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The role of neuronal plasticity and repair on the final functional outcome following traumatic brain injury (TBI) remains poorly understood. Moreover, the relationship of the magnitude of post-traumatic secondary injury and neurodegeneration to the potential for neuronal repair has not been explored. To address these questions, we employed Western immunoblotting techniques to examine how injury severity affects the spatial and temporal expression of markers of axonal growth (growth-associated protein GAP-43) and synaptogenesis (pre-synaptic vesicular protein synaptophysin) following either moderate (0.5 mm, 3.5 M/s) or severe (1.0 mm, 3.5 M/s) lateral controlled cortical impact traumatic brain injury (CCI-TBI) in young adult male CF-1 mice. Moderate CCI increased GAP-43 levels at 24 and 48 h post-insult in the ipsilateral hippocampus relative to sham, non-injured animals. This increase in axonal plasticity occurred prior to maximal hippocampal neurodegeneration, as revealed by de Olmos silver staining, at 72 h. However, moderate CCI-TBI did not elevate GAP-43 expression in the ipsilateral cortex where neurodegeneration was extensive by 6 h post-TBI. In contrast to moderate injury, severe CCI-TBI failed to increase hippocampal GAP-43 levels and instead resulted in depressed GAP-43 expression in the ipsilateral hippocampus and cortex at 48 h post-insult. In regards to injury-induced changes in synaptogenesis, we found that moderate CCI-TBI elevated synaptophysin levels in the ipsilateral hippocampus at 24, 48, 72 h and 21 days, but this effect was not present after severe injury. Together, these data highlights the adult brain's ability for axonal and synaptic plasticity following a focal cortical injury, but that severe injuries may diminish these endogenous repair mechanisms. The differential effects of moderate versus severe TBI on the post-traumatic plasticity response may be related to the calpain-mediated proteolytic activity occurring after a severe injury preventing increased expression of proteins required for plasticity. Supporting this hypothesis is the fact that GAP-43 is a substrate for calpain along with our data demonstrating that calpain-mediated degradation of the cytoskeletal protein, alpha-spectrin, is approximately 10 times greater in ipsilateral hippocampal tissue following severe compared to moderate CCI-TBI. Thus, TBI severity has a differential effect on the injury-induced neurorestorative response with calpain activation being one putative factor contributing to neuroregenerative failure following severe CCI-TBI. If true, then calpain inhibition may lead to both neuroprotective effects and an enhancement of neuronal plasticity/repair mechanisms post-TBI.

Activation of the vestibular system can either increase or decrease ventilation. The objectives of the present study were to clarify whether these different responses are the result of activating different vestibular subnuclei, by addressing three questions. Do neurones within the medial, lateral and spinal vestibular nuclei (VN(M), VN(L) and VN(S), respectively) function differently in respiratory modulation? Is the ventral medullary nucleus gigantocellularis (NGC) required to fully express the VN-mediated respiratory responses? Is glutamate, by acting on N-methyl-D-aspartic acid (NMDA) receptors in the vestibular subnuclei, capable of modulating respiration? In anaesthetized, tracheotomized and spontaneously breathing rats, electrical stimuli (10 s) applied in the VN(L) and VN(S) significantly elevated ventilation by 35 % and 30 % (P0.05), respectively. However, VN(M) stimulation produced statistically significant (P0.05) changes that differed depending upon the stimulation site: either ventilatory inhibition (by 40 % in 57 % of the trials) or excitation (by 55 % in 43 % of trials), and which were often accompanied by a pressor response. These electrical-stimulation-evoked cardiorespiratory responses were almost eliminated following microinjection of ibotenic acid into the stimulation sites (P0.05) or bilaterally into the NGC (P0.05). As compared to vehicle, microinjection of NMDA into the unilateral VN(M), VN(L) and VN(S) significantly increased ventilation to 74 %, 58 % and 60 % (P0.05), respectively, with no effect on arterial blood pressure. These data suggest that neurones within the vestibular subnuclei play different roles in cardiorespiratory modulation, and that the integrity of the NGC is essential for the full expression of these VN-mediated responses. The evoked respiratory excitatory responses are probably mediated by glutamate acting on NMDA receptors, whereas the neurotransmitters involved in VN(M)-mediated respiratory inhibition and hypertension remain unknown.

Acute neuropathology following experimental traumatic brain injury results in the rapid necrosis of cortical tissue at the site of injury. This primary injury is exacerbated in the ensuing hours and days via the progression of secondary injury mechanism(s) leading to significant neurological dysfunction. Recent evidence from our laboratory demonstrates that the immunosuppressant cyclosporin A significantly ameliorates cortical damage following traumatic brain injury. The present study extends the previous findings utilizing a unilateral controlled cortical impact model of traumatic brain injury in order to establish a dose-response curve and optimal dosing regimen of cyclosporin A. Following injury to adult rats, cyclosporin A was administrated at various dosages and the therapy was initiated at different times post-injury. In addition to examining the effect of cyclosporin A on the acute disruption of the blood-brain barrier following controlled cortical impact, we also assessed the efficacy of cyclosporin A to reduce tissue damage utilizing the fluid percussion model of traumatic brain injury. The findings demonstrate that the neuroprotection afforded by cyclosporin A is dose-dependent and that a therapeutic window exists up to 24h post-injury. Furthermore, the optimal cyclosporin dosage and regimen markedly reduces disruption of the blood-brain barrier acutely following a cortical contusion injury, and similarly affords significant neuroprotection following fluid percussion injury. These findings clearly suggest that the mechanisms responsible for tissue necrosis following traumatic brain injury are amenable to pharmacological intervention.

The present study examined the neuropathology of the lateral controlled cortical impact (CCI) traumatic brain injury (TBI) model in mice utilizing the de Olmos silver staining method that selectively identifies degenerating neurons and their processes. The time course of ipsilateral and contralateral neurodegeneration was assessed at 6, 24, 48, 72, and 168 h after a severe (1.0 mm, 3.5 M/sec) injury in young adult CF-1 mice. At 6 hrs, neurodegeneration was apparent in all layers of the ipsilateral cortex at the epicenter of the injury. A low level of degeneration was also detected within the outer molecular layer of the underlying hippocampal dentate gyrus and to the mossy fiber projections in the CA3 pyramidal subregions. A time-dependent increase in cortical and hippocampal neurodegeneration was observed between 6 and 72 hrs post-injury. At 24 h, neurodegeneration was apparent in the CA1 and CA3 pyramidal and dentate gyral granule neurons and in the dorsolateral portions of the thalamus. Image analysis disclosed that the overall volume of ipsilateral silver staining was maximal at 48 h. In the case of the hippocampus, staining was generalized at 48 and 72 h, indicative of damage to all of the major afferent pathways: perforant path, mossy fibers and Schaffer collaterals as well as the efferent CA1 pyramidal axons. The hippocampal neurodegeneration was preceded by a significant increase in the levels of calpain-mediated breakdown products of the cytoskeletal protein alpha-spectrin that began at 6 h, and persisted out to 72 h post-injury. Damage to the corpus callosal fibers was observed as early as 24 h. An anterior to posterior examination of neurodegeneration showed that the cortical damage included the visual cortex. At 168 h (7 days), neurodegeneration in the ipsilateral cortex and hippocampus had largely abated except for ongoing staining in the cortical areas surrounding the contusion lesion and in hippocampal mossy fiber projections. Callosal and thalamic neurodegeneration was also very intense. This more complete neuropathological examination of the CCI model shows that the associated damage is much more widespread than previously appreciated. The extent of ipsilateral and contralateral neurodegeneration provides a more complete anatomical correlate for the cognitive and motor dysfunction seen in this paradigm and suggests that visual disturbances are also likely to be involved in the post-CCI neurological deficits.

Electrical stimulation of the rostral fastigial nucleus (FNr) alters respiration via activation of local neurons. We hypothesized that this FNr-mediated respiratory response was dependent on the integrity of the nucleus gigantocellularis of the medulla (NGC). Electrical stimulation of the FNr in 15 anesthetized and tracheotomized spontaneously breathing rats significantly altered ventilation by 35.2 ± 11.0% ( P < 0.01) with the major effect being excitatory (78%). This respiratory response did not significantly differ from control after lesions of the NGC via bilateral microinjection of kainic or ibotenic acid (4.5 ± 1.9%; P > 0.05) but persisted in sham controls. Eight other rats, in which horseradish peroxidase (HRP) solution was previously microinjected into the left NGC, served as nonstimulation controls or were exposed to either 15-min repeated electrical stimulation of the right FNr or hypercapnia for 90 min. Histochemical and immunocytochemical data showed that the right FNr contained clustered HRP-labeled neurons, most of which were double labeled with c-Fos immunoreactivity in both electrically and CO2-stimulated rats. We conclude that the NGC receives monosynaptic FNr inputs and is required for fully expressing FNr-mediated respiratory responses.

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.