Differential regulation of the growth-associated proteins, GAP-43 and SCG-10, in response to unilateral cortical ablation in adult rats

Loss of mouse Stmn2 function causes motor neuropathy

Amyotrophic lateral sclerosis (ALS) is characterized by motor neuron degeneration accompanied by aberrant accumulation and loss of function of the RNA-binding protein TDP43. Thus far, it remains unresolved to what extent TDP43 loss of function directly contributes to motor system dysfunction. Here, we employed gene editing to find whether the mouse ortholog of the TDP43-regulated gene STMN2 has an important function in maintaining the motor system. Both mosaic founders and homozygous loss-of-function Stmn2 mice exhibited neuromuscular junction denervation and fragmentation, resulting in muscle atrophy and impaired motor behavior, accompanied by an imbalance in neuronal microtubule dynamics in the spinal cord. The introduction of human STMN2 through BAC transgenesis was sufficient to rescue the motor phenotypes observed in Stmn2 mutant mice. Collectively, our results demonstrate that disrupting the ortholog of a single TDP43-regulated RNA is sufficient to cause substantial motor dysfunction, indicating that disruption of TDP43 function is likely a contributor to ALS.

Factors Involved in the Functional Motor Recovery of Rats with Cortical Ablation after GH and Rehabilitation Treatment: Cortical Cell Proliferation and Nestin and Actin Expression in the Striatum and Thalamus

Previously we demonstrated, in rats, that treatment with growth hormone (GH) and rehabilitation, carried out immediately after a motor cortical ablation, significantly improved the motor affectation produced by the lesion and induced the re-expression of nestin in the contralateral motor cortex. Here we analyze cortical proliferation after ablation of the frontal motor cortex and investigate the re-expression of nestin in the contralateral motor cortex and the role of the striatum and thalamus in motor recovery. The rats were subjected to ablation of the frontal motor cortex in the dominant hemisphere or sham-operated and immediately treated with GH or the vehicle (V), for five days. At 1 dpi (days post-injury), all rats received daily injections (for four days) of bromodeoxyuridine and five rats were sacrificed at 5 dpi. The other 15 rats (n = 5/group) underwent rehabilitation and were sacrificed at 25 dpi. GH induced the greatest number of proliferating cells in the perilesional cortex. GH and rehabilitation produced the functional recovery of the motor lesion and increased the expression of nestin in the striatum. In the thalamic ventral nucleus ipsilateral to the lesion, cells positive for nestin and actin were detected, but this was independent on GH. Our data suggest that GH-induced striatal nestin is involved in motor recovery.

Quantification of synaptic density in corticostriatal projections from rat medial agranular cortex

Medial agranular cortex (AGm) has a prominent bilateral projection to the dorsocentral striatum (DCS). We wished to develop a normal baseline by which to assess neuronal plasticity in this corticostriatal system in rats with neglect resulting from a unilateral lesion in AGm, followed by treatment with agents that promote sprouting and functional recovery in other systems. Injections of biotinylated dextran amine were made into AGm in normal rats, and unbiased sampling was used to quantify the density of axons and axonal varicosities present in DCS (the latter represent presynaptic profiles). Labeling density in contralateral DCS is approximately half of that seen in ipsilateral DCS (this ratio is 0.50 for axons, 0.55 for varicosities). The ratio of varicosities is stable over a greater than seven-fold range of absolute densities. There is no consistent relationship between the absolute density of axons and axon varicosities; however, the ratio measures are strongly correlated. We conclude that changes in the contralateral/ipsilateral ratio of axon density after experimental treatments do reflect changes in synaptic density, but axon varicosities are likely to be the most sensitive anatomical parameter by which to assess plasticity at the light microscopic level.

Nogo-A inhibition induces recovery from neglect in rats

Neglect is a complex human cognitive spatial disorder typically induced by damage to prefrontal or posterior parietal association cortices. Behavioral treatments for neglect rarely generalize outside of the therapeutic context or across tasks within the same therapeutic context. Recovery, when it occurs, is spontaneous over the course of weeks to months, but often it is incomplete. A number of studies have indicated that anti-Nogo-A antibodies can be used to enhance plasticity and behavioral recovery following damage to motor cortex, and spinal cord. In the present studies the anti-Nogo-A antibodies IN-1, 7B12, or 11C7 were applied intraventricularly to adult rats demonstrating severe neglect produced by unilateral medial agranular cortex lesions in rats. The three separate anti-Nogo-A antibody groups were treated immediately following the medial agranular cortex lesions. Each of the three antibodies induced dramatic significant behavioral recovery from neglect relative to controls. Severing the corpus callosum to destroy inputs from the contralesional hemisphere resulted in reinstatement of severe neglect, pointing to a possible role of interhemispheric mechanisms in behavioral recovery from neglect.

Intrastriatal dopamine D1 antagonism dampens neural plasticity in response to motor cortex lesion

Motor cortex lesions in rats partially denervate the striatum, producing behavioral deficits and inducing reactive neuroplasticity. Plastic responses include changes in growth-associated protein marker expression and anatomical restructuring. Corticostriatal plasticity is dependent on dopamine at the striatal target, where D1 receptor signaling reinforces behaviorally relevant neural activity. To determine whether striatal dopamine D1 receptor signaling is important for the growth-associated protein responses and behavioral recovery that follow unilateral motor cortex aspiration, the dopamine D1 receptor antagonist SCH23390 was intrastriatally infused in cortically lesioned animals. After a cortical aspiration lesion in Long Evans rats, the growth-associated proteins SCG10 and GAP-43 were upregulated in the cortex contralateral to the lesion at 30 days post-lesion. However, continuous unilateral intrastriatal infusion of SCH23390 prevented this aspiration-induced upregulation. Furthermore, lesioned rats demonstrated spontaneous sensorimotor improvement, in terms of limb-use symmetry, about 1 month post-lesion. This improvement was prevented with chronic intrastriatal SCH23390 infusion. The D1 receptor influence may be important to normalize corticostriatal activity (and observable behavior), either in a long-term manner or temporarily until other more permanent means of synaptic regulation, such as sprouting or synaptogenesis, may be implemented.

Brain-derived neurotrophic factor enhances expression of superior cervical ganglia clone 10 in lateral geniculate nucleus and visual cortex of developing kittens

Neuronal growth-associated proteins, including superior cervical ganglia clone 10 (SCG10) family molecules, play roles in neurite outgrowth and network formation as well as structural and functional plasticity. The present ontogenetic study revealed that the expression of neuronal growth-associated proteins in the visual cortex (VC) exhibited a sharp peak in the early postnatal period when growing lateral geniculate nucleus (LGN) axon terminals segregate into the ocular dominance columns depending on retinal activity. We then hypothesized that SCG10 family molecules, known for catastrophic factors of microtubules, play important roles in the formation of ocular dominance columns. To test this hypothesis, we studied whether: (i) monocular blockade of retinal activity changed the SCG10 expression in LGN and VC and (ii) brain-derived neurotrophic factor (BDNF) cortical infusion modified the expression of SCG10 family molecules and the number of excitatory/inhibitory cortical synapses. Using northern blot and in situ hybridization, we revealed that: (i) silencing retinal activity with tetrodotoxin eye injections dynamically reduced the expression of SCG10 mRNA and (ii) it was enhanced by BDNF in VC and LGN of kittens but not adult cats. These findings suggest that cortical infusion of BDNF and retinal activity up-regulate the expression of SCG10 in the LGN and VC and that up-regulated SCG10 in turn initiates marked reorganization of the microtuble network, eventually resulting in increase in synapse formation in the VC.

Site-specific phosphorylation of SCG10 in neuronal plasticity: role of Ser73 phosphorylation by N-methyl D-aspartic acid receptor activation in rat hippocampus

Accumulated evidence suggests that actin and microtubule regulating proteins contribute to neuronal structural dynamics, which subsequently affect neuronal plasticity. SCG10 is a neuronal-specific stathmin protein with microtubule destabilizing activity that is affected by multiple phosphorylation, at least in vitro. SCG10 has four major phosphorylation sites: Ser50 and Ser97 targeted by protein kinase A (PKA), and Ser62 and Ser73 targeted by mitogen-activated protein kinase (MAPK). To explore the potential roles of site-specific phosphorylation in physiological models, we developed phosphorylation site-specific antibodies and examined the SCG10 status in primary cultured hippocampal neurons and tissues. Although SCG10 is concentrated in growth cones and the Golgi apparatus in primary cultured neurons, the phosphorylated form was also detected in both regions, suggesting that MT dynamics within the growth cone may be regulated by protein phosphorylation. In the adult hippocampus, an intense stimulus such as kainate treatment induced a rapid phosphorylation of Ser73 within 15 min that was sustained for at least 60 min. This response was mediated through the N-methyl D-aspartic acid (NMDA) receptor and was ablated by the antagonist MK-801. The MAPK enzyme Erk2 was simultaneously activated along a similar time course to SCG10, suggesting that Erk2 may directly phosphorylate Ser73. These results demonstrate that changes in the phosphorylation status of SCG10 in vivo, dependent upon neural activity and/or plasticity, could affect the microtubule dynamics in neuronal dendrites.

Time-sensitive enhancement of motor learning with the less-affected forelimb after unilateral sensorimotor cortex lesions in rats

Unilateral damage to the forelimb region of the sensorimotor cortex (FLsmc) results in time-dependent changes in neuronal activity, structure and connectivity in the contralateral motor cortex of adult rats. These changes have been linked to facilitation of motor skill learning in the less-affected/ipsilesional forelimb, which is likely to promote its use in the development of behavioral compensation. The goal of this study was to determine whether an early post-lesion-sensitive time period exists for this enhanced learning and whether it is linked to synaptogenesis in the contralesional motor cortex. Rats were trained for 21 days on a skilled reaching task with the ipsilesional forelimb beginning 4 or 25 days after unilateral ischemic (endothelin-1-induced) FLsmc lesions or sham operations. As found previously, reaching performance was significantly enhanced in rats trained early post-lesion compared with sham-operates. In rats trained later post-lesion, performance was neither significantly different from time-matched sham-operates nor strikingly different from animals trained earlier post-lesion. In layer V of the contralesional motor cortex, stereological methods for light and electron microscopy revealed significantly more total, multisynaptic bouton and perforated synapses per neuron compared with sham-operates, but there were no significant differences between early- and late-trained lesion groups. Thus, there appears to be a sensitive time window for the maximal expression of the enhanced learning capacity of the less-affected forelimb but this window is broadly, rather than sharply, defined. These results indicate that relatively long-lasting lesion-induced neuronal changes are likely to underlie the facilitation of learning with the less-affected forelimb.

Differential regulation of the growth-associated proteins GAP-43 and superior cervical ganglion 10 in response to lesions of the cortex and substantia nigra in the adult rat

Investigation of the elements underlying synapse replacement after brain injury is essential for predicting the neural compensation that can be achieved after various types of damage. The growth-associated proteins superior cervical ganglion-10 and growth-associated protein-43 have previously been linked with structural changes in the corticostriatal system in response to unilateral deafferentation. To examine the regulation of this response, unilateral cortical aspiration lesion was carried out in combination with ipsilateral 6-hydroxydopamine lesion of the substantia nigra, and the time course of the contralateral cortical molecular response was followed. Unilateral cortical aspiration lesion in rats corresponds with an upregulation of superior cervical ganglion-10 mRNA at 3 and 10 days post-lesion, and protein, sustained from three to at least 27 days following lesion. With the addition of substantia nigra lesion, the response shifts to an upregulation of growth-associated protein-43 mRNA at 3 and 10 days post-lesion, and protein after 10 days. Nigral lesion alone does not alter contralateral expression of either gene. Likewise, motor function assessment using the rotorod test revealed no significant long-term deficits in animals that sustained only nigrostriatal damage, but cortical lesion was associated with a temporary deficit which was sustained when nigrostriatal input was also removed. Growth-associated protein-43 and superior cervical ganglion-10, two presynaptic genes that are postulated to play roles in lesion-induced sprouting, are differentially upregulated in corticostriatal neurons after cortical versus combined cortical/nigral lesions. The shift in contralateral gene response from superior cervical ganglion-10 to growth-associated protein-43 upregulation and associated behavioral deficit following combined cortical and nigral denervation suggest that nigrostriatal afferents regulate cortical lesion-induced gene expression and ultimate functional outcome.

Unilateral ischemic sensorimotor cortical damage induces contralesional synaptogenesis and enhances skilled reaching with the ipsilateral forelimb in adult male rats

Unilateral damage to the forelimb representation area of the sensorimotor cortex (SMC) results in a compensatory reliance on the unimpaired (ipsilateral to the lesion) forelimb as well as reorganization of neuronal structure and connectivity in the contralateral motor cortex. Recently, male rats with unilateral electrolytic SMC lesions were found to have enhanced skilled reaching performance with the ipsilesional forelimb compared with sham-operated controls. The present study was performed to determine whether these behavioral findings are replicable using an ischemic lesion and whether there is a link between the enhanced learning and synaptogenesis in motor cortical layer V opposite the trained limb and lesion, as assessed using stereological methods for light and electron microscopy. Rats were given a sham operation or an endothelin-1 (ET-1) induced ischemic SMC lesion. They were then trained for 20 days on a skilled reaching task with the unimpaired limb or received control procedures. As with previous findings using electrolytic lesions, rats with unilateral ischemic SMC lesions performed significantly better using the unimpaired forelimb than did sham-operates. Lesions, but not training, significantly increased the total number of motor cortical layer V synapses per neuron as well as the number of perforated and multisynaptic bouton (MSB) synapses per neuron compared with shams. Thus, in addition to a net increase in synapses, the improved reaching ability was coupled with an increase in synapse subtypes that have previously been linked to enhanced synaptic efficacy. The failure to induce synaptogenesis in layer V with reach training alone is in contrast to previous findings and may be related to training intensity.

Unilateral ischemic sensorimotor cortical damage in female rats: forelimb behavioral effects and dendritic structural plasticity in the contralateral homotopic cortex

Previous studies in male rats with unilateral sensorimotor cortical (SMC) damage have demonstrated dendritic structural plasticity in the contralateral homotopic cortex and an enhancement of skilled reaching performance in the forelimb ipsilateral to the lesion compared to sham-operated rats. The purpose of this study was to determine if these findings could be replicated in an ischemic lesion model in female rats. Female rats were given sham operations or unilateral ischemic (endothelin-1 induced) damage in the forelimb representation area of the SMC opposite their preferred forelimb. Animals then received either 20 consecutive days of training on a skilled reaching task with the non-preferred/unimpaired forelimb or no-training control procedures. The surface density of dendrites immunoreactive (IR) for microtubule-associated protein 2 (MAP2) was then measured in the motor cortex opposite the trained limb and/or lesion. Female rats with sufficiently large, but not very small, lesions performed better with the unimpaired forelimb than sham-operated rats on the reaching task. The post-lesion reaching performance was not found to be significantly dependent upon estrous stage at the time of surgery, in agreement with previous studies that failed to find sex or sex-hormone effects after other types of SMC damage. Additionally, there were major laminar-dependent increases in the surface density of MAP2 IR dendrites in the cortex opposite lesions and trained limbs. These findings in female rats are consistent with the dendritic and behavioral changes previously found in male rats. They extend these previous findings by indicating that lesion size is an important variable in the enhancement of reaching performance.

Microarray analysis of fluoro-gold labeled rat dopamine neurons harvested by laser capture microdissection

The cellular heterogeneity of brain tissue presents a challenge to gene expression profiling of specific neuronal cell types. The present study employed a fluorescent neural tracer to specifically label midbrain dopamine neurons and non-dopamine cortical neurons. The labeled cells were then used to visually guide harvesting of the cells by laser capture microdissection (LCM). RNA extracted from the two populations of harvested cells was then amplified, labeled and co-hybridized to high density cDNA microarrays for two-color differential expression profiling. Many of the genes most highly enriched in the dopamine neurons were found to be genes previously known to define the dopamine neuronal phenotype. However, results from the microarray were only partially validated by quantitative RT-PCR analysis. The results indicate that LCM harvesting of specific neuronal phenotypes can be effectively guided in a complex cellular environment by specific pre-labeling of the target cell populations and underlie the importance of independent validation of microarray results.

Time-course study of SCG10 mRNA levels associated with LTP induction and maintenance in the rat Schaffer-CA1 pathway in vivo

The maintenance of long-term potentiation (LTP) depends on altered gene expression. Previously, we found the expression of neuronal growth associated protein SCG10, which is involved in neurite outgrowth and neural regeneration, was up-regulated by LTP induction in the rat hippocampal Schaffer-collateral CA1 pathway. Here we studied the temporal expression pattern of SCG10 mRNA after LTP induction using permanently implanted electrodes in the same CA1 pathway. The real-time RT-PCR showed that both SCG10 mRNA 1 and 2 kb forms were increased at the 3 h, but not at 1 or 24 h. In situ hybridization revealed an increase of SCG10 2 kb mRNA level in ipsilateral CA3 and CA1 areas, but not their contralateral counterparts or either side of dentate gyrus. These results suggest that SCG10 may play a role in the maintenance of synaptic plasticity through a transient regulation of microtubule dynamics, which facilitates the structural remodeling of the presynaptic element during the consolidation period.

Efficacy of rehabilitative experience declines with time after focal ischemic brain injury

To maximize the effectiveness of rehabilitative therapies after stroke, it is critical to determine when the brain is most responsive (i.e., plastic) to sensorimotor experience after injury and to focus such efforts within this period. Here, we compared the efficacy of 5 weeks of enriched rehabilitation (ER) initiated at 5 d (ER5), ER14, or ER30 after focal ischemia, as judged by functional outcome and neuromorphological change. ER5 provided marked improvement in skilled forelimb reaching ability and ladder-rung- and narrow-beam-walking tasks and attenuated the stroke-induced reliance on the unaffected forepaw for postural support. ER14 provided improvement to a somewhat lesser extent, whereas recovery was diminished after ER30 such that motor function did not differ from ischemic animals exposed to social housing. To examine potential neural substrates of the improved function, we examined dendritic morphology in the undamaged motor cortex because our previous work (Biernaskie and Corbett, 2001) suggested that recovery was associated with enhanced dendritic growth in this region. ER5 increased the number of branches and complexity of layer V neurons compared with both social housing and control animals. Dendritic arbor after ER14 (although increased) and ER30 did not differ from those exposed to social housing. These data suggest that the poststroke brain displays heightened sensitivity to rehabilitative experience early after the stroke but declines with time. These findings have important implications for rehabilitation of stroke patients, many of whom experience considerable delays before therapy is initiated.

Facilitation of motor skill learning by callosal denervation or forced forelimb use in adult rats

Unilateral forelimb sensorimotor cortex lesions in adult rats produce a compensatory hyper-reliance on the forelimb ipsilateral to the lesion and temporally related glial and neural plasticity in the contralateral homotopic cortex. Recently, we found that these lesions enhance acquisition of a motor skills task with the ipsilateral, non-impaired, forelimb in comparison to shams. This effect might be related to a denervation-induced facilitation of neuroplastic changes in the motor cortex opposite the lesion and/or to the lesion-induced hyper-reliance on the non-impaired forelimb. The present study assessed whether increased forelimb use, denervation of motor cortical callosal afferents, or a combination of the two influences acquisition of a skilled reaching task. Adult rats with partial corpus callosum transections or sham procedures were either forced to rely on one forelimb or permitted normal forelimb use for 8 days. Rats were then trained for 14 days with their previously non-preferred forelimb (and the forced-use limb) on a unilateral pellet retrieval task. Compared to shams, transections produced a greater acquisition rate and asymptotic performance level on the task. Forced-use improved reaching performance relative to controls, but this effect was less enduring than the improvements produced by transections alone. The addition of forced-use to transections did not further enhance performance. These findings suggest that denervation-induced changes are likely to be a major contributor to the enhanced learning observed after unilateral sensorimotor cortex lesions.

Transcriptional profiling of neuronal differentiation by human embryonal carcinoma stem cells in vitro

Pluripotent stem cell lines can be induced to differentiate into a range of somatic cell types in response to various stimuli. Such cell-based systems provide powerful tools for the investigation of molecules that modulate cellular development. For instance, the formation of the nervous system is a highly regulated process, controlled by molecular pathways that determine the expression of specific proteins involved in cell differentiation. To begin to decipher this mechanism in humans, we used oligonucleotide microarrays to profile the complex patterns of gene expression during the differentiation of neurons from pluripotent human stem cells. Samples of mRNA were isolated from cultured NTERA2 human embryonal carcinoma stem cells and their retinoic-acid-induced derivatives and were prepared for hybridization on custom microarrays designed to detect the expression of genes primarily associated with the neural lineage. In response to retinoic acid, human NTERA2 cells coordinately regulate the expression of large numbers of neural transcripts simultaneously. Transcriptional profiles of many individual genes aligned closely with expression patterns previously recorded by developing neural cells in vitro and in vivo, demonstrating that cultured human pluripotent stem cells appear to form neurons in a conserved manner. These experiments have produced many new expression data concerning neuronal differentiation from human stem cells in vitro. Of particular interest was the regulated expression of Pax6 and Nkx6.1 mRNA and the absence of Pax7 transcription, indicating that neurons derived from NTERA2 pluripotent stem cells are characteristic of neuroectodermal cells of the ventral phenotype.

Synapse replacement in the striatum of the adult rat following unilateral cortex ablation

Defining the selective pattern of synapse replacement that occurs in different areas of the damaged brain is essential for predicting the limits of functional compensation that can be achieved after various types of brain injury. Here we describe the time course of dendritic reorganization, spine loss and recovery, and synapse replacement in the striatum following a unilateral cortex ablation. We found that the time course for the transient loss and recovery of dendritic spines on medium spiny I (MSI) neurons, the primary postsynaptic target for corticostriatal axons, paralleled the time course for the removal of degenerating axon terminals from the neuropil and the formation of new synapses on MSI neurons. Reinnervation of the deafferented striatum occurred chiefly by axon terminals that formed asymmetric synapses with dendritic spines of MSI neurons, and the mean density of asymmetric synapses recovered to 86% of the sham-operated rat value by 30 days postlesion. In addition, the synaptic circuitry of the reconstructed striatum was characterized by an increase in the number of multiple synaptic boutons (MSBs), i.e., presynaptic axon terminals that make contact with more than one dendritic spine. Whether the postsynaptic contacts of MSBs are formed with the dendritic spines of the same or a different parent dendrite in the striatum is unknown. Nevertheless, these data suggest that the formation of MSBs is an essential part of the compensatory response to the loss of input from the ipsilateral cortex following the aspiration lesion and may serve to modulate activity-dependent adaptive changes in the reconstructed striatum that can lead to functional recovery.

Identification of upregulated SCG10 mRNA expression associated with late-phase long-term potentiation in the rat hippocampal Schaffer-CA1 pathway in vivo

The maintenance of long-term potentiation (LTP) depends on alteration of gene transcription. By screening a subtracted cDNA library that is enriched in upregulated transcripts in rat hippocampus 3 hr after Schaffer-CA1 LTP induction in vivo, we identified a neural growth-associated protein SCG10 (superior cervical ganglia clone 10) gene. The semiquantitative reverse transcription-PCR and Northern blot experiments confirmed that SCG10 mRNA levels were elevated in tetanized rat hippocampi compared with those of sham controls that received only low-frequency stimulation. Both 1 and 2 kb forms of SCG10 mRNAs contributed to the increased expression. Using a riboprobe with a sequence specific to the 3'-untranslated region of rat SCG10 mRNA, in situ hybridization further revealed a significant increase of the SCG10 mRNA 2 kb form in the ipsilateral CA3 and CA1 regions of LTP animals. In addition, we systemically injected the competitive NMDA receptor antagonist d,l-3[(+/-)-2-carboxypiperazine-4-yl]-propyl-1-phosphonic acid (CPP) to determine whether the alteration of SCG10 expression depends on NMDA receptor activation or tetanus alone. Administration of CPP 1 hr before tetanus completely blocked LTP induction and the increase of SCG10 mRNA levels. Thus, these results suggest that the transcription of SCG10 in vivo is regulated by long-lasting synaptic activity and may contribute to the maintenance of long-term synaptic plasticity via a presynaptic remodeling mechanism.

SCG10-related neuronal growth-associated proteins in neural development, plasticity, degeneration, and aging

Neuronal growth-associated proteins (nGAPs) are in general neuron-specific gene products whose expression correlates tightly with neuronal process outgrowth and/or regeneration, and are mostly good downstream targets of neurotrophin stimulation. Expression of genes encoding nGAPs such as GAP-43, SCG10, and stathmin is upregulated following lesioning of cortical and hippocampal regions of the adult rat brain. In the brains of aged animals, however, the magnitude of the response is reduced, whereas the time course of the response is mostly unchanged when compared with that for brains of young ones. Expression of GAP-43 and stathmin is reduced by aging, and is also changed in age-related neurodegenerative conditions such as Alzheimer's disease in humans. Certain nGAPs are induced during long-term potentiation (LTP) and also during critical periods of song-learning and ocular dominance column formation in birds and cats, respectively. Recent evidence further supports the idea that functional synaptic modulation is often associated with remodeling of synaptic structures. These results suggest that neurotrophin-responsive nGAPs serve as molecular markers of neuronal plasticity during development and aging, and that the neuronal plasticity decreases, at least in certain neuronal circuits, in the aged brain and neurodegenerative diseases. Recent findings on the roles of stathmin and SCG10-related proteins in microtubule destabilization and its functional block by phosphorylation further support the importance of the SCG10 family proteins in neuronal cytoskeletal regulation, particularly as to microtubule dynamics. We summarize here a decade of research on SCG10 and its related molecules with special interests to brain aging and disease.

Plasticity-associated molecular and structural events in the injured brain

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

The behavioral and dendritic growth effects of focal sensorimotor cortical damage depend on the method of lesion induction

Using different models of focal cortical injury in adult rats, the neural structural and behavioral outcomes of unilateral lesions of the forelimb representation of the sensorimotor cortex (SMC) were assessed. Lesions were produced using either electrolytic, aspiration, or combined ('electroaspiration') techniques. Measurements of dendritic arborization in layer V of the motor cortex opposite the lesion revealed a growth of pyramidal neuron dendritic processes following electrolytic lesions in comparison to shams. This effect was not found in either the aspiration or electroaspiration lesion groups. Behaviorally, animals in all lesion groups developed a hyper-reliance on the forelimb ipsilateral to the lesion and proportionate disuse of the contralateral (impaired) forelimb for postural support behaviors. In comparison to sham-operated animals, the initial asymmetries in behaviors expressed during movement were similar between lesion groups, but were less enduring following electrolytic lesions than following aspiration and electroaspiration lesions. Furthermore, both aspiration lesion groups had more prevalent adduction of the impaired forelimb than the electrolytic-only lesion rats. Thus, cortical aspiration resulted in more severe and enduring forelimb impairments than the electrolytic lesions, despite similar lesion sizes, as assessed using cortical volume measures. These findings suggest that the aspiration lesion procedures, at least as performed in the present study, exacerbate the behavioral effects of focal cortical injury and limit compensatory plasticity in the contralateral cortex.

Nestin immunoreactivity in local neurons of the adult rat striatum after remote cortical injury

Nestin is a marker for the neuronal and glial precursor cells and is expressed in reactive astrocytes after brain injury. Following restricted neocortical injury, we found that cells with neuronal morphology in the adult rat striatum became immunoreactive for both nestin and the neuronal marker, microtubule-associated protein 2 (MAP-2), but not for the astroglial marker, glial fibrillary acidic protein (GFAP). The number of nestin-positive cells transiently increased in the striatum. Continuous administration of 5-bromo-2'-deoxyuridine (BrdU) after cortical injury did not reveal any newly generated neurons in the striatum. Double-labeling fluorescent immunocytochemistry revealed that the nestin-positive striatal cells were also substance-P-positive. These findings suggest that some factors released from the injured cortex may induce nestin immunoreactivity in striatal neurons.

Gene expression related to synaptogenesis, neuritogenesis, and MAP kinase in behavioral sensitization to psychostimulants

The most important characteristic of behavioral sensitization to psychostimulants, such as amphetamine and cocaine, is the very long-lasting hypersensitivity to the drug after cessation of exposure. Rearrangement and structural modification of neural networks in CNS must be involved in behavioral sensitization. Previous microscopic studies have shown that the length of dendrites and density of dendritic spines increased in the nucleus accumbens and frontal cortex after repeated exposure to amphetamine and cocaine, but the molecular mechanisms responsible are not well understood. We investigated a set of genes related to synaptogenesis, neuritogenesis, and mitogen-activated protein (MAP) kinase after exposure to methamphetamine. Synaptophysin mRNA, but not VAMP2 (synaptobrevin 2) mRNA, which are considered as synaptogenesis markers, increased in the accumbens, striatum, hippocampus, and several cortices, including the medial frontal cortex, after a single dose of 4 mg/kg methamphetamine. Stathmin mRNA, but not neuritin or narp mRNA, which are markers for neuritic sprouting, increased in the striatum, hippocampus, and cortices after a single dose of methamphetamine. The mRNA of arc, an activity-regulated protein associated with cytoskeleton, but not of alpha-tubulin, as markers for neuritic elongation, showed robust increases in the striatum, hippocampus, and cortices after a single dose of methamphetamine. The mRNAs of MAP kinase phosphatase-1 (MKP-1), MKP-3, and rheb, a ras homologue abundant in brain, were investigated to assess the MAP kinase cascades. MKP-1 and MKP-3 mRNAs, but not rheb mRNA, increased in the striatum, thalamus, and cortices, and in the striatum, hippocampus, and cortices, respectively, after a single methamphetamine. Synaptophysin and stathmin mRNAs did not increase again after chronic methamphetamine administration, whereas the increases in arc, MKP-1, and MKP-3 mRNAs persisted in the brain regions after chronic methamphetamine administration. These findings indicate that the earlier induction process in behavioral sensitization may require various plastic modifications, such as synaptogenesis, neuritic sprouting, neuritic elongation, and activation of MAP kinase cascades, throughout almost the entire brain. In contrast, later maintenance process of sensitization may require only limited plastic modification in restricted regions.

Expression of super cervical ganglion-10 (SCG-10) mRNA in the monkey cerebral cortex during postnatal development

We used Northern blot analysis to measure SCG10 mRNA expression in various areas of the monkey cerebral cortex during postnatal development. In all areas, SCG10 mRNA expression was highest immediately after birth, decreased sharply until postnatal day 70 (P70) and then decreased slowly until the adult stage. Expression levels were similar in all areas at all time points during development, including the adult stage. These findings confirm that axonal growth in the monkey cerebral cortex is most vigorous before or during the perinatal period, progresses similarly in all areas until P70, and continues at lower levels during late development.

Effect of genetic selection for group productivity and longevity on immunological and hematological parameters of chickens

A line of White Leghorn chickens was selected for high group productivity and longevity resulting in improved survival and feather score as well as reduced cannibalism and flightiness. Improvements in survival might have also been due to improved immunity. The present study was designed to test the hypothesis that selection for high (HGPS) and low (LGPS) group productivity and survivability also altered immune and hematological parameters. The LGPS line was an intense reverse selected line of the HGPS line at the eighth generation of development. Hens were randomly assigned to individual cages at 17 wk of age. Blood samples were collected from the hens at 21 wk of age. Subsets of T lymphocytes (CD4+, CD8+, and gammadelta cells) were measured using flow cytometry. Concentrations of plasma IgG were quantified with western blot analysis and immunoprecipitation assay. Hematological parameters were collected from blood smears. The HGPS hens had significantly higher percentages of blood lymphocytes and CD4+:CD8+ ratios of circulating T cells (P < 0.01) and tended to have more, but not significantly, gammadelta T cells (P = 0.07) than the LGPS hens. In contrast, the LGPS hens exhibited eosinophilia and heterophilia and greater heterophil:lymphocyte ratios (P < 0.01). The concentrations of plasma IgG were also significantly higher in the LGPS hens (P < 0.01). These results suggest that genetic selection for group productivity and longevity also alters the immunological and hematological systems of hens. The line difference in regulation of T cells, leukocytes, and production of IgG may suggest that different genes or modes of gene action are involved.

Stathmin family proteins display specific molecular and tubulin binding properties

Stathmin family phosphoproteins (stathmin, SCG10, SCLIP, and RB3/RB3'/RB3") are involved in signal transduction and regulation of microtubule dynamics. With the exception of stathmin, they are expressed exclusively in the nervous system, where they display different spatio-temporal and functional regulations and hence play at least partially distinct and possibly complementary roles in relation to the control of development, plasticity, and neuronal activities. At the molecular level, each possesses a specific "stathmin-like domain" and, with the exception of stathmin, various combinations of N-terminal extensions involved in their association with intracellular membrane compartments. We show here that each stathmin-like domain also displays specific biochemical and tubulin interaction properties. They are all able to sequester two alpha/beta tubulin heterodimers as revealed by their inhibitory action on tubulin polymerization and by gel filtration. However, they differ in the stabilities of the complexes formed as well as in their interaction kinetics with tubulin followed by surface plasmon resonance as follows: strong stability and slow kinetics for RB3; medium for SCG10, SCLIP, and stathmin; and weak stability and rapid kinetics for RB3'. These results suggest that the fine-tuning of their stathmin-like domains contributes to the specific functional roles of stathmin family proteins in the regulation of microtubule dynamics within the various cell types and subcellular compartments of the developing or mature nervous system.

Perforant path lesion induces up-regulation of stathmin messenger RNA, but not SCG10 messenger RNA, in the adult rat hippocampus

In this study, we performed in situ hybridization analysis of the expression pattern of two growth-associated proteins, stathmin and SCG10, in the hippocampus after unilateral lesion of the perforant pathway, the main excitatory input from the entorhinal cortex to the hippocampus. Stathmin is one of the major neural-enriched cytosolic phosphoproteins and a potential target of cyclic-AMP-dependent kinases [Jin L. W. et al. (1996) Neurobiol. Aging 17, 331-341; Leighton I. A. et al. (1993) Molec. Cell Biochem. 127/128, 151-156]. Three days after the lesion, stathmin messenger RNA was up-regulated ipsilaterally in the hilus, in the granule cell layer of the dentate gyrus and in the pyramidal cell layer of the CA1 region. Simultaneously, the hilar region of the contralateral dentate gyrus showed an increased stathmin messenger RNA expression. This altered expression pattern was observed until 15 days after lesion. Stathmin messenger RNA expression returned to a normal level until 21 days after lesion in all regions analysed. SCG10, a membrane-bound neuronal growth-associated protein belonging to the SCG10/stathmin gene family, did not show any alteration of messenger RNA expression after perforant path lesion. The temporal changes of stathmin messenger RNA expression in the ipsilateral hippocampus correspond well to the process of reactive synaptogenesis. The enhanced messenger RNA expression in the hilar region of the contralateral dentate gyrus might suggest a role in neurite elongation, since this region is the origin of commissural fibres involved in the sprouting response in the deafferented hippocampus. The present study provides evidence that the induction of specific growth-associated proteins is differentially regulated in the hippocampus.

Spatiotemporal distribution of GAP-43 in the developing rat spinal cord: a histological and quantitative immunofluorescence study

In the rat spinal cord we studied developmental changes in spatiotemporal expression of the growth-associated protein GAP-43, which is known to play an important role in neural development, axonal regeneration, and modulation of synaptic function. GAP-43 was expressed predominantly in the white matter at embryonic day 13 to postnatal day 7, evenly in the white and gray matter at the 2nd to the 3rd postnatal week, and predominantly in the gray matter after the 5th postnatal week. The shifting of predominance was quantitatively assessed. On the basis of histological findings and quantitative assessment of GAP-43 immunoreactivity, it appears likely that the development proceeds from the phase of mostly axonal elongation during the embryonic period and the 1st postnatal week, via the phase of axonal elongation and formation of end arbors and synaptic organization during the 2nd to the 4th postnatal week, to the phase of final maturation of synaptic organization. GAP-43 was continuously expressed through adulthood in neuropil of the gray matter, the pyramidal tract, and the dorsal portion of the lateral funiculus that was identified as serotonergic by confocal laser scanning microscopic studies. The continuous expression may imply perpetual remodeling in these structures even in adulthood.

Alterations in rat striatal glutamate synapses following a lesion of the cortico- and/or nigrostriatal pathway

Ultrastructural changes within the ipsilateral dorsolateral striatum were investigated 1 month following a unilateral ablation of the rat frontal cortex (CTX), removing corticostriatal input, or injection of the neurotoxin, 6-hydroxydopamine (6-OHDA), into the substantia nigra pars compacta, removing nigrostriatal input. In addition, a combined ipsilateral cortical and 6-OHDA lesion (CTX/6-OHDA) was carried out. We find that following a CTX, 6-OHDA, or CTX/6-OHDA lesion, there was a significant decrease in the density of striatal nerve terminal glutamate immunoreactivity compared to the control group. There was also a significant increase in all three lesion groups in the mean percentage of asymmetrical synapses associated with a perforated postsynaptic density. There was a large increase within the CTX/6-OHDA-lesioned group and a smaller but still significant increase in the CTX-lesioned group in the percentage of terminals or boutons with multiple synaptic contacts (i.e., multiple synaptic boutons, MSBs), compared to either the 6-OHDA or the control group. There was no change in any of these measurements within the contralateral striatum. There was a significant decrease in the number of apomorphine-induced contralateral rotations in the CTX/6-OHDA versus the 6-OHDA-lesioned group. Animals receiving just the single CTX or 6-OHDA lesion recovered in motor function compared to the control group as measured by the Rotorod test, while the CTX/6-ODA-lesioned group recovered to less than 50% of the control level. The data suggest that following a CTX and/or 6-OHDA lesion, there is an increase in striatal glutamatergic function. The large increase in the percentage of MSBs in the combined lesion group suggests that dopamine or other factors released by the dopamine terminals assist in regulating synapse formation.

Expression of GAP-43 and SCG10 mRNAs in lateral geniculate nucleus of normal and monocularly deprived macaque monkeys

We performed nonradioactive in situ hybridization histochemistry (ISH) in the lateral geniculate nucleus (LGN) of the macaque monkey to investigate the distribution of mRNA for two growth-associated proteins, GAP-43 and SCG10. GAP-43 and SCG10 mRNAs were coexpressed in most neurons of both magnocellular layers (layers I and II) and parvocellular layers (layers III-VI). Double-labeling using nonradioactive ISH and immunofluorescence revealed that both GAP-43 and SCG10 mRNAs were coexpressed with the alpha-subunit of type II calcium/calmodulin-dependent protein kinase, indicating that both mRNAs are expressed also in koniocellular neurons in the LGN. We also showed that GABA-immunoreactive neurons in the LGN did not contain GAP-43 and SCG10 mRNAs, indicating that neither GAP-43 nor SCG10 mRNAs were expressed in inhibitory interneurons in the LGN. GABA-immunoreactive neurons in the perigeniculate nucleus, however, contained both GAP-43 and SCG10 mRNAs, indicating that both mRNAs were expressed in inhibitory neurons in the perigeniculate nucleus, which project to relay neurons in the LGN. Furthermore, to determine whether the expression of GAP-43 and SCG10 mRNAs is regulated by visual input, we performed nonradioactive ISH in the LGN and the primary visual area of monkeys deprived of monocular visual input by intraocular injections of tetrodotoxin. Both mRNAs were downregulated in the LGN after monocular deprivation for 5 d or longer. From these results, we conclude that both GAP-43 and SCG10 mRNAs are expressed in the excitatory relay neurons of the monkey LGN in an activity-dependent manner.

The SCG10-related gene family in the developing rat retina: persistent expression of SCLIP and stathmin in mature ganglion cell layer

Neuronal growth-associated proteins (GAPs), such as GAP-43 and SCG10, are thought to play crucial roles in both axonal and dendritic outgrowth during neural development and regeneration, although the underlying mechanisms remain largely unknown. The recent finding that SCG10 is a microtubule regulator and also the identification of RB3 and SCLIP as two new SCG10-related members prompted us to investigate the roles of SCG10-related family in neural development, using the retina as a model system. We determined the temporal expression and the spatial distribution of SCG10-related mRNAs in the developing rat retina. Semiquantitative analysis by RT-PCR revealed that in prenatal retina, levels of SCG10 and stathmin mRNAs were higher than those of RB3 and SCLIP. In the postnatal retina, the level of SCLIP increased, whereas the level of RB3 remained low. In situ hybridization revealed that GAP-43 and all of the SCG10-related family mRNAs were present in the retinal ganglion cells (RGCs) at all stages of retinal development, and that stathmin mRNA was present in mitotic neuroblastic cells. Differential expression of SCG10 and other members of the family became more evident as retinal development proceeded; SCG10 and RB3 expression were relatively specific in the RGCs and amacrine cells, whereas SCLIP was also evident in bipolar and horizontal cells. Stathmin mRNA was highly expressed both in the RGCs and other interneurons. These results indicate that multiple SCG10-related proteins are expressed in single neurons including RGCs, and suggest that these nGAPs play similar but distinct roles in differentiation and functional maintenance of retinal neurons.