Quantitative studies of superior cervical sympathetic ganglia in a variety of primates including man. I. The ratio of preganglionic fibers to ganglionic neurons

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Action potential subpopulations within human muscle sympathetic nerve activity: Discharge properties and governing mechanisms

Sympathetic emissions directed towards the skeletal muscle circulation - muscle sympathetic nerve activity (MSNA) - represent a key mechanism for maintaining homeostasis and supporting human survival during physiological stress. Pulse-rhythmic bursts formed by the synchronous discharge of differently-sized sympathetic action potentials (APs) represent the primary characteristic of MSNA. Of the APs firing under baseline conditions (reflecting low-threshold c-fibre activity), a range of subpopulations exists, of which three general categories can be discussed based on their peak-to-peak amplitude in the filtered raw neurogram - small, medium, and large. These subpopulations express nonuniform discharge, recruitment, and synchronization patterns. The subpopulation of medium APs fires synchronously in most bursts, while the subpopulations of small and large APs fire less often. However, 30% of total AP discharge occurs asynchronously between sympathetic bursts, a pattern expressed most often by small APs. In response to physiological stress (e.g., baroreflex unloading), the subpopulation of medium APs exhibits the largest increase in firing probability and a subpopulation of previously-silent larger and faster-conducting APs (reflecting high-threshold c-fibre activity) becomes recruited. Heterogeneous discharge, synchronization, and recruitment thresholds among AP subpopulations stem from differential regulation within the sympathetic organization including the arterial baroreflex and paravertebral ganglia. Indeed, the arterial baroreflex strongly regulates medium APs at baseline and enhances its control over this subpopulation during periods of baroreflex unloading. Conversely, small and large APs express weak baroreflex control. Trimethaphan infusion has revealed that ganglionic processes including nicotinic and non-nicotinic mechanisms may contribute to heterogenous firing behaviours among low-threshold AP subpopulations. This review highlights recent work revealing new insight to the discharge properties expressed by, and mechanisms governing, AP subpopulations within human MSNA.

Peripheral and central autonomic nervous system: does the sympathetic or parasympathetic nervous system bear the brunt of the pathology during the course of sporadic PD?

It is a well-established fact that the sympathetic, parasympathetic and enteric nervous systems are affected at early stages in Parkinson's disease (PD). However, it is not yet clarified whether the earliest pathological events preferentially occur in any of these three divisions of the autonomic nervous system (ANS). Significant involvement of the peripheral autonomic nervous system of the heart and gastrointestinal tract has been documented in PD. Accumulating evidence suggests that the PD pathology spreads centripetally from the peripheral to central nervous system through autonomic nerve fibers, implicating the ANS as a major culprit in PD pathogenesis and a potential target for therapy. This study begins with a brief overview of the structures of the central and peripheral autonomic nervous system and then outlines the major clinicopathological manifestations of cardiovascular and gastrointestinal disturbances in PD.

Overview of the Anatomy, Physiology, and Pharmacology of the Autonomic Nervous System

Comprised of the sympathetic nervous system, parasympathetic nervous system, and enteric nervous system, the autonomic nervous system (ANS) provides the neural control of all parts of the body except for skeletal muscles. The ANS has the major responsibility to ensure that the physiological integrity of cells, tissues, and organs throughout the entire body is maintained (homeostasis) in the face of perturbations exerted by both the external and internal environments. Many commonly prescribed drugs, over-the-counter drugs, toxins, and toxicants function by altering transmission within the ANS. Autonomic dysfunction is a signature of many neurological diseases or disorders. Despite the physiological relevance of the ANS, most neuroscience textbooks offer very limited coverage of this portion of the nervous system. This review article provides both historical and current information about the anatomy, physiology, and pharmacology of the sympathetic and parasympathetic divisions of the ANS. The ultimate aim is for this article to be a valuable resource for those interested in learning the basics of these two components of the ANS and to appreciate its importance in both health and disease. Other resources should be consulted for a thorough understanding of the third division of the ANS, the enteric nervous system. © 2016 American Physiological Society. Compr Physiol 6:1239-1278, 2016.

The developing and restructuring superior cervical ganglion of guinea pigs (Cavia porcellus var. albina)

Post-natal development comprises both maturation (from newborn to adult) and ageing (from adult to senility) and, during this phase, several adaptive mechanisms occur in sympathetic ganglia, albeit they are not fully understood. Therefore, the present study aimed at detecting whether post-natal development would exert any effect on the size and number of a guinea pig's superior cervical ganglion (SCG) neurons. Twenty right SCGs from male subjects were used at four ages, i.e. newborn (7 days), young (30 days), adult (7 months) and old animals (50 months). Using design-based stereological methods the volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated using the vertical nucleator. The main findings of this study were a combination of post-natal-dependent increases and decreases in some variables: (i) 27% increase in ganglion volume, (ii) 24% and 43% decreases in the total number of mono and binucleate neurons, respectively, and (iii) 27.5% and 40% decreases in the mean perikaryal volume of mono and binucleate neurons, respectively. Despite the fall in neuron numbers found here, post-natal development is not only associated with neuron loss, but also embraces other structural adaptive mechanisms, which are discussed in this paper.

Asymmetric post-natal development of superior cervical ganglion of paca (Agouti paca)

Functional asymmetry has been reported in sympathetic ganglia. Although there are few studies reporting on body side-related morphoquantitative changes in sympathetic ganglion neurons, none of them have used design-based stereological methods to address this issue during post-natal development. We therefore aimed at detecting possible asymmetry-related effects on the quantitative structure of the superior cervical ganglion (SCG) from pacas during ageing, using very precise design-based stereological methods. Forty (twenty left and twenty right) SCG from twenty male pacas were studied at four different ages, i.e. newborn, young, adult and aged animals. By using design-based stereological methods the total volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated, using the vertical nucleator. The main findings of this study were: (1) the right SCG from aged pacas has more mononucleate and binucleate neurons than the left SCG in all other combinations of body side and animal age, showing the effect of the interaction between asymmetry (right side) and animal age, and (2) right SCG neurons (mono and binucleate) are bigger than the left SCG neurons (mono and binucleate), irrespective of the animal age. This shows, therefore, the exclusive effect of asymmetry (right side). At the time of writing there is still no conclusive explanation for some SCG quantitative changes exclusively assigned to asymmetry (right side) and those assigned to the interaction between asymmetry (right side) and senescence in pacas. We therefore suggest that forthcoming studies should focus on the functional consequences of SCG structural asymmetry during post-natal development. Another interesting investigation would be to examine the interaction between ganglia and their innervation targets using anterograde and retrograde neurotracers. Would differences in the size of target organs explain ganglia structural asymmetry?

Dynamics of the remodeling of neural connections in the superior cervical ganglion in rats after dosed compression of the preganglionic trunk

The aim of the present work was to obtain a quantitative evaluation of post-traumatic regeneration of nerve cells in the superior cervical ganglion (SCG) by measuring the ratio of the number of neurons (N) in the ganglion to the number of preganglionic myelinated fibers (F) in the cervical sympathetic trunk (N/F). This was addressed using light and electron microscopy. Studies were performed using white male rats divided into three groups: intact (aged seven months), age controls (aged 19 months), and experimental - one year after compression of the sympathetic trunk at the base of the SCG performed at age seven months. N/F in intact rats was 1:210. With age, N/F changed to 1:173; the value one year after trauma was 1:745. These data led to the conclusion that normalization of the structure of the neural connections of the ganglion did not occur. The process of post-traumatic regeneration was incomplete and became chronic.

The Gross Anatomy of the Cranial Cervical Ganglion in the Guinea Pig (Cavia porcellus)

The right and left cranial cervical ganglia in the heads of 10 adult guinea pigs (5 male, 5 female) were dissected in detail. The cranial cervical ganglion (CCG) was located on the caudo-ventral aspect of the distal ganglion of the vagus nerve, and medial to the digastric and styloglossal muscles. It was present also ventral to the tympanic bulla, ventro-lateral to the longus capitis muscle, and between the ascending pharyngeal and the internal carotid arteries. The branches of the CCG included the internal and external carotid nerves, the jugular nerve and connecting branches to the pharynx, vagus, glossopharyngeal, accessory, cranial laryngeal, first and second cervical nerves, and vessels in the carotid body region. The number of nerves ramifying from the CCG of the guinea pig varied among cases. Compared to other species, there are also differences in the number of nerve branches and the course patterns. No sex differences are present as far as the guinea pig CCG is concerned.

Size and number of binucleate and mononucleate superior cervical ganglion neurons in young capybaras

The total number of neurons in the superior cervical ganglion (SCG) of adult capybaras is known from a previous study, where a marked occurrence of binucleate neurons (13%) was also noted. Here, distribution, number and fate of binucleate neurons were examined in younger, developing capybaras, aged 3 months. The mean neuronal cross-sectional area was 575.2 microm2 for mononucleate neurons and 806.8 microm2 in binucleate neurons. Frequency of binucleate neurons was about 36%. The mean ganglion volume was about 190 mm3 in young capybaras and the mean neuronal density was about 9,517 neurons/mm3. The total number of neurons per ganglion was about 1.81 mill. Neuronal cell bodies constituted 22.5% of the ganglion volume and the average neuronal volume was 23,600 microm3. By comparing the present data with those previously published the conclusion is drawn that the maturation period was characterized by the following points: a 26% remarkable decrease in neuronal density which was significant (P < 0.05) and a significant 16% (P < 0.05) decrease in the total number of SCG neurons accompanied by a 23% decrease in the total number of SCG binucleate neurons.

Arborization pattern of sympathetic preganglionic axons in the rat superior cervical and stellate ganglia

Anterograde labeling technique with Phaseolus Vulgaris leucoagglutinin (PHA-L) was employed to observe how a single preganglionic axon arborizes in the superior cervical ganglion (SCG) and stellate ganglion (STG) of rats. PHA-L was injected into the intermediolateral nucleus of the spinal cord at the middle point between segments T1 and T2, and labeled axons were detected immunohistochemically in serial sections. We traced and drew three preganglionic axons over their full length in the SCG and STG. In SCG, the labeled axons bifurcated repeatedly and extended to a length of 600-700 microns in the rostrocaudal direction, and about 200 microns in the transverse direction. These three preganglionic axons made 11, 14 and 11 dense terminal plexus regions along their trajectory. The pattern of the most dense terminal plexus corresponded to the pericellular type dendritic plexus, one of the plexus patterns of dendritic collaterals of SCG neurons. In the STG, the extent of axonal arborization was more variable than that in the SCG, ranging from 400 to 800 microns in the rostrocaudal direction and about 400 microns in the transverse direction. The three analyzed axons made 21, 19 and 20 dense terminal plexus regions along their trajectory, with a similar pattern to those in SCG. These results indicated that there might be a columnar or ellipsoidal organization of postganglionic neurons which are innervated by single preganglionic 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.

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.

Variation and symmetry in the lumbar and thoracic dorsal root ganglion cell populations of newly metamorphosed Xenopus laevis

The sizes of the lumbar and thoracic dorsal root ganglion cell populations in normally developing newly metamorphosed Xenopus laevis were measured in order to determine whether these neuron populations have the same characteristics as the hindlimb motoneuron population (i.e., large individual as well as sibling group differences, striking bilateral symmetry, and a rough correspondence between neuron number and body size that suggests some peripheral control of cell number during normal development (Sperry, J. Comp. Neurol. 264:250-267). Among animals from three sibling groups, the total numbers of thoracic and lumbar ganglion cells are highly variable and symmetrical, although symmetry is not uniformly present at the level of individual ganglion pairs. Significant sibling group differences in neuron number are also present. Metamorphic body size and cell number in the thoracic but not in the lumbar ganglia are significantly correlated. The motoneurons innervating the hindlimbs were also counted and measured in the same animals. While variable as well as symmetrical, motoneuron number and metamorphic body size are correlated in only two of the three sibling groups. Interestingly, the numbers of motoneurons and lumbar ganglion cells, two populations of neurons whose sizes one might predict would be significantly correlated in normally developing animals, are not correlated. The relationship between these observations and currently held views concerning how neuron numbers might be controlled during normal development is discussed.

Trophic regulation of nerve cell morphology and innervation in the autonomic nervous system

A remarkable feature of nerve cells is the complex and variable pattern of their axonal and dendritic branches. Quantitative studies of a simple part of the nervous system in mammals provide evidence that neuronal geometry and innervation are regulated by long-term trophic interactions between neurons and their targets. This trophic linkage may explain how nerve cells adjust their function to the needs of bodies that vary markedly in size and form.

Somatotopy within the medullary electrosensory nucleus of the little skate, Raja erinacea

The dorsal octavolateral nucleus is the primary electrosensory nucleus in the elasmobranch medulla. We have studied the topographic organization of electrosensory afferent projections within the dorsal nucleus of the little skate, Raja erinacea, by anatomical (HRP) and physiological experiments. The electrosensory organs (ampullae of Lorenzini) in skates are located in four groups on each side of the body, and each group is innervated by a separate ramus of the anterior lateral line nerve (ALLN). Transganglionic transport of HRP in individual rami demonstrated that electroreceptor afferents in each ramus project to a separate, nonoverlapping division of the central zone of the ipsilateral dorsal nucleus. These divisions, which are distinct areas separated by compact cell plates, are somatopically arranged. The volume of each division of the dorsal nucleus that is related to a single ramus is proportional to the number of ampullae innervated by the ramus, but not to the body surface area on which the receptors are distributed. Nearly one-half of the nucleus is devoted to electrosensory inputs from the buccal and superficial ophthalmic ampullae concentrated in a small area on the ventral surface of the head rostral to the mouth. Multiple and single unit recordings demonstrated that adjacent cells in the nucleus have similar receptive fields on the body surface and revealed a detailed point-to-point somatotopy within the nucleus. With threshold stimuli most single units have ipsilateral receptive fields made up by excitatory inputs from 2-5 ampullary organs. The somatotopy within the mechanosensory medial nucleus, also revealed by the HRP fills of individual ALLN rami, appears less rigid than that in the dorsal nucleus, as extensive overlap is present in the terminal fields of separate ALLN rami.

The ratio of preganglionic axons to postganglionic cells in the sympathetic nervous system of the rat

Previously reported preganglionic-postganglionic ratios for the sympathetic system are a major part of the evidence for the widely accepted idea that the sympathetic innervation of the viscera is diffuse. Unfortunately, the previous reports did not assess the non-preganglionic fibers in the nerves examined, and the limitations of light microscopy precluded accurate unmyelinated fiber counts. Thus, a recalculation of these ratios is necessary. The present study recalculates these ratios for the cervical sympathetic system of the rat. All fiber counts are done with the electron microscope which has the resolution necessary for accurately determining axon numbers. Selective surgical procedures establish that 84% of the axons in the cervical sympathetic trunk are preganglionic, 11% are postganglionic, and 5% are sensory. Thus, the numbers of preganglionic fibers can now be accurately assessed and compared to the number of postganglionic neurons in the superior cervical ganglion. When this is done, a preganglionic/postganglionic ratio of approximately 1:4 is obtained. This ratio differs considerably from those previously published.

An 'on the slide' modification of the De Olmos-Heimer horseradish peroxidase method

The De Olmos-Heimer horseradish peroxidase method has been simplified without losing its sensitivity. The modification involves the use of cryostat sections and omitting several steps from the original procedure. The modification is especially suitable for small pieces of tissue that would otherwise require imbedding.

A new microelectrophoretic procedure for delivery of horseradish peroxidase

A new procedure for microelectrophoretic delivery of horseradish peroxidase (HRP) is described. A dilute solution (1.5--3% w/v) of fluorescein isothiocyanate-conjugated HRP is deposited according to a standard microelectrophoretic method and the tissue reacted according to a sensitive histochemical procedure. A major advantage of this method is the reduced secondary diffusion of the enzyme present at the injection site.

Interpeduncular nucleus afferents in the rat

Afferents to the interpeduncular nucleus (IPN) of the rat were studied with the horseradish peroxidase (HRP) retrograde transport method. HRP was deposited microelectrophoretically in the IPN of adult rats. Major projections to the IPN originate in the medial habenular nucleus, the region surrounding the dorsal tegmental nucleus (accessory dorsal tegmental nucleus and the so-called dorsal tegmental nucleus pars lateralis), and the midbrain raphe (nucleus centralis superior and nucleus raphe dorsalis). Also, minor projections originate in the central gray and nucleus locus coeruleus. Our results indicate that the habenulointerpeduncular projection originates solely from the medial habenular nuclei and is topographically organized; medial regions of the medial habenular nuclei project to ventral portions of IPN and lateral regions project to the dorsal IPN.

Quantitative studies of sympathetic ganglia and spinal cord intermedio-lateral gray columns in familial dysautonomia

In adult patients with familial dysautonomia the mean volume of superior cervical sympathetic ganglia is reduced to 34% of the normal of 222 mm3. Packing density of neurons is reduced to 37% of normal. The mean total number of ganglionic neurons is 120,000 as compared to 1,060,000 in controls. The mean totals of preganglionic neurons in the first three thoracic cord segments are 13,600 in patients and 25,150 in controls. Deficits in sympathetic neurons account for many of the clinical, pharmacological and biochemical manifestations of familial dysautonomia.

Cobalt iontophoresis techniques for tracing afferent and efferent connections in the vertebrate CNS

In recent years several dye and cobalt iontophoresis techniques have been successfully used by invertebrate neurophysiologists for the localization of neuron somata and their processes. The cobalt iontophoresis technique has now been extended for use in the tracing of nerve fiber pathways and the localization of neuron somata in vertebrates. The brain and spinal cord of an animal are removed following perfusion with saline, and placed in a dish of cold saline. A suction electrode, filled with 300 mM cobalt chloride, is then placed over the cut end of the nerve trunk. Cobalt ions are then iontophoresed (by means of a voltage divider) within the nerve fibers, along their course. Following iontophoresis, the brain is bathed in an ammonium sulfide solution to precipitate the cobalt as black cobalt sulfide. The brain is then processed for histological procedures. A wide variety of vertebrates has been used, including amphibians, reptiles, aves and mammals, with uniform success. The cobalt iontophoresis technique presently in use has a wide range of applicability for neuroanatomical studies.