, synaptophysin and synapsin. A week after HGN crush, axon collaterals grew from parasympathetic pelvic ganglion neurons, shown by the presence of numerous varicose fibers immunostained for vasoactive intestinal peptide (VIP). These VIP fibers were poorly stained or unstained for synaptophysin, even after 7 weeks. At early post-operative times the VIP fibers grew irregularly; however, with longer post-operative times they appeared to target particular VIP-negative, noradrenergic neurons. Our results also indicate that some lumbar preganglionic axons regenerated during the post-operative period, although this only affected a minority of sympathetic neurons. These reinnervated sympathetic neurons were not associated with VIP fibers, suggesting that the new intrinsic connections may have precluded regeneration or targeting of preganglionic axons. Together these results demonstrate that there is considerable remodelling within pelvic ganglia after partial deafferentation. This occurs under conditions where spinal preganglionic axons can regenerate. New intra-ganglionic connectivity may be permanent and may impact on this regeneration.

Artificial autonomic reflexes: using functional electrical stimulation to mimic bladder reflexes after injury or disease

Autonomic reflexes controlling bladder storage (continence) and emptying (micturition) involve spinal and supraspinal nerve pathways, with complex mechanisms coordinating smooth muscle activity of the lower urinary tract with voluntary muscle activity of the external urethral sphincter (EUS). These reflexes can be severely disrupted by various diseases and by neurotrauma, particularly spinal cord injury (SCI). Functional electrical stimulation (FES) refers to a group of techniques that involve application of low levels of electrical current to artificially induce or modify nerve activation or muscle contraction, in order to restore function, improve health or rectify physiological dysfunction. Various types of FES have been developed specifically for improving bladder function and while successful for many urological patients, still require substantial refinement for use after spinal cord injury. Improved knowledge of the neural circuitry and physiology of human bladder reflexes, and the mechanisms by which various types of FES alter spinal outflow, is urgently required. Following spinal cord injury, physical and chemical changes occur within peripheral, spinal and supraspinal components of bladder reflex circuitry. Better understanding of this plasticity may determine the most suitable methods of FES at particular times after injury, or may lead to new FES approaches that exploit this remodeling or perhaps even influence the plasticity. Advances in studies of the neuroanatomy, neurophysiology and plasticity of lumbosacral nerve circuits will provide many further opportunities to improve FES approaches, and will provide "artificial autonomic reflexes" that much more closely resemble the original, healthy neuronal regulatory mechanisms.

Neurturin signalling via GFRα2 is essential for innervation of glandular but not muscle targets of sacral parasympathetic ganglion neurons

Neurturin, a member of the glial cell-derived neurotrophic factor familys of ligands, is important for development of many cranial parasympathetic ganglion neurons. We have investigated the sacral component of the parasympathetic nervous system in mice with gene deletions for neurturin or its preferred receptor, GFRalpha2. Disruption of neurturin signalling decreased cholinergic VIP innervation to the mucosa of the reproductive organs, but not to the smooth muscle layers of these organs or to the urinary bladder. Thus, neurturin and its receptor are involved in parasympathetic innervation of a select group of pelvic visceral tissues. In contrast, noradrenergic innervation was not affected by the gene ablations. The epithelium of reproductive organs from knockout animals was atrophied, indicating that cholinergic innervation may be important for the maintenance of normal structure. Cholinergic neurons express GFRalpha2 on their terminals and somata, indicating they can respond to neurotrophic support, and their somata are smaller when neurturin signalling is disrupted. Colocalisation studies showed that many peripheral glia express GFRalpha2 although its role in these cells is yet to be determined. Our results indicate that neurturin, acting through GFRalpha2, is essential for parasympathetic innervation of the mucosae of reproductive organs, as well as for maintenance of a broader group of sacral parasympathetic neurons.

Rapid actions of estradiol on cyclic amp response-element binding protein phosphorylation in dorsal root ganglion neurons

Actions of gonadal steroids have not been widely investigated in the peripheral nervous system, although many dorsal root ganglion (DRG) and autonomic pelvic ganglion (PG) neurons express estrogen receptors (ERs). We have studied the effects of 17beta-estradiol exposure on cultured DRG and PG neurons from adult rats. Western blotting analysis of DRG extracts detected phosphorylation of ERK1 and ERK2 (extracellular signal-regulated kinases) that peaked 10 min after exposure to 17beta-estradiol. These extracts contain both neurons and glia; therefore, to determine if this response occurred in DRG neurons, we developed an immunocytochemical method to specifically measure activation in individual neurons. These measurements showed that estradiol increased phosphorylation of CREB (cyclic AMP response-element binding protein), which was consistently blocked by the ERK pathway inhibitor PD98059 but not by the inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002. 17beta-Estradiol activation of CREB in DRG neurons was reduced by the ER antagonist, ICI182780. In contrast, in PG neurons estradiol did not affect CREB phosphorylation, highlighting a difference in E2 responses in different populations of peripheral neurons. This study has shown that estrogens can rapidly activate signaling pathways associated with CREB-mediated transcriptional regulation in sensory neurons. As these pathways also mediate many effects of neurotrophic factors, changes in estrogen levels (e.g. during puberty, pregnancy or menopause) could have broad-ranging genomic and non-genomic actions on urogenital pain sensation and reflex pathways.

Differential expression of calcium channels in sympathetic and parasympathetic preganglionic inputs to neurons in paracervical ganglia of guinea-pigs

Neurons in pelvic ganglia receive nicotinic excitatory post-synaptic potentials (EPSPs) from sacral preganglionic neurons via the pelvic nerve, lumbar preganglionic neurons via the hypogastric nerve or both. We tested the effect of a range of calcium channel antagonists on EPSPs evoked in paracervical ganglia of female guinea-pigs after pelvic or hypogastric nerve stimulation. omega-Conotoxin GVIA (CTX GVIA, 100 nM) or the novel N-type calcium channel antagonist, CTX CVID (100 nM) reduced the amplitude of EPSPs evoked after pelvic nerve stimulation by 50-75% but had no effect on EPSPs evoked by hypogastric nerve stimulation. Combined addition of CTX GVIA and CTX CVID was no more effective than either antagonist alone. EPSPs evoked by stimulating either nerve trunk were not inhibited by the P/Q calcium channel antagonist, omega-agatoxin IVA (100 nM), nor the L-type calcium channel antagonist, nifedipine (30 microM). SNX 482 (300 nM), an antagonist at some R-type calcium channels, inhibited EPSPs after hypogastric nerve stimulation by 20% but had little effect on EPSPs after pelvic nerve stimulation. Amiloride (100 microM) inhibited EPSPs after stimulation of either trunk by 40%, while nickel (100 microM) was ineffective. CTX GVIA or CTX CVID (100 nM) also slowed the rate of action potential repolarization and reduced afterhyperpolarization amplitude in paracervical neurons. Thus, release of transmitter from the terminals of sacral preganglionic neurons is largely dependent on calcium influx through N-type calcium channels, although an unknown calcium channel which is resistant to selective antagonists also contributes to release. Release of transmitter from lumbar preganglionic neurons does not require calcium entry through either conventional N-type calcium channels or the variant CTX CVID-sensitive N-type calcium channel and seems to be mediated largely by a novel calcium channel.

Functional organization of vasodilator neurons in pelvic ganglia of female guinea pigs: comparison with uterine motor neurons

Neurons producing vasodilation during reproductive activity constitute a large population of neurons in pelvic autonomic ganglia. We used intracellular recording, dye-filling and multiple-labeling immunohistochemistry to determine the morphology and electrophysiological properties of, and number of synaptic inputs to, vasodilator pelvic neurons in female guinea pigs. Vasodilator neurons, identified by their immunoreactivity for vasoactive intestinal peptide (VIP) and their location in paracervical ganglia, had simple dendritic arbors (1 primary dendrite) compared with nonvasodilator neurons (3 dendrites). Vasodilator neurons had more depolarized resting membrane potentials (-47 mV) than other paracervical neurons (-55 mV) and had smaller apparent cell capacitances (65 pF vs. 110 pF). Vasodilator and nonvasodilator neurons could not be distinguished on the basis of their action potential discharge characteristics or current voltage relationships. Most pelvic neurons ( approximately 70%) had tonic (slowly adapting) discharges. Fifty-five percent of vasodilator and 60% of nonvasodilator neurons showed inward rectification when hyperpolarized below -90 mV. Around 65% of neurons showed evidence of M-current. Both vasodilator and nonvasodilator neurons ( approximately 80%) expressed an A-like current. Vasodilator neurons and nonvasodilator neurons received 1-2 fast synaptic inputs following stimulation of pelvic or hypogastric nerve trunks. Most neurons received a least one strong synaptic input. These results indicate that vasodilator neurons and neighboring neurons projecting to other pelvic targets, primarily in the myometrium, express a similar range of ionic conductances and integrate few synaptic inputs. The similarities between these two populations of neurons may be related to their coactivation as part of spinal somato-pelvic reflexes. Vasodilation and uterine contraction during reproductive behavior in female guinea pigs are likely to involve input from preganglionic neurons at both lumbar and sacral spinal levels.

Immunohistochemical characterisation of pelvic autonomic ganglia in male mice

Pelvic ganglia are mixed sympathetic-parasympathetic ganglia and provide the majority of the autonomic innervation to the urogenital organs. Here we describe the structural and histochemical features of the major pelvic ganglion in the male mouse and compare two different mouse strains. The basic structural features of the ganglion are similar to those in the male rat. Almost all pelvic ganglion cells are monopolar and most are cholinergic. All contain either neuropeptide Y (NPY) or vasoactive intestinal peptide (VIP), or both peptides together. The peptide coexistence varies between strains, with C57BL/6 mice having similar proportions of neurons with NPY alone, VIP alone or both peptides. In contrast, virtually all pelvic neurons in the Quackenbush-Swiss (QS) strain express NPY, i.e. the level of VIP/NPY coexistence is much higher. Cholinergic axons provide the major nerve supply to epithelia of reproductive organs, bladder smooth muscle and, as described previously, penile erectile tissue. They also provide a minor component of the smooth muscle innervation of the prostate gland, seminal vesicles and vas deferens. Virtually all non-cholinergic pelvic ganglion cells are noradrenergic and contain NPY. Their major target is smooth muscle of reproductive organs. This study shows that the male mouse pelvic ganglion bears many similarities to that in the rat, but that VIP/NPY colocalisation is much more common in the mouse. We also show that there are differences in peptide expression in parasympathetic pelvic neurons between strains of mice. These studies provide the framework for future investigations on neural regulation of urogenital function, particularly in transgenic and knockout models.

Postnatal maturational changes in rat pelvic autonomic ganglion cells: a mixture of steroid-dependent and -independent effects

Androgens have potent effects on the maturation and maintenance of a number of neural pathways involved in reproductive behaviors in males. Most studies in this area have focused on central pathways, but androgen receptors are expressed by many peripheral neurons innervating reproductive organs, and previous studies have demonstrated structural and chemical changes in these neurons at puberty and after castration. We have performed the first electrophysiological comparison of pelvic autonomic ganglion neurons in male rats before and after puberty and following pre- or postpubertal castration. Studies were performed in vitro on intact ganglia with hypogastric and pelvic nerves attached to allow synaptic activation of sympathetic or parasympathetic neurons, respectively. Pelvic ganglion neurons underwent many changes in their passive and active membrane properties over the pubertal period, and some of these changes were dependent on exposure to circulating androgens. The most pronounced steroid-dependent effects were on membrane capacitance (soma size) in sympathetic neurons and duration of the action potential afterhyperpolarization in tonic neurons. Our study also showed that rat pelvic ganglion cells and their synaptic inputs were more diverse than previously reported. In conclusion, this study demonstrated that rat pelvic ganglion neurons undergo considerable postnatal changes in their electrophysiological properties. The steroid dependence of some of these changes indicates that circulating androgens may influence reproductive behaviors at many locations within the nervous system not just in the brain and spinal cord.

Maturational and maintenance effects of testosterone on terminal axon density and neuropeptide expression in the rat vas deferens

Testosterone causes growth of many pelvic ganglion cells at puberty and their maintenance during adulthood. Here we have focused on two populations of pelvic ganglion cells that project to the rat vas deferens: noradrenergic neurons that innervate the smooth muscle and synthesize neuropeptide Y, and cholinergic neurons that primarily innervate the mucosa and contain vasoactive intestinal peptide. We have assessed the muscle innervation after pre- or postpubertal castration, using immunohistochemistry to determine axon density and radioimmunoassay to quantify levels of neuropeptides in tissue extracts. Our results show that androgen deprivation in each period causes substantial effects. Noradrenergic axons in the muscle increase in density after castration, partly due to organ size being smaller than age-matched controls. However, when corrected for target size, there is an overall decrease in total number of axons. This implies that androgen exposure at puberty has a direct effect on neurons to ensure that the adult pattern of innervation is attained, and that this is not simply by matching terminal field to target size. Similar effects of pre- and postpubertal castration imply that continued exposure to testosterone is necessary to maintain normal target innervation. Castration in both time periods increased the density of axons containing vasoactive intestinal peptide, however the effects of castration on the total number of these axons in the muscle were more variable. The concentration of vasoactive intestinal peptide increased substantially following either pre- or postpubertal castration although absolute amounts per vas deferens were decreased. Effects on neuropeptide Y concentration were less pronounced but the total amount per vas deferens was decreased after pre- or postpubertal castration. Our study shows that the action of testosterone (or a metabolite) on a pelvic ganglion cell soma is likely to reflect a change in its terminal field, but that these effects are not mediated simply by testosterone influencing the size of its target organ.

An investigation of the effects of zaprinast, a PDE inhibitor, on the nitrergic control of the urethra in anaesthetized female rats

1. The effects of L-NAME and zaprinast were investigated (i.v.) on reflex-evoked changes in bladder and urethral pressures in urethane-anaesthetized female rats. 2. L-NAME attenuated reflex-evoked urethral relaxations (65+/-10%), while zaprinast potentiated these responses (68+/-24%). L-NAME and zaprinast also increased baseline urethral pressure and urethral striated muscle (EUS-EMG) activity. These drugs had little effect on the bladder. 3. Following pre-treatment with alpha-bungarotoxin (i.v.) to block urethral striated muscle, L-NAME and zaprinast failed to increase baseline urethral pressure. Further zaprinast failed to alter the size of reflex-evoked urethral relaxations. 4. Intra-urethral zaprinast caused a significant increase while sodium nitroprusside (SNP) and isoprenaline caused decreases in urethral pressure (+14+/-3%, -25+/-5%, -29+/-7%, respectively). These changes were associated with increases in EUS-EMG activity. After chlorisondamine (i.v.), zaprinast caused a significant fall in urethral pressure, while the decrease in urethral pressure caused by SNP and isoprenaline was potentiated. No changes in EUS-EMG activity occurred. 5. These results indicate that a nitrergic pathway mediates reflex-evoked urethral smooth muscle relaxations. The data also indicates that there is a background release of NO, which reduces sphincter skeletal muscle activity. Further, the ability of zaprinast to potentiate nitrergic evoked urethral relaxations involves an increase in striated muscle tone. This appears to be an indirect result of smooth muscle relaxation and is mediated, at least in part, by a chlorisondamine-sensitive mechanism.

Testosterone and nerve growth factor have distinct but interacting effects on structure and neurotransmitter expression of adult pelvic ganglion cells in vitro

Circulating testosterone has potent effects on the structure and function of many pelvic ganglion cells in adult rats in vivo. However not all androgen-sensitive pelvic neurones possess androgen receptors and testosterone effects may therefore be indirect, by an action on the target organs. Here we have examined if testosterone influences neuronal structure in vitro in pelvic ganglion cells cultured from adult male rats. We have also used multiple label immunofluorescence to monitor the expression of transmitter-synthesising enzymes and peptides under various culture conditions. Testosterone was a more potent stimulant of noradrenergic soma growth in culture than nerve growth factor. Whereas nerve growth factor increased the number, branching and length of neurites, testosterone stimulated growth of a small number of very short processes, each of which bore numerous short protrusions. Testosterone also impeded the longer neurite growth induced by nerve growth factor. Many pelvic ganglion cells altered their expression of transmitters/neuropeptides under different culture conditions. In particular, under control conditions or during nerve growth factor treatment, vasoactive intestinal peptide was up-regulated in noradrenergic and cholinergic neurones; testosterone impeded this up-regulation in noradrenergic neurones. Choline acetyltransferase immunoreactivity could only be visualised when nerve growth factor was present in the cultures, and cholinergic neurones showed less neurite outgrowth than noradrenergic neurones under all culture conditions. Nerve growth factor did not stimulate levels of this enzyme as strongly if testosterone was present. This study has shown that testosterone has potent effects on the structure of many pelvic ganglion cells in vitro. It is possible that these effects are mediated indirectly, e.g. by stimulating glial-derived substances, however our results suggest that the effects are not mediated by nerve growth factor. The results also show that testosterone influences some of the actions of nerve growth factor, suggesting that there may be complex interactions between steroid signalling and neurotrophic factors in maintaining neuronal structure and function in vivo.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

Cocaine- and amphetamine-regulated transcript peptide in the rat epididymis: an immunohistochemical and electrophysiological study

Cocaine- and amphetamine-regulated transcript (CART) is a novel family of peptides, of which CART peptide fragments 55-102 and 62-102 are reported to be the endogenous, physiologically active peptides. Immunohistochemical studies with an antiserum directed against the CART peptide fragment 55-102 revealed CART-like immunoreactive (CART-LI) nerve fibers in the rat epididymis. The number was highest in the cauda epididymis and became progressively fewer toward the caput epididymis; the vas deferens exhibited an abundance of CART-LI fibers. Injection of the retrograde tracer Fluorogold (Fluorochrome, Inc., Englewood, CO) to the junction between the vas deferens and cauda epididymis labeled a large number of neurons in the major pelvic ganglion, some of which were CART-positive. Double-labeling the ganglion sections with tyrosine hydroxylase (TH) and CART antisera revealed that CART-LI and TH-LI were expressed in two distinct populations of ganglion cells. Some of the TH-LI cells in the ganglia, however, were covered with web-like CART-LI endings. The effects of CART peptide 55-102, referred to herein as CART, on anion secretion in the form of short circuit currents (Isc) were assessed in cultured epithelia. The CART (1 to 5 microM) applied to the basolateral or apical side of the cultured epithelia caused no significant responses on Isc, whereas lys-bradykinin (1 microM) produced a large Isc response in the same preparations. Our results show that CART-LI is present in a population of rat pelvic ganglion cells, which may give rise to CART-LI nerve fibers as observed in the vas deferens and the epididymis. The biological function of CART in the rat epididymis is not known, but it apparently is not involved in ion secretion across the epithelium.

Transmitter profile and spinal inputs of pelvic ganglion cells projecting with preganglionic axons along the hypogastric and pelvic nerves of the male rat

Pelvic autonomic ganglion cells receive spinal preganglionic inputs via the hypogastric (lumbar) or pelvic (sacral) nerves. Damage to these nerves stimulates axogenesis (sprouting) from pelvic ganglion cells and two possible triggers are deafferentation (decentralisation) or, if some ganglion cells project centrally in these nerves, axotomy. We have used a combination of retrograde tracing and immunohistochemistry in male rats to identify the number of pelvic ganglion cells that project centrally along these nerves, their transmitter type and the spinal level of their preganglionic inputs. Only a small number (<1%) of pelvic ganglion cells project along these nerves; 29-65 project in each hypogastric nerve and 41-71 in each pelvic nerve. These neurons comprise of both cholinergic and noradrenergic classes and the majority receive preganglionic inputs from the nerve in which they also project. These results suggest that damage of the hypogastric and pelvic nerves close to the pelvic ganglion is unlikely to cause axotomy of many pelvic ganglion cells. Therefore deafferentation rather than axotomy is likely to be the primary trigger of axogenesis occurring in pelvic ganglia after these lesions.