Light and electron microscopic localization of B-50 (GAP43) in the rat spinal cord during transganglionic degenerative atrophy and regeneration

Mild Fluid Percussion Injury Induces Diffuse Axonal Damage and Reactive Synaptic Plasticity in the Mouse Olfactory Bulb

Despite the regenerative capacity of the olfactory bulb (OB), head trauma causes olfactory disturbances in up to 30% of patients. While models of olfactory nerve transection, olfactory receptor neuron (ORN) ablation, or direct OB impact have been used to examine OB recovery, these models are severe and not ideal for study of OB synaptic repair. We posited that a mild fluid percussion brain injury (mFPI), delivered over mid-dorsal cortex, would produce diffuse OB deafferentation without confounding pathology. Wild type FVB/NJ mice were subjected to mFPI and OB probed for ORN axon degeneration and onset of reactive synaptogenesis. OB extracts revealed 3 d postinjury elevation of calpain-cleaved 150-kDa αII-spectrin, an indicator of axon damage, in tandem with reduced olfactory marker protein (OMP), a protein specific to intact ORN axons. Moreover, mFPI also produced a 3-d peak in GFAP+ astrocyte and IBA1+ microglial reactivity, consistent with postinjury inflammation. OB glomeruli showed disorganized ORN axons, presynaptic degeneration, and glial phagocytosis at 3 and 7 d postinjury, all indicative of deafferentation. At 21 d after mFPI, normal synaptic structure re-emerged along with OMP recovery, supporting ORN afferent reinnervation. Robust 21 d postinjury upregulation of GAP-43 was consistent with the time course of ORN axon sprouting and synapse regeneration reported after more severe olfactory insult. Together, these findings define a cycle of synaptic degeneration and recovery at a site remote to non-contusive brain injury. We show that mFPI models diffuse ORN axon damage, useful for the study of time-dependent reactive synaptogenesis in the deafferented OB.

Time course and spatial profile of Nogo-A expression in experimental autoimmune encephalomyelitis in C57BL/6 mice

Inhibition of the myelin-associated neurite outgrowth inhibitor Nogo-A has been found to be beneficial in experimental autoimmune encephalomyelitis (EAE), but there are little data on its expression dynamics during the disease course. We analyzed Nogo-A mRNA and protein during the course of EAE in 27 C57BL/6 mice and in 8 controls. Histopathologic and molecular analyses were performed on Day 0 (naive), preclinical (Day 10), acute (Days 18-22) and chronic (Day 50) time points. In situ hybridization and real-time polymerase chain reaction analyses revealed reduced Nogo-A mRNA expression at preclinical (p < 0.0001) and acute phases (p < 0.0001), followed by upregulation during the chronic phase (p < 0.0001). Nogo-A mRNA was expressed in neurons and oligodendrocytes. By immunohistochemistry and Western blot, there was increased Nogo-A protein expression (p < 0.001) in the chronic phase. Moreover, spatial differences were observed within EAE lesions. The pattern of Nogo-A protein expression inversely correlated with axonal regeneration growth-associated protein 43-positive axons (60% of which were Nogo-A contact-free during the acute phase) and axonal injury (β-amyloid precursor protein-positive axons). Cortical Nogo-66 receptor protein and mRNA levels increased during the chronic phase. The results indicate that Nogo-A and Nogo receptor are actively regulated in EAE lesions; this may indicate a specific time window for localized axonal regeneration in the acute phase of EAE.

Reconnecting neuronal networks in the auditory brainstem following unilateral deafening

When we disturbed the auditory input of the adult rat by cochleotomy or noise trauma on one side, several substantial anatomical, cellular, and molecular changes took place in the auditory brainstem. We found that: (1) cochleotomy or severe noise trauma both lead to a considerable increase of immunoreactivity of the growth-associated protein GAP-43 in the ventral cochlear nucleus (VCN) of the affected side; (2) the expression of GAP-43 in VCN is restricted to presynaptic endings and short fiber segments; (3) axon collaterals of the cholinergic medial olivocochlear (MOC) neurons are the path along which GAP-43 reaches VCN; (4) partial cochlear lesions induce the emergence of GAP-43 positive presynaptic endings only in regions tonotopically corresponding to the extent of the lesion; (5) judging from the presence of immature fibers and growth cones in VCN on the deafened side, at least part of the GAP-43 positive presynaptic endings appear to be newly formed neuronal contacts following axonal sprouting while others may be modified pre-existing contacts; and (6) GAP-43 positive synapses are formed only on specific postsynaptic profiles, i.e., glutamatergic, glycinergic and calretinin containing cell bodies, but not GABAergic cell bodies. We conclude that unilateral deafening, be it partial or total, induces complex patterns of reconnecting neurons in the adult auditory brainstem, and we evaluate the possibility that the deafness-induced chain of events is optimized to remedy the loss of a bilaterally balanced activity in the auditory brainstem.

Association of extracellular acetylcholinesterase with gustatory nerve terminal fibers in the nucleus of the solitary tract

Acetylcholinesterase (AChE) staining is associated with terminal fields of the glossopharyngeal and chorda tympani nerves in the nucleus of the solitary tract (NST). To address AChE function at these sites, the location of the staining was examined at the fine structural level in combination with the labeling of chorda tympani nerve fibers with biotinylated dextran in golden Syrian hamsters. AChE staining was located in the endoplasmic reticulum of geniculate ganglion neuronal somata, and extracellularly, surrounding labeled chorda tympani terminal fibers and boutons in the NST. Neuronal profiles adjacent to these labeled fibers were stained less intensely, whereas most non-adjacent profiles were unstained. The location of staining is consistent with the secretion of AChE into the extracellular space by primary afferent chorda tympani fibers. AChE staining was reduced in the dextran-labeled chorda tympani fibers and terminals as well as adjacent non-labeled profiles 2 weeks following nerve transection and dextran application. The distribution of staining outside synapses and the loss of staining following denervation is suggestive of a non-cholinergic role for AChE in the intact gustatory system.

Resection of sciatic nerve re-triggers central sprouting of A-fibre primary afferents in the rat

We have investigated whether nerve injury or target deprivation is responsible for the injury induced central sprouting of A-fibres. Cholera toxin B subunit conjugated horseradish peroxidase was used to trace the termination of A-fibre primary afferents. Transection of the sciatic nerve induces central sprouting of sciatic myelinated A-fibre primary afferents into the spinal dorsal horn lamina II, which normally is the termination site of unmyelinated C-fibre primary afferents. The sprouting A-fibre terminals withdrew from lamina II after six to eight months. A second cut to the previously sectioned and ligated sciatic nerve re-triggered the central sprouting of A-fibre primary afferents into the spinal dorsal horn lamina II, suggesting that nerve injury per se rather than the deprivation of target tissues is the cause of central sprouting of A-fibre primary afferents.

Increased expression of growth-associated protein (GAP-43) in lower urinary tract pathways following cyclophosphamide (CYP)-induced cystitis

Alterations in the expression of growth-associated protein 43 (GAP-43) were examined in lower urinary tract micturition reflex pathways in a chronic model of cyclophosphamide (CYP)-induced cystitis. In control animals, expression of GAP-43 was present in specific regions of the gray matter in the rostral lumbar and caudal lumbosacral spinal cord, including: (1) the dorsal commissure; (2) the dorsal horn and (3) the regions of the intermediolateral cell column (L1-L2) and the sacral parasympathetic nucleus (L6-S1) and (4) in the lateral collateral pathway of Lissauer in L6-S1 spinal segments. Densitometry analysis has demonstrated significant increases (p</=0.001; 1.5-4.0-fold increase) in GAP-43-immunoreactivity (IR) in these regions of the rostral lumbar (L1-L2) and caudal lumbosacral (L6-S1) spinal cord following CYP-induced urinary bladder inflammation. Changes in GAP-43-IR were restricted to those segmental levels examined (L1-L2 and L6-S1) that are involved in lower urinary tract reflexes. Changes in GAP-43-IR were not observed at the L5 segmental level. In contrast to significant increases in GAP-43-IR in specific regions of the rostral lumbar and caudal lumbosacral spinal cord, no changes in GAP-43-IR were observed in the L1, L2 or L6, S1 dorsal root ganglia (DRG). In control animals, virtually all retrogradely labeled (Fast Blue) bladder afferent cells in the L1, L2 and L6, S1 DRG expressed GAP-43-IR. This percentage (approximately 100%) of bladder afferent cells expressing GAP-43-IR was unchanged following CYP-induced urinary bladder inflammation. Alterations in GAP-43-IR following chronic cystitis may suggest a reorganization of bladder afferent projections and spinal elements involved in bladder reflexes consistent with alterations in bladder function observed in animal models of cystitis.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.

The role of globo-series glycolipids in neuronal cell differentiation--a review

Alterations in glycolipid composition as well as glycosyltransferase activities during cellular differentiation and growth have been well documented. However, the underlying mechanisms for the regulation of glycolipid expression remain obscure. One of the major obstacles has been the lack of a well defined model system for studying these phenomena. We have chosen PC12 pheochromocytoma cells as a model because (a) the properties of these cells have been well characterized, and (b) they respond to nerve growth factor (NGF) by differentiating into sympathetic-like neurons and are amenable to well-controlled experimentation. Thus, PC12 cells represent a suitable model for studying changes in glycolipid metabolism in relation to cellular differentiation. We have previously shown that subcloned PC12 cells accumulate a unique series of globo-series neutral glycolipids which are not expressed in parental PC12 cells. This unusual change in glycolipid distribution is accompanied by changes in the activities of specific glycosyltransferases involved in their synthesis and is correlated with neuritogenesis and/or cellular differentiation in this cell line. We have further demonstrated that changes in the glycosyltransferase activities may be modulated by the phosphorylation states of the cells via protein kinase systems. We conclude that these unique globo-series glycolipids may play a functional role in the initiation and/or maintenance of neurite outgrowth in PC12 cells.

B-50, the growth associated protein-43: modulation of cell morphology and communication in the nervous system

The growth-associated protein B-50 (GAP-43) is a presynaptic protein. Its expression is largely restricted to the nervous system. B-50 is frequently used as a marker for sprouting, because it is located in growth cones, maximally expressed during nervous system development and re-induced in injured and regenerating neural tissues. The B-50 gene is highly conserved during evolution. The B-50 gene contains two promoters and three exons which specify functional domains of the protein. The first exon encoding the 1-10 sequence, harbors the palmitoylation site for attachment to the axolemma and the minimal domain for interaction with G0 protein. The second exon contains the "GAP module", including the calmodulin binding and the protein kinase C phosphorylation domain which is shared by the family of IQ proteins. Downstream sequences of the second and non-coding sequences in the third exon encode species variability. The third exon also contains a conserved domain for phosphorylation by casein kinase II. Functional interference experiments using antisense oligonucleotides or antibodies, have shown inhibition of neurite outgrowth and neurotransmitter release. Overexpression of B-50 in cells or transgenic mice results in excessive sprouting. The various interactions, specified by the structural domains, are thought to underlie the role of B-50 in synaptic plasticity, participating in membrane extension during neuritogenesis, in neurotransmitter release and long-term potentiation. Apparently, B-50 null-mutant mice do not display gross phenotypic changes of the nervous system, although the B-50 deletion affects neuronal pathfinding and reduces postnatal survival. The experimental evidence suggests that neuronal morphology and communication are critically modulated by, but not absolutely dependent on, (enhanced) B-50 presence.

Growth-associated protein 43 immunoreactivity in the superficial dorsal horn of the rat spinal cord is localized in atrophic C-fiber, and not in sprouted A-fiber, central terminals after peripheral nerve injury

Peripheral nerve injury induces the up-regulation in dorsal root ganglion cells of growth-associated protein 43 (GAP-43) and its transport to the superficial laminae of the dorsal horn of the spinal cord, where it is located primarily in unmyelinated axons and growth-cone like structures. Peripheral nerve injury also induces the central terminals of axotomized myelinated axons to sprout and form novel synaptic contacts in lamina II of the dorsal horn. To investigate whether the sprouting of A-fiber central terminals into lamina II is the consequence of GAP-43 incorporation into their terminal membranes, we have used an ultrastructural analysis with double labelling to identify the localization of GAP-43 immunoreactivity. Transganglionic transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to identify C-fiber terminals. Transganglionic transport of the B fragment of cholera toxin conjugated to horseradish peroxidase (B-HRP) was used to label A-fiber sciatic nerve central terminals in combination with GAP-43 immunocytochemistry. GAP-43 was found to colocalize only with WGA-HRP- and not with B-HRP-labelled synapses or axons. In addition, many single-labelled GAP-43 synapses were observed. Many of the WGA-HRP-labelled terminals that were characterized by degenerative changes were GAP-43 immunoreactive. Our results indicate that peripheral nerve injury induces novel synapse formation of A fibers in lamina II but that up-regulated levels of GAP-43 are present mainly in other axon projections to the superficial dorsal horn.

B-50/GAP-43 phosphorylation and PKC activity are increased in rat hippocampal synaptosomal membranes after an inhibitory avoidance training

Several lines of evidence indicate that protein kinase C (PKC) is involved in long-term potentiation (LTP) and in certain forms of learning. Recently, we found a learning-specific, time-dependent increase in [3H]phorbol dibutyrate binding to membrane-associated PKC in the hippocampus of rats subjected to an inhibitory avoidance task. Here we confirm and extend this observation, describing that a one trial inhibitory avoidance learning was associated with rapid and specific increases in B-50/GAP-43 phosphorylation in vitro and in PKC activity in hippocampal synaptosomal membranes. The increased phosphorylation of B-50/GAP-43, was seen at 30 min (+35% relative to naive or shocked control groups), but not at 10 or 60 min after training. This learning-associated increase in the phosphorylation of B-50/GAP-43 is mainly due to an increase in the activity of PKC. This is based on three different sets of data: 1) PKC activity increased by 24% in hippocampal synaptosomal membranes of rats sacrificed 30 min after training; 2) B-50/GAP-43 immunoblots revealed no changes in the amount of this protein among the different experimental groups; 3) phosphorylation assays, performed in the presence of bovine purified PKC or in the presence of the selective PKC inhibitor CGP 41231, exhibited no differences in B-50/GAP-43 phosphorylation between naive and trained animals. In conclusion, these results support the contention that hippocampal PKC participates in the early neural events of memory formation of an aversively-motivated learning task.

Time course of degenerative and regenerative changes in the dorsal horn in a rat model of peripheral neuropathy

The time course of histochemical changes in the dorsal horn of rats subjected to an experimental peripheral neuropathy has been examined. Qualitative and quantitative analyses of the changes in dorsal horn staining were made for soybean agglutinin (SBA)-binding glycoconjugates, the soluble lectins RL-14.5 and RL-29, the growth-associated protein (GAP)-43, and the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP). These analyses were made at various time points after chronic constriction of the sciatic nerve. Quantitative analysis indicated that staining density increased in the normal territories stained for SBA-binding glycoconjugates, RL-14.5, RL-29, and GAP-43 on the neuropathic side compared with the control side. In addition, there was an extension of the territories stained for SBA-binding glycoconjugates and RL-29 ipsilateral to the injury. The peak increases occurred at 14 or 28 days, followed by a decrease toward control levels by 70 days. In contrast, the staining density for SP in the ipsilateral dorsal horn decreased at 3 and 5 days and reached a peak decrease at 14 days. Then, the staining for SP returned toward control values. The staining for CGRP was unchanged at all time points examined. Dorsal rhizotomies ipsilateral to the nerve injury in neuropathic rats indicated that the increases in staining were attributable to changes in primary afferent neurons. These data suggest that peripheral neuropathy causes complex degenerative and regenerative changes in the central branches of primary afferent neurons. The associated synaptic reorganization may contribute to the sensory abnormalities that accompany peripheral neuropathy.

Expression of a unique globo-series glycolipid in cultured rat dorsal root ganglion neurons: relationship with neuronal development

Previous studied from the laboratory demonstrated the presence of a UDP-galactose:Gb3Cer alpha 1-3galactosyltansferase activity responsible for the synthesis of a unique glycosphingolipid (GSL), Gal alpha 1-3Gb3Cer, in cultured PC12 pheochromocytoma cells (21). In this investigation, we examined the presence of this enzyme activity in isolated rat embryonic dorsal root ganglion neurons (DRGN), which, like pheochromocytoma cells, originate from the neural crest cells. DRGN exhibited the alpha-galactosyltransferase activity and the activity was comparable to that of the PC12 cells while several other rat tissues, with the exception of kidney, showed minimal activity. In order to define the spatial and temporal expression of Gal alpha 1-3Gb3Cer in DRGN, we examined the expression of Gal alpha 1-3Gb3Cer in cultured DRGN derived from embryonic day 16 rat embryos. Using a polyclonal antibody raised against Gal alpha 1-3Gb3Cer, we examined the localization of this glycolipid in DRGN cells after 5, 8, 12, and 15 days in culture. Immunostaining was restricted to the neurons while Schwann cells were negative. At day 5, the immunostaining was weak and confined to the cell body of the DRGN, though neurites were present at this stage. The period between days 5 and 15 represented a period of rapid neuritic growth and continued enlargement of the cell bodies. Immunoreactivity in the cell bodies increased dramatically by day 8. By day 12, immunoreactivity was present in neurites, and by day 15, was strong in both cells bodies and neurites. The expression of Gal alpha 1-3Gb3Cer in vivo was confirmed by immunostaining of frozen sections of dorsal root ganglia. Our present studies which demonstrate neuron-specific expression of Gal alpha 1-3Gb3Cer during neurotigenesis combined with previous observations for its expression in PC12 cells, strongly implicates this GSL in neuronal development.

B-50 (GAP-43) in the rat spinal cord caudal to hemisection: lack of intraspinal sprouting by dorsal root axons

The controversial hypothesis that intraspinal sprouting by dorsal root axons promotes reinnervation of partially denervated neurons caudal to a low thoracic cord hemisection was re-investigated in rats using quantitative immunohistochemical analysis of the neural specific growth-associated protein B-50 (GAP-43) at postoperative survival times of 3, 10, 21, 42, and 90 days. The lack of increase in B-50-immunoreactivity in all segments below the hemisection at all survival times does not support the concept of intraspinal sprouting following the removal of supraspinal descending pathways.

The increase in B-50/GAP-43 in regenerating rat sciatic nerve occurs predominantly in unmyelinated axon shafts: a quantitative ultrastructural study

The growth-associated protein B-50/GAP-43 is thought to play a crucial role in axonal growth. We investigated, by quantitative immunoelectron microscopy, whether there are differences in the subcellular distribution of B-50 in unmyelinated and myelinated axons of intact and regenerating sciatic nerves. Adult rats received an unilateral sciatic nerve crush and were euthanized 8 days later. Nerve pieces proximal from the crush site were embedded, and B-50 was visualized by specific B-50 antibodies and immunogold detection in ultrathin sections. The density of B-50 at the plasma membrane of unmyelinated axon shafts was significantly increased in the ipsilateral regenerating nerve in comparison to that of the contralateral intact nerve. In contrast, there was no significant difference in the B-50 density at the axolemma of myelinated regenerating and intact axon shafts. In the contralateral intact nerve, more B-50 was associated with the axolemma of unmyelinated axons than with the plasma membrane of myelinated axons. The density of axoplasmic B-50 was similar in intact unmyelinated and myelinated axon shafts, but was higher in regenerating nerve than in intact nerve. This suggests that enhanced axonal transport of B-50 occurs during axon outgrowth. Our study demonstrates a differential subcellular distribution of B-50 in unmyelinated and myelinated axon shafts in both the intact and regenerating sciatic nerve, indicating a differential inducible capacity for remodeling of the axon shafts.

Light-microscopic study of phosphoprotein B-50 in myopathies

The growth-associated protein B-50, also termed GAP-43, is a membrane-bound phosphoprotein that is expressed in neurons. It is particularly abundant during periods of axonal outgrowth in development and regeneration of the central and peripheral nervous system. In this paper we study the expression of B-50 in inflammatory and dystrophic myopathies. To investigate the state of regeneration, N-CAM and vimentin serial sections were performed, because N-CAM and cytoskeletal protein vimentin are excellent markers for regenerating muscle. Light-microscopic evaluation showed that muscle fiber regeneration in myopathies corresponds closely to B-50 immunoreactivity in satellite cells, myoblasts, myotubes and small regenerating myocytes in cytoplasmatic distribution. In normal muscle and in biopsies of neurogenic muscular atrophy, however, no light-microscopically demonstrable B-50 staining was found. B-50 in muscles apparently plays a role in the growth morphology of regenerating myocytes, and the phosphoprotein B-50 can no longer be regarded as a neuron-specific molecule.

Deafferentation-induced expression of GAP-43, NCAM, and NILE in the adult rat dorsal horn following pronase injection of the sciatic nerve

The expression of growth-associated protein 43 (GAP-43), neural cell adhesion molecule (NCAM), and nerve-growth-factor-inducible large external glycoprotein (NILE) in the adult rat dorsal horn was examined at several survival times after unilateral pronase injection of the sciatic nerve. Pronase injection produces a permanent major loss of sciatic primary afferents in the dorsal horn, and there is a later sprouting of saphenous afferents into the sciatic territory. Small-diameter myelinated and nonmyelinated saphenous afferents sprout within the superficial dorsal horn, and larger, myelinated afferents sprout within the deep dorsal horn. In the present study, GAP-43 and NCAM immunoreactivity increased in the superficial dorsal horn by 10 days after injection. By 20 days, the increase spread into the deep dorsal horn; NCAM returned to normal after 1-2 months, but GAP-43 persisted up to 4 months. NILE immunoreactivity appeared in laminae I and II by 10 days and increased up to 30 days; by 2 months no NILE remained. NILE never spread into the deeper dorsal horn, regardless of survival time. These data suggest a correlation in the expression of both NCAM and NILE with the sprouting of fine-diameter sprouting afferents in laminae I and II, and of NCAM expression with the sprouting of larger-diameter afferents in the deep dorsal horn.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of growth associated protein 43 and neural cell adhesion molecule in congenital fibre type disproportion with interstitial myositis

We report on the expression of growth associated protein (GAP)43 and neural cell adhesion molecule (NCAM) in congenital fibre type disproportion (CFTD) with myopathological additional signs of interstitial myositis. We assume that sarcolemmal GAP43 in developmental disordered myocytes plays a role in maintenance of growth morphology. In muscular dystrophy light microscopical evaluation reveals no GAP43 immunoreactivity in regenerating fibres. The expression of GAP43 seems to be a characteristic feature of CFTD. The expression of NCAM, particularly in the sarcolemma of small muscle fibres of CFTD, indicates a functional state of permanent partial denervation. Whether the steroid-responsive interstitial myositis is pathogenetically related to CFTD or a coincidental inflammation is not known. Because of the clinical and myopathological data the differential diagnosis of Emery-Dreifuss muscular dystrophy is considered.

De novo synthesis of GAP-43: in situ hybridization histochemistry and light and electron microscopy immunocytochemical studies in regenerating motor neurons of cranial nerve nuclei in the rat brain

In order to investigate the modulation of the synthesis and the subcellular localization of the growth associated protein GAP-43 in neuronal cell bodies we have taken advantage of the well known regenerative properties of axotomized motor neurons of the facial and hypoglossal nuclei. Alterations in the levels of GAP-43 mRNA containing cells were studied by in situ hybridization histochemistry. The protein localization was examined using immunohistochemistry at the light and electron microscopic levels. Neurons from the control side showed undetectable levels of both GAP-43-like immunoreactivity and GAP-43 mRNA levels. Whereas axotomized neurons exhibited a marked increase in GAP-43 mRNA levels and in GAP-43-like immunoreactivity. Three to 50 days after axotomy, motor neurons ipsilateral to the lesion displayed a dense reticular or filamentous perinuclear distribution of the immunoreactivity in somata and proximal dendritic processes, corresponding to the location of the Golgi apparatus in these neurons. At the electron microscopic level the immunoreactivity was located in the cisternae of the Golgi complex and found to be associated with trans-side vesicles of these complexes. The myelinated fibers of the transectomized facial nerve also presented an intense GAP-43-like immunoreactivity. Twenty-one days after the axotomy a decay in the number of immunostained neurons and in the intensity of immunolabeled somata was observed. Our study reveals a rapid induction of GAP-43 mRNA and protein after axotomy. The localization of the newly synthesized GAP-43-like immunoreactivity to the Golgi apparatus seen in the present work suggests an early association of this protein with newly formed membranes prior to transport toward the terminals through the axons.

B-50 (GAP-43) in the spinal cord caudal to hemisection: indication for lack of intraspinal sprouting in dorsal root axons

Sprouting of dorsal root axons has been suggested to occur in the mature cat spinal cord caudal to a hemisection at a low thoracic level sparing the dorsal columns. The lesion interrupts supraspinal descending projections, while leaving ascending collaterals of dorsal root axons intact. This hypothesis was re-evaluated by comparing the light and electron microscopic immunoreactivity of B-50 (GAP-43) on both sides of the postulated target regions for sprouting, the intermediate gray and the dorsal horn. The neural-specific phosphoprotein B-50 is involved in regenerative and developmental axonal outgrowth and synaptic plasticity. The light microscopic distribution pattern and density of B-50 immunostaining, measured by quantitative densitometry, were bilaterally symmetrical in all segments below the hemisection 3.5, 8, 14, 21, and 56 days postoperatively, as they were in the intact animal. Ultrastructurally, growth cone-like profiles were not detectable during putative periods of sprouting in regions of interest. After removal of degenerated axon terminals, vacated postsynaptic places appeared to be covered by astrocytic processes. These results indicate that, under the present experimental conditions, sprouting of primary afferents in adult cats is unlikely to be involved in functional plasticity after removal of descending pathways.

Restoration of substance P and calcitonin gene-related peptide in dorsal root ganglia and dorsal horn after neonatal sciatic nerve lesion

Dorsal root ganglion (DRG) neurons decrease their substance P (SP) synthesis after peripheral nerve lesions. Levels in the dorsal horn also decline but return to normal if regeneration is successful. In adults, when regeneration is prevented, recovery of SP in the dorsal horn is slow and incomplete, whereas in newborns, recovery is rapid and complete even though retrograde cell death of DRG neurons is greater than in adults. We have examined the mechanisms that might account for the rapid and complete recovery of SP and calcitonin-gene related peptide (CGRP) in the dorsal horn after peripheral nerve injury in newborns. Peptides were compared in the L4 and L5 DRG and spinal cord segments of normal rats and in rats surviving 6 days to 4 months after sciatic nerve section/ligation within 24 hours of birth. Sciatic nerve section/ligation produced 50% neuron death in L4 and L5 DRGs, but immunocytochemical methods showed that both SP-immunoreactivity (-IR) and CGRP-IR recovered completely in dorsal horn. Radioimmunoassay confirmed that recovery of SP was not an artefact due to shrinkage. beta-Preprotachykinin (PPT)-mRNA hybridization and SP-IR were observed mostly in small neurons; alpha-CGRP-mRNA-hybridized and CGRP-IR neurons were more heterogeneous. The percentage of DRG neurons that contained SP (approximately 25%) or CGRP (approximately 50%) was the same in normal newborn and adult rats. Neither selective cell survival nor change in neuron phenotype was likely to contribute to the recovery seen in the dorsal horn, and DRG neurons ipsilateral to the lesion exhibited the same level of hybridized beta-PPT-mRNA and alpha-CGRP-mRNA as intact DRG neurons. Because neither the constitutive level of expression of the genes nor peptide levels increased above those observed in intact DRG neurons, these mechanisms were also not responsible. Axotomized DRG neurons, however, contributed to recovery. Recovery was also due to sprouting by neurons in intact DRGs rostral and caudal to L4 and L5.

B-50 (GAP-43) in Onuf's nucleus of the adult cat

The nucleus of Onuf in the sacral spinal cord contains motoneurons that innervate the pelvic floor muscles and possess somatic and autonomic characteristics. We show in this study that in the intact adult cat, the immunocytochemical labelling of the nervous tissue-specific growth-associated protein, B-50 (GAP-43), which persists in Onuf's nucleus, differs markedly from that in the remaining 'purely somatic' motor nuclei of the sacral spinal cord. At the light microscopic level, an intense B-50 (GAP-43) immunoreactivity (B-50-IR) in the neuropil of Onuf's nucleus contrasts with a faint staining in the other spinal motor nuclei. Ultrastructurally, B-50-IR is found in Onuf's nucleus within some unmyelinated small diameter nerve fibres and numerous axon terminals on dendritic and somatic surfaces. Conversely, in all other motor nuclei only a few of these structures are stained. No other cellular profiles show B-50-IR in the tissue examined. According to the proposed functions of B-50 (GAP-43), its persistence in mature spinal axon terminals may indicate a latent capability of functional and structural remodeling, as well as an involvement in long-term enhancement in synaptic transmission. If so, these properties would be considerably more pronounced in Onuf's nucleus as compared to purely somatic motor nuclei.

Immunocytochemistry of B-50 (GAP-43) in the spinal cord and in dorsal root ganglia of the adult cat

The distribution of the neural-specific growth associated protein B-50 (GAP-43), which persists in the mature spinal cord and dorsal root ganglia, has been studied by light and electron microscopic immunohistochemistry in the cat. Throughout the spinal cord, B-50 immunoreactivity was seen confined to the neuropil, whereas neuronal cell bodies were unreactive. The most conspicuous immunostaining was observed in the dorsal horn, where it gradually decreased from superficial laminae (I-II) toward more ventral laminae (III-V), and in the central portion of the intermediate gray (mainly lamina X). In these regions, the labelling was localized within unmyelinated, small diameter nerve fibres and axon terminals. In the rest of the intermediate zone (laminae VI-VIII), B-50 immunoreactivity was virtually absent. The intermediolateral nucleus in the thoracic and cranial lumbar cord showed a circumscribed intense B-50 immunoreactivity brought about by the labelling of many axon terminals on preganglionic sympathetic neurons. In motor nuclei of the ventral horn (lamina IX), low levels of B-50 immunoreactivity were present in a few axon terminals on dendritic and somal profiles of motoneurons. In dorsal root ganglia, B-50 immunoreactivity was mainly localized in the cell bodies of small and medium-sized sensory neurons. The selective distribution of persisting B-50 immunoreactivity in the mature cat throughout sensory, motor, and autonomic areas of the spinal cord and in dorsal root ganglia suggests that B-50-positive systems retain in adult life the capacity for structural and functional plasticity.

Chronic peripheral nerve section results in a rearrangement of the central axonal arborizations of axotomized A beta primary afferent neurons in the rat spinal cord

In order to investigate the reorganization of the neuropil of the dorsal horn following peripheral nerve injury, the central terminal arborizations of 35 A beta primary afferent neurons, chronically injured by a cut and ligation of the sural nerve 6-12 weeks previously, were studied by the intra-axonal injection of horseradish peroxidase. Their morphology was compared to 13 intact sural nerve hair follicle afferents. Following axotomy, three kinds of morphological abnormalities were observed in the collateral arbors of the 26 afferents that were hair follicle-like. Atrophy with thin stem axons and reduced terminal branch patterns with few boutons was seen in 5 afferents. Sprouting of bouton-containing terminals into lamina I and IIo was found in 8 afferents. Finally, abnormal arborization patterns in the deeper laminae were observed in 29% of the collateral arbors. Changes included the loss in some arbors of a flame-shaped appearance, which is characteristic of hair follicle afferents, atypical branching patterns and ventrally directed axons producing wider and deeper arbors, compared to normal. Axotomy also caused a disruption of the normal somatotopic organization of sural nerve A beta afferents. This disruption manifested as a variability in the normally mediolaterally restricted terminal sheet, with a consequent loss of the strict somatotopic register in the rostrocaudal direction. Damage to the peripheral axon of A beta primary afferents induces a structural reorganization of their central terminals in the dorsal horn of the spinal cord, which may modify sensory input to the central nervous system.