Ablation of the chemokine monocyte chemoattractant protein-1 delays retrograde neuronal degeneration,attenuates microglial activation,and alters expression of cell death molecules

The mechanisms regulating retrograde neuronal degeneration and subsequent death of thalamic neurons following cortical injury are not well understood. However, the delay in the onset of retrograde cell death and observed morphological changes are consistent with apoptosis. Our previous studies demonstrated that monocyte chemoattractant protein-1 (MCP-1), a beta-chemokine that attracts cells of monocytic origin to sites of injury, is rapidly and specifically expressed in the lateral geniculate nucleus following visual cortical lesions. To determine the potential role of MCP-1 in retrograde degeneration, the present study examined the effect of genetic deletion of MCP-1 (MCP-1 KO or -/-) or its high affinity receptor CCR2 (CCR2 KO or -/-) on thalamic microglial activation and neuronal cell death following aspiration lesions of the visual cortex in adult mice. Deletion of the MCP-1 gene delayed microglial activation and transiently improved the survival of thalamic neurons. Deletion of the CCR2 receptor resulted in a significant increase in apoptosis as measured by nucleosomal fragmentation after injury compared to wild-type mice, but did not alter neuron survival, suggesting that glial apoptosis is increased in the receptor knockout mice. Investigation of Bcl-2, Bax, Fas, Fas ligand (FasL) and activated caspase-3, key regulators of apoptosis that can be modulated by cytokines, revealed complex alterations of mRNA and protein levels in MCP-1(-/-) and CCR2(-/-) mice. As examples, Bcl-2 protein was detected in wild-type, but not in MCP-1(-/-) mice. Caspase-3 activity was higher in MCP-1(-/-) mice compared to wild-type and CCR2(-/-) mice at 5 days after injury. High levels of activated caspase-3 correlate with the beginning of a period of delayed, but rapid cell death in the thalami of MCP-1(-/-) mice. In summary, our data strongly suggest that MCP-1 is involved in early microglial response to axotomy and that modulation of this chemokine could provide a novel strategy for improved neuronal survival following injury to the central nervous system.     

Thalamic projections to the lateral suprasylvian visual area in cats with neonatal or adult visual cortex damage.

Previous transneuronal anterograde tracing studies have shown that the retino-thalamic pathway to the posteromedial lateral suprasylvian (PMLS) visual area of cortex is heavier than normal in adult cats that received neonatal damage to visual cortical areas 17, 18, and 19. In contrast, the strength of this projection does not appear to differ from that in normal animals in cats that experienced visual cortex damage as adults. In the present study, we used retrograde tracing methods to identify the thalamic cells that project to the PMLS cortex in adult cats that had received a lesion of visual cortex during infancy or adulthood. In five kittens, a unilateral visual cortex lesion was made on the day of birth, and horseradish peroxidase (HRP) was injected into the PMLS cortex of both hemispheres when the animals were 10.5 to 13 months old. For comparison, HRP was injected bilaterally into the PMLS cortex of three cats 6.5 to 13.5 months after they received a similar unilateral visual cortex lesion as adults. In cats with a neonatal lesion, retrograde labeling was found in the large neurons that survive in the otherwise degenerated layers A and A1 of the lateral geniculate nucleus (LGN) ipsilateral to the lesion. Retrograde labeling of A-layer neurons was not seen in the undamaged hemisphere of these animals or in either hemisphere of animals that had received a lesion as adults. As in normal adult cats, retrograde labeling also was present in the C layers of the LGN, the medial interlaminar nucleus, the posterior nucleus of Rioch, the lateral posterior nucleus, and the pulvinar nucleus ipsilateral to a neonatal or adult lesion. Quantitative estimates indicate that the number of labeled cells is much larger than normal in the C layers of the LGN ipsilateral to a neonatal visual cortex lesion. Thus the results indicate that the heavier than normal projection from the thalamus to PMLS cortex that exists in adult cats after neonatal visual cortex damage arises, at least in part, from surviving LGN neurons in the A and C layers of the LGN. Although several thalamic nuclei, as well as the C layers of the LGN, continue to project to PMLS cortex after an adult visual cortex lesion, these projections appear not to be affected significantly by the lesion.     

Axotomy-induced neuronal death and reactive astrogliosis in the lateral geniculate nucleus following a lesion of the visual cortex in the rat

Following a unilateral lesion of the visual cortex (cortical areas 17, 18, and 18a) in adult rats, neurons in the ipsilateral dorsal lateral geniculate nucleus (LGN) are axotomized, which leads to their atrophy and death. The time course of this neuronal degeneration was studied quantitatively, and the astroglial response was examined with glial fibrillary acidic protein immunohistochemistry. More than 95% of the neurons in the ipsilateral LGN survive during the first 3 days following a lesion of the visual cortex. However, in the next 4 days, massive neuronal death ensues, reducing the number of surviving neurons to approximately 33% of normal by the end of the first postoperative week. Between 2 weeks and 24 weeks postoperatively, the number of neurons present in the LGN declines very gradually from 34% to 17% of normal. Three days after a lesion of the visual cortex, the mean cross-sectional areas of ipsilateral LGN neurons are 13% smaller than normal (87%). By 1 week after the operation, surviving LGN neurons have atrophied to 66% of their normal area. Subsequently, the size of surviving neurons declines slowly to approximately 50% of normal at 24 weeks after the cortical lesion. Astrocytes in the ipsilateral LGN also react to cortical damage. At 1 day after a lesion of the visual cortex, glial fibrillary acidic protein immunoreactivity in the LGN is almost undetectable, but a distinct increase in immunoreactivity is seen at 3 days. Immunoreactivity peaks between 1 week and 2 weeks postoperatively and, thereafter, remains intense for at least 24 weeks. Thus, following a lesion of the visual cortex, the somata of neurons in the LGN remain essentially normal morphologically for about 3 days before the onset of rapid atrophy and death. Moreover, most of the neural cell death that occurs in the LGN after axotomy takes place in the last half of the first postoperative week. J. Comp. Neurol. 392:252–263, 1998. © 1998 Wiley-Liss, Inc.     

Neural damage in the rat thalamus after cortical infarcts.

Histopathologic changes in the thalamus of 23 rats after somatosensory cortical infarction produced by middle cerebral artery occlusion were examined using the Fink-Heimer silver staining method, immunohistochemistry with antibodies against glial fibrillary acidic protein and laminin, and conventional stains. Middle cerebral artery occlusion produced cortical infarcts in the lateral parietal region, with variable involvement of the frontoparietal parasagittal sensorimotor cortex. Within 3 days after occlusion, massive terminal degeneration but no neuronal changes were apparent in the ipsilateral thalamus. By 1 week after occlusion, abnormal neurons with darkly stained, shrunken nuclei and atrophic perikarya were present in the ipsilateral thalamic nuclei. These neurons were densely argyrophilic in Fink-Heimer sections. Rats with small lateral parietal cortical lesions had degenerating neurons limited to the medial ventroposteromedial nucleus. Large lesions involving the parasagittal sensorimotor cortex resulted in widespread neuronal damage in the ventroposteromedial, ventroposterolateral, intralaminar, and posterior nuclear regions but nowhere else. Immunoreactivity to laminin antibody decreased, and astrocytic proliferation was abundant in affected thalamic areas. These findings are consistent with retrograde neuronal degeneration due to thalamocortical fiber damage in ischemic cortical regions. Such lesions remote from the infarct may influence functional recovery in patients with stroke.     

Recombinant basic fibroblast growth factor spares thalamic neurons from retrograde degeneration after ablation of the somatosensory cortex in rats

Retrograde degeneration of thalamic neurons after cortical ablation has long been recognized. Neuronal loss following axotomy eliminates the possibility of regeneration and might prevent the recovery from axonal injury in patients with brain trauma. We investigated whether CS23, a stable recombinant variant of human basic fibroblast growth factor (bFGF), could protect neurons from retrograde degeneration. Four weeks after ablation of the somatosensory cortex in young female rats, there was extensive neuronal degeneration and loss in the lateral ventro-posterior nucleus (VPL) of the ipsilateral thalamus. When Gelfoam soaked in bFGF(CS23) (1 μg/0.l ml) was applied topically at the time of surgery, this neuronal degeneration in the VPL was markedly reduced and macroscopic atrophy of the lateral and medial ventroposterior nucleus (VPL + VPM) was significantly reduced. In contrast, application of bFGF at three days after surgery failed to prevent retrograde degeneration. These resuts indicate that bFGF can prevent thalamic atrophy after ablation of the somatosensory cortex and that administration of bFGF is only effective in the very early period after brain injury.     

Injury-induced apoptosis of neurons in adult brain is mediated by p53-dependent and p53-independent pathways and requires Bax

The mechanisms of injury-induced apoptosis of neurons within the CNS are not understood. We used a model of cortical injury in rat and mouse to induce retrograde neuronal apoptosis in thalamus. In this animal model, unilateral ablation of the occipital cortex causes unequivocal apoptosis of corticopetal projection neurons in the dorsal lateral geniculate nucleus (LGN) by 7 days postlesion. We tested the hypothesis that p53 and Bax regulate this retrograde neuronal apoptosis. We found, by using immunocytochemistry, that p53 accumulates in nuclei of neurons destined to undergo apoptosis. By immunoblotting, p53 levels increase ( approximately 150% of control) in nuclear-enriched fractions of the ipsilateral LGN by 5 days after occipital cortex ablation. p53 is functionally activated in nuclear fractions of the ipsilateral LGN at 5 days postlesion, as shown by DNA binding assay (approximately fourfold increase) and by immunodetection of phosphorylated p53. The levels of procaspase-3 increase at 4 days postlesion, and caspase-3 is activated prominently at 5 days postlesion. To identify whether neuronal apoptosis in the adult brain is dependent on p53 and Bax, cortical ablations were done on p53 and bax null mice. Neuronal apoptosis in the dorsal LGN is significantly attenuated (approximately 34%) in p53(-/-) mice. In lesioned p53(+/+) mice, Bax immunostaining is enhanced in the ipsilateral dorsal LGN and Bax immunoreactivity accumulates at perinuclear locations in dorsal LGN neurons. The enhancement and redistribution of Bax immunostaining is attenuated in lesioned p53(-/-) mice. Neuronal apoptosis in the dorsal LGN is blocked completely in bax(-/-) mice. We conclude that neuronal apoptosis in the adult thalamus after cortical injury requires Bax and is modulated by p53.     

Ischemic axonal injury and its recovery after focal cerebral ischemia

After focal cerebral infarction by occluding the middle cerebral artery (MCA) of the rat, the neuronal death occurred in the ipsilateral thalamic neurons, because axons of the thalamic neurons were injured by infarction and retrograde degeneration occurred in the thalamic neurons. However, cortical neurons adjacent to the infarction survived despite their axons injured by ischemia. We employed immunohistochemical staining for 200 kilodalton (kD) neurofilament (NF), in order to study those responses of cortical and thalamic neurons against axonal injury caused by focal cerebral infarction. In the sham operated rats the immunoreactivity to the anti-200 kD NF antibody was only detected in the axon but not in the cell bodies and dendrites. At 3 days after MCA occlusion, axonal swelling proximal to the site of ischemic injury was found in the caudoputamen and internal capsule of the ipsilateral side. At 7 days after occlusion, cell bodies and dendrites of the neurons in the ipsilateral cortex and thalamus were strongly stained with anti-NF antibodies. At 2 weeks after occlusion these responses disappeared in the cortex, but lasted in the thalamus. These phenomena are caused by stasis of the slow axonal transport, because the NF is transported by slow axonal transport. In the cortical neurons impairment of slow axonal transport recovered in the early phase after injury, but in the thalamic neurons the impairment prolonged up to 3 weeks after occlusion. The early recovery of axonal transport from ischemia seemed to be essential for survival of neurons after ischemic axonal injury.     

Traumatic brain injury in the immature mouse brain: characterization of regional vulnerability

We characterized the regional and temporal patterns of neuronal injury and axonal degeneration after controlled cortical impact of moderate severity in mice at postnatal day 21. Animals were euthanized at 1, 3, or 7 days after injury or sham operation. The brains were removed and prepared for immunolocalization of neurons and microglia/macrophages or subjected to Fluoro-Jade and silver stains, indicators of irreversible neuronal cell injury and axonal degeneration. There was significant neuronal loss in both the ipsi- and the contralateral cortices, ipsilateral hippocampus, and ipsilateral thalamus by 7 days post injury compared to sham-operated animals. Activated microglia/macrophages were most prominent in regions of neuronal loss including the ipsilateral cortex, hippocampus, and thalamus. Neuronal injury, as evidenced by Fluoro-Jade labeling, was not apparent in sham-operated animals. In injured animals, labeling was identified in the ipsilateral cortex and hippocampus at 1 and 3 days post injury. Silver- and Fluoro-Jade-labeled degenerating axons were observed in the ipsilateral subcortical white matter by 1 day post injury, in the ipsilateral external capsule, caudate putamen, and contralateral subcortical white matter by 3 days post injury, and in the internal capsule, pyramidal tracts, and cerebellar peduncles by 7 days post injury. Our findings demonstrate that controlled cortical impact in the developing brain generates neuronal loss in both the ipsilateral and the contralateral cortex, a temporally distinct pattern of subcortical neuronal injury/death, and widespread white matter damage. These observations serve as an important baseline for studying human brain injury and optimizing therapies for the brain-injured child.     

Neuronal network disturbance after focal ischemia in rats

We studied functional disturbances following left middle cerebral artery occlusion in rats. Neuronal function was evaluated by [14C]2-deoxyglucose autoradiography 1 day after occlusion. We analyzed the mechanisms of change in glucose utilization outside the infarct using Fink-Heimer silver impregnation, axonal transport of wheat germ agglutinin-conjugated-horseradish peroxidase, and succinate dehydrogenase histochemistry. One day after occlusion, glucose utilization was remarkably reduced in the areas surrounding the infarct. There were many silver grains indicating degeneration of the synaptic terminals in the cortical areas surrounding the infarct and the ipsilateral cingulate cortex. Moreover, in the left thalamus where the left middle cerebral artery supplied no blood, glucose utilization significantly decreased compared with sham-operated rats. In the left thalamus, massive silver staining of degenerated synaptic terminals and decreases in succinate dehydrogenase activity were observed 4 and 5 days after occlusion. The absence of succinate dehydrogenase staining may reflect early changes in retrograde degeneration of thalamic neurons after ischemic injury of the thalamocortical pathway. Terminal degeneration even affected areas remote from the infarct: there were silver grains in the contralateral hemisphere transcallosally connected to the infarct and in the ipsilateral substantia nigra. Axonal transport study showed disruption of the corticospinal tract by subcortical ischemia; the transcallosal pathways in the cortex surrounding the infarct were preserved. The relation between neural function and the neuronal network in the area surrounding the focal cerebral infarct is discussed with regard to ischemic penumbra and diaschisis.     

Striate cortex projections to the lateral geniculate and other thalamic nuclei: a study using degeneration and autoradiographic tracing methods in the marmoset Callithrix

The thalamic projections of the striate cortex were investigated in the New World primateCallithrix jacchus with the experimental-anatomical method of anterograde fiber degeneration after cortical destruction and with autoradiography of tritiated proteins transported by axoplasmic flow after injection of [³H]proline into area 17. The findings of both methods were in accord with respect to the target loci: fibers of striate cortex origin were found to terminate in the ipsilateral nucleus geniculatus lateralis (LGN), nucleus praegeniculatus, nucleus reticularis thalami, nucleus pulvinaris lateralis, nucleus pulvinaris inferior, and nucleus posterior thalami. The projection upon the LGN appeared to be the most pronounced of the corticofugal projections of area 17.A characteristics finding in the autoradiographs of the LGN was a distinct labeling of the neuronal perikarya and of the walls of blood vessels within the focus of radioactivity. Since similar features were observed in the LGN after intraocular injection of [³H]proline, this neuronal labeling very probably was not due to retrograde transport but no a transneuronal transfer of labeled material.     

Expression of BCL-2 via adeno-associated virus vectors rescues thalamic neurons after visual cortex lesion in the adult rat

Lesions of the mammalian visual cortex cause the retrograde degeneration of the thalamic neurons projecting to the damaged cortex. The proto-oncogene bcl-2 is known to inhibit neuronal apoptosis induced by a variety of noxious stimuli and preserve the functional integrity of the injured cells. Here we have tested whether the overexpression of bcl-2 via adeno-associated virus (AAV) vectors is able to protect the neurons in the lateral geniculate nucleus after visual cortex ablation in adult rats. Recombinant AAV vectors encoding Bcl-2 (AAV-Bcl-2) or green fluorescent protein (AAV-GFP) as a control were stereotaxically injected into the geniculate. Three weeks after vector injection, the ipsilateral visual cortex was removed by aspiration, and cell survival was assessed 2 weeks later. We found that 20% of the geniculate neurons were transduced by the Bcl-2 vector. These cells were completely protected from death following cortical ablation. Delivery of AAV-GFP transduced an identical number of geniculate neurons but had no effect on cell survival after lesion. The total number of surviving geniculate neurons was found to be significantly higher in animals injected with AAV-Bcl-2 than in rats injected with AAV-GFP or in control lesioned rats. These data indicate that Bcl-2 gene therapy with AAV vectors represents an effective treatment to promote neuronal survival after central nervous system insults.     

Noradrenergic sprouting and beta-adrenergic receptor binding in the lateral geniculate nucleus of rats after unilateral visual cortex ablation

One and two weeks after unilateral visual cortex (VC) ablation beta-adrenergic receptor binding is increased in the lateral geniculate nucleus (LGN) of both sides. 6 month later beta-receptor binding in the LGN is decreased again and no differences to untreated control animals are detectable. Using the glyoxylic acid fluorescence method for the visualization of amines a transient increase in the density of noradrenergic fibers in the dorsal part of the ipsilateral LGN can be demonstrated with a maximum 2 weeks after VC ablation. With longer survival time noradrenergic fibre density in the ipsilateral dorsal LGN (LGNd) decreases again and one year after the operation only few fluorescent fibres can be observed in the lateral part of the LGN compared to untreated control animals. Histologically an increased gliosis in the ipsilateral LGNd develops following removal of the visual cortex. In addition, degenerative changes in nerve fibers and terminals as well as neuronal degenerative changes are present and are most pronounced in the medial part of the ipsilateral dorsal LGN. Electron microscopically degenerating terminals in the dorsal part of the ipsilateral LGN can be identified as cortical afferents. Using potassium permanganate fixation typical noradrenergic axons with small dense core vesicles can be demonstrated in the LGN. In the denervated LGNd (i.e. the ipsilateral LGNd after visual cortex ablation) axon terminals with dense core vesicles appear exhibiting the structural peculiarities of growth cones seen during ontogenesis. They could be regarded as ultrastructural equivalent of the newly formed noradrenergic sprouts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic correlates of lesion-specific plasticity: an in vivo imaging study

High-resolution positron emission tomography (microPET) allows for repeated observations of brain function in the same animal. In a previous study, using [(18)F] fluorodeoxyglucose (FDG) microPET, we demonstrated diminished glucose metabolism and subsequent recovery in the Neostriatum and thalamus ipsilateral to cortical aspiration (ASP) lesions. Thermocoagulation (TCL) of pial vessels has been shown to result in the same degree of cortical injury but induce more compensatory re-organization than ASP. In the present work, FDG microPET was used to compare glucose metabolism following both TCL and ASP lesions in order to determine whether metabolic differences correlate with the previously described anatomical and functional changes in the two lesion models. Animals were scanned 3-day, 10-day and 1-month post-injury. Estimated cortical lesion size did not differ between the two models at 1 month following injury. Both lesions induced ipsilateral neostriatal and thalamic hypometabolism 3-day post-injury, with subsequent metabolic improvement over time. However, complete recovery was not observed by 1 month in either group. ASP lesions resulted in an overall greater metabolic deficit in the subcortical structures and a greater cortical deficit 1 month following injury when compared to the TCL. Contralateral cortical glucose metabolism at 3 days following injury was not different in the two lesions. These data demonstrate that the two lesions differ somewhat in their metabolic response to injury, and that the relative hypometabolism observed following ASP may be a reflection of the diminished capacity of the contralateral cortex to compensate for ASP as compared to TCL.     

Chronic histopathological consequences of fluid-percussion brain injury in rats: effects of post-traumatic hypothermia

Early outcome measures of experimental traumatic brain injury (TBI) are useful for characterizing the traumatic severity as well as for clarifying the pathomechanisms underlying patterns of neuronal vulnerability. However, it is increasingly apparent that acute outcome measures may not always be accurate predictors of chronic outcome, particularly when assessing the efficacy of potential therapeutic regimens. This study examined the chronic histopathological outcome in rats 8 weeks following fluid-percussive TBI coupled with moderate post-traumatic brain hypothermia, a protocol that provides acute neuronal protection. Animals received a moderate parasagittal percussive head injury (2.01–2.38 atm) or sham procedure followed immediately by 3 h of brain hypothermia (30°C) or normothermia (37°C). Eight weeks following TBI, serial tissue sections were stained with hematoxylin and eosin or immunostained for glial fibrillary acidic protein. Tissue damage, gliosis and immunoreactive astrocytes were observed in the ipsilateral thalamus, hippocampus, and in the neocortex lateral to the injury site. Within the thalamus, focal necrosis was restricted to selective thalamic nuclei. Significant hippocampal cell loss was found in the ipsilateral dentate hilar region of both TBI groups. Quantitative volume measurements revealed significant decreases in cortical, thalamic and hippocampal volume ipsilateral to the impact in both TBI groups. Lateral ventricles were substantially enlarged in the TBI-normothermia group, an effect which was significantly attenuated by post-TBI hypothermia. The attenuation of lateral ventricular dilation by post-traumatic hypothermia is indicative of chronic neuroprotection in this TBI model. These data provide new information concerning the chronic histopathological consequence of experimental TBI and the relevance of this trauma model to chronic human head injury. Received: 10 May 1996 / Revised: 8 August 1996 / Revised, accepted: 11 September 1996     

Production of platelet-activating factor by neuronal cells in the rat brain with cold injury

The production and localization of platelet-activating factor (PAF) in the brain following focal brain injury were examined. Immunofluorescent staining was used to detect PAF in the rat brain with cold-induced local brain injury. After cold injury, immediate-early PAF staining was observed within the cold lesion followed later by immunoreactivity in the ipsilateral white matter. PAF immunoreactivity was also clearly seen both in cortical neurons adjacent to the cold lesion and in the ipsilateral hippocampus which showed delayed neuronal degeneration. The data suggest that PAF synthesis occurs in the neuronal cells in the perilesional area and hippocampus as well as within the cold lesion site during the early stages of cold-induced brain injury. PAF expression may contribute to the onset and progression of further brain damage, such as delayed axotomy and delayed neuronal loss.     

Early Neurodegeneration after Hypoxia-Ischemia in Neonatal Rat Is Necrosis while Delayed Neuronal Death Is Apoptosis

We used silver staining to demonstrate neuronal cell body, axonal, and terminal degeneration in brains from p7 rat pups recovered for 0, 1.5, 3, 6, 24, 48, 72 h, and 6 days following hypoxia-ischemia. We found that initial injury is evident in ipsilateral forebrain by 3 h following hypoxia-ischemia, while injury in ventral basal thalamus develops at 24 h. A secondary phase of injury occurs at 48 h in ipsilateral cortex, but not until 6 days in basal ganglia. Initial injury in striatum and cortex is necrosis, but in thalamus the neurodegeneration is primarily apoptosis. Degeneration also occurs in bilateral white matter tracts, and in synaptic terminal fields associated with apoptosis in regions remote from the primary injury. These results show that hypoxia-ischemia in the developing brain causes both early and delayed neurodegeneration in specific systems in which the morphology of neuronal death is determined by time, region, and potentially by patterns of neuronal connectivity.     

Mild traumatic brain injury to the infant mouse causes robust white matter axonal degeneration which precedes apoptotic death of cortical and thalamic neurons

The immature brain in the first several years of childhood is very vulnerable to trauma. Traumatic brain injury (TBI) during this critical period often leads to neuropathological and cognitive impairment. Previous experimental studies in rodent models of infant TBI were mostly concentrated on neuronal degeneration, while axonal injury and its relationship to cell death have attracted much less attention. To address this, we developed a closed controlled head injury model in infant (P7) mice and characterized the temporospatial pattern of axonal degeneration and neuronal cell death in the brain following mild injury. Using amyloid precursor protein (APP) as marker of axonal injury we found that mild head trauma causes robust axonal degeneration in the cingulum/external capsule as early as 30 min post-impact. These levels of axonal injury persisted throughout a 24 h period, but significantly declined by 48 h. During the first 24 h injured axons underwent significant and rapid pathomorphological changes. Initial small axonal swellings evolved into larger spheroids and club-like swellings indicating the early disconnection of axons. Ultrastructural analysis revealed compaction of organelles, axolemmal and cytoskeletal defects. Axonal degeneration was followed by profound apoptotic cell death in the posterior cingulate and retrosplenial cortex and anterior thalamus which peaked between 16 and 24 h post-injury. At early stages post-injury no evidence of excitotoxic neuronal death at the impact site was found. At 48 h apoptotic cell death was reduced and paralleled with the reduction in the number of APP-labeled axonal profiles. Our data suggest that early degenerative response to injury in axons of the cingulum and external capsule may cause disconnection between cortical and thalamic neurons, and lead to their delayed apoptotic death.     

Thalamic retrograde degeneration in the congenitally hydrocephalic rat is attributable to apoptotic cell death

Congenitally hydrocephalic HTX rats develop ventricular dilatation with extensive damage of the cerebral white matter. Recently, we have reported that neuronal cell death also occurs in the thalamus of HTX rats. To investigate the mechanism underlying this thalamic degeneration in these animals, we carried out a histopathological study of the brain at different phases of postnatal development. Eosinophilic neurons with condensed chromatin or fragmented nuclei were observed in the thalamus from postnatal day 17 onward. The incidence of cell death in the thalamus increased with the progression of hydrocephalus. Ultrastructurally, thalamic neurons occasionally had apoptotic features including nuclear chromatin condensation and marginalization. Immunohistochemically, single‐stranded DNA‐positive neuronal nuclei were found in the thalamus. They were also positively stained with the TUNEL method. Marked loss of myelin and axons with many TUNEL‐positive oligodendrocytes were found in the cerebral white matter. These findings suggest that the neuronal cell death observed in the thalamus in hydrocephalic HTX rats is retrograde degeneration due to extensive damage of axons in the cerebral white matter and that the thalamic retrograde degeneration is attributable to apoptotic cell death.     

Effects of cerebral cortical lesions on the ipsilateral thalamus

An injury to the central nervous system causes a focal logical disturbance, and further may affect the blood flow, metabolism, and function of other brain regions. Recent studies using PET or SPECT have demonstrated that impairment of regional hemodynamics or metabolism in cerebrovascular disease involves not only the site of the lesion itself but also more remote areas. Although depression of the metabolism of the ipsilateral thalamus in patients with cerebral cortical lesions has been shown by PET study, the pathophysiological implications of this remain unclear. The functional and morphological effects of cortical infarcts on the ipsilateral thalamus were studied by assessment of cerebral blood flow using 123I-IMP SPECT and by determining atrophic changes on CT or MRI. Nine out of 17 patients with cortical infarcts showed hypoperfusion of the ipsilateral thalamus, especially patients with larger infarcts involving the frontal or parietal cortex. Thalamic hypoperfusion persisted from early after the insult to several months or even years later. In addition, atrophy of the ipsilateral thalamus was not uncommon following larger cortical infarcts. This tended to be evident about 1 year after the infarct and progressed over several years. Furthermore, atrophic changes in the thalamus was often demonstrated in such patients as hypoperfusion in the later stages. Thus, cortical lesions had functional and morphological effects on the ipsilateral thalamus ranging from early hypoperfusion to later irreversible atrophic changes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synaptic reorganization in the degenerating lateral geniculate nucleus of the rabbit

An investigation of synaptic plasticity in the lateral geniculate nucleus has been carried out in rabbits surviving one day to one year following ipsilateral visual cortex removal. There is extensive retrograde degeneration of LGN neurons, and the altered nucleus thus provides a model for examining reorganization of optic tract axons which have been deprived of their normal postsynaptic membrane. The distribution of synaptic contacts in normal LGN was quantitatively determined. In the animals surviving 1–14 days after cortex ablation, there was extensive cell death and loss of the axodendritic synapses of cortical origin, which constitute the most numerous synaptic type in normal LGN. In animals surviving 4–12 months, there were few remaining neurons and dendrites. The fine structure of the nucleus was characterized by a shift from axodendritic synaptic contacts, as in the normal, to a ten–fold increase in axoaxonal synapses, which became the dominant population. The contribution of optic axons to this synaptic population was determined by contralateral retinal removal. It was found that the synaptic axoaxonal organization in the altered LGN follows the rules of normal organization, in that optic afferents are invariably the presynaptic component in round to flat vesicle axoaxonal synapses. The LGN's undergoing chronic retrograde degeneration shrank to about twothirds the size of the normal nucleus. There was no evidence of reduction in the length of optic tract axons within the nucleus. The evidence indicates that there are new synaptic contacts formed between surviving axons in the degenerating LGN, as a consequence of the loss of postsynaptic dendritic membrane. The new synapse formation is guided by the normal rules of axoaxonal organization, indicating a maintenance of recognition of appropriate membrane for synaptic contact in the reordered LGN. It cannot be stated whether sprouting of axons accompanies the formation of new synapses or whether the new synaptic contacts are exclusively between preexisting synaptic knobs in LGN.