Evidence for activation of the terminal pathway of complement and upregulation of sulfated glycoprotein (SGP)-2 in the hypoglossal nucleus following peripheral nerve injury

Synaptic Plasticity on Motoneurons After Axotomy: A Necessary Change in Paradigm

Motoneurons axotomized by peripheral nerve injuries experience profound changes in their synaptic inputs that are associated with a neuroinflammatory response that includes local microglia and astrocytes. This reaction is conserved across different types of motoneurons, injuries, and species, but also displays many unique features in each particular case. These reactions have been amply studied, but there is still a lack of knowledge on their functional significance and mechanisms. In this review article, we compiled data from many different fields to generate a comprehensive conceptual framework to best interpret past data and spawn new hypotheses and research. We propose that synaptic plasticity around axotomized motoneurons should be divided into two distinct processes. First, a rapid cell-autonomous, microglia-independent shedding of synapses from motoneuron cell bodies and proximal dendrites that is reversible after muscle reinnervation. Second, a slower mechanism that is microglia-dependent and permanently alters spinal cord circuitry by fully eliminating from the ventral horn the axon collaterals of peripherally injured and regenerating sensory Ia afferent proprioceptors. This removes this input from cell bodies and throughout the dendritic tree of axotomized motoneurons as well as from many other spinal neurons, thus reconfiguring ventral horn motor circuitries to function after regeneration without direct sensory feedback from muscle. This process is modulated by injury severity, suggesting a correlation with poor regeneration specificity due to sensory and motor axons targeting errors in the periphery that likely render Ia afferent connectivity in the ventral horn nonadaptive. In contrast, reversible synaptic changes on the cell bodies occur only while motoneurons are regenerating. This cell-autonomous process displays unique features according to motoneuron type and modulation by local microglia and astrocytes and generally results in a transient reduction of fast synaptic activity that is probably replaced by embryonic-like slow GABA depolarizations, proposed to relate to regenerative mechanisms.

Chaperone Proteins in the Central Nervous System and Peripheral Nervous System after Nerve Injury

Injury to axons of the central nervous system (CNS) and the peripheral nervous system (PNS) is accompanied by the upregulation and downregulation of numerous molecules that are involved in mediating nerve repair, or in augmentation of the original damage. Promoting the functions of beneficial factors while reducing the properties of injurious agents determines whether regeneration and functional recovery ensues. A number of chaperone proteins display reduced or increased expression following CNS and PNS damage (crush, transection, contusion) where their roles have generally been found to be protective. For example, chaperones are involved in mediating survival of damaged neurons, promoting axon regeneration and remyelination and, improving behavioral outcomes. We review here the various chaperone proteins that are involved after nervous system axonal damage, the functions that they impact in the CNS and PNS, and the possible mechanisms by which they act.

Neural stem/progenitor cells transplanted to the hypoglossal nucleus integrates with the host CNS in adult rats and promotes motor neuron survival

Transplantation of neural stem cells and the mobilization of endogenous neuronal precursors in the adult brain have been proposed as therapeutic strategies for central nervous system disorders and injuries. The aim of the present study was to investigate the possible survival and integration of grafted neural progenitor cells (NPCs) from the subventricular zone (SVZ) in a hypoglossal nerve avulsion model with substantial neuronal loss. Adult neural progenitor cells (NPCs) from the subventricular zone (SVZ) were cultured from inbred transgenic eGFP Lewis rats and transplanted to the hypoglossal nucleus of inbred Lewis rat from the same family but that were not carrying the eGFP strain after avulsion of the hypoglossal nerve. Grafted cells survived in the host more than 3 months and differentiated into neurons [βIII tubulin (Tuj-1 staining)] with fine axon- and dendrite-like processes as well as astrocytes (GFAP) and oligodendrocytes (O4) with typical morphology. Staining for synaptic structures (synaptophysin and bassoon) indicated integration of differentiated cells from the graft with the host CNS. Furthermore, transplantation of NPCs increased the number of surviving motoneurons in the hypoglossal nucleus after nerve avulsion that, if untreated, result in substantial neuronal death. The NPCs used in this study expressed VEGF in vitro as well as in vivo following transplantation that may mediate the rescue effect of the axotomized motoneurons.

Quantitative iTRAQ analysis of retinal ganglion cell degeneration after optic nerve crush

Retinal ganglion cells (RGCs) are central nervous system (CNS) neurons that transmit visual information from the retina to the brain. Apoptotic RGC degeneration causes visual impairment that can be modeled by optic nerve crush. Neuronal apoptosis is also a salient feature of CNS trauma, ischemia (stroke), and diseases of the CNS such as Alzheimer's, Parkinson's, multiple sclerosis, and amyotrophic lateral sclerosis. Optic nerve crush induces the apoptotic cell death of ∼ 70% of RGCs within the first 14 days after injury. This model is particularly attractive for studying adult neuron apoptosis because the time-course of RGC death is well established and axon regeneration within the myelinated optic nerve can be concurrently evaluated. Here, we performed a large scale iTRAQ proteomic study to identify and quantify proteins of the rat retina at 1, 3, 4, 7, 14, and 21 days after optic nerve crush. In total, 337 proteins were identified, and 110 were differentially regulated after injury. Of these, 58 proteins were upregulated (>1.3 ×), 46 were downregulated (<0.7 ×), and 6 showed both positive and negative regulation over 21 days, relative to normal retinas. Among the differentially expressed proteins, Thymosin-β4 showed an early upregulation at 3 days, the time-point that immediately precedes the induction of RGC apoptosis after injury. We examined the effect of exogenous Thymosin-β4 administration on RGC death after optic nerve injury. Intraocular injections of Thymosin-β4 significantly increased RGC survival by ∼ 3-fold compared to controls and enhanced axon regeneration after crush, demonstrating therapeutic potential for CNS insults. Overall, our study identified numerous proteins that are differentially regulated at key time-points after optic nerve crush, and how the temporal profiles of their expression parallel RGC death. This data will aid in the future development of novel therapeutics to promote neuronal survival and regeneration in the adult CNS.

Genetic regulation of microglia activation, complement expression, and neurodegeneration in a rat model of traumatic brain injury

Secondary brain damage following traumatic brain injury in part depends on neuroinflammation, a process where genetic factors may play an important role. We examined the response to a standardized cortical contusion in two different inbred rat strains, Dark Agouti (DA) and Piebald Virol Glaxo (PVG). Both are well characterized in models of autoimmune neuroinflammation, where DA is susceptible and PVG resistant. We found that infiltration of polymorphonuclear granulocytes (PMN) at 3-day postinjury was more pronounced in PVG. DA was more infiltrated by T cells at 3-day postinjury, showed an enhanced glial activation at 7-day postinjury and higher expression of C3 complement at 7-day postinjury. Neurodegeneration, assessed by Fluoro-Jade, was also more pronounced in the DA strain at 30-day postinjury. These results demonstrate differences in the response to cortical contusion injury attributable to genetic influences and suggest a link between injury-induced inflammation and neurodegeneration. Genetic factors that regulate inflammation elicited by brain trauma may be important for the development of secondary brain damage.

Innate immunity in the nervous system

The complement (C) system plays a central role in innate immunity and bridges innate and adaptive immune responses. A fine balance of C activation and regulation mediates the elimination of invading pathogens and the protection of the host from excessive C deposition on healthy tissues. If this delicate balance is disrupted, the C system may cause injury and contribute to the pathogenesis of various diseases, including neurodegenerative disorders and neuropathies. Here we review evidence indicating that C factors and regulators are locally synthesized in the nervous system and we discuss the evidence supporting the protective or detrimental role of C activation in health, injury, and disease of the nerve.

Upregulation of complement inhibitors in association with vulnerable cells following contusion-induced spinal cord injury

We have previously described the activation of the classical, alternative, and terminal complement cascade pathways after acute contusion spinal cord injury using the New York University (NYU) weight-drop impactor. In the present study, we examined the induction of protein regulators of the complement cascade, factor H (FH), and clusterin, in the same experimental paradigm. The spinal cord of laminectomized adult rats was subjected to mild or severe injury using impactor weight-drop heights of 12.5 and 50 mm, respectively. The spinal cords of control and injured animals were evaluated at 1, 7, and 42 days after injury. Immunocytochemistry revealed a robust increase in the numbers and intensity of staining of FH, and clusterin-positive cells in the injured cord at all three time points, with the highest increases observed at 1 and 42 days after injury. FH and clusterin-positive cells were observed among neurons as well as oligodendrocytes. The increased expression was detected both rostrally and caudally from the injury site, in the latter case at distances up to 20 mm. The precise biological significance of injury-induced upregulation of these proteins remains to be determined. However, FH and clusterin are potent regulators of complement activity targeting upstream (FH) and downstream (clusterin) molecules of the pro-inflammatory cascade, which could be of vital importance in preventing a "runaway" inflammatory reaction in the injured spinal cord.

Adult motor neurons show increased susceptibility to axotomy-induced death in mice lacking clusterin

Clusterin is a highly conserved, amphiphatic glycoprotein present in most tissues. It has been shown to be involved in the regulation of lipid transportation, clearance of cellular debris from the extracellular space and intracellular signal transduction. Clusterin is markedly up-regulated after neural injury but the functional significance of this response is unclear. Here, we show that clusterin up-regulation is substantially greater in hypoglossal motor neurons after hypoglossal nerve avulsion compared with nerve transection. Quantitative analyses of motor neuron numbers after the same lesions in clusterin(-/-) and clusterin(+/+) mice showed significantly larger numbers of surviving motor neurons in clusterin(+/+) mice. These results suggest that clusterin has a neuroprotective role after axotomy.

Expression of clusterin in Müller cells of the rat retina after pressure-induced ischemia

We have investigated the expression and cellular localization of clusterin in the rat retina following ischemia induced by transiently increasing the intraocular pressure. In the normal retina, weak clusterin immunoreactivity was visible in Müller cell profiles located in the inner nuclear layer. Following ischemia and reperfusion, strong immunoreactivity appeared in Müller cell somata and processes up to 3 days postlesion. Quantitative evaluation by immunoblotting confirmed that clusterin expression continuously increased and showed a peak value at 3 days after ischemic injury (to 1300% of control levels), and then decreased again to 400% of controls at 4 weeks postlesion. Immunocytochemistry using antisera against clusterin or glutamine synthase combined with the TUNEL method or immunocytochemistry using antisera activated caspase 3 and electron microscopy revealed that some clusterin-labeled Müller cells underwent apoptotic cell death. Our findings demonstrate that some Müller cells die by apoptosis, and suggest that clusterin produced and released by Müller cell may play an important role in the pathogenesis of ischemic injury in the rat retina.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Complement Activation following Optic Nerve Crush in the Adult Rat

Activation of the complement cascade following peripheral nerve axotomy and following traumatic brain injury has been demonstrated in previous studies. This study investigates the temporal pattern of microglia/macrophages and complement activation following axotomy of sensory CNS neurons, using a standardized experimental crush injury of the optic nerve in adult rats. Numerous ED1-labeled macrophages were found at the lesion site and distal to the injury at 7 days post injury (dpi). Complement C3-mRNA was upregulated 2-28 days post lesion, indicating local synthesis of complement in the optic nerve. Furthermore, increased immunoreactivity (IR) for the end product of the complement cascade, the membrane attack complex (MAC), was detected along disintegrating axons co-labeled with anti-neurofilament distal to the injury. Double-labeling for microglia show MAC-immunoreactivity expressed in their immediate vicinity, indicating a key role of microglia/macrophages in complement activation. The complement regulator Clusterin was upregulated in astrocytes at the lesion site as well as in the distal portion of the injured optic nerve, suggesting activation of a defense response to endogenous complement attack. A crush injury of the optic nerve leads to complement activation at the site of lesion and along the distal portion of the nerve, as well as upregulation of the complement inhibitor Clusterin at least in astrocytes. Reactive microglial cells seem to have a key role in complement activation as a local source of C3. We suggest that the balance between complement activation and their regulators may have impact on axonal degeneration following optic nerve injury.

Neuroprotective action of melatonin on neonatal rat motoneurons after sciatic nerve transection

The neuronal isoform of nitric oxide synthase (nNOS), a NADPH-dependent diaphorase, is considered to play a role in motoneuron death induced by sciatic nerve transection in neonatal rats. Neuronal loss in these circumstances has been correlated with nitric oxide (NO) production and NADPH-diaphorase positivity in motoneurons after axotomy. In the present study we looked for a possible protective effect of melatonin, an antioxidant agent and inhibitor of nNOS, on spinal motoneurons after axonal injury. Neonatal Wistar rats (P2) were submitted to sciatic nerve transection and allowed to survive to P7. Melatonin at doses of 1, 5, 10, 50 and 100 mg/kg was given subcutaneously before and at intervals after the surgery. Controls operated in the same way received dilution vehicle or no treatment. The animals were killed by perfusion of fixative and the spinal cord was examined in serial paraffin sections. The motoneurons of the sciatic pool were counted in the axotomized and contralateral sides. Immunohistochemistry for nNOS and glial fibrillary acidic protein was used to evaluate nNOS expression in the axotomized cells and the astrocytic response. We found that melatonin at doses of 1-50 mg/kg decreased neuronal death. Astrocytic hypertrophy in melatonin treated animals was less intense. There were no differences in nNOS expression between treated and control rats, and surviving motoneurons of the sciatic pool did not express the enzyme, suggesting that nNOS may not be involved in neuronal death or survival in these experimental conditions. Possible mechanisms of melatonin neuroprotection, which was equally effective at doses of 1-50 mg/kg, are discussed. Doses of 50 and 100 mg/kg caused failure to thrive, seizures or death. The fact that neuroprotective doses were far smaller than toxic ones should encourage testing of melatonin in neurologic diseases.

Complement activation in the human brain after traumatic head injury

The complement cascade has been suggested to be involved in the development of secondary brain injuries following brain contusions, based on animal experiments. The aim of the present study was to examine the possible involvement of the complement cascade following traumatic head injury in the human brain. Sixteen patients were included in this study, 12-77 years of age, treated at the neurointensive care unit for traumatic brain contusions. All of these patients were operated with frontal or temporal lobe resection due to intractable intracranial hypertension. The resected tissue was analyzed with regard to components related to complement activation. The time interval between accident and operation was 2-82 h. Brain tissue from three patients operated with hippocampectomy due to epilepsy, including temporal lobe resection, were used as controls. We found increased immunoreactivity for complement components C1q, C3b, and C3d and the membrane attack complex (MAC), C5b-9, in the immediate vicinity of neurons in the penumbra area of the contusion. These findings constitute histological evidence for activation of the complement cascade in the penumbra of cortical contusions in the human brain. Using in situ hybridization, we also found C3-mRNA in the penumbra, suggesting a local synthesis of complement. Furthermore, upregulation of the endogenous complement regulator clusterin was found in some neurons in the same area. We suggest that unknown compounds in the debris from injured neurons or myelin breakdown products trigger complement activation, including formation of C5b-9. Activated complement components may stimulate accumulation of inflammatory cells and formation of brain edema, as well as having membrane destructive effects by the end product MAC, thereby being mediators in the development of secondary brain damage.

Exposure to short-lasting impulse noise causes microglial and astroglial cell activation in the adult rat brain

Exposure to impulse noise, i.e. pressure waves, is above a certain intensity, harmful to auditory function. Intense, short-lasting impulse noise of 198 or 202 dB affects the heavy subunit of neurofilament proteins in neuronal perikarya of the cerebral cortex and hippocampus. There was as well an increased expression of immediate early gene products and induction of neuronal apoptosis. Here, we show that this range of exposure also affects glial cells. We identified microglial cells with an antibody against the complement receptor type 3 (OX-42) and astrocytes with an antibody against the glial fibrillary acidic protein (GFAP). The pattern of damage included microglial activation as early as 2 h after exposure to 202 dB. The activation increased further at 18 h. There was a significant increase of the area occupied by microglial cells in the anterior and posterior hypothalamus and in the lateral septal nucleus. Astrogliosis was observed in the cerebral cortex, the dentate gyrus and in the pyramidal cell layers as well as in white matter of the hippocampus. Both the microglial and astrocytic reactivities remained at 21 days. Exposure to 198 dB, caused similar, but less prominent activation in both cell types.

Immunopathology of secondary-progressive multiple sclerosis

Twenty-three plaques obtained at early autopsy from 2 patients with secondary-progressive multiple sclerosis were examined immunohistochemically for microglia/macrophages, and for immunoglobulins and components of activated complement. Most of the lesions examined in both cases exhibited evidence of low-grade active demyelination of an unusual type (frustrated phagocytosis) in periplaque white matter. This included linear groups of microglia engaging short segments of disrupted myelin that were associated with deposits of C3d, an opsonin formed during complement activation. Similar microglia/C3d/myelin profiles were not observed in newly forming lesions in cases of acute multiple sclerosis or other central white matter diseases. As C3d coupling is known to increase the immunogenicity of potential antigens enormously, present findings point to disrupted myelin close to plaques as a possible source of the putative multiple sclerosis antigen. Ongoing myelin destruction found in a high proportion of old, established plaques was surprising. It suggests that slowly expanding lesions (progressive plaques), in which ongoing myelin breakdown occurs in the absence of florid perivascular cell cuffing or other histological signs of acute inflammation, contribute to disease progression in cases of secondary-progressive multiple sclerosis.

Microglial activation, emergence of ED1-expressing cells and clusterin upregulation in the aging rat CNS, with special reference to the spinal cord

With advancing age, the incidence of neuronal atrophy and dystrophy increases and, in parallel, behavioural sensorimotor impairment becomes overt. Activated microglia has been implicated in cytotoxic and inflammatory processes in neurodegenerative diseases as well as during aging. Here we have used immunohistochemistry and in situ hybridization to examine the expression of OX42, ED1, ED2, GFAP and clusterin in CNS of young adult and behaviourally tested aged rats (30-month-old), to study the occurrence of activated microglia/ED1 positive macrophages in senescence and to what extent this correlates with astrogliosis and signs of sensorimotor impairment among the individuals. The results show a massive region-specific increase in activated microglia and ED1 expressing cell profiles in aged rats. The infiltration was most prominent in the spinal cord dorsal columns, including their sensory relay nuclei, and the outer portions of the lateral and ventral columns. At such sites the occurrence of macrophages coincided with increased levels of GFAP and positive correlations were evident between the labeling for, on the one hand, OX42 and, on the other, GFAP and ED1. Also, the ventral and dorsal roots were heavily infiltrated by ED1 positive cells. The signs of gliosis were most pronounced among aged rats with advanced sensorimotor impairment. In contrast, the grey matter of aged rats showed very few activated microglia/ED1 labeled cells despite signs of focal astrogliosis. ED2 expression was confined to perivascular cells and leptominges with a similar labeling pattern in young and aged rats. In aged rats increased expression of clusterin was observed in GFAP-immunoreactive profiles of the white matter only. It is suggested that this increase may reflect a response to degenerative/inflammatory processes.

Calreticulin binding and other biological activities of survival peptide Y-P30 including effects of systemic treatment of rats

Neuron survival-promoting peptide Y-P30, purified from oxidatively stressed neural cell lines, inhibits the appearance of microglia and rescues neurons 1 week after direct application to lesions of the rat cerebral cortex (7). Y-P30 affinity matrices treated with solubilized membranes from a variety of cell lines including human neuroblastoma SY5Y, mouse hippocampal cells HN 33.1, and human promonocytes HL-60, as well as with cerebral cortex tissue from both humans and rats, showed highly specific binding to calreticulin, a ubiquitous calcium binding protein that may be critical for integrin function. Treatment of cultures with 0.1 nM Y-P30 stabilized all these cell types whether differentiated or not, while 1 microM peptide also inhibited the morphological differentiation of the HL-60 cells into macrophages. Western analysis of the medium of SY5Y cell cultures suggested Y-P30-stimulated release of calreticulin, a result consistent with its other biological activities. Likewise, single dose systemic application of Y-P30 in unoperated rats and in rats with cerebral cortex lesions produced significant reductions in cerebral cortex membrane-associated calreticulin. Both direct and intravenous treatment with peptide also reduced cortical neuron atrophy 4 days after these lesions but only direct application consistently inhibited the appearance of ED-1(+) monocyte derivatives. We suggest that in vitro and in vivo mechanisms of Y-P30 effects are similar and involve the targeting of calreticulin. The results also suggest that some of these activities are apparent in the cerebral cortex after systemic application of this peptide.

Complement C1q is dramatically up-regulated in brain microglia in response to transient global cerebral ischemia

Recent evidence suggests that the pathophysiology of neurodegenerative and inflammatory neurological diseases has a neuroimmunological component involving complement, an innate humoral immune defense system. The present study demonstrates the effects of experimentally induced global ischemia on the biosynthesis of C1q, the recognition subcomponent of the classical complement activation pathway, in the CNS. Using semiquantitative in situ hybridization, immunohistochemistry, and confocal laser scanning microscopy, a dramatic and widespread increase of C1q biosynthesis in rat brain microglia (but not in astrocytes or neurons) within 24 h after the ischemic insult was observed. A marked increase of C1q functional activity in cerebrospinal fluid taken 1, 24, and 72 h after the ischemic insult was determined by C1q-dependent hemolytic assay. In the light of the well-established role of complement and complement activation products in the initiation and maintenance of inflammation, the ischemia-induced increase of cerebral C1q biosynthesis and of C1q functional activity in the cerebrospinal fluid implies that the proinflammatory activities of locally produced complement are likely to contribute to the pathophysiology of cerebral ischemia. Pharmacological modulation of complement activation in the brain may be a therapeutic target in the treatment of stroke.

Increased complement biosynthesis by microglia and complement activation on neurons in Huntington's disease

In this study complement activation and biosynthesis have been analysed in the brains of Huntington's disease (HD) (n = 9) and normal (n = 3) individuals. In HD striatum, neurons, myelin and astrocytes were strongly stained with antibodies to C1q, C4, C3, iC3b-neoepitope and C9-neoepitope. In contrast, no staining for complement components was found in the normal striatum. Marked astrogliosis and microgliosis were observed in all HD caudate and the internal capsule samples but not in normal brain. RT-PCR analysis and in-situ hybridisation were carried out to determine whether complement was synthesised locally by activated glial cells. By RT-PCR, we found that complement activators of the classical pathway C1q C chain, C1r, C4, C3, as well as the complement regulators, C1 inhibitor, clusterin, MCP, DAF, CD59, were all expressed constitutively and at much higher level in HD brains compared to normal brain. Complement anaphylatoxin receptor mRNAs (C5a receptor and C3a receptor) were strongly expressed in HD caudate. In general, we found that the level of complement mRNA in normal control brains was from 2 to 5 fold lower compared to HD striatum. Using in-situ hybridisation, we confirmed that C3 mRNA and C9 mRNA were expressed by reactive microglia in HD internal capsule. We propose that complement produced locally by reactive microglia is activated on the membranes of neurons, contributing to neuronal necrosis but also to proinflammatory activities. Complement opsonins (iC3b) and anaphylatoxins (C3a, C5a) may be involved in the recruitment and stimulation of glial cells and phagocytes bearing specific complement receptors.

Clusterin upregulation following rubrospinal tract lesion in the adult rat

We have examined the expression of the multifunctional protein clusterin in the axotomized red nucleus, at the lesion site in the lateral funiculus of C3, as well as along the Wallerian degeneration in the lateral funiculus of T1. There was a marked increase in clusterin-immunoreactivity (IR) and clusterin mRNA in red nucleus nerve cell bodies. An early, transient occurrence of large, heavily clusterin-IR globules were found in axons in the spinal cord at the lesion site in C3 as well as a marked upregulation of mRNA for clusterin, presumably associated with reactive astrocytes and oligodendrocytes from 1 to 4 weeks postoperatively. Clusterin-IR and its mRNA were markedly increased in the zone of Wallerian degeneration at T1, where some strongly expressing cells were identified as oligodendrocytes. Taken together with previous changes in clusterin expression following peripheral nerve and dorsal root injury, we suggest that this protein is involved in regenerative as well as degenerative neural responses.

Inflammatory pathogenesis in Alzheimer's disease: biological mechanisms and cognitive sequeli

Experimental evidence from molecular biology, biochemistry, epidemiology and behavioral research support the conclusion that brain inflammation contributes to the pathogenesis of Alzheimer's disease and other types of human dementias. Aspects of neuroimmunology relating to the pathogenesis of Alzheimer's disease are briefly reviewed. The effects of brain inflammation, mediated through cytokines and other secretory products of activated glial cells, on neurotransmission (specifically, nitric oxide, glutamate, and acetylcholine), amyloidogenesis, proteolysis, and oxidative stress are discussed within the context of the pathogenesis of learning and memory dysfunction in Alzheimer's disease. Alzheimer's disease is proposed to be an etiologically heterogeneous syndrome with the common elements of amyloid deposition and inflammatory neuronal damage.

Nimodipine-induced improved survival rate of facial motor neurons following intracranial transection of the facial nerve in the adult rat

OBJECT

Neuronal survival is an important factor in the achievement of functional restitution after peripheral nerve injuries. Intracranial tumors or trauma may cause patients to exhibit a temporary or permanent facial nerve palsy. Nimodipine, which acts as an antagonist to L-type voltage-gated calcium channels, has been shown to be neuroprotective in various lesion models of the central and peripheral nervous systems. The aim of the present study was to evaluate the effect of nimodipine on motor neuron survival in the facial motor nucleus following intracranial transection of the adult rat facial nerve.

METHODS

The facial nerve was cut intracranially in the posterior cranial fossa. Nimodipine was administered orally preoperatively for 3 days and postoperatively for up to 1 month, after which the number of neuronal profiles was quantified. The glial reaction was studied in the facial nucleus for up to 1 month by using immunocytochemical analysis. There was a significantly larger proportion of surviving motor neurons 1 month postinjury in animals treated with nimodipine (61+/-6.7%) in comparison with untreated animals (26.8+/-11.3%). Immunocytochemical analysis showed an increase in the amount of OX42 (microglia), ED1 (macrophages), and anti-glial fibrillary acidic protein (astrocytes) ipsilateral to the nerve injury; however, there was no difference between the two experimental groups of animals 2 to 28 days after surgery.

CONCLUSIONS

The authors propose a neuroprotective role for nimodipine, which may be useful as a "cranial nerve protective agent" following insults such as head injury or skull base surgery.

Expressed-sequence-tag approach to identify differentially expressed genes following peripheral nerve axotomy

Gene expression profiles in the rat hypoglossal nucleus after axotomy were demonstrated using expressed-sequence-tag (EST) approach. To demonstrate the gene-expression profiles after axotomy, nerve-transected hypoglossal nuclei were dissected and collected from about 1000 rats, with which a cDNA library was constructed. More than 750 clones were sub-cloned and sequenced from the library. The clones which hit frequently are likely to be associated with mitochondrial respiratory chain, cytoskeletal protein and protein synthesis. One hundred three clones from among the sequenced clones were further processed for histological screening using unilateral-hypoglossal nerve-transected brain sections by in situ hybridization histochemistry. In situ hybridization study revealed that 26% of clones examined showed upregulated expression of mRNA in response to axotomy. They included genes encoding proteins associated with glucose, lipid and protein metabolism, cytoskeleton, neurotransmission and immune reaction. The present EST analysis may have an advantage in targeting genes which are associated with nerve injury with a good efficacy, as compared with other methods such as differential display and subtraction.

Complement activation and CD59 expression in the motor facial nucleus following intracranial transection of the facial nerve in the adult rat

Intracranial transection of the facial nerve has been shown to cause a massive neuronal cell death in the motor facial nucleus. Complement activation has been proposed to contribute to neuronal degeneration following axotomy. Using immunocytochemistry and in situ hybridization we show in the present study that there is complement activation in the facial nucleus after intracranial facial nerve transection as well as increase of the complement regulators CD59 and clusterin. We propose a neuroprotective role for the complement regulators CD59 and clusterin against homologous attack of complement to facial motor neurons.

Central neuron-glial and glial-glial interactions following axon injury

Axon injury rapidly activates microglial and astroglial cells close to the axotomized neurons. Following motor axon injury, astrocytes upregulate within hour(s) the gap junction protein connexin-43, and within one day glial fibrillary acidic protein (GFAP). Concomitantly, microglial cells proliferate and migrate towards the axotomized neuron perikarya. Analogous responses occur in central termination territories of peripherally injured sensory ganglion cells. The activated microglia express a number of inflammatory and immune mediators. When neuron degeneration occurs, microglia act as phagocytes. This is uncommon after peripheral nerve injury in the adult mammal, however, and the functional implications of the glial cell responses in this situation are unclear. When central axons are injured, the glial cell responses around the affected neuron perikarya appears to be minimal or absent, unless neuron degeneration occurs. Microglia proliferate, and astrocytes upregulate GFAP along central axons undergoing anterograde, Wallerian, degeneration. Although microglia develop into phagocytes, they eliminate the disintegrating myelin very slowly, presumably because they fail to release molecules which facilitate phagocytosis. During later stages of Wallerian degeneration, oligodendrocytes express clusterin, a glycoprotein implicated in several conditions of cell degeneration. A hypothetical scheme for glial cell activation following axon injury is discussed, implying the injured neurons initially interact with adjacent astrocytes. Subsequently, neighbouring resting microglia are activated. These glial reactions are amplified by paracrine and autocrine mechanisms, in which cytokines appear to be important mediators. The specific functional properties of the activated glial cells will determine their influence on neuronal survival, axon regeneration, and synaptic plasticity. The control of the induction and progression of these responses are therefore likely to be critical for the outcome of, for example, neurotrauma, brain ischemia and chronic neurodegenerative diseases.

Increased expression of peripheral benzodiazepine receptors in the facial nucleus following motor neuron axotomy

Peripheral benzodiazepine receptors (PBRs) are expressed in a variety of tissues but are normally found at low levels in the brain. Following various types of nerve injury, a reactive gliosis results that exhibits a high expression of this receptor. To further characterize the expression of PBRs following neuronal injury, we evaluated PBR expression in the facial nucleus following facial nerve axotomy (FNA). Injury to a peripheral nerve results in a complex series of metabolic and morphological changes around the injured neuron. Transections of the facial nerve results in a rapid activation of both astrocytes and microglia around axotomized motor neurons. FNA resulted in an increase in the staining for both astrocytes (glial fibrillary acidic protein) and activated microglia (OX42). There was also a reduction in synaptic contacts with the motor nucleus as evidenced by reduced staining for the synaptic marker, synaptophysin. In sections labeled with [3H]-PK11195, the subsequent autoradiograms displayed marked increases in the labeling for PBRs. This increase was observed at 5, 7 and 10 days after nerve transection. The increase was primarily in the level of expression (Bmax), with no change in the affinity of the ligand (Kd). The increase in PBR expression after FNA supports the hypothesis that PBRs can be used as a sensitive marker for CNS injury.

Response of glial cells and activation of complement following motorneuron degeneration induced by toxic ricin

Motor nerve transection in adult rats induce a series of metabolic and structural changes in the injured neurons as well as in surrounding glial cells; however, without substantial neuronal degeneration. In the present study we found, in contrast with axotomy, a massive neuronal death in the ipsilateral hypoglossal nucleus following injection of toxic ricin (RCA) into the hypoglossal nerve, which is in line with previous observations. Injection of RCA enables examination of the glial reaction in a situation where neuronal degeneration is profound, which has been the approach in the present study. We found an increase in OX42-, GFAP-, and transferrin-immunoreactivity in microglial, astroglial, and oligodendroglial cells respectively, in the ipsilateral hypoglossal nucleus three to seven days following injection of toxic ricin in the hypoglossal nerve. Proliferation was found in astrocytes as well as in microglial cells, as shown by uptake of bromodeoxyuridine. In addition, the complement cascade was activated locally in the ipsilateral hypoglossal nucleus, as demonstrated by immunohistochemical detection of complement components C3d and C9. Complement activation may serve several effects in the glial-neuronal interactions. Stimulation of phagocytosis by reactive microglia is probably the most important one. Furthermore, the degenerative neuronal somata showed increased immunoreactivity for clusterin, which is a known complement inhibitor, but a decrease in clusterin-mRNA. In conclusion, the glial cell response was in several aspects principally different following massive motorneuron degeneration induced by toxic ricin in comparison to previous findings reported after axotomy.

Complement and clusterin in the injured nervous system

Peripheral nerve injury and neuronal degeneration resulting from toxic ricin induce activation of the classical pathway of complement close to the injured motorneuron perikarya or sensory terminals. In contrast, degeneration of central myelinated fibers is not accompanied by complement expression. The main source of complement in peripheral nerve injury and toxic ricin degeneration appears to be microglia. Brain contusion is associated with complement activation. Some of the complement in this situation may derive from plasma, because the blood-brain barrier is disrupted. Clusterin expression is increased in astrocytes along with their activation in the vicinity of lesioned neurons. In addition, axotomized motorneurons show a marked clusterin upregulation. A relationship between clusterin and cell death is suggested by the prominent aggregation of clusterin in neuronal perikarya destroyed by the effects of toxic ricin, as well as by the neosynthesis of clusterin in apparently degenerating nonneuronal cells, presumed to be oligodendrocytes. Our findings indicate that the expression of complement and clusterin are prominent features of neural degeneration and regeneration, as it is in Alzheimer's disease brains as well. The nerve injury conditions described, therefore, offer attractive experimental models to elucidate the roles of these molecular components in neurodegenerative disorders, thereby providing useful insights into potentially new therapeutic approaches in these conditions.

Activation of the complement cascade and increase of clusterin in the brain following a cortical contusion in the adult rat

The aim of the present study was to examine the glial cell response and the possible involvement of the complement cascade following a cerebral cortical contusion. The lesion was produced using a standardized weight-drop technique in adult rats. The blood-brain barrier was damaged, as demonstrated by a decrease of immunoreactivity for a tight junction protein normally expressed by endothelial cells of small vessels in the central nervous system. Increased immunoreactivity for microglial (OX42) and astroglial cells (glial fibrillary acidic protein), as well as macrophages expressing ED1-immunoreactivity (IR) were found in the vicinity of the lesion at all postoperative survival times (2-14 days). In the present study complement factor C3d- and C9-IR was found around the lesion, indicating that activation of the complement cascade had taken place. Furthermore, immunoreactivity for the putative complement inhibitor clusterin (sulfated glycoprotein-2) was found in some of the injured neurons. The contralateral hemisphere showed no evidence of the reaction found in the ipsilateral hemisphere. The balance between complement activation and complement inhibitors may have an impact on the degenerative components in the brain following traumatic injury and in particular on the events leading to nerve cell death.

Inflammatory mechanisms in neurodegeneration and Alzheimer's disease: the role of the complement system

This review discusses key findings indicating potential roles of the complement (C)-system in chronic inflammation in Alzheimer's disease (AD) brain. Although there is no means to cure or prevent the disease, recent studies suggest that antiinflammatory drugs may delay the onset of AD dementia. One target of these drugs may be the (C)-system, which is best known for its roles in inflammatory processes in peripheral tissues. However, recent data show C-system expression and regulation in brain cells, and C-system protein deposition in AD plaques. It is still nuclear whether C-system activation contributes to neuropathology in the AD brain, as shown in multiple sclerosis (MS). New clinical studies with antiinflammatory agents are now under general consideration by the Alzheimer's Disease Cooperative Study program. In this review I outline research directions which address possible C-system contributions to neurodegeneration. Finally, I discuss potential pharmacological interventions designed to control segments of classical inflammatory cascades in which the C-system is highly implicated. These aspects are critical to the understanding of C-mediated responses in normal and pathologic brain.

Complement and clusterin in the spinal cord dorsal horn and gracile nucleus following sciatic nerve injury in the adult rat

We provide evidence for activation of the complement cascade in the dorsal horn of the spinal cord and in the gracile nucleus in the brainstem following sciatic nerve transection in the adult rat. Immunocytochemical analyses showed immunoreactivity for endogenous immunoglobulin G as shown by immunostaining with F(ab')2 antibodies, as well as complement factors C1, C1q, C3, C3d and C9 in the appropriate central termination areas of the injured sciatic nerve. Results from double labelling immunocytochemistry showed a strong association between immunoglobulin and complement factors on the one hand and reactive microglia on the other. However, some complement immunoreactivity was also found in the neuropil, possibly representing secreted complement. In situ hybridization with an oligonucleotide probe showed a marked increase in C3 messenger RNA, indicating local synthesis of C3 protein. In parallel with activation of complement, there was an increased immunoreactivity for the putative complement inhibitor clusterin, which co-localized with glial fibrillary acidic protein-positive astrocytes. In situ hybridization showed an increased labelling of clusterin messenger RNA. These findings indicate that complement activation and up-regulation of complement inhibitors are prominent central responses to peripheral sensory nerve injury. These responses may therefore be important elements underlying so-called transganglionic degenerative changes in primary sensory axons and terminals.