Non-noradrenergic sympathetic neurons project to extramuscular feed arteries and proximal intramuscular arteries of skeletal muscles in guinea-pig hindlimbs

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.

Changes in the axon terminals of primary afferents from a single vibrissa in the rat trigeminal nuclei after active touch deprivation or exposure to an enriched environment

Lasting modifications of sensory input induce structural and functional changes in the brain, but the involvement of primary sensory neurons in this plasticity has been practically ignored. Here, we examine qualitatively and quantitatively the central axonal terminations of a population of trigeminal ganglion neurons, whose peripheral axons innervate a single mystacial vibrissa. Vibrissa follicles are heavily innervated by myelinated and unmyelinated fibers that exit the follicle mainly through a single deep vibrissal nerve. We made intraneural injections of a mixture of cholera-toxin B (CTB) and isolectin B4, tracers for myelinated and unmyelinated fibers, respectively, in three groups of young adult rats: controls, animals subjected to chronic haptic touch deprivation by unilateral whisker trimming, and rats exposed for 2 months to environmental enrichment. The regional and laminar pattern of terminal arborizations in the trigeminal nuclei of the brain stem did not show gross changes after sensory input modification. However, there were significant and widespread increases in the number and size of CTB-labeled varicosities in the enriched condition, and a prominent expansion in both parameters in laminae III-IV of the caudal division of the spinal nucleus in the whisker trimming condition. No obvious changes were detected in IB4-labeled terminals in laminae I-II. These results show that a prolonged exposure to changes in sensory input without any neural damage is capable of inducing structural changes in terminals of primary afferents in mature animals, and highlight the importance of peripheral structures as the presumed earliest players in sensory experience-dependent plasticity.

Neural Control of Vascular Function in Skeletal Muscle

The sympathetic nervous system represents a fundamental homeostatic system that exerts considerable control over blood pressure and the distribution of blood flow. This process has been referred to as neurovascular control. Overall, the concept of neurovascular control includes the following elements: efferent postganglionic sympathetic nerve activity, neurotransmitter release, and the end organ response. Each of these elements reflects multiple levels of control that, in turn, affect complex patterns of change in vascular contractile state. Primarily, this review discusses several of these control layers that combine to produce the integrative physiology of reflex vascular control observed in skeletal muscle. Beginning with three reflexes that provide somewhat dissimilar vascular patterns of response despite similar changes in efferent sympathetic nerve activity, namely, the baroreflex, chemoreflex, and muscle metaboreflex, the article discusses the anatomical and physiological bases of postganglionic sympathetic discharge patterns and recruitment, neurotransmitter release and management, and details of regional variations of receptor density and responses within the microvascular bed. Challenges are addressed regarding the fundamentals of measurement and how conclusions from one response or vascular segment should not be used as an indication of neurovascular control as a generalized physiological dogma. Whereas the bulk of the article focuses on the vasoconstrictor function of sympathetic neurovascular integration, attention is also given to the issues of sympathetic vasodilation as well as the impact of chronic changes in sympathetic activation and innervation on vascular health. © 2016 American Physiological Society.

Site-dependent differences in density of sympathetic nerve fibers in muscle-innervating nerves of the human head and neck

The autonomic nerve supply of skeletal muscle has become a focus of interest because it is closely related to the adaptation of energy metabolism with aging. We have performed an immunohistochemistry study on tyrosine hydroxylase (TH) and neuronal nitric oxide synthase (nNOS) using specimens obtained from ten selected elderly cadavers (mean age 83.3 years) in which we examined muscle-innervating nerves (abbreviated ‘‘muscle-nerves’’ hereafter) of ten striated muscles (soleus, infraspinatus, extra-ocular inferior rectus, lateral rectus, superior obliquus, temporalis, orbicularis oculi, posterior cricoarytenoideus, trapezius and genioglossus) and, as a positive control, the submandibular ganglion. We found that the extra-ocular muscles received no or very few TH-positive nerve fibers. Muscle-nerves to the other head and neck muscles contained a few or several TH-positive fibers per section, but their density (proportional area of TH-positive fibers per nerve cross-section) was one-half to one-third of that in nerves to the soleus or infraspinatus. We did not find nNOS-positive fibers in any of these muscle-nerves. In the head and neck muscles, with the exception of those of the tongue, there appeared to be very few TH-positive nerve fibers along the feeding artery. Consequently, the head and neck muscles seemed to receive much fewer sympathetic nerves than limb muscles. There was no evidence that nNOS-positive nerves contributed to vasodilation of feeding arteries in striated muscles. This site-dependent difference in sympathetic innervation would reflect its commitment to muscle activity. However, we did not find any rules determining the density of nerves according to muscle fiber type and the mode of muscle activity.

Nerves in the intersphincteric space of the human anal canal with special reference to their continuation to the enteric nerve plexus of the rectum

In the intersphincteric space of the anal canal, nerves are thought to "change" from autonomic to somatic at the level of the squamous-columnar epithelial junction of the anal canal. To compare the nerve configuration in the intersphincteric space with the configuration in adjacent areas of the human rectum, we immunohistochemically assessed tissue samples from 12 donated cadavers, using antibodies to S100, neuronal nitric oxide synthase (nNOS), and tyrosine hydroxylase (TH). Antibody to S100 revealed a clear difference in intramuscular nerve distribution patterns between the circular and longitudinal muscle layers of the most inferior part of the rectum, with the former having a plexus-like configuration, while the latter contained short, longitudinally running nerves. Most of the intramural ganglion cells in the anal canal were restricted to above the epithelial junction, but some were located just below that level. Near or at the level of the epithelial junction, the nerves along the rectal adventitia and Auerbach's nerve plexus joined to form intersphincteric nerves, with all these nerves containing both nNOS-positive parasympathetic and TH-positive sympathetic nerve fibers. Thus, it was histologically difficult to distinguish somatic intersphincteric nerves from the autonomic Auerbach's plexus. In the intersphincteric space, the autonomic nerve elements with intrapelvic courses seemed to "borrow" a nerve pathway in the peripheral branches of the pudendal nerve. Injury to the intersphincteric nerve during surgery may result in loss of innervation in the major part of the internal anal sphincter.

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.

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.

Regulation of Norepinephrine Release from Isolated Bovine Irides by Histamine

In the present study, we investigated the effect of histamine on sympathetic neurotransmission from isolated, superfused bovine irides. We also studied the pharmacology of prejunctional histamine receptors that regulate the release of norepinephrine (NE) from this tissue. The effect of exogenous histamine and various histamine receptor agonists was examined on the release of [(3)H]-norepinephrine ([(3)H]NE) triggered by electrical field stimulation using the Superfusion Method. Histamine receptor agonists caused a concentration-dependent inhibition of field-stimulated [(3)H]NE overflow with the following rank order of potency: imetit > histamine > R-alpha-methylhistamine. In all cases, the inhibitory action of histamine receptor agonists was attenuated at high concentrations of these compounds. The histamine receptor antagonists, clobenpropit (H(3)-antagonist/H(4)-agonist) and thioperamide (H(3)-antagonist) blocked the inhibitory response elicited by R-alpha-methylhistamine and imetit, respectively. Inhibitory effects of R-alpha-methylhistamine and clonidine were not additive suggesting that prejunctional H(3)- and alpha(2)-adrenoceptors coexist at neurotransmitter release sites. We conclude that histamine produces an inhibitory action on sympathetic neurotransmission in the bovine iris, an effect mimicked by selective H(3)-receptor agonists and blocked by H(3)-antagonists.

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.

Chemical sympathectomy alters regulation of body weight during prolonged ICV leptin infusion

To assess the importance of the sympathetic nervous system in regulating body weight during prolonged leptin infusion, we evaluated food intake, body weight, and physical activity in conscious, unrestrained rats. Initial studies illustrated that prolonged intracerebroventricular (ICV) infusion of leptin enhanced substrate oxidation so that adipose tissue lipid stores were completely ablated, and muscle triglyceride and liver glycogen stores were depleted. After neonatal chemical sympathectomy, changes in weight and food intake were compared in groups of sympathectomized (SYM) and control (CON) adult animals during ICV infusion of leptin. CON animals lost 60 +/- 9 g over 10 days vs. 25 +/- 3 g in the SYM animals when food intake was matched between the two groups. Greater weight loss despite similar energy intake points to an important role of the sympathetic nervous system in stimulating energy expenditure during ICV leptin infusion by increasing the resting metabolic rate, since no differences in physical activity were observed between CON and SYM groups. In conclusion, activation of the SNS by leptin increases energy expenditure by augmenting the resting metabolic rate.

Functional organization of peripheral vasomotor pathways

AIM

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

RESULTS

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

CONCLUSIONS

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

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

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

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.

Absence of cholinergic sympathetic innervation from limb muscle vasculature in rats and mice

Although the existence of cholinergic sympathetic vasodilatory innervation in limb muscle vasculature is well established for some species, previous pharmacological studies have failed to reveal the presence of such innervation in rats. Recently, Schafer and colleagues [Schafer, M.K., Eiden, L.E., Weihe, E., 1998. Cholinergic neurons and terminal fields revealed by immunohistochemistry for the vesicular acetylcholine transporter. II. The peripheral nervous system. Neuroscience 84(2), 361-376] reported that vesicular acetylcholine transporter immunoreactivity (VAChT-IR), a marker for cholinergic terminals, is present in the innervation of the microvasculature of rat hindlimb skeletal muscle and concluded that rats possess cholinergic sympathetic innervation of limb muscle vasculature. Because of our interest in identifying targets of cholinergic sympathetic neurons, we have analyzed the transmitter properties of the innervation of muscle vessels in rat and mouse limbs. We found that the innervation of vasculature in muscle is noradrenergic, exhibiting robust catecholamine histofluorescence and immunoreactivity for tyrosine hydroxylase (TH) and the peptide transmitters, neuropeptide Y (NPY) and occasionally vasoactive intestinal peptide (VIP). In contrast, cholinergic phenotypic markers,VAChT-IR and acetylcholinesterase (AChE) activity, are absent. Neuron cell bodies in sympathetic ganglia, retrogradely labeled with injections of tracer into limb muscles, also lacked VAChT but contained TH-IR. The innervation of large extramuscular feed arteries in hindlimbs was also devoid of cholinergic markers, as were the cell bodies of sympathetic neurons innervating extramuscular femoral arteries. These results, like those of previous physiological studies, provide no evidence for the presence of cholinergic sympathetic innervation of muscle vasculature in rats or mice.

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.

Autonomic control of skeletal muscle blood flow at the onset of exercise

The purpose of this study was to determine whether the autonomic nervous system is involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries. Before treadmill exercise at 3 miles/h, 0% grade, hexamethonium (10 mg/kg) and atropine (0.2 mg/kg) or saline was infused intravenously. Ganglionic blockade increased resting heart rate from 87 +/- 5 to 145 +/- 8 beats/min (P < 0.01) and reduced mean arterial pressure from 100 +/- 4 to 88 +/- 5 mmHg (P < 0.01). During steady-state exercise, heart rate was unaffected by ganglionic blockade (from 145 +/- 8 to 152 +/- 5 beats/min), whereas mean arterial pressure was reduced (from 115 +/- 4 to 72 +/- 4 mmHg; P < 0.01). Immediate and rapid increases in iliac blood flow and conductance occurred with initiation of exercise with or without ganglionic blockade. Statistical analyses of hindlimb conductance at 5-s intervals over the first 30 s of exercise revealed a statistically significant difference between the control and ganglionic blockade conditions at 20, 25, and 30 s (P < 0.01) but not at 5, 10, and 15 s of exercise. Hindlimb conductance at 1 min of exercise was 9.21 +/- 0.68 and 11.82 +/- 1.32 ml. min(-1). mmHg(-1) for the control and ganglionic blockade conditions, respectively. Because ganglionic blockade did not affect the initial rise in iliac conductance, we concluded that the autonomic nervous system is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs. Autonomic control of skeletal muscle blood flow during exercise is manifested through vasoconstriction and not vasodilation.

Cellular and molecular determinants of sympathetic neuron development

The development of the sympathetic nervous system can be divided into three overlapping stages. First, the precursors of sympathetic neurons arise from undifferentiated neural crest cells that migrate ventrally, aggregate adjacent to the dorsal aorta, and ultimately differentiate into catecholaminergic neurons. Second, cell number is refined during a period of cell death when neurotrophic factors determine the number of neuronal precursors and neurons that survive. The final stage of sympathetic development is the establishment and maturation of synaptic connections, which for sympathetic neurons can include alterations in neurotransmitter phenotype. Considerable progress has been made recently in elucidating the cellular and molecular mechanisms that direct each of these developmental decisions. We review the current understanding of each of these, focusing primarily on events in the peripheral nervous system of rodents.

The specification of sympathetic neurotransmitter phenotype depends on gp130 cytokine receptor signaling

Sympathetic ganglia are composed of noradrenergic and cholinergic neurons. The differentiation of cholinergic sympathetic neurons is characterized by the expression of choline acetyltransferase (ChAT) and vasoactive intestinal peptide (VIP), induced in vitro by a subfamily of cytokines, including LIF, CNTF, GPA, OSM and cardiotrophin-1 (CT-1). To interfere with the function of these neuropoietic cytokines in vivo, antisense RNA for gp130, the common signal-transducing receptor subunit for neuropoietic cytokines, was expressed in chick sympathetic neurons, using retroviral vectors. A strong reduction in the number of VIP-expressing cells, but not of cells expressing ChAT or the adrenergic marker tyrosine hydroxylase (TH), was observed. These results reveal a physiological role of neuropoietic cytokines for the control of VIP expression during the development of cholinergic sympathetic neurons.

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

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

Parasympathetic innervation of cephalic arteries in rabbits: comparison with sympathetic and sensory innervation

We investigated the distribution of parasympathetic, sympathetic, and sensory perivascular nerve fibers in rabbit cephalic arteries supplying the brain, exocrine glands, nasal mucosa, masseter muscles, tongue, and skin in the face and also examined cranial autonomic and sensory ganglia. NADPH diaphorase (NADPHd)-positive and vasoactive intestinal peptide-like immunoreactive (VIP-LI) neurons were located in the cranial parasympathetic ganglia. Neuropeptide Y (NPY)-LI neurons occurred mainly, and dopamine beta-hydroxylase (DBH)-LI neurons occurred exclusively, in the superior cervical (sympathetic) ganglion. Substance P (SP)-LI and calcitonin gene-related peptide (CGRP)-LI neurons occurred only in the trigeminal (sensory) ganglion. Therefore, it was assumed that NADPHd-positive and VIP-LI perivascular nerve fibers in cephalic arteries were parasympathetic, all DBH-LI and most NPY-LI fibers were sympathetic, and SP-LI and CGRP-LI fibers were sensory in nature. In the cerebral arteries, NADPHd-positive and VIP-LI varicose fibers were more numerous in the rostral than in the caudal half of the Circle of Willis. In the extracranial arteries, NADPHd-positive and VIP-LI fibers were most abundant in the lingual, lacrimal, and supraorbital arteries; sparse in the parotid and submandibular arteries; and absent in the ear artery. There was an obvious proximal-to-distal density gradient along individual cephalic arterial trees. In contrast, DBH-LI, NPY-LI, SP-LI, and CGRP-LI varicose nerve fibers were similar in density in all cephalic arteries and their branches. These neuroanatomical findings suggest that differential parasympathetic innervation in cephalic arteries may play a role in the partitioning of blood flow between different cephalic tissues.