Dendritic morphology of presumptive vasoconstrictor and pilomotor neurons and their relations with neuropeptide-containing preganglionic fibres in lumbar sympathetic ganglia of guinea-pigs

Selective tracking of FFAR3-expressing neurons supports receptor coupling to N-type calcium channels in mouse sympathetic neurons

Activation of short-chain free fatty acid receptors 3 (FFAR3) has been suggested to promote sympathetic outflow in postganglionic sympathetic neurons or hamper it by a negative coupling to N-type calcium (Ca_V2.2) channels. Heterogeneity of FFAR3 expression in sympathetic neurons, however, renders single neurons studies extremely time-consuming in wild-type mice. Previous studies demonstrated large variability of the degree of Ca_V2.2 channel inhibition by FFAR3 in a global population of rat sympathetic neurons. Therefore, we focused on a small subpopulation of mouse sympathetic neurons using an FFAR3 antibody and an Ffar3 reporter mouse to perform immunofluorescent and electrophysiological studies. Whole-cell patch-clamp recordings of identified FFAR3-expressing neurons from reporter mice revealed a 2.5-fold decrease in the Ca_V2.2-FFAR3 inhibitory coupling variability and 1.5-fold increase in the mean I_Ca²⁺ inhibition, when compared with unlabeled neurons from wild-type mice. Further, we found that the ablation of Ffar3 gene expression in two knockout mouse models led to a complete loss-of-function. Subpopulations of sympathetic neurons are associated with discrete functional pathways. However, little is known about the neural pathways of the FFAR3-expressing subpopulation. Our data indicate that FFAR3 is expressed primarily in neurons with a vasoconstrictor phenotype. Thus, fine-tuning of chemically-coded neurotransmitters may accomplish an adequate outcome.

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.

Primary afferent neurons containing calcitonin gene-related peptide but not substance P in forepaw skin, dorsal root ganglia, and spinal cord of mice

In mice dorsal root ganglia (DRG), some neurons express calcitonin gene-related peptide (CGRP) without substance P (SP; CGRP(+) SP(-) ). The projections and functions of these neurons are unknown. Therefore, we combined in vitro axonal tracing with multiple-labeling immunohistochemistry to neurochemically define these neurons and characterize their peripheral and central projections. Cervical spinal cord, DRG, and forepaw skin were removed from C57Bl/6 mice and multiple-labeled for CGRP, SP, and either marker for the sensory neuron subpopulations transient receptor potential vanilloid type 1 (TRPV1), neurofilament 200 (NF200), or vesicular glutamate transporter 2 (VGluT1). To determine central projections of CGRP(+) SP(-) neurons, Neurobiotin (NB) was applied to the C7 ventral ramus and visualized in DRG and spinal cord sections colabeled for CGRP and SP. Half (50%) of the CGRP-immunoreactive DRG neurons lacked detectable SP and had a mean soma size of 473 ± 14 μm(2) (n = 5); 89% of the CGRP(+) SP(-) neurons expressed NF200 (n = 5), but only 32% expressed TRPV1 (n = 5). Cutaneous CGRP(+) SP(-) fibers were numerous within dermal papillae and around hair shafts (n = 4). CGRP(+) SP(-) boutons were prevalent in lateral lamina I and in lamina IV/V of the dorsal horn (n = 5). NB predominantly labeled fibers penetrating lamina IV/V, 6 ± 3% contained CGRP (n = 5), and 21 ± 2% contained VGluT1 (n = 3). CGRP(+) SP(-) afferent neurons are likely to be non-nociceptive. Their soma size, neurochemical profile, and peripheral and central targets suggest that CGRP(+) SP(-) neurons are polymodal mechanoceptors.

Sensory nerve fibers containing calcitonin gene-related peptide in gastrocnemius, latissimus dorsi and erector spinae muscles and thoracolumbar fascia in mice

Chronic pain is a significant burden and much is attributed to back muscles. Back muscles and their associated fasciae make important and distinct contributions to back pain. Peptidergic nociceptors innervating these structures contribute to central transmission and pain modulation by peripheral and central actions. Plastic changes that augment and prolong pain are exhibited by neurons containing calcitonin gene-related peptide (CGRP) following muscle injury. Subpopulations of neurons containing this peptide have been identified in dorsal root ganglia but the distribution of their fibers in skeletal muscles and associated fasciae has not been fully documented. This study used multiple-labeling immunofluorescence and retrograde axonal tracing to identify dorsal root ganglion cells associated with muscle, and to characterize the distribution and density of their nerve fibers in mouse gastrocnemius and back muscles and in the thoracolumbar fascia. Most nerve fibers in these tissues contained CGRP and two major subpopulations of neurons were found: those containing CGRP and substance P (SP) and those containing CGRP but not SP. Innervation density was three times higher in the thoracolumbar fascia than in muscles of the back. These studies show mouse back and leg muscles are predominantly innervated by neurons containing CGRP, an important modulator of pain signal transmission. There are two distinct populations of neurons containing this peptide and their fibers were three times more densely distributed in the thoracolumbar fascia than back muscles.

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.

Non-peptidergic small diameter primary afferents expressing VGluT2 project to lamina I of mouse spinal dorsal horn

BACKGROUND

Unmyelinated primary afferent nociceptors are commonly classified into two main functional types: those expressing neuropeptides, and non-peptidergic fibers that bind the lectin IB4. However, many small diameter primary afferent neurons neither contain any known neuropeptides nor bind IB4. Most express high levels of vesicular glutamate transporter 2 (VGluT2) and are assumed to be glutamatergic nociceptors but their terminations within the spinal cord are unknown. We used in vitro anterograde axonal tracing with Neurobiotin to identify the central projections of these putative glutamatergic nociceptors. We also quantitatively characterised the spatial arrangement of these terminals with respect to those that expressed the neuropeptide, calcitonin gene-related peptide (CGRP).

RESULTS

Neurobiotin-labeled VGluT2-immunoreactive (IR) terminals were restricted to lamina I, with a medial-to-lateral distribution similar to CGRP-IR terminals. Most VGluT2-IR terminals in lateral lamina I were not labeled by Neurobiotin implying that they arose mainly from central neurons. 38 ± 4% of Neurobiotin-labeled VGluT2-IR terminals contained CGRP-IR. Conversely, only 17 ± 4% of Neurobiotin-labeled CGRP-IR terminals expressed detectable VGluT2-IR. Neurobiotin-labeled VGluT2-IR or CGRP-IR terminals often aggregated into small clusters or microdomains partially surrounding intrinsic lamina I neurons.

CONCLUSIONS

The central terminals of primary afferents which express high levels of VGluT2-IR but not CGRP-IR terminate mainly in lamina I. The spatial arrangement of VGluT2-IR and CGRP-IR terminals suggest that lamina I neurons receive convergent inputs from presumptive nociceptors that are primarily glutamatergic or peptidergic. This reveals a previously unrecognized level of organization in lamina I consistent with the presence of multiple nociceptive processing pathways.

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.

Structure of peripheral synapses: autonomic ganglia

Final motor neurons in sympathetic and parasympathetic ganglia receive synaptic inputs from preganglionic neurons. Quantitative ultrastructural analyses have shown that the spatial distribution of these synapses is mostly sparse and random. Typically, only about 1%-2% of the neuronal surface is covered with synapses, with the rest of the neuronal surface being closely enclosed by Schwann cell processes. The number of synaptic inputs is correlated with the dendritic complexity of the target neuron, and the total number of synaptic contacts is related to the surface area of the post-synaptic neuron. Overall, most neurons receive fewer than 150 synaptic contacts, with individual preganglionic inputs providing between 10 and 50 synaptic contacts. This variation is probably one determinant of synaptic strength in autonomic ganglia. Many neurons in prevertebral sympathetic ganglia receive additional convergent synaptic inputs from intestinofugal neurons located in the enteric plexuses. The neurons support these additional inputs via larger dendritic arborisations together with a higher overall synaptic density. There is considerable neurochemical heterogeneity in presynaptic boutons. Some synapses apparently lack most of the proteins normally required for fast transmitter release and probably do not take part in conventional ganglionic transmission. Furthermore, most preganglionic boutons in the ganglionic neuropil do not form direct synaptic contacts with any neurons. Nevertheless, these boutons may well contribute to slow transmission processes that need not require conventional synaptic structures.

Physiological classification of sympathetic neurons in the rat superior cervical ganglion

A new scheme is presented for identifying three sympathetic phenotypes in the rat superior cervical ganglion using electrophysiology and neuropeptide Y expression. Postganglionic compound action potentials recorded from the external and internal carotid nerves each contained two peaks, 1 and 2, with distinct preganglionic stimulus thresholds. Peak 2 in the external carotid response contained subpeaks 2a and 2b having a similar stimulus threshold. Neurons corresponding to peaks 1, 2a, and 2b were identified intracellularly by antidromic stimulation, graded preganglionic stimulation, injection with neurobiotin and immunostaining. Seventeen of 53 neurons studied this way had a low threshold for preganglionic stimulation of firing that corresponded to activation of extracellular peak 1. All low-threshold neurons were neuropeptide Y (NPY)-negative. The other 36 neurons had a high presynaptic stimulus threshold that corresponded to activation of extracellular peak 2, and 12 of these cells contained NPY. Together with other known features of ganglionic organization, the results indicate that low-threshold NPY-negative neurons are secretomotor cells projecting to salivary glands, that high-threshold NPY-negative neurons are pilomotor cells responsible for extracellular peak 2a, and that high-threshold, NPY-positive neurons are vasoconstrictor cells responsible for peak 2b. Secreto-, pilo-, and vasomotor neurons identified in this way had distinct axonal conduction velocities (0.52, 0.20, and 0.10 m/s) and diameters (33, 29, and 25 microm) but were indistinguishable in terms of preganglionic conduction velocities (0.30-0.34 m/s) and number of primary dendrites (8.4-8.6). The cell classification scheme presented here will allow future comparison of ganglionic integration in different sympathetic modalities.

Most peptide-containing sensory neurons lack proteins for exocytotic release and vesicular transport of glutamate

We used multiple-labeling immunohistochemistry and confocal microscopy to examine co-expression of immunoreactivity for vesicular glutamate transporters (VGluTs), synaptic vesicle proteins, and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins in peptide-containing sensory neurons of guinea pigs, mice, and toads. Axon terminals in the superficial layers of the dorsal horn of the spinal cord with immunoreactivity (IR) for both substance P (SP) and calcitonin gene-related peptide (CGRP) lacked IR for synaptosome-associated protein of 25 kDa (SNAP-25), syntaxin, synaptotagmin, synaptophysin, and synapsin, although adjacent varicosities without neuropeptides had IR for these synaptic proteins. Similarly, peptide-containing axon terminals in the superficial dorsal horn lacked IR for VGluT1 and VGluT2, despite the presence of VGluT2-IR in nearby nonpeptide varicosities. VGluT3-IR was sparse in the dorsal horn of the mouse spinal cord and was not present in peptide-containing axons. Most peripheral terminals of sensory neurons with both SP-IR and CGRP-IR in the skin, viscera, and autonomic ganglia of guinea pigs and mice also lacked IR for synaptic vesicle proteins, SNARE proteins, VGluT1, and VGluT2. In dorsal root ganglia from guinea pigs and mice, most small neurons with IR for both SP and CGRP lacked IR for SNAP-25, VGluT1, and VGluT2. Thus, proteins considered essential for vesicular uptake and exocytotic release of glutamate are not expressed at detectable levels by most sensory neurons containing SP and CGRP in rodents and toads. These data raise the possibility that most peptide-containing sensory neurons may not normally release glutamate as a transmitter.

Histochemical features of neurons in the cat stellate ganglion during postnatal ontogenesis

Changes in the distribution of NADPH-diaphorase (NADPH-d) and acetylcholinesterase (AChE) were studied in neurons of the stellate ganglion in newborn, 10-, 20-day-old, 1-, 2-, 4- and 6-month-old kittens. AChE-positive neurons were revealed in the stellate ganglion (SG) from birth onwards. The number of these neurons increased until 20 days of postnatal life and then declined in 1- and 2-month-old kittens. A small number of weakly stained, NADPH-d-positive cells were found in newborn kittens, while intensely stained neurons first appeared in 10-day-old animals and increased in number up to the second month of life. The size of AChE-positive neurons was larger in comparison with NADPH-d-positive cells in the stellate ganglion of all animals under study. We suggest that putative vasodilator neurons or cells innervating sweat glands exhibit different development patterns from the moment of birth.

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.

Synaptic density, convergence, and dendritic complexity of prevertebral sympathetic neurons

Prevertebral sympathetic ganglia contain a unique population of final motor neurons receiving convergent synaptic inputs not only from spinal preganglionic neurons, but also from peripheral intestinofugal neurons projecting from the gut. We used quantitative confocal and ultrastructural immunohistochemistry to determine how this increased synaptic convergence is accommodated by sympathetic final motor neurons in the celiac ganglion of guinea pigs. Terminals of intestinofugal neurons were identified by their immunoreactivity to vasoactive intestinal peptide. Stereologic analyses were based on transects and point counts at confocal and ultrastructural levels. The relative amount of dendritic neuropil in the medial regions of the ganglion was approximately 2.5 times greater than in the lateral regions of the ganglion, consistent with the 2 to 3 times difference in average dendritic field size of neurons in these regions. The total numbers of boutons and synaptic profiles showed significant positive correlations with the relative amount of neuropil in a region. However, the overall density of synaptic boutons was twice as high in the medial region of the ganglion compared with the lateral regions. Because the relative density of preganglionic synapses was similar in each region, this difference was due to the selective projection of intestinofugal inputs to neurons in the medial celiac ganglion, where they provided 45% of synaptic contacts. These results show that, compared with vasoconstrictor neurons, sympathetic neurons regulating gastrointestinal activity support a higher number of convergent inputs in two ways: in addition to having larger dendritic fields, they also have a twofold higher density of synapses.

Estrogen receptor-alpha and neural circuits to the spinal cord during pregnancy

Estrogen receptor immunoreactivity and mRNAs are present in spinal cord neurons in locations that are associated with sensory and autonomic innervation of female reproductive organs. The present study was undertaken to examine the expression of estrogen receptor-alpha in the spinal cord during different stages of pregnancy and to determine whether estrogen receptor-alpha-expressing neurons are related to uterine afferent nerves bringing information to the spinal cord at parturition. Immunohistochemistry showed estrogen receptor-alpha-immunoreactive neurons in the dorsal one-half of the spinal cord, i.e., dorsal horn, dorsal intermediate gray areas (dorsal commissural nucleus), and around the central canal and sacral parasympathetic autonomic nucleus of the lumbosacral spinal cord. Neurons in these areas corresponded topographically to the distribution of central processes of visceral primary afferent neurons (e.g., containing calcitonin gene-related peptide and substance P) that innervate and activate second-order spinal cord neurons (evidenced by their expression of Fos) at parturition. Western blots showed that estrogen receptor-alpha increases in the spinal cord, with a peak at day 20 of gestation, followed by a slight decrease by 2 days postpartum. These studies show that estrogen receptor-alpha is expressed by neurons in autonomic and sensory areas of the lumbosacral spinal cord that have connections with the female reproductive system and that the level of estrogen receptor-alpha changes over the course of pregnancy, which may follow profiles of steroid hormones. Many of these neurons may be involved in processing information related to reproductive organ function, changes during pregnancy, and relays to other CNS centers.

Occurrence, co-occurrence and topographic distribution of choline acetyl transferase, Met-enkephalin and neurotensin in the stellate ganglion of the cat

The presence of the classical ganglionic transmitter acetylcholine (ACh), its occurrence and possible co-occurrence with the neuromodulator peptides methionine enkephalin (Met-ENK) and neurotensin (NT), as well as the possible coexistence of these peptides in the preganglionic axon terminals of the cat stellate ganglia were investigated with light and confocal microscopy using immunofluorescence. Choline acetyltransferase (ChAT), Met-ENK, and NT immunoreactivity was detected with light microscopy in axon terminals near tyrosine hydroxylase (TH) immunoreactive (IR) cells. Cell bodies immunopositive for ChAT or Met-ENK were also detected and were TH-negative or TH-positive. Denervation by sectioning preganglionic axons produced two effects: the almost complete elimination of IR fibers and an increase in the number of ChATIR and Met-ENKIR cell bodies, together with the appearance of NTIR cell bodies. Preganglionic ChATIR fibers and boutons form a dense network throughout the entire ganglion, with a homogeneous regional distribution. ChAT, Met-ENK, and NT are essentially stored in different nerve endings, although a low level of co-occurrence was detected. NTIR and Met-ENKIR networks of boutons were observed to have independent and somewhat complementary regional distributions. Further analysis with simultaneous triple labeling for NT, Met-ENK, and TH, and confocal microscopy showed fibers and boutons containing Met-ENK or NT reached distinct neurons separately, or both converge onto the same cells. This finding suggests that modulation (the facilitation-inhibition balance) of ganglionic transmission is achieved mainly by the selective and complementary innervation of boutons containing NT (facilitation) and Met-ENK (inhibition) and only rarely by terminals which coexpress both peptides.

Sensory nerves and neuropeptides in uterine cervical ripening

At the time of parturition (fetal delivery) the uterine cervix must "ripen," becoming soft, pliable, and dilated to accommodate the fetus' delivery. The fundamental processes underlying cervical ripening remain poorly understood. Knowledge that abundant autonomic and sensory nerves supply the uterine cervix, that transection of afferent nerves supplying the cervix blocks parturition, and that some of the changes in the cervix resemble those seen in inflammatory reactions suggests nerves may have a role in the cervical ripening changes. The present study utilized immunohistochemistry, plasma extravasation, and solution hybridization-nuclease protection assay to elucidate the complement of primary afferent nerves and some receptors in the rat cervix during pregnancy, and to determine if they may have roles in the ripening process at term. This study revealed an abundance of nerves associated with the cervical vasculature and myometrial smooth muscle containing immunoreactivity for substance P, calcitonin gene-related peptide, secretoneurin, and nitric oxide synthase throughout pregnancy. Many of these are small unmyelinated capsaicin-sensitive C-fibers. Substance P- (NK1-) and calcitonin gene-related peptide receptors were apparent on uterine cervix vasculature from pregnant, parturient, and postpartum rats. NK1 receptor mRNA was maximal at 20 days of pregnancy. Plasma extravasation of i.v. administered Evans Blue or Monastral Blue was most pronounced at parturition (shortly after NK1 mRNA is maximal); this was similar to plasma extravasation evoked by i.v. administration of substance P or capsaicin-treatment. This study revealed new data about the nervous system of the rat uterine cervix and that these nerves and their transmitters could very well be part of a neurogenic inflammatory process involved in cervical ripening.

Sympathetic neurons of the cat stellate ganglion in postnatal ontogenesis: morphometric analysis

Basic morphometric parameters (the maximal diameter, cross-sectional area), the distribution density of neurons were determined in the zones of the emergence of the basic nerves and in the center of the stellate ganglion (SG) in newborn, 10-, 20-day-old as well as 1- and 2-month-old kittens. Most of the investigated neurons in all animals were oval in their profile. In parallel to the increase of the average diameters, the number of small neurons decreased and the percentage of large neurons increased in postnatal ontogenesis. In all kittens, neurons with larger average size were located in the cranial pole of the ganglion. In 10-day-old kittens and older animals, the average size of neurons was more in the left SG in comparison to the right one. Only in 1-month-old kittens the density of location of neurons in the right ganglion exceeded such parameters of neurons located at the left side. The number of neurons in the SG was not constant in postnatal ontogenesis and reduced from newborn to 20-day-old animals.

Neurochemical differentiation of functionally distinct populations of autonomic neurons

The coeliac ganglion of guinea pigs displays a unique topographical arrangement of neurochemically and functionally distinct populations of sympathetic neurons. The authors used multiple-labeling immunohistochemistry to investigate the neurochemical differentiation of these neurons during embryonic and fetal development. Sympathoadrenal precursors, located on either side of the abdominal aorta, were intensely immunoreactive for tyrosine hydroxylase (TH-IR), neurofilament, and the human natural killer 1 antibody at midembryonic stages (Carnegie stages 16-19). During late embryonic stages (stages 20-23), a single bilobed ganglion had formed. At this time, neuropeptide Y immunoreactivity (NPY-IR) was widely expressed in sympathetic neurons (with moderate TH-IR) and chromaffin cells (with intense TH-IR). The onset of somatostatin (Som-IR) expression followed that of NPY-IR and was restricted to sympathetic neurons. However, at late embryonic stages, most TH-IR neurons with Som-IR also expressed NPY-IR (a combination of peptides not found in the mature coeliac ganglion). Between late embryonic stages and the end of the early fetal period, there was a significant increase in the proportion of neurons in lateral regions that had both NPY-IR and TH-IR. At the same time, there was an increase in the proportion of neurons in medial regions that had both Som-IR and TH-IR. Neurons expressing both Som-IR and TH-IR were rarely observed in lateral regions of the coeliac ganglion. Thus, a clear topography within the coeliac ganglion is established during late embryonic and early fetal stages of development and reflects that found in the mature animal by the end of the early fetal period.

Morphological features of neurons innervating different viscera in the cat stellate ganglion in postnatal ontogenesis

Retrograde axonal transport of horseradish peroxidase (HRP) was used in this study to determine morphological parameters in the stellate ganglion (SG) in newborn, 10-, 20-day- and 1-month-old kittens. Neurons with the largest average size participated in innervation of the heart in newborn kittens and in innervation of the sternocleidomastoid muscle in other animals. The number of neurons sending their axons to target-organs also changed in postnatal ontogenesis. Regardless of the site of HRP injection at animals of all ages labeled neurons in the SG were located in certain zones on a topographical basis. Thus, it is concluded that in postnatal ontogenesis the neuronal organization of the SG changes in parallel to the increase of neuronal sizes and ganglion cross section area and practically finishes at 1 month of age.

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.

Reflex patterns in preganglionic sympathetic neurons projecting to the superior cervical ganglion in the rat

Reflex patterns in preganglionic neurons projecting in the cervical sympathetic trunk (CST) were analyzed in response to stimulation of various afferent systems. We focused on the question whether these preganglionic neurons can be classified into functionally distinct subpopulations. Reflex responses were elicited by stimulation of trigeminal and spinal nociceptive, thermoreceptive as well as baroreceptor and chemoreceptor afferents. Multi- and single fiber preparations were studied in baroreceptor intact and sino-aortically denervated animals. Spontaneous activity of 36 preganglionic single neurons ranged from 0.2 to 3.5 imp/s (median= 1.11 imp/s). The degree of cardiac rhythmicity (CR) in the activity of sympathetic neurons was 69.5+/-13% (mean+/-S.D.; N=52; range=39-95%). Noxious stimulation of acral skin activated the majority (67%) of sympathetic preparations by 37+/-25% (N=35) above pre-stimulus activity; 15% were inhibited. In these neurons the response to noxious stimulation of acral skin was significantly correlated with the degree of CR (P<0.001, N=52) in that neurons showing the strongest excitation to noxious stimulation displayed the strongest CR. Noxious mechanical stimulation of body trunk skin (N=60) inhibited the majority (80%) of fiber preparations tested (by 34+/-18% of pre-stimulus activity, N=48); an activation was not observed. Cold stimulation of acral (N=9) and body trunk skin (N=42) activated most fiber preparations. Trigeminal stimulation evoked a uniform reflex activation of preganglionic neurons (+79+/-73% of pre-stimulus activity, N=32). Chemoreceptor stimulation by systemic hypercapnia elicited inhibitory (-31+/-19%, N=8) as well as excitatory (+59+/-5%, N=4) responses. These results show that preganglionic sympathetic neurons projecting to target organs in the head exhibit distinct reflex patterns to stimulation of various afferent systems; however, a clear classification into different functional subgroups did not emerge. Furthermore, reflex patterns showed a segmental organization to noxious cutaneous stimulation of acral parts and body trunk reflecting a differential central integration of spinal afferent input. Compared with the cat the reflex organization of sympathetic neurons projecting to the head seems to be less differentiated in the anesthetized rat.

Neuronal morphology and the synaptic organisation of sympathetic ganglia

In this article, we provide a short review of the structure and synaptic organisation of the final motor neurons in the sympathetic ganglia of mammals. Combinations of pathway tracing, multiple-labelling immunofluorescence and intracellular dye injection have shown that neurons in different functional pathways differ not only in their patterns of neuropeptide expression, but also in the size of their cell bodies and dendritic fields. Thus, vasoconstrictor neurons consistently are smaller than any other major functional class of neurons. Serial section ultrastructural analysis of dye filled neurons, together with electron microscopic and confocal microscopic analysis of immunolabelled synaptic inputs to sympathetic final motor neurons indicate that synapses are rare and randomly distributed over the surface of the neurons. The total number of synapses is simply proportional to the total surface area of the neurons. Many terminal boutons of peptide-containing preganglionic neurons do not make conventional synapses with target neurons. Furthermore, there is a spatial mismatch in the distribution of peptide-containing terminals and neurons expressing receptors for the corresponding peptides. Together, these results suggest that there are likely to be significant differences in the ways that the final sympathetic motor neurons in distinct functional pathways integrate their synaptic inputs. In at least some pathways, heterosynaptic actions of neuropeptides probably contribute to subtle modulation of ganglionic transmission.

Distribution and origin of secretoneurin-immunoreactive nerves in the female rat uterus

Secretoneurin is a 33-amino acid peptide derived from secretogranin II. Secretoneurin immunoreactivity has been localized in the peripheral nervous system where it exerts potent chemotactic activity for monocytes and may play a role in inflammation. Secretoneurin could play a role in this process, although the presence and distribution of secretoneurin-immunoreactive neurons in the female reproductive system has not been documented. Thus, this study was undertaken to examine secretoneurin immunoreactivity in nerves of the rat uterus and uterine cervix. A moderate plexus of secretoneurin-immunoreactive nerve fibers was present in the myometrium and endometrium of the uterus as well as in the smooth muscle and endocervix of the cervix. Many of these fibers were associated with the vasculature as well as the myometrium. Secretoneurin immunoreactivity was present in small- to medium-sized neurons of dorsal root and nodose ganglia. Retrograde tracing with FluoroGold indicated that some of these sensory neurons project axons to the cervix and uterine horns. Secretoneurin-immunoreactive terminal-like structures were associated with neurons in the sacral parasympathetic nucleus of the lumbosacral spinal cord. In addition, some secretoneurin terminals were apposed to pelvic parasympathetic neurons in the paracervical ganglia that projected axons to the uterus and cervix. Double-immunostaining indicated co-existence of calcitonin gene-related peptide or substance P with secretoneurin in some sensory neurons, in some terminals of the pelvic ganglia, as well as nerve fibers in the uterine horn and cervix. Finally, fibers in the uterus and cervix were depleted of secretoneurin by capsaicin treatment. This study indicates that secretoneurin is present in the uterus in C-afferent nerve fibers whose cell bodies are located in sensory ganglia. Some of these fibers contain both secretoneurin and calcitonin gene-related peptide or substance P. These substances have functions in inflammatory reactions. Further, secretoneurin could influence postganglionic parasympathetic "uterine-related" neurons in the pelvic ganglia and preganglionic parasympathetic neurons in the lumbosacral spinal cord.

Electrophysiological and morphological diversity of mouse sympathetic neurons

We have used multiple-labeling immunohistochemistry, intracellular dye-filling, and intracellular microelectrode recordings to characterize the morphological and electrical properties of sympathetic neurons in the superior cervical, thoracic, and celiac ganglia of mice. Neurochemical and morphological characteristics of neurons varied between ganglia. Thoracic sympathetic ganglia contained three main populations of neurons based on differential patterns of expression of immunoreactivity to tyrosine hydroxylase, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In the celiac ganglion, nearly all neurons contained immunoreactivity to both tyrosine hydroxylase and NPY. Both the overall size of the dendritic tree and the number of primary dendrites were greater in neurons from the thoracic and celiac ganglia compared with those from the superior cervical ganglion. The electrophysiological properties of sympathetic neurons depended more on their ganglion of origin rather than their probable targets. All neurons in the superior cervical ganglion had phasic firing properties and large afterhyperpolarizations (AHPs). In addition, 34% of these neurons displayed an afterdepolarization preceding the AHP. Superior cervical ganglion neurons had prominent I(M), I(A), and I(H) currents and a linear current-voltage relationship between -60 and -110 mV. Neurons from the thoracic ganglia had significantly smaller action potentials, AHPs, and apparent cell capacitance compared with superior cervical ganglion neurons, and only 18% showed an afterdepolarization. All neurons in superior cervical ganglia and most neurons in celiac ganglia received at least one strong preganglionic input. Nearly one-half the neurons in the celiac ganglion had tonic firing properties, and another 15% had firing properties intermediate between those of tonic and phasic neurons. Most celiac neurons showed significant inward rectification below -90 mV. They also expressed I(A), but with slower inactivation kinetics than that of superior cervical or thoracic neurons. Both phasic and tonic celiac ganglion neurons received synaptic inputs via the celiac nerves in addition to strong inputs via the splanchnic nerves. Multivariate statistical analysis revealed that the properties of the action potential, the AHP, and the apparent cell capacitance together were sufficient to correctly classify 80% of neurons according to their ganglion of origin. These results indicate that there is considerable heterogeneity in the morphological, neurochemical, and electrical properties of sympathetic neurons in mice. Although the morphological and neurochemical characteristics of the neurons are likely to be related to their peripheral projections, the expression of particular electrophysiological traits seems to be more closely related to the ganglia within which the neurons occur.

Patterns of innervation of sympathetic vascular neurons by peptide-containing primary sensory fibers

The purpose of this study was to determine whether there is a specific organization of the primary sensory innervation on to identified vascular neurons in the inferior mesenteric ganglion (IMG) in guinea-pig. Retrograde tracers were placed intraluminally in inferior mesenteric artery (IMA) or inferior mesenteric vein (IMV) in vitro to identify ganglionic neurons as arterial, venous or unlabeled neurons. The distribution of primary sensory nerve fibers containing calcitonin gene-related peptide (CGRP), neuronal nitric oxide synthase (NOS) and substance P immunoreactivity (SP-IR) was compared before and after treatment with capsaicin. In control animals the density of immunoreactivity varied both with the transmitter and the type of neuron innervated. The density of immunoreactivity for all the three substances was reduced by capsaicin treatment. The degree of reduction of immunoreactivity in the fibers varied with the transmitter and the type of neuron. The density of CGRP and SP immunoreactive fibers was greatest around unlabeled neurons; 78% of the CGRP fibers were of primary sensory origin and all of the SP fibers were primary sensory. Around arterial neurons 44% of the CGRP fibers were of primary sensory origin and around venous 68% were primary sensory. NOS positive innervation around venous neurons was denser than around arterial neurons and all of it was completely (97%) eliminated by capsaicin, indicating that it was solely of primary sensory origin. We conclude that the primary sensory fibers innervating the IMG are differentially distributed to arterial and venous neurons and that the pattern of distribution is characteristic for each sensory neurotransmitter.

Synaptic organisation of neuropeptide-containing preganglionic boutons in lumbar sympathetic ganglia of guinea pigs

Within the lumbar sympathetic ganglia of guinea pigs, the endings of different populations of neuropeptide-containing preganglionic neurons form well-defined pericellular baskets of boutons around target neurons in specific functional pathways. We have used multiple-labelling immunofluorescence, confocal microscopy, and ultrastructural immunocytochemistry to investigate synaptic organisation within pericellular baskets labelled for immunoreactivity to calcitonin gene-related peptide (CGRP), substance P (SP), or the pro-enkephalin-derived peptide, met-enkephalin-arg-gly-leu (MERGL) in relation to their target neurons. Different functional populations of neurons, identified by their neurochemical profile, showed a significant degree of spatial clustering and predicted well the distribution of specific classes of pericellular baskets. Most of the boutons in a basket were completely surrounded by Schwann cell processes and did not form synapses. The synapses that were present were made mostly onto dendrites enclosed by the Schwann cell sheath surrounding the neuron within the basket. These dendrites probably originated from neurochemically similar neighbouring neurons. Nevertheless, some of the boutons in the baskets did form synapses with the cell body or proximal dendrites of the neuron they surrounded. Occasionally, cell bodies received a relatively high number of synapses and close appositions from boutons in a pericellular basket. Synaptic convergence of two immunohistochemically distinct types of preganglionic inputs was found in baskets of SP-immunoreactive or MERGL-immunoreactive, but not CGRP-immunoreactive, boutons. Taken together, our results show that the appearance of pericellular baskets is primarily due to the packing of the target neurons. The grouping of functionally similar classes of neurons with their pathway-specific projections of peptide-containing preganglionic neurons suggests that peptides could exert their effects in relatively well-defined zones within the ganglia.

Peripheral fields of sympathetic vasoconstrictor neurons in guinea pigs

We have combined retrograde axonal tracing using Fast Blue and Dil, with immunohistochemistry, to estimate the maximum size of peripheral fields of identified sympathetic vasoconstrictor neurons projecting to guinea-pig ear tips. Many neurons in the superior cervical ganglia were labelled with both Fast Blue and Dil after dye injections up to 7 mm apart. Few neurons were labelled when dye injections were 8-10 mm apart. Neurons labelled with both Dil and Fast Blue after dye injections 5-7 mm apart had, on average, larger somata (436 +/- 84 microm2, mean +/- SEM, n = 47) than neurons labelled with Dil only (388 +/- 11 microm2, n = 147). Typically, 50-100 neurons innervated a region of vasculature 1 mm in diameter. We conclude that sympathetic vasoconstrictor neurons branch widely before converging on to their target blood vessels. Progressive recruitment of vasoconstrictor neurons with increasing field size would provide an efficient mechanism for graded neural control of the circulation.

Differential distribution of substance P binding sites in guinea-pig sympathetic ganglia

We have used a combination of autoradiographic and immunohistochemical techniques to investigate the distribution of binding sites for substance P in relation to the distribution of substance P-immunoreactive nerve fibres and specific functional populations of neurons in the sympathetic ganglia of guinea-pigs. There was considerable heterogeneity in the density of binding sites for Bolton Hunter labelled 125I - substance P (BHSP). Binding sites were more dense in the prevertebral ganglia, such as the coeliac and inferior mesenteric ganglia, than in the paravertebral ganglia, such as the superior cervical or lumbar chain ganglia. The binding sites tended to be clumped within the ganglia. Within the prevertebral ganglia, they were associated predominantly with neurons projecting to the enteric plexuses. Many of these neurons contained somatostatin immunoreactivity. In the lumbar sympathetic chain ganglia, there was a weak association of binding sites with neurons containing immunoreactivity to vasoactive intestinal peptide. Overall, the density of binding sites matched the density of nerve fibres containing immunoreactivity to substance P in different ganglia. However, within particular ganglia, there was little, if any, correlation between the distribution of binding sites and nerve fibres containing substance P. Most of the binding sites in the ganglia had the pharmacological characteristics of NK1 receptors. Our results show that there is considerable heterogeneity in the expression of NK1 receptors in the sympathetic ganglia of guinea-pigs. However, given the relatively poor spatial correlation between the distribution of binding sites and potential sites of substance P release from intraganglionic nerve fibres, we suggest that substance P may diffuse for relatively large distances through the ganglia, with actions only on those neurons selectively expressing NK1 receptors.

Distribution and coexistence of neuropeptides in nerve fibres in the temporomandibular joint of late gestation fetal sheep

The density and distribution of nerve fibres immunoreactive to antisera for PGP 9.5 (general neuronal marker), calcitonin gene related peptide (CGRP) and substance P (SP) (markers for sensory neurons), as well as neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and tyrosine hydroxylase (TH) (markers for autonomic fibres), were examined in the temporomandibular joint (TMJ) of late gestation fetal sheep. This work formed part of a project investigating the influence of age and osteoarthritis on the innervation of the TMJ, and was undertaken to determine whether the innervation of the joint at 140 d gestation (17 d before birth) differed from that in the mature adult. Immunofluorescence microscopy was applied to serial sections of the capsule, disc and synovial membrane of 10 joints from 5 fetuses and image analysis was used for the quantitative assessment. The capsule, synovial membrane and the disc contained fibres immunoreactive (IR) to antisera for PGP 9.5, SP and CGRP. NPY-IR fibres were only visible in the loose connective tissue of the capsule. No VIP- or TH-IR nerve fibres were detected in the fetal TMJ. There was no statistically detectable difference between the density of nerve fibres immunoreactive to CGRP or PGP 9.5 antisera in the capsule or disc. Substance P-immunoreactivity (IR) was relatively weak in all samples examined. Scattered branches of CGRP-IR fibres were found deep in the disc proper. The lack of receptor endings, other than free nerve endings in the TMJ of the late fetal sheep, might be a reflection of the functional and anatomical immaturity of the TMJ, as reflected in the immature, gross and microscopic appearance of the disc, the inferior joint compartment and articular surface of the condyle at this stage. These results demonstrate that the capsule, synovial membrane and disc in the TMJ of fetal sheep at 140 d gestation age are innervated with sensory fibres, while autonomic fibres are located in the capsule only. The findings also support the view that the disc is innervated at an early stage of life but at a later stage the density of innervation in the central part of the disc regresses and the innervation remains only peripherally in the adult TMJ disc. Further work is required to determine (1) at what stage sympathetic fibres innervate the disc and the synovium, and (2) when the mechanoreceptive nerve endings develop.

Sympathetic vasoconstrictor neurons projecting from the guinea-pig superior cervical ganglion to cutaneous or skeletal muscle vascular beds can be distinguished by soma size

We have used a combination of retrograde axonal tracing and intracellular dye injections to determine the soma size of sympathetic vasoconstrictor neurons projecting from the superior cervical ganglion to the cutaneous vascular bed of the eartips, or to the vascular beds of the masseter muscle, of guinea-pigs. Neurons projecting to vasculature of the masseter muscle had a cross-sectional area of 956 +/- 295 microns2 (mean +/- SD; n = 45 cells) and were significantly larger than neurons projecting to the vasculature of the eartip skin (mean cross-sectional area +/- SD, 604 +/- 251 microns2; n = 39 cells). These results are consistent with physiological observations showing that muscle vasoconstrictor neurons have faster conduction velocities than cutaneous vasoconstrictor neurons. Furthermore, they suggest that muscle vasoconstrictor neurons may innervate a larger volume of vasculature compared with cutaneous vasoconstrictor neurons.