An immunocytochemical and biochemical study of the microtubule-associated protein MAP-2 during post-lesion dendritic remodeling in the central nervous system of adult rats

Accumulating Evidence for Axonal Translation in Neuronal Homeostasis

The specialized structure of the neuron requires that homeostasis is sustained over the meter or more that may separate a cell body from its axonal terminus. Given this impressive distance and an axonal volume that is many times that of the cell body, how is such a compartment grown during development, re-grown after injury, and maintained throughout adulthood? While early answers to these questions focused on the local environment or the cell soma as supplying the needs of the axon, it is now well-established that the axon has some unique needs that can only be met from within. Decades of research have revealed local translation as an indispensable mechanism of axonal homeostasis during development and regeneration in both invertebrates and vertebrates. In contrast, the extent to which the adult, mammalian axonal proteome is maintained through local translation remains unclear and controversial. This mini-review aims to highlight important experiments that have helped to shape the field of axonal translation, to discuss conceptual arguments and recent evidence that supports local translation as important to the maintenance of adult axons, and to suggest experimental approaches that have the potential to further illuminate the role of axonal translation in neuronal homeostasis.

Plasmin deficiency leads to fibrin accumulation and a compromised inflammatory response in the mouse brain

BACKGROUND

Excess fibrin in blood vessels is cleared by plasmin, the key proteolytic enzyme in fibrinolysis. Neurological disorders and head trauma can result in the disruption of the neurovasculature and the entry of fibrin and other blood components into the brain, which may contribute to further neurological dysfunction.

OBJECTIVES

While chronic fibrin deposition is often implicated in neurological disorders, the pathological contributions attributable specifically to fibrin have been difficult to ascertain. An animal model that spontaneously acquires fibrin deposits could allow researchers to better understand the impact of fibrin in neurological disorders.

METHODS

Brains of plasminogen (plg)- and tissue plasminogen activator (tPA)-deficient mice were examined and characterized with regard to fibrin accumulation, vascular and neuronal health, and inflammation. Furthermore, the inflammatory response following intrahippocampal lipopolysaccharide (LPS) injection was compared between plg(-/-) and wild type (WT) mice.

RESULTS AND CONCLUSIONS

Both plg(-/-) and tPA(-/-) mice exhibited brain parenchymal fibrin deposits that appear to result from reduced neurovascular integrity. Markers of neuronal health and inflammation were not significantly affected by proximity to the vascular lesions. A compromised neuroinflammatory response was also observed in plg(-/-) compared to WT mice following intrahippocampal LPS injection. These results demonstrate that fibrin does not affect neuronal health in the absence of inflammation and suggest that plasmin may be necessary for a normal neuroinflammatory response in the mouse CNS.

Progesterone effects on neuronal ultrastructure and expression of microtubule-associated protein 2 (MAP2) in rats with acute spinal cord injury

(1) Following acute spinal cord injury, progesterone modulates several molecules essential for motoneuron function, although the morphological substrates for these effects are unknown. (2) The present study analyzed morphological changes in motoneurons distal to the lesion site from rats with or without progesterone treatment. We employed electron microscopy to study changes in nucleus and cytoplasm and immunohistochemistry for the microtubule-associated protein 2 (MAP2) for changes in cytoskeleton. (3) After spinal cord injury, the nucleoplasm appeared more finely dispersed resulting in reduced electron opacity and the nucleus adopted an eccentric position. Changes of perikarya included dissolution of Nissl bodies and dissociation of polyribosomes (chromatolysis). After progesterone treatment for 3 days, the deafferented motoneurons now presented a clumped nucleoplasm, a better-preserved rough endoplasmic reticulum and absence of chromatolysis. Progesterone partially prevented development of nuclear eccentricity. Whereas 50% of injured motoneurons showed nuclear eccentricity, only 16% presented this phenotype after receiving progesterone. Additionally, injured rats showed reduced immunostaining for MAP2 in dendrites, pointing to cytoskeleton abnormalities, whereas progesterone treatment attenuated the injury-induced loss of MAP2. (4) Our data indicated that progesterone maintained in part neuronal ultrastructure, attenuated chromatolysis, and preclude the loss of MAP2, suggesting a protective effect during the early phases of spinal cord injury.

Neonatal lesions of the entorhinal cortex induce long-term changes of limbic brain regions and maze learning deficits in adult rats

We here investigated the effects of neonatal lesions of the entorhinal cortex (EC) in rats on maze learning and on structural alterations of its main projection region, the hippocampus, as well as other regions with anatomical connections to the EC that are involved in maze learning. Since early brain damage is considered to be involved in certain neuropsychiatric diseases, this approach sought to model certain aspects of this etiopathogenesis. Bilateral neonatal lesions were induced on postnatal day 7 by microinjection of ibotenic acid (1.3 microg/0.2 microl phosphate-buffered saline (PBS)) into the EC. Naive and sham-lesioned rats served as controls. Rats were trained and tested on an eight-arm radial maze for allocentric and egocentric learning. Subsequently, gold-chloride staining and immunohistochemical staining for the microtubule-associated protein MAP-2 was used to assess myelination and dendritic density in the hippocampus, striatum and medial prefrontal cortex (mPFC) of these rats. Additionally, parvalbumin-expressing, presumably GABAergic interneurons, were evaluated in these regions. Performance in both the allocentric and the egocentric strategy was disturbed after neonatal EC lesion as shown by an increase of repeated arm entries, which indicates disturbed working memory. Histological evaluation revealed that the density of parvalbumin-immunopositive neurons and myelin sheaths was reduced in the hippocampus but not in the striatum and mPFC in neonatally lesioned rats. Density of MAP-2 staining did not differ between groups in all regions tested. Since structural alterations were only found in the EC and hippocampus our findings support their eminent role in working memory and show that no functional restoration occurs after neonatal lesions.

Level and Distribution of Microtubule- Associated Protein-2 (MAP2) as an Index of Dendritic Structural Dynamics

Optical density of MAP2 immunoreactivity (OD), the ratio between the MAP2 stained area/total test area (area fraction: AF), the total length of MAP2 labeled profiles (TL) and the ratio perimeter/area of the immunostained profiles (pleomorphism index [PI]) were measured by quantitative immunohistochemistry in the brain of rats of different ages. In old rats versus young and adult animals, OD and AF were significantly lower, whereas PI was significantly higher, in dentate gyrus molecular layer, CA1 stratum radiatum and olfactory bulb. These findings lend support to the many converging results on the higher vulnerability to aging of the CNS areas featuring higher plasticity.

Microtubule-associated protein MAP2 expression in olfactory bulb in schizophrenia

Previous studies have described alterations in presynaptic and postsynaptic elements in various parts of the CNS in schizophrenia, which may, at least in part, be due to abnormalities in neurodevelopmental processes. The olfactory bulb (OB) is a unique CNS area for examining synaptic development and plasticity in schizophrenia because it undergoes continuous reinnervation throughout life. Moreover, olfactory deficits and reduced OB volume have been observed in schizophrenia. We investigated the expression in the OB of the microtubule-associated protein MAP2, which has been shown to be abnormally expressed in the hippocampal region in schizophrenia. In both developing and mature neurons, MAP2 is an important structural component of dendrites and participates in the modification of synaptic organization. We used immunocytochemistry with phosphoepitope-specific and phosphorylation-state-independent antibodies to examine MAP2 expression in the glomerular layer of the OB in elderly subjects with chronic schizophrenia and controls. Phosphorylation-independent MAP2 expression was significantly reduced in schizophrenia, while phosphorylated MAP2 expression did not differ between groups. These results are consistent with faulty OB innervation in schizophrenia.

Differential regulation of MAP2 and αCamKII expression in hippocampal neurones by forskolin and calcium ionophore treatment

The genes encoding microtubule-associated protein 2 (MAP2), and the alpha subunit of calcium/calmodulin-dependent protein kinase II (alphaCaMKII), are members of a small number of genes whose expression is increased in hippocampal neurones during the intermediate phase of long-term potentiation (LTP)-a phase dependent on mRNA translation but not on gene transcription. However, the intracellular signalling pathways which mediate these increases in expression are largely unknown. Organotypic slice cultures of rat hippocampus were exposed to either forskolin (to elevate cAMP levels), A23187 (to increase intracellular Ca(2+) levels) or the corresponding vehicle. The levels of immunoreactive (ir-) MAP2 were increased 4 h after forskolin treatment, but were unaffected by A23187 treatment. Conversely, the levels of ir-alphaCaMKII were increased 4 h after A23187 treatment, but were unaffected by forskolin. The regulation of the expression of these proteins was the same in the CA3 region as in the CA1 and dentate gyrus of the hippocampus. While rapamycin reduced the basal levels of ir-MAP2, it did not affect the ability of either forskolin or A23187 to enhance ir-MAP2 or ir-alphaCaMKII levels. These results suggest that cAMP and Ca(2+) differentially modulate the expression of these two plasticity-related genes, and that translational enhancement via the mammalian target of rapamycin kinase is not involved in these effects.

Changes in MAP2 and tyrosinated alpha-tubulin expression in cochlear inner hair cells after amikacin treatment in the rat

The expression of MAP2 (microtubule-associated protein 2) and of tyrosinated alpha-tubulin was investigated immunocytochemically in the cochleas of normal and amikacin-treated rats. For MAP2, two different antibodies were used: anti-MAP2ab, against the high molecular weight forms, and anti-MAP2abc, additionally against the embryonic form c. In the cochlea of the normal rat, the outer (OHCs) and inner (IHCs) hair cells were labeled for MAP2abc. The labeling was weaker in IHCs than in OHCs. The hair cells were rarely labeled for MAPab. Both OHCs and IHCs were labeled for tyrosinated alpha-tubulin. In the cochlea of the amikacin-treated rat, aggregates of anti-MAP2abc and anti-tyrosinated alpha-tubulin antibodies were seen in the apical region of the IHCs as early as the end of the antibiotic treatment. In rats investigated during the following week, the cell body of most of the surviving IHCs were not labeled for MAP2abc and tyrosinated alpha-tubulin. Then, labeling for these two antibodies reappeared in the surviving IHCs, including their giant stereocilia. Fewer surviving IHCs were labeled for tyrosinated alpha-tubulin than for MAP2abc. The amikacin-poisoned IHCs were rarely labeled for MAP2ab. These results suggest that cochlear hair cells essentially express form c of MAP2. In the amikacin-damaged cochlea, the apical aggregation of MAP2c and tyrosinated alpha-tubulin within the poisoned IHCs could be implicated in a cell degenerative process. By contrast, the extinction and recovery of MAP2c and tyrosinated alpha-tubulin labeling in the remaining IHCs suggest the occurrence of a limited repair process. A possible role of MAP2 and tubulin in hair cell survival is discussed.

Nestin expression in ganglioglioma

It has been suggested that gangliogliomas represent a neoplastic transformation of a dysplastic focus or heterotopia. Other theories propose that gangliogliomas arise from multipotent stem cells with the ability to differentiate along glial and neuronal cell lines. Our goal was to characterize the expression of nestin, a neuroepithelial precursor/stem cell antigen, in gangliogliomas along with other pathological and clinical features of this entity. The clinical and operative features of 18 recent cases meeting the histological criteria for ganglioglioma were reviewed. The expression of nestin, microtubule-associated protein 2 (MAP2), neurofilament, and glial fibrillary acidic protein (GFAP) was assessed by immunohistochemistry and confocal scanning laser microscopy. Abundant MAP2- and nestin-positive neuronal cells were found by immunohistochemistry in all 18 gangliogliomas. GFAP staining was found in reactive and lesional astrocytes but not in cells of neuronal morphology. Confocal microscopy demonstrated colocalization of nestin and MAP2 in select neuronal cells. The true lineage of gangliogliomas remains controversial. Our findings confirm the presence of cells within these lesions that harbor a persistent stem cell cytoskeletal protein (nestin). Further insight into the cytoskeletal derangement of nestin-positive neuronal cells may shed further light on the pathogenesis of gangliogliomas and its associated epilepsy.

Nestin expression in cortical dysplasia

OBJECT

It is recognized that cortical dysplasia (CD) is associated with an increased incidence of glioneuronal neoplasms. Among hypothetical considerations, there is the possibility that CD and other neuronal migration abnormalities harbor dysmature cells with the potential to give rise to glioneuronal neoplasms. Such cells, if present, would be reasonably expected to display immature features. The goal of the present study was to characterize the expression of nestin, a neuroepithelial precursor/stem cell antigen, in CD, along with other pathological and clinical features of this entity.

METHODS

Clinical and surgical features of 10 recent cases meeting the histological criteria for CD were reviewed. Expressions of nestin, MAP2, neurofilament, and glial fibrillary acidic protein (GFAP) were assessed using immunohistochemical analysis and confocal scanning laser microscopy. Immunoreactivity for both glial and neuronal antigens as well as nestin was found in a select group of cells within regions of CD. Immunohistochemical and confocal microscopic findings demonstrated that these cells with neuronal or ambiguous features are a mixed population, some of which are dysmature neurons (positive for nestin and MAP2), whereas others are astrocytic (positive for nestin and GFAP).

CONCLUSIONS

Further insight into the nature of nestin-positive neurons may shed light on the cause and pathogenesis of the associated glioneuronal tumors and the accompanying chronic seizures.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Deafferentation of the hippocampus results in the induction of AT8 positive 'granules' in the rat

Hyperphosphorylated tau is a pathological hallmark of Alzheimer's disease, but the mechanisms that lead to its formation are poorly understood. To investigate what effect deafferentation of the hippocampus has on the phosphorylation state of tau, we lesioned the entorhinal cortex in rats and looked for hyperphosphorylated tau in the hippocampus at various days post lesioning. After 7 and 21 days, small AT8-positive 'granules' appeared in the molecular layer of the dentate gyrus on the lesioned side. No such staining was seen in the animals injected with saline. This study shows that deafferentation leads to induction of hyperphosphorylated tau. The AT8 positive 'granules' seen resemble the argyrophilic grains that characterize Argyrophilic Grain disease suggesting that lesioning the perforant pathway may serve as a useful model for inducing argyrophilic grains in vivo.

Staging of cytoskeletal and beta-amyloid changes in human isocortex reveals biphasic synaptic protein response during progression of Alzheimer's disease

We have examined the relationships between dementia, loss of synaptic proteins, changes in the cytoskeleton, and deposition of beta-amyloid plaques in the neocortex in a clinicopathologically staged epidemiological cohort using a combination of biochemical and morphometric techniques. We report that loss of synaptic proteins is a late-stage phenomenon, occurring only at Braak stages 5 and 6, or at moderate to severe clinical grades of dementia. Loss of synaptic proteins was seen only after the emergence of the full spectrum of tau and beta-amyloid pathology in the neocortex at stage 4, but not in the presence of beta-amyloid plaques alone. Contrary to previous studies, we report increases in the levels of synaptophysin, syntaxin, and SNAP-25 at stage 3 and of alpha-synuclein and MAP2 at stage 4. Minimal and mild clinical grades of dementia were associated with either unchanged or elevated levels of synaptic proteins in the neocortex. Progressive aggregation of paired helical filament (PHF)-tau protein could be detected biochemically from stage 2 onwards, and this was earliest change relative to the normal aging background defined by Braak stage 1 that we were able to detect in the neocortex. These results are consistent with the possibility that failure of axonal transport associated with early aggregation of tau protein elicits a transient adaptive synaptic response to partial de-afferentation that may be mediated by trophic factors. This early abnormality in cytoskeletal function may contribute directly to the earliest clinically detectable stages of dementia.

Changes in dendritic structure and function following hippocampal lesions: correlations with developmental events?

Recovery after nervous system lesions may lead to partial re-institution of developmental schemes and processes. Here we review several of these proposed schemes, with the conclusion that though some processes may involve re-expression of embryonic phenotypes, there are many processes invoked during recovery from lesions that do not mirror developmental phenomena. The inability to fully revert to embryonic schemes because of adult phenotype may partially account for the decreased recovery observed in adults compared to that noted after lesions during development.

Spatiotemporal changes in hippocampal NMDA receptor binding as a consequence of trimethyltin neurotoxicity in the rat

In the present study we examined the presumable changes in the distribution of N-methyl-D-aspartate (NMDA) receptors in the hippocampus of rat exposed to a potent neurotoxic drug, trimethyltin (TMT). Using in vitro receptor binding autoradiography, [3H]MK801 labelling was determined at 7, 14, 21, 30 and 60 days after treatment with TMT (single dose of 8 mg/kg, i.p.) in various hippocampal areas thought to be affected by the neurotoxin. At 21-60 days after exposure, a decrease in receptor binding was observed in CA1 hippocampal subfield (10-20%, P< 0.05). A reduction in binding density also occurred in CA4/ CA3c, where labelling vanished completely at longer times. In the molecular layer (ML) of the dentate gyrus (DG), however, 16-37% (P<0.05) increase in receptor binding was found at 14-60 days postexposure. These results suggest that exposure to TMT leads to an altered topography of NMDA receptor density sites in the rat hippocampus. Dynamics of the reduction in receptor binding in CA4/CA3c and CA1 followed the development of the well-known degenerative effects induced by the neurotoxin. In contrast, the enhanced binding density in the ML of the DG may be a part of a mechanism of plastic response of granule cells to denervation/reinnervation.

Disruption of MAP-2 immunostaining in rat hippocampus after traumatic brain injury

The effects of diffuse brain injury on dendritic morphology in rat hippocampus and cortex were examined in this study using the recently described impact acceleration model of traumatic brain injury (Marmarou et al., 1994). Dendritic structure was visualized using immunostaining of microtubule associated protein-2 (MAP-2). Brains were studied 24, 48, and 72 h after brain injury. Results from immunohistochemistry and light microscopy indicated a time-dependent disruption of dendritic cytoarchitecture in the CA1 subregion and in the hilus of the hippocampus but not in the dentate gyrus or CA3 subregion. Similar disruption was observed in the cortical mantle overlying the hippocampus. Although disruption of dendritic structure was observed at 24 h, the most severe damage was at 48 h after injury with evidence of at least partial recovery of MAP-2 immunostaining by 72 h. In the most severe damage, dendrites appeared to be fragmented, scattered, and unaligned, consisting of irregularly spaced and darkly stained swollen segments. A mixed pattern of immunostaining was observed in somata of hilar cells, with some appearing normal while others stained only faintly, appearing to have lost their typical polygonal shape. Semiquantitative rankings confirmed these qualitative findings. Immediate post-injury behavioral evaluations of injury severity were compared to the degree of disruption of MAP-2 immunostaining. The results of this study indicate that diffuse brain injury is associated not only with axonal damage but also with injury to dendrites.

Increased apolipoprotein E mRNA in the hippocampus in Alzheimer disease and in rats after entorhinal cortex lesioning

The distribution of apolipoprotein E (ApoE) mRNA was characterized in the hippocampus of humans with Alzheimer disease (AD) and in rats with experimental lesions (unilateral ablation of the entorhinal cortex) that model selected features of AD. In both AD and the lesion model, we observed a shift in the location of astrocytes containing prevalent ApoE mRNA from the neuropil to regions with densely packed neurons. The increased abundance of ApoE mRNA in astrocytes close to neuron cell bodies could be indicative of lipid uptake in regions where neurons are degenerating or where synaptic remodeling is taking place.

Lesion-induced plasticity of central neurons: sprouting of single fibres in the rat hippocampus after unilateral entorhinal cortex lesion

In response to a central nervous system trauma surviving neurons reorganize their connections and form new synapses that replace those lost by the lesion. A well established in vivo system for the analysis of this lesion-induced plasticity is the reorganization of the fascia dentata following unilateral entorhinal cortex lesions in rats. After general considerations of neuronal reorganization following a central nervous system trauma, this review focuses on the sprouting of single fibres in the rat hippocampus after entorhinal lesion and the molecular factors which may regulate this process. First, the connectivity of the fascia dentata in control animals is reviewed and previously unknown commissural fibers to the outer molecular layer and entorhinal fibres to the inner molecular layer are characterized. Second, sprouting of commissural and crossed entorhinal fibres after entorhinal cortex lesion is described. Single fibres sprout by forming additional collaterals, axonal extensions, boutons, and tangle-like axon formations. It is pointed out that the sprouting after entorhinal lesion mainly involves unlesioned fibre systems terminating within the layer of fibre degeneration and is therefore layer-specific. Third, molecular changes associated with axonal growth and synapse formation are considered. In this context, the role of adhesion molecules, glial cells, and neurotrophic factors for the sprouting process are discussed. Finally, an involvement of sprouting processes in the formation of neuritic plaques in Alzheimer's disease is reviewed and discussed with regard to the axonal tangle-like formations observed after entorhinal cortex lesion.

Transgenic mice overexpressing the neurotrophic factor S-100 beta show neuronal cytoskeletal and behavioral signs of altered aging processes: implications for Alzheimer's disease and Down's syndrome

S-100 beta is a neurotrophic factor released by astroglial cells and localized to chromosome 21, within the region which is considered obligate for Down's syndrome (DS). S-100 beta is increased in the postmortem brains of both DS and Alzheimer's disease. Transgenic mice, produced by insertion of the human gene for S-100 beta, were examined for dendritic development at two ages, using an antibody against microtubule associated protein-2 (MAP-2). At the earliest stages, the density of dendrites within the hippocampus of transgenic animals exceeded that of controls. Also, MAP-2 immunostaining was evident in the region of the cell body. By 1 year of age, the transgenic animals had significant loss of dendrites compared to controls and the number of cells showing cell body staining was further increased. These pathological changes could be indicative of the presence of neurofibrillary tangles and cytoskeletal collapse. Behaviorally, younger transgenic animals could not perform in a learning task as well as controls. Together, these findings suggest that increased S-100 beta in brain may lead to accelerated development, followed by increased aging. The pathological changes may prove useful as an animal model of Down's syndrome and Alzheimer's disease.

Basal expression, subcellular distribution, and up-regulation of the proto-oncogene c-JUN in the rat dentate gyrus after unilateral entorhinal cortex lesion

The expression of the transcription factor c-JUN was investigated in the rat fascia dentata under normal conditions and after entorhinal cortex lesion. As shown by immunocytochemistry and in situ hybridization histochemistry c-JUN and its messenger RNA are present in the principal cell layers of the dentate gyrus and Ammon's horn (except hippocampal region CA2). Pre-embedding immunogold electron microscopy revealed an almost exclusive nuclear localization of c-JUN, where it is associated with chromatin. In addition, double immunolabelling for c-JUN and parvalbumin demonstrated that c-JUN immunoreactivity is primarily found in principal neurons since GABAergic parvalbumin-positive interneurons did not express c-JUN. After unilateral electrolytic lesion of the entorhinal cortex c-JUN was strongly up-regulated in the ipsilateral dentate gyrus within 2 h postlesion. This up-regulation was also present in the contralateral fascia dentata 12 h after entorhinal cortex lesion and returned to control levels on both sides 24 h postlesion. The cellular distribution of c-JUN did not change after entorhinal cortex lesion: parvalbumin-positive interneurons never contained c-JUN. These results point to a specific role of c-JUN in the granule cells of the fascia dentata in the normal animal and in rats with entorhinal cortex lesions. The selective induction of c-JUN after entorhinal lesion could be one of the first molecular steps that regulate transneuronal changes within granule cells after their denervation. A different mechanism has to be assumed for GABAergic interneurons known to receive an entorhinal innervation as well.

Serotonin depletion during synaptogenesis leads to decreased synaptic density and learning deficits in the adult rat: a possible model of neurodevelopmental disorders with cognitive deficits

Studies in the past have revealed serotonin to play a role in regulating the development and maturation of the mammalian brain, largely through the release of the astroglial protein S-100beta. S-100beta plays a role in neurite extension, microtubule and dendritic stabilization and regulation of the growth associated protein GAP-43, all of which are key elements in the production of synapses. Depletion of serotonin, and thus of S-100beta, during synaptogenesis should lead to a loss of synapses and the behaviors dependent on those synapses. The current study was undertaken to test this hypothesis. In order to assess the influence of serotonin we have looked at the synaptic density in the adult after depletion, by using immunodensitometry of synaptic markers (synaptophysin and MAP-2) and by studying behaviors thought to be highly dependent on synaptic plasticity and density. Male Sprague-Dawley rats were depleted of serotonin on postnatal days (PND) 10-20 by treating with the tryptophan hydroxylase inhibitor parachlorophenylalanine (PCPA; 100 mg/kg, s.c.). On PND's 30 and 62, animals were perfused for immunodensitometry. Littermates were used for behavioral testing. At PND 55-62, the animals were tested in an interchangeable maze with olfactory cues and in an eight-arm radial maze. Our results show a loss of both synaptic markers in the hippocampus on PND 30. At PND 62, the only remaining loss was of the dendritic marker MAP-2. The animals had deficits in both behaviors tested, suggestive of spacial learning deficits and of the failure to extinguish learned behaviors or to re-learn in a new set. Our findings show the long-term consequences of interfering with the role of serotonin in brain development on the morphology and function of the adult brain. These findings may have implications for human diseases, including schizophrenia, thought to be related to neurodevelopmental insults such as malnutrition, hypoxia, viruses or in utero drug exposure. Moreover, they provide further insights into the functioning of serotonin and S-100beta in development and aging.

Age-dependent organotypic expression of microtubule-associated proteins (MAP1, MAP2, and MAP5) in rat brain

Age-dependent changes in the distribution of microtubule-associated proteins (MAPs) were analyzed in young (3-months, N = 3) and old (24-months, N = 3) rat brain. In the young rats, MAP1 and MAP5 exhibited prominent immunostaining in the perikarya and dendrites whereas MAP2 was selectively localized in the dendrites. In the cerebellum, MAP2 was preferentially localized in finer and distal branches of Purkinje cell dendrites and in punctate deposits surrounding glomeruli. In general, aging resulted in obvious declines in MAP2- >> MAP1- and MAP5-immunoreactivities in the hippocampus and parietal cortex but no change in cerebellum. The results indicate that: (1) hippocampus is the most affected and cerebellum is the least affected region with regard to declines in MAPs-immunoreactivities in the aged rat brain; (2) dendrite-specific MAP2 is almost completely depleted from most dendrites in the hippocampus and cortex. In summary, loss of MAP2-immunoreactivity in the affected brain areas may be associated with age-related impairment of synaptic plasticity, cognition and memory functions.

Expression and distribution of IGF-1 receptors containing a beta-subunit variant (betagc) in developing neurons

Betagc is a beta-subunit variant of the insulin-like growth factor-1 (IGF-1) receptor highly enriched in growth cone membranes prepared by subcellular fractionation of fetal rat brain (). The present study is focused on the expression and on the cellular and subcellular distribution of betagc in developing neurons and differentiating PC12 cells. In the developing cerebral cortex and, at least at early stages, in cultured primary neurons, betagc expression was found to be correlated with neurite outgrowth. In PC12 cells betagc expression was nerve growth factor (NGF)-dependent and also paralleled neurite outgrowth. In contrast, beta-subunits of the insulin receptor and/or of other IGF-1 receptors ("betaP5"; detected with antibody AbP5) were downregulated as betagc expression increased. Immunofluorescence studies confirmed the enrichment of betagc at growth cones and demonstrated morphologically its spatial separation from betaP5, which is confined to the perikaryon. At the growth cone, betagc colocalizes and associates in a proximal region with microtubules, but it seems independent of the more peripheral microfilaments. Some betagc immunoreactivity is detected in the perinuclear region of PC12 cells, most likely the Golgi complex and its vicinity. betagc seems to emerge from the periphery of this structure in an apparently vesicular compartment distinct from that carrying synaptophysin to the growth cones. The facts that (1) betagc expression is correlated closely with neurite outgrowth, that (2) it is regulated in PC12 cells by a neurotrophin, NGF, and that (3) betagc is concentrated in the proximal growth cone region raise new questions regarding a possible role of IGF-1 receptors containing betagc in the regulation of neurite growth.

Protein kinase C may be involved in synaptic repair of auditory neuron dendrites after AMPA injury in the cochlea

A suitable model of sudden deafness occurring after acoustic trauma or ischemia, is obtained in guinea pigs by an acute intracochlear perfusion of 200 microM alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), a glutamate analog. By overloading the AMPA/kainate receptors, located post-synaptically to inner hair cells (IHCs), it induces a massive swelling of primary auditory neuron dendrites, which disconnects the IHCs. This synaptic uncoupling and the resulting hearing loss are followed by a progressive regrowth of dendrites, which make new synapses with IHCs, leading to a functional recovery of auditory responses that is completed after 5 days. Knowing the role of protein kinase C in neuroplastic events, we studied the expression of its isoforms alpha,beta(I,II) and gamma, respectively pre- and post-synaptic, in auditory neurons at various times after AMPA administration. In untreated cochleas, we observed an expression of PKC alpha,beta(I,II) and gamma in cell bodies of primary auditory neurons. After the intracochlear administration of AMPA, both isozymes were transiently overexpressed, with a peak at 3-6 h, followed by a decrease after about 24 h. At this point in time immuno-electron microscopy revealed some regrowing dendrites immunoreactive for PKCgamma. Five days after AMPA, when the auditory responses were restored, PKCgamma levels were still elevated in ganglion cell bodies.

Increased dendritic extent in hippocampal CA1 neurons from aged F344 rats

Age-related dendritic alterations were evaluated in F344 rats following a water maze assessment of spatial memory. Based on the probe trial times, 39% of the aged animals were designated impaired. CA1 pyramidal neurons were labeled intracellularly with neurobiotin in brain slices prepared from these animals. Neurons (aged: n = 15; young: n = 11) were reconstructed using a microscope-based three-dimensional system. Increased dendritic length was observed in the aged neurons both for basal dendrites (aged = 4.54 mm and young = 3.33 mm) and the entire neurons (aged = 14.8 mm and young = 10.8 mm). However, dendritic length values did not correlate with the individual animal's probe trial time. Sholl analysis revealed a diffuse increase in dendritic branch intersections in the cells from aged rats, which on branch order analysis was noted to be due to an increased number of distal branches. Mean electrotonic distance to dendritic terminals, a functional assessment of synaptic efficacy, was longer in the aged neurons (aged = 0.67 lambda and young = 0.55 lambda). These results suggest a lengthening and increased complexity of CA1 pyramidal neurons with successful aging, which may represent either an intrinsic response to aging or a reactive partial denervation response to a loss of afferent inputs.

The dendritic trees of neurons from the hippocampal formation of protein-deprived adult rats. A quantitative Golgi study

We have recently shown that lengthy periods of low-protein feeding of the adult rat lead to deficits in the number of hippocampal granule and pyramidal cells, and in the number of mossy fiber synapses. These findings prompted us to analyze the dendrites of these neurons to evaluate whether, under the same experimental conditions, degenerative and/or plastic changes also take place at the dendritic level. The hippocampal formations from five 8-month-old rats fed a low-protein diet (casein 8%) for 6 months from the age of 2 months and from five age-matched controls were Golgi-impregnated and the morphology of the dendritic trees quantitatively studied. We found that in malnourished animals there was a reduction in the number of dendritic branches in the dentate granule cells and in the apical dendritic arborizations of CA3 pyramidal neurons. In addition, in the dentate granule cells the spine density was markedly increased and the terminal dendritic segments were elongated in malnourished animals. No alterations were found in the apical dendrites of CA1 pyramidal cells. The results obtained show that long periods of malnutrition induce marked, although not uniform, changes in the dendritic domain of the hippocampal neurons, which reflect the presence of both degenerating and regrowing mechanisms. These alterations are likely to affect the connectivity pattern of the hippocampal formation and, hence, the activity of the neuronal circuitries in which this region of the brain is involved.

Enhanced expression of microtubule-associated protein 2 in large neurons of cortical dysplasia

To evaluate neuronal cytoarchitectural changes in cortical dysplasia, we examined microtubule-associated protein 2 (MAP2) expression in surgically resected specimens obtained from 20 patients (age range, 3 months to 10 years) treated for intractable epilepsy. Large neurons were investigated in the specimens from all patients and showed significantly strong immunoreactivity with antibodies against MAP2 in the perikaryon and proximal portion of their processes. In situ hybridization with MAP2 antitense riboprobe showed increased hybridization signal intensities in the large neurons, which correlated with the pattern of immunoreactivity for MAP2. We conclude that MAP2 is strongly expressed in the large neurons in cortical dysplasia. The results of preliminary immunoblotting in 1 patient with focal cortical dysplasia showed that the low-molecular-weight form of MAP2 (MAP2c) was strongly expressed in the dysplastic cortex, suggesting that MAP2c may be a major component contributing to the increased expression of MAP2 in the large neurons of cortical dysplasia. Since it has been suggested that MAP2 plays a crucial role in the branching and remodeling of neuronal processes, increased expression of MAP2 may reflect activated plasticity of the large neurons in cortical dysplasia.

The process of reinnervation in the dentate gyrus of adult rats: gene expression by neurons during the period of lesion-induced growth

Neurons in the hippocampal dentate gyrus are extensively reinnervated following the destruction of their normal inputs from the ipsilateral entorhinal cortex (EC). The present study evaluates gene expression by dentate granule neurons and the neurons giving rise to the sprouting connections during the period of synapse growth. Adult male rats were prepared for in situ hybridization at 2, 4, 6, 8, 10, 12, 14, 20, and 30 days following unilateral EC lesions. Sections were hybridized using 35S-labeled cRNA probes for mRNAs that encode proteins thought to be important for neuronal structure and/or synapse function, including (1) mRNAs that are normally present in dendrites--the mRNAs for the high molecular weight microtubule-associated protein 2 (MAP2) and the alpha-subunit of calcium/calmodulin-dependent protein kinase II (CAMII kinase), (2) mRNAs that are upregulated in neurons that are regenerating their axons (T alpha 1 tubulin and F1/GAP43) and (3) mRNAs for proteins that are the principal constituents of neurofilaments and microtubules (the low molecular weight neurofilament protein NF68 and beta-tubulin). Although there were small changes in the levels of labeling for the mRNAs that are normally present in dendrites, there were no dramatic increases in the levels of any of the mRNAs either in dentate granule cells or in neurons giving rise to the reinnervating fibers at any postlesion interval. These results indicate that neurons in mature animals can substantially remodel their synaptic terminals and their dendrites in the absence of large-scale changes in gene expression (at least as measured by steady-state mRNA levels at various time points).

Changes in the microtubule proteins in the developing and transected spinal cords of the bullfrog tadpole: induction of microtubule-associated protein 2c and enhanced levels of Tau and tubulin in regenerating central axons

The distribution of tubulin, microtubule-associated protein 2 and Tau in the spinal cords of bullfrog tadpoles during development and after transection was studied. alpha-Tubulin or beta-tubulin immunoreactivity was present in the axons, neuronal perikarya and dendrites, as revealed by immunocytochemistry. The axonal staining intensity of the tubulins in the tadpoles was significantly stronger than that in the adult bullfrog. Microtubule-associated protein 2 immunoreactivity was localized largely to dendrites and expanded from distal to proximal dendrites with time; a high-molecular-weight microtubule-associated protein 2 was seen on the immunoblots of cord homogenates throughout development Tau1 stained mainly the axons. Two-dimensional gel immunoblotting disclosed that the tadpole contained a greater number of isoforms of Tau than the frog. Complete transection of the spinal cords of stage IV tadpoles was followed by regeneration of the damaged cord region. The levels of tubulin and Tau immunoreactivity in the regenerating axons of the ventral fasciculi were generally increased. Strikingly, microtubule-associated protein 2 immunoreactivity appeared in the regenerating axons and the chromatolytic cell bodies of axotomized motor neurons, paralleling the induction of microtubule-associated protein 2c in the regenerating cord segment shown by immunoblotting. The chromatolytic cell bodies were also markedly labeled by Tau1, whereas the high-molecular-weight microtubule-associated protein 2 diminished on the immunoblots, in accordance with the reduced level of staining for the dendrites. It is apparent that the changes in the cytoskeletal proteins in the regenerating axons mostly recapitulated their developmental patterns. Moreover, the data indicate a close relationship between tubulin and microtubule-associated proteins in axonal growth as well as providing evidence for similar molecular mechanisms underlying successful regeneration for central and peripheral axons.

Reexpression of developmentally regulated MAP2c mRNA after ischemia: colocalization with hsp72 mRNA in vulnerable neurons

Levels of mRNAs encoding the microtubule-associated proteins MAP2b and MAP2c as well as the 70-kDa stress protein [72-kDa heat shock protein (hsp72)] were evaluated in postischemic rat brain by in situ hybridization with oligonucleotide probes corresponding to the known rat sequences. Rats were subjected to 10-min cardiac arrest, produced by compression of major thoracic vessels, followed by resuscitation. The normally expressed MAP2b mRNA showed transient twofold elevations in all hippocampal neuron populations at 6-h recirculation, followed by a return to control levels by 24 h. MAP2b hybridization was progressively lost thereafter from the vulnerable CA1 and outer cortical layers, preceding both the fall in immunoreactive MAP2b and the eventual cell loss in these regions. The depletion of MAP2b mRNA coincided with an increase in the alternatively spliced MAP2c in vulnerable regions during 12-48 h of recirculation, precisely overlapping the late component of hsp72 expression that persisted in these cell populations. Previous studies have suggested that the initial induction of hsp72 provides an index of potential postischemic injury in neuron populations that may or may not be injured, while lasting hsp72 mRNA expression is associated with cell damage. In contrast, the present results demonstrate that MAP2c expression under these conditions occurs uniquely in neuron populations subject to injury. Available evidence suggests that MAP2c expression represents a plastic response in subpopulations of neurons that will survive in these regions, although it remains to be explicitly determined whether it may also be transiently expressed in dying cells. In any case, these observations demonstrate that reexpression of developmentally regulated MAP2c mRNA is a relatively late postischemic response in vulnerable cell populations, indicating that pathways regulating MAP2 splicing may be closely associated with mechanisms of neuron injury and/or recovery.

Selective regulation of dendritic MAP2 mRNA levels in hippocampal granule cells by nitric oxide

Application of NMDA, or agents releasing nitric oxide (NO), onto the dendrites of hippocampal granule cells increased the levels of the mRNA encoding MAP2, a cytoskeletal component induced during periods of neurite outgrowth. Furthermore, local increases in the hybridisation signal in the molecular layer, representing dendritic MAP2 mRNA, occurred independently of changes in MAP2 mRNA levels in the cell body layer. The selective modulation of MAP2 mRNA in dendrites reveals a mechanism allowing a sustained stimulation of dendritic outgrowth to be confined to those regions of a neuron's dendritic arbour local to glutamate receptor stimulation.

Denervation-induced dendritic alterations in CA1 pyramidal cells following kainic acid hippocampal lesions in rats

Kainic acid (KA) lesions of the CA3 region of the hippocampus lead to denervation of ipsilateral CA1 neurons. To assess denervation-induced post-synaptic changes, intracellular physiological recordings were performed in the CA1 region in vitro, from both control and KA-treated tissue. The neurons were intracellularly stained with neurobiotin, reconstructed using a quantitative three-dimensional system and analyzed for morphometric and electrotonic parameters. Total dendritic length was slightly longer in the denervated CA1 cells and there was a selective and significant increase in both branches and terminals in the mid-stratum radiatum (300-550 microns from the soma using Sholl analysis) in the KA-treated rats compared to untreated controls, particularly for cells at 5 days post-lesion and later, which exhibited graded synaptically-evoked bursts. However, there was no significant difference in the basal dendritic arborization. Electrotonic modelling of the dendritic structure revealed specific membrane resistivity values of 33.4 k omega.cm2 for the normal CA1 cells and 29.8 K omega-cm2 for the KA-treated cells, assuming an internal resistivity of 200 omega.cm2, shrinkage correction of 1.57 and a spatial distribution of dendritic spines. The number of dendritic terminals of these denervated CA1 neurons at electrotonic distances between 0.5 lambda and 0.7 lambda also significantly increased in the cells from KA-treated animals. These findings indicate that there is a selective and specific increase in the number of apical terminals and dendritic branches following the unilateral kainic acid lesion. These apical branch changes may represent dendritic sprouting as a post-synaptic response to the denervation, which was particularly marked in neurons exhibiting graded synaptic bursting behavior.

Dynamics of synapsin I gene expression during the establishment and restoration of functional synapses in the rat hippocampus

Synapse development and injury-induced reorganization have been extensively characterized morphologically, yet relatively little is known about the underlying molecular and biochemical events. To examine molecular mechanisms of synaptic development and rearrangement, we looked at the developmental pattern of expression of the neuron-specific gene synapsin I in granule cell neurons of the dentate gyrus and their accompanying mossy fibers during the main period of synaptogenic differentiation in the rat hippocampus. We found a significant difference between the temporal expression of synapsin I messenger RNA in dentate granule somata and the appearance of protein in their mossy fiber terminals during the postnatal development of these neurons. Next, to investigate the regulation of neuron-specific gene expression during the restoration of synaptic contacts in the central nervous system, we examined the expression of the synapsin I gene following lesions of hippocampal circuitry. These studies show marked changes in the pattern and intensity of synapsin I immunoreactivity in the dendritic fields of dentate granule cell neurons following perforant pathway transection. In contrast, changes in synapsin I messenger RNA expression in target neurons, and in those neurons responsible for the reinnervation of this region of the hippocampus, were not found to accompany new synapse formation. On a molecular level, both developmental and lesion data suggest that the expression of the synapsin I gene is tightly regulated in the central nervous system, and that considerable changes in synapsin I protein may occur in neurons without concomitant changes in the levels of its messenger RNA. Finally, our results suggest that the appearance of detectable levels of synapsin I protein in in developing and sprouting synapses coincides with the acquisition of function by those central synapses.

The role of microtubule-associated protein 2 (MAP-2) in neuronal growth, plasticity, and degeneration

Microtubule associated protein 2 (MAP-2) historically has been perceived primarily as a static, structural protein, necessary along with other cytoskeletal proteins to maintain neuroarchitecture but somewhat removed from the "mainstream" of neuronal response mechanisms. Quite to the contrary, MAP-2 is exquisitely sensitive to many inputs and recent investigations have revealed dynamic functions for MAP-2 in the growth, differentiation, and plasticity of neurons, with key roles in neuronal responses to growth factors, neurotransmitters, synaptic activity, and neurotoxins. These discoveries indicate that modification and rearrangement of MAP-2 is an early obligatory step in many processes which modify neuronal function.

Expression of the class III beta-tubulin isotype in developing neurons in culture

The expression of the class III beta-tubulin isotype was studied in cultured brain neurons by means of a monoclonal antibody (TuJ1). The results obtained indicate that during early axonal outgrowth most of the class III beta-tubulin is not incorporated into microtubules, a phenomenon which is also observed under conditions which alter the rate and extent of the neurite outgrowth response. On the other hand, a dramatic increase in its incorporation into microtubules is observed after the neurons have differentiated their neurites as axons and dendrites. In addition, the appearance of colchicine-resistant microtubules containing this isotype, a phenomenon which occurs late in neurite development, is highly coincident with the appearance of stable microtubules containing high molecular weight microtubule-associated proteins (MAPs). This pattern is different from that of the accumulation and incorporation of other beta-tubulin isotypes into microtubules. Taken collectively, our results indicate that differences exist in the in vivo utilization of tubulin isotypes in developing brain neurons and suggest that the class III beta-tubulin isotype is not a primary factor involved in the regulation of microtubule assembly during early neurite outgrowth, but that it may be important for maintaining further neurite elongation and/or determining some unique binding property of MAPs to specific microtubule subsets.

The effect of axon injury on microtubule-associated proteins MAP2, 3 and 5 in the hypoglossal nucleus of the adult rat

Microtubule-associated proteins appear to be critical elements in the stabilization of microtubules during neurite development. Axon injury results in a new burst of axonal growth activity as well as in partial dendritic involution. With this background we have examined the immunocytochemical staining pattern for microtubule-associated proteins 2, 3 and 5 in the hypoglossal nucleus of adult rats following unilateral hypoglossal nerve resection. From four days to six weeks postlesion a significant reduction in microtubule-associated protein 2-like immunoreactivity was observed in the neuropil and neuronal perikarya of the hypoglossal nucleus ipsilateral to nerve transaction. Microtubule-associated protein 5-like immunoreactivity was reduced in neuronal perikarya and neuropil four days to two weeks after injury. After six weeks microtubule-associated protein 5-like immunoreactivity had returned to normal levels. Microtubule-associated protein 3-like immunoreactivity, which was observed in glial cell perikarya and axons, but not neuronal perikarya or dendrites, appeared to be essentially unaltered. The reduced levels of microtubule-associated proteins 2 and 5 may be factors contributing to previously documented axotomy-induced dendritic retraction. The decrease in microtubule-associated protein 5 staining and absence of microtubule-associated protein 3 expression in axotomized neurons contrast with the situation in developing neurons, and demonstrate that the neuronal reaction to axon injury in mature mammals involves a specific series of events distinct from the developmental process.

Passive electrical properties of motoneurons in aged cats following axotomy

The objective of this study was to determine whether the aging process influences the changes in the electrophysiological properties of motoneurons that occur as a consequence of axotomy. Accordingly, using intracellular recording and stimulating techniques, the basic electrical properties of control (unaxotomized) and axotomized spinal cord motoneurons of aged cats were determined. Compared with control motoneurons, axotomized motoneurons exhibited increases in input resistance (Rin), membrane time constant (tau b) and the equalizing time constant (tau c). While the electrotonic length (L) remained unchanged, axotomy induced a decrease in the total cell capacitance (Ccell). The post-axotomy reduction of Ccell indicates that the motoneuron surface area was reduced and the increased membrane time constant indicates that there was an increase in membrane resistivity (Rm). The post-axotomy conservation of L accompanied by an increase in Rm suggests that aged axotomized motoneurons undergo geometrical changes. Furthermore, calculations based on cable theory suggest that the diameter of the equivalent cylinder (d) decreased following axotomy, whereas the equivalent cylinder length (l) remained unaffected. It is concluded that axotomy produces significant alterations in the soma-dendritic portion of aged spinal motoneurons, as indicated by the changes found in their passive electrophysiological properties, and that the pattern of the response that occurs in axotomized motoneurons of adult cats is also present in axotomized motoneurons of aged animals.

Microtubule-associated protein 2 levels decrease in hippocampus following traumatic brain injury

We examined microtubule-associated protein 2 (MAP2) levels in hippocampal and cortical tissue 3 h following moderate traumatic brain injury (TBI) in the rat. MAP2 levels were assayed by quantitative immunoreactivity in tissue fractions obtained from naive, sham-injured, or fluid percussion-injured animals. Tissues were homogenized in the presence of protease inhibitors (0.3 mM phenylmethylsulfonyl fluoride, PMSF), a specific calpain inhibitors (0.1 mM leupeptin), and chelators (2 mM ethylene glycol-bis-tetraacetic acid, EGTA; 1 mM ethylenedinitrilo-tetraacetic acid, EDTA) to eliminate in vitro MAP2 proteolysis during tissue processing. Compared to naive rats, sham injury had no effect on soluble MAP2 levels in either cortex (105.0 +/- 4.4% of naive value) or hippocampus (106.6 +/- 5.2% of naive value). However, TBI caused a significant (p < 0.005) decrease in hippocampal MAP2 levels (55.7 +/- 5.9% of sham-injured controls). The effect appeared to be regionally selective, since the MAP2 decrease did not occur in cortex (89.1 +/- 1.4%). The degree of MAP2 decrease in hippocampus was similar in both membrane (57.8%) and cytosolic (55.7%) fractions, ruling out the possibility of partitioning artifacts. The data suggest that sublethal alterations of neuronal structure and function caused by MAP2 degradation may play an important role in the development of TBI-induced functional deficits. Since MAP2 is exclusively associated with the cytoskeleton in somal and dendritic compartments of neurons, the pathophysiology of sublethal magnitudes of TBI may also involve dendritic and somal dysfunction.

Evidence that protein constituents of postsynaptic membrane specializations are locally synthesized: time course of appearance of recently synthesized proteins in synaptic junctions

Previous studies have led to the hypothesis that some protein constituents of postsynaptic membrane specializations are locally synthesized near postsynaptic sites. The present study focuses on one prediction of this hypothesis, specifically, that if some proteins of the postsynaptic membrane specialization are locally synthesized, then the delay between synthesis and assembly into synaptic junctional membrane could be short. We evaluate the time course of appearance of recently synthesized protein in synaptic junctions by pulse-labeling hippocampal slices maintained in vitro with radiolabeled protein precursors, and then isolating subcellular fractions enriched in synaptic plasma membranes (SPM) and synaptic junctional complexes (SJC). We report that there is no evidence of a delay in the appearance of recently synthesized proteins in SPM and SJC fractions. Labeled proteins could be detected as early as 15 min after the initiation of the pulse-labeling period, and the extent of labeling increased monotonically thereafter. The labeling could not be accounted for by contamination of synaptic membrane fractions with other membranes, because the relative specific activity of the SPM and SJC fractions was the same or higher than that of the less pure fractions from which these synaptic fractions were derived. One-dimensional PAGE-fluorography was used to provide an initial characterization of which proteins were labeled in SJC fractions. We found that the most prominent labeled bands were at apparent molecular weights of approximately 43-44, 55-56, and 60 kd, with more lightly labeled bands at about 38 and 116 kd. In some preparations, there was a labeled doublet at about 36-38 kd. There were also other lightly labeled bands at other molecular weights. These bands were much less heavily labeled than the bands at 43-44, 55-56, and 60 kd, however. There was little labeling in the molecular weight range of the "major psd protein" (the alpha subunit of CAM-kinase), although there was diffuse labeling throughout the 45-52 kd region. These results are consistent with the hypothesis that some of the protein constituents of the postsynaptic junctional complex are synthesized by polyribosomes which are selectively localized beneath synaptic junctions.

Degradation of microtubule-associated protein 2 and brain spectrin by calpain: a comparative study

The in vitro degradation of microtubule-associated protein 2 (MAP-2) and spectrin by the calcium-dependent neutral protease calpain was studied. Five major results are reported. First, MAP-2 isolated from twice-cycled microtubules (2 X MT MAP-2) was extremely sensitive to calpain-induced hydrolysis. Even at an enzyme-to-substrate ratio (wt/wt) of 1:200, 2 X MT MAP-2 was significantly degraded by calpain. Second, MAP-2 purified from the total brain heat-stable fraction (total MAP-2) was significantly more resistant to calpain-induced hydrolysis compared with 2 X MT MAP-2. Third, MAP-2a and MAP-2b were proteolyzed similarly by calpain, although some relative resistance of MAP-2b was observed. Fourth, the presence of calmodulin significantly increased the extent of calpain-induced hydrolysis of the alpha-subunit of spectrin. Fifth, the two neuronal isoforms of brain spectrin (240/235 and 240/235E, referred to as alpha/beta N and alpha/beta E, respectively) showed different sensitivities to calpain. alpha N-spectrin was significantly more sensitive to calpain-induced degradation compared to alpha E-spectrin. Among other things, these results suggest a role for the calpain-induced degradation of MAP-2, as well as spectrin, in such physiological processes as alterations in synaptic efficacy, dendritic remodeling, and in pathological processes associated with neurodegeneration.

Spatial distributions of cytoskeletal proteins and the nerve growth factor receptor in septal transplants in oculo: protection from abnormal immunoreactivity by hippocampal co-grafts

Intraocular grafts of embryonic rat septum and co-grafts of septum plus hippocampus were studied with immunohistochemical markers after one and six months (short term) and 12 months (long term) of survival. Neurons in all the septal tissues expressed the epitope for the rat beta-nerve growth factor receptor in sections reacted with the monoclonal antibody 192-IgG. Stained fibers traversed the interface of the short and long term co-grafts and 192-IgG-positive processes were most prominent in the septum when combined with the hippocampal formation. In contrast, labeled processes were sparse and the perikarya of positive neurons appeared shrunken in the long term single septal transplants. Axon and dendrite profiles in the grafts were examined with antibodies that recognize the phosphorylated heavy neurofilament unit (RT97) and the high molecular weight microtubule-associated protein termed MAP 2, respectively. In the short term single and double grafts, characteristic arrays of RT97-positive processes defined the tissues and axonal tracts connecting the septum with the hippocampus. Typical immunostaining of the neuronal somas and the dendrite arbors were were outlined with the MAP 2 antibody. After one year in oculo, extensive changes in the patterns of axonal and dendritic immunoreactivity were noted in the isolated septal grafts. Abnormalities identified with the RT97 antibody included hypertrophied axons, short fragments of kinked axons and neurofilaments in the neuronal perikarya. The formation of circular "abnormal fiber aggregates" composed of densely packed abnormal and normal axonal processes were also distinctive in only the long term single septal transplants. In addition, a reduction in the density of dendrites and the presence of truncated arbors stained with the MAP 2 antibody suggested that regression of the dendrites had occurred. These spatial modifications in axonal and dendritic staining were not present in the septal portion of the combined preparations. In astrocytes, an increase in the antigenicity to glial fibrillary acidic protein paralleled the age of the transplant and was most extensive in the septal grafts. The results illustrate that intraocular co-grafts of hippocampus protect septal neurons and glial cells from abnormal changes in immunoreactivity to antibodies directed against cytoskeletal proteins and exemplify the long term supportive effects of the hippocampus on the morphology of septal neurons, including neurons that express the receptor for nerve growth factor.

The pattern of GAP-43 immunostaining changes in the rat hippocampal formation during reactive synaptogenesis

The reactive synaptogenesis that takes place in the rat hippocampal formation after certain experimental manipulations affords an opportunity to investigate the molecular events that underlie structural remodeling in the adult CNS. Between 2 and 4 days after lesioning the perforant pathway, levels of the synaptic phosphoprotein, GAP-43 (B50, F1, pp46, neuromodulin), were found to increase markedly in the inner molecular layer (iml) of the dentate gyrus, coincident with the time at which commissural-associational (CA) fibers begin to sprout axon collaterals into dendritic portions denervated by the lesion. GAP-43 immunostaining in the iml began to decline by 8 days but continued to define an expanded CA projection for at least one month. In the outer molecular layer (oml), GAP-43 levels decreased after the loss of perforant pathway terminals and did not return for 2-3 weeks, the time at which sprouting of septal inputs into this layer can be visualized by cholinesterase histochemistry. These results demonstrate that GAP-43 levels change during reactive synaptogenesis, and point to differences among neural systems in their expression of this protein.

The expression of acetylated microtubules during axonal and dendritic growth in cerebellar macroneurons which develop in vitro

The distribution of acetylated microtubules in cerebellar macroneurons which develop in culture was studied with 6-11B-1, a monoclonal antibody specific for acetylated alpha-tubulin. In these neurons 6-11B-1 helps to define a subset of stable, colchicine-resistant, microtubules that during early neuronal development are exclusively localized in the neuron's axon. On the other hand, in mature neurons acetylated microtubules display a widespread distribution being localized in the axon and thick dendritic trunks, a phenomenon correlated with an increase in the levels of acetylated alpha-tubulin and colchicine-resistant microtubules. Taken collectively, these observations suggest that the acetylation of alpha-tubulin is important for differentiating microtubules during neurite growth: in young neurons this post-translational modification may contribute to determine a selective stabilization of microtubules accompanying axonal differentiation.

Microtubule formation and neurite growth in cerebellar macroneurons which develop in vitro: evidence for the involvement of the microtubule-associated proteins, MAP-1a, HMW-MAP2 and Tau

The relationship between the expression of microtubule-associated proteins (MAPs) and microtubule formation was studied in embryonic cerebellar macroneurons maintained in culture. The results obtained suggest that in these neurons high molecular weight-MAP2 (HMW-MAP2) acts as a promoter of tubulin assembly since its induction and pattern of distribution are highly correlated with the increase in microtubule mass which parallels axonal and dendritic growth; MAP-1a may have a similar role but restricted to the assembly of dendritic microtubules. On the other hand, Tau expression and accumulation follows a time course identical to that of the induction of stable microtubules; besides, at all stages of neurite differentiation and growth this protein seems to be preferentially associated with this subset of microtubules as opposed to the other MAPs, observations which suggest an important role for this protein in determining microtubule stability during axonal and dendritic elongation. Finally, the present results show that environmental stimuli are capable of regulating the expression of these MAPs; the induction of each of them varies as a function of the type of signal. Thus, while diffusable substances are able to dramatically induce HMW-MAP2, MAP-1a and Tau inductions depend on cell substrate attachment and/or cell-cell interactions.