Immunocytochemical localization of the neural cell adhesion molecules L1, N-CAM, and J1 in Pacinian corpuscles of the mouse during development, in the adult and during regeneration

Localization and distribution of laminin in the basal lamina of certain mechanoreceptors—an immunogold study

The applied immunogold cytochemical technique in investigating the cytologic distribution of the laminin (LAM) molecule in the capsulated Pacinian and Herbst mechanoreceptors shows the presence of LAM around most elements of the receptor structures. The LAM immunoreactivity (LAM-IR) is best expressed in the vicinity of the perineural capsule cells of both receptor types, where it is primarily concentrated around the perinuclear regions as well as the cytoplasmic lamellae. Such a localization overlaps with the already known ultrastructural localization of a basal lamina (BL) around these cells. Laminin immunoreactivity is less well expressed around the modified Schwann cells. Even in these cells, however, there is an apparent immunoreaction around the cytoplasmic lamellae regardless of the lamellar location. In both receptor types, there is no LAM-IR in the cells of the subcapsular space. Of particular significance we consider the localization of gold particles (respectively the presence of a BL) between the innermost lamellae of the modified Schwann cells and the non-myelinated part of the receptor nerve fiber and their endings, as well as around the axoplasmic protrusions of the nerve endings. We discuss the role of the BL and LAM in the investigated rapidly adapting mechanoreceptors and their trophic influence upon the sensory regions. We also assume the arresting and selective effect of these membranes in building up the ion channels of the axolemma which probably has a certain importance in mechanotransduction.

Effects of motor versus sensory nerve grafts on peripheral nerve regeneration

Autologous nerve grafting is the current standard of care for nerve injuries resulting in a nerve gap. This treatment requires the use of sensory grafts to reconstruct motor defects, but the consequences of mismatches between graft and native nerve are unknown. Motor pathways have been shown to preferentially support motoneuron regeneration. Functional outcome of motor nerve reconstruction depends on the magnitude, rate, and precision of end organ reinnervation. This study examined the role of pathway type on regeneration across a mixed nerve defect. Thirty-six Lewis rats underwent tibial nerve transection and received isogeneic motor, sensory or mixed nerve grafts. Histomorphometry of the regenerating nerves at 3 weeks demonstrated robust nerve regeneration through both motor and mixed nerve grafts. In contrast, poor nerve regeneration was seen through sensory nerve grafts, with significantly decreased nerve fiber count, percent nerve, and nerve density when compared with mixed and motor groups (P < 0.05). These data suggest that use of motor or mixed nerve grafts, rather than sensory nerve grafts, will optimize regeneration across mixed nerve defects.

Localization of beta and gamma subunits of ENaC in sensory nerve endings in the rat foot pad

The molecular mechanisms underlying mechanoelectrical transduction and the receptors that detect light touch remain uncertain. Studies in Caenorhabditis elegans suggest that members of the DEG/ENaC cation channel family may be mechanoreceptors. Therefore, we tested the hypothesis that subunits of the mammalian epithelial Na(+) channel (ENaC) family are expressed in touch receptors in rat hairless skin. We detected betaENaC and gammaENaC, but not alphaENaC transcripts in cervical and lumbar dorsal root ganglia (DRG). Using immunofluorescence, we found betaENaC and gammaENaC expressed in medium to large lumbar DRG neurons. Moreover, we detected these two subunits in Merkel cell-neurite complexes, Meissner-like corpuscles, and small lamellated corpuscles, specialized mechanosensory structures of the skin. Within these structures, betaENaC and gammaENaC were localized in the nerve fibers believed to contain the sensors responsive to mechanical stress. Thus beta and gammaENaC subunits are good candidates as components of the molecular sensor that detects touch.

Development of Meissner-like and Pacinian sensory corpuscles in the mouse demonstrated with specific markers for corpuscular constituents

The development of Meissner-like and Pacinian corpuscles was studied in mice [from postnatal day (Pd) 0 to 42] by using immunohistochemistry for specific corpuscular constituents. The battery of antigens investigated included PGP 9.5 protein and neurofilaments, as markers for the central axon; S100 protein, vimentin, and p75(LNGFR) protein, to show Schwann-related cells; and epithelial membrane antigen to identify perineurial-related cells. In Meissner-like corpuscles immunoreactivity (IR) for neuronal markers was found by Pd7 and later. The lamellar cells of these corpuscles expressed first S100 protein IR (Pd7 to Pd42), then vimentin IR (Pd12 to Pd42), and transitory p75(LNGFR) IR (Pd7 to Pd19-20). Vimentin IR, but not epithelial membrane antigen, was detected in the capsule-like cells of the Meissner-like corpuscles. On the other hand, the density of Meissner-like corpuscles progressively increased from Pd0 to Pd19-20. Pacinian corpuscles were identified by Pd7. From this time to Pd42 the central axon showed IR for neuronal markers, and the inner core cells were immunoreactive for S100 protein. Moreover, vimentin IR was detected in the inner core cells by Pd19 and later. Unexpectedly, the central axons displayed S100 protein IR (from Pd7 to P28), while p75(LNGFR) protein IR or epithelial membrane antigen IR were never detected. Taken together, and based on the expression of the assessed antigens alone, the present results suggest that the Meissner-like and the Pacinian corpuscles in mice become mature around Pd19-Pd28 and Pd20, respectively. Furthermore, these results provide a baseline timetable for future studies in the normal or altered development of sensory corpuscles in mice since specific sensory corpuscles are functionally associated with different subtypes of sensory neurons the development of which is selectively disturbed in genetically manipulated mice.

The clustering of axonal sodium channels during development of the peripheral nervous system

The distribution of Na+ channels in rat peripheral nerve was measured during development by using immunofluorescence. Small segments of sciatic nerve from postnatal day 0-13 (P0-P13) pups were labeled with an antibody raised against a well conserved region of the vertebrate Na+ channel. At day P0 axons contained almost no Na+ channel aggregates. The number of clusters increased dramatically throughout the first week. In almost all cases Na+ channels clustered in the vicinity of Schwann cell processes. At least four classes of aggregates were noted. Clusters formed singly at Schwann cell edges, in pairs or in broad regions between neighboring Schwann cells, and in more focal zones at presumptive nodes. Almost all Na+ channel aggregates had reached the latter stage by the end of the first week. Histograms plotting the frequency of occurrence of each cluster type suggested a sequence of events in node formation involving the initiation of channel aggregation by Schwann cell processes. The requirement for Schwann cells during sodium channel clustering was tested by blocking proliferation of these cells with the antimitotic agent mitomycin C. Na+ channel clustering was sharply reduced, whereas node formation was normal at a distal site along the same nerve. Immunocytochemical detection of myelin-associated glycoprotein (MAG) indicated that Schwann cells must begin to ensheathe axons before inducing Na+ channel clustering.

Onion bulb cells in mice deficient for myelin genes share molecular properties with immature, differentiated non-myelinating, and denervated Schwann cells

Onion bulb formation is a pathological feature observed in peripheral nerves of patients suffering from inherited peripheral neuropathies such as Charcot-Marie-Tooth and Déjérine-Sottas diseases. An onion bulb consists of small circumferentially oriented (supernumerary) cells and their processes surrounding a large caliber axon. In the present study, we investigated the molecular phenotype of supernumerary cells at the light and electron microscopic levels. The major motor (quadriceps muscle) branch of the femoral nerve from 16- to 24-month-old mice with an inactivated allele of the myelin protein zero gene or deficient for myelin-associated glycoprotein (MAG; P0(+)- and MAG--mice, respectively), which have numerous onion bulbs, was teased to obtain single nerve fibers, which were then processed for immunocytochemistry. Corresponding nerves from wild-type mice served as controls. In both P0(+)- and MAG--mice, supernumerary cells expressed S-100, the low-affinity nerve growth factor receptor (p75, NGFr), the cell adhesion molecule L1, the neural cell adhesion molecule (N-CAM), and glial fibrillary acidic protein (GFAP). At the electron microscopic level, the cell surface of supernumerary cells was NGFr immunoreactive and L1 and N-CAM were expressed at points of contact between supernumerary cells. NGFr, L1, and N-CAM were also present in the basal lamina surrounding myelinated axons associated with onion bulbs. Both S-100 and GFAP immunoreactivities were seen in the cytoplasm of supernumerary cells. In contrast, in wild-type mice myelinating Schwann cells only expressed S-100 intracellularly and L1 and N-CAM in their basal lamina, whereas non-myelinating Schwann cells expressed all five molecules investigated. The present study indicates that supernumerary cells in onion bulbs have a molecular phenotype characteristic of immature, differentiated non-myelinating, and denervated Schwann cells, thus excluding the possibility that supernumerary cells are perineurial cells.

Degeneration and regeneration of cutaneous sensory nerve formations

Auxiliary structures of the cutaneous sensory nerve formations (SNF) are dependent on sensory innervation during their critical period of development. Denervation of mature cutaneous corpuscles results in survival of the terminal Schwann cells and the capsular structures which are probably responsible for successful reinnervation of the cutaneous SNF. In addition, the basal lamina tubes of Schwann cells are connected with the terminal Schwann cells and play an important role in the guidance of regrowing axons to their original targets. Long-lasting denervation causes atrophic changes of the terminal Schwann cells and alterations of their molecular equipment. These atrophic changes in the terminal Schwann cells may be responsible for erroneous reinnervation of cutaneous SNF. A population of the cutaneous Merkel cells surviving denervation may also serve as targets for regrowing sensory axons. The basal laminae of terminal Schwann cells are produced under control of the sensory terminals during maturation of cutaneous SNF. In adult animals, the basal laminae are capable of stimulating differentiation of migrated Schwann cells to the terminal Schwann cells without the presence of the sensory terminals. Nonspecific cholinesterase (nChE) is secreted by the terminal Schwann cells and is attached to their extracellular matrix. The synthesis of these molecules in adult animals is not influenced by the sensory terminals. However, the presence of nChE molecules is associated with living terminal Schwann cells. Fetal orthotopically grafted dorsal root ganglion (DRG) neurons have the ability to reinnervate cutaneous SNF of adult hosts. When cutaneous areas are denervated, axons from adjacent sensory nerves may extend collateral branches into this area. The capacity for such extension is dependent on: (1) type of sensory nerve ending, C and A delta fibers having significantly greater capacity than sensory axons of larger caliber; (2) age of the animal, immature animals generally showing a greater capacity for collateral sprouting; (3) the state of the adjacent axons, those already in a growth mode being more capable than "resting" ones; and (4) the regional and mechanical conditions at the site of denervation, hindpaw skin being much less extensively reinnervated by collateral fibers than that of the trunk.

Peripheral nerve regeneration

Peripheral nerve regeneration comprises the formation of axonal sprouts, their outgrowth as regenerating axons and the reinnervation of original targets. This review focuses on the morphological features of axonal sprouts at the node of Ranvier and their subsequent outgrowth guided by Schwann cells or by Schwann cell basal laminae. Adhesion molecules such as N-CAM, L1 and N-cadherin are involved in the axon-to-axon and axon-to-Schwann cell attachment, and it is suggested that integrins such as alpha 1 beta 1 and alpha 6 beta 1 mediate the attachment between axons and Schwann cell basal laminae. The presence of synaptic vesicle-associated proteins such as synaptophysin, synaptotagmin and synapsin I in the growth cones of regenerating axons indicates the possibility that exocytotic fusion of vesicles with the surface axolemma supplies the membranous components for the extension of regenerating axons. Almost all the subtypes of protein kinase C have been localized in growth cones both in vivo and in vitro. Protein kinase C and GAP-43 are implicated to be involved in at least some part of the adhesion of growth cones to the substrate and their growth activity. The significance of tyrosine kinase in growth cones is emphasized. Tyrosine kinase plays an important role in intracellular signal transduction of the growth of regenerating axons mediated by both nerve trophic factors and adhesion molecules. Growth factors such as NGF, BDNF, CNTF and bFGF are also discussed mainly in terms of the influence of Schwann cells on regenerating axons.

Interaction of astrochondrin with extracellular matrix components and its involvement in astrocyte process formation and cerebellar granule cell migration

We have recently characterized a chondroitin sulfate proteoglycan from the murine central nervous system which is expressed by astrocytes in vitro and carries the L2/HNK-1 and L5 carbohydrate structures. In the present study, we provide evidence that its three core proteins of different size are similar in their proteolytic peptide maps and thus designate this group of structurally related molecules astrochondrin. During development, astrochondrin and the L5 carbohydrate were hardly detectable in the brain of 14-d-old mouse embryos by Western blot analysis. Expression of astrochondrin and the L5 epitope was highest at postnatal day 8, the peak of cerebellar granule cell migration and Bergmann glial process formation, and decreased to weakly detectable levels in the adult. Immunocytochemical localization of astrochondrin in the cerebellar cortex of 6-d-old mice showed association of immunoreactivity with the cell surface of astrocytes, including Bergmann glial processes and astrocytes in the internal granular layer or prospective white matter. Endfeet of astrocytes contacting the basal lamina of endothelial and meningeal cells and contact sites between Bergmann glial processes and granule cells also showed detectable levels of astrochondrin. Furthermore, granule cell axons in the molecular layer were astrochondrin immunoreactive. In the adult, astrochondrin immunoreactivity was weakly present in the internal granular layer and white matter. Both Fab fragments of polyclonal antibodies to astrochondrin and monovalent fragments of the L5 monoclonal antibody reduced the formation of processes of mature GFAP-positive astrocytes on laminin and collagen type IV, but not on fibronectin as substrata. Interestingly, the initial attachment of astrocytic cell bodies was not disturbed by these antibodies. Antibodies to astrochondrin also reduced the migration of granule cells in the early postnatal mouse cerebellar cortex. In a solid phase radioligand binding assay, astrochondrin was shown to bind to the extracellular matrix components laminin and collagen type IV, being enhanced in the presence of Ca2+, but not to fibronectin, J1/tenascin or other neural recognition molecules. Furthermore, astrochondrin interacted with collagen types III and V, less strongly with collagen types I, II, and IX, but not with collagen type VI. The interaction of astrochondrin with collagen types III and V was saturable and susceptible to increasing ionic strength, and could be competed by chondroitin sulfate, heparin, and dextran sulfate, but not by hyaluronic acid, glucose-6-phosphate, or neuraminic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein kinase C (alpha, beta, gamma) in Pacinian corpuscle

Immunocytochemical demonstration of protein kinase C (PKC) subspecies (alpha, beta, gamma) was carried out in Pacinian corpuscles of rat hind feet using monoclonal or polyclonal antibodies against each of these subspecies. The inner core cells and lamellae and the Schwann cell cytoplasm of the nerve fiber innervating the corpuscle were strongly positive for PKC alpha-immunoreactivity (IR). In contrast, the axon terminal and the outer core did not display any positive alpha-IR. Very weak PKC beta-IR was detected in the ultraterminal region of the axon terminal, while the trunk region showed no immunoreactivity. Very faint PKC beta-IR was found also in the lamellar cells located at the periphery of the inner core and the endoneurial fibroblasts in the intermediate layer. PKC gamma-IR was not detected in any part of the corpuscle. The strong PKC alpha-IR in the inner core and the presence or absence of PKC alpha-, beta-, and gamma-IR in the axon terminal are discussed from the point of view of the functional aspects of each part.

Immunocytochemical localization of the L1 and N-CAM cell adhesion molecules and their shared carbohydrate epitope L2/HNK-1 in the developing and differentiated gustatory papillae of the mouse tongue

The localization of the cell adhesion molecules L1 and N-CAM, and their shared carbohydrate epitope L2/HNK-1, was investigated at the light and electron microscopic levels in developing and adult fungiform and circumvallate gustatory papillae of the mouse tongue. At embryonic day 13, the earliest stage investigated, the tongue epithelium was still undifferentiated and was not yet innervated by sensory fibres. At this stage none of the three molecules was detectable within the tongue epithelium. At embryonic day 15 the primordia of the gustatory papilla became unequivocally discernible when the papillary epithelium was already innervated by few sensory axons. At this stage N-CAM was the first molecule expressed on epithelial cells and was confined to those parts of the papillary epithelium destined to become the chemosensory cells of the taste buds. The sensory axons were N-CAM-, L1- and L2/HNK-1-positive when fasciculating or contacting their accompanying Schwann cells or the cells of the papillary epithelium. Contacts between Schwann cells were also prominently labelled by antibodies to the three antigens. The mesenchymal tissue underlying the prospective sensory epithelium expressed N-CAM at all embryonic stages, but ceased to be N-CAM positive within the first six postnatal days. From embryonic day 16 onward a weak L1 immunoreactivity was detectable within the basal and intermediate layers of the lingual epithelium and remained present in adulthood. Cytodifferentiation of epithelial cells into spindle-shaped sensory cells and organization into taste buds began at postnatal day two. Simultaneously, L1 and L2/HNK-1 immunoreactivity increased on taste bud cells and N-CAM disappeared from the non-sensory extragemmal parts of the papillary epithelium. At approximately postnatal day six, taste bud formation was complete and the pattern of cell adhesion molecule expression was comparable to that found in the adult in that L1 was strongly expressed on the apposing surfaces of all cells, whereas N-CAM was confined to cell contacts between a subpopulation of intragemmal cells. The L2/HNK-1 epitope was visible on the surfaces of taste bud cells, on intragemmal axons, and in a small portion of extracellular matrix directly underlying the taste buds, but was no longer expressed on those parts of the sensory fibres embedded in the subepithelial mesenchyme. The L2/HNK-1 epitope may thus be regarded as a cell surface marker for the cellular elements of mature taste buds. The highly sialylated form of N-CAM was not detectable at any stage investigated.(ABSTRACT TRUNCATED AT 400 WORDS)

Complex expression pattern of tenascin during innervation of the posterior limb buds of the developing chicken

The histological localization of the extracellular matrix glycoprotein tenascin was studied during the formation of peripheral nerves in the developing chick hindlimb (embryonic stages 21.5 to 30) by light and electron microscopic immunological methods to obtain insights into the molecule's functional role in the pathway formation by motor and sensory nerves. At stages 21.5 and 23, nerve roots and plexus were surrounded by high tenascin-immunoreactivity, whereas the not yet innervated limb bud was not immunoreactive. During innervation of the limb bud at stages 24.5 and 25, tenascin was detectable at the limb bud base and restricted in its expression to the proximal nerve regions. The nerve tips did not contact areas of elevated tenascin-immunoreactivity. At stages 26 to 28 the dorsal and ventral trunks of the crural and sciatic nerves were surrounded by tenascin-immunoreactivity, which was localized between Schwann and mesenchymal cells. The tips of the growing nerve had now reached the tenascin-positive interface between bone and muscle anlagen. This interface was contacted tangentially rather than penetrated by the nerve tips. The medial and lateral femoral cutaneous nerves were surrounded by high and weak tenascin-immunoreactivity, respectively. In both nerves, tenascin-immunoreactivity was absent where the nerves branched extensively to innervate the skin. The cutaneous nerves diverging from the sciatic nerve were of very low tenascin-immunoreactivity or tenascin-negative at all developmental stages tested. At stages 29 and 30, muscle nerves, having just entered the tenascin-negative muscles, exhibited strong immunoreactivity, whereas the more proximally situated trunks of the sciatic nerve were weakly and discontinuously labeled, particularly at sites where smaller nerves were branching off. Since the cutaneous branches of the sciatic nerve were always of low tenascin-immunoreactivity, the question was raised whether tenascin expression in the sciatic nerve depended on the presence of motor axons. Spinal cords of stage 19 or 20 embryos were therefore removed and tenascin expression was investigated at stages 26 and 27. Some of the residual nerves were weakly tenascin-immunoreactive, whereas others were tenascin-negative. Our observations suggest that tenascin is not involved in the initial guidance of peripheral nerves to their targets. Rather, neuron-induced tenascin appears to stabilize the proximal nerve trunks during a transient time period, possibly by preventing axons and Schwann cells from intermingling with the surrounding mesenchyme, thus contributing to nerve fiber compaction. Conversely, nerve branching may be elicited by reduced levels of tenascin. Furthermore, tenascin may divert growth cones from the developing bone tissue and direct muscle afferents to their appropriate targets.

Reinnervation of transplanted pacinian corpuscles by ventral root axons: ultrastructure of the regenerated nerve terminals

This study addresses two questions. Can mature, denervated and transplanted Pacinian corpuscles accept innervation from motor axons? If so, does the alien target influence the structural characteristics of the regenerated motor axon terminals? Pacinian corpuscles from the hind leg of young rats, together with a segment of the nerve branch through which they receive their sensory innervation, were autotransplanted to the surface of the spinal cord and the nerve stump anastomosed to the central stump of a transected lumbar ventral root. Between 4 and 5 months later the grafts were studied by electron microscopy. Ventral root axons regenerated through the endoneurial tubes of the grafted nerve to reach the corpuscles, most of which became reinnervated by one to three myelinated fibres. The fibres lost their myelin sheaths before entering the inner core, branched, and gave rise to multiple terminals in the inner core. The regenerated terminals were packed with spherical synaptic vesicles and closely resembled normal motor nerve terminals. Thus motor axons are able to reinnervate Pacinian corpuscles but the structural characteristics of the terminals are apparently not modified by the alien target tissue. This finding contrasts with previous studies, in which it was found that terminals of the central axons of large dorsal root ganglion cells, induced to reinnervate Pacinian corpuscles, displayed the structural characteristics of peripheral sensory endings rather than those of dorsal root terminals in the spinal cord.

Enhanced expression of the extracellular matrix molecule J1/tenascin in the regenerating adult mouse sciatic nerve

We have investigated the expression of J1/tenascin in the sciatic nerve of the adult mouse under normal and regenerating conditions by immunocytological and immunochemical methods. In the normal nerve, J1/tenascin expression was confined to the extracellular matrix at the node of Ranvier and in the perineurium. At 2 days after nerve transection, J1/tenascin was detectable in the fibroblast-containing caps of the distal and proximal nerve stumps, in the distal nerve stump along its entire length and in the distal end of the proximal nerve stump. In the nerve stumps immunoreactivity was predominantly associated with extracellular matrix consisting of collagen fibrils and Schwann cell basal laminae. Approximately 7 days after transection, the caps of the nerve stumps had usually grown together forming a bridge. This bridge consisted of a J1/tenascin-negative perineurium-like structure and an inner part of predominantly fibroblasts, endothelial cells and macrophages. All cell types in this inner part were embedded in a J1/tenascin-positive matrix of collagen fibrils indicating the prospective direction of growth of neural elements. A few days later, J1/tenascin in the bridge was confined to the extracellular matrix around small Schwann cell-containing nerve fascicles. In nerves chronically denervated for 19 days, J1/tenascin was poorly detectable in the cap of the distal stump, although Schwann cells had infiltrated this cap. Approximately 19 days after the lesion, J1/tenascin expression returned to control levels in the proximal nerve stump. In the distal nerve stump, J1/tenascin immunoreactivity reached a peak at approximately 14 days after nerve transection and vanished only at approximately 35 days, thus correlating with the time of active regrowth of axons into the distal nerve stump. This reduction was prevented by chronic denervation, suggesting that reinnervation of target structures may be related to the down-regulation of J1/tenascin. These combined observations suggest that J1/tenascin is differentially regulated in the individual parts of the regenerating nerve, possibly triggered by different cellular and molecular signals.