COX-2 regulation and TUNEL-positive cell death differ between genders in the secondary inflammatory response following experimental penetrating focal brain injury in rats.

INTRODUCTION: Traumatic brain injury is followed by secondary neuronal degeneration, largely dependent on an inflammatory response. This response is probably gender specific, since females are better protected than males in experimental models. The reasons are not fully known. We examined aspects of the inflammatory response following experimental TBI in male and female rats to explore possible gender differences at 24 h and 72 h after trauma, times of peak histological inflammation and neuronal degeneration. METHODS: A penetrating brain injury model was used to produce penetrating focal TBI in 20 Sprague-Dawley rats, 5 males and 5 females for each time point. After 24 and 72 h the brains were removed and subjected to in situ hybridization and immunohistochemical analyses for COX-2, iNOS, osteopontin, glial fibrillary acidic protein, 3-nitrotyrosine, TUNEL and Fluoro-Jade. RESULTS: COX-2 mRNA and protein levels were increased in the perilesional area compared to the uninjured contralateral side and significantly higher in males at 24 h and 72 h (p < 0.05). iNOS mRNA was significantly increased in females at 24 h (p < 0.05) although protein was not. TUNEL was increased in male rats after 24 h (p < 0.05). Glial fibrillary acidic protein, osteopontin, 3-nitrotyrosine and Fluoro-Jade stained degenerating neurons were increased in the perilesional area, showing no difference between genders. CONCLUSIONS: COX-2 regulation differed between genders after TBI. The increased COX-2 expression in male rats correlated with increased apoptotic cell death detected by increased TUNEL staining at 24 h, but not with neuronal necrosis measured by Flouro-Jade. Astrogliosis and microgliosis did not differ, confirming a comparable level of trauma. The gender-specific trait of the secondary inflammatory response may be connected to prostaglandin regulation, which may partially explain gender variances in outcome after TBI.

Neuronal myosin-X is upregulated after peripheral nerve injury and mediates laminin-induced growth of neurites.

The successful outcome of peripheral neuronal regeneration is attributed both to the growth permissive milieu and the intrinsic ability of the neuron to initiate appropriate cellular responses such as changes in gene expression and cytoskeletal rearrangements. Even though numerous studies have shown the importance of interactions between the neuron and the extracellular matrix (ECM) in axonal outgrowth, the molecular mechanisms underlying the contact between ECM receptors and the cellular cytoskeleton remain largely unknown. Unconventional myosins constitute an important group of cytoskeletal-associated motor proteins. One member of this family is the recently described myosin-X. This protein interacts with several members of the axon growth-associated ECM receptor family of integrins and could therefore be important in neuronal outgrowth. In this study, using radioactive in situ hybridization, we found that expression of myosin-X mRNA is upregulated in adult rat sensory neurons and spinal motoneurons after peripheral nerve injury, but not after central injury. Thus, myosin-X was upregulated after injuries that can be followed by axonal regeneration. We also found that the protein is localized to neuronal growth cones and that silencing of myosin-X using RNA interference impairs the integrin-mediated growth of neurites on laminin, but has no effect on non-integrin mediated growth on N-cadherin.

Shock wave trauma leads to inflammatory response and morphological activation in macrophage cell lines, but does not induce iNOS or NO synthesis.

BACKGROUND: Experimental CNS trauma results in post-traumatic inflammation for which microglia and macrophages are vital. Experimental brain contusion entails iNOS synthesis and formation of free radicals, NO and peroxynitrite. Shock wave trauma can be used as a model of high-energy trauma in cell culture. It is known that shock wave trauma causes sub-lytic injury and inflammatory activation in endothelial cells. Mechanical disruption of red blood cells can induce iNOS synthesis in experimental systems. However, it is not known whether trauma can induce activation and iNOS synthesis in inflammatory cell lines with microglial or macrophage lineage. We studied the response and activation in two macrophage cell lines and the consequence for iNOS and NO formation after shock wave trauma. METHODS: Two macrophage cell lines from rat (NR8383) and mouse (RAW264.7) were exposed to shock wave trauma by the Flyer Plate method. The cellular response was investigated by Affymetrix gene arrays. Cell survival and morphological activation was monitored for 24 h in a Cell-IQ live cell imaging system. iNOS induction and NO synthesis were analyzed by Western blot, in cell Western IR-immunofluorescence, and Griess nitrite assay. RESULTS: Morphological signs of activation were detected in both macrophage cell lines. The activation of RAW264.7 was statistically significant (p < 0.05), but activation of NR8383 did not pass the threshold of statistical significance alpha (p > 0.05). The growth rate of idle cells was unaffected and growth arrest was not seen. Trauma did not result in iNOS synthesis or NO induction. Gene array analyses showed high enrichment for inflammatory response, G-protein coupled signaling, detection of stimulus and chemotaxis. Shock wave trauma combined with low LPS stimulation instead led to high enrichment in apoptosis, IL-8 signaling, mitosis and DNA-related activities. LPS/IFN-É£ stimulation caused iNOS and NO induction and morphological activation in both cell lines. CONCLUSIONS: Shock wave trauma by the Flyer Plate method caused an inflammatory response and morphological signs of activation in two macrophage cell lines, while iNOS induction appeared to require humoral signaling by LPS/IFN-É£. Our findings indicated that direct energy transfer by trauma can activate macrophages directly without humoral mediators, which comprises a novel activation mechanism of macrophages.

The loop diuretic bumetanide blocks posttraumatic p75NTR upregulation and rescues injured neurons.

Injured neurons become dependent on trophic factors for survival. However, application of trophic factors to the site of injury is technically extremely challenging. Novel approaches are needed to circumvent this problem. Here, we unravel the mechanism of the emergence of dependency of injured neurons on brain-derived neurotrophic factor (BDNF) for survival. Based on this mechanism, we propose the use of the diuretic bumetanide to prevent the requirement for BDNF and consequent neuronal death in the injured areas. Responses to the neurotransmitter GABA change from hyperpolarizing in intact neurons to depolarizing in injured neurons. We show in vivo in rats and ex vivo in mouse organotypic slice cultures that posttraumatic GABA(A)-mediated depolarization is a cause for the well known phenomenon of pathological upregulation of pan-neurotrophin receptor p75(NTR). The increase in intracellular Ca(2+) triggered by GABA-mediated depolarization activates ROCK (Rho kinase), which in turn leads to the upregulation of p75(NTR). We further show that high levels of p75(NTR) and its interaction with sortilin and proNGF set the dependency on BDNF for survival. Thus, application of bumetanide prevents p75(NTR) upregulation and neuronal death in the injured areas with reduced levels of endogenous BDNF.

Classical major histocompatibility complex class I molecules in motoneurons: new actors at the neuromuscular junction.

Major histocompatibility complex (MHC) class I molecules have fundamental functions in the immune system. Recent studies have suggested that these molecules may also have non-immune functions in the nervous system, in particular related to synaptic function and plasticity. Because adult motoneurons express mRNAs for MHC class I molecules, we have examined their subcellular expression pattern in vivo and their role for the synaptic connectivity of these neurons. We observed immunoreactivity for classical MHC class I (Ia) protein in motoneuron somata, but the predominant expression was found in axons and presynaptically at neuromuscular junctions (NMJs). Peripheral nerve lesion induced a strong increase of motoneuron MHC class Ia (H2-K(b)/D(b)) mRNA, indicating a role for MHC class Ia molecules during regeneration. Accordingly, there was an accumulation of MHC class Ia proteins at the cut ends and in growth cones of motor axons after lesion. In K(b-/-)D(b-/-) mice (lacking MHC class Ia molecules), the time course for recovery of grip ability in reinnervated muscles was significantly delayed. Muscles from K(b-/-)D(b-/-) mice displayed an increased density and a disturbed distribution of NMJs and fewer terminal Schwann cells/NMJ compared with wild-type mice. A population of Schwann cells in sciatic nerves expressed the paired Ig receptor B, which binds to MHC class I molecules. These results provide the first evidence that neuronal MHC class Ia molecules are present in motor axons, that they are important for organization of NMJs and motor recovery after nerve lesion, and that their actions may be mediated via Schwann cells.

Altered expression of nectin-like adhesion molecules in the peripheral nerve after sciatic nerve transection.

Following axotomy several processes involving cell-cell interaction occur, such as loss of synapses, axon guidance, and remyelination. Two recently discovered families of cell-cell adhesion molecules, nectins and nectin-like molecules (necls) are involved in such processes in vitro and during development, but their roles in nerve injury have been largely unknown until recently. We have previously shown that axotomized motoneurons increase their expression of nectin-1 and nectin-3 and maintain a high expression of necl-1. We here investigate the expression of potential binding partners for motoneuron nectins and necls in the injured peripheral nerve. In situ hybridization (ISH) revealed a decreased signal for necl-1 mRNA in the injured nerve, whereas no signal for necl-2 was detected before or after injury. The signals for necl-4 and necl-5 mRNA both increased in the injured nerve and necl immunoreactivity displayed a close relation to axon and Schwann cell markers. Finally, signal for mRNA encoding necl-5 increased in axotomized spinal motoneurons. We conclude that peripheral axotomy results in altered expression of several necls in motoneurons and Schwann cells, suggesting involvement of the molecules in regeneration.

Integrin-laminin interactions controlling neurite outgrowth from adult DRG neurons in vitro.

A prerequisite for axon regeneration is the interaction between the growth cone and the extracellular matrix (ECM). Laminins are prominent constituents of ECM throughout the body, known to support axon growth in vitro and in vivo. The regenerative capacity of adult neurons is greatly diminished compared to embryonic or early postnatal neurons. Since most lesions in the nervous system occur in the adult, we have examined neurite outgrowth from adult mouse DRG neurons on four laminin isoforms (laminin-1/LM-111, laminin-2/LM-211, laminin-8/LM-411 and laminin-10/LM-511) in vitro. The growth on laminin-1 and -10 was trophic factor-independent and superior to the one on laminin-2 and -8, where growth was very poor in the absence of neurotrophins. Among other ECM proteins, laminins were by far the most active molecules. Using function-blocking antibodies to laminin-binding integrins, we identified non-overlapping functions of integrins alpha3beta1, alpha7beta1 and alpha6beta1 on different laminin isoforms, in that alpha3beta1 and alpha7beta1 integrins appeared to be specific receptors for both laminin-1 and-2, whereas integrin alpha6beta1 was a receptor for laminin-8 and-10. Lastly, by use of immunohistochemistry, expression of subunits of laminin-1, -2, -8 and -10 in sensory organs in the human epidermis could be demonstrated, supporting an important role for these laminins in relation to primary sensory axons.

Impeded interaction between Schwann cells and axons in the absence of laminin alpha4.

The Schwann cell basal lamina (BL) is required for normal myelination. Loss or mutations of BL constituents, such as laminin-2 (alpha2beta1gamma1), lead to severe neuropathic diseases affecting peripheral nerves. The function of the second known laminin present in Schwann cell BL, laminin-8 (alpha4beta1gamma1), is so far unknown. Here we show that absence of the laminin alpha4 chain, which distinguishes laminin-8 from laminin-2, leads to a disturbance in radial sorting, impaired myelination, and signs of ataxia and proprioceptive disturbances, whereas the axonal regenerative capacity is not influenced. In vitro studies show poor axon growth of spinal motoneurons on laminin-8, whereas it is extensive on laminin-2. Schwann cells, however, extend longer processes on laminin-8 than on laminin-2, and, in contrast to the interaction with laminin-2, solely use the integrin receptor alpha6beta1 in their interaction with laminin-8. Thus, laminin-2 and laminin-8 have different critical functions in peripheral nerves, mediated by different integrin receptors.

Integrin messenger RNAs in the red nucleus after axotomy and neurotrophic administration.

Integrins are cell surface receptors known to be important for regeneration in the peripheral nervous system. We have investigated the expression of integrin messenger RNAs in red nucleus neurons of adult rats after axotomy and administration of neurotrophic factors. Using radioactive in situ hybridization, messenger RNA for integrin subunits beta1, alpha3, alpha7 and alphaV could be detected. No change of any alpha subunit could be detected after axotomy. In contrast, a small upregulation of beta1 was detected after lesion. Administration of neurotrophin-3 induced a robust further increase in beta1 messenger RNA levels, whereas brain-derived neurotrophic factor did not. By analogy to the peripheral nervous system, we propose that integrins may be important for a regenerative response in central nervous system neurons.

The Temporal Pattern of Changes in Serum Biomarker Levels Reveals Complex and Dynamically Changing Pathologies after Exposure to a Single Low-Intensity Blast in Mice.

Time-dependent changes in blood-based protein biomarkers can help identify the -pathological processes in blast-induced traumatic brain injury (bTBI), assess injury severity, and monitor disease progression. We obtained blood from control and injured mice (exposed to a single, low-intensity blast) at 2-h, 1-day, 1-week, and 1-month post-injury. We then determined the serum levels of biomarkers related to metabolism (4-HNE, HIF-1α, ceruloplasmin), vascular function (AQP1, AQP4, VEGF, vWF, Flk-1), inflammation (OPN, CINC1, fibrinogen, MIP-1a, OX-44, p38, MMP-8, MCP-1 CCR5, CRP, galectin-1), cell adhesion and the extracellular matrix (integrin α6, TIMP1, TIMP4, Ncad, connexin-43), and axonal (NF-H, Tau), neuronal (NSE, CK-BB) and glial damage (GFAP, S100ß, MBP) at various post-injury time points. Our findings indicate that the exposure to a single, low-intensity blast results in metabolic and vascular changes, altered cell adhesion, and axonal and neuronal injury in the mouse model of bTBI. Interestingly, serum levels of several inflammatory and astroglial markers were either unchanged or elevated only during the acute and subacute phases of injury. Conversely, serum levels of the majority of biomarkers related to metabolic and vascular functions, cell adhesion, as well as neuronal and axonal damage remained elevated at the termination of the experiment (1 month), indicating long-term systemic and cerebral alterations due to blast. Our findings show that the exposure to a single, low-intensity blast induces complex pathological processes with distinct temporal profiles. Hence, monitoring serum biomarker levels at various post-injury time points may provide enhanced diagnostics in blast-related neurological and multi-system deficits.

Neuroprotective effects of N-acetylcysteine amide on experimental focal penetrating brain injury in rats.

We examined the effects of N-acetylcysteine amide (NACA) in the secondary inflammatory response following a novel method of focal penetrating traumatic brain injury (TBI) in rats. N-acetylcysteine (NAC) has limited but well-documented neuroprotective effects after experimental central nervous system ischemia and TBI, but its bioavailability is very low. We tested NACA, a modified form of NAC with higher membrane and blood-brain barrier permeability. Focal penetrating TBI was produced in male Sprague-Dawley rats randomly selected for NACA treatment (n=5) and no treatment (n=5). In addition, four animals were submitted to sham surgery. After 2 hours or 24 hours the brains were removed, fresh frozen, cut in 14 µm coronal sections and subjected to immunohistochemistry, immunofluorescence, Fluoro-Jade and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analyses. All treated animals were given 300 mg/kg NACA intraperitoneally (IP) 2 minutes post trauma. The 24 hour survival group was given an additional bolus of 300 mg/kg IP after 4 hours. NACA treatment decreased neuronal degeneration by Fluoro-Jade at 24 hours with a mean change of 35.0% (p<0.05) and decreased TUNEL staining indicative of apoptosis at 2 hours with a mean change of 38.7% (p<0.05). Manganese superoxide dismutase (MnSOD) increased in the NACA treatment group at 24 hours with a mean change of 35.9% (p<0.05). Levels of migrating macrophages and activated microglia (Ox-42/CD11b), nitric oxide-producing inflammatory enzyme iNOS, peroxynitrite marker 3-nitrotyrosine, NFκB translocated to the nuclei, cytochrome C and Bcl-2 were not affected. NACA treatment decreased neuronal degeneration and apoptosis and increased levels of antioxidative enzyme MnSOD. The antiapoptotic effect was likely regulated by pathways other than cytochrome C. Therefore, NACA prevents brain tissue damage after focal penetrating TBI, warranting further studies towards a clinical application.

Dorsal root ganglion neurons up-regulate the expression of laminin-associated integrins after peripheral but not central axotomy.

The favorable prognosis of regeneration in the peripheral nervous system after axonal lesions is generally regarded as dependent on the Schwann cell basal lamina. Laminins, a heterotrimeric group of basal lamina molecules, have been suggested to be among the factors playing this supportive role. For neurons to utilize laminin as a substrate for growth, an expression of laminin binding receptors, integrins, is necessary. In this study, we have examined the expression of laminin binding integrin subunits in dorsal root ganglion (DRG) neurons after transection to either their peripherally projecting axons, as in the sciatic nerve, followed by regeneration, or the centrally projecting axons in dorsal roots, followed by no or weak regenerative activity. In uninjured DRG, immunohistochemical staining revealed a few neurons expressing integrin subunit alpha6, whereas integrin subunits alpha7 and foremost beta1 were expressed in a majority of neurons. After an injury to the sciatic nerve, mRNAs encoding all three integrins were up-regulated in DRG neurons. By anterograde tracing, immunoreactivity for all studied integrins was also found in association with growing axons after a sciatic nerve crush lesion in vivo. In contrast, mRNA levels remained constant in DRG neurons after a dorsal root injury. Together with previous findings, this suggests that integrin subunits alpha6, alpha7, and beta1 have an important role in the regenerative response following nerve injury and that the lack of regenerative capacity following dorsal root injury could in part be explained by the absence of response in integrin regulation.

A novel mouse model of penetrating brain injury.

Penetrating traumatic brain injury (pTBI) has been difficult to model in small laboratory animals, such as rats or mice. Previously, we have established a non-fatal, rat model for pTBI using a modified air-rifle that accelerates a pellet, which hits a small probe that then penetrates the experimental animal's brain. Knockout and transgenic strains of mice offer attractive tools to study biological reactions induced by TBI. Hence, in the present study, we adapted and modified our model to be used with mice. The technical characterization of the impact device included depth and speed of impact, as well as dimensions of the temporary cavity formed in a brain surrogate material after impact. Biologically, we have focused on three distinct levels of severity (mild, moderate, and severe), and characterized the acute phase response to injury in terms of tissue destruction, neural degeneration, and gliosis. Functional outcome was assessed by measuring bodyweight and motor performance on rotarod. The results showed that this model is capable of reproducing major morphological and neurological changes of pTBI; as such, we recommend its utilization in research studies aiming to unravel the biological events underlying injury and regeneration after pTBI.

Alteration in BDNF and its receptors, full-length and truncated TrkB and p75(NTR) following penetrating traumatic brain injury.

The evidence that BDNF is involved in neuroprotection, neuronal repair and recovery after traumatic brain injury (TBI) is substantial. We have previously shown that the polymorphism of the human BDNF gene predicts cognitive recovery and outcome following penetrating TBI. The distribution of expression of BDNF and its receptors after penetrating TBI has not been investigated. In this study we examined the expression of these genes in a rat model of penetrating TBI. The injury is produced by a controlled penetration of a 2mm thick needle-shaped object, which is accelerated with a pellet from an air gun. We used in situ hybridization and investigated the mRNA expression of BDNF and its receptors: the full-length and the truncated TrkB and p75(NTR), from 1 day to 8 weeks following penetrating TBI. In addition, the protein level of BDNF in frontal cortex and hippocampus was measured by reverse phase protein microarray (RPPM). The mRNA expression of BDNF and its receptors decreased in the hippocampus in the border zone ipsilateral to the injury while there was an increase in mRNA expression at the contralateral side. The increase in BDNF mRNA expression in the hippocampus was sustained for 2 weeks following injury, with the highest expression noted in the CA3 cell layer. Furthermore, the protein analysis by RPPM showed increased levels of BDNF in the frontal cortex and the hippocampus up to 2 weeks after TBI. At 8 weeks following injury there was an intense labeling of the truncated TrkB receptor and the p75(NTR) in the area surrounding the cavity. Our study is the first report on the expression of BDNF and its receptors following penetrating TBI and suggests that their expression is altered long after the acute phase of injury. Further studies are needed to investigate if the late expressions of these receptors are beneficial or deleterious. In either case it indicates the possibility to influence the recovery after brain injury during the chronic phase and the development of treatments that may improve the outcome of TBI patients.

Proregenerative properties of ECM molecules.

After traumatic injuries to the nervous system, regrowing axons encounter a complex microenvironment where mechanisms that promote regeneration compete with inhibitory processes. Sprouting and axonal regrowth are key components of functional recovery but are often counteracted by inhibitory molecules. This review covers extracellular matrix molecules that support neuron axonal outgrowth.

Integrin manipulation to improve regeneration.

After central nervous system (CNS) insults, such as spinal cord injury or traumatic brain injury, neurons encounter a complex microenvironment where mechanisms that promote regeneration compete with inhibitory processes. Sprouting and axonal re-growth are key components of functional recovery, but are often counteracted by inhibitory molecules. Several strategies are being pursued whereby these inhibitory molecules are either being neutralized with blocking antibodies, with enzymatic degradation or downstream signaling events are being interfered with. Two recent studies ( 1) (,) ( 2) show that activating integrin signaling in dorsal root ganglion (DRG) neurons renders them able to overcome inhibitory signals, and could possibly lead to new strategies to improve neuronal regeneration.

Osteopontin is upregulated after mechanical brain injury and stimulates neurite growth from hippocampal neurons through ß1 integrin and CD44.

Brain trauma induces a multitude of reactions at molecular, cellular, and tissue levels, some of which are beneficial to recovery, whereas others are detrimental. Osteopontin (OPN), a glycosylated phosphoprotein, can be found in both the soluble form and as an extracellular matrix constituent in several tissues in the vertebrate body, but its function after brain injury is largely unknown. In this study, the expression of OPN after an experimental traumatic brain injury in rats was examined and its effects on hippocampal neurons and cortical astrocytes were studied using cell-culture techniques. OPN had no influence astrocyte behavior in a scratch assay. However, hippocampal neurons grew well on an OPN substrate with growth comparable to that seen on laminin, but showed a higher degree of primary neurites. Finally, growth on OPN was mediated through ß1 intregrins and CD44. These findings indicate that injury-induced OPN may support neurite sprouting, suggesting a role for this molecule in recovery from central nervous system trauma.

Characterization of a novel rat model of penetrating traumatic brain injury.

A penetrating traumatic brain injury (pTBI) occurs when an object impacts the head with sufficient force to penetrate the skin, skull, and meninges, and inflict injury directly to the brain parenchyma. This type of injury has been notoriously difficult to model in small laboratory animals such as rats or mice. To this end, we have established a novel non-fatal model for pTBI based on a modified air rifle that accelerates a pellet, which in turn impacts a small probe that then causes the injury to the experimental animal's brain. In the present study, we have focused on the acute phase and characterized the tissue destruction, including increasing cavity formation, white matter degeneration, hemorrhage, edema, and gliosis. We also used a battery of behavioral models to examine the neurological outcome, with the most noteworthy finding being impairment of reference memory function. In conclusion, we have described a number of events taking place after pTBI in our model. We expect this model will prove useful in our efforts to unravel the biological events underlying injury and regeneration after pTBI and possibly serve as a useful animal model in the development of novel therapeutic and diagnostic approaches.

A Model for Mild Traumatic Brain Injury that Induces Limited Transient Memory Impairment and Increased Levels of Axon Related Serum Biomarkers.

Mild traumatic brain injury (mTBI) is one of the most common neuronal insults and can lead to long-term disabilities. mTBI occurs when the head is exposed to a rapid acceleration-deceleration movement triggering axonal injuries. Our limited understanding of the underlying pathological changes makes it difficult to predict the outcome of mTBI. In this study we used a scalable rat model for rotational acceleration TBI, previously characterized for the threshold of axonal pathology. We have analyzed whether a TBI just above the defined threshold would induce any detectable behavioral changes and/or changes in serum biomarkers. The effect of injury on sensory motor functions, memory and anxiety were assessed by beam walking, radial arms maze and elevated plus maze at 3-7 days following TBI. The only behavioral deficits found were transient impairments in working and reference memory. Blood serum was analyzed at 1, 3, and 14 days after injury for changes in selected protein biomarkers. Serum levels of neurofilament heavy chain and Tau, as well as S100B and myelin basic protein showed significant increases in the injured animals at all time points. No signs of macroscopic injuries such as intracerebral hematomas or contusions were found. Amyloid precursor protein immunostaining indicated axonal injuries at all time points analyzed. In summary, this model mimics some of the key symptoms of mTBI, such as transient memory impairment, which is paralleled by an increase in serum biomarkers. Our findings suggest that serum biomarkers may be used to detect mTBI. The model provides a suitable foundation for further investigation of the underlying pathology of mTBI.

On acute gene expression changes after ventral root replantation.

Replantation of avulsed spinal ventral roots has been show to enable significant and useful regrowth of motor axons in both experimental animals and in human clinical cases, making up an interesting exception to the rule of unsuccessful neuronal regeneration in central nervous system. Compared to avulsion without repair, ventral root replantation seems to rescue lesioned motoneurons from death. In this study we have analyzed the acute response to ventral root avulsion and replantation in adult rats with gene arrays combined with cluster analysis of gene ontology search terms. The data show significant differences between rats subjected to ventral replantation compared to avulsion only. Even though number of genes related to cell death is similar in the two models after 24 h, we observed a significantly larger number of genes related to neurite growth and development in the rats treated with ventral root replantation, possibly reflecting the neuroregenerative capacity in the replantation model. In addition, an acute inflammatory response was observed after avulsion, while effects on genes related to synaptic transmission were much more pronounced after replantation than after avulsion alone. These data indicate that the axonal regenerative response from replantation is initiated at an earlier stage than the possible differences in terms of neuron survival. We conclude that this type of analysis may facilitate the comparison of the acute response in two types of injury.