Adrenergic sympathectomy ablates unmyelinated fibers in the rat 'preganglionic' cervical sympathetic trunk

C-fiber (Remak) bundles contain both isolectin B4-binding and calcitonin gene-related peptide-positive axons

Unmyelinated nerve fibers (Remak bundles) in the rodent sciatic nerve typically contain multiple axons. This study asked whether C-fiber bundles contain axons arising from more than one type of neuron. Most small neurons of the lumbar dorsal root ganglion (DRG) are either glial cell line-derived neurotrophic factor dependent or nerve growth factor dependent, binding either isolectin B4 (IB4) or antibodies to calcitonin gene-related peptide (CGRP), respectively. Injection of IB4-conjugated horseradish peroxidase into a lumbar DRG resulted in intense labeling of IB4 axons, with very low background. Visualized by confocal fluorescence, IB4-binding and CGRP-positive nerve fibers originating from different DRG neurons came together and remained closely parallel over long distances, suggesting that these two types of axon occupy the same Remak bundle. With double-labeling immunogold electron microscopy (EM), we confirmed that IB4 and CGRP axons were distinct and were found together in single Remak bundles. Previous studies indicate that some DRG neurons express both CGRP and IB4 binding. To ensure that our immunogold results were not a consequence of coexpression, we studied large populations of unmyelinated axons by using quantitative single-label EM. Tetramethylbenzidine, a chromogen with strong intrinsic signal amplification of IB4-horseradish peroxidase, labeled as many as 52% of unmyelinated axons in the dorsal root. Concomitantly, 97% of the Remak bundles with more than one axon contained at least one IB4-labeled axon. Probabilistic modeling using binomial distribution functions rejected the hypothesis that IB4 axons segregate into IB4-specific bundles (P < 0.00001). We conclude that most Remak bundle Schwann cells simultaneously support diverse axon types with different growth factor dependences.

Nicotinic acetylcholine receptor subtypes in the rat sympathetic ganglion: pharmacological characterization, subcellular distribution and effect of pre- and postganglionic nerve crush

Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in autonomic ganglia, which innervate and control the activity of most visceral organs. By combining ultrastructural, immunocytochemical, and pharmacological analyses, we characterized the nAChR subtypes in the rat superior cervical ganglion (SCG) and the effect of pre- and postganglionic nerve crush on their number in the ganglion and their distribution at the intraganglionic synapses. Binding with radioactive nicotinic ligands, immunoprecipitation, and immunolocalization experiments revealed the presence of different nAChR subtypes: those containing the alpha3 subunit associated with beta4 and/or beta2 subunits that bind 3H-Epibatidine with high affinity, and those containing the alpha7 subunit that bind 125I-alphaBungarotoxin. After postganglionic nerve crush, the number of nicotinic receptors and immunopositive intraganglionic synapses for each nAChR subunit strongly decreased. Both the number of nAChRs and immunoreactivity recovered 26 days after injury, when regenerating postganglionic fibers had reinnervated the peripheral target organs, as shown by the restoration of tyrosine hydroxylase immunoreactivity in the iris. This observation and the lack of any effect of preganglionic nerve crush on the number of nicotinic receptors suggest that the peripheral targets affect the organization of intraganglionic synapses in adult SCG.

Nerve and ganglion blood flow in diabetes: an appraisal

Vasa nervorum, the vascular supply to peripheral nerve trunks, and their associated cell bodies in ganglia have unique anatomical and physiological characteristics. Several different experimental approaches toward understanding the changes in vase nervorum following injury and disease have been used. Quantative techniques most widely employed have been microelectrode hydrogen clearance palarography and [14C]iodoantipyrine autoradiographic distribution, whereas estimates of red blood cell flux using a fiber-optic laser Doppler probe offer real time data at different sites along the nerve trunk. There are important caveats about the use of these techniques, their advantages, and their limitations. Reports of nerve blood flow require careful documentation of physiological variables, including mean arterial pressure and nerve temperature during the recordings. Several ischemic models of the peripheral nerve trunk have addressed the ischemic threshold below which axonal degeneration ensues (< 5ml/100 g/min). Following injury, rises in local blood flow reflect acitons of vasoactive peptides, nitric oxide, and the development of angiogenesis. In experimental diabetes, a large number of studies have documented reductions in nerve blood flow and tandem corrections of nerve blood flow and conduction slowing. A significant proportions, however, of the work can be criticized on the basis of methodology and interpretation. Similarly, not all work has confirmed that reductions of nerve blood flow are an invariable feature of experimental or human diabetic polyneuropathy. Therefore, while there is disagreement as to whether early declines in nerve blood flow "account" for diabetic polyneuropathy, there is unquestioned eveidence of early microangiopathy. Abnormalities of vase nervorum and micorvessels supplying ganglia at the very least develop parallel to and together with changes in neurons, Schwann cells, and axons.

The ratio of pre- to postganglionic neurons and related issues in the autonomic nervous system

The motor outflow of the autonomic nervous system (ANS) is differentiated into two major divisions, parasympathetic (PSNS) and sympathetic (SNS). Both are organized hierarchically into pre- and postganglionic levels, but classically the two divisions have been assumed to differ in their ratios of pre- to postganglionic neurons. The PSNS been characterized as having lower ('one-to-few') ratios, whereas the SNS has been described as possessing higher ('one-to-many') ratios. These patterns have been assumed to measure differing divergences of the outflows. In this review, a ratio of pre- to postganglionic neurons is called a ratio index, and the idea that the PSNS and SNS have characteristically different ratio indexes and divergences is called the ratio rule. The putative differences in the ratio indexes of the two divisions - as well as Fulton's influential proposal that they form one of the bases of contrasting functional capacities of the PSNS and SNS - have been widely accepted for nearly for nearly three quarters of a century. A survey of the original observations yielding the concept of the ratio rule as well as the more recent estimates of pre- and postganglionic numbers, however, challenges both the generality and the adequacy of the ratio rule and indexes. The originally formulated differences between the PSNS and SNS represent an overgeneralization since they were based on observations of only two ganglia, the ciliary ganglion in the PSNS and the superior cervical ganglion in the SNS. Furthermore, these original estimates were based on limited samples and were subject to a number of counting artifacts. A survey of the literature suggests that ratio indexes vary much more within each ANS division than they do between the two divisions. When ganglia other than the ciliary and superior cervical are examined, the two divisions of the ANS have broad, largely overlapping ranges of ratio indexes. Additionally, other PSNS-SNS pairs can be found in which the relative sizes of their respective indexes are completely contrary to the ratio rule. For a given ganglion, there are substantial differences in the ratio index between species, between individuals of the same species, and between stages of development in the same species. Furthermore, both divisions of the ANS have wide and largely overlapping ranges of physiological effects varying from specific to diffuse, from local to widespread. Finally, the ratio index measure ignores the degree of convergence found in different ganglia, and it is insensitive to the fact that many ganglia have multiple functionally distinct motor neuron pools, each with separate inputs varying in their degrees of divergence and/or convergence. Thus ratio indexes do not differentiate the PSNS from the SNS, and conclusions based on such putative distinctions are questionable.

Autonomic involvement in Guillain-Barré syndrome: a review

Autonomic neuropathy is an important and common complication of Guillain-Barré syndrome (GBS). Manifestations be present in cardiovascular, sudomotor, gastrointestinal and other systems involving both sympathetic and parasympathetic fibers. Some apparently selective acute autonomic neuropathies may be subvarieties of GBS. Experimental work in animal models, pathological studies of GBS patients, and autonomic function studies have provided some help in the understanding of this complication. In managing GBS patients with autonomic dysfunction there are important practical considerations that can improve their care. In this article we review the literature on autonomic neuropathy in GBS and propose a management scheme to accommodate it in the overall treatment of the neuropathy.

Distribution of GABA-immunoreactive nerve fibers and cells in the cervical and thoracic paravertebral sympathetic trunk of adult rat: evidence for an ascending feed-forward inhibition system

Neurochemical and immunohistochemical evidence suggests that the superior cervical ganglion (SCG) contains all components of a gamma-aminobutyric acid (GABA)ergic transmission system, which includes GABAergic axons of unknown origin. The number of nerve fibers with and without GABA-like immunoreactivity was determined in interganglionic connectives at all cervical and thoracic levels of the paravertebral sympathetic trunk. In addition, the distribution of GABA-immunoreactive (IR) neurons was established within the ganglion chain and compared with the relative frequency of principal neurons richly innervated by GABA-IR axon terminals. The following results were obtained: 1) the total number of nerve fibers in cross sections did not significantly vary between the cervical levels, but it increased steadily from upper to lower thoracic segments; 2) in contrast, the number of GABA-IR fibers decreased from the cervical sympathetic trunk below the SCG (approximately 300 fibers) down to the seventh to tenth thoracic ganglion, below which no such fiber was seen; 3) GABA-IR nerve fibers originate from a subclass of GABA-IR cells; these are small, bipolar neurons with predominantly ascending, unmyelinated axon-like processes; 4) the number of principal neurons richly innervated by GABA-IR nerve fibers decreased from the SCG to the upper thoracic ganglia, and was very small below; and 5) apart from basket-like innervation, GABA-IR axons also formed diffuse networks around GABA-negative principal neurons predominantly in cervical and upper thoracic ganglia. These data suggest that the GABAergic innervation of paravertebral sympathetic ganglia is more complex than previously suspected. What appears as preganglionic afferents from several spinal segments (C8-Th7) innervate GABAergic neurons in the sympathetic trunk which have ascending axons and focus their inhibitory effects on the cervical sympathetic ganglia, predominantly the SCG. These data suggest that GABAergic small interganglionic neurons form a feed-forward inhibition system, which may be driven by multisegmental spinal input in the paravertebral sympathetic ganglion chain.

The localization of sympathetic and vagal neurones innervating the carotid sinus in the rabbit

The distribution of neurones innervating the carotid sinus of the rabbit was determined by inserting chips of horseradish peroxidase (HRP) into the adventitial layer of the carotid sinus. Labelled neurones were found in the superior cervical ganglion, along the cervical sympathetic trunk and in the nodose ganglion (mean counts of 1876, 139 and 232, respectively). No labelled neurones were located in the middle cervical ganglion or the stellate ganglion. Within the superior cervical ganglion, the fraction of labelled neurones found in equal longitudinal quadrants of the ganglion were, from rostral to caudal, 2%, 12%, 42% and 44%. Thus the majority of neurones were located in the caudal region of the superior cervical ganglion. The primary pathway for sympathetic fibres innervating the carotid sinus was shown to be in branches of the external carotid nerve. The greatest number of labelled neurones in the nodose ganglion were located in the most rostral quadrants of the ganglion.

Guanethidine sympathectomy increases substance P concentration in the superior sympathetic ganglion of adult rats

Adult rats received intraperitoneal injections of guanethidine or saline for 5 weeks. Six to 8 weeks following completion of treatment, concentrations of substance P and neuropeptide Y (NPY) were measured by radioimmunoassay in the superior cervical ganglion (SCG) and thoracic spinal cord. The SCG was also immunostained for NPY and substance P. No differences were observed in thoracic spinal cord content of either NPY or substance P. We observed depletion of NPY immunoreactive neurons and NPY levels in the SCG, and pharmacologic evidence of postganglionic denervation in guanethidine-treated rats. In guanethidine-treated rats, there was a marked increase of substance P levels in the SCG, where substance P was localized in fibers, but not cell bodies. Thus, sprouting of substance P-containing sensory fibers in the sympathetic ganglia occurs following postganglionic sympathectomy in adult rats.

Effect of chemical sympathectomy on scintigraphic gastric and small bowel transit in the rat

Our aims were to measure gastric and small bowel transit of radiolabeled chow or liquids in rats and to assess the effect of pharmacologically induced chronic sympathectomy of at least 5 weeks duration. Three series of experiments were performed. In series I, four rats in each group underwent i.p. chloral hydrate anesthesia, tracheostomy with intubation and mechanical ventilation: they received by gavage 1.0 g rat chow dissolved in 1.5 ml saline labeled with 1.0 mCi 99mTc-DTPA In series II, four rats in each group were anesthetized with only i.p. chloral hydrate and received 1.5 ml labeled saline. Rats were placed on a gamma camera for dynamic acquisition of 1-min images for 7 h in series I, and 4 h in series II. Activity was quantitated in stomach and cecum; gastric emptying was analyzed by the power exponential model. In series III, four rats in each group were studied for 1 h on gamma camera and sacrificed after 5 h. At the end of each study, the stomach, small bowel, cecum and colon were removed and radioactivity counted in each organ in a dose calibrator. Quantitation of radioactivity by gamma camera was highly accurate: labeled chow in the stomach at 7 h was identical by external camera and counting of the excised organ (linear regression slope = 1.01, r = 0.97, P less than 0.0001). Similar precision was observed with labeled liquids (slope = 0.93, r = 0.93, P = 0.001). Chow emptied slower than liquid in both groups (P = 0.048). Ileocecal movement of isotope occurred by bolus transfers.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular recordings from "recurrent neurons" in the rat superior cervical ganglion

Intracellular recordings in the isolated superior cervical ganglion of the rat showed that electrical stimulation of the cervical sympathetic trunk elicited in a cluster of neurons localized in the caudal part of the ganglion synaptically driven action potentials, and propagated potentials having the features of typical antidromic spikes. The results demonstrate that these neurons, besides synapsing with common preganglionic fibres, project their axons to the cervical sympathetic trunk. The recurrent neurons showed a very low threshold to direct intracellular stimulation and a high input resistance, suggesting that they have a small size. Almost all recurrent neurons were activated synaptically also by stimulating the postganglionic trunks, indicating that they are innervated by collaterals of preganglionic through-fibres which are known to sustain a direct pathway between pre- and postganglionic nerves. Moreover, some recurrent neurons could also be activated antidromically following stimulation of the external carotid nerve, indicating that their axons divide into collaterals which project not only to the preganglionic trunk but also to a postganglionic nerve. The presence of recurrent neurons in the superior cervical ganglion of the rat provides further evidence for the concept that sympathetic ganglia consist of discrete cell subpopulations which are segregated in different regions and probably subserve different functions.

Guanethidine-induced adrenergic sympathectomy augments endoneurial perfusion and lowers endoneurial microvascular resistance

Chronic administration of guanethidine sulfate in the rat induces a selective adrenergic neuropathy. We studied the effects of guanethidine-induced adrenergic sympathectomy on rat sciatic nerve blood flow (NBF), microvascular resistance (MR), vessel caliber and norepinephrine (NE) content. A control group of animals was studied following chronic administration of mammalian Ringer's solution. NBF and MR were measured with an endoneurial microelectrode, using the technique of hydrogen clearance (HC). Following HC, the sciatic nerve was perfused with India Ink, removed, frozen and sectioned. Measurements were made of endoneurial microvessel numbers, diameter, circumference and area. The contralateral sciatic nerve was removed for measurements of NE content. In guanethidine-treated animals we observed elevated NBF, reduced MR and dilated microvessels. Numbers of microvessels and fascicular areas were similar to controls. NE content was markedly reduced following sympathectomy. These studies suggest that NBF, unlike cerebral blood flow (CBF), is regulated by its adrenergic input. Removal of adrenergic innervation of the vasa nervorum appears to result in a loss of tonic vasoconstrictive action.