Vasoconstrictor, vasodilator and pilomotor pathways in sympathetic ganglia of guinea-pigs

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.

Distribution, nature, and origin of CXCL14-immunoreactive fibers in rat parotid gland

The distribution and nature of CXCL14-immunoreactive nerve fibers in salivary glands, especially the parotid gland was immunohistochemically investigated. Furthermore, the origin of parotid CXCL14-immunoreactive nerve fibers was determined by retrograde tracing experiments. CXCL14-immunoreactive nerve fibers were localized in the parotid, submandibular, and sublingual glands, particularly in the parotid gland. Double staining using identical sections revealed that a subpopulation of cells neuropeptide Y (NPY)-containing fibers was immunopositive for CXCL14 in the parotid gland. In the peripheral regions of acinar cells, CXCL14-immunoreactive fibers tended to coexist with NPY; however, perivascular NPY-immunoreactive fibers tended to be immunonegative for CXCL14. Parotid CXCL14-immunoreactive fibers were immunopositive for tyrosine hydroxylase (TH) but immunonegative for choline acetyltransferase and vasoactive intestinal peptide (VIP). After injection of horseradish peroxidase-labeled wheat germ agglutinin (WGA-HRP) in the parotid gland, retrogradely labeled neurons were seen in the superior cervical ganglion (SCG) and otic ganglion. Some of the WGA-immunoreactive somata in the SCG were immunopositive for CXCL14; however, no doubly-labeled somata were noted in the otic ganglion. These results indicate that CXCL14-immunoreactive nerve fibers originate in the SCG, and are sympathetic in nature. The coexistence of CXCL14 with NPY/TH suggests that CXCL14 may be associated with NPY/TH functions as a neuromodulatory chemokine in the parotid gland. The localization of CXCL14 nerve fibers around the acinar cells of the parotid gland indicates its involvement in acinar cell function, but not vasoconstriction.

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.

A Calcium-Dependent Chloride Current Increases Repetitive Firing in Mouse Sympathetic Neurons

Ca2+-activated ion channels shape membrane excitability in response to elevations in intracellular Ca2+. The most extensively studied Ca2+-sensitive ion channels are Ca2+-activated K+ channels, whereas the physiological importance of Ca2+-activated Cl- channels has been poorly studied. Here we show that a Ca2+-activated Cl- currents (CaCCs) modulate repetitive firing in mouse sympathetic ganglion cells. Electrophysiological recording of mouse sympathetic neurons in an in vitro preparation of the superior cervical ganglion (SCG) identifies neurons with two different firing patterns in response to long depolarizing current pulses (1 s). Neurons classified as phasic (Ph) made up 67% of the cell population whilst the remainders were tonic (T). When a high frequency train of spikes was induced by intracellular current injection, SCG sympathetic neurons reached an afterpotential mainly dependent on the ratio of activation of two Ca2+-dependent currents: the K+ [IK(Ca)] and CaCC. When the IK(Ca) was larger, an afterhyperpolarization was the predominant afterpotential but when the CaCC was larger, an afterdepolarization (ADP) was predominant. These afterpotentials can be observed after a single action potential (AP). Ph and T neurons had similar ADPs and hence, the CaCC does not seem to determine the firing pattern (Ph or T) of these neurons. However, inhibition of Ca2+-activated Cl- channels with anthracene-9'-carboxylic acid (9AC) selectively inhibits the ADP, reducing the firing frequency and the instantaneous frequency without affecting the characteristics of single- or first-spike firing of both Ph and T neurons. Furthermore, we found that the CaCC underlying the ADP was significantly larger in SCG neurons from males than from females. Furthermore, the CaCC ANO1/TMEM16A was more strongly expressed in male than in female SCGs. Blocking ADPs with 9AC did not modify synaptic transmission in either Ph or T neurons. We conclude that the CaCC responsible for ADPs increases repetitive firing in both Ph and T neurons, and it is more relevant in male mouse sympathetic ganglion neurons.

Individual sympathetic postganglionic neurons coinnervate myenteric ganglia and smooth muscle layers in the gastrointestinal tract of the rat

A full description of the terminal architecture of sympathetic axons innervating the gastrointestinal (GI) tract has not been available. To label sympathetic fibers projecting to the gut muscle wall, dextran biotin was injected into the celiac and superior mesenteric ganglia (CSMG) of rats. Nine days postinjection, animals were euthanized and stomachs and small intestines were processed as whole mounts (submucosa and mucosa removed) to examine CSMG efferent terminals. Myenteric neurons were counterstained with Cuprolinic Blue; catecholaminergic axons were stained immunohistochemically for tyrosine hydroxylase. Essentially all dextran-labeled axons (135 of 136 sampled) were tyrosine hydroxylase-positive. Complete postganglionic arbors (n = 154) in the muscle wall were digitized and analyzed morphometrically. Individual sympathetic axons formed complex arbors of varicose neurites within myenteric ganglia/primary plexus and, concomitantly, long rectilinear arrays of neurites within circular muscle/secondary plexus or longitudinal muscle/tertiary plexus. Very few CSMG neurons projected exclusively (i.e., ∼100% of an arbor's varicose branches) to myenteric plexus (∼2%) or smooth muscle (∼14%). With less stringent inclusion criteria (i.e., ≥85% of an axon's varicose branches), larger minorities of neurons projected predominantly to either myenteric plexus (∼13%) or smooth muscle (∼27%). The majority (i.e., ∼60%) of all individual CSMG postganglionics formed mixed, heterotypic arbors that coinnervated extensively (>15% of their varicose branches per target) both myenteric ganglia and smooth muscle. The fact that ∼87% of all sympathetics projected either extensively or even predominantly to smooth muscle, while simultaneously contacting myenteric plexus, is consistent with the view that these neurons control GI muscle directly, if not exclusively. J. Comp. Neurol. 524:2577-2603, 2016. © 2016 Wiley Periodicals, Inc.

Characterization of axons expressing the artemin receptor in the female rat urinary bladder: a comparison with other major neuronal populations

Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family that has been strongly implicated in development and regeneration of autonomic nerves and modulation of nociception. Whereas other members of this family (GDNF and neurturin) primarily target parasympathetic and nonpeptidergic sensory neurons, the artemin receptor (GFRα3) is expressed by sympathetic and peptidergic sensory neurons that are also the primary sites of action of nerve growth factor, a powerful modulator of bladder nerves. Many bladder sensory neurons express GFRα3 but it is not known if they represent a specific functional subclass. Therefore, our initial aim was to map the distribution of GFRα3-immunoreactive (-IR) axons in the female rat bladder, using cryostat sections and whole wall thickness preparations. We found that GFRα3-IR axons innervated the detrusor, vasculature, and urothelium, but only part of this innervation was sensory. Many noradrenergic sympathetic axons innervating the vasculature were GFRα3-IR, but the noradrenergic innervation of the detrusor was GFRα3-negative. We also identified a prominent source of nonneuronal GFRα3-IR that is likely to be glial. Further characterization of bladder nerves revealed specific structural features of chemically distinct classes of axon terminals, and a major autonomic source of axons labeled with neurofilament-200, which is commonly used to identify myelinated sensory axons within organs. Intramural neurons were also characterized and quantified. Together, these studies reveal a diverse range of potential targets by which artemin could influence bladder function, nerve regeneration, and pain, and provide a strong microanatomical framework for understanding bladder physiology and pathophysiology.

Development of neuropeptide Y-containing neurons in sympathetic ganglia of rats

Expression of neuropeptide Y (NPY) in the sympathetic ganglia was investigated by immunohistochemistry and tract tracing. The distribution of NPY immunoreactivity (IR) was studied in the superior cervical ganglion (SCG), stellate ganglion (SG) and celiac ganglion (CG) from rats of different ages (newborn, 10-day-old, 20-day-old, 30-day-old, 2-month-old, 6-month-old, 24-month-old). We observed that the percentage of NPY-IR neuronal profiles increased during early postnatal development. In the SCG and SG, the percentage of NPY-IR profiles enlarged in the first month of life from 43±3.6% (SCG) and 46±3.8% (SG) until 64±4.1% (SCG) and 58±3.5% (SG). The percentage of NPY-IR profiles in the CG increased during the period between 20days (65±3.8%) and 30days (82±5.1%) of animals' life and did not change in further development. In newborn and 10-day-old rats, a large portion of NPY-IR neurons was also calbindin D28K (CB)-IR in all sympathetic ganglia. The proportion of CB-IR substantially decreased during next 10days in the SCG, SG and CG. NPY-IR was approximately present in a half of the postganglionic neurons innervating muscle vessels of the neck and forearm, and the percentage of labeled NPY-IR profiles did not change during the development. Only single Ki67-IR neurons were also NPY-IR in the SCG, SG and CG in newborns and not in older animals. No NPY+/caspase 3+IR neurons were observed. Finally, the process of morphological changes in the size and percentages of NPY-IR profiles is complete in rats by the first month of life.

Immunohistochemical characterization of superior cervical ganglion neurons supplying porcine parotid salivary gland

The main goal of our study was to investigate the chemical coding of the superior cervical ganglion (SCG) sympathetic neurons supplying the porcine parotid gland. Additionally, the chemical nature of the vicinal nerve fibers surrounding the parotid SCG perikarya was investigated. Fast blue (FB) retrograde tracing of the parotid gland and immunofluorescent labelling of SCG neurons were studied in juvenile female pigs. Microscopic analysis revealed that only ipsilateral SCG neurons were retrogradely labelled. The labelled neurons formed a discrete cluster in the middle and caudal region of the ganglion. Immunofluorescent labelling revealed that virtually all of the FB-positive parotid gland neurons were immunoreactive to tyrosine hydroxylase (TH), confirming their sympathetic nature. In addition to TH, the majority of the FB-positive neurons were found to be immunoreactive to calbindin (CB) and to a lesser extent for neuropeptide Y (NPY), leu-enkephalin (LENK) and galanin (GAL). In the close proximity of the FB-traced perikarya, a large number of immunoreactive (IR) vasoactive intestinal peptide (VIP-IR), pituitary adenylate cyclase-activating polypeptide (PACAP-IR), nitric oxide synthase (NOS-IR) processes were identified. Moreover, calcitonin gene related peptide-immunoreactive (CGRP-IR), substance P-immunoreactive (SP-IR), vesicular acetylcholine transporter (VAChT-IR), calretinin (CRT-IR), GAL-IR, LENK-IR and CB-IR protrusions were observed. The results of the present study provide a detailed characteristic of the location and neurochemical coding of sympathetic SCG neurons innervating the parotid salivary gland of the pig and lay ground for more advanced, clinical studies on salivary gland innervations.

Neuropeptide coding of sympathetic preganglionic neurons; focus on adrenally projecting populations

Chemical coding of sympathetic preganglionic neurons (SPN) suggests that the chemical content of subpopulations of SPN can define their function. Since neuropeptides, once synthesized are transported to the axon terminal, most demonstrated chemical coding has been identified using immunoreactive terminals at the target organ. Here, we use a different approach to identify and quantify the subpopulations of SPN that contain the mRNA for pituitary adenylate cyclase activating polypeptide (PACAP) or enkephalin. Using double-labeled immunohistochemistry combined with in situ hybridization (ISH) we firstly identified the distribution of these mRNAs in the spinal cord and determined quantitatively, in Sprague-Dawley rats, that many SPN at the T4-T10 spinal level contain preproPACAP (PPP+, 80 ± 3%, n=3), whereas a very small percentage contain preproenkephalin (PPE+, 4 ± 2%, n=4). A similar neurochemical distribution was found at C8-T3 spinal level. These data suggest that PACAP potentially regulates a large number of functions dictated by SPN whereas enkephalins are involved in few functions. We extended the study to explore those SPN that control adrenal chromaffin cells. We found 97 ± 5% of adrenally projecting SPN (AP-SPN) to be PPP+ (n=4) with only 47 ± 3% that were PPE+ (n=5). These data indicate that adrenally projecting PACAPergic SPN regulate both adrenal adrenaline (Ad) and noradrenaline (NAd) release whereas the enkephalinergic SPN subpopulation must control a (sub) population of chromaffin cells - most likely those that release Ad. The sensory innervation of the adrenal gland was also determined. Of the few adrenally projecting dorsal root ganglia (AP-DRG) observed, 74 ± 12% were PPP+ (n=3), whereas 1 ± 1% were PPE+ (n=3). Therefore, if sensory neurons release peptides to the adrenal medulla, PACAP is most likely involved. Together, these data provide a neurochemical basis for differential control of sympathetic outflow particularly that to the adrenal medulla.

Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.

Segregation of met-enkephalin from vesicular acetylcholine transporter and choline acetyltransferase in sympathetic preganglionic varicosities mostly lacking synaptophysin and synaptotagmin

Sympathetic preganglionic neurons (SPN) coexpress the acetylcholine (ACh)-synthesizing enzyme choline acetyltransferase and different peptides in their cell bodies, but can express them independently in separate varicosities, indicating that SPN segregate transmitters to different synapses. Consequently, there are populations of preganglionic varicosities (peptidergic and noncholinergic) that store peptides but not ACh. We studied in the cell bodies and axon processes of the rat SPN the expression and the proportional coexpression of the vesicular ACh transporter-like immunoreactivity (VAChT), a specific marker of cholinergic synaptic vesicles or ChAT-like immunoreactivity (ChAT), and the peptide methionine enkephalin-like immunoreactivity (mENK), and confirmed the presence of a population of SPN peptidergic, noncholinergic varicosities. We characterized these varicosities by exploring the occurrence of synaptophysin-like immunoreactivity (Syn), a marker of small clear vesicles, and synaptotagmin-like immunoreactivity (Syt), a preferential marker of large dense core vesicles. We found that (i) VAChT and mENK, like ChAT-mENK, were coexpressed in only 59% of the mENK-containing varicosities, although they colocalized in the SPN cell bodies; and (ii) almost 60% of the population of mENK-containing varicosities did not express Syn or Syt, and over 80% of the mENK-containing varicosities negative for VAChT also lacked Syn. These data prove that SPN segregate mENK from VAChT and ChAT, and show that most of the subset of mENKergic varicosities negative for VAChT also does not express Syn, suggesting the presence of a different vesicular pattern in these sympathetic preganglionic varicosities.

Peripheral projections of NESP55 containing neurons in the rat sympathetic ganglia

The peripheral projections of neurons expressing neuroendocrine secretory protein 55 (NESP55), a novel member of the chromogranin family, were studied by retrograde tracing technique. It was found that NESP55 positive neurons in the rat superior cervical ganglion projected to a number of targets including the submandibular gland, the cervical lymph nodes, the forehead skin, the iris, but not to the thyroid. Among these NESP55 positive target-projecting neurons, a subpopulation contained neuropeptide Y (NPY), a vasoconstrictor. Forepaw pad projecting neurons were found exclusively in the stellate ganglion, almost all of which (approximately 90%) were immunoreactive to NESP55. Colocalization of NESP55 and calcitonin gene-related peptide (CGRP), a peptide involved in sudomotor effects, was observed in a subpopulation of these paw pad projecting neurons, as was colocalization of NESP55 and NPY. The data suggest that NESP55 may have a functional role in some populations of sympathetic neurons.

Disruption of prepulse inhibition after stimulation of central but not peripheral alpha-1 adrenergic receptors

Prepulse inhibition (PPI) refers to the attenuation of startle when a weak prestimulus precedes the startling stimulus. PPI is deficient in several psychiatric illnesses involving poor sensorimotor gating. Previous studies indicate that alpha1 adrenergic receptors regulate PPI, yet the extent to which these effects are mediated by central vs peripheral receptors is unclear. The present studies compared the effects of intracerebroventricular (ICV) vs intraperitoneal (IP) delivery of several alpha1 receptor agonists on PPI. Male Sprague-Dawley rats received either cirazoline (0, 10, 25, 50 microg/5 microl), methoxamine (0, 30, 100 microg/5 microl), or phenylephrine (0, 3, 10, 30 microg/5 microl) ICV immediately before testing. Separate groups received either cirazoline (0, 0.25, 0.50, 0.75 mg/kg), methoxamine (0, 2, 5, 10 mg/kg), or phenylephrine (0, 0.1, 2.0 mg/kg) IP 5 min before testing. PPI, baseline startle responses, and piloerection, an index of autonomic arousal, were measured. Cirazoline disrupted PPI; effective ICV doses were approximately six times lower than effective IP doses. Methoxamine disrupted PPI after ICV infusion but failed to affect PPI with IP doses that were up to 30-fold higher than the effective ICV dose. Phenylephrine disrupted PPI with ICV administration, but did not alter PPI after IP injection of even a 20-fold higher dose. None of the ICV treatments altered baseline startle magnitude, but phenylephrine and methoxamine lowered startle after administration of high systemic doses. Piloerection was induced by cirazoline via either route of administration, and by IP methoxamine and phenylephrine, but not by ICV infusion of methoxamine or phenylephrine. These findings indicate that alpha1 receptor-mediated PPI disruption occurs exclusively through stimulation of central receptors and is dissociable from alterations in baseline startle or autonomic effects.

Choline acetyl transferase and neuropeptide immunoreactivities are colocalized in somata, but preferentially localized in distinct axon fibers and boutons of cat sympathetic preganglionic neurons

Cholinergic sympathetic preganglionic neurons (SPN) coexpress the biosynthetic enzyme for acetylcholine, choline acetyl-transferase (ChAT), and neuropeptides such as enkephalin (ENK) in their cell bodies. However, it is not clear whether they also coexpress ChAT and neuropeptides in axon fibers and boutons. To explore coexpression of ChAT and neuropeptides in somata and axon processes of SPN, we investigated, using immunohistochemistry, retrograde labeling, confocal analysis, and tridimensional reconstruction, whether ChAT and the peptides neurotensin, methionine-ENK, somatostatin, calcitonin gene-related peptide, and vasoactive intestinal peptide colocalize in somata, axons fibers, and boutons of cat SPN. Practically, complete colocalization for these peptides and ChAT was observed in SPN somata. Conversely, in most instances we observed independent localization of immunoreactivity (IR) for ChAT and the peptides in axon fibers and boutons. The minor colocalization between ChAT- and peptide-IR in preganglionic fibers could correspond to a sequential axonal transport of ChAT and peptides, since we observed coexistence of these transmitters after blocking axonal transport. Contrary to Dale's principle, our results suggest that SPN can synthesize ChAT and peptides in their cell bodies and route them to distinct axon boutons or terminals in sympathetic ganglia. Presence of axon boutons containing either ChAT or neuropeptides lead us to suggest a new neurochemical pattern of cotransmission in sympathetic ganglia based on the concurrent release of transmitters and cotransmitters from distinct presynaptic boutons, rather than in the corelease of these mediators from the same axon process. The possibility that cellular segregation could be transient and depend on functional requirements is considered.

Dual mechanisms of angiotensin-induced activation of mouse sympathetic neurones

Ang II directly activates neurones in sympathetic ganglia. Our goal was to define the electrophysiological basis of this activation. Neurones from mouse aortic-renal and coeliac ganglia were identified as either 'tonic' or 'phasic'. With injections of depolarizing currents, action potentials (APs) were abundant and sustained in tonic neurones (TNs) and scarce or absent in phasic neurones (PNs). Resting membrane potentials were equivalent in TNs (-48 +/- 2 mV, n = 18) and PNs (-48 +/- 1 mV, n = 23) while membrane resistance was significantly higher in TNs. Ang II depolarized and increased membrane resistance equally in both TNs (n = 8) and PNs (n = 8) but it induced APs only in TNs, and enhanced current-evoked APs much more markedly in TNs (P < 0.05). The AT1 receptor antagonist losartan (2 microm, n = 6) abolished all responses to Ang II, whereas the AT2 receptor blocker PD123,319 had no effect. The transient K+ current (IA), which was more than twice as large in TNs as in PNs, was significantly inhibited by Ang II in TNs only whereas the delayed sustained K+ current (IK), which was comparable in both TNs and PNs, was not inhibited. M currents were more prominent in PNs and were inhibited by Ang II. The IA channel blocker 4-aminopyridine triggered AP generation in TNs and prevented the Ang II-induced APs but not the depolarization. Blockade of M currents by oxotremorine M or linopirdine prevented the depolarizing action of Ang II. The protein kinase C (PKC) inhibitor H7 (10 microm, n = 9) also prevented the Ang II-induced inhibition of IA and the generation APs but not the depolarization nor the inhibition of M currents. Conversely, the PKC agonist phorbol 12-myristate 13-acetate mimicked the Ang II effects by triggering APs. The results indicate that Ang II may increase AP generation in sympathetic neurones by inducing a PKC-dependent inhibition of IA currents, and a PKC-independent depolarization through inhibition of M currents. The differential expression of various K+ channels and their sensitivity to phosphorylation by PKC may determine the degree of activation of sympathetic neurones and hence may influence the severity of the hypertensive response.

How many types of cholinergic sympathetic neuron are there in the rat stellate ganglion?

Sympathetic cholinergic postganglionic neurons are present in many sympathetic ganglia. Three classes of sympathetic cholinergic neuron have been reported in mammals; sudomotor neurons, vasodilator neurons and neurons innervating the periosteum. We have examined thoracic sympathetic ganglia in rats to determine if any other classes of cholinergic neurons exist. We could identify cholinergic sudomotor neurons and neurons innervating the rib periosteum, but confirmed that cholinergic sympathetic vasodilator neurons are absent in this species. Sudomotor neurons contained vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) and always lacked calbindin. Cholinergic neurons innervating the periosteum contained VIP and sometimes calbindin, but always lacked CGRP. Cholinergic neurons innervating the periosteum were usually surrounded by terminals immunoreactive for CGRP. We conclude that if any undiscovered populations of cholinergic neurons exist in the rat thoracic sympathetic chain, then they are indistinguishable in size, neurochemistry and inputs from sudomotor or cholinergic neurons innervating the periosteum. It may be that the latter two populations account for all cholinergic neurons in the rat thoracic sympathetic chain ganglia.

Phosphorylated extracellular signal-regulated kinase 1/2 immunoreactivity identifies a novel subpopulation of sympathetic preganglionic neurons

Distinct chemical codes are thought to reflect functional specificity in sympathetic preganglionic neurons (SPN). Although a number of chemical candidates have been identified including neurotransmitter-related, calcium-binding and other proteins, signal transduction proteins have been largely neglected. Not only might these chemicals allow discrimination of functionally unique chemical signatures, but they may also identify activated neurons. Immunoreactivity (ir) to phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) was differentially located within the thoracic spinal cord depending upon which of three forms of killing was used: the only exception to this was the intermediolateral cell column (IML) which was consistently, densely labeled. The presence or absence of p-ERK1/2 in SPN (n=17,541) within the IML of the thoraco-lumbar spinal cord was determined in seven rats. SPN were identified on the basis of their location, size and that they contained choline acetyltransferase ir. On average, 58% of SPN contained p-ERK1/2, however, more SPN in both the upper (72%; C8-T4) and lower (78%; T11-L3) thoraco-lumbar spinal cord contained p-ERK1/2-ir than the middle thoracic region (47%; T4-T10). p-ERK1/2-ir was also examined in SPN (n=1895) innervating the adrenal medulla (identified by retrograde tracing using cholera toxin B subunit) combined with localization of neuronal nitric oxide synthase (nNOS) in three rats. On average, 64% of adrenal SPN contain p-ERK1/2-ir, and it was confirmed that all adrenal SPN contain nNOS-ir. It appears that p-ERK1/2-ir SPN, described in this study, have tonically activated receptors that are coupled to intracellular signal transduction pathways that lead to the phosphorylation of ERK1/2.

Immunocytochemical properties of stellate ganglion neurons during early postnatal development

Neurotransmitter features in sympathetic neurons are subject to change during development. To better understand the neuroplasticity of sympathetic neurons during early postnatal ontogenesis, this study was set up to immunocytochemically investigate the development of the catecholaminergic, cholinergic, and peptidergic phenotypes in the stellate ganglion of mice and rats. The present study was performed on Wistar rats and Swiss mice of different ages (newborn, 10-day-old, 20-day-old, 30-day-old, and 60-day-old). To this end, double labeling for tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), vasoactive intestinal (poly)peptide (VIP), neuropeptide Y (NPY), galanin (GAL), and somatostatin (SOM) was applied. The results obtained indicate that the majority of the neurons in the stellate ganglion of both species were TH-positive from birth onward and that a large part of these neurons also contained NPY. The percentage of neurons containing TH and NPY invariably increased with age up to 60 days postnatally. A smaller portion of the stellate ganglion neurons contained other types of neuropeptides and showed a distinct chronological pattern. The proportion of VIP- and ChAT-positive neurons was maximal in 10-day-old animals and then decreased up to 60 days of age, whereas the number of SOM-positive cells in rats significantly decreased from birth onward. In newborn rats, VIP-, ChAT- and SOM-positive neurons were largely TH-positive, while their proportions decreased in 10-day-old and older rats. Accordingly, the largest part of VIP-positive neurons also expressed SOM immunoreactivity at birth, after which the number of neurons containing both peptides diminished. The VIP- and SOM-positive cells did not contain NPY in any of the age groups studied. In rats up to 10 days of life, GAL-immunoreactive (-IR) neurons were scarce, after which their number increased to reach a maximal value in 30-day-old animals and then declined again. The SOM-reactive cells had the smallest size in all rats, while the largest neurons were those containing ChAT. In the mouse stellate ganglion, VIP- and ChAT-IR neurons were larger in comparison to NPY- and TH-IR cells. Our study further revealed some species differences: compared to mice the proportion of neurons containing TH and NPY was higher in rats at all ages under study. Furthermore, no GAL-immunostained neurons were found in mice and the number of SOM-positive cells in mice was limited compared to that observed in rats. In conclusion, the development of neurotransmitter composition is complete in rats and mice by their second month of life. At this age, the percentages of immunopositive cells have become similar to those reported in adult animals.

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.

Chemical coding of sympathetic neurons controlling the tarsal muscle of the rat

Sympathetic axons in the upper eyelid and in tissues in the superior retro-orbital space were examined for NPY immunoreactivity. Sympathetic nerve terminals containing co-localised NPY were associated with blood vessels, the conjunctiva and the Meibomian glands. The acini of the Harderian gland completely lacked sympathetic innervation. Sympathetic axons lacking NPY were only found in the tarsal muscle. In addition, a minority of terminals, located in the more proximal part of the tarsal muscle, contained weak immunoreactivity to NPY. Injections of the retrograde tracer, Fast Blue, into the eyelid or retro-orbital space labelled postganglionic somata in the superior cervical ganglion. While many retrogradely labelled somata were immunoreactive for NPY, around half lacked NPY immunoreactivity and so are likely to project to the tarsal muscle. Most of the retrogradely labelled postganglionic somata lacking NPY were surrounded by terminals immunoreactive for met-enkephalin, leu-enkephalin and met-enkephalin arg-gly-leu which were all found to be present in the same nerve terminals. Sectioning the cervico-sympathetic trunk eliminated all enkephalin-immunoreactive pericellular baskets. Many enkephalin-immunoreactive pericellular terminals contained co-localised VAChT, calretinin and calbindin immunoreactivity, but completely lacked nitric oxide synthase immunoreactivity. A second population of nerve terminals that were immunoreactive for nitric oxide synthase also surrounded tarsal muscle-projecting neurons, but these terminals lacked immunoreactivity to enkephalin. Thus, postganglionic neurons projecting to the tarsal muscle are of at least two chemical phenotypes (with or without NPY) and they receive convergent input from at least two populations of preganglionic neurons with distinctive chemical phenotypes.

Re-establishment of neurochemical coding of preganglionic neurons innervating transplanted targets

We investigated the effect on neurochemical phenotype of changing the targets innervated by sympathetic preganglionic neurons. In neonatal rats, the adrenal gland was transplanted into the neck, to replace the postganglionic neurons of the superior cervical ganglion. Transplanted adrenal glands survived, and contained noradrenergic and adrenergic chromaffin cells, and adrenal ganglion cells. Retrograde tracing from the transplants showed that they were innervated by preganglionic neurons that would normally have supplied postganglionic neurons of the superior cervical ganglion. The neurochemical phenotypes of preganglionic axons innervating transplanted chromaffin cells were compared with those innervating the normal adrenal medulla or superior cervical ganglion neurons. As in the normal adrenal gland, preganglionic nerve fibres apposing transplanted chromaffin cells were cholinergic. The peptide and calcium-binding protein content of preganglionic fibres was similar in normal and transplanted adrenal glands. In both cases, cholinergic fibres immunoreactive for enkephalin targeted adrenergic chromaffin cells, whilst cholinergic fibres with co-localised calretinin-immunoreactivity innervated noradrenergic chromaffin cells and adrenal ganglion cells. In contrast to the innervation of normal adrenal glands, these axons lacked immunoreactivity to nitric oxide synthase. In a set of control experiments, the superior cervical ganglion was subjected to preganglionic denervation in rat pups the same age as those that received adrenal transplants, and the ganglion was allowed to be re-innervated over the same time course as the adrenal transplants were studied. When the superior cervical ganglion was re-innervated by preganglionic nerve fibres, we observed that all aspects of chemical coding were restored, including cholinergic markers, nitric oxide synthase, enkephalin, calcitonin gene-related peptide and calcium binding proteins in predicted combinations, although the density of nerve fibres was always lower in re-innervated ganglia. These data show that the neurochemical phenotypes expressed by preganglionic neurons re-innervating adrenal chromaffin cells are selective and similar to those seen in the normal adrenal gland. Two explanations are advanced: either that contact of preganglionic axons with novel target cells has induced a switch in their neurochemical phenotypes, or that there has been target-selective reinnervation by pre-existing fibres of appropriate phenotype. Regardless of which of these alternatives is correct, the restoration of normal preganglionic codes to the superior cervical ganglion following denervation supports the idea that the target tissue influences the neurochemistry of innervating preganglionic neurons.

Heterogeneous expression of SNAP-25 and synaptic vesicle proteins by central and peripheral inputs to sympathetic neurons

Neurons in prevertebral sympathetic ganglia receive convergent synaptic inputs from peripheral enteric neurons in addition to inputs from spinal preganglionic neurons. Although all inputs are functionally cholinergic, inputs from these two sources have distinctive neurochemical and functional profiles. We used multiple-labeling immunofluorescence, quantitative confocal microscopy, ultrastructural immunocytochemistry, and intracellular electrophysiologic recordings to examine whether populations of inputs to the guinea pig coeliac ganglion express different levels of synaptic proteins that could influence synaptic strength. Boutons of enteric intestinofugal inputs, identified by immunoreactivity to vasoactive intestinal peptide, showed considerable heterogeneity in their immunoreactivity to synaptosome-associated protein of 25 kDa (SNAP-25), synapsin, synaptophysin, choline acetyltransferase, and vesicular acetylcholine transporter. Mean levels of immunoreactivity to these proteins were significantly lower in terminals of intestinofugal inputs compared with terminals of spinal preganglionic inputs. Nevertheless, many boutons with undetectable levels of SNAP-25 immunoreactivity formed morphologically normal synapses with target neurons. Treatment with botulinum neurotoxin type A (20-50 nM for 2 hours in vitro) generated significant cleavage of SNAP-25 and produced similar dose- and time-dependent inhibitions of synaptic transmission from all classes of inputs, regardless of their mean level of SNAP-25 expression. The simplest interpretation of these results is that only synaptic boutons with detectable levels of SNAP-25 immunoreactivity contribute significantly to fast cholinergic transmission. Consequently, the low synaptic strength of intestinofugal inputs to final motor neurons in sympathetic pathways may be due in part to the low proportion of their boutons that express SNAP-25 and other synaptic proteins.

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.

Innervation of guinea-pig stellate ganglia by nitric oxide synthase, cocaine- and amphetamine-regulated transcript protein- and pituitary adenylate cyclase activating polypeptide-immunoreactive fibers

The present study analyzed using immunohistochemical labeling the distribution and co-localization of nitric oxide synthase (NOS), cocaine- and amphetamine-regulated transcript peptide (CARTp) and pituitary adenylate cyclase activating polypeptide (PACAP) with choline acetyltransferase (ChAT)-immunoreactive fibers in the guinea-pig stellate ganglia. ChAT-immunoreactive fibers make pericellular baskets around virtually all stellate ganglia neurons. Pericellular baskets of NOS, CARTp and PACAP fibers were also present around numerous stellate ganglia neurons. Although all the NOS and PACAP fibers also exhibited ChAT immunoreactivity, only some of the CARTp fibers were ChAT-immunoreactive. No evidence of co-localization of NOS, PACAP and CARTp was obtained.These results indicate that NOS, PACAP and CARTp are present in distinct preganglionic axons innervating the guinea-pig stellate ganglia.

The developmental expression of vasoactive intestinal peptide (VIP) in cholinergic sympathetic neurons depends on cytokines signaling through LIFRβ-containing receptors

Sympathetic ganglia are composed of noradrenergic and cholinergic neurons. Cholinergic sympathetic neurons are characterized by the expression of choline acetyl transferase (ChAT), vesicular acetylcholine transporter (VAChT) and the vasoactive intestinal peptide (VIP). To investigate the role of cytokine growth factor family members in the development of cholinergic sympathetic neurons, we interfered in vivo with the function of the subclass of cytokine receptors that contains LIFRβ as essential receptor subunit. Expression of LIFRβ antisense RNA interfered with LIFRβ expression and strongly reduced the developmental induction of VIP expression. By contrast, ganglion size and the number of ChAT-positive cells were not reduced. These results demonstrate a physiological role of cytokines acting through LIFRβ-containing receptors in the control of VIP expression in sympathetic neurons.

The development of postganglionic sympathetic neurons: coordinating neuronal differentiation and diversification

The fine-tuned operation of the nervous system is accomplished by a diverse set of neurons which differ in their morphology, biochemistry and, consequently, their functional properties. The accurate interconnection between different neuron populations and their target tissues is the prerequisite for physiologically appropriate information processing. This is exemplified by the regulatory action of the autonomic nervous system in vertebrates to sustain homeostasis under changing physiological demands. For this purpose, the coordination of divergent regulatory responses is required in a multitude of tissues spread over the entire body. To meet this task, diverse neuronal populations interact at different levels. In the sympathetic system. chemical relations between preganglionic and postganglionic neurons appear to differ along the rostrocaudal axis. In addition, postganglionic neurons innervating different target tissues at a segmental level have distinct properties. Differences in their preganglionic innervation and their integrative membrane properties result in diverse activation patterns upon reflex stimulation. Moreover, postganglionic neurons differ in the transmitter molecules they employ to convey information to the target tissues. The segregation of noradrenaline and acetylcholine to different populations of postganglionic sympathetic neurons is well established. A combination of cellular and molecular approaches has begun to uncover how such a complex system may be generated during development. Growth and transcription factors involved in noradrenergic and cholinergic differentiation are characterised. Interestingly, they can also promote the expression of proteins involved in transmitter secretion. As the proteins participating in the vesicle cycle are expressed in many neuron populations, whereas the enzymes of transmitter biosynthesis are restricted to subpopulations of neurons, the findings suggest that early in neuronal development subpopulation-specific and more widely expressed neuronal properties can be commonly induced. Still, many details concerning the signals involved in the induction of the neurotransmitter synthesis and release machinery remain to be worked out. Likewise, the regulatory processes resulting in differences of electrophysiological membrane properties and the specific recognition between pre- and postganglionic neurons have to be determined. Ultimately, this will lead to an understanding at the molecular level of the development of a nervous system with diverse neuronal populations that are specifically interconnected to distinct input neurons and target tissues as required for the performance of a complex regulatory function.

Selective projections of cholecystokinin-8 immunoreactive fibers to galanin immunoreactive sympathetic preganglionic neurons in a teleost, Stephanolepis cirrhifer

In the cellular column of sympathetic preganglionic neurons (SPNs) of the filefish Stephanolepis cirrhifer, neurons containing galanin (GAL) form a distinct population projecting specifically to non-adrenergic postganglionic neurons in the celiac and cranial sympathetic ganglia. The present study showed that virtually all of the GAL-immunopositive SPNs made contact with many nerve terminals immunopositive for cholecystokinin octapeptide (CCK-8). GAL-negative preganglionic neurons made contact with only 26% of this type of nerve terminal; CCK-8-immunopositive nerve fibers appeared to project selectively to GAL-immunopositive SPNs with projections to specific targets. The CCK-8-positive nerve fibers might be of primary sensory origin, and participate in the visceral reflexes.

Growth and neurotrophic factors regulating development and maintenance of sympathetic preganglionic neurons

The functional anatomy of sympathetic preganglionic neurons is described at molecular, cellular, and system levels. Preganglionic sympathetic neurons located in the intermediolateral column of the spinal cord connect the central nervous system with peripheral sympathetic ganglia and chromaffin cells inside and outside the adrenal gland. Current knowledge is reviewed of the development of these neurons, which share their origin with progenitor cells, giving rise to somatic motoneurons in the ventral horn. Their connectivities, transmitters involved, and growth factor receptors are described. Finally, we review the distribution and functions of trophic molecules that may have relevance for development and maintenance of preganglionic sympathetic neurons.

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.

The early expression of VAChT and VIP in mouse sympathetic ganglia is not induced by cytokines acting through LIFRbeta or CNTFRalpha

Sympathetic ganglia consist of noradrenergic and cholinergic neurons. The cholinergic marker protein vesicular acetylcholine transporter (VAChT) and the neuropeptide vasoactive intestinal peptide (VIP), co-expressed in mature cholinergic sympathetic neurons, are first detectable during embryonic development of rat sympathetic ganglia. However, the subpopulation of cholinergic sympathetic neurons which innervates sweat glands in mammalian footpads starts to express VAChT and VIP during the first postnatal weeks, under the influence of sweat gland-derived signals. In vitro evidence suggests that the sweat gland-derived cholinergic differentiation factor belongs to a group of neuropoietic cytokines, including LIF, CNTF and CT-1, that act through a LIFRbeta-containing cytokine receptor. To investigate whether the embryonic expression of cholinergic properties is elicited by a related cytokine, the expression of VAChT and VIP was analyzed in stellate ganglia of mice deficient for the cytokine receptor subunits LIFRbeta or CNTFRalpha. The density of VAChT- and VIP-immunoreactive cells in stellate ganglia of new-born animals was not different in LIFRbeta(-/-) and CNTFRalpha(-/-) ganglia as compared to ganglia from wild-type mice. These results demonstrate that the early, embryonic expression of VAChT and VIP is not induced by cytokines acting through LIFRbeta- or CNTFRalpha-containing receptors.

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.

Sympathetic and sensory innervations are heterogeneously distributed in relation to the blood vessels at the extensor carpi radialis brevis muscle origin of man

By using immunohistochemistry and antibodies to a general nerve marker, protein gene product (PGP) 9.5, the overall innervation at the extensor carpi radialis brevis (ECRB) muscle origin was investigated in patients with tennis elbow and in healthy controls. The autonomic innervation was studied by using antibodies to neuropeptide Y (NPY), tyrosine hydroxylase (TH), and vasoactive intestinal peptide (VIP). The sensory innervation was visualized by using antibodies to substance P and calcitonin gene-related peptide. PGP 9.5 immunoreactions were detected in association with small blood vessels and arteries and within nerve bundles. There was, however, heterogeneity in the perivascular nerve fiber distribution since some blood vessels exhibited a high degree of PGP 9.5 innervation and some negligible or no such innervation at all. There was marked TH/NPY innervation in the walls of a subpopulation of the arteries, basically no VIP-containing nerves, and sensory innervation restricted to the small blood vessels. These observations show that the ECRB muscle origin is supplied with heterogeneously distributed sympathetic and sensory innervations and, furthermore, that there appears to be an imbalance between the vasoconstrictor and vasodilator innervations along the vascular tree in this region.

The sympathomimetic agent, 6-hydroxydopamine, accelerates cutaneous wound healing

Using pharmacological stimulation of sympathetic terminals, the present study examines the role of sympathetic post-ganglionic neurons in cutaneous wound healing. Effects of local stimulation of sympathetic post-ganglionic neurons with 0.2 mg/kg 6-hydroxydopamine were studied on the healing of full-thickness skin incisions in rats. Epidermal wound healing was measured by a novel non-invasive quantitative method based on the increasing electrical resistance of healing skin. Dermal healing was determined by measuring wound breaking strength using an Instron Universal Testing device. We report a 35% increase in the rate of epidermal wound healing (P < 0.05. n(e) = 21, n(c) = 18) and a 43% increase in dermal strength (P < 0.05, n(e) = 13, n(c) = 10) after 6-hydroxydopamine treatment. Thus, our results show that pharmacological stimulation of sympathetic post-ganglionic neurons markedly accelerates skin wound healing at both the epidermal and dermal levels. This is the first study to show that peripheral nerve stimulation and specifically sympathetic stimulation accelerates cutaneous wound healing. We discuss these results in relation to neurogenic inflammation.

Central control of the cardiovascular and respiratory systems and their interactions in vertebrates

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

Pathway-specific expression of PKC and PKA in sympathetic neurons

We used multiple-labelling immunofluorescence, intracellular dye injection, electrophysiological recording and confocal microscopy to examine the expression of immunoreactivity to protein kinase C (PKC) and protein kinase A (PKA) in sympathetic ganglia of guinea-pigs. PKCalpha and PKCgamma were widespread in vasoconstrictor and pilomotor neurons. High levels of PKA RIIalpha and RIIbeta were restricted to neurons that lacked significant expression of PKC, including somatostatin-containing neurons projecting to the gut, and non-noradrenergic vasodilator neurons. In coeliac ganglia, most neurons with PKC contained neuropeptide Y and displayed phasic patterns of action potential firing, often with a long after-hyperpolarization. Tonically firing neurons lacked both neuropeptide Y and PKC. These results show remarkably pathway-specific expression of protein kinases in functionally identified populations of sympathetic neurons.

Two populations of sympathetic neurons project selectively to mesenteric artery or vein

The objective of this study was to determine whether sympathetic neurons of the inferior mesenteric ganglion (IMG) projecting to mesenteric arteries could be distinguished by their localization, neurochemical phenotype, and electrophysiological properties from neurons projecting to mesenteric veins. In an in vitro intact vasculature-IMG preparation, neurons were labeled following intraluminal injection of Fluoro-Gold or rhodamine beads into the inferior mesenteric artery (IMA) or vein (IMV). The somata of neurons projecting to IMA were localized in the central part of the IMG, whereas those projecting to IMV were localized more peripherally. None of the labeled neurons was doubly labeled. Neuropeptide Y immunoreactivity was found in 18.9% of neurons innervating the IMA, but not in neurons innervating the IMV. Identified neurons were dissociated and characterized using whole cell patch-clamp recording. After direct soma depolarization, all of the labeled arterial and venous neurons were classified as tonic firing, compared with only 40% of unlabeled neurons; the remaining 60% of unlabeled neurons were phasic firing. The results indicate that IMG neurons projecting to mesenteric arteries are distinct from neurons projecting to mesenteric veins.

Quantitative analysis of the sympathetic innervation of the rat knee joint

Retrograde tracing with Fluoro-Gold (FG) was used to identify the complete population of knee joint sympathetic postganglionic efferents in the lumbar sympathetic chain of adult female Wistar rats. In 6 rats, the total number and distribution of FG-labelled neurons in the lumbar sympathetic chain was determined. The rat knee joint is supplied by an average of 187+/-57 sympathetic afferents with the majority at the L3 and L4 levels. Immunohistochemistry using antibodies specific for tyrosine hydroxylase (TH), somatostatin (SS) or vasoactive intestinal polypeptide (VIP) revealed that 33 % of knee joint sympathetic afferents contained TH, 42 % contained VIP, and none contained somatostatin. Retrograde tracing with FG provided accurate and reproducible labelling of the joint-innervating subpopulation of sympathetic efferent neurons. This model lends itself to the further study of the molecular responses of this neuronal population in the various disorders and conditions affecting joints.