[Progressive ataxic hemiparesis with asymmetric cortical and cerebral peduncular atrophy--report of two cases]

We report two patients, 73- and 70-year-old men, characterized by progressive hemiparesis and homolateral limb ataxia as the main clinical symptoms; magnetic resonance (MR) imaging of the brain revealed asymmetric cerebral cortical and peduncular atrophy; 99mTc-ECD single photon emission computed tomography (SPECT) of brain showed decreased RI uptake in the cerebral hemisphere correlated with clinical deficits. Brain SPECT of case 1 showed decreased RI uptake in the cortex of the right hemisphere and the left cerebellar hemisphere ("crossed cerebellar diaschisis; CCD"). These findings indicate that ataxia of our patients may depend on the lesions of the corticopontocerebellar tracts, although it is possible that ataxia may be related to lack of spatial orientation associated with parietal lobe lesion. The mechanism of the occurrence of asymmetric cerebral peduncular atrophy would be explained by wallerian degeneration of the pyramidal tract and other cortically originated fibers associated with the cortical degeneration. From these clinical and radiologic features, it seems likely that our two patients are categorized in the "asymmetric cortical degeneration syndromes", and we propose the term "progressive ataxic hemiparesis" for our patients.

Glial cells in transected optic nerves of immature rats. II. An immunohistochemical study

The glia response to Wallerian degeneration was studied in optic nerves 21 days after unilateral enucleation (PED21) of immature rats, 21 days old (P21), using immunohistochemical labelling. Nerves from normal P21 and P42 nerves were also studied for comparison. At PED21, there was a virtual loss of axons apart from a few solitary fibres of unknown origin. The nerve comprised a homogeneous glial scar tissue formed by dense astrocyte processes, oriented parallel to the long axis of the nerve along the tracks of degenerated axons. Astrocytes were almost perfectly co-labelled by antibodies to glial fibrillary acid protein and vimentin in both normal and transected nerves. However, there was a small population of VIM+GFAP- cells in normal P21 and P42 nerves, and we discuss the possibility that they correspond to O-2A progenitor cells described in vitro. Significantly, double immunofluorescence labelling in transected nerves revealed a distinct population of hypertrophic astrocytes which were GFAP+VIM-. These cells represented a novel morphological and antigenic subtype of reactive astrocyte. It was also noted that the number of oligodendrocytes in transected nerves did not appear to be less than in normal nerves, on the basis of double immunofluorescence staining for carbonic anhydrase II, myelin oligodendrocyte glycoprotein, myelin basic protein, glial fibrillary acid protein and ED-1 (for macrophages), although it was not excluded that a small proportion may have been microglia. A further prominent feature of transected nerves was that they contained a substantial amount of myelin debris, notwithstanding that OX-42 and ED1 immunostaining showed that there were abundant microglia and macrophages, sufficient for the rapid and almost complete removal of axonal debris. In conclusion, glial cells in the immature P21 rat optic nerve reacted to Wallerian degeneration in a way equivalent to the adult CNS, i.e. astrocytes underwent pronounced reactive changes and formed a dense glial scar, oligodendrocytes persisted and were not dependent on axons for their continued survival, and there was ineffective phagocytosis of myelin possibly due to incomplete activation of microglia/macrophages.

Glial cells in transected optic nerves of immature rats. I. An analysis of individual cells by intracellular dye-injection

The glial response to Wallerian degeneration was studied in optic nerves following unilateral enucleation in immature rats, aged 21 days old (P21). The three-dimensional morphology of dye-filled glia was determined in intact nerves, at post-enucleation day 21 in normal nerves from untreated P21 rats, by correlating laser scanning confocal microscopy and camera lucida drawings of single cells. In normal and transected nerves, the majority of dye-filled cells comprized astrocytes (54% and 65%, respectively). In normal P21 nerves, the predominant astrocyte form had a complex stellate morphology and had a centrally-located cell body from which branching processes extended randomly. Two other distinct forms were transverse and longitudinal astrocytes, which had a polarized process extension in a plane perpendicular or parallel to the long axis of the nerve, respectively. These forms were recognized in transected nerves also, but astrocytes in transected nerves had a simple morphology on the whole, and extended few, dense processes which branched infrequently. Quantitative analysis of astrocyte morphology confirmed that individual astrocytes underwent considerable remodelling in response to Wallerian degeneration. A prominent reaction was that astrocytes had withdrawn radial processes and extended a greater proportion of processes longitudinally, parallel to the long axis of the nerve and along the course of degenerated axons. A further, notable feature of transected nerves was the development of novel longitudinal forms and of hypertrophic astroglia. These results indicated that all astrocytes became reactive following enucleation and that glial scar formation was not the function of a single astrocyte subtype. Oligodendrocytes in transected nerves had lost their myelin sheaths and appeared as small cells with numerous bifurcating processes which extended radially, but a small number of oligodendrocytes were recognized which apparently supported myelin sheaths (9%, compared to 40% in normal nerves). In addition, there was a significant population of indeterminate cells in transected nerves (26%, compared to 6% in normal nerves) and, although some of these were identified as microglia/macrophages, it was concluded that many were likely to be dedifferentiated oligodendrocytes.

Preferential growth of neonatal rat dorsal root ganglion cells on homotypic peripheral nerve substrates in vitro

Developing sensory neurons interact with molecular signals in the local environment to generate stereotypic nerve pathways. Regenerating neurons seem to lose the ability to reinnervate their original sites in the targets, resulting in abnormal sensory input and consequent clinical pathophysiology. The specificity of reinnervation of peripheral targets by regenerating axons is thus crucial for normal recovery of function. In this study, we have examined evidence for selectivity of interactions between primary afferent neurons from identified levels of the spinal cord and different peripheral nerve environments by culturing these neurons on sections of nerves to muscle and viscera. We have compared the growth of a population of sensory afferents normally innervating somatic targets (dorsal root ganglion cells from L4 and L5) with populations containing many afferents innervating visceral targets (L6 and S1 dorsal root ganglia and nodose ganglion). These neurons, from newly born rats, were cultured on unfixed cryostat sections of normal and prelesioned gastrocnemius nerve, pelvic spinal nerve and vagus nerve from adult rats. Normal muscle nerve was seen to support the regeneration of a significantly greater proportion of somatic neurons, with longer neurites, than the visceral nerves. Similarly, much higher proportions of the 'visceral' population of afferent neurons were seen to extend neurites on the normal visceral nerve substrates, with longer neurites, than on the muscle nerve substrate. The selectivity displayed by the sensory neurons for their normal nerve substrates was abolished when they were cultured on prelesioned nerve substrates subjected to Wallerian degeneration, which was apparent from the equivalent and increased proportions of growing neurons having comparable neurite lengths, on all the nerve substrates. We conclude that sensory neurons recognize and respond to substrate-specific and substrate-bound molecules present in normal adult peripheral nerves, and that these differences are lost in prelesioned nerves following Wallerian degeneration.

Wallerian degeneration in peripheral nerve disease

Wallerian-like degeneration can be regarded as the final shared pathway of the most prevalent diseases of the peripheral nervous system, including many degenerative, metabolic, heritable, toxic, inflammatory and ischaemic disorders. The cellular responses that take place during Wallerian degeneration, including the elaboration of neurotrophins, are increasingly recognized to set the stage for the success or failure of subsequent regeneration, and manipulations of Wallerian degeneration are being investigated as a potential means of altering the outcome of nerve regeneration.

Axons regulate the distribution of Schwann cell microtubules

It is well established that axons regulate Schwann cell phenotype. The purpose of the present study was to determine whether axons influence the arrangement of Schwann cell microtubules (MTs). Using double-labeling immunocytochemistry and confocal microscopy, we show that MTs in undifferentiated Schwann cells are nucleated from and attached to a single MT organizing center (MTOC) that is associated with the centrosome. Physical contact with appropriate axons initiates a myelin-forming phenotype that disperses MT minus ends and induces multiple MT-nucleating sites in Schwann cell perinuclear cytoplasm. The axonal signal that initiates myelin breakdown during Wallerian degeneration induces multiple MTOCs and MT bundles in Schwann cell perinuclear cytoplasm and in cytoplasm between degenerating myelin ovoids. These results establish that axons influence Schwann cell MT distribution by regulating the location and number of MT-nucleation sites.

Multiexponential T2 relaxation in degenerating peripheral nerve

The multiexponential T2 relaxation spectrum of peripheral nerve undergoing Wallerian degeneration has been measured both in vivo and in vitro. Degeneration of the sciatic nerve of the amphibian Xenopus laevis was induced by crush injury, and T2 relaxation spectra of the nerve were measured at several times up to 35 days following injury. Histologic evidence verified that the nerve underwent Wallerian degeneration. Relaxation spectra were observed to undergo measurable changes as degeneration progressed, the most evident being a reduction from three well-resolved T2 components to one and a decline in the fraction of the spectra associated with the shortest T2 component. The former appears to reflect the collapse and loss of myelinated fibers, while the latter a combination of interstitial edema and myelin loss.

Reduction in peripheral nerve allograft antigenicity with warm and cold temperature preservation

Lymphocyte migration into fresh and preserved peripheral nerve allografts was assessed to determine the effects of preservation time, preservation temperature, and graft harvest technique on the immunologic response to the peripheral nerve allograft. Peroneal nerve was harvested from either live or cadaveric (tissue) donors and stored as 1.5-cm segments at 5 degrees C or 37 degrees C for 1, 3, 5, or 7 days. Each of nine outbred ewes then received multiple segments of peroneal autograft, fresh allograft, and preserved nerve allograft implants. Lymphocyte migration was studied 7 days after implantation by intravenous injection of autologous 111In-labeled lymphocytes and quantified by gamma counter. Lymphocyte migration into fresh allografts (7212 +/- 1575) increased an average of 4.1 times over fresh autograft tissue (1758 +/- 421; p < 0.05). Short-term preservation (24 hours) at both temperatures enhanced lymphocyte migration into pretreated allograft tissue (12684 +/- 2575 at 5 degrees C, 8751 +/- 1577 at 37 degrees C) as compared with fresh allograft (7212 +/- 1575). Conversely, 7 days of pretreatment at both 5 degrees C (3586 +/- 1421) and 37 degrees C (1570 +/- 414) resulted in migration values not significantly different from autograft. No statistically significant difference was seen between grafts harvested from live (5710 +/- 1651) versus cadaveric (tissue) donors (4013 +/- 832) after 5 days of cold preservation.

Differential macrophage responses in the peripheral and central nervous system during wallerian degeneration of axons

We characterized quantitatively the macrophage response following axonal injury in both the peripheral (PNS) and central nervous system (CNS) of adult mammals. A monoclonal antibody (ED-1) which stains monocytes, macrophages, and activated microglia was employed. In one model, Wallerian degeneration of the sciatic nerve was studied. An increase in the number of macrophages was seen as early as 1 day following nerve transection. Macrophage number increased synchronously along the length of degenerating nerve over a 21-day period. In a second model, transection of a spinal dorsal sensory root allowed us to compare and contrast the macrophage response along the PNS and CNS portions of a single axonal pathway. An increased number of macrophages restricted to the PNS portion of this pathway was seen by 3 days and continued to increase over a 14-day period. Myelin breakdown occurred in association with an increase in the number of macrophages by 3 days in the PNS but not the CNS portion of the degenerating dorsal root axon pathway. Low-affinity nerve growth factor receptor immunohistochemical staining increased by Day 1 in the PNS but not the CNS portion of this pathway, occurring prior to the invasion of macrophages. In both models, the morphology of infiltrating macrophages changed over time from small slender ramified cells to large elongated multivacuolated cells. In conclusion, our results demonstrate that the macrophage response during Wallerian degeneration of axons in adult mammals is much more rapid and robust in the PNS, where axonal regeneration occurs, than in the CNS, where axonal regeneration is far more limited.

Periaxin expression in myelinating Schwann cells: modulation by axon-glial interactions and polarized localization during development

Periaxin is a newly described protein that is expressed exclusively by myelinating Schwann cells. In developing nerves, periaxin is first detected as Schwann cells ensheathe axons, prior to the appearance of the proteins that characterize the myelin sheath. Periaxin is initially concentrated in the adaxonal membrane (apposing the axon) but, during development, as myelin sheaths mature, periaxin becomes predominately localized at the abaxonal Schwann cell membrane (apposing the basal lamina). In permanently axotomized adult nerves, periaxin is lost from the abaxonal and adaxonal membranes, becomes associated with degenerating myelin sheaths and is phagocytosed by macrophages. In crushed nerves, in which axons regenerate and are remyelinated, periaxin is first detected in the adoxonal membrane as Schwann cells ensheathe regenerating axons, but again prior to the appearance of other myelin proteins. Periaxin mRNA and protein levels change in parallel with those of other myelin-related genes after permanent axotomy and crush. These data demonstrate that periaxin is expressed by myelinating Schwann cells in a dynamic, developmentally regulated manner. The shift in localization of periaxin in the Schwann cell after completion of the spiralization phase of myelination suggests that periaxin participates in membrane-protein interactions that are required to stabilize the mature myelin sheath.

Schwann cell properties: 3. C-fos expression, bFGF production, phagocytosis and proliferation during Wallerian degeneration

The role of Schwann cells (SC) during Wallerian degeneration has been controversial. The consensus opinion is that monocytes/macrophages are mainly responsible for myelin removal although SC were shown to phagocytose myelin in vitro and in vivo. In the present study, we correlate proto-oncogene expression with phenotypic changes in SC during Wallerian degeneration using immunohistochemistry and electron microscopy. The proliferative cells are labeled with proliferative cell nuclear antigen (PCNA), and macrophages are labeled with ED1 macrophage marker. We demonstrate c-fos expression in SC at the onset of axon disintegration 12 hours post-axotomy followed by expression of ED1, basic fibroblast growth factor (bFGF) and PCNA after 1 day. The myelin sheath fragments at the nodal region and forms ellipsoids. Schwann cells move to internodes and undergo nuclear and cytoplasmic hypertrophy; they phagocytose myelin ellipsoids with thick vimentin-rich processes and undergo mitosis. Resident macrophages express c-fos and phagocytose myelin debris sequestered into endoneurium by SC after 3 days, but they do not enter the tube until the fifth day. We believe that SC are induced by signals from injured axons to express c-fos which activates downstream genes that lead to the acquisition of phagocytic and proliferative activities. Myelin debris processed by SC may act as an inducer and a chemoattractant for resident macrophages. Cytokines produced by macrophages may stimulate SC proliferation and production of neurotrophic factors.

Persistence of neuromuscular junctions after axotomy in mice with slow Wallerian degeneration (C57BL/WldS)

The present study was undertaken to examine the fate of neuromuscular junctions in C57BL/WldS mice (formerly known as OLA mice) after nerve injury. When a peripheral nerve is injured, the distal axons normally degenerate within 1-3 days. For motor axons, an early event is deterioration of motor nerve terminals at neuromuscular junctions. Previously, the vulnerability of motor terminals has been attributed either to a 'signal' originating at the site of nerve injury and transported rapidly to the terminals or to their continual requirement for essential maintenance factors synthesized in the motor neuron cell body and supplied to the terminals by fast axonal transport. Mice of the WldS strain have normal axoplasmic transport but show an abnormally slow rate of axon and myelin degeneration. Structure and function are retained in the axons of distal nerve stumps for several days or even weeks after nerve injury in these mice. The results of the present study show that WldS neuromuscular junctions are also preserved and continue to release neurotransmitter and recycle synaptic vesicle membrane for at least 3 days and in some cases up to 2 weeks after nerve injury. Varying the site of the nerve lesion delayed degeneration by approximately 1-2 days per centimetre of distal nerve remaining. These findings suggest that the mechanisms of nerve terminal degeneration after injury are more complex than can be accounted for simply by the failure of motor neuron cell bodies to supply their terminals with essential maintenance factors. Rather, the data support the view that nerve section normally activates cellular components or processes already present, but latent, in motor nerve endings, and that in WldS mice either the trigger or the cellular response is abnormal.

Electrophysiological, morphological, and morphometric effects of aging on nerve regeneration in rats

To investigate the influence of age on the process of nerve regeneration, the right common peroneal nerves of 14 2 month old and 14 10 month old rats were transected and resutured. At four and eight weeks after the nerve repair, the motor nerve conduction velocity (MNCV), latency, and amplitude of the evoked potential from the peroneus longus muscle were measured. The number of regenerated myelinated fibres, axon diameter, axon area, axon circumference, and myelin thickness were also measured. Compared with the control side (left common peroneal nerve and muscle), MNCV, latency, and amplitude showed higher recovery rates (recovery rate (%) = operated/control x 100) in 2 month old rats than in 10 month old rats, particularly at four weeks after the operation. In the morphometric study, axon diameter, axon area, and myelin thickness also recovered more quickly (recovery rate (%) = operated/control x 100) in 2 month old rats, particularly four weeks after the operation. Morphologically, myelin remnants were not found in 2 month old rats eight weeks after the operation, though they remained in 10 month old rats. These studies show that the recovery rate was significantly greater in 2 month old rats than in 10 month old rats. The explanation seems to be the difference in the speed of Wallerian degeneration, axonal regeneration, and myelin regeneration.

Guillain-Barré syndrome in northern China. The spectrum of neuropathological changes in clinically defined cases

The pathology of the Guillain-Barré syndrome remains controversial, and autopsied cases available for study by contemporary techniques are uncommon. Large numbers of cases clinically diagnosed as Guillain-Barré syndrome occur in northern China. In this study we examined the neuropathological changes in 12 autopsied cases from Hebei Province, China. Eleven died early in the course of their disease. In all cases tissue was specially handled and fixed for electron microscopy and for immunocytochemistry. Three of these 12 cases had typical acute inflammatory demyelinating polyneuropathy (AIDP) with lymphocytic infiltration and macrophage-mediated demyelination, reproducing the pathological picture most often reported in Guillain-Barré syndrome in North America, Europe, and Australia. Six cases had predominantly axonal involvement, characterized by Wallerian-like degeneration of nerve fibres, with only minimal demyelination and with minimal inflammation in five. Three cases, even though paralysed at the time of death, had only very mild changes in the spinal roots and sciatic nerves. Within the group of six predominantly axonal cases, there were important differences both in the severity of the abnormalities and in the classes of fibres involved. Three cases had extensive Wallerian-like degeneration of sensory as well as motor fibres [acute motor-sensory axonal neuropathy (AMSAN)], while in the other three cases the fibre degeneration affected the motor nerve fibres almost exclusively. These latter cases establish a structural basis for the clinical and electrophysiological picture termed the acute motor axonal neuropathy (AMAN) pattern. In both the AMAN and the AMSAN patterns, a prominent feature was the presence of macrophages within the periaxonal space, surrounding or displacing the axon, and surrounded by an intact myelin sheath. These studies show that the early pathological changes in cases clinically diagnosed as the Guillain-Barré syndrome are diverse and not restricted to the well-known pattern of AIDP, and that the predominant pathological patterns may differ in different parts of the world. The differences in pathological findings between acute inflammatory demyelinating polyneuropathy and the axonal patterns are likely to reflect differences in the pathogenetic mechanisms. The periaxonal macrophages in the axonal patterns suggest that an important epitope may be localized to the axolemma or periaxonal space. The mild cases indicate that severe paralysis can occur early in Guillain-Barré syndrome without prominent structural changes along the nerve, suggesting that physiological block or nerve terminal changes may be implicated.

Fibroblasts that reside in mouse and frog injured peripheral nerves produce apolipoproteins

Apolipoprotein synthesis and secretion is upregulated in wallerian degenerating peripheral nerves. A commonly expressed view has been that macrophages are solely responsible for their production. In the present study we provide evidence that (1) nerve-derived fibroblasts contribute to apolipoprotein production, (2) apolipoprotein production is confined to regions where myelin destruction and phagocytosis occur, and (3) some experimental procedures are detrimental for the production of apolipoproteins. Apolipoprotein production was studied in C57BL/6/NHSD (N) and C57/BL/6-WLD/OLA/NHSD (W) mice that display, respectively, rapid and slow progression of wallerian degeneration. In N nerves, apolipoprotein E (apo-E) is produced during in vitro and in vivo degeneration, and in vivo after freeze damage. In W nerves, apo-E is produced at the injury region where degeneration occurs but not farther distally where degeneration fails to develop. Apo-E is also produced in W nerves during in vitro degeneration and in vivo after freeze damage. In culture, N and W mice nerve-derived fibroblasts, but neither macrophages nor Schwann cells produced apo-E. Two apolipoproteins are produced in in vivo wallerian degenerating and freeze-damaged frog nerves, i.e., apo-39 and apo-29. Only apo-39 is produced in in vitro degenerating nerves. Neither apo-39 nor apo-29 is produced during in vivo degeneration in diffusion chambers. In culture, apo-39 is produced by nerve-derived fibroblasts and macrophages but not by Schwann cells.

Pathological basis of spinal cord cavitation in syringomyelia: analysis of 105 autopsy cases

This report summarizes neuropathological, clinical, and general autopsy findings in 105 individuals with nonneoplastic syringomyelia. On the basis of detailed histological findings, three types of cavities were distinguished: 1) dilations of the central canal that communicated directly with the fourth ventricle (47 cases); 2) noncommunicating (isolated) dilations of the central canal that arose below a syrinx-free segment of spinal cord (23 cases); and 3) extracanalicular syrinxes that originated in the spinal cord parenchyma and did not communicate with the central canal (35 cases). The incidence of communicating syrinxes in this study reflects an autopsy bias of morbid conditions such as severe birth defects. Communicating central canal syrinxes were found in association with hydrocephalus. The cavities were lined wholly or partially by ependyma and their overall length was influenced by age-related stenosis of the central canal. Non-communicating central canal syrinxes arose at a variable distance below the fourth ventricle and were associated with disorders that presumably affect cerebrospinal fluid dynamics in the spinal subarachnoid space, such as the Chiari I malformation, basilar impression, and arachnoiditis. These cavities were usually defined rostrally and caudally by stenosis of the central canal and were much more likely than communicating syrinxes to dissect paracentrally into the parenchymal tissues. The paracentral dissections of the central canal syrinxes occurred preferentially into the posterolateral quadrant of the spinal cord. Extracanalicular (parenchymal) syrinxes were found typically in the watershed area of the spinal cord and were associated with conditions that injure spinal cord tissue (for example, trauma, infarction, and hemorrhage). A distinguishing feature of this type of cavitation was its frequent association with myelomalacia. Extracanalicular syrinxes and the paracentral dissections of central canal syrinxes were lined by glial or fibroglial tissue, ruptured frequently into the spinal subarachnoid space, and were characterized by the presence of central chromatolysis, neuronophagia, and Wallerian degeneration. Some lesions extended rostrally into the medulla or pons (syringobulbia). Although clinical information was incomplete, simple dilations of the central canal tended to produce nonspecific neurological findings such as spastic paraparesis, whereas deficits associated with extracanalicular syrinxes and the paracentral dissections of central canal syrinxes included segmental signs that were referable to affected nuclei and tracts. It is concluded that syringomyelia has several distinct cavitary patterns with different mechanisms of pathogenesis that probably determine the clinical features of the condition.

[Degeneration and regeneration of the peripheral nervous system with aging]

Clinical and experimental studies have shown that with aging there appear neurological changes which affect both the Central Nervous System (CNS) as well as the Peripheral Nervous System (PNS), bringing about a series of cognitive, sensory and physical disabilities in older people. Nerve lesions also cause disability. The basic mechanisms which begin with lesioned neurons have proved an interesting field of study for many neuroscientists since as far back as the mid-nineteenth century. However the influence of age on these postlesion neuronal processes has not aroused the same level of interest even though many authors have, out of curiosity, published reports of changes which take place in regenerative neurons as a result of age. The progressive increase in the aged population in industrialised nations warrants a detailed study into the influence of age on such neuronal processes. The PNS, due to its accessibility and greater regenerative potential vis-à-vis the CNS, may be a good model for this purpose. From results obtained by both other authors and ourselves it is clear that aging causes a decline in the regenerative abilities of peripheral nerve fibres. Functional recovery is not only slowed down but also decreases with age. The number of regenerative axons and their capacity for end sprouting, together with the biosynthesis and transport of new materials in the regenerative neurons, as well as the proliferation and synthesis of trophic factors by Schwann cells also decay. All of this leads to the fact that the regenerative capacity of nerve fibres is lesser with age, and that functional disabilities after a lesion are greater in older than in younger people.

The temporal and spatial activation of microglia in fiber tracts undergoing anterograde and retrograde degeneration following spinal cord lesion

The role of microglia in the response to CNS injury is not fully understood. We characterized the temporal activation of microglia in the adult spinal cord following a lesion that severed the axons of the dorsal columns and corticospinal tract at T8. Two days after lesion, microglia in the severed T4-T5 fasciculus (f.) gracilis were ameboid and expressed intense OX42 and increased class I major histocompatibility complex (MHC) antigen (OX18) immunoreactivities. No activated microglia were seen in the intact f. cuneatus or the corticospinal tract. Five days postlesion, OX42 immunoreactivity was slightly decreased in the f. gracilis, and OX18 expression was slightly enhanced. By 12 days postlesion, OX42 and OX18 immunoreactivities were near control levels. At L1-L2, activated microglia with increased OX18 expression were restricted to the corticospinal tract and were maximal 5 days postlesion, returning to near control levels by 12 days postlesion. In the medulla, enhanced OX42 and OX18 immunoreactivities were seen in the nucleus (n.) gracilis, but not the n. cuneatus, at 2 days postlesion. At 5 days postlesion, OX42 immunoreactivity was markedly decreased, but class I MHC antigen expression was still enhanced. GFAP immunoreactivity increased only in the n. gracilis and remained elevated 2-12 days postlesion. Microglial activation is an early lesion-induced event in the CNS, and activated microglia may play a role in mediating the regenerative capacity of injured CNS axons.

A note on the relative rates of degeneration in the crossed and the uncrossed retinofugal fibres in the opossum Didelphis marsupialis

The rates at which the crossed and the uncrossed components of the retinofugal pathway degenerate in Didelphis has been studied by light and electron microscopical methods. We have found that in Didelphis, as in Monodelphis the two components can be clearly distinguished at the level of the chiasm. However, in contrast to the situation previously described for Monodelphis, where the uncrossed component degenerates more rapidly than the crossed, both components degenerate at the same rate.

Elongation of wallerian degenerating nerve with a tissue expander: a functional, morphometrical, and immunohistochemical study

The purpose of this experimental study was to investigate the usefulness and mechanism of the expansion of wallerian degenerating nerve. The study consisted of two experiments: Experiment I, functional and morphometrical analysis, and Experiment II, immunohistochemical analysis. In Experiment I, the rat nerve crush model was used to assess the effects of mechanical expansion of wallerian degenerating nerves on axonal regeneration. In Experiment II, the rat sciatic nerve cut model was used to investigate the effects of nerve expansion on Schwann cell events in wallerian degenerating nerves. In both experiments, nerve expansion was carried out between days 5 and 9 after nerve injury, using a rubber tissue expander placed beneath the sciatic nerve. In Experiment I, rats were divided into the following three groups according to the volume of saline injected: control group (nerves were crushed, without saline injection); 8-ml injection group; and 11-ml injection group. Functional recovery was assessed using the sciatic functional index until 54 days after nerve injury. Rats in all three groups showed good functional recovery, and the morphometrical analysis revealed no significant differences among the three groups. In Experiment II, anti-S-100 protein polyclonal antibody and anti-proliferating cell nuclear antigen monoclonal antibody were used to identify proliferating Schwann cells. Rats were divided into two groups: control group (nerves were cut, without expansion) and nerve expansion group. In the control group, proliferating Schwann cells were observed only between days 3 and 7. By contrast, these cells continued to be seen in the expanded nerves until day 16. These results suggest that the expansion of wallerian degenerating nerve does not have a deleterious effect on the axon-promoting property of Schwann cell tubes and that the expansion is dependent not only on the viscoelasticity of the nerves but also on enhanced proliferation of Schwann cells.

Serotonin 1B receptor regulation after dorsal subiculum deafferentation

The subiculum may be the key structure in the transfer of relevant processed information from the hippocampal formation to cortical areas. We investigated the location of the serotonin 1B receptor (5-HT1B) in the hippocampus with the specific ligand serotonin-O-carboxymethyl-glycyl[125I]tyrosinamide in rat brain sections using in vitro autoradiography. A high density of 5-HT1B binding sites was found in the dorsal subiculum (DS), in the lacunosum moleculare, and in the most dorsal layer of the stratum oriens of the CA1 field. CA1 pyramidal neurons that contain 5-HT1B mRNA project primarily to the DS. We interrupted the pyramidal CA1 axons unilaterally by a stereotaxic knife cut. Histological analysis showed that the lesion was restricted to a trial of cells lost between CA1 and DS. Specific 5-HT1B binding site density was decreased in the DS on the ipsilateral side of the lesion compared to the contralateral side. We conclude that 5-HT1B receptors are located on CA1 pyramidal axon terminals in the DS. Serotonin, acting on these receptors, should inhibit CA1 neurotransmitter release and, in this way, modulate subicular functions.

Macrophage recruitment in different models of nerve injury: lysozyme as a marker for active phagocytosis

Macrophages play critical roles in both degenerative and regenerative processes following peripheral nerve injury. These include phagocytosis of debris, stimulation of Schwann cell dedifferentiation and proliferation, and salvage of myelin lipids for reutilization during regeneration. To better define the role of macrophages, we studied models of primary demyelination (tellurium intoxication) and secondary demyelination (nerve crush and cut). Sections of paraformaldehyde-fixed rat sciatic nerves at various stages of demyelination were stained with monoclonal antibody ED1, a standard macrophage marker, and a polyclonal antiserum specific for lysozyme (LYS). Near the peak of demyelination in all three models, LYS immunoreactivity colocalized with ED1 staining. Macrophages present in nerve after the period of maximal phagocytosis of myelin were much less immunoreactive for LYS. These results suggest LYS is a good marker for macrophages which are active in phagocytosis. Tellurium intoxication, which causes synchronous demyelination and subsequent remyelination of only about 25% of myelin internodes, recruited more macrophages (and induced more lysozyme expression) than either nerve crush or cut, which cause demyelination of all internodes distal to the injury site. This suggests that Schwann cells may recruit macrophages soon after metabolic insult and prior to actual demyelination. The final signal for macrophage recruitment is not directly related to the amount of damaged myelin. In the models listed above, steady state mRNA levels for apolipoprotein E (ApoE; possible mediator of cholesterol salvage), LYS, and P0 (major structural protein of PNS myelin), were analyzed by Northern blot analysis. LYS mRNA levels peaked sharply in all models, with a temporal pattern consistent with the expected presence of activated, phagocytic macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)