Untersuchungen �ber den Feinbau von Spinalganglien

Calcium-binding protein parvalbumin in the spinal cord and dorsal root ganglia

Parvalbumin is one of the calcium-binding proteins. In the spinal cord, it is mainly expressed in inhibitory neurons; in the dorsal root ganglia, it is expressed in proprioceptive neurons. In contrast to in the brain, weak systematization of parvalbumin-expressing neurons occurs in the spinal cord. The aim of this paper is to provide a systematic review of parvalbumin-expressing neuronal populations throughout the spinal cord and the dorsal root ganglia of mammals, regarding their mapping, co-expression with some functional markers. The data reviewed are mostly concerning rodentia species because they are predominantly presented in literature.

Ultrastructure of dorsal root ganglia

Dorsal root ganglia (DRG) contains thousands of sensory neurons that transmit information about our external and internal environment to the central nervous system. This includes signals related to proprioception, temperature, and nociception. Our understanding of DRG has increased tremendously over the last 50 years and has established the DRG as an active participant in peripheral processes. This includes interactions between neurons and non-neuronal cells such as satellite glia cells and macrophages that contribute to an increasingly complex cellular environment that modulates neuronal function. Early ultrastructural investigations of the DRG have described subtypes of sensory neurons based on differences in the arrangement of organelles such as the Golgi apparatus and the endoplasmic reticulum. The neuron-satellite cell complex and the composition of the axon hillock in DRG have also been investigated, but, apart from basic descriptions of Schwann cells, ultrastructural investigations of other cell types in DRG are limited. Furthermore, detailed descriptions of key components of DRG, such as blood vessels and the capsule that sits at the intersection of the meninges and the connective tissue covering the peripheral nervous system, are lacking to date. With rising interest in DRG as potential therapeutic targets for aberrant signalling associated with chronic pain conditions, gaining further insights into DRG ultrastructure will be fundamental to understanding cell-cell interactions that modulate DRG function. In this review, we aim to provide a synopsis of the current state of knowledge on the ultrastructure of the DRG and its components, as well as to identify areas of interest for future studies.

Modulation of Sensory Nerve Function by Insulin: Possible Relevance to Pain, Inflammation and Axon Growth

Insulin, besides its pivotal role in energy metabolism, may also modulate neuronal processes through acting on insulin receptors (InsRs) expressed by neurons of both the central and the peripheral nervous system. Recently, the distribution and functional significance of InsRs localized on a subset of multifunctional primary sensory neurons (PSNs) have been revealed. Systematic investigations into the cellular electrophysiology, neurochemistry and morphological traits of InsR-expressing PSNs indicated complex functional interactions among specific ion channels, proteins and neuropeptides localized in these neurons. Quantitative immunohistochemical studies have revealed disparate localization of the InsRs in somatic and visceral PSNs with a dominance of InsR-positive neurons innervating visceral organs. These findings suggested that visceral spinal PSNs involved in nociceptive and inflammatory processes are more prone to the modulatory effects of insulin than somatic PSNs. Co-localization of the InsR and transient receptor potential vanilloid 1 (TRPV1) receptor with vasoactive neuropeptides calcitonin gene-related peptide and substance P bears of crucial importance in the pathogenesis of inflammatory pathologies affecting visceral organs, such as the pancreas and the urinary bladder. Recent studies have also revealed significant novel aspects of the neurotrophic propensities of insulin with respect to axonal growth, development and regeneration.

Atlas of Normal Microanatomy, Procedural and Processing Artifacts, Common Background Findings, and Neurotoxic Lesions in the Peripheral Nervous System of Laboratory Animals

The ability to differentiate among normal structures, procedural and processing artifacts, spontaneous background changes, and test article–related effects in the peripheral nervous system (PNS) is essential for interpreting microscopic features of ganglia and nerves evaluated in animal species commonly used in toxicity studies evaluating regulated products and chemicals. This atlas provides images of findings that may be encountered in ganglia and nerves of animal species commonly used in product discovery and development. Most atlas images are of tissues from control animals that were processed using routine methods (ie, immersion fixation in neutral-buffered 10% formalin, embedding in paraffin, sectioning at 5 µm, and staining with hematoxylin and eosin) since these preparations are traditionally applied to study materials produced during most animal toxicity studies. A few images are of tissues processed using special procedures (ie, immersion or perfusion fixation using methanol-free 4% formaldehyde, postfixation in glutaraldehyde and osmium, embedding in hard plastic resin, sectioning at 1 µm, and staining with toluidine blue), since these preparations promote better stabilization of lipids and thus optimal resolution of myelin sheaths. Together, this compilation provides a useful resource for discriminating among normal structures, procedure- and processing-related artifacts, incidental background changes, and treatment-induced findings that may be seen in PNS tissues of laboratory animals.

Cryopreservation of Canine Primary Dorsal Root Ganglion Neurons and Its Impact upon Susceptibility to Paramyxovirus Infection

Canine dorsal root ganglion (DRG) neurons, isolated post mortem from adult dogs, could provide a promising tool to study neuropathogenesis of neurotropic virus infections with a non-rodent host spectrum. However, access to canine DRG is limited due to lack of donor tissue and the cryopreservation of DRG neurons would greatly facilitate experiments. The present study aimed (i) to establish canine DRG neurons as an in vitro model for canine distemper virus (CDV) infection; and (ii) to determine whether DRG neurons are cryopreservable and remain infectable with CDV. Neurons were characterized morphologically and phenotypically by light microscopy, immunofluorescence, and functionally, by studying their neurite outgrowth and infectability with CDV. Cryopreserved canine DRG neurons remained in culture for at least 12 days. Furthermore, both non-cryopreserved and cryopreserved DRG neurons were susceptible to infection with two different strains of CDV, albeit only one of the two strains (CDV R252) provided sufficient absolute numbers of infected neurons. However, cryopreserved DRG neurons showed reduced cell yield, neurite outgrowth, neurite branching, and soma size and reduced susceptibility to CDV infection. In conclusion, canine primary DRG neurons represent a suitable tool for investigations upon the pathogenesis of neuronal CDV infection. Moreover, despite certain limitations, cryopreserved canine DRG neurons generally provide a useful and practicable alternative to address questions regarding virus tropism and neuropathogenesis.

Morphological and functional diversity of first-order somatosensory neurons

First-order somatosensory neurons transduce and convey information about the external or internal environment of the body to the central nervous system. They are pseudo unipolar neurons with cell bodies residing in one of several ganglia located near the central nervous system, with the short branch of the axon connecting to the spinal cord or the brain stem and the long branch extending towards the peripheral organ they innervate. Besides their sensory transducer and conductive role, somatosensory neurons also have trophic functions in the tissue they innervate and participate in local reflexes in the periphery. The cell bodies of these neurons are remarkably diverse in terms of size, molecular constitution, and electrophysiological properties. These parameters have provided criteria for classification that have proved useful to establish and study their functions. In this review, we discuss ways to measure and classify populations of neurons based on their size and action potential firing pattern. We also discuss attempts to relate the different populations to specific sensory modalities.

Unbiased classification of sensory neuron types by large-scale single-cell RNA sequencing

The primary sensory system requires the integrated function of multiple cell types, although its full complexity remains unclear. We used comprehensive transcriptome analysis of 622 single mouse neurons to classify them in an unbiased manner, independent of any a priori knowledge of sensory subtypes. Our results reveal eleven types: three distinct low-threshold mechanoreceptive neurons, two proprioceptive, and six principal types of thermosensitive, itch sensitive, type C low-threshold mechanosensitive and nociceptive neurons with markedly different molecular and operational properties. Confirming previously anticipated major neuronal types, our results also classify and provide markers for new, functionally distinct subtypes. For example, our results suggest that itching during inflammatory skin diseases such as atopic dermatitis is linked to a distinct itch-generating type. We demonstrate single-cell RNA-seq as an effective strategy for dissecting sensory responsive cells into distinct neuronal types. The resulting catalog illustrates the diversity of sensory types and the cellular complexity underlying somatic sensation.

B-Afferents: A fundamental division of the nervous system mediating homeostasis?

The peripheral nervous system (PNS) has classically been separated into a somatic division composed of both afferent and efferent pathways and an autonomic division containing only efferents. J. N. Langley, who codified this asymmetrical plan at the beginning of the twentieth century, considered different afferents, including visceral ones, as candidates for inclusion in his concept of the “autonomic nervous system” (ANS), but he finally excluded all candidates for lack of any distinguishing histological markers. Langley's classification has been enormously influential in shaping modern ideas about both the structure and the function of the PNS. We survey recent information about the PNS and argue that many of the sensory neurons designated as “visceral” and “somatic” are in fact part of a histologically distinct group of afferents concerned primarily autonomic function. These afferents have traditionally been known as “small dark” neurons or B-neurons. In this target article we outline an association between autonomic and B-neurons based on ontogeny, cell phenotype, and functional relations, grouping them together as part of a common reflex system involved in homeostasis. This more parsimonious classification of the PNS, made possible by the identification of a group of afferents associated primarily with the ANS, avoids a number of confusions produced by the classical orientation. It may also have practical implications for an understanding of nociception, homeostatic reflexes, and the evolution of the nervous system.

Extracellular signal-regulated kinase and phosphatidylinositol-3-kinase/AKT signalling pathways in the human carotid body and peripheral ganglia

Extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K)/AKT signalling pathways are involved in various cell functions, but their developmental regulation in the carotid body and peripheral ganglia has not yet been fully investigated. ERK and AKT immunolocalisation and activation were studied by anti-ERK, -pERK, -AKT and -pAKT immunohistochemistry in carotid bodies and peripheral (sympathetic and sensory) ganglia, sampled at autopsy from 4 foetuses (mean gestational age 177 days), 8 infants (mean age 10 months), 8 young adults (mean age 38 years) and 6 aged adults (mean age 72.4 years). ERK and AKT immunopositivity and activation were demonstrated in both glomic type I cells and peripheral ganglionic cells and are ascribed to local action by neuromodulators or neurotrophic factors. Mean percentages of ERK- and pERK-immunopositive glomic type I cells were lower in foetuses than in infants and young adults, and those of AKT-immunopositive glomic type I cells were lower in foetuses than in young and old adults, suggesting incomplete maturation of these two signalling pathways in foetal life. Both pERK and pAKT immunoreactions were detected only in post-natal sympathetic and sensory ganglia, demonstrating that, also in peripheral ganglia, these pathways are not yet fully operative during the foetal stage.

Peptide neurons in peripheral tissues including the urinary tract: immunohistochemical studies

Using the indirect immunofluorescence technique of Coons and collaborators, neurons containing substance P-, enkephalin-, vasoactive intestinal polypeptide (VIP)--and somatostatin-like immuno-reactivity have been identified in the peripheral nervous system. They have a widespread distribution, particularly in the gastrointestinal and urinary tracts. Whereas part of these peptide containing fibres may belong to sensory neurons, the majority seem to have their origin in peripheral autonomic ganglia, indicating a complex built up of the autonomic nervous system. There is evidence that some noradrenergic neurons contain somatostatin, which may suggest that one neuron can synthesize and store two transmitters. The significance of such neurons, as well as of peripheral peptide neurons in general, remains to be elucidated.

Biosynthesis, axonal transport and turnover of neuronal substance P

In dorsal root ganglia substance P is synthesized ribosomally, probably via a precursor. A second peptide, apparently a modified form of substance P (8-11), is cosynthesized with substance P and transported with it down both dorsal roots and peripheral branches. Four times as much substance P-like immunoreactivity is transported peripherally as centrally. Only 30% of axonal substance P-like immunoreactivity is available for rapid axonal transport and this is transported at a rate of 4.9 mm h-1. Axonal transport is not necessary for substance P synthesis. Doses of anisomycin which inhibit CNS protein synthesis by more than 95% do not cause any fall in substance P levels over an eight-hour period in ganglia, spinal cord or brain, suggesting that turnover is slower than that of conventional transmitters. However, stimulation of the hindlimbs of these animals reduces substance P levels in the dorsal horn. The turnover rate of spinal cord substance P, estimated either by relating the amount transported down dorsal roots to that in terminals or by measuring the decline of substance P levels after intrathecal colchicine, is four to five days. The functional organization of the substance P neuron is discussed with particular reference to the maintenance of peptide levels in terminals.

Developmental patterns of caspase-3, bax and bcl-2 proteins expression in the human spinal ganglia

The distribution of the bcl-2, bax and caspase-3 proteins was investigated in the cells of developing human spinal ganglia. Paraffin sections of 10 human conceptuses between 5th and 9th gestational weeks were analysed morphologically, immunohistochemically and by TUNEL-method. Cells positive to caspase-3 had brown stained nuclei or nuclear fragmentations. At earliest stages, 6% of ganglion population were caspase-3 positive cells. Later on, a significant increase in number of caspase-3 positive cells appeared, particularly in the ventral part of ganglia (12%), and subsequently decreased to 6%. TUNEL-positive cells had the same distribution pattern as caspase-3 positive cells. Bax-positive cells followed the developmental pattern similar to caspase-3 cells, changing in range between 20% and 32%. There were 8% of bcl-2 positive cells at earliest stages. They increased significantly in dorsal part of the ganglion during the 7th week (28%), and than dropped to 15% by the end of the 8th week. These findings suggest a ventro-dorsal course of development in human spinal ganglia. Number of bcl-2, bax and caspase-3 positive cells changed in a temporally and spatially restricted manner, coincidently with ganglion differentiation. While apoptosis might control cell number, bcl-2 could act in suppression of apoptosis and enhancement of cell differentiation.

Phylogenetic investigation of Dogiel's pericellular nests and Cajal's initial glomeruli in the dorsal root ganglion

Cajal's initial glomeruli (IG) and Dogiel's pericellular nests (PCNs) were first described from methylene blue preparations of healthy animal tissues around the beginning of the last century. Since that time, although many reports have been published concerning these structures, few have focused on their development and phylogeny in healthy animals. The aim of this study was to examine the phylogenetic development of the sensory neurons in Cajal's IG (also called axonal glomeruli) and Dogiel's PCNs in the dorsal root ganglion (DRG) of the healthy adult frog, chick, rat, and rabbit. The three-dimensional architecture of the neurons was observed in ganglia by scanning electron microscopy after removal of the connective tissue. The neurons in the DRG of fish are known to be bipolar, but DRG neurons in the species examined here were found to be pseudounipolar, with single stem processes. The proportion of neurons having IG or PCNs increased with increasing phylogenetic complexity in the species examined here. Cajal's initial glomeruli, the convolution of the stem process near the parent cell body: In frogs, the ganglia were small and the neuronal stem processes were very short and straight. In chicks, the stem processes were longer; sometimes very long, tortuous processes were observed. However, no neurons with typical IG were observed in either species. Typical IG were observed in rats and rabbits; their occurrence was much more frequent in rabbits. Pseudounipolarization, i.e., the transition from bipolar to pseudounipolar neurons, is thought to save space, limit the length of neuronal processes, and reduce conduction time. However, an explanation of the evolutionary advantage of the IG, which is formed by the excessive prolongation of the stem process, remains elusive. The cytological and electrophysiological importance of IG has been discussed. Dogiel's pericellular nests (PCNs), which resemble balls of yarn made of thin unmyelinated nerve fibers around DRG neurons, have been observed in the DRG of rats and rabbits, but not in frogs or chicks. This interesting structure shows not only ontogenetic development in healthy animals but also phylogenetic development among species. The nerve fibers in the PCNs were less than 1.2 mum in diameter and had some varicosities. An immunohistochemical study using anti-tyrosine hydroxylase (TH) antibody revealed that some PCNs contain TH-positive nerve fibers and varicosities. Such TH-positive PCNs disappear after sympathectomy. These results suggest that the PCNs are made up of autonomic nerve fibers.

Differential growth of axons from sensory and motor neurons through a regenerative electrode: A stereological, retrograde tracer, and functional study in the rat

Polyimide regenerative electrodes (RE) constitute a promising neural interface to selectively stimulate regenerating fibers in injured nerves. The characteristics of the regeneration through an implanted RE, however, are only beginning to be established. It was recently shown that the number of myelinated fibers distal to the implant reached control values 7 months postimplant; however, the functional recovery remained substantially below normal [J Biomed Mater Res 60 (2002) 517]. In this study we sought to determine the magnitude, and possible selectivity, of axonal regeneration through the RE by counting sensory and motor neurons that were retrogradely labeled from double tracer deposits in the sciatic nerve. Adult rats had their right sciatic nerves transected, and the stumps were placed in silicone tubes; some simply were filled with saline (Tube group), and others held a RE in its center (RE group). Simultaneously, the proximal stump was exposed to Diamidino Yellow. Two months later the nerves were bilaterally excised distal to the implant, and exposed to Fast Blue. Electrophysiological recordings, and skin nociceptive responses confirmed previous findings of partial functional recovery. In controls, an average of 20,000 and 3080 neurons were labeled in L4-L5 dorsal root ganglia (with minor contributions from L3 and/or L6), and in the ventral horn of the lumbar spinal cord, respectively. In the regenerating side, 35% of the DRG neurons were double-labeled, without differences between groups. In contrast, only 7.5% of motoneurons were double-labeled in the RE group, vs. 21% in the Tube group. Moreover, smaller ganglion cells regenerated better than large neurons by a significant 13.8%. These results indicate that the RE is not an obstacle for the re-growth of sensory fibers, but partially hinders fiber regeneration from motoneurons. They also suggest that fine fibers may be at an advantage over large ones to regenerate through the RE.

No further loss of dorsal root ganglion cells after axotomy in p75 neurotrophin receptor knockout mice

The role of the p75 neurotrophin receptor for neuronal survival after nerve crush was studied in L5 dorsal root ganglia (DRG) of knockout mice and controls with assumption-free stereological methods. Numbers of neuronal A- and B-cells were obtained using the optical fractionator and optical disector techniques. At birth, the total number of DRG neurons was 10,000 +/- 2,600 in control mice compared with 5,100 +/- 1,300 in p75 knockout mice. During postnatal development, 1,400 neuronal B-cell bodies were lost in p75 knockouts (2P < 0.05) and 1,100 in controls (NS), whereas the A-cell population remained stable. After a sciatic nerve crush, the total neuron loss in controls was 15.4% +/- 3.5% (2P < 0.05) and 22.7% +/- 5.1% (2P < 0.05) at days 14 and 42, respectively. In contrast, there was no loss in total number of neurons after crush in p75 knockout mice. Neuronal A-cell number was unchanged after the crush in p75 knockouts as well as in controls at both times. At 14 days, the population of B-cells was reduced by 24.8% +/- 3.6% in controls and by 6.1% +/- 3.5% in p75 knockouts, this difference being significant (2P < 0.001). At 42 days, the B-cell loss was 29.6% +/- 5.5% in controls and 4.2% +/- 6.4% in p75 knockouts (2P < 0.001). In conclusion, the lack of the p75 receptor results in neuronal DRG cells that are resistant to nerve injury, pointing to a role for the receptor in apoptosis.

Neonatal anandamide treatment results in prolonged mitochondrial damage in the vanilloid receptor type 1-immunoreactive B-type neurons of the rat trigeminal ganglion

Capsaicin acting on the vanilloid type 1 receptor (VR1) excites a subset of primary sensory neurons. Systemic capsaicin treatment of adult or neonatal rats results in selective damage of the B-type neurons in the rat sensory ganglia by causing a long-lasting mitochondrial lesion that has been described in detail in previous studies. The endocannabinoid, anandamide, exhibits an agonist effect on VR1 receptors. The physiological role of anandamide as a VR1 agonist is still uncertain. This study addresses whether high doses of anandamide induce similar ultrastructural changes to those described for capsaicin. The effect of neonatally administered anandamide (1 mg/kg) on neurons of the trigeminal ganglia and the hippocampal formation was examined in the light and electron microscope from the first day after injections to the 20th week after treatment. Anandamide was found to cause mitochondrial damage of the B-type neurons of trigeminal ganglia similar to what has been described for capsaicin. The time course of damage was also comparable. In addition to the cells of the trigeminal ganglia, B-type cells of dorsal root ganglia were also damaged. A-type neurons and satellite glial cells were not affected either in the trigeminal or in the dorsal root ganglia. In the hippocampal formation, where a subpopulation of local circuit neurons is known to contain cannabinoid type 1 (CB1) but not VR1 receptors, anandamide did not cause morphological changes of mitochondria either in the dentate gyrus or in Ammon's horn. At 3 weeks of age, all VR1-immunoreactive neurons in the trigeminal ganglia of animals treated neonatally with anandamide displayed swollen mitochondria. The results suggest that anandamide, at pharmacologically relevant doses, acts on the VR1 receptor and causes prolonged and selective mitochondrial damage of B-type sensory neurons, as has previously been described for capsaicin.

Perikaryal surface specializations of neurons in sensory ganglia

Slender projections, similar to microvilli, are the main specialization of the perikaryal surface of sensory ganglion neurons. The extent of these projections correlates closely with the volume of the corresponding nerve cell body. It is likely that the role of perikaryal projections of sensory ganglion neurons, which lack dendrites, is to maintain the surface-to-volume ratio of the nerve cell body above some critical level for adequate metabolic exchange. Satellite cells probably have the ability to promote, or provide a permissive environment for, the outgrowth of these projections. It is not yet known whether the effect of satellite cells is mediated by molecules associated with their plasma membrane or by diffusible factors. Furthermore, receptor molecules for numerous chemical agonists are located on the nerve cell body surface, but it is not known whether certain molecules are located exclusively on perikaryal projections or are also present on the smooth surface between these projections. Further study of the nerve cell body surface and of the influence that satellite cells exert on it will improve our understanding of the interactions between sensory ganglion neurons and satellite neuroglial cells.

Age-related mitochondrial damage in the B-type cells of the rat trigeminal ganglia

Aging is associated with signs of sensory impairment and neurological symptoms. Advancing age is characterized by increased thresholds of thermal, tactile and vibratory sensations. One important cause of the sensory disturbances has been stated to be the loss of neurons. Decreases have been observed in the number of peripheral nerve fibers and in the number of neurons in the spinal ganglia of rats. In the present study, the cytoplasmic organelles of the neurons of the trigeminal ganglia were examined in young and senescent rats in order to reveal the cause of cell loss during aging. Mitochondrial alterations, swelling and loss of internal cristae were observed from 23 week of age in the B-type neurons of the trigeminal ganglia. Other cytoplasmic elements were intact. Mitochondrial damage was never seen in A-type neurons and satellite glial cells. It was concluded that the ultrastructural changes in the mitochondria of the B-type cells may contribute to the nervous disturbances that occur in senescent individuals. The diminution of mitochondrial damage and the protection of B-type neurons through the use of nerve growth factors may prevent the sensory impairment late in life.

Neonatal capsaicin treatment results in prolonged mitochondrial damage and delayed cell death of B cells in the rat trigeminal ganglia

Capsaicin acts on the vanilloid receptor subtype 1, a noxious heat-gated cation channel located on a major subgroup of nociceptive primary afferent neurons. Following the systemic capsaicin treatment of neonatal rats, the loss of B-type sensory neurons in trigeminal ganglion of adult rats with chemoanalgesia and abolition of neurogenic inflammation was investigated. Our quantitative morphometric analysis revealed that in the trigeminal ganglion of neonatal rats treated with 50 mg/kg s.c. capsaicin, the total number of neurons, morphology of B-type cells and cell-size histograms did not differ from that of the controls 1 or 5 days after treatment. These observations indicate that early cell death does not play a significant part in the loss of B-type cells, which in our sample was 39.4% on the 19th day. However under the electron microscope pronounced selective mitochondrial swelling with disorganized cristae was observed in B-type neurons at 1-20 weeks after capsaicin treatment. Daily treatment with nerve growth factor (NGF, 10 x 100 microg/kg s.c.), started 1 day after capsaicin injection, prevented the loss of B-type cells but did not counteract the development of long-lasting mitochondrial damage. After NGF treatment, partial restitution of chemonociception to capsaicin instillation into the eye occurred but capsaicin-induced inhibition of neurogenic plasma extravasation in the hindpaw evoked by topical application of mustard oil remained unaltered. We conclude, that capsaicin treatment in neonatal rats, as in the adults, destroys terminal parts of the sensory neurons supplied by vanilloid receptors and induces long-lasting mitochondrial swelling in the soma. We hypothesize that loss of NGF uptake results in delayed cell death of B-type neurons in neonates.

Identification of RanBP2- and kinesin-mediated transport pathways with restricted neuronal and subcellular localization

Ran-binding proteins, karyopherins, and RanGTPase mediate and impart directionality to nucleocytoplasmic transport processes. This biological process remains elusive in neurons. RanBP2 has been localized at the nuclear pore complexes and is very abundant in the neuroretina. RanBP2 mediates the assembly of a large complex comprising RanGTPase, CRM1/exportin-1, importin-beta, KIF5-motor proteins, components of the 19S cap of the 26S proteasome, ubc9 and opsin. Here, we show RanBP2 is abundant in the ellipsoid compartment of photoreceptors and RanGTPase-positive particles in cytoplasmic tracks extending away from the nuclear envelope of subpopulations of ganglion cells, suggesting RanBP2's release from nuclear pore complexes. KIF5C and KIF5B are specifically expressed in a subset of neuroretinal cells and differentially localize with RanBP2 and importin-beta in distinct compartments. The C-terminal domains of KIF5B and KIF5C, but not KIF5A, associate directly with importin-beta in a RanGTPase-dependent fashion in vivo and in vitro, indicating importin-beta is an endogenous cargo for a subset of KIF5s in retinal neurons. The KIF5 transport pathway is absent from the myoid region of a topographically distinct subclass of blue cones and the distribution of kinesin-light chains is largely distinct from its KIF5 partners. Altogether, the results identify the existence of neuronal- and subtype-specific kinesin-mediated transport pathways of importin-beta-bound cargoes to and/or from RanBP2 and indicate RanBP2 itself may also constitute a scaffold carrier for some of its associated partners. The implications of these findings in protein kinesis and pathogenesis of degenerative neuropathies are discussed.

Vanilloid receptor homologue, VRL1, is expressed by both A- and C-fiber sensory neurons

The capsaicin receptor (VR1) homologue, VRL1, is thought to be responsible for transducing high-threshold heat responses in Adelta-fiber neurons. In the present study, the expression of VRL1 by A- or C-fiber sensory neurons in rats was investigated by using a VRL1 and 200 kDa neurofilament (NF200, an A-fiber marker) double immunohistochemical staining method. Approximately 46% of VRL-positive neurons were NF200 positive. Though double-labeled neurons tended to be medium to large, many VRL1 single-labeled neurons were large. Dense VRL1 immunoreactivity was also found in laminae I and II of the spinal dorsal horn, where nociceptive Adelta- and C-fibers normally terminate. These results suggest that both C-fiber and Adelta-fiber primary sensory neurons express VRL1, and VRL1 may play an important role in nociception.

Developmental shift of vanilloid receptor 1 (VR1) terminals into deeper regions of the superficial dorsal horn: correlation with a shift from TrkA to Ret expression by dorsal root ganglion neurons

The cloned vanilloid receptor VR1 can be activated by capsaicin and by thermal stimuli. The pattern of nerve terminals that contain VR1 in adult rat spinal cord does not correspond to axons that arise from a single subset of dorsal root ganglion neurons. Thus, we postulated that the basis underlying this complexity might be better understood from a developmental perspective. First, using capsaicin-induced hyperalgesia as a measure of VR1 function, we found that vanilloid receptors were functional as early as postnatal day 10 (P10), although hyperalgesia was of longer duration in adult. Interestingly, the appearance of VR1 protein in terminals of dorsal root ganglion neurons shifts over this postnatal period. From embryonic day 16 to P20, the majority of VR1 protein in the spinal cord was observed in lamina I. As animals matured, VR1 protein became more abundant in lamina II, particularly in the inner portion. Consistent with these observations, the number of dorsal root ganglion neurons coexpressing VR1 and isolectin B4 binding sites doubled while the number of neurons that had both VR1 and substance P remained relatively constant from P2 to P10. In peripheral processes, the number of VR1-positive nerve fibres and terminals in cutaneous structures in postnatal day 10 was half of that in adults. We also show that the association of VR1 with Ret is the reciprocal of the association of VR1 with Trk A. These results suggest that neurotrophins may regulate the extent to which populations of dorsal root ganglion neurons express VR1.

Delayed loss of small dorsal root ganglion cells after transection of the rat sciatic nerve

The present study deals with changes in numbers and sizes of primary afferent neurons (dorsal root ganglion [DRG] cells) after sciatic nerve transection. We find that this lesion in adult rats leads to death of some DRG cells by 8 weeks and 37% by 32 weeks after the lesion. The loss of cells appears earlier in and is more severe in B-cells (small, dark cells with unmyelinated axons) than A-cells (large, light cells with myelinated axons). With regard to mean cell volumes, there is a tendency for both categories of DRG cells to be smaller, but except for isolated time points, these differences are not statistically significant. These findings differ from most earlier reports in that the cell loss takes place later than usually reported, that the loss is more severe for B-cells, and that neither A- or B-cells change size significantly. Accordingly, we conclude that sciatic nerve transection in adult rats leads to a slowly developing but relatively profound loss of primary afferent neurons that is more severe for B-cells. These results can serve as a basis for studies to determine the effectiveness of trophic or survival factors in avoiding axotomy induced cell death.

Effect of nerve crush on perikaryal number and volume of neurons in adult rat dorsal root ganglion

Assumption-free stereological methods were applied to assess the effect of nerve crush on perikaryal number and mean volume of neuronal subpopulations in adult rat dorsal root ganglion (DRG). The L5 spinal nerve of 20 Wistar rats was crushed approximately 7 mm distal to the DRG, and the contralateral spinal nerve and DRG were left intact and used as controls. After four, 15, 45, and 120 days, the rats were killed, and the tissue was fixed and processed for subsequent preparation of 30-microm-thick sections. Estimates of neuron number were obtained with the optical fractionator technique and estimates of the mean perikaryal volume with the vertical planar rotator principle. Perikaryal loss was progressive during the early study period but stabilized 45 days after nerve injury. The mean number (n) of all neurons in intact L5 DRG was 16,400 (S.D. = 2,000). The loss of perikarya was 16% (P < 0.05) after four days, 15% (P < 0.05) after 15 days, 30% (P = 0.059) after 45 days, and 34% (P < 0. 05) after 120 days. B cells were lost at an earlier time than were A cells, and the B cell loss was more pronounced (39% vs. 22%, respectively, after 120 days). For A cells, the mean perikaryal volume was initially reduced but was normalized at the end of the study. Distributions of perikaryal volume showed that the curves of both A and B cells were uniformly displaced toward smaller values 15 and 45 days after injury. Neuronal loss caused by crush seems similar to that seen in rats exposed to permanent axotomy (Vestergaard et al. [1997] J Comp Neurol 388:307-312) at the same location, indicating that survival of perikarya is not dependent on possibility for fiber growth.

Distribution and induction of cytochrome P450 1A1 and 1A2 in rat brain

Cytochromes P450 1A1 and 1A2 are involved in the oxidation of a wide spectrum of endogenous compounds and xenobiotics. Although their presence has been repeatedly confirmed in brain tissue, reports regarding their distribution in the brain are often contradictory. In the present study the possibility was examined that CYP1A1 and CYP1A2 are localized and inducible in the brain-CSF barrier and regions with a leaky blood brain barrier, where they may serve as a protective metabolic barrier. CYP1A1 and CYP1A2 levels were determined in subcellular fractions of multiple brain regions, as well as tissue homogenates of circumventricular organs, and the meninges by Western blotting and catalytic activity in control male rats and rats treated with the inducer beta-naphthoflavone (BNF). In control animals CYP1A1 immunoreactive protein was undetectable in regional brain microsomes or whole tissue homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, median eminence, and pituitary. However, low levels of ethoxyresorufin O-deethylase (EROD) activity were observed in homogenates of the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary. Western blotting revealed only low levels of CYP1A2 immunoreactive protein in brain microsomes from the cortex, cerebellum, brainstem, thalamus, hippocampus, and striatum from control animals. Following BNF treatment, EROD activity was induced 12-42-fold in the arachnoid, choroid plexus, dura mater, pineal gland, pituitary, and median eminence. Western blot analysis revealed CYP1A1 to be induced in the arachnoid, dura mater, choroid plexus, pineal gland, and pituitary, while CYP1A2 was undetectable. No induction of CYP1A1 or CYP1A2 protein was observed in brain microsomes from the olfactory bulb, cortex, striatum, hippocampus, cerebellum, or brainstem following BNF treatment, providing that the arachnoid membranes and choroid plexus had been carefully removed prior to brain dissection. Neither CYP1A1, 1A2 protein, nor EROD activity were detected in purified brain mitochondria, regardless of treatment or region. In conclusion, catalytically active CYP1A1 is located in the meninges as well as certain circumventricular organs, is inducible by BNF, and appears to be absent or expressed constitutively at very low levels in the majority of the brain parenchyma. The localization of CYP1A1 in the blood-CSF barrier and circumventricular tissues likely plays a role in protecting the brain from xenobiotics.

Morphological and morphometrical changes in dorsal root ganglion neurons innervating the regenerated lizard tail

The variations occurring in neurons from dorsal root ganglia that provide innervation to the regenerated tail of the lizard (vicarious ganglia) are analysed. Vicarious ganglion neurons, when compared to control ganglion neurons (i.e. ganglia from the same animal that were not involved in the reinnervation process), show a size increase of the soma (cell hypertrophy) which applies to all cell types and subtypes. No statistically significant differences in the relative percentage of neurofilament-poor (type D) and neurofilament-rich (type L) neurons were found between vicarious dorsal root ganglia compared to controls in all animals. On the contrary, within L neuron sub-types, a statistically significant increase in sub-type L2 (very rich in neurofilaments), and the appearance of sub-type L3 neuron which is not detectable in controls, were demonstrated in vicarious dorsal root ganglia. In spite of these variations in size and percentage distribution, no structural and ultrastructural differences of the various cell types and sub-types are detectable, except for the appearance of the sub-type L3 neurons. However, this neuron sub-type might not be considered specific of hypertrophy since the same morphological features have been observed, in normal conditions, in lizard dorsal root ganglia from cervical and lumbar spinal levels that provide innervation to limb plexuses.

[Substance P in the primary sensory neurons innervating the dental pulp in the guinea pig]

Primary sensory trigeminal neurons supplying the dental pulp of incisors in guinea pigs were labelled by retrograde axonal transport. Using an autometallographic intensification procedure, 48 h after injection of wheat germ agglutinin/colloidal gold in the pulp, gold particles were detected in the cytoplasm of the neurons as black granulations. A morphometric study showed a bimodal repartition of the labelled neurons of the ganglion. By submitting ganglion slices to an anti-substance P immunserum revealed by immunocytochemistry, it could be observed that, among the neurons supplying the dental pulp of incisors, the majority of the largest were substance P immunopositive while the smallest were substance P immunonegative. These observations suggest that there could be at least two different populations of nerve fibres supplying the guinea pig incisor dental pulp. Substance P negative neurons could express different neurotransmitters.

Morphometrical analysis of types and sub-types of neurons in dorsal root ganglia of the lizard Podarcis sicula

In the present study, we conducted a morphometrical analysis of the different types and sub-types of lizard DRG neurons at various spinal levels. This analysis demonstrated significant differences in size distribution among the various neuron types and sub-types, as well as a significant shift to greater values in neurons from the dorsal root ganglia at the cervical and the lumbar spinal levels. The results are critically evaluated in relation to methodological issues, and the implications of these findings are discussed.

Sensory innervation of the guinea pig extraocular muscles: a 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate tracing and calcitonin gene-related peptide immunohistochemical study

The sensory apparatus of the extraocular muscles attains special interest because of the great variation among different species with respect to the proprioceptors. The sensory innervation of the guinea pig extraocular muscles, lacking both muscle spindles and tendon organs, was investigated with a fluorescence double-labelling method. Primary sensory perikarya were assessed by postmortem application of 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (Di-I) to the extraocular muscle nerves. Traced neurons were found in the ipsilateral ophthalmic part of the trigeminal ganglion. This is in line with findings in other species. Calcitonin gene-related peptide (CGRP) was detected immunohistochemically within the trigeminal ganglion. No somatotopic organization was observed for CGRP-like immunoreactive perikarya. Small (maximal diameter below 30 microm), medium (maximal diameter between 30 and 50 microm), and large (maximal diameter larger than 50 microm) trigeminal ganglion cells were found among the primary afferent perikarya from extraocular muscles. Among CGRP-like immunoreactive cells, only small and medium cells were observed. Double-labelling experiments indicated the CGRP content of primary afferents of the guinea pig extraocular muscles. The relationship to former morphological categories of ganglion cells is discussed. Primary afferent neurons with CGRP-like immunoreactivity might have efferent functions and might also be involved in inflammatory processes of extraocular muscles.

Neurogenesis of subpopulations of rat lumbar dorsal root ganglion neurons including neurons projecting to the dorsal column nuclei

The time of birth of subpopulations of dorsal root ganglion (DRG) neurons was studied with immunohistochemistry for 5-bromodeoxyuridine (BrdU). Pregnant rats were injected with BrdU i.p. to label the neurons on one of the embryonic days (E) E11-E16. When they were adults, the rats were given injections of Fluoro-Gold (FG) into the gracile nucleus to identify DRG neurons projecting to this structure. Following a 5 day survival period, the animals were perfused with aldehyde fixative. Sections from the L3-L5 DRGs were processed for BrdU immunohistochemistry followed by either immunostaining for the antineurofilament antibody RT97, as marker of the light neuronal subpopulation, or histochemical staining for the B4 isolectin from Griffonia simplicifolia I, as marker of the small dark subpopulation. The results indicated that the DRG neurons were generated between E12 and E16. The RT97+ neurons were generated on E12-E15, with a peak at E13. FG+ neurons, the majority of which were RT97+, were also generated on E12-E15. The B4+ neurons were generated on E13-E16, with a peak around E14. The overall pattern of neurogenesis of the DRG neurons showed that the RT97+ neurons were produced prior to the B4+ neurons. These findings are in agreement with earlier observations that the large DRG neurons are generated earlier than the small dark neurons. Our findings also suggest the existence of a third neuronal subpopulation that might be produced at the latest period of DRG neurogenesis at E15-E16.

Segmental distribution of afferent neurons innervating the canine testis

To clarify the afferent innervation of the canine scrotal contents, retrograde labeling of neurons in the dorsal root ganglia (DRG) has been carried out using two methods: (1) horseradish peroxidase (HRP) injection into the surface of the testis and epididymis; and (2) exposure of the superior spermatic nerve to a fluorescent dye (Fast blue; FB). Injections of HRP resulted in labeling of DRG cells located predominantly from T10 to L4 (87%) and, to a lesser extent, at S1-S3 (13%). Transection of the vas deferens previous to testicular injections eliminated labeling in the S1-S3 DRG, but not at thoracolumbar levels. These findings indicated that primary afferent fibers of the testis and epididymis project mainly to the DRG at higher than L4 through the superior spermatic nerve, but an additional population of the fibers also projects the sacral level through the inferior spermatic nerve. Exposure of the superior spermatic nerve to FB resulted in a similar distribution of labeled cells as compared with testicular injections of HRP after vasectomy. Labeled cells (8.1%) were also observed in the contralateral T13-L3 DRG. In both FB and HRP groups, the major part of the labeled cells was located in L1 and L2. The sizes of HRP- and FB-labeled cells were smaller than those of unlabeled cells in the L1 and L2 DRG. The cumulative frequency distribution histogram for the diameter of HRP- and FB-labeled cells could be fitted by a normal distribution.

A stereological analysis of the numerical distribution of neurons in dorsal root ganglia C4-T2 in adult macaque monkeys

The numbers of neurons in dorsal root ganglia C4-T2 of adult monkeys (M. nemestrina) were estimated in celloidin-embedded material by means of the optical fractionator, a stereological procedures that combines the optical disector with a fractionator sampling scheme. On each side, counts of A-type, B-type, and total neurons were performed for the whole set of ganglia, as well as separately for ganglia C7, C8, and T1. Sampling and counting in this study were carried out with the help of an interactive computer system, the test grids being provided by the GRID general stereological software package (Olympus Denmark). The precision of the estimates for each animal was evaluated by computing the coefficient of error, which was kept at or below 0.10. The mean number of neurons on each side of the C4 - T2 set was 236,500 with a coefficient of variation among animals (CV) of 0.13. Of these neurons, 42% were A-type and 56% were B-type. Mean left-right differences among animals were below 1%, with low variability (CV = 0.07). The mean numbers of neurons in ganglia C7, C8, and T1 were, respectively, 46,000 (CV = 0.20), 51,000 (CV = 0.18), and 41,000 (CV = 0.22). Mean side differences for individual ganglia were 17%, 16%, and 12%, respectively, with high variability among animals. Intraanimal side differences were low for the whole set of ganglia (4%), as well as for the C7-T1 group (5%), but increased substantially when ganglia were considered separately (up to 17% on average in C7) or even in pairs of adjacent ganglia. These findings provide a quantitative frame for developmental or lesion studies in the peripheral somatosensory system of macaques, and warn against using single ganglia in studies requiring quantitative side comparisons.

Location of sensory nerve cells that provide calbindin-containing laminar nerve endings in myenteric ganglia of the rat esophagus

To determine the origin of the calbindin-containing laminar nerve endings in the myenteric ganglia of the rat esophagus, retrograde tracing experiments combined with immunohistochemistry using an antibody for calbindin were carried out. After Fast blue was injected into the cervical portion of the esophagus, labeled neurons were found bilaterally in the nodose ganglion and dorsal root ganglia of C1 to T3. 80% of the total neurons in the nodose ganglion and 20% of those in the dorsal root ganglia showed calbindin immunoreactivity. Moreover, 79% of Fast-blue-labeled neurons found in the nodose ganglion and 18% of those in the dorsal root ganglia were immunoreactive for calbindin. These results suggest that the calbindin antibody we used is useful as a marker for identifying esophageal vagal afferents derived from the nodose ganglion. The calbindin-immunoreactive nerve fibers forming the laminar endings in the myenteric ganglia of the rat cervical esophagus are mainly derived from sensory neurons in the nodose ganglion and partly derived from those in the cervical and upper thoracic dorsal root ganglia. Calbindin-containing laminar nerve endings may be related to mechanoreceptors in the esophagus.