Origin of contralateral reactive gliosis in surgically injured rat cerebral cortex

The S100A4 Protein Signals through the ErbB4 Receptor to Promote Neuronal Survival

Understanding the mechanisms of neurodegeneration is crucial for development of therapies to treat neurological disorders. S100 proteins are extensively expressed in the injured brain but S100's role and signalling in neural cells remain elusive. We recently demonstrated that the S100A4 protein protects neurons in brain injury and designed S100A4-derived peptides mimicking its beneficial effects. Here we show that neuroprotection by S100A4 involves the growth factor family receptor ErbB4 and its ligand Neuregulin 1 (NRG), key regulators of neuronal plasticity and implicated in multiple brain pathologies. The neuroprotective effect of S100A4 depends on ErbB4 expression and the ErbB4 signalling partners ErbB2/Akt, and is reduced by functional blockade of NRG/ErbB4 in cell models of neurodegeneration. We also detect binding of S100A4 with ErbB1 (EGFR) and ErbB3. S100A4-derived peptides interact with, and signal through ErbB, are neuroprotective in primary and immortalized dopaminergic neurons, and do not affect cell proliferation/motility - features which make them promising as potential neuroprotectants. Our data suggest that the S100-ErbB axis may be an important mechanism regulating neuronal survival and plasticity.

Correlation Between Extravasation and Alterations of Cerebrovascular Laminin and β-Dystroglycan Immunoreactivity Following Cryogenic Lesions in Rats

The blood-brain barrier becomes "leaky" following lesions. Former studies revealed that following lesions the immunoreactivity of cerebrovascular laminin becomes detectable whereas that of β-dystroglycan disappears. These alterations may be indicators of glio-vascular decoupling that may result in the impairment of the blood-brain-barrier. This study investigates correlation between the post-lesion extravasation and the above-mentioned immunohistochemical alterations. Following cryogenic lesions, the survival periods lasted 5, 10, 30 minutes, 1 or 12 hours, or 1 day. Some brains were fixed immediately post-lesion. Immunofluorescent reactions were performed in floating sections. The extravasation was detected with immunostaining for plasma fibronectin and rat immunoglobulins. When the survival period was 30 minutes or longer, the area of extravasation corresponded to the area of altered laminin and β-dystroglycan immunoreactivities. Following immediate fixation some laminin immunoreactivity was already detected. The extravasation seemed to precede this early appearance of laminin immunoreactivity. The β-dystroglycan immunoreactivity disappeared later. When the extravasation spread into the corpus callosum, vascular laminin immunoreactivity appeared but the β-dystroglycan immunoreactivity persisted. It seems that extravasation separates the glial and vascular basal laminae, which results in the appearance of laminin immunoreactivity. The disappearance of β-dystroglycan immunoreactivity is neither a condition nor an inevitable consequence of the 2 other phenomena.

The role of different strain backgrounds in bacterial endotoxin-mediated sensitization to neonatal hypoxic-ischemic brain damage

•

Strain background plays a role in the response to hypoxia–ischemia.

•

LPS sensitizes the immature brain to hypoxia–ischemia across several mouse strains.

•

Vehicle injection may induce immune response and sensitization to hypoxia–ischemia.

Genetic background is known to influence the outcome in mouse models of human disease, and previous experimental studies have shown strain variability in the neonatal mouse model of hypoxia–ischemia. To further map out this variability, we compared five commonly used mouse strains: C57BL/6, 129SVJ, BALB/c, CD1 and FVB in a pure hypoxic–ischemic setup and following pre-sensitization with lipopolysaccharide (LPS).

Postnatal day 7 pups were subjected to unilateral carotid artery occlusion followed by continuous 30 min 8% oxygen exposure at 36 °C. Twelve hours prior, a third of the pups received a single intraperitoneal LPS (0.6 μg/g) or a saline (vehicle) administration, respectively; a further third underwent hypoxia–ischemia alone without preceding injection. Both C57BL/6 and 129SVJ strains showed minimal response to 30 min hypoxia–ischemia alone, BALB/c demonstrated a moderate response, and both CD1 and FVB revealed the highest brain damage. LPS pre-sensitization led to substantial increase in overall brain infarction, microglial and astrocyte response and cell death in four of the five strains, with exception of BALB/c that only showed a significant effect with terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Saline administration prior to hypoxia–ischemia resulted in an increase in inflammatory-associated markers, particularly in the astroglial activation of C57BL/6 mice, and in combined microglial activation and neuronal cell loss in FVB mice. Finally, two of the four strongly affected strains – C57BL/6 and CD1 – revealed pronounced contralateral astrogliosis with a neuroanatomical localization similar to that observed on the occluded hemisphere.

Overall, the current findings demonstrate strain differences in response to hypoxia–ischemia alone, to stress associated with vehicle injection, and to LPS-mediated pre-sensitization, which partially explains the high variability seen in the neonatal mouse models of hypoxia–ischemia. These results can be useful in future studies of fetal/neonatal response to inflammation and reduced oxygen–blood supply.

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

Brain resting-state functional MRI connectivity: morphological foundation and plasticity

Despite the immense ongoing efforts to map brain functional connections and organizations with resting-state functional MRI (rsfMRI), the mechanisms governing the temporally coherent rsfMRI signals remain unclear. In particular, there is a lack of direct evidence regarding the morphological foundation and plasticity of these rsfMRI derived connections. In this study, we investigated the role of axonal projections in rsfMRI connectivity and its plasticity. Well-controlled rodent models of complete and posterior corpus callosotomy were longitudinally examined with rsfMRI at 7T in conjunction with intracortical EEG recording and functional MRI tracing of interhemispheric neuronal pathways by manganese (Mn(2+)). At post-callosotomy day 7, significantly decreased interhemispheric rsfMRI connectivity was observed in both groups in the specific cortical areas whose callosal connections were severed. At day 28, the disrupted connectivity was restored in the partial callosotomy group but not in the complete callosotomy group, likely due to the compensation that occurred through the remaining interhemispheric axonal pathways. This restoration - along with the increased intrahemispheric functional connectivity observed in both groups at day 28 - highlights the remarkable adaptation and plasticity in brain rsfMRI connections. These rsfMRI findings were paralleled by the intracortical EEG recording and Mn(2+) tracing results. Taken together, our experimental results directly demonstrate that axonal connections are the indispensable foundation for rsfMRI connectivity and that such functional connectivity can be plastic and dynamically reorganized atop the morphological connections.

The metastasis-promoting S100A4 protein confers neuroprotection in brain injury

Identification of novel pro-survival factors in the brain is paramount for developing neuroprotective therapies. The multifunctional S100 family proteins have important roles in many human diseases and are also upregulated by brain injury. However, S100 functions in the nervous system remain unclear. Here we show that the S100A4 protein, mostly studied in cancer, is overexpressed in the damaged human and rodent brain and released from stressed astrocytes. Genetic deletion of S100A4 exacerbates neuronal loss after brain trauma or excitotoxicity, increasing oxidative cell damage and downregulating the neuroprotective protein metallothionein I+II. We identify two neurotrophic motifs in S100A4 and show that these motifs are neuroprotective in animal models of brain trauma. Finally, we find that S100A4 rescues neurons via the Janus kinase/STAT pathway and, partially, the interleukin-10 receptor. Our data introduce S100A4 as a therapeutic target in neurodegeneration, and raise the entire S100 family as a potentially important factor in central nervous system injury.

Histocompatibility and in vivo signal throughput for PEDOT, PEDOP, P3MT, and polycarbazole electrodes

Stimulation and recording of the in vivo electrical activity of neurons are critical functions in contemporary biomedical research and in treatment of patients with neurological disorders. The electrodes presently in use tend to exhibit short effective lifespans due to degradation of signal transmission resulting from the tissue response at the electrode-brain interface, with signal throughput suffering most at the low frequencies relevant for biosignals. To overcome these limitations, new electrode designs to minimize tissue responses, including conducting polymers (CPs) have been explored. Here, we report the short-term histocompatibility and signal throughput results comparing platinum and CP-modified platinum electrodes in a Sprague-Dawley rat model. Two of the polymers tested elicited significantly decreased astrocyte responses relative to platinum. These polymers also showed improved signal throughput at low frequencies and comparable signal-to-noise ratios during targeted intracranial electroencephalograms. These results suggest that CP electrodes may present viable alternatives to the metal electrodes that are currently in use.

Essential role of mitogen-activated protein kinase pathways in protease activated receptor 2-mediated nitric-oxide production from rat primary astrocytes

Protease-activated receptors (PARs) play important roles in the regulation of brain function such as neuroinflammation by transmitting the signal from proteolytic enzymes such as thrombin and trypsin. We and others have reported that a member of the family, PAR-2 is activated by trypsin, whose involvement in the neurophysiological process is increasingly evident, and is involved in the neuroinflammatory processes including morphological changes of astrocytes. In this study, we investigated the role of PAR-2 in the production of nitric oxide (NO) in rat primary astrocytes. Treatment of PAR-2 agonist trypsin increased NO production in a dose-dependent manner, which was mediated by the induction of inducible nitric-oxide synthase. The trypsin-mediated production of NO was mimicked by PAR-2 agonist peptide and reduced by either pharmacological PAR-2 antagonist peptide or by siRNA-mediated inhibition of PAR-2 expression, which suggests the critical role of PAR-2 in this process. NO production by PAR-2 was mimicked by PMA, a PKC activator, and was attenuated by Go6976, a protein kinase C (PKC) inhibitor. PAR-2 stimulation activated three subtypes of mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. NO production by PAR-2 was blocked by inhibition of ERK, p38, and JNK pathways. PAR-2 stimulation also activated nuclear factor-kappaB (NF-kappaB) DNA binding and transcriptional activity as well as IkappaBalpha phosphorylation. Inhibitors of NF-kappaB pathway inhibited PAR-2-mediated NO production. In addition, inhibitors of MAPK pathways prevented transcriptional activation of NF-kappaB reporter constructs. These results suggest that PAR-2 activation-mediated NO production in astrocytes is transduced by the activation of MAPKs followed by NF-kappaB pathways.

"Listening" and "talking" to neurons: implications of immune activation for pain control and increasing the efficacy of opioids

It is recently become clear that activated immune cells and immune-like glial cells can dramatically alter neuronal function. By increasing neuronal excitability, these non-neuronal cells are now implicated in the creation and maintenance of pathological pain, such as occurs in response to peripheral nerve injury. Such effects are exerted at multiple sites along the pain pathway, including at peripheral nerves, dorsal root ganglia, and spinal cord. In addition, activated glial cells are now recognized as disrupting the pain suppressive effects of opioid drugs and contributing to opioid tolerance and opioid dependence/withdrawal. While this review focuses on regulation of pain and opioid actions, such immune-neuronal interactions are broad in their implications. Such changes in neuronal function would be expected to occur wherever immune-derived substances come in close contact with neurons.

Characterization of the temporo-spatial effects of chronic bilateral intrahippocampal cannulae on interleukin-1beta

The implantation of a foreign object in the brain produces an acute neuroinflammatory state in which glia (astrocytes and microglia) may remain chronically activated in response to the inert foreign object. Activated glia can exhibit a sensitized pro-inflammatory response to immunogenic stimuli. This may be relevant to intracranial cannula implantation, which is commonly used to administer substances directly into the brain. If intracranial cannulation activates glia, a subsequent neuroinflammatory stimulus might induce a potentiated pro-inflammatory response, thereby introducing a potential experimental confound. We tested the temporal and spatial responses of interleukin-1beta (IL-1beta) to an acute immune challenge produced by lipopolysaccharide (LPS) in animals with chronic bilateral intrahippocampal cannulae implants (stainless steel). Cannulation increased the gene expression of the microglia activation antigens MHC II and CD11b, but not the astrocyte antigen GFAP. Moreover, this activation was temporally and spatially dependent. In addition, IL-1beta mRNA, but not IL-1beta protein, was significantly elevated in cannulated animals. Administration of LPS, however, significantly potentiated the brain IL-1beta response in cannulated animals, but not in stab wounded or naïve animals. This IL-1beta response was also temporo-spatially dependent. Thus, the pro-inflammatory sequelae of intracranial cannulation should be considered when designing studies of neuroinflammatory processes.

Abnormalities in skilled reaching movements are improved by peripheral anesthetization of the less-affected forelimb after sensorimotor cortical infarcts in rats

Unilateral damage to sensorimotor cortical (SMC) regions can profoundly impair skilled reaching function in the contralesional forelimb. Such damage also results in impairments and compensatory changes in the less-affected/ipsilesional forelimb, but these effects remain poorly understood. Furthermore, anesthetization of the ipsilesional hand in humans with cerebral infarcts has been reported to produce transient functional improvements in the paretic hand [Floel A, Nagorsen U, Werhahn KJ, Ravindran S, Birbaumer N, Knecht S, et al. Influence of somatosensory input on motor function in patients with chronic stroke. Ann Neurol 2004;56:206-12; Voller B, Floel A, Werhahn KJ, Ravindran S, Wu CW, Cohen LG. Contralateral hand anesthesia transiently improves poststroke sensory deficits. Ann Neurol 2006;59:385-8]. One aim of this study was to sensitively assay the bilateral effects of unilateral ischemic SMC damage on performance of a unimanual skilled reaching task (the single pellet retrieval task) that rats had acquired pre-operatively with each forelimb. The second aim was to determine whether partially recovered contralesional reaching function is influenced by anesthetization of the ipsilesional forelimb. Unilateral SMC lesions were found to result in transient ipsilesional impairments in reaching success and significant ipsilesional abnormalities in reaching movements compared with sham-operates. There were major contralesional reaching impairments which improved during a 4 week training period, but movements remained significantly abnormal. Anesthetization of the ipsilesional forelimb with lidocaine at this time attenuated the contralesional movement abnormalities. These findings indicate that unilateral ischemic SMC lesions impair skilled reaching behavior in both forelimbs. Furthermore, after partial recovery in the contralesional forelimb, additional improvements can be induced by transient anesthetization of the ipsilesional forelimb. This is consistent with the effects of unilateral anesthetization in humans which have been attributed to the modulation of competitive interhemispheric interactions. The present findings suggest that such interactions are also likely to influence skilled reaching function in rats.

Magnetic resonance spectroscopy as a measure of brain damage in multiple sclerosis

Recent MR studies have emphasised the importance of neuronal and axonal damage in multiple sclerosis. In this respect, proton MR spectroscopy (by monitoring levels of N-acetylaspartate, a putative marker of axonal integrity) has been particularly illuminating by showing indirect evidence of neurodegeneration in both lesional and non-lesional brain tissues from the earliest stages of the disease. The importance of these changes to patients' clinical disability argues for the primary role of neuronal pathology in the pathogenesis of the disease.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

Contralateral response of macrophages and astrocytes to injury in the cerebral hemisphere of 6‐day‐old rat following prenatal gamma irradiation

Wistar pregnant rats were exposed to a single 1.0 Gy dose of gamma rays on gestational days 13, 15, 17 or 19 (E13, E15, E17 and E19, respectively). When offsprings of the irradiated females became 6-day-old, they received a mechanical injury of the cerebral hemisphere. One or 2 days after the injury, [3H]thymidine was injected and the animals were perfused. Brain sections were processed for BSI-B4 isolectin histochemistry or immunohistochemistry for glial fibrillary acidic protein (GFAP) or S-100-beta protein and subjected to autoradiography to visualise proliferating and non-proliferating macrophages or proliferating astrocytes. Significant changes in the contralateral response to injury related to the day of prenatal irradiation could be detected. The response was minimal following irradiations performed on E15 and E17. At those stages of prenatal development, the majority of cortical neurons with interhemispheric connections were formed. Therefore, irradiation-induced reduction of the neurons might minimise transfer of pathogenic stimuli to contralateral areas via degenerating nerve fibers. Consequently, the degree at which the contralateral glial response reflected reactive changes at the lesion site might also be minimal. Results of the present study do not show in detail mechanisms underlying the differences in the contralateral reactivity to injury. They, however, might be of importance to histopathological investigations using animal models of cerebral dysplasia.

Specific features of chronic astrocyte gliosis after experimental central nervous system (CNS) xenografting and in Wobbler neurological mutant CNS

This study sets out to compare and contrast the astrocyte reaction in two unrelated experimental designs both resulting in marked chronic astrogliosis and natural motoneuron death in the wobbler mutant mouse and brain damage in the context of transplantation of xenogeneic embryonic CNS tissue into the striatum of newborn mice. The combined use of GFAP-labeling and confocal imaging allows the morphological comparison between these two different types of astrogliosis. Our findings demonstrate that, in mice, after tissue transplantation in the striatum, gliosis is not restricted to the regions of damage: it occurs not only near the site of transplantation, the striatum, but also in more distant regions of the CNS and particularly in the spinal cord. In the wobbler mutant mouse, a strong gliosis is observed in the spinal cord, site of motoneuronal cell loss. However, moderate astrocytic reaction (increased GFAP-immunoreactivity) can also be found in other wobbler CNS regions, remote from the spinal cord. In the wobbler ventral horn, where neurons degenerate, the hypertrophied reactive astrocytes exhibit a dramatic increase of glial fibrils and surround the motoneuron cell bodies, occupying most of the motoneuron environment. The striking and specific presence of hypertrophic astrocytes in wobbler mice accompanied by a dramatic increase of glial fibrils located in the vicinity of motoneuron cell bodies suggests that short astrogliosis fills the space left by degenerating motoneurons and interferes with their survival. In the spinal cord of xenografted mice, chronic astrogliosis is also observed, but only glial processes without hypertrophied cell bodies are found in the neuronal micro-environment. It is tempting to speculate that gliosis in the wobbler spinal cord, the local accumulation of astrocyte cell bodies, and high density of astrocytic processes may interfere with the diffusion of neuroactive substances in gliotic tissue, some of which are neurotoxic, and cooperate or even trigger neuronal death.

Mechanical trauma induces rapid astroglial activation of ERK/MAP kinase: Evidence for a paracrine signal

Astrogliosis is a prominent and ubiquitous reaction of astrocytes to many forms of CNS injury, often implicated in the poor regenerative capacity of the adult mammalian CNS. Transmembrane signals that rapidly trigger and maintain astroglial responses to injury are largely undefined. Several candidate inducers of astrogliosis, including growth factors and neuropeptides, act via the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway. We previously observed chronically activated ERK/MAPK in human reactive astrocytes. To investigate mechanisms of pathway activation in a defined in vitro model, primary cultured astroglial monolayers were subjected to focal mechanical injury. Within 2-10 min, ERK/MAPK was activated, but only in cells near the wound edge. By 30 min, the entire monolayer showed activation, which persisted for 4 to 8 h. ERK/MAPK activation was specifically blocked by application of the MEK inhibitors, PD98059 and U0126. Cell-cell contact was not necessary for intercellular spread of ERK/MAPK activation, and ERK/MAPK-stimulating activity was found in the injury-conditioned medium. The activating factor was shown to have a native size of 50-100 kD and did not signal through the classical EGF receptor. Injury-induced signaling to ERK/MAPK required Ras, as demonstrated by specific blockade after transient transfection with a dominant negative Ha-RasN17 construct. Finally, we demonstrated that focal lesioning of adult rat cortex induces a rapid activation and spreading of astroglial ERK/MAPK, suggesting that similar mechanisms may operate in astroglial activation following acute brain injury.

Early and specific expression of monocyte chemoattractant protein-1 in the thalamus induced by cortical injury

For many years it has been known that retrograde degeneration of thalamic neurons occurs following damage to the cerebral cortex, however, the molecular mechanisms which control this process are unknown. Recent studies have demonstrated microglial activation in thalamic nuclei well before the onset of retrograde neuronal cell death. Activated monocytes and microglia synthesize factors detrimental to neuronal survival as well as phagocytose damaged and dying neurons. Our previous studies demonstrated that monocyte chemoattractant protein-1 (MCP-1), a beta chemokine which attracts cells of monocytic origin to sites of injury, is rapidly expressed in the brain following visual cortical lesions. The present study examined the expression of MCP-1 messenger RNA and protein in the thalamus following a visual cortical lesion. Aspiration lesions of visual cortex were made in adult mice. At specific times after lesion, brains were harvested and dissected into specific regions. MCP-1 message as detected using northern analysis was absent in uninjured brain, but was elevated in the ipsilateral thalamus as rapidly as 1 h following the lesion. In situ hybridization localized MCP-1 message to subpial glial cells of the lateral geniculate nucleus (LGN) of the ipsilateral thalamus after injury. ELISA showed that MCP-1 protein levels were significantly elevated in the ipsilateral thalamus at 6 h, peaked at 12 h, and remained above baseline levels for at least 1 week post lesion. In addition, anti-GFAP staining demonstrated activated astrocytes localized to the ipsilateral LGN at 24 and 72 h after injury. The early expression and regional localization of MCP-1 mRNA and protein strongly suggest that MCP-1 is a critical molecule in the regulation of thalamic retrograde neuronal degeneration.

The hippocampus in spontaneously hypertensive rats: a quantitative microanatomical study

The influence of hypertension on the morphology of hippocampus was assessed in spontaneously hypertensive rats of two, four and six months and in age-matched normotensive Wistar-Kyoto rats. Values of systolic pressure were slightly increased in two-month-old spontaneously hypertensive rats in comparison with age-matched Wistar-Kyoto rats and augmented progressively with age in spontaneously hypertensive rats. No microanatomical changes were observed in the hippocampus of spontaneously hypertensive rats of two months in comparison with age-matched Wistar-Kyoto rats, whereas a decrease of white matter volume was observed in the CA(1) subfield and in the dentate gyrus of four-month-old spontaneously hypertensive rats. In the hippocampus of six-month-old spontaneously hypertensive rats a reduction of grey matter volume both in the CA(1) subfield and in the dentate gyrus, a loss of neurons affecting to a greater extent the CA(1) subfield and an increase of glial fibrillary acid protein-immunoreactive astrocytes was found. The occurrence of apoptosis and/or necrosis identified using the terminal deoxyribonucleotidyl transferase-mediated biotin-16-dUTP nick end labelling technique was also observed in the CA(1) subfield and to a lesser extent in the dentate gyrus. The only change noticeable in the CA(3) subfield of six-month-old spontaneously hypertensive rats was a slight increase in the number of glial fibrillary acid protein-immunoreactive astrocytes. These findings indicate the occurrence of neuronal loss and of astrocyte changes in the hippocampus of spontaneously hypertensive rats of six months, being the CA(1) subfield the area most affected. The relevance of these neurodegenerative changes in hypertension and the possible occurrence of apoptosis and/or necrosis as expression of hypertensive brain damage is discussed.

Diffusion barriers evoked in the rat cortex by reactive astrogliosis

Changes in extracellular space (ECS) diffusion parameters in astrogliotic tissue around a unilateral cortical stab wound were determined from concentration-time profiles of tetramethylammonium (TMA(+)) using TMA(+)-selective microelectrodes. Three diffusion parameters-ECS volume fraction alpha (alpha = ECS volume/ total tissue volume), tortuosity lambda (lambda(2) = D/ADC; where D is the free and ADC is the apparent diffusion coefficient of TMA(+) in the brain), and nonspecific TMA(+)uptake k'-were determined at 3, 7, 21, and 35 days postwounding (dpw), in the hemispheres ipsilateral and contralateral to the lesion. Following diffusion experiments, tissue sections were immunostained for glial fibrillary acidic protein (GFAP) and chondroitin-sulphate proteoglycans (CSPG). In the area 300-1000 micron around the wound, alpha was increased at 3, 7, and 21 dpw by about 20% but returned to control values at 35 dpw; lambda was increased at all four intervals, reaching a maximum at 7 dpw. k' was lower than in the contralateral hemisphere at 7, 21, and 35 dpw. Measurements 1,500-2,000 micron from the wound revealed only an increase in lambda at 7 dpw. The time course of changes in ECS diffusion parameters closely correlated with increased staining for GFAP and CSPG. Our results show that astrogliosis significantly changes the diffusion properties of nervous tissue, making it less permissive. Both hypertrophied astrocytic processes and an enhanced formation of some extracellular matrix molecules could affect, through changes in the diffusion of molecules in the ECS, neuron-glia communication, "cross-talk" between synapses, extrasynaptic transmission, and regenerative processes.

In vivo evidence for axonal dysfunction remote from focal cerebral demyelination of the type seen in multiple sclerosis

To test for axonal damage or dysfunction in white matter tracts remote from acute demyelinating lesions, we used brain proton magnetic resonance spectroscopic imaging to measure changes in N-acetyl aspartate (NAA), an index of neuronal integrity, in the white matter of the normal-appearing hemisphere of three patients with large, solitary brain demyelinating lesions of the type seen early in multiple sclerosis. During the acute phase of their disease, all patients showed normal ratios of NAA to creatine (Cr) resonance intensity throughout the hemisphere contralateral to the lesion. However, on examination 1 month later, all of the patients showed abnormally low NAA/Cr resonance intensity ratios (reduction of NAA/Cr by 22-35%) in voxels of the contralateral hemisphere which were homologous to the demyelinating lesion. Other voxels in the normal-appearing hemisphere showed normal NAA relative resonance intensities. The decrease in NAA/Cr in voxels of the normal-appearing hemispheres resolved in all patients after 6 months, with a time course similar to that observed for NAA from voxels within the lesions. We conclude that effects of damage or dysfunction to axons traversing inflammatory lesions can be transmitted over long distances in the normal-appearing white matter. Such remote, secondary effects may be an expression of dysfunction of axons in projection pathways or of the reorganization of functional pathways seen in brains recovering from an acute injury.

Chemical and anatomical changes in the striatum and substantia nigra following quinolinic acid lesions in the striatum of the rat: a detailed time course of the cellular and GABA(A) receptor changes

The pattern and time-course of cellular, neurochemical and receptor changes in the striatum and substantia nigra were investigated following unilateral quinolinic acid lesions of the striatum in rats. The results showed that in the central region of the striatal lesion there was a major loss of Nissl staining of the small to medium sized cells within 2 h and a substantial loss of neuronal staining within 24 h after lesioning. Immunohistochemical studies showed a total loss of calbindin immunoreactivity, a known marker of GABAergic striatal projection neurons, throughout the full extent of the quinolinic acid lesion within 24 h. Similarly, within 24 h, there was a total loss of somatostatin/neuropeptide Y cells in the centre of the lesion but in the periphery of the lesion these cells remained unaltered at all survival times. Striatal GABA(A) receptors remained unchanged in the lesion for 7 days, and then declined in density over the remainder of the time course. Glial fibrillary acidic protein immunoreactive astrocytes were present in the periphery of the lesion at 7 days, occupied the full extent of the lesion by 4 weeks, and remained elevated for up to 2 months. In the substantia nigra, following placement of a striatal quinolinic acid lesion, there was: a loss of substance P immunoreactivity within 24 h; a marked astrocytosis evident from 1-4 weeks postlesion; and, a major increase in GABA(A) receptors in the substantia nigra which occurred within 2 h postlesion and was sustained for the remainder of the time course (15 months). This study shows that following quinolinic acid lesions of the striatum there is a major loss of calbindin and somatostatin/neuropeptide Y immunoreactive cells in the striatum within 24 h, and a marked increase in GABA(A) receptors in the substantia nigra within 2 h. These findings are similar to the changes in the basal ganglia in Huntington's disease and provide further evidence supporting the use of the quinolinic acid lesioned rat as an animal model of Huntington's disease.

Astrocyte changes in aging cerebral cortex and hippocampus: a quantitative immunohistochemical study

Glial cells are sensitive to aging, but the real extent of age-related quantitative and qualitative changes of these brain cellular elements has not yet been clarified. Brain volume undergoes age-related changes, but several studies on the number of glial cells have not taken this important variable into account. In this study we quantitatively evaluated the number and morphology of glial fibrillary acidic protein (GFAP)-immunoreactive astroglia in the frontal cortex and in the CA1 subfield of the hippocampus of male Sprague-Dawley rats of aged 12 and 24 months, considered adult and aged, respectively. The volume of frontal cortex was unchanged in the two age groups investigated, whereas the volume of hippocampus was higher in aged rats. An increase in the number and size of GFAP-immunoreactive astrocytes was observed in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats. The numeric increase in astrocytes was more pronounced in the hippocampus than in the frontal cortex, whereas age-related hypertrophy of astroglia was more accentuated in the frontal cortex. The possible significance of hyperplasia and hypertrophy of GFAP-immunoreactive astrocytes in the frontal cortex and in the CA1 subfield of the hippocampus of aged rats is discussed.

Selective chemokine mRNA expression following brain injury

Injury in non-neuronal tissues stimulates chemokine expression leading to recruitment of inflammatory cells responsible for orchestration of repair processes. The signals involved in directing repair of damage to the brain are less well understood. We hypothesized that following brain injury, chemokines are expressed and regulate the rate and pattern of inflammatory cell accumulation. The two chemokine subfamilies are alpha(alpha)-chemokines, which primarily function as neutrophil chemoattractants, and the beta(beta)-chemokines, which function primarily as monocyte chemoattractants. We assessed alpha and beta chemokine mRNA expression patterns and leukocyte accumulation following a cerebral cortical lesion. Cortical lesions were produced with and without addition of endotoxin, Escherichia coli lipopolysaccharide (LPS), which stimulates cytokine expression. We studied the expression of the beta-chemokines: monocyte chemoattractant protein (gene product JE; MCP-1/JE), macrophage inflammatory protein-1 alpha and beta (MIP-1alpha and MIP-1beta), and the regulated upon activation normal T expressed and secreted chemokine (RANTES) as well as the alpha-chemokines: interferon-gamma-inducible protein (IP-10) and N51/KC (KC; a murine homologue of MIP-2). Changes in gene expression were analyzed by Northern analysis at different time points following injury. Leukocyte and macrophage densities were analyzed by immunohistochemistry at the same time intervals. All chemokines were elevated following cortical injury/endotoxin. MCP-1 and MIP-1alpha were elevated at 2 h and peaked 6 h, MIP-1beta peaked at 6 h, but declined more rapidly than MCP-1 or MIP-1alpha, and IP-10 peaked at 6 h and showed the most rapid decline. KC was elevated at 1 h, and peaked at 6 h following LPS. RANTES was elevated at 1 h and achieved a plateau level between 6 and 18 h, then declined. In contrast, sterile injuries produced in the absence of endotoxin only induced the mRNA of the beta-chemokine MCP-1, and its expression was delayed compared to the cortical injury/endotoxin group. The presence of chemokine message as early as 1 h indicates that expression of this class of molecules is an early response in the repair process following traumatic brain injury. Macrophage/microglia accumulation occurred more rapidly, activated microglia further from the lesion border, and more cells accumulated in cortical injury/endotoxin than in cortical lesions produced under sterile conditions. Thus, there was a positive correlation between beta-chemokine expression and the number of beta-chemokine responsive cells (i.e. microglia) accumulating in injury sites. This is the first comprehensive study using a panel of chemokine probes and specific marcophage/microglial markers to study in vivo activation of the brain following injury. Our data show that the brain is capable of expression of multiple chemokine genes upon appropriate stimulation (e.g. LPS-treatment). The gradient of microglial activation is consistent with physical damage stimulating release of chemokines that diffuse from the injury site. These data strongly suggest that chemokines are instrumental in the initiation of repair processes following brain injury.

Histological markers of neuronal, axonal and astrocytic changes after lateral rigid impact traumatic brain injury

The model of lateral, rigid impact traumatic brain injury is widely used but remains relatively poorly characterized by comparison with fluid percussion injury models. Thus, whilst the gross morphological changes that occur over the short- and long-term post-injury have been described, more subtle measures of neuronal injury and activation, and markers of axonal and glial reactions have not been investigated, complicating interpretation of data from this model. To address this issue, a variety of neurohistological markers were examined in adult male rats which had been subjected to open brain, lateral rigid impact injury. A piston device was unilaterally driven 3.0 mm into the somatosensory cortex at a speed of 3.2 m/s. Neuronal activation evidenced by Fos-like immunoreactivity showed a complex pattern at 3 h after injury which appeared to be related both to proximity to the impact site and cortical efferent connectivity. At 24 h after injury, acid fuchsin staining demonstrated dying neurons in the margin of the injury and in ipsilateral hippocampus and dorsal thalamus. Injured cells identified by heat-shock protein immunoreactivity showed a similar distribution. Axonal injury demonstrated with 68 kDa neurofilament immunoreactivity was more widely distributed. Less axonal damage was found with increasing distance from the injury site. At 7 days post-injury, glial fibrillary acidic protein immunoreactive astrocytes were prolific in the ipsilateral thalamus, hippocampus and striatum and throughout the injured cortex. In general, controlled, lateral rigid impact injury provides a more focused injury than is seen with lateral fluid percussion which may have implications for the behavioral deficits seen in this injury model.

Astrogliosis in the neonatal and adult murine brain post-trauma: elevation of inflammatory cytokines and the lack of requirement for endogenous interferon-gamma

The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF)-alpha, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-alpha mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-gamma could be responsible for the observed increases in IL-1 and TNF-alpha, because IFN-gamma is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-gamma was demonstrated by three lines of evidence. First, no increase in IFN-gamma transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-gamma did not attenuate astrogliosis. Third, in IFN-gamma knockout adult mice, astrogliosis and increases in levels of IL-1alpha and TNF-alpha were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.

Metabolic and pathological effects of temporal lobe epilepsy in rat brain detected by proton spectroscopy and imaging

The goal of these experiments was to test the hypothesis that in an animal model of temporal lobe epilepsy (TLE), magnetic resonance spectroscopic measurement of N-acetylaspartate (NAA) and other metabolites, together with magnetic resonance imaging, provides a sensitive in vivo method to localize and monitor the progression of neuronal cell death and gliosis. Seizures were induced in rats by unilateral hippocampal injection of kainate. Magnetic resonance measurements were made from 1 to 84 days using proton spectroscopic imaging (1H-MRSI), T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI). The results were compared with findings on histological sections. Decreased NAA and creatine levels and increased apparent diffusion coefficient of water were found in the ipsilateral hippocampus after 14 days where neuronal loss and gliosis were observed. In the contralateral hippocampus a significant increase of choline level was observed. These results suggest that 1H-MRSI is a useful in vivo method for localizing neuronal loss and may also indicate additional pathological and metabolic alterations. In addition, DWI may be a useful method for in vivo detection of tissue alterations due to TLE.

Induction of astroglial gene expression by experimental seizures in the rat: spatio-temporal patterns of the early stages

The levels of glial fibrillary acidic protein mRNA were analysed by in situ hybridization during the first 6 h in experimental models of status epilepticus in the rat. Two different models of status epilepticus were studied: one is produced by the administration of pilocarpine to lithium-treated rats and the other by the intracerebroventricular administration of kainate. Results obtained in the present study showed a very rapid (as early as 1.5 h in periventricular zones of hypothalamus, cerebral cortex, and hippocampal area) up-regulation of GFAP mRNA levels following the pharmacological induction of seizures. Several other areas showed a GFAP activation starting at 3 h such as septum, habenular nuclei, corpus callosum, and cingulum. The comparison of the results obtained in the two models of status epilepticus revealed interesting differences in some brain areas, such as cerebellum and striatum, which can be related to the specific neurotransmitter receptors and neurochemical pathways stimulated by the drugs. Interestingly, some brain areas whose neurons are strongly activated by pilocarpine and kainate (amygdala and CA3 hippocampal field) and that undergo neuronal degeneration did not show the early GFAP response. An interesting spatial feature was observed in several brain regions examined (striatum, septum, and hypothalamus): the response first appeared in the periventricular zones and then diffused to the rest of the brain area. In general GFAP responses in the periventricular zones were early and intense.

On the significance of brain extracellular uric acid detected with in-vivo monitoring techniques: a review

The concentration of uric acid [UA] in the extracellular fluid (ECF) estimated with in-vivo voltammetry and microdialysis data is compared for probes of different diameters from the day of implantation (acute) to several days (chronic) or even months after surgery. For small probes (diameter < 160 microns) the acute [UA] of ca. 5 microM decreased significantly to ca. 1 microM under chronic conditions. For larger probes (e.g., 320-microns diameter) the acute [UA] was also ca. 5 microM, but this value significantly increased to ca. 50 microM under chronic conditions. Associated with this difference in [UA], there were parallel differences in the extent of gliosis around the probes. These findings are discussed in terms of possible sources of extracellular UA and their implications for in-vivo monitoring techniques in behaving animals.

Chronological study of peripheral benzodiazepine binding sites in the rat brain stab wounds using [3H] PK-11195 as a marker for gliosis

Chronological studies of the development of the peripheral benzodiazepine receptor sites were undertaken with the goal of evaluating the sensitivity of this marker for the study of the gliosis development in the injured brain. No significant increase in [3H] PK-11195 binding occurred in the rat brain stab wound one day following the puncture. A significant increase in the receptor density (Bmax) from the second day onward was observed. The Bmax reached its highest levels in the grey matter on the sixth day after a 23-gauge needle wound (8.75 +/- 0.09; pmol mg-tissue-1) and on the seventh day after an 18-gauge needle wound (8.98 +/- 0.31 pmol mg-tissue-1). In the white matter, the Bmax was greatest seven days after the wound (3.42 +/- 0.07; pmol mg-tissue-1; 23-gauge needle and 3.56 +/- 0.1 pmol mg-tissue-1 in the 18-gauge needle injury). Between 30 and 60 days after the wound, the Bmax was significantly lower than the Bmax observed between 6 and 14 days. The Bmax in the wound produced with needles was seven to eight times greater than the Bmax in the grey matter of the ipsilateral and contralateral cortices. Histological examination showed that there were no astrocytes or macrophages in the stab wound one day after the lesion. However, the glial fibrillary acidic protein positive cells and macrophages appeared on D3 after an injury. Gliosis, as measured by the PK-11195 binding, was also observed in the remote contralateral cortex. Data shows that PK-11195 binding is a very sensitive method of evaluating brain injury and could be of great value in studying progressive injuries in the living human brain in conjunction with positron emission tomography.

The concept of trophic units in the central nervous system

The present paper proposes that trophic interplay among cells may represent the final common pathway for both genetic and environmental influences, and hence new criteria for the understanding of central nervous system (CNS) connectivity can be suggested. In particular, trophic signals may make up the common "language" through which genetic and epigenetic influences mold the CNS during development and the adult life. Furthermore, it will put forward the hypothesis that the developmental trophic interplay among cells leads to the formation of trophic units in the adult brain. A trophic unit is defined as the smallest set of cells, within the CNS, which act in a complementary way to support each other's trophism. The trophic units consist of neurons, glial cells, blood vessels, extracellular matrix (ECM). In particular, ECM gives support to the thin elongated cell processes and gives rise to selective chemical bridges between cell surfaces or between cell surfaces and the extracellular milieu. The trophic unit is a plastic device that not only assures neuronal survival, but also operates to adapt neuronal networks to new tasks by controlling extension of neuronal processes, synapse turnover and ECM characteristics. These plastic responses depend on the interplay of all the elements that constitute the trophic units. The concept of trophic unit may help to understand some features of neurodegenerative diseases, for example, the clustering of tangles in the neocortex and in the entorhinal cortex of Alzheimer's patients [corrected].

Bilateral gliosis in unilaterally lesioned septohippocampal system: changes in GFAP immunoreactivity and content

Unilateral damage to the lateral fimbria led to a bilateral gliosis in the septum and hippocampus. The gliosis was manifested by an increase in GFAP staining, accompanied by an increased number of glial fibrillary acidic protein (GFAP)(+) cells and GFAP content; the latter however was not visible in the contralateral septum. In general, the contralateral reaction appeared weaker than the ipsilateral one. The pattern of contralateral increase in GFAP-immunoreactivity (IR) matched almost exactly that observed on the ipsilateral side in the hippocampus (the most evident increase was seen in the oriens and pyramidal layers of cornu Ammonis 3 and in polymorphic area of gyrus dentatus). In the septum the bilateral increase in GFAP-IR was mainly visible in the dorsolateral quadrant of the structure; however in the ipsilateral side it spread over the whole half of the structure. The astrocytic responses in the septum and hippocampus were not equivalent: they differed mainly with regard to the increase of GFAP(+) cells (over 300% of control in the anterior part of the septum and only about 120% in the dorsal hippocampus). The differences between the percentage increases of other gliotic indices: GFAP-IR and GFAP content. Various possibilities that may account for the occurrence of contralateral gliosis are discussed, the most plausible being the contribution of interhemispheric and intraseptal links and the action of some diffusible agents. We suggest that bilateral gliosis may have an impact on compensatory postlesion processes, possibly by providing trophic support to impaired neurons.

The oligodendroglial reaction to brain stab wounds: an immunohistochemical study

Myelin/oligodendrocyte specific protein was compared to glial fibrillary acidic protein and 2'3'-cyclic nucleotide 3'-phosphodiesterase expression in normal rat brains and following stab wounds to the cerebral cortex, corpus callosum and hippocampus. Animals with stab wounds were allowed to recover for 5, 15, 28, 45 and 70 days post-operation before fixation by perfusion. Sections were reacted with antibodies against myelin/oligodendrocyte specific protein, glial fibrillary acidic protein and 2'3'-cyclic nucleotide 3'-phosphodiesterase, and observed by light and electron microscopy. Normal cerebral cortex had very few myelin/oligodendrocyte specific protein-positive and 2'3'-cyclic nucleotide 3'-phosphodiesterase-positive cells, but some glial fibrillary acidic protein-positive cells. The myelinated fibres of the corpus callosum were heavily stained for myelin/oligodendrocyte specific protein but unstained by glial fibrillary acidic protein or 2'3'-cyclic nucleotide 3'-phosphodiesterase antibodies. Some immunopositive cells were present in the corpus callosum and hippocampus with all three antibodies. After stab wound myelin/oligodendrocyte specific protein-positive reactive cells had more and longer processes and stained more intensely than equivalent cells in normal brain. These cells were distributed along the wound track, including within the cerebral cortex. The numbers of these cells increased until 28 days post-operation and then decreased so that very few were found at 70 days post-operation except in the corpus callosum. Where demyelination occurred myelin/oligodendrocyte specific protein-staining was lost. Staining for 2'3-cyclic nucleotide 3'-phosphodiesterase revealed a similar pattern. Glial fibrillary acidic protein-positive reactive cells, which were also more robust than the normal cells, were more widely distributed. They increased in number throughout the time periods studied and gliosis was evident on the contralateral side. The glial fibrillary acidic protein-positive astrocytes were also different from the myelin/oligodendrocyte specific protein-positive and 2'3'-cyclic nucleotide 3'-phosphodiesterase-positive oligodendrocytes in terms of cell shape. With electron microscopy myelin/oligodendrocyte specific protein-positive cells showed features typical of immature oligodendrocytes. We conclude that the injury caused a numerical increase in oligodendrocytes and that myelin/oligodendrocyte specific protein is a good marker for the oligodendroglial response and demyelination in pathological conditions.

Increase in cortical procholecystokinin gene expression induced by a meningo-cortical injury: studies on the involvement of the "immediate early gene" c-fos

In rat cortex, a meningo-cortical injury causes complex changes in the expression of the "immediate early" genes c-fos and c-jun as well as the neuropeptide gene procholecystokinin. Within 1 h, mRNA levels of c-fos and c-jun are enhanced. Three hours later they have returned to control values. Twenty-four hours after the injury, there is a second rise in the level of c-fos-mRNA, which is accompanied by an increase in procholecystokinin-mRNA. In the present study, it was investigated whether these events are causally connected. When MK-801 (1.5 mg/kg), an ion-channel blocker, was injected 7 and 19 h after the injury, i.e. after the first rise in expression of both "immediate early" genes, it prevented the later increase in procholecystokinin-mRNA. When given 30 min prior to the injury, MK-801 (4 mg/kg) prevented the increased expression of c-fos but did not affect the later rise in procholecystokinin-mRNA. In a third experiment the cortex injury was performed in a manner which did not increase procholecystokinin-mRNA in frontal cortex. Nevertheless, expression of the c-fos gene was enhanced when determined 24 h after the operation. It is concluded that the injury-induced rise in the expression of the procholecystokinin gene is not connected with the changes in c-fos-mRNA.

Expression of insulin-like growth factor I by astrocytes in response to injury

Astrocytes are known to express several growth factors in response to injury and neurological disease. Insulin-like growth factor I (IGF-I) induces astrocytes to divide in vitro and is expressed by developing, but not adult astrocytes both in vivo and in vitro. We tested whether IGF-I is re-expressed by reactive astrocytes in response to injury. We found that astrocytes surrounding the lesioned parenchyma after introduction of a cannula through the cerebral cortex, hippocampus and midbrain contain high levels of immunoreactive IGF-I, as determined by immunocytochemistry using a highly sensitive and specific anti-IGF-I monoclonal antibody. Interestingly, the contralateral hippocampus also contained IGF-I positive astrocytes although in substantial lower numbers. Intact animals showed no detectable IGF-I immunoreactivity in astrocytes. IGF-I was detected at the first time point tested after the lesion was made, 1 week, and for at least 1 month thereafter. Reactive astrocytes expressing high levels of glial fibrillary acidic protein were found in a much wider distribution all along the lesioned area and beyond. We conclude that mechanical injury of the brain induces a specific pattern of expression of IGF-I by a subpopulation of astrocytes. These findings suggest that IGF-I is participating in the response of astrocytes to injury.

Quantitative aspects of reactive gliosis: a review

Recent studies of gliosis in a variety of animal models are reviewed. The models include brain injury, neurotoxic damage, genetic diseases and inflammatory demyelination. These studies show that reactive gliosis is not a stereotypic response, but varies widely in duration, degree of hyperplasia, and time course of expression of GFAP immunostaining, content and mRNA. We conclude that there are different biological mechanisms for induction and maintenance of reactive gliosis, which, depending on the kind of tissue damage, result in different expressions of the gliotic response.

In vivo effects of beta-amyloid implants in rodents: lack of potentiation of damage associated with transient global forebrain ischemia

Recent studies have shown that the principal component of the senile plaque in Alzheimer's disease (AD), beta-amyloid protein (beta AP) can exert direct and indirect neurotoxicity in vitro. Because of the studies that demonstrated potentiation of excitatory amino acid toxicity by beta AP, we decided to test whether beta AP was able to potentiate damage in an in vivo model where excitotoxic damage is thought to be important. The present study evaluated the in vivo effects of beta AP implants in the brain of rats before and after being subjected to 10 min of transient global forebrain ischemia by 4-vessel occlusion (4-VO). Implants of either synthetic beta AP or prolactin (PRL), which was used as a control protein, were made into the striatum and the hippocampus of either the left (beta AP) or the right (PRL) cerebral hemisphere. The implants were made in a lipophilic, non-toxic vehicle so as to try and achieve sustained beta AP exposure. One group of animals was evaluated for direct in vivo effects within 1 week following implantation; the other group was subjected to 4-VO 3-4 days post-implantation for evaluation of potential indirect effects. This latter group was compared to the histopathology of animals subjected to 4-VO without prior implantation. In the group of animals evaluated for direct effects, no evidence of neurotoxicity was observed. Bielschowsky silver staining and immunostaining for ubiquitin were unremarkable in all lesions. beta AP was detected by immunocytochemistry in the parenchymal tissue that received beta AP implants. Marked glial activation was observed to be associated with experimental and control implants. Under the experimental conditions employed in this study, significant protection from ischemia rather than potentiation of damage was observed. These results suggest that beta AP may not be neurotoxic in rodents in vivo and that the lesions and/or trauma produced by the implantation procedure 3-4 days prior to 4-VO may have induced factors that were protective against ischemia-induced damage.