Temporal profile of nerve growth factor-like immunoreactivity after transient focal cerebral ischemia in rats

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

Neurovascular Unit as a Source of Ischemic Stroke Biomarkers-Limitations of Experimental Studies and Perspectives for Clinical Application

Cerebral stroke, which is one of the most frequent causes of mortality and leading cause of disability in developed countries, often leads to devastating and irreversible brain damage. Neurological and neuroradiological diagnosis of stroke, especially in its acute phase, is frequently uncertain or inconclusive. This results in difficulties in identification of patients with poor prognosis or being at high risk for complications. It also makes difficult identification of these stroke patients who could benefit from more aggressive therapies. In contrary to the cardiovascular disease, no single biomarker is available for the ischemic stroke, addressing the abovementioned issues. This justifies the need for identifying of effective diagnostic measures characterized by high specificity and sensitivity. One of the promising avenues in this area is studies on the panels of biomarkers characteristic for processes which occur in different types and phases of ischemic stroke and represent all morphological constituents of the brains' neurovascular unit (NVU). In this review, we present the current state of knowledge concerning already-used or potentially applicable biomarkers of the ischemic stroke. We also discuss the perspectives for identification of biomarkers representative for different types and phases of the ischemic stroke, as well as for different constituents of NVU, which concentration levels correlate with extent of brain damage and patients' neurological status. Finally, a critical analysis of perspectives on further improvement of the ischemic stroke diagnosis is presented.

The Protective Effect of Human Umbilical Cord Blood CD34+ Cells and Estradiol against Focal Cerebral Ischemia in Female Ovariectomized Rat: Cerebral MR Imaging and Immunohistochemical Study

Human umbilical cord blood derived CD34+ stem cells are reported to mediate therapeutic effects in stroke animal models. Estrogen was known to protect against ischemic injury. The present study wished to investigate whether the protective effect of CD34+ cells against ischemic injury can be reinforced with complemental estradiol treatment in female ovariectomized rat and its possible mechanism. Experiment 1 was to determine the best optimal timing of CD34+ cell treatment for the neuroprotective effect after 60-min middle cerebral artery occlusion (MCAO). Experiment 2 was to evaluate the adjuvant effect of 17β-estradiol on CD34+ cell neuroprotection after MCAO. Experiment 1 showed intravenous infusion with CD34+ cells before MCAO (pre-treatment) caused less infarction size than those infused after MCAO (post-treatment) on 7T magnetic resonance T2-weighted images. Experiment 2 revealed infarction size was most significantly reduced after CD34+ + estradiol pre-treatment. When compared with no treatment group, CD34+ + estradiol pre-treatment showed significantly less ADC reduction at 2 h and 2 d, less CBF reduction at 2 h and less hyperperfusion at 2 d. The immunoreactivity of c-Fos, c-Jun and GFAP was attenuated, and BDNF showed significant recovery from 2 h to 2 d after MCAO, especially after CD34+ + estradiol pre-treatment. The present study suggests pre-treatment with CD34+ cells with complemental estradiol can be most protective against ischemic injury, which may act through stabilization of cerebral hemodynamics and normalization of the expressions of immediate early genes and BDNF.

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome

INTRODUCTION

An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis.

MATERIALS AND METHODS

Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell.

RESULTS

Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%.

CONCLUSION

An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.

Neural growth factor expression in the lateral retinaculum in painful patellofemoral malalignment

We studied 7 samples of lateral retinaculae excised at the time of surgical realignments. They were obtained from patients with isolated symptomatic patellofemoral malalignment resistant to conservative treatment and were evaluated with immunohistochemistry and immunoblotting. We found that neural growth factor is higher in patients with pain than in those with instability as the main symptom. Neural growth factor is related to neural proliferation in vessels and perivascular tissue and to the release of neuroceptive transmitters, such as substance P. We postulate that both mechanisms are involved in the pathogenesis of pain in isolated symptomatic patellofemoral malalignment.

The Varying Patterns of Neurotrophin Changes in the Perinatal Period

Neurotrophins (NTs), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, and NT-4 are of major importance in prenatal and postnatal brain development, due to their neuroprotective action. Developmental changes alter the neuronal responsiveness to certain NTs, which subsequently are variously expressed, to properly balance their action. The following study aimed at examining the pattern of perinatal changes of the four NTs--NGF, BDNF, NT-3, and NT-4 in 30 appropriate for gestational age (AGA) full-term fetuses and neonates by determining their circulating levels at characteristic time points. This study show a gradual decrease of circulating levels of the NTs, NT-3 and NT-4 from umbilical cord (UC) to neonates day 4 (N4), while circulating levels of NGF and BDNF present the opposite pattern: an increase from UC to N4. These patterns of perinatal changes differ according to their impact on the process of neuronal development and their reaction to perinatal stress. NT3 and NT4 have been documented to act at early stages of neuronal development and to decrease after hypoxia-ischemia, while NGF and BDNF to increase. Further studies should investigate these patterns in premature or full-term infants, presenting various pathological conditions in the perinatal period.

Hypertension downregulates the expression of brain-derived neurotrophic factor in the ischemia-vulnerable hippocampal CA1 and cortical areas after carotid artery occlusion

We studied the effect of hypertension on brain damage and brain-derived neurotrophic factor (BDNF) expression in the hippocampal formation and cerebral cortex after permanent occlusion of bilateral common carotid arteries (CCA). Two groups of rats were used, including normotensive Wistar-Kyoto (WKY) rat and spontaneous hypertensive rat (SHR). Each group contained sham operation, 1 week and 4 weeks after bilateral CCA occlusion (n=5-10 in each time point). The blood pressure showed a significant elevation in WKY rats from 1 h after operation to 4 weeks before sacrifice (P<0.05), but was not changed in SHR (P>0.05). However, rectal temperature showed no significant change after operation in WKY rat and SHR (P>0.05) and showed no significant difference at any time point between WKY rat and SHR (P>0.05). Hematoxylin and eosin staining showed SHR had a significantly larger necrotic volume than WKY rats (n=10 in each group, 6044+/-6895 microm(3) vs. 144+/-174 microm(3), P<0.05) at 4 weeks after ischemia. In SHR, BDNF immunoreactivity and mRNA decreased significantly from 1 week to 4 weeks in both the hippocampal CA1 and cortical areas (P<0.01) but decreased transiently in dentate gyrus. However, in WKY rats, BDNF immunoreactivity and mRNA decreased transiently at 1 week (P<0.05) and recovered at 4 weeks after cerebral ischemia. Our study demonstrates that after bilateral CCA occlusion, preexisting hypertension may aggravate the brain injury and downregulate the expression of BDNF immunoreactivity and mRNA in the ischemia-vulnerable hippocampal CA1 and cortical areas but not in ischemia-resistant dentate gyrus.

Behaviorally induced synaptogenesis and dendritic growth in the hippocampal region following transient global cerebral ischemia are accompanied by improvement in spatial learning

Reports have shown that damage to the adult brain can result in adaptive changes in regions adjacent or surrounding the site of the principal injury and that these changes may be modulated by rehabilitation training. In this study, we examined the influence of complex environment housing as a rehabilitation strategy on ischemia-induced synaptic and dendritic changes in the hippocampus. Thirty-six adult male Wistar rats were included in the study and assigned to either transient global cerebral ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either complex environment housing (EC) or social condition (SC, paired housing) group during the rehabilitation period. Following 14 days of rehabilitation, rats were tested in the water maze. Our results showed that: (1) ischemic injury and EC housing were able to independently influence synaptogenesis and dendritic growth in the hippocampal area adjacent to the site of injury, and (2) EC housing-induced synaptic and dendritic changes were accompanied by enhanced functional recovery after transient global cerebral ischemia. These data suggest that behavioral experience during the rehabilitation period may be able to alter the neuronal circuitry in the surrounding region where primary neuronal damage was seen and that such modification may have contributed to functional improvement.

Dendritic plasticity in the adult rat following middle cerebral artery occlusion and Nogo-a neutralization

Our work has shown that following focal ischemic lesion in adult rats, neutralization of the axon growth inhibitor Nogo-A with the monoclonal antibody (mAb) IN-1 results in functional recovery. Furthermore, new axonal connections were formed from the contralesional cortex to subcortical areas corresponding to the observed functional recovery. The present study investigated whether dendritic changes, also known to subserve functional recovery, paralleled the axonal plasticity shown after ischemic lesion and treatment with mAb IN-1. Golgi-Cox-stained layer V pyramidal neurons in the contralesional sensorimotor cortex were examined for evidence of dendritic sprouting. Results demonstrated increased dendritic arborization and spine density in the mAb IN-1-treated animals with lesion. Interestingly, administration of mAb IN-1 without lesion resulted in transient dendritic outgrowth with no change in spine density. These results suggest a novel role for Nogo-A in limiting dendritic plasticity after stroke.

Histologic retinacular changes associated with ischemia in painful patellofemoral malalignment

Ischemic changes in 31 samples of lateral retinacula excised at surgical realignment in patients with isolated symptomatic patellofemoral malalignment resistant to conservative treatment were evaluated with conventional histology, electron microscopy, immunohistochemistry, and molecular biology. Morphologic and ultrastructural changes associated with ischemia including hypervascularization and increased vascular endothelial growth factor release were identified in painful patellofemoral malalignment. It is hypothesized that periodic short episodes of ischemia could be implicated in the pathogenesis of anterior knee pain in most cases of isolated symptomatic patellofemoral malalignment in active young patients by triggering neural proliferation.

Infrapatellar fat pad pressure and volume changes of the anterior compartment during knee motion: possible clinical consequences to the anterior knee pain syndrome

This biomechanical study was performed to measure tissue pressure in the infrapatellar fat pad and the volume changes of the anterior knee compartment during knee flexion-extension motion. Knee motion from 120 degrees of flexion to full extension was simulated on ten fresh frozen human knee specimens (six from males, four from females, average age 44 years) using a hydraulic kinematic simulator (30, 40, and 50 Nm extension moment). Infrapatellar tissue pressure was measured using a closed cell sensor. Infrapatellar volume change in the anterior knee compartment was evaluated subsequent to removal of the fat pad using a water-filled bladder. We found a significant increase of the infrapatellar tissue pressure during knee flexion, at flexion angles of <20 degrees and >100 degrees . The average tissue pressure ranged from 343 (+/-223) mbar at 0 degrees to 60 (+/-64) mbar at 60 degrees of flexion. The smallest volume in the anterior knee compartment was measured at full extension and 120 degrees of flexion, whereas the maximum volume was observed at 50 degrees of flexion. In conclusion, the data suggest a biomechanical function of the infrapatellar fat pad at flexion angles of <20 degrees and >100 degrees , which suggests a role of the infrapatellar fat pad in stabilizing the patella in the extremes of knee motion.

Changes in number of synapses and mitochondria in presynaptic terminals in the dentate gyrus following cerebral ischemia and rehabilitation training

Damage to the adult brain can result in adaptive plasticity in regions adjacent to the site of the principal insult and that the plastic changes may be modulated by post-injury rehabilitation training. In this study, we examined the effects of rehabilitation training on synaptic morphology in the dentate gyrus following transient global cerebral ischemia and the metabolic correlates of the ultrastructural changes. Forty adult male Wistar rats were included in the study and assigned to either ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either complex environment housing (EC), exercise (EX), or social condition (SC, paired housing) group. Electron microscopy and unbiased stereological methods were used to evaluate synaptic plasticity and the number and size of mitochondria in synaptic axon terminals. Increased number of granule neurons was seen in all ischemic groups and in the sham EC rats. Changes in the number of synapses per neuron in the outer and inner molecular layers of the dentate gyrus parallel those seen in granule neurons. Similarly, ischemia and behavioral experience in EC independently increased the number of synaptic mitochondria in presynaptic terminals in both the outer and inner molecular layers; however, no significant changes were seen in mitochondrial size. These data suggest a link between behavioral training and synaptic plasticity in the region adjacent to the injury and that the likely metabolic correlate of this synaptic plasticity is increased number of mitochondria at synaptic axon terminals.

Behaviorally-induced ultrastructural plasticity in the hippocampal region after cerebral ischemia

Behavioral training has been shown to induce synaptic plasticity in both intact and injured animals. Because of the possibility that the adaptive changes after ischemic damage may make the brain more malleable to behavioral training, we examined the effects of complex environment (EC) housing and exercise (EX) after global cerebral ischemia on synaptic structural alterations. Forty-two adult male Wistar rats were included in the study and assigned to either ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either EC, EX, or social condition (SC, paired housing) group. CA1 was processed for electron microscopy and unbiased stereological techniques were used to evaluate plasticity. Significantly decreased neuron density was seen in anterior and medial CA1 in ischemic animals regardless of behavioral training. Neuron density in anterior CA1 was 31% less than the medial area. Synaptogenesis was influenced by cerebral ischemia and behavioral training in that all ischemic groups and sham EC animals showed greater number of synapses per neuron compared to the sham EX and SC groups. Analysis of synapse configuration showed that the synaptogenesis in ischemia EX and SC rats was formed mainly by synapses with single synaptic boutons, whereas in the ischemia EC and sham EC rats synaptogenesis was formed mainly by synapses with multiple synaptic boutons. Furthermore, housing of sham and ischemia rats in EC resulted in increased number of synapses with perforated postsynaptic density. Together, these data suggest that behavioral experience in EC after insult may be able to enhance synaptic plasticity.

Morphological transformations of cells immunopositive for GFAP, TrkA or p75 in the CA1 hippocampal area following transient global ischemia in the rat. A quantitative study

Transient global ischemia induces intensive neuronal degeneration in the hippocampal CA1 pyramidal layer, accompanied by reactive transformation of glial cells. Previously, we have shown using the double immunostaining method that the NGF receptors (NGFR) p75 and TrkA are expressed mainly on subpopulations of GFAP+ astrocytes, and this expression increases progressively after ischemia. In the presented study, we analyzed quantitatively the morphological transformations of cells immunopositive for GFAP or NGF receptors in the stratum radiatum of the CA1 hippocampal area in different survival periods after ischemia, evoked by 10-min cardiac arrest in adult rats. In control brains, NGF receptors were expressed only on small cells with poorly ramified processes. After ischemia, the NGFR+ cells increased in size and morphological complexity (measured using fractal analysis). However, even 2 weeks after ischemia these cells did not reach the size and value of the fractal dimension typical of the largest GFAP+ astrocytes. Moreover, the reaction of NGFR+ cells was significantly delayed in comparison with the total astrocyte population. The obtained results suggest that NGF receptors are expressed mainly by immature astrocytes and ischemia induces the maturation of these cells.

The temporal profile of the reaction of microglia, astrocytes, and macrophages in the delayed onset paraplegia after transient spinal cord ischemia in rabbits

In the present study, we sought to elucidate the temporal profile of the reaction of microglia, astrocytes, and macrophages in the progression of delayed onset motor dysfunction after spinal cord ischemia (15 min) in rabbits. At 2, 4, 8, 12, 24, and 48 h after reperfusion (9 animals in each), hind limb motor function was assessed, and the lumbar spinal cord was histologically examined. Delayed motor dysfunction was observed in most animals at 48 h after ischemia, which could be predicted by a poor recovery of segmental spinal cord evoked potentials at 15 min of reperfusion. In the gray matter of the lumbar spinal cord, both microglia and astrocytes were activated early (2 h) after reperfusion. Microglia were diffusely activated and engulfed motor neurons irrespective of the recovery of segmental spinal cord evoked potentials. In contrast, early astrocytic activation was confined to the area where neurons started to show degeneration. Macrophages were first detected at 8 h after reperfusion and mainly surrounded the infarction area later. Although the precise roles of the activation of microglia, astrocytes, and macrophages are to be further determined, the results indicate that understanding functional changes of astrocytes may be important in the mechanism of delayed onset motor dysfunction including paraplegia.

IMPLICATIONS

Microglia and macrophages play a role in removing tissue debris after transient spinal cord ischemia. Disturbance of astrocytic defense mechanism, breakdown of the blood-spinal cord barrier, or both seemed to be involved in the development of delayed motor dysfunction.

The effect of a global birth asphyxia on the ontogeny of BDNF and NGF protein expression in the juvenile brain

Neurotrophic growth factors are strongly upregulated following brain injury in order to limit the amount of delayed apoptotic cell death. In particular, the neurotrophins NGF and BDNF are upregulated following injury and offer neuroprotection when administered after brain injury. Further, both growth factors are involved in the control of neural proliferation and plasticity during both development and recovery from injury. We used a model of global birth asphyxia in the rat to follow the ontogeny of BDNF and NGF protein levels within the normal and asphyctic hippocampus and cerebellum for the first 28 days of postnatal life. In contrast to what is seen in the injured adult brain, we see an early and long lasting decrease in NGF content within the asphyctic hippocampus, whereas cerebellar NGF content showed a delayed increase following asphyxia. Asphyxia also caused a delayed increase in BDNF content within the hippocampus but decreased BDNF levels within the cerebellum. Further, a comparison of the ontogeny of plasma corticosterone over development shows that endogenous BDNF protein levels are not sensitive to the dramatic increase in circulating corticosterone that occurs at the end of the stress hyporesponsive period. In summary, we find that perinatal birth asphyxia causes opposing changes in NGF and BDNF protein expression in a spatio-temporal-dependent manner. These results point to the need for more detailed studies on the mechanisms of action of BDNF and NGF within the developing brain before these can be used therapeutically following birth asphyxia in man.

Neuroprotection by complement (C1) inhibitor in mouse transient brain ischemia

The authors investigated the effect of the C1 inhibitor (C1-INH), the only known inhibitor of complement C1, in a murine model of transient focal ischemia. Ischemia was induced by intraluminal occlusion of the middle cerebral artery. After 2 hours, reperfusion was produced by removing the nylon monofilament occluding the artery. The effect of 15 U C1-INH (intravenously) was evaluated in terms of general and focal neurologic deficits, ischemic volume, neutral red staining (to identify the brain areas subject to ischemic damage), and glial fibrillary acidic protein immunoreactivity (to show astrocytic response). Forty-eight hours after ischemia, C1-INH significantly improved general and focal deficits by 36% and 54%, respectively, and significantly reduced infarct volume (CI-INH, 6.69% +/- 2.93%; saline, 24.24% +/- 8.24%) of total brain. Neutral red staining further showed the strong protective effect of C1-INH in cortex, hippocampus, and striatum. Astrocyte activation induced by ischemia was not affected by C1-INH. These findings show that C1-INH displayed a potent neuroprotective action by effectively reducing ischemia-reperfusion injury.

Expression disparity of brain-derived neurotrophic factor immunoreactivity and mRNA in ischemic hippocampal neurons

We studied the spatial and temporal expression of BDNF immunoreactivity and mRNA in the hippocampal formation after transient forebrain ischemia in gerbils. Our study demonstrated that in the vulnerable CA1 neurons, there was a prolonged expression disparity between BDNF immunoreactivity and mRNA and the BDNF level was reduced, in contrast to the ischemia-resistant dentate gyrus neurons that showed transient expression disparity and maintained the BDNF level. This expression disparity of the neurotrophic factor may be related to delayed neuronal death. Double immunostaining showed that reactive astroglia and microglia could express BDNF, suggesting a possible involvement of these cells in the mechanism of neuronal survival after ischemia.

Expression of the p75 neurotrophin receptor by striatal cholinergic neurons following global ischemia in rats is associated with neuronal degeneration

The induction of the p75 neurotrophin receptor (p75NTR) on striatal cholinergic neurons by global hypoxic-ischemia has been reported to promote neuron survival. We have found, however, while the p75NTR-expressing neurons survive the insult for the first 5 days, subsequently they undergo shrinkage, loss of choline acetyl transferase (ChAT) expression, and more than 96% are eventually lost by 8 days. In contrast ChAT-expressing cells in the surrounding region of the infarction, do not express p75NTR and there is no evidence of neuronal loss. These results suggest the expression of p75NTR on cholinergic interneurons of the rat striatum is associated with delayed neuronal degeneration.

Plasticity-associated molecular and structural events in the injured brain

Injury to the brain appears to create a fertile ground for functional and structural plasticity that is, at least partly, responsible for functional recovery. Increases in dendritic arborization, spine density, and synaptogenesis in both peri-injury and intact cortical areas are the potential morphological strategies that enable the brain to reorganize its neuronal circuits. These injury-initiated alterations are time-dependent and frequently proceed in interaction with behavior-related signals. A complex concert of a variety of genes/proteins is required to tightly control these changes. Two broad categories of molecules appear to be involved. First, regulatory molecules or effector molecules with regulatory function, such as immediate early genes/transcription factors, kinase network proteins, growth factors, and neurotransmitter receptors, and second, structural proteins, such as adhesion molecules and compounds of synapses, growth cones, and cytoskeleton. A better understanding of the processes contributing to postinjury plasticity may be an advantage for developing new and more effective therapeutic approaches. This knowledge might also shed light on other forms of brain plasticity, such as those involved in learning processes or ontogeny.

Stress and nerve growth factor: findings in animal models and humans

Stress is elicited by environmental, social or pathological conditions occurring during the life of animals and humans that determine changes in the nervous, endocrine and immune systems. In the present review, we present data supporting the hypothesis that stress-related events both in animal models and humans are characterized by modifications of endogenous nerve growth factor (NGF) synthesis and/or utilization. Stress inducing alteration in NGF synthesis and/or utilization appears to be more severe during neurogenesis and in early postnatal life. However, NGF endogenously released during stress may promote remodeling of damaged tissues following acute and/or chronic stressful events.

Sources of anterior knee pain

The anterior part of the knee consists mainly of structures belonging to the patellofemoral joint, which includes a variety of tissues, such as cartilage, subchondral bone, synovial plicae, infrapatellar fat pad, retinacula, capsule, and tendons. Each of these structures, alone or in combination, can be a source of anterior knee pain. Unphysiologic load or changed metabolic activities can lead to structural failure with loss of homeostatic conditions.

Stereological assessment of vulnerability of immunocytochemically identified striatal and hippocampal neurons after global cerebral ischemia in rats

Detailed quantitative analysis of the vulnerability of different hippocampal and striatal neurons to global forebrain ischemia has not previously been performed. Here we have studied the survival of immunocytochemically identified neurons using an unbiased stereological method in rats subjected to global forebrain ischemia for 30 min and sacrificed 48 h, 1 week or 4 weeks thereafter. Within the hippocampal formation, there was extensive, progressive loss of CA1 pyramidal neurons and dentate hilar neuropeptide Y (NPY)-positive interneurons. In contrast, no reduction of the number of CA3 and CA4 pyramidal neurons or hilar parvalbumin-positive interneurons was detected. In the dorsolateral striatum, the insult caused a major loss of projection neurons immunoreactive to dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kilodalton (DARPP-32). The number of parvalbumin-positive striatal interneurons was significantly reduced, while NPY-positive interneurons were resistant. All striatal cholinergic interneurons survived the ischemic insult. At 48 h following the ischemia, the cholinergic interneurons within the lesioned striatum transiently expressed the p75 neurotrophin receptor (p75(NTR)), as shown by double-label immunocytochemistry. Furthermore, there was a significant increase in the number of choline acetyltransferase (ChAT)- and TrkA-immunoreactive interneurons at 4 weeks after the insult. Injections with the cell mitotic division marker BrdU provided no evidence that the elevated cholinergic cell number was due to neurogenesis. Probably, the higher number of ChAT- and TrkA-positive interneurons reflected increased intracellular levels of the corresponding proteins leading to more cells detectable with immunocytochemistry. This study gives the first quantitative description of the vulnerability of defined hippocampal and striatal neurons after global forebrain ischemia. The ischemia-induced increases of p75(NTR), TrkA and ChAT in cholinergic striatal interneurons at various time points after the insult suggest that neurotrophin signaling might be important for the survival and function of these cells in the post-ischemic phase.

Sleep deprivation but not a whisker trim increases nerve growth factor within barrel cortical neurons

Sleep is hypothesized to influence activity-driven changes in the brain microcircuitry. A change in the barrel cortex following the removal of the mystacial whiskers in rats is a model for synaptic plasticity. This model was combined with sleep deprivation and immunoreactivity for nerve growth factor (NGF) was determined. Sleep deprivation for 6 h after light onset significantly increased the number of NGF-immunoreactive pyramidal neurons in layer V of the barrel cortex. However, unilateral trimming of mystacial whiskers did not affect NGF immunoreactivity in the contralateral or ipsilateral barrel cortices when rats were allowed to sleep. If the rats received a unilateral whisker cut at light onset, and subsequently were deprived of sleep, increases in the NGF-immunoreactive neurons were only observed in the barrel cortex on the side that received input from the remaining intact whiskers. In contrast, NGF immunoreactivity on the side contralateral to the cut whiskers decreased in sleep-deprived animals to levels below those observed in the control animals that were allowed to sleep. These results suggest that NGF expression is influenced by the interaction of sleep, afferent input and the nature of ongoing synaptic reorganization. Further, results are consistent with the hypothesis that growth factors, such as NGF, form part of the mechanism responsible for sleep regulation and that they also form one facet of sleep-related synaptic plasticity.

Does fucose or piracetam modify the effect of hypoxia preconditioning against pentylenetetrazol-induced seizures?

To clarify the question whether the duration of hypoxia exposure has an influence on the point in time or the strength of hypoxic preconditioning, hypoxia exposure of rats lasting 1 and 8 h was tested regarding the modification of susceptibility to acute pentylenetetrazol-induced seizures. Following the short-lasting (1 h) hypoxia, the maximum level of preconditioning action was observed 7 days after hypoxia, whereas the longer-lasting hypoxia (8 h) produced the maximum level of protection 14 days after hypoxia. We investigated the influence of fucose and piracetam on the effect of hypoxia preconditioning by the application of the substances 20 min before the beginning of hypoxia exposure. Fucose did not modify the result of hypoxia preconditioning. But after the treatment with piracetam, the preconditioning effect was prevented following hypoxia lasting 1 and 8 h. We suggest that the radical scavenger properties of piracetam are responsible for the absence of protection against pentylenetetrazol-evoked seizures.

Expression of fos-related antigen-2 in rat hippocampus after middle cerebral arterial occlusion

AP-1 transcription factors have been shown to be induced in the brain after ischemic injury. However, their roles in neuronal survival or death have yet to be defined. Here, we report the discovery of elevated nuclear levels of fos-related antigen-2 (FRA-2) in the nuclei of hippocampal neurons seven days after middle cerebral artery occlusion (MCAO). Expression of FRA-2 and AP-1 DNA binding activity is elevated in hippocampi ipsilateral as well as contralateral to MCAO. Using Fluoro-Jade staining as a marker of neurodegeneration, FRA-2 was not found to be expressed in degenerating neurons. Thus, FRA-2 is expressed in neurons that survive ischemic insult suggesting a role for this transcription factor in neuronal adaptation to the post-injury state.

Glial cells as targets and producers of neurotrophins

Glial cells fulfill important tasks within the neural network of the central and peripheral nervous systems. The synthesis and secretion of various polypeptidic factors (cytokines) and a number of receptors, with which glial cells are equipped, allow them to communicate with their environment. Evidence has accumulated during recent years that neurotrophins play an important role not only for neurons but also for glial cells. This brief update of some morphological, immunocytochemical, and biochemical characteristics of glial cell lineages conveys our present knowledge about glial cells as targets and producers of neurotrophins under normal and pathological conditions. The chapter discusses the presence of neurotrophin receptors on glial cells, glial cells as producers of neurotrophins, signaling pathways downstream Trk and p75NTR, and the significance of neurotrophins and their receptors for glial cells during development, in cell death and survival, and in neurological disorders.

Ischemic tolerance in murine cortical cell culture: critical role for NMDA receptors

Murine cortical cultures containing both neurons and glia (days in vitro 13-15) were exposed to periods of oxygen-glucose deprivation (5-30 min) too brief to induce neuronal death. Cultures "preconditioned" by sublethal oxygen-glucose deprivation exhibited 30-50% less neuronal death than controls when exposed to a 45-55 min period of oxygen-glucose deprivation 24 hr later. This preconditioning-induced neuroprotection was specific in that neuronal death induced by exposure to excitotoxins or to staurosporine was not attenuated. Neuroprotection was lost if the time between the preconditioning and severe insult were decreased to 7 hr or increased to 72 hr and was blocked if the NMDA antagonist 100 microM 3-((D)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid was applied during the preconditioning insult. This was true even if the duration of preconditioning was increased as far as possible (while still remaining sublethal). A similar preconditioning effect was also produced by sublethal exposure to high K+, glutamate, or NMDA but not to kainate or trans-1-aminocyclopentane-1, 3-dicarboxylic acid.

Recruitment of several neuroprotective pathways after permanent focal ischemia in mice

After an ischemic episode induced by the electrocoagulation of the left middle cerebral artery (MCA) in mouse, neurons within the damaged territory die either by an apoptotic or by a necrotic process. Most of the cortical neurons within the ischemic area display both morphological and biochemical signs of programmed cell death: nuclear condensation, DNA degradation, formation of apoptotic bodies, and glutathione depletion. In fact, apoptosis essentially contributes to the expansion of the ischemic lesion and the maximum of damaged territory is reached 24 h postocclusion. Several potentially neuroprotective pathways have been evidenced in different experimental models of ischemia including the activation of antioxidant enzyme activities and/or the recruitment of neurotrophic as well as antiapoptotic factors. In our model of permanent focal ischemia induced by MCA occlusion, we measured the temporal synthesis of nerve growth factor (NGF) and examined the status of antioxidant enzymes as well as Bcl-2 antiapoptotic product. We detected in both cortices a transient increase of NGF which peaks at 6 h. Moreover, we reported that glutathione peroxidase is recruited with a time course which parallels NGF synthesis. Finally, we observed the induction of Bcl-2 in safe neurons; this may represent a self-protective response against ischemia-induced apoptosis. We provide evidence that in a model of permanent focal ischemia, several neuroprotective pathways could be coactivated.

High potassium enhances secretion of neurotrophic factors from cultured astrocytes

Elevation of extracellular potassium concentration ([K+]o) in the central nervous system (CNS), which is observed such after physiological stimuli and during ischemia, is known to be regulated by astrocytes. We suspected that in response to increased [K+]o, astrocytes might secrete some neurotrophic factor(s) to promote the survival of active and/or ischemically damaged neurons. In the present study, we examined neurotrophic activity contained in HK-ACM, i.e., astrocyte-conditioned medium (ACM) obtained after culturing astrocytes in 40 mM potassium-containing medium (HK medium). Addition of HK-ACM to basal forebrain cultures from postnatal 2-week-old (P2w) rats increased both the choline acetyltransferase (ChAT) activity (4.40-fold) and the number of ChAT-positive neurons (2.01-fold) as compared with non-conditioned HK medium. On the other hand, the neurotrophic effects of LK-ACM, i.e., ACM collected after culturing astrocytes in 4 mM potassium-containing medium (LK medium), were much weaker (2.85- and 1.41-fold for ChAT activity and number of ChAT-positive neurons, respectively) than those of HK-ACM. The neurotrophic effects of ACMs increased in a manner dependent on potassium concentration and on astrocyte culture time. Addition of an antibody against nerve growth factor (NGF) neutralized the neurotrophic effects of HK- and LK-ACMs. Direct quantification of NGF protein in ACMs by the two-site ELISA method demonstrated that a high concentration of potassium enhanced NGF secretion from cultured astrocytes. These results suggested that astrocytes secrete NGF in response to [K+]o elevation in the CNS.

Neurotrophin-mediated neuroprotection by solid fetal telencephalic graft in middle cerebral artery occlusion: a preventive approach

In the present study, embryonic rat neocortex was implanted into the parietal subcortical area of adult naive animals. On the 7th day, the middle cerebral artery was permanently occluded ipsilateral to the graft. Twenty-four hours after middle cerebral artery occlusion, the extent of infarct was visualized by means of 2,3,5-triphenyltetrazolium chloride histochemistry and quantified in four different standardized coronal plains. Subsequently, the effects of fetal tissue grafting and those of transplantation were identified by using glial fibrillary acidic protein and nerve growth factor immunocytochemistry. The grafts integrated well into their new environment and significantly reduced the size of infarct in middle cerebral artery-occluded animals compared with both sham-operated and control rats 24 h postoperation. The underlying mechanism of this phenomenon might be an increased neurotrophic, particularly nerve growth factor, release by the grafted fetal tissue. Moreover, reactive astroglial cells may also trigger the neuroprotection by additional ischemia-induced nerve growth factor release. The present data demonstrate the potential neurotrophin-mediated protective effects of fetal brain tissue implanted into the adult rat brain before unilateral middle cerebral artery occlusion and the beneficial effects of astrocyte activation.

Expression of nerve growth factor and trkA after transient focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

In vitro studies have shown that nerve growth factor (NGF) is protective to cortical neurons against various insults. However, the role of NGF in relation to its high-affinity trkA receptor in the cortical neurons has not been well discussed. In this experiment, we studied the possible involvement of the NGF/receptor system in the ischemic injury of cortical neurons after focal cerebral ischemia in rats.

METHODS

Male Wistar rats received right middle cerebral artery occlusion of 90 minutes' duration. The rats were decapitated at different reperfusion time points: hour 4 and days 1, 3, 7, and 14 of recirculation. Brain sections at the level of striatum were immunostained against NGF, trkA, glial fibrillary acidic protein (GFAP), and stress protein HSP70. Double immunostaining against NGF and GFAP was also performed. Optical density of NGF immunoreactivity in the ischemic and nonischemic cortexes was compared between sham-control and ischemic animals.

RESULTS

In the sham-control rats, NGF immunoreactivity was present in the cortical and striatal neurons. However, beginning at hour 4 after recirculation, there was a significant decrease of NGF in the ischemic cortex and striatum. Beginning at day 1, NGF was absent completely in the infarcted striatum and cortex. However, in the peri-infarct penumbra area, despite a decrease in NGF at hour 4 and day 1, NGF recovered beginning at day 3 and returned almost to the sham-control level at day 14. In the nonischemic cortex, NGF increased beginning at hour 4, peaked at day 7, and returned almost to the sham-control level at day 14. The trkA and HSP70 immunoreactivities were not present in the sham-control cortex. However, trkA was induced at hour 4 in the ischemic cortex and at days 1 and 3 in the peri-infarct penumbra cortex. The HSP70 was induced at days 1 and 3 in the peri-infarct penumbra area. Double immunostaining showed that the number of GFAP-positive cells increased gradually, and NGF immunoreactivity in the GFAP-positive cells became gradually intense after ischemia.

CONCLUSIONS

Our study demonstrated a temporal profile of NGF and trkA in the ischemic cortex and NGF expression by reactive astrocytes. Our data suggest that the NGF/receptor system may play a role in the astrocyte/neuron interaction under certain pathological conditions, such as focal cerebral ischemia.

Focal cerebral ischemia in rats induces expression of P75 neurotrophin receptor in resistant striatal cholinergic neurons

Expression of p75 neurotrophin receptor and survival of medium-sized spiny projection neurons and cholinergic interneurons in the rat striatum were studied using immunocytochemistry at different times after transient, unilateral middle cerebral artery occlusion. Thirty minutes of middle cerebral artery occlusion caused a major loss of projection neurons, identified by their immunoreactivity to dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein with a molecular weight of 32,000, in the lateral part of the striatum, as observed at 48 h following the insult with no further change at one week. In contrast, no reduction of the number of choline acetyltransferase-positive, cholinergic interneurons, which also expressed TrkA, was detected at either time-point. At 48 h following middle cerebral artery occlusion, expression of p75 neurotrophin receptor was observed in striatal cells which, by the use of double-label immunostaining, were identified as the cholinergic interneurons. No p75 neurotrophin receptor immunoreactivity remained in cholinergic cells after one week of reperfusion. Based on current hypotheses regarding the function of the p75 neurotrophin receptor, the transient expression of this receptor in striatal cholinergic interneurons might contribute to their high resistance to ischemic neuronal death. However, the expression of p75 neurotrophin receptor could also be a first step in a pathway leading to apoptosis, which is inhibited after the present insult due to concomitant activation of TrkA.

Reduction of cortical infarction and impairment of apoptosis in NGF-transgenic mice subjected to permanent focal ischemia

The neuroprotective potential of the nerve growth factor (NGF) against permanent ischemic brain damage has been investigated in vivo using NGF-transgenic (tg) mice. The expression of the transgene is driven by part of the promoter of the proto-oncogene c-fos, which belongs to the first set of genes activated after brain ischemic insult. Wild-type (wt) mice and tg mice were subjected to permanent focal ischemia induced by electrocoagulation of the middle cerebral artery. Twenty four hours (h) after the ischemic shock, when compared to wt, tg mice displayed a 40% reduction of the infarcted area, which lasted up to 1 week. However, infarcted brain areas were similar in wt and tg mice within the first hours post-occlusion, indicating that NGF acted to block the progression of neuronal damage. Kinetics of NGF synthesis assessed by ELISA was in good agreement with the observed neuroprotective effect, since NGF content peaked 6 h post-ischemia. This was further correlated with the time-course of c-Fos immunoreactivity, detectable only from 6 h post-ischemia. The neuroprotective effect of NGF involved the impairment of apoptotic cell death, as evidenced by a marked decrease of the number of apoptotic profiles inside the ischemic zone in tg mice. These results underline the potential of c-fos-NGF-tg mice to study in vivo the molecular and cellular mechanisms of the NGF-induced neuroprotective effect against ischemic damage.

GM1 ganglioside potentiates trimethyltin-induced expression of interleukin-1 beta and the nerve growth factor in reactive astrocytes in the rat hippocampus: an immunocytochemical study

This study demonstrates potentiation by GM1 ganglioside treatment of trimethyltin (TMT) induced reactivity of astrocytes, and the expression of astroglial interleukin-1 beta (IL-1 beta) and nerve growth factor (NGF) immunoreactivities in the rat hippocampus. GM1 treatment also results in an increase of the number of IL-1 beta and NGF immunoreactive astrocytes. Both the intensity of gliosis and stimulation of IL-1 beta and NGF expression in astrocytes mostly occurs in the regions of heaviest neurodegeneration in the hippocampus (CA4/CA3c and CA1). It is tempting to assume that enhancement of astroglial NGF expression by GM1 ganglioside may play a role in the protective action of GM1 against neurotoxic insult.

Time-course changes of nerve growth factor, corticotropin-releasing hormone, and nitric oxide synthase isoforms and their possible role in the development of inflammatory response in experimental allergic encephalomyelitis

In this paper we report a time-course study of development of experimental allergic encephalomyelitis in Lewis rats, by monitoring neuroendocrine regulation of the hypothalamus-pituitary-adrenal axis through corticotropin-releasing hormone mRNA expression, inflammatory cellular infiltrate, macrophagic and neuronal nitric oxide synthase, nerve growth factor (NGF), and NGF p75 and trkA receptors in the brain and spinal cord. We analyzed animals during 20 days after immunization, a time interval that corresponds to the acute immunological phase. We have described a severe, early fall of corticotropin-releasing hormone mRNA expression, which could account for the decreased response of the hypothalamus-pituitary-adrenal axis to inflammatory stress. During this period, an increase of neuronal nitric oxide synthase was observed in the cerebral cortex and spinal cord, and macrophagic nitric oxide synthase positive cells were found in the inflammatory cellular infiltrate, which was abundant in perivascular and submeningeal areas 20 days after immunization. Concomitantly, we found a dramatic up-regulation of NGF receptors on the wall of blood vessels and adjacent neurons in perivascular areas. NGF content also had increased in some brain areas, such as the thalamus, while it had decreased in others, like the spinal cord and medulla oblongata, at time points in which the most serious cellular infiltrate was found.