P-type calcium channels in rat central and peripheral neurons

The peptide toxin omega-Aga-IVA blocked P-type Ca2+ channel current in rat Purkinje neurons (KD approximately 2 nM) but had no effect on identified T-type, L-type, or N-type currents in a variety of central and peripheral neurons. omega-Aga-IVA blocked a substantial fraction of high threshold Ca2+ channel current in neurons from the hippocampal CA1 region (mean 26%), visual cortex (32%), spinal cord (45%), and dorsal root ganglia (23%), but less in hippocampal CA3 neurons (14%) and none in sympathetic neurons. In all cases, omega-Aga-IVA block could be reversed by a brief train of strong depolarizations. There was no overlap between current blocked by omega-Aga-IVA and the fractions blocked by dihydropyridines and omega-conotoxin GVIA, but not all current resistant to dihydropyridines and omega-conotoxin was blocked by omega-Aga-IVA. The results suggest that omega-Aga-IVA is highly selective for P-type channels and that many central neurons and some peripheral neurons possess substantial P-type current.

GAP43, MARCKS, and CAP23 modulate PI(4,5)P(2) at plasmalemmal rafts, and regulate cell cortex actin dynamics through a common mechanism

The dynamic properties of the cell cortex and its actin cytoskeleton determine important aspects of cell behavior and are a major target of cell regulation. GAP43, myristoylated alanine-rich C kinase substrate (MARCKS), and CAP23 (GMC) are locally abundant, plasmalemma-associated PKC substrates that affect actin cytoskeleton. Their expression correlates with morphogenic processes and cell motility, but their role in cortex regulation has been difficult to define mechanistically. We now show that the three proteins accumulate at rafts, where they codistribute with PI(4,5)P(2), and promote its retention and clustering. Binding and modulation of PI(4, 5)P(2) depended on the basic effector domain (ED) of these proteins, and constructs lacking the ED functioned as dominant inhibitors of plasmalemmal PI(4,5)P(2) modulation. In the neuron-like cell line, PC12, NGF- and substrate-induced peripheral actin structures, and neurite outgrowth were greatly augmented by any of the three proteins, and suppressed by DeltaED mutants. Agents that globally mask PI(4,5)P(2) mimicked the effects of GMC on peripheral actin recruitment and cell spreading, but interfered with polarization and process formation. Dominant negative GAP43(DeltaED) also interfered with peripheral nerve regeneration, stimulus-induced nerve sprouting and control of anatomical plasticity at the neuromuscular junction of transgenic mice. These results suggest that GMC are functionally and mechanistically related PI(4,5)P(2) modulating proteins, upstream of actin and cell cortex dynamics regulation.

NeuN: a useful neuronal marker for diagnostic histopathology

The monoclonal antibody A60 specifically recognizes the DNA-binding, neuron-specific protein NeuN, which is present in most neuronal cell types of vertebrates. In this study we demonstrate the potential use of NeuN as a diagnostic neuronal marker using a wide range of formalin-fixed, paraffin-embedded human surgical and autopsy specimens from the central and peripheral nervous system. After microwave antigen retrieval, almost all neuronal populations revealed strong immunoreactivity for NeuN in nuclei, perikarya, and some proximal neuronal processes, whereas more distal axon cylinders and dendritic ramifications were not stained. The stain greatly enhanced the gray matter architecture. NeuN immunoreactivity was not detected in Purkinje cells, most neurons of the internal nuclear layer of the retina, and in sympathetic chain ganglia. We examined nine gangliogliomas and 14 dysembryoplastic neuroepithelial tumors, one ganglioneuroma, and one dysplastic cerebellar gangliocytoma. The neuronal component of all of these lesions showed marked immunoreactivity for NeuN. In addition, NeuN immunoreactivity was focally seen in one of seven medulloblastomas with prominent neuronal differentiation. There was no staining of non-neuronal structures. The results indicate that NeuN immunoreactivity is a sensitive and specific neuronal marker in formalin-fixed, paraffin-embedded tissues, and may be useful in diagnostic histopathology.

Wallerian degeneration in the peripheral nervous system: participation of both Schwann cells and macrophages in myelin degradation

This study examined the role of Schwann cells and hematogenous macrophages in myelin degradation and Ia antigen expression during Wallerian degeneration of rodent sciatic nerve. To identify and distinguish between macrophages and Schwann cells we used, in addition to electron microscopy, immunocytochemical staining of teased nerve fibres and 1 microns thick cryosections. Before the appearance of adherent macrophages the myelin sheath fragmented into ovoids, small whorls of myelin debris appeared within Schwann cell cytoplasm and the Schwann cell displayed numerous lipid droplets. However, at least in large fibres most myelin degradation and removal was accomplished or assisted by macrophages, identified by their expression of the ED1 marker. These cells began entering the nerve from blood vessels by day 2, migrated to degenerating nerve fibres and adhered to nerve fibres in the regions of the ovoids. There they penetrated the Schwann cell basal lamina to occupy an intratubal position and phagocytose myelin. During Wallerian degeneration a subpopulation of ED1-positive monocytes/macrophages expressed Ia antigen; Schwann cells were Ia-negative. Ia expression by monocytes/macrophages appeared to be a transient event and was not seen in post-phagocytic macrophages, as indicated by the fact that ED1-positive phagocytes with large vacuoles were Ia-negative. Our data show that both Schwann cells and macrophages play important roles in degrading and removing myelin during Wallerian degeneration. The expression of Ia antigen during Wallerian degeneration indicates that Ia expression need not necessarily reflect specific immune events but in some instances can represent a nonspecific response to PNS damage.

Spatial-temporal progress of peripheral nerve regeneration within a silicone chamber: parameters for a bioassay

The spatial-temporal progress of peripheral nerve regeneration across a 10-mm gap within a silicone chamber was examined with the light and electron microscope at 2-mm intervals. A coaxial, fibrin matrix was observed at 1 week with a proximal-distal narrowing that extended beyond the midpoint of the chamber. At 2 weeks, Schwann cells, fibroblasts, and endothelial cells had migrated into the matrix from both nerve stumps. There was a delay of 7-14 days after nerve transection and chamber implantation before regenerating axons appeared in the chamber. At 2 weeks, nonmyelinated axons were seen only in the proximal 1-5 mm of the chamber in association with Schwann cells. Axons reached the distal stump by 3 weeks and a proximal-distal gradient of myelination was observed. These observations define the parameters of a morphologic assay for regeneration in this chamber model which can be used to investigate cellular and molecular mechanisms underlying the success of peripheral nerve regeneration.

Compact myelin dictates the differential targeting of two sodium channel isoforms in the same axon

Voltage-dependent sodium channels are uniformly distributed along unmyelinated axons, but are highly concentrated at nodes of Ranvier in myelinated axons. Here, we show that this pattern is associated with differential localization of distinct sodium channel alpha subunits to the unmyelinated and myelinated zones of the same retinal ganglion cell axons. In adult axons, Na(v)1.2 is localized to the unmyelinated zone, whereas Na(v)1.6 is specifically targeted to nodes. During development, Na(v)1.2 is expressed first and becomes clustered at immature nodes of Ranvier, but as myelination proceeds, Na(v)1.6 replaces Na(v)1.2 at nodes. In Shiverer mice, which lack compact myelin, Na(v)1.2 is found throughout adult axons, whereas little Na(v)1.6 is detected. Together, these data show that sodium channel isoforms are differentially targeted to distinct domains of the same axon in a process associated with formation of compact myelin.

The mutant mdx: inherited myopathy in the mouse. Morphological studies of nerves, muscles and end-plates

The mdx mutant mouse was first observed during a survey of genetic variations of pyruvate kinase in the mouse. Affected mice have high serum levels of this enzyme and although showing little disability they have widespread and severe muscle disease. Light and electron microscopy, muscle enzyme histochemistry and combined cholinesterase-silver impregnations were used for the study of affected and control animals aged 1 day to 1 year. An early ultrastructural abnormality present already at 1 day was scattered focal streaming of Z-lines. Later there was also segmental muscle fibre necrosis and regeneration. The proportion of muscle fibres showing either necrosis, regeneration or internal nuclei was assessed in several muscles, at ages ranging from 10 days to 1 year. Acute segmental necrosis and regeneration were most marked at 1 to 2 months, although they were present at all ages. The number of fibres with internal nuclei increased progressively until 3 months when 70-80% showed this abnormality. Nerve terminals were unaffected but there was a reduction in the number and depth of postsynaptic folds at motor end-plates in adult animals, confirmed by morphometric analysis. Quantitative study of L4 motor root and tibial nerve showed that fibre numbers, axonal calibres and myelin sheath thickness were normal at all ages. No qualitative abnormalities were found in the CNS or other organs. The findings strongly suggest that the mdx mutant has a primary muscle disease and that the nervous system is normal.

Mice deficient for the myelin-associated glycoprotein show subtle abnormalities in myelin

Using homologous recombination in embryonic stem cells, we have generated mice with a null mutation in the gene encoding the myelin-associated glycoprotein (MAG), a recognition molecule implicated in myelin formation. MAG-deficient mice appeared normal in motor coordination and spatial learning tasks. Normal myelin structure and nerve conduction in the PNS, with N-CAM overexpression at sites normally expressing MAG, suggested compensatory mechanisms. In the CNS, the onset of myelination was delayed, and subtle morphological abnormalities were detected in that the content of oligodendrocyte cytoplasm at the inner aspect of most myelin sheaths was reduced and that some axons were surrounded by two or more myelin sheaths. These observations suggest that MAG participates in the formation of the periaxonal cytoplasmic collar of oligodendrocytes and in the recognition between oligodendrocyte processes and axons.

Chronic relapsing polyneuritis

Clinical, electrophysiological and pathological findings in 23 patients with subacute and relapsing idiopathic demyelinating polyneuropathies are described. In 17 patients with relapsing polyneuropathy, the neurological illness was unaccompanied by any systemic disturbances. The term preferred for the neuropathy in this group of patients is chronic relapsing polyneuritis. The findings in this group suggest that the common form of this syndrome is due to a single disease entity. Chronic relapsing polyneuritis differs from acute idiopathic polyneuritis chiefly in regard to the rate of evolution and the severity of the initial episode of polyneuropathy. If these two polyneuropathies have the same pathogenesis, the factor which determines whether the disease is acute and self-limiting or chronically relapsing is often present at the time of onset of the disease. The relationship of chronic relapsing polyneuritis to relapsing hypertrophic polyneuropathy and progressive hypertrophic polyneuropathy is also discussed and it is concluded that these diseases may constitute a spectrum of pathogenetically related disorders. In chronic relapsing polyneuritis, as in other demyelinating polyneuropathies, a marked segmental reduction in axon diameter accompanies demyelination. This corresponds to a more than 50% reduction in the volume of the affected region of the axon and it is associated with increased packing of axoplasmic organelles and wrinkling of the axolemma. It is suggested that in the normal myelinated nerve fibre, the Schwann cell and myelin sheath maintain fluid locally within the axon.

Macrophage dependence of peripheral sensory nerve regeneration: possible involvement of nerve growth factor

The levels of NGF and NGF receptor mRNA, the degree of macrophage recruitment, and the ability of sensory and motor axons to regenerate were measured in C57BL/Ola mice, in which Wallerian degeneration following a nerve lesion is very slow. Results were compared with those from C57BL/6J and BALB/c mice, in which degeneration is normal. We found that in C57BL/Ola mice, apart from the actual lesion site, recruitment of macrophages was much lower, levels of mRNA for both NGF and its receptor were raised only slightly above normal, and sensory axon regeneration was much impaired. Motor axons regenerated quite well. These results provide in vivo evidence that macrophage recruitment is an important component of NGF synthesis and of sensory (but not motor) axon maintenance and regrowth.

Schwann cell-derived Desert hedgehog controls the development of peripheral nerve sheaths

We show that Schwann cell-derived Desert hedgehog (Dhh) signals the formation of the connective tissue sheath around peripheral nerves. mRNAs for dhh and its receptor patched (ptc) are expressed in Schwann cells and perineural mesenchyme, respectively. In dhh-/- mice, epineurial collagen is reduced, while the perineurium is thin and disorganized, has patchy basal lamina, and fails to express connexin 43. Perineurial tight junctions are abnormal and allow the passage of proteins and neutrophils. In nerve fibroblasts, Dhh upregulates ptc and hedgehog-interacting protein (hip). These experiments reveal a novel developmental signaling pathway between glia and mesenchymal connective tissue and demonstrate its molecular identity in peripheral nerve. They also show that Schwann cell-derived signals can act as important regulators of nerve development.

Delayed macrophage responses and myelin clearance during Wallerian degeneration in the central nervous system: the dorsal radiculotomy model

All aspects of Wallerian degeneration (WD)--axonal breakdown, glial and macrophage responses, and clearance of myelin debris--have generally been considered to occur more slowly in the central nervous system (CNS) than in the peripheral nervous system (PNS). We reevaluated this issue by comparing the temporal pattern of Wallerian degeneration in nerve fibers with segments extending through both the PNS and the CNS. The L4, L5, and L6 dorsal roots in the rat were transected, and WD in the dorsal roots and the dorsal columns was compared at intervals up to 8 months, using electron microscopy and immunostaining to identify and characterize the different cell types. The initial breakdown of axoplasm was complete by 72 h both in the PNS and in the CNS portions of these axons. All other aspects of WD were strikingly delayed in the CNS when compared to those in the PNS. Macrophages (from the circulation) increased in number (Days 2-4 after axotomy) in the root. In contrast, although there was an early and transient period (peaking at Day 3) of microglial activation in the degenerating dorsal column, the appearance of round macrophages was delayed until Days 18-21. Both axonal debris and myelin debris were almost completely cleared by 30 days in the PNS, but remained over 90 days in the CNS. Axonal regeneration was vigorous in the dorsal root but these sprouts did not invade the dorsal columns. The dorsal root entry zone provided a sharp anatomic demarcation between the PNS and CNS patterns of Wallerian degeneration. These results suggest that circulating macrophages have ready access to degenerating peripheral nerves, but are largely or completely excluded from degenerating CNS tracts, so that the macrophages (that ultimately appear) originate primarily from the stellate microglia.

The extracellular matrix of the central and peripheral nervous systems: structure and function

The extracellular matrix (ECM) is the naturally occurring substrate upon which cells migrate, proliferate, and differentiate. The ECM functions as a biological adhesive that maintains the normal cytoarchitecture of different tissues and defines the key spatial relationships among dissimilar cell types. A loss of coordination and an alteration in the interactions between mesenchymal cells and epithelial cells separated by an ECM are thought to be fundamental steps in the development and progression of cancer. Although a substantial body of knowledge has been accumulated concerning the role of the ECM in most other tissues, much less is known of the structure and function of the ECM in the nervous system. Recent experiments in mammalian systems have shown that an increased knowledge of the ECM in the nervous system can lead to a better understanding of complex neurobiological processes under developmental, normal, and pathological conditions. This review focuses on the structure and function of the ECM in the peripheral and central nervous systems and on the importance of ECM macromolecules in axonal regeneration, cerebral edema, and cerebral neoplasia.

Ultrastructural studies of the dying-back process. III. The evolution of experimental peripheral giant axonal degeneration

The spatio-temporal evolution of peripheral giant axonal degeneration has been studied in rats during the development of concurrent peripheral (PNS) and central (CNS) nervous system dying-back disease after chronic intoxication with the neurotoxic hexacarbons n-hexane (CH3CH2CH2CH2CH2CH3), methyl n-butyl ketone (MBK) (CH3COCH2CH2CH2CH3), or 2,5-hexanedione (CH3COCH2CH2CHOCH3), a neurotoxic metabolite of MBK. Each compound caused animals insidiously to develop identical, symmetrical peripheral neuropathies characterized by eversion and drop of hindfeet, inability to extend hindlimbs and upper extremity weakness. Teased fiber studies demonstrated that giant axonal swellings first developed on the proximal sides of multiple paranodes sited in distal, non-terminal regions of large myelinated fibers. Later, swellings developed at internodal sites. Smaller myelinated and unmyelinated fibers also underwent multifocal, giant axonal swelling. In affected myelinated fibers, swollen nodal and paranodal axons were frequently associated with retracted paranodal myelin sheaths. Adjacent distal internodes were attenuated and corrugated. Demyelinated paranodes apparently underwent local shrinkage and remyelination before complete distal fiber breakdown commenced. The proximal limits of chains of homogeneous myelin ovoids were interfaced with proximal, preserved regions at sites of giant axonal swellings. Regeneration of myelinated axons also occurred during intoxication. Regenerating fibers wre composed of multiple, short, branched internodes which sometimes appeared multifocally swollen. Interfaces between regenerating and preserved portions of fibers were unswollen. Thick section studies showed that pronounced endoneurial edema accompanied fiber degeneration in peripheral nerve trunks. Ultrastructural studies revealed multifocal, giant axonal swellings containing masses of 10 nm neurofilaments and sometimes, clustered mitochondria, neurotubules and smooth endoplasmic reticulum. Enlarged granular mitochondria, interdigitated Schwann cell/axon networks and corrugated myelin sheaths were common findings. Dense granules, vesicles and hexagonal particles were also noted in the axoplasm. These findings provide new insights into the nature of the dying-back process: although there was a retrograde, temporal spread of axonal swelling up affected nerve trunks, axonal degeneration neither began in the nerve terminal nor spread seriatim centripetally along individual nerve fibers. The dying-back process was further examined in a companion study in this issue (32) which analyzed some of the factors determining the differential vulnerability of PNS and CNS fibers in animals intoxicated either with these neurotoxic hexacarbons or with acrylamide.

Absence of the major dense line in myelin of the mutant mouse "shiverer"

The myelin of the central nervous system (CNS) of the mutant mouse Shiverer is characterized by the absence of the major dense line (MDL). The intraperiod line, as seen in conventional electron micrographs and in freeze-fractured replicas, appears normal. Peripheral myelin, as seen in ventral and dorsal roots of spinal cord, is unaffected by the mutation. During the period of active myelination, the cytoplasm of most oligodendrocytes (ODs) is packed with electron-lucent vacuoles in continuity with the Golgi apparatus and with bundles of microtubules. It is concluded that a metabolic pathway possibly involving the Golgi apparatus, and contributing to the formation of the MDL is selectively affected in this mutant.

A new approach for cryofixation by high-pressure freezing

A newly designed high-pressure freezing machine for cryofixation was established and tested (Leica EMPACT), based on ideas originally proposed by Moor & Riehle in 1968. The new machine, essentially an improved version of our prototype, pressurizes the sample to 2000 bar in a small container (using methylcyclohexane as hydraulic fluid) and at the same time cools the outer surface of the container with a jet of liquid nitrogen. The advantage of this approach is that the machine uses little liquid nitrogen and can be built small and light. The machine is able to vitrify and freeze well a variety of specimens, for example, plant leaves, yeast cells, liver or nerve tissue (more samples are shown at: http://www.ana.unibe.ch/empact). Cooling efficiency is the same as in the traditional machines that use liquid nitrogen to pressurize and simultaneously cool the sample.

Ultrastructural studies of the dying-back process. IV. Differential vulnerability of PNS and CNS fibers in experimental central-peripheral distal axonopathies

A companion paper in this issue (46) described the evolution of peripheral nervous system dying-back disease of the giant axonal type in animals chronically intoxicated with the neurotoxic hexacarbons n-hexane (CH3CH2CH2CH2CH2CH3), methyl n-butyl ketone or MBK (CH3COCH2CH2CH2CH3), and 2,5-hexanedione (CH3COCH2CH2COCH3). The present study compares the distribution and pattern of peripheral (PNS) and central nervous system (CNS) dying-back disease produced by these three neurotoxic hexacarbons with that produced by acrylamide (CH2CHCONH2), and, in addition, employs these compounds to address unresolved issues in the dying-back process. In the PNS, large myelinated fibers in tibial nerve branches supplying calf muscles were especially sensitive in rats intoxicated with hexacarbons. These nerve branches and sensory plantar nerves in the hindfeet were equally vulnerable in acrylamide-treated rats. In both conditions, fibers located at these sites commenced degeneration before the distal regions of much longer and smaller diameter nerve fibers in nerve branches supplying the flexor digitorum brevis muscle and, in rats intoxicated with hexacarbons, before equivalent regions of plantar sensory branches to the digits. Pacinian corpuscles sited in the hindfeet of intoxicated cats were much less vulnerable to MBK than to acrylamide. Rats and cats intoxicated with hexacarbons displayed giant axonal swellings in vulnerable regions of the PNS degeneration in these animals was accompanied by pronounced endoneurial edema. In the CNS, rostral regions of long, ascending tracts (dorso-spino-cerebellar, gracile and, later, the cuneate) and the caudal end of long, descending tracts (lateral colums, ventrolateral and ventromedial tracts) of hexacarbon-treated animals were especially vulnerable. After prolonged intoxication of cats with MBK, giant axonal swelling was also found in preterminal and terminal axons in Rexed laminae V-VII at spinal levels C4 through S3-Neurofilament proliferation without giant axonal swelling was seen in CNS fibers of rats intoxicated with acrylamide. Taken in concert, the findings underline the importance of axon diameter and length in determining the hierarchy of fiber vulnerability and indicate the common sensitivity of selected regions of the PNS and CNS. The term central-peripheral distal axonopathy is introduced to emphasize the widespread, distal distribution of disease in these and in similar experimental conditions. It is suggested that certain human neuropathies (toxic, nutritional, uremic, diabetic and some hereditary polyneuropathies, and the neuropathy associated with multiple myeloma) are additional examples of central-peripheral distal axonopathies.

Unique role of dystroglycan in peripheral nerve myelination, nodal structure, and sodium channel stabilization

Dystroglycan is a central component of the dystrophin-glycoprotein complex implicated in the pathogenesis of several neuromuscular diseases. Although dystroglycan is expressed by Schwann cells, its normal peripheral nerve functions are unknown. Here we show that selective deletion of Schwann cell dystroglycan results in slowed nerve conduction and nodal changes including reduced sodium channel density and disorganized microvilli. Additional features of mutant mice include deficits in rotorod performance, aberrant pain responses, and abnormal myelin sheath folding. These data indicate that dystroglycan is crucial for both myelination and nodal architecture. Dystroglycan may be required for the normal maintenance of voltage-gated sodium channels at nodes of Ranvier, possibly by mediating trans interactions between Schwann cell microvilli and the nodal axolemma.

Regeneration in cellular and acellular autografts in the peripheral nervous system

The regeneration that occurs in cellular autografts of sciatic nerve has been compared with that seen in acellular models prepared either by cycles of alternating freezing and thawing, or by detergent-extraction. The responses to either fresh or pre-degenerate grafts (cellular and acellular) have been examined electron microscopically. It was found that whereas neurites grew into a fresh autograft and rapidly re-established functional relationships with vital Schwann cells lying in bands of Büngner within the graft, penetration of acellular grafts was less efficient. Many basal lamina tubes in the acellular grafts remained either empty or filled with debris-laden macrophages for the first 2 weeks after suture, although subsequently reinnervation did occur. The roles of Schwann cells, macrophages and basal laminae during reinnervation are discussed.

Preparation of antisera to neurofilament protein from chicken brain and human sciatic nerve

Antigens isolated by hydroxyapatite chromatography from human sciatic nerve (SN1 protein) and from 8 M urea extracts of chicken brain were selectively localized by immunofluorescence to neurofibrils in rat and chicken CNS. Absorption of the antisera with SN1 protein, chicken antigen or GFA protein abolished the staining. Antisera raised against antigen isolated with the same procedure from buffer extracts of chicken brain stained both neurofibrils and glial fibrils by immunofluorescence. Neurofibrillary staining was selectively abolished by absorption of the antisera with SN1 protein. Antisera prepared against axonal preparations isolated from bovine white matter only stained astroglia and were thus undistinguishable from anti-GFA sera in this respect. The data suggested that the protein subunits of neurofilament and glial filaments, although difficult to separate in brain extracts by standard biochemical procedures and by subcellular fractionation in bovine white matter, still retain immunological specificity. In addition, the immunological cross reactivity between human and chicken antigens suggested that neurofilaments, as other constituents of the cytoskeleton such as microtubules and actin microfilaments, show a high degree of evolutionary stability.

Neurofilament proteins of rat peripheral nerve and spinal cord

Intact neurofilaments were isolated in parallel from rat peripheral nerve and spinal cord by osmotic shock into hypotonic media containing divalent cation chelators. Isolated neurofilaments were washed and separated by multiple centrifugations in 0.1 M NaCl. Abundant intact neurofilaments were identified in the washed pellets by negative staining techniques. Their origin from neurofilaments was confirmed by immune electron microscopy. Washed neurofilaments were extracted from lipid and membranous components with 8 M urea. Analyses of neurofilament isolates on sodium dodecyl sulfate gels showed that proteins of 200,000, 150,000, and 69,000 mol wt were the major components of intact neurofilaments derived from rat peripheral and central nervous systems. These same proteins were identified in whole tissue homogenates of both sources and became enriched during the isolation of intact neurofilaments. A minor component of 64,000 mol wt arose during isolation. Other proteins were identified as contaminants. Small amounts of proteins with electrophoretic migration of tubulin and actin remain in neurofilament isolates.

The effect of inhibiting Schwann cell mitosis on the re-innervation of acellular autografts in the peripheral nervous system of the mouse

Reactive gliosis in the zone immediately proximal to transection of the sciatic nerve has been inhibited by intraneural injection of mitomycin C, an anti-mitotic agent known to arrest Schwann cell division after transection, crush or demyelination. Mitomycin C-pretreated proximal stumps were subsequently sutured to cellular or acellular autografts (0.5 cm long) and neurite growth into and within the grafts was examined during a 5-week post-operative period. Neurites grew into cellular autografts and became associated with the resident population of Schwann cells within the grafts, to the extent that remyelination was well established in the majority of Schwann cell basal lamina tubes by week 5 post-suture. In marked contrast, very few neurites grew into acellular grafts during this time, and where axons and Schwann cells were seen they tended to be grouped in 'minifascicles'. The results suggest that neurite outgrowth from proximal stumps is dependent upon active Schwann cell participation.

Central projections of the sciatic, saphenous, median, and ulnar nerves of the rat demonstrated by transganglionic transport of choleragenoid-HRP (B-HRP) and wheat germ agglutinin-HRP (WGA-HRP)

The central projections of the rat sciatic, saphenous, median, and ulnar nerves were labeled by injecting each nerve with 0.05 mg B-HRP, or 0.5 mg WGA-HRP, or a mixture of both. The B-HRP labeled large dorsal root ganglion cells (30-50 microns) and, correspondingly, 98% of axons labeled in a rootlet were meyelinated; although all sizes of myelinated axons were labeled, a greater proportion fell in the large ranges (2-6.5 microns axon diameter) than in the small ranges (0.5-2 microns). Primary afferents labeled with B-HRP were distributed in laminae I, III, IV, and V of the dorsal horn and extended into the intermediate grey and the ventral horn; Clarke's column and the respective dorsal column nuclei were also densely labeled. Motoneurons of the nerve were densely labeled by B-HRP, including extensive regions of their dendritic trees. In contrast, WGA-HRP labeled small dorsal root ganglion cells (15-25 microns) and in the dorsal rootlets, 84% of the labeled axons were nonmyelinated; the small population of labeled myelinated afferents mainly fell within the smaller ranges (0.5-2.0 microns). Terminal fields of WGA-HRP labeled afferents were restricted to the superficial dorsal horn (laminae I-III), and to limited regions in the dorsal column nuclei. Sciatic nerve projections traced by labeling with B-HRP alone or in combination with WGA-HRP were more extensive than previously described when using either native HRP or WGA-HRP. Afferents to the dorsal horn extended from L1-S1, to Clarke's nucleus from T8-L1, to the ventral horn from L2-L5, and extended throughout the medial and dorsal region of the gracilie nucleus. Motoneurons were found from L4-L6. Using the same tracers, saphenous projections extended in the superficial dorsal horn from caudal L1 to rostral L4, in the deep dorsal horn to mid L4 and along the length of the central part of the gracilie nucleus. The median nerve projected to the internal basilar nucleus from C1-C6, the dorsal horn from C3-T2, Clarke's nucleus from T1-T6, the external cuneate nucleus, and a large central area throughout the length of the cuneate nucleus. Motoneurons were located in dorsolateral and ventrolateral nuclear groups from C4 through C8. The ulnar nerve projections were less extensive but also included the internal basilar nucleus from C1-C6, the medial region of the dorsal horn from C4-T1, Clarke's nucleus from T1-T6, the external cuneate nucleus, and the medial part of the cuneate nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Postnatally induced inactivation of gp130 in mice results in neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects

The pleiotrophic but overlapping functions of the cytokine family that includes interleukin (IL)-6, IL-11, leukemia inhibitory factor, oncostatin M, ciliary neurotrophic factor, and cardiotrophin 1 are mediated by the cytokine receptor subunit gp130 as the common signal transducer. Although mice lacking individual members of this family display only mild phenotypes, animals lacking gp130 are not viable. To assess the collective role of this cytokine family, we inducibly inactivated gp130 via Cre-loxP-mediated recombination in vivo. Such conditional mutant mice exhibited neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects, demonstrating the widespread importance of gp130-dependent cytokines.