Five inhibitory transmitters coexist in pelvic autonomic vasodilator neurons

The diversity of neuronal phenotypes in rodent and human autonomic ganglia

Selective sympathetic and parasympathetic pathways that act on target organs represent the terminal actors in the neurobiology of homeostasis and often become compromised during a range of neurodegenerative and traumatic disorders. Here, we delineate several neurotransmitter and neuromodulator phenotypes found in diverse parasympathetic and sympathetic ganglia in humans and rodent species. The comparative approach reveals evolutionarily conserved and non-conserved phenotypic marker constellations. A developmental analysis examining the acquisition of selected neurotransmitter properties has provided a detailed, but still incomplete, understanding of the origins of a set of noradrenergic and cholinergic sympathetic neuron populations, found in the cervical and trunk region. A corresponding analysis examining cholinergic and nitrergic parasympathetic neurons in the head, and a range of pelvic neuron populations, with noradrenergic, cholinergic, nitrergic, and mixed transmitter phenotypes, remains open. Of particular interest are the molecular mechanisms and nuclear processes that are responsible for the correlated expression of the various genes required to achieve the noradrenergic phenotype, the segregation of cholinergic locus gene expression, and the regulation of genes that are necessary to generate a nitrergic phenotype. Unraveling the neuron population-specific expression of adhesion molecules, which are involved in axonal outgrowth, pathway selection, and synaptic organization, will advance the study of target-selective autonomic pathway generation.

Morphological and neurochemical differences in peptidergic nerve fibers of the mouse vagina

The vagina is innervated by a complex arrangement of sensory, sympathetic, and parasympathetic nerve fibers that contain classical transmitters plus an array of neuropeptides and enzymes known to regulate diverse processes including blood flow and nociception. The neurochemical characteristics and distributions of peptide-containing nerves in the mouse vagina are unknown. This study used multiple labeling immunohistochemistry, confocal maging and analysis to investigate the presence and colocalization of the peptides vasoactive intestinal polypeptide (VIP), calcitonin-gene related peptide (CGRP), substance P (SP), neuropeptide tyrosine (NPY), and the nitric oxide synthesizing enzyme neuronal nitric oxide synthase (nNOS) in nerve fibers of the murine vaginal wall. We compared cervical and vulvar areas of the vagina in young nullipara and older multipara C57Bl/6 mice, and identified differences including that small ganglia were restricted to cervical segments, epithelial fibers were mainly present in vulvar segments and most nerve fibers were found in the lamina propria of the cervical region of the vagina, where a higher number of fibers containing immunoreactivity for VIP, CGRP, SP, or nNOS were found. Two populations of VIP-containing fibers were identified: fibers containing CGRP and fibers containing VIP but not CGRP. Differences between young and older mice were present in multiple layers of the vaginal wall, with older mice showing overall loss of innervation of epithelium of the proximal vagina and reduced proportions of VIP, CGRP, and SP containing nerve fibers in the distal epithelium. The distal vagina also showed increased vascularization and perivascular fibers containing NPY. Immunolabeling of ganglia associated with the vagina indicated the likely origin of some peptidergic fibers. Our results reveal regional differences and age- or parity-related changes in innervation of the mouse vagina, effecting the distribution of neuropeptides with diverse roles in function of the female genital tract.

Functional organization of autonomic neural pathways

There is now abundant functional and anatomical evidence that autonomic motor pathways represent a highly organized output of the central nervous system. Simplistic notions of antagonistic all-or-none activation of sympathetic or parasympathetic pathways are clearly wrong. Sympathetic or parasympathetic pathways to specific target tissues generally can be activated tonically or phasically, depending on current physiological requirements. For example, at rest, many sympathetic pathways are tonically active, such as those limiting blood flow to the skin, inhibiting gastrointestinal tract motility and secretion, or allowing continence in the urinary bladder. Phasic parasympathetic activity can be seen in lacrimation, salivation or urination. Activity in autonomic motor pathways can be modulated by diverse sensory inputs, including the visual, auditory and vestibular systems, in addition to various functional populations of visceral afferents. Identifying the central pathways responsible for coordinated autonomic activity has made considerable progress, but much more needs to be done.

Sensory and autonomic neurons project both to the smooth retractor penis and to the striated bulbospongiosus muscles. Neurochemical features of the sympathetic subset

Aim of the present study was to verify, by means of double retrograde neuronal tracers technique, the hypothesis that a subpopulation of sensory and autonomic neurons send collateral axons to both smooth and striated genital muscles. We also wanted to define the neurochemical content of the eventually retrogradelly double labeled (RDL) neurons in the sympathetic trunk ganglia (STG). We used six intact pigs and we injected the tracer Diamidino Yellow (DY) in the smooth left retractor penis muscle (RPM) and the tracer Fast Blue (FB) in the striated left bulbospongiosus muscle (BSM). Rare (2 ± 0.6) RDL neurons were found in the ipsilateral S2 spinal ganglion (SG), 220 ± 42 in the ipsilateral STGs, from L3 to S3, 19 ± 15 in the contralateral S1-S2 ones and 22 ± 5 in the bilateral caudal mesenteric ganglia (CMG). The RDL neurons of the STG were IR for TH (85 ± 13%), DβH (69 ± 17%), NPY (69 ± 23%), nNOS (60 ± 11%), LENK (54 ± 19%), VIP (53±26%), SOM (40 ± 8%), CGRP (34 ± 12%), SP (31 ± 16%), and VAChT (28 ± 3%). Our research highlights the presence of sensory and sympathetic neurons with qualitatively different neurochemical content sending axons both to the smooth RPM and to the striated BSM of the pig. These RDL neurons are likely to project to the smooth vasal musculature to create the ideal physiological conditions in which these muscles can optimize the erectile function.

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.

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.

Atrial and ventricular rat coronary arteries are differently supplied by noradrenergic, cholinergic and nitrergic, but not sensory nerve fibres

The present immunohistochemical study set out to determine the extent of perivascular innervation in the rat heart, using markers for noradrenergic sympathetic fibres (tyrosine hydroxylase = TH), cholinergic parasympathetic fibres (vesicular acetylcholine transporter = VAChT), nitrergic fibres (neuronal NO synthase = nNOS), and peptidergic sensory fibres (calcitonin gene-related peptide = CGRP). For each of these antigens, the vascular innervation density was assessed separately in the atria, the basal and the apical parts of the ventricles, and was correlated to the inner vascular diameter. The four major findings are: (1) Each of these neurochemically defined populations shows an individual distribution pattern significantly different from the others with respect to correlation with vascular diameter and occurrence along atrial versus ventricular vessels. (2) Among autonomic efferent axons, nNOS-containing fibres are far less numerous than cholinergic and noradrenergic fibres. (3) Autonomic efferent axons (noradrenergic, cholinergic, nitrergic) are much more abundant around atrial than ventricular vessels, whereas perivascular CGRP-immunoreactive sensory nerve fibres are equally distributed in the various parts of the heart. (4) Noradrenergic and cholinergic axons preferentially innervate small-diameter vessels (negative linear correlation between index of innervation and vascular diameter), whereas the supply with CGRP-immunoreactive sensory nerve fibres does not change with vascular diameter. Collectively, the present study shows individual distribution patterns for each of the neurochemically defined populations of perivascular axons along the atrial and ventricular coronary arteries, indicating a highly differentiated nervous regulation of atrial versus ventricular, and large-diameter versus resistance vessels.

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.

Differential involvement of N-type calcium channels in transmitter release from vasoconstrictor and vasodilator neurons

1. The effects of calcium channel blockers on co-transmission from different populations of autonomic vasomotor neurons were studied on isolated segments of uterine artery and vena cava from guinea-pigs. 2. Sympathetic, noradrenergic contractions of the uterine artery (produced by 200 pulses at 1 or 10 Hz; 600 pulses at 20 Hz) were abolished by the N-type calcium channel blocker omega-conotoxin (CTX) GVIA at 1-10 nm. 3. Biphasic sympathetic contractions of the vena cava (600 pulses at 20 Hz) mediated by noradrenaline and neuropeptide Y were abolished by 10 nm CTX GVIA. 4. Neurogenic relaxations of the uterine artery (200 pulses at 10 Hz) mediated by neuronal nitric oxide and neuropeptides were reduced <50% by CTX GVIA 10-100 nm. 5. Capsaicin (3 microm) did not affect the CTX GVIA-sensitive or CTX GVIA-resistant neurogenic relaxations of the uterine artery. 6. The novel N-type blocker CTX CVID (100-300 nm), P/Q-type blockers agatoxin IVA (10-100 nm) or CTX CVIB (100 nm), the L-type blocker nifedipine (10 microm) or the 'R-type' blocker SNX-482 (100 nm), all failed to reduce CTX GVIA-resistant relaxations. The T-type channel blocker NiCl(2) (100-300 microm) reduced but did not abolish the remaining neurogenic dilations. 7. Release of different neurotransmitters from the same autonomic vasomotor axon depends on similar subtypes of calcium channels. N-type channels are responsible for transmitter release from vasoconstrictor neurons innervating a muscular artery and capacitance vein, but only partly mediate release of nitric oxide and neuropeptides from pelvic vasodilator neurons.

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.

Functional organization of peripheral vasomotor pathways

AIM

In this article, we review the functional organization of the peripheral autonomic pathways regulating the vasculature.

RESULTS

The final motor neurones in vasomotor pathways tend to be smaller than neurones in other autonomic pathways. This suggests that they have relatively smaller target territories and receive fewer pre-ganglionic inputs than non-vasomotor neurones. Nevertheless, single vasomotor neurones project to large areas of the vasculature separated by up to 7 mm. Different functional pools of vasomotor neurones project to specific segments of the vasculature, allowing for the selective neural control of resistance in vessels in proximal or distal regions of the vascular bed. In many cases, each functional pool of vasomotor neurones utilizes a characteristic combination of cotransmitters. The various pools of final motor neurones in vasomotor pathways receive convergent synaptic input from different pools of pre-ganglionic neurones, many of which also contain neuropeptides which enhance the excitability of the final motor neurones. The excitability of vasomotor neurones regulating gastrointestinal and mesenteric blood flow, also can be increased by the actions of peptides such as substance P that are released from visceral nociceptors.

CONCLUSIONS

We propose that autonomic pathways regulating the vasculature are organized into 'vasomotor units'. Each vasomotor unit consists of a pre-ganglionic neurone, the final motor neurones it innervates, and the blood vessels that they regulate. The vasomotor units are likely to be grouped into functional pools that can be recruited as necessary to provide highly specific, graded control of blood flow both within and between vascular beds.

Quantitative immunohistochemical investigation of the intrinsic vasodilator innervation of the guinea pig lingual artery

The vasculature of the guinea pig tongue is supplied by parasympathetic vasodilator nerve fibres of intrinsic origin. Here, we investigated first to what extent neuropeptides and the synthesizing enzymes of NO, CO and acetylcholine are contained and colocalized within periarterial lingual vasodilator axons of intrinsic origin. Then it was determined whether perivascular innervation by these fibre types changes with vascular diameter, in particular in comparison with the sensory substance P (SP)-positive and sympathetic noradrenergic vascular innervation. To this end, single, double and triple labelling histochemical techniques were performed on control tongues and tongues kept in short-term organotypic culture to induce degeneration of extrinsically originating nerve fibres. Cell bodies of intrinsic microganglia and their periarterial axons contained, simultaneously, NO synthase, vasoactive intestinal peptide and the acetylcholine-synthesizing enzyme choline acetyltransferase. Additionally, neuropeptide Y (NPY) was observed in a small percentage (12%) of neurons that increased to 39% after 36 h of organotypic culture. The CO synthesizing enzyme heme oxygenase-2 was detected only in perikarya but not in periarterial axons. Intrinsic vasodilator fibres were invariably present at arteries down to a luminal diameter of 150 microm, and reached 65% of section profiles of smallest arterioles, while noradrenergic and substance P-positive axons reached 80% of arteriolar profiles. These findings show that the intrinsic lingual vasodilator innervation of the guinea pig is far extending although slightly less developed than that by sensory and sympathetic axons, and differs both in this aspect and in patterns of colocalization from that reported for other organs, e.g. lung and pelvic organs.

Peptidergic innervation of blood vessels and interstitial cells in the testis of the cat

We studied the innervation of the cat testis using a panel of antisera against the following neuronal markers: protein gene product 9.5 (PGP), neuropeptide Y, C-terminal peptide of neuropeptide Y, galanin, vasoactive intestinal peptide (VIP), calcitonin gene-related peptide, and substance P. Immunoreactivity against PGP, a general neuronal label, demonstrated the arrangement of fibers from the superior spermatic nerve (SSN) in the testicular pedicle and the cephalic testicular pole, and those of the inferior spermatic nerve (ISN) along the vas deferens and the inferior testicular ligament. The testicular parenchyma exhibited a very rich innervation, mainly distributed to blood vessels and Leydig cell nests, but also in close association with seminiferous tubules. Numerous peptidergic fibers were present in the SSN and ISN, albeit in different proportions. Thus, VIP-immunoreactive fibers were almost absent in the SSN, but were the most abundant subpopulation of the ISN. The testicular interstitium contained numerous peptidergic fibers, associated with blood vessels, interstitial Leydig cells, and seminiferous tubules. Similar fibers were related to the rete testis. Parenchymatous VIP-immunoreactive nerves disappeared after bilateral vasectomy. Stimulation of the ISN under experimental conditions was associated with an increase of blood flow, and induced a large release of VIP into the spermatic vein. The extensive and selective distribution of nerve fibers within the cat testicular parenchyma supports the importance of spermatic nerves for testicular function. Furthermore, the differences in the fiber composition of the SSN and ISN can be correlated with their opposing effects on testosterone secretion and testicular blood flow.

Differential inhibition by botulinum neurotoxin A of cotransmitters released from autonomic vasodilator neurons

The role of the soluble NSF attachment protein receptor (SNARE) protein complex in release of multiple cotransmitters from autonomic vasodilator neurons was examined in isolated segments of guinea pig uterine arteries treated with botulinum neurotoxin A (BoNTA; 50 nM). Western blotting of protein extracts from uterine arteries demonstrated partial cleavage of synaptosomal-associated protein of 25 kDa (SNAP-25) to a NH2-terminal fragment of approximately 24 kDa by BoNTA. BoNTA reduced the amplitude (by 70-80%) of isometric contractions of arteries in response to repeated electrical stimulation of sympathetic axons at 1 or 10 Hz. The amplitude of neurogenic relaxations mediated by neuronal nitric oxide (NO) was not affected by BoNTA, whereas the duration of peptide-mediated neurogenic relaxations to stimulation at 10 Hz was reduced (67% reduction in integrated responses). In contrast, presynaptic cholinergic inhibition of neurogenic relaxations was abolished by BoNTA. These results demonstrate that the SNARE complex has differential involvement in release of cotransmitters from the same autonomic neurons: NO release is not dependent on synaptic vesicle exocytosis, acetylcholine release from small vesicles is highly dependent on the SNARE complex, and neuropeptide release from large vesicles involves SNARE proteins that may interact differently with regulatory factors such as calcium.

M2-receptor subtype does not mediate muscarine-induced increases in [Ca(2+)](i) in nociceptive neurons of rat dorsal root ganglia

Multiple muscarinic receptor subtypes are present on sensory neurons that may be involved in the modulation of nociception. In this study we focused on the presence of the muscarinic receptor subtypes, M2 and M3 (M2R, M3R), in adult rat lumbar dorsal root ganglia (DRG) at the functional ([Ca(2+)](i) measurement), transcriptional (RT-PCR), and translational level (immunohistochemistry). After 1 day in culture exposure of dissociated medium-sized neurons (20-35 micrometer diam) to muscarine was followed by rises in [Ca(2+)](i) in 76% of the neurons. The [Ca(2+)](i) increase was absent after removal of extracellular calcium and did not desensitize after repetitive application of the agonist. This rise in [Ca(2+)](i) may be explained by the expression of M3R, which can induce release of calcium from internal stores via inositoltrisphospate. Indeed the effect was antagonized by the muscarinic receptor antagonist atropine as well as by the M3R antagonist, 4-diphenylacetoxy-N-(2 chloroethyl)-piperidine hydrochloride (4-DAMP). The pharmacological identification of M3R was corroborated by RT-PCR of total RNA and single-cell RT-PCR, which revealed the presence of mRNA for M3R in lumbar DRG and in single sensory neurons. In addition, RT-PCR also revealed the expression of M2R, which did not seem to contribute to the calcium changes since it was not prevented by the M2 receptor antagonist, gallamine. Immunohistochemistry demonstrated the presence of M2R and M3R in medium-sized lumbar DRG neurons that also coexpressed binding sites for the lectin I-B4, a marker for mainly cutaneous nociceptors. The occurrence of muscarinic receptors in putative nociceptive I-B4-positive neurons suggests the involvement of these acetylcholine receptors in the modulation of processing of nociceptive stimuli.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Muscarinic M2-receptors in rat thoracic dorsal root ganglia

The occurrence and distribution of the muscarinic M2-receptor subtype (M2R) was investigated in rat thoracic dorsal root ganglia (DRG). Messenger RNA for M2R was demonstrated by RT-PCR in total RNA from DRG. Immunoreactivity to M2R-protein was localized to 26% of sensory neurons, the majority of them (85%) belonging to the size class of 25-40 microm in diameter. Double-labeling (immuno)histochemistry revealed that all M2R-immunoreactive neurons bind the lectin, I-B4, whereas they are generally devoid of substance P-immunoreactivity. These data show the presence of M2R on a subpopulation of presumably nociceptive primary afferent neurons, thereby extending previous pharmacological and electrophysiological studies that indicated a role of M2R and/or M4R in inhibition of calcium channel currents in rat sensory neurons (Wanke, E., Bianchi, L., Mantegazza, M., Guatteo, E., Macinelli, E. and Ferroni, A., Muscarinic regulation of Ca2+ currents in rat sensory neurons: channel and receptor types, dose-response relationships and cross-talk pathways. Eur. J. Neurosci., 6 (1994) 381-391).

Neurochemical distinction between skeletal muscle vasodilator neurons and pelvic vasodilator neurons in guinea-pigs

This study sets out to compare the combinations of potential vasodilator transmitters expressed by sympathetic and pelvic vasodilator neurons of guinea-pigs. Triple-labelling fluorescence immunohistochemistry was used to examine immunoreactivity (IR) to vasoactive intestinal peptide (VIP), nitric oxide synthase (NOS) and calcitonin gene-related peptide (CGRP) in lumbar sympathetic ganglia, and in perivascular axons supplying hindlimb skeletal muscles or pelvic viscera. Only 0.2% of VIP-IR nerve cell bodies in lumbar sympathetic ganglia (n = 4632 VIP-IR nerve cell profiles) contained NOS-IR, and one VIP-IR neuron contained CGRP-IR. The VIP-IR perivascular axons along the common and external iliac arteries, femoral artery and arteries to hindlimb muscles lacked NOS-IR and CGRP-IR. In contrast, all VIP-IR perivascular axons projecting from pelvic ganglia to the main uterine artery, and half of the VIP-IR axons along the internal iliac artery, contained NOS-IR and CGRP-IR. Thus, the neurochemical content of sympathetic vasodilator neurons to skeletal muscle arteries was clearly distinguishable from that of pelvic vasodilator neurons to the uterine vasculature. Furthermore, the autonomic dilation in each vascular bed is likely to be qualitatively different, and matched to the functional requirements of each target organ.