Plasticity-associated molecular and structural events in the injured brain

Role of Semaphorins in Ischemic Stroke

Ischemic stroke is one of the major causes of neurological morbidity and mortality in the world. Although the management of ischemic stroke has been improved significantly, it still imposes a huge burden on the health and property. The integrity of the neurovascular unit (NVU) is closely related with the prognosis of ischemic stroke. Growing evidence has shown that semaphorins, a family of axon guidance cues, play a pivotal role in multiple pathophysiological processes in NVU after ischemia, such as regulating the immune system, angiogenesis, and neuroprotection. Modulating the NVU function via semaphorin signaling has a potential to develop a novel therapeutic strategy for ischemic stroke. We, therefore, review recent progresses on the role of semphorin family members in neurons, glial cells and vasculature after ischemic stroke.

The active kinome: The modern view of how active protein kinase networks fit in biological research

Biological regulatory networks are dynamic, intertwined, and complex systems making them challenging to study. While quantitative measurements of transcripts and proteins are key to investigate the state of a biological system, they do not inform the "active" state of regulatory networks. In consideration of that fact, "functional" proteomics assessments are needed to decipher active regulatory processes. Phosphorylation, a key post-translation modification, is a reversible regulatory mechanism that controls the functional state of proteins. Recent advancements of high-throughput protein kinase activity profiling platforms allow for a broad assessment of protein kinase networks in complex biological systems. In conjunction with sophisticated computational modeling techniques, these profiling platforms provide datasets that inform the active state of regulatory systems in disease models and highlight potential drug targets. Taken together, system-wide profiling of protein kinase activity has become a critical component of modern molecular biology research and presents a promising avenue for drug discovery.

Effect of environmental enrichment on behavioral and morphological outcomes following neonatal hypoxia-ischemia in rodent models: A systematic review and meta-analysis

Neonatal hypoxia-ischemia (HI) is a major cause of mortality and morbidity in newborns and, despite recent advances in neonatal intensive care, there is no definitive treatment for this pathology. Once preclinical studies have shown that environmental enrichment (EE) seems to be a promising therapy for children with HI, the present study conducts a systematic review and meta-analysis of articles with EE in HI rodent models focusing on neurodevelopmental reflexes, motor and cognitive function as well as brain damage. The protocol was registered a priori at PROSPERO. The search was conducted in PubMed, Embase and PsycINFO databases, resulting in the inclusion of 22 articles. Interestingly, EE showed a beneficial impact on neurodevelopmental reflexes (SMD= -0.73, CI= [-0.98; -0.47], p< 0.001, I²= 0.0%), motor function (SMD= -0.55, CI= [-0.81; -0.28], p< 0.001, I²= 62.6%), cognitive function (SMD= -0.93, CI= [-1.14; -0.72], p< 0.001, I²= 27.8%) and brain damage (SMD= -0.80, CI= [-1.03; -0.58], p< 0.001, I²= 10.7%). The main factors that potentiate EE positive effects were enhanced study quality, earlier age at injury as well as earlier start and longer duration of EE exposure. Overall, EE was able to counteract the behavioral and histological damage induced by the lesion, being a promising therapeutic strategy for HI.

Drosophila as a model to explore secondary injury cascades after traumatic brain injury

Drosophilae are emerging as a valuable model to study traumatic brain injury (TBI)-induced secondary injury cascades that drive persisting neuroinflammation and neurodegenerative pathology that imposes significant risk for long-term neurological deficits. As in mammals, TBI in Drosophila triggers axonal injury, metabolic crisis, oxidative stress, and a robust innate immune response. Subsequent neurodegeneration stresses quality control systems and perpetuates an environment for neuroprotection, regeneration, and delayed cell death via highly conserved cell signaling pathways. Fly injury models continue to be developed and validated for both whole-body and head-specific injury to isolate, evaluate, and modulate these parallel pathways. In conjunction with powerful genetic tools, the ability for longitudinal evaluation, and associated neurological deficits that can be tested with established behavioral tasks, Drosophilae are an attractive model to explore secondary injury cascades and therapeutic intervention after TBI. Here, we review similarities and differences between mammalian and fly pathophysiology and highlight strategies for their use in translational neurotrauma research.

Putative dendritic correlates of chronic traumatic encephalopathy: A preliminary quantitative Golgi exploration

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder that is associated with repetitive head impacts. Neuropathologically, it is defined by the presence of perivascular hyperphosphorylated tau aggregates in cortical tissue (McKee et al., 2016, Acta Neuropathologica, 131, 75-86). Although many pathological and assumed clinical correlates of CTE have been well characterized, its effects on cortical dendritic arbors are still unknown. Here, we quantified dendrites and dendritic spines of supragranular pyramidal neurons in tissue from human frontal and occipital lobes, in 11 cases with (M_age = 79 ± 7 years) and 5 cases without (M_age = 76 ± 11 years) CTE. Tissue was stained with a modified rapid Golgi technique. Dendritic systems of 20 neurons per region in each brain (N = 640 neurons) were quantified using computer-assisted morphometry. One key finding was that CTE neurons exhibited increased variability and distributional changes across six of the eight dendritic system measures, presumably due to ongoing degeneration and compensatory reorganization of dendritic systems. However, despite heightened variation among CTE neurons, CTE cases exhibited lower mean values than Control cases in seven of the eight dendritic system measures. These dendritic alterations may represent a new pathological marker of CTE, and further examination of dendritic changes could contribute to both mechanistic and functional understandings of the disease.

Region-specific expression of precursor and mature brain-derived neurotrophic factors after chronic alcohol exposure

BACKGROUND

Alcohol abuse is a serious health problem worldwide that causes a variety of physical and mental disorders. Research has shown that the brain-derived neurotrophic factor (BDNF) plays an important role in alcohol addiction. The BDNF precursor (proBDNF) exhibits different actions than BDNF through separate receptors and pathways in the central nervous system. However, the effects of proBDNF and BDNF in alcohol addiction are not fully known.

OBJECTIVES

The objective was to identify the expression patterns and effects of proBDNF and BDNF after chronic alcohol exposure.

METHODS

A total of 40 male adult mice were studied. A mouse psychomotor sensitization (PS) model was established to explore the effects of BDNF and proBDNF treatment following chronic alcohol exposure. Reverse transcription PCR (RT-PCR) was performed to measure mRNA levels for BDNF, TrkB, P75NTR, and sortilin in the prefrontal cortex, hippocampus, and dorsal striatum of Kunming mice after chronic alcohol exposure.

RESULTS

In Kunming mice, chronic alcohol exposure up-regulated BDNF and TrkB mRNA levels in the prefrontal cortex, but decreased sortilin and P75 mRNA levels in the dorsal striatum. No changes in mRNA levels were found in other measured brain regions in the alcohol and control groups.

CONCLUSION

Chronic alcohol exposure induced the region-specific expression of BDNF and proBDNF and their respective receptors in the brain. These results suggest that BDNF and proBDNF signaling pathways may play major roles in alcohol preference and addiction.

Spinal cord injury induces widespread chronic changes in cerebral white matter

Traumatic spinal cord injuries (SCIs) lead to axonal damage at the trauma site, as well as disconnections within the central nervous system. While the exact mechanisms of the long-term pathophysiological consequences of SCIs are not fully understood, it is known that neuronal damage and degeneration are not limited to the direct proximity of the trauma. Instead, the effects can be detected even in the cerebrum. We examined SCI-induced chronic brain changes with a case-control design using 32 patients and 70 control subjects. Whole-brain white matter (WM) tracts were assessed with diffusion tensor imaging (DTI). In addition, we analysed associations between DTI metrics and several clinical SCI variables. Whole-brain analyses were executed by tract-based spatial statistics (TBSS), with an additional complementary atlas-based analysis (ABA). We observed widespread, statistically significant (P ≤ 0.01) changes similar to neural degeneration in SCI patients, both in the corticospinal tract (CST) and beyond. In addition, associations between DTI metrics and time since injury were found with TBSS and ABA, implying possible long-term post-injury neural regeneration. Using the ABA approach, we observed a correlation between SCI severity and DTI metrics, indicating a decrease in WM integrity along with patient sensory or motor scores. Our results suggest a widespread neurodegenerative effect of SCI within the cerebrum that is not limited to the motor pathways. Furthermore, DTI-measured WM integrity of chronic SCI patients seemed to improve as time elapsed since injury. Hum Brain Mapp 38:3637-3647, 2017. © 2017 Wiley Periodicals, Inc.

Neural Substrate Expansion for the Restoration of Brain Function

Restoring neurological and cognitive function in individuals who have suffered brain damage is one of the principal objectives of modern translational neuroscience. Electrical stimulation approaches, such as deep-brain stimulation, have achieved the most clinical success, but they ultimately may be limited by the computational capacity of the residual cerebral circuitry. An alternative strategy is brain substrate expansion, in which the computational capacity of the brain is augmented through the addition of new processing units and the reconstitution of network connectivity. This latter approach has been explored to some degree using both biological and electronic means but thus far has not demonstrated the ability to reestablish the function of large-scale neuronal networks. In this review, we contend that fulfilling the potential of brain substrate expansion will require a significant shift from current methods that emphasize direct manipulations of the brain (e.g., injections of cellular suspensions and the implantation of multi-electrode arrays) to the generation of more sophisticated neural tissues and neural-electric hybrids in vitro that are subsequently transplanted into the brain. Drawing from neural tissue engineering, stem cell biology, and neural interface technologies, this strategy makes greater use of the manifold techniques available in the laboratory to create biocompatible constructs that recapitulate brain architecture and thus are more easily recognized and utilized by brain networks.

Neuronal adhesion and synapse organization in recovery after brain injury

Few specific therapeutic targets exist to manage brain injury, despite the prevalence of stroke or traumatic brain injury. With traumatic brain injury, characteristic neuronal changes include axonal swelling and degeneration, and the loss of synapses, the sites of communication between neurons. This is followed by axonal sprouting and alterations in synaptic markers in recovery. The resulting changes in neuronal connectivity are likely to contribute to the effects of traumatic brain injury on cognitive functions and the underlying mechanisms may represent points of therapeutic intervention. In agreement, animal studies implicate adhesion and signaling molecules that organize synapses as molecular players in neuronal recovery. In this article, the authors focus on the role of cell surface interactions in the recovery after brain injury in humans and animals. The authors review cellular and synaptic alterations that occur with injury and how changes in cell adhesion, protein expression and modification may be involved in recovery. The changes in neuronal surface interactions as potential targets and their possible value for the development of therapeutics are also discussed.

Cortical reorganization after experimental traumatic brain injury: a functional autoradiography study

Cortical sensorimotor (SM) maps are a useful readout for providing a global view of the underlying status of evoked brain function, as well as a gross overview of ongoing mechanisms of plasticity. Recent evidence in the rat controlled cortical impact (CCI) injury model shows that the ipsilesional (injured) hemisphere is temporarily permissive for axon sprouting. This would predict that size and spatial alterations in cortical maps may occur much earlier than previously tested and that they might be useful as potential markers of the postinjury plasticity period as well as indicators of outcome. We investigated the evolution of changes in brain activation evoked by affected hindlimb electrical stimulation at 4, 7, and 30 days following CCI or sham injury over the hindlimb cortical region of adult rats. [(14)C]-iodoantipyrine autoradiography was used to quantitatively examine the local cerebral blood flow changes in response to hindlimb stimulation as a marker for neuronal activity. The results show that although ipsilesional hindlimb SM activity was persistently depressed from 4 days, additional novel regions of ipsilesional activity appeared concurrently within SM barrel and S2 regions as well as posterior auditory cortex. Simultaneously with this was the appearance of evoked activity within the intact, contralesional cortex that was maximal at 4 and 7 days, compared to stimulated sham-injured rats, where activation was solely unilateral. By 30 days, however, contralesional activation had greatly subsided and existing ipsilesional activity was enhanced within the same novel cortical regions that were identified acutely. These data indicate that significant reorganization of the cortical SM maps occurs after injury that evolves with a particular postinjury time course. We discuss these data in terms of the known mechanisms of plasticity that are likely to underlie these map changes, with particular reference to the differences and similarities that exist between rodent models of stroke and traumatic brain injury.

Diffusion tensor imaging detects white matter abnormalities and associated cognitive deficits in chronic adolescent TBI

PRIMARY OBJECTIVE

This study examined long-term alterations in white matter microstructure following TBI in adolescence using diffusion tensor imaging (DTI). It was hypothesized that white matter integrity would be compromised in adolescents with TBI and would correlate with measures of executive functioning and cognitive abilities.

RESEARCH DESIGN

This study employed whole-brain, voxel-wise, statistical comparison of DTI indices in youth of 12-17 years old (mean = 15.06) with TBI vs an age- and gender-matched cohort (mean age = 15.37).

METHODS AND PROCEDURES

This study scanned 17 adolescents with complicated-mild-to-severe TBI, 1-3 years after injury, and 13 healthy adolescents. Tract-Based Spatial Statistics (TBSS) was employed for DTI analysis.

MAIN OUTCOMES AND RESULTS

Overall diffusivity elevations were found in the TBI group with increases in axial diffusivity in the right hemisphere. White matter integrity was associated with word reading, planning and processing times in the TBI group, but not healthy controls.

CONCLUSIONS

The detected abnormalities in axial diffusivity may reflect neuronal regeneration and cerebral reorganization after injury. These findings provide tentative evidence of persistent white matter alteration following TBI in adolescence. Associations of DTI indices with cognitive performance following TBI provide tentative support for links between white matter integrity and performance post-TBI.

The neuropathology and neurobiology of traumatic brain injury

The acute and long-term consequences of traumatic brain injury (TBI) have received increased attention in recent years. In this Review, we discuss the neuropathology and neural mechanisms associated with TBI, drawing on findings from sports-induced TBI in athletes, in whom acute TBI damages axons and elicits both regenerative and degenerative tissue responses in the brain and in whom repeated concussions may initiate a long-term neurodegenerative process called dementia pugilistica or chronic traumatic encephalopathy (CTE). We also consider how the neuropathology and neurobiology of CTE in many ways resembles other neurodegenerative illnesses such as Alzheimer's disease, particularly with respect to mismetabolism and aggregation of tau, β-amyloid, and TDP-43. Finally, we explore how translational research in animal models of acceleration/deceleration types of injury relevant for concussion together with clinical studies employing imaging and biochemical markers may further elucidate the neurobiology of TBI and CTE.

Music listening after stroke: beneficial effects and potential neural mechanisms

Music is an enjoyable leisure activity that also engages many emotional, cognitive, and motor processes in the brain. Here, we will first review previous literature on the emotional and cognitive effects of music listening in healthy persons and various clinical groups. Then we will present findings about the short- and long-term effects of music listening on the recovery of cognitive function in stroke patients and the underlying neural mechanisms of these music effects. First, our results indicate that listening to pleasant music can have a short-term facilitating effect on visual awareness in patients with visual neglect, which is associated with functional coupling between emotional and attentional brain regions. Second, daily music listening can improve auditory and verbal memory, focused attention, and mood as well as induce structural gray matter changes in the early poststroke stage. The psychological and neural mechanisms potentially underlying the rehabilitating effect of music after stroke are discussed.

sAPPα rescues deficits in amyloid precursor protein knockout mice following focal traumatic brain injury

The amyloid precursor protein (APP) is thought to be neuroprotective following traumatic brain injury (TBI), although definitive evidence at moderate to severe levels of injury is lacking. In the current study, we investigated histological and functional outcomes in APP-/- mice compared with APP+/+ mice following a moderate focal injury, and whether administration of sAPPα restored the outcomes in knockout animals back to the wildtype state. Following moderate controlled cortical impact injury, APP-/- mice demonstrated greater impairment in motor and cognitive outcome as determined by the ledged beam and Barnes Maze tests respectively (p < 0.05). This corresponded with the degree of neuronal damage, with APP-/- mice having significantly greater lesion volume (25.0 ± 1.6 vs. 20.3 ± 1.6%, p < 0.01) and hippocampal damage, with less remaining CA neurons (839 ± 245 vs. 1353 ± 142 and 1401 ± 263). This was also associated with an impaired neuroreparative response, with decreased GAP-43 immunoreactivity within the cortex around the lesion edge compared with APP+/+ mice. The deficits observed in the APP-/- mice related to a lack of sAPPα, as treatment with exogenously added sAPPα post-injury improved APP-/- mice histological and functional outcome to the point that they were no longer significantly different to APP+/+ mice (p < 0.05). This study shows that endogenous APP is potentially protective at moderate levels of TBI, and that this neuroprotective activity is related to the presence of sAPPα. Importantly, it indicates that the mechanism of action of exogenously added sAPPα is independent of the presence of endogenous APP.

Reflections of experience-expectant development in repair of the adult damaged brain

Behavioral experience has long been known to influence functional outcome after brain injury, but only recently has its pervasive role in the reorganization of the adult brain after damage become appreciated. We briefly review findings from animal models on the role of experience in shaping neuronal events after stroke-like injury. Experience-dependent neural plasticity can be enhanced or impaired by brain damage, depending upon injury parameters and timing. The neuronal growth response to some experiences is heightened due to interactions with denervation-induced plasticity. This includes compensatory behavioral strategies developed in response to functional impairments. Early behavioral experiences can constrain later experience-dependent plasticity, leading to suboptimal functional outcome. Time dependencies and facets of neural growth patterns are reminiscent of experience-expectant processes that shape brain development. As with sensitive periods in brain development, this process may establish behavioral patterns early after brain injury which are relatively resistant to later change.

Alterations of brain-derived neurotrophic factor serum levels in patients with alcohol dependence

BACKGROUND

Alcohol dependence is a chronic relapsing disorder characterized by repetitive alcohol drinking patterns and a loss of control over alcohol consumption. Recent studies have hypothesized that dysregulations in brain neurotrophic support regulated by neurotrophins may be involved in the vulnerability to dependence and in the brain damage caused by chronic alcohol consumption. The neurotrophin brain-derived neurotrophic factor (BDNF) plays a pivotal role in neurodevelopment and in the maintenance of adult brain homeostasis through the regulation of neurogenesis and neuronal plasticity. The role of BDNF and its signaling in the mechanisms of alcohol dependence has been well documented in studies of animal models, but a few studies have been conducted in human peripheral tissues. On the basis of this rationale, we compared BDNF levels in both serum and plasma in alcohol-dependent patients and healthy volunteers.

METHODS

Thirty-seven patients with a principal diagnosis of alcohol dependence were recruited. In parallel, a control group of 37 unrelated volunteers matched for gender and age was enrolled. Serum and plasma BDNF levels were measured by ELISA.

RESULTS

A significant reduction in BDNF serum levels was observed in the patient group compared to healthy subjects (p = 0.028). On the contrary, no difference in BDNF plasma levels was evident between patients and controls.

CONCLUSIONS

In conclusion, our data show an alteration of BDNF peripheral content in patients with alcohol dependence, suggesting the involvement of this neurotrophin in this psychopathology.

Music and Speech Listening Enhance the Recovery of Early Sensory Processing after Stroke

Our surrounding auditory environment has a dramatic influence on the development of basic auditory and cognitive skills, but little is known about how it influences the recovery of these skills after neural damage. Here, we studied the long-term effects of daily music and speech listening on auditory sensory memory after middle cerebral artery (MCA) stroke. In the acute recovery phase, 60 patients who had middle cerebral artery stroke were randomly assigned to a music listening group, an audio book listening group, or a control group. Auditory sensory memory, as indexed by the magnetic MMN (MMNm) response to changes in sound frequency and duration, was measured 1 week (baseline), 3 months, and 6 months after the stroke with whole-head magnetoencephalography recordings. Fifty-four patients completed the study. Results showed that the amplitude of the frequency MMNm increased significantly more in both music and audio book groups than in the control group during the 6-month poststroke period. In contrast, the duration MMNm amplitude increased more in the audio book group than in the other groups. Moreover, changes in the frequency MMNm amplitude correlated significantly with the behavioral improvement of verbal memory and focused attention induced by music listening. These findings demonstrate that merely listening to music and speech after neural damage can induce long-term plastic changes in early sensory processing, which, in turn, may facilitate the recovery of higher cognitive functions. The neural mechanisms potentially underlying this effect are discussed.

Niacin treatment of stroke increases synaptic plasticity and axon growth in rats

BACKGROUND AND PURPOSE

Niacin is the most effective medication in current clinical use for increasing high-density lipoprotein cholesterol. We tested the hypothesis that niacin treatment of stroke promotes synaptic plasticity and axon growth in the ischemic brain.

METHODS

Male Wistar rats were subjected to 2 hours of middle cerebral artery occlusion and treated with or without Niaspan (a prolonged-release formulation of niacin, 40 mg/kg) daily for 14 days starting 24 hours after middle cerebral artery occlusion. The expression of synaptophysin, Nogo receptor, Bielschowsky silver, brain-derived neurotrophic factor, and its receptor tropomyosin-related kinase B were measured by immunohistostaining and Western blot, respectively, in the ischemic brain. Complementing in vivo studies, primary cultured neurons were used to test the effect of niacin and high-density lipoprotein on neurite outgrowth and brain-derived neurotrophic factor/tropomyosin-related kinase B expression.

RESULTS

Niaspan treatment of stroke significantly increased synaptophysin, Bielschowsky silver, brain-derived neurotrophic factor/tropomyosin-related kinase B expression, and decreased Nogo receptor expression in the ischemic brain compared with middle cerebral artery occlusion control animals (P<0.05, n=8/group). Niacin and high-density lipoprotein treatment significantly increased neurite outgrowth and brain-derived neurotrophic factor/tropomyosin-related kinase B expression in primary cultured neurons. Tropomyosin-related kinase B inhibitor attenuated niacin-induced neurite outgrowth (P<0.05, n=6/group).

CONCLUSIONS

Niacin treatment of stroke promotes synaptic plasticity and axon growth, which is mediated, at least partially, by the brain-derived neurotrophic factor/tropomyosin-related kinase B pathways.

Semaphorin 6A improves functional recovery in conjunction with motor training after cerebral ischemia

We have previously identified Semaphorin 6a (Sema6A) as an upregulated gene product in a gene expression screen in cortical ischemia [1]. Semaphorin 6a was regulated during the recovery phase following ischemia in the cortex. Semaphorin 6a is a member of the superfamily of semaphorins involved in axon guidance and other functions. We hypothesized that the upregulation indicates a crucial role of this molecule in post-stroke rewiring of the brain. Here we have tested this hypothesis by overexpressing semaphorin 6a in the cortex by microinjection of a modified AAV2-virus. A circumscribed cortical infarct was induced, and the recovery of rats monitored for up to 4 weeks using a well-established test battery (accelerated rotarod training paradigm, cylinder test, adhesive tape removal). We observed a significant improvement in post-ischemic recovery of animals injected with the semaphorin 6a virus versus animals treated with a control virus. We conclude that semaphorin 6a overexpressed in the cortex enhances recovery after cerebral ischemia. Semaphorin 6a may represent a novel therapeutic candidate for the treatment of chronic stroke.

Synaptotagmins in neurodegeneration

Synaptotagmins (Syts) are transmembrane proteins involved in the regulation of membrane trafficking. Here, we summarize literature data that provide growing evidence that several Syts are involved in the pathophysiological mechanisms of temporal lobe epilepsy and Parkinson's disease, as well as few reports related to brain ischemia and Alzheimer's disease (AD). We also report new data from our laboratories, showing changes of the expression of several Syts in Tg2576 mouse model of AD that may be related to neuroinflammation surrounding the beta-amyloid plaques. Furthermore, we demonstrate N-methyl-D-aspartate receptor-mediated upregulation of Syt 4 mRNA in a model of excitotoxic striatal lesion induced by unilateral striatal injection of quinolinic acid, associating the upregulation of Syt 4 with mechanisms of excitotoxicity. We propose that pharmacological manipulation of Syt expression in animal models of neurodegeneration should be further explored, as it may help to clarify the role of individual Syt isoforms in the regulation of membrane trafficking in neurodegeneration.

Emotion perception deficits following traumatic brain injury: a review of the evidence and rationale for intervention

While the cognitive disturbances that frequently follow severe traumatic brain injury (TBI) are relatively well understood, the ways in which these affect the psychosocial functioning of people with TBI are yet to be determined and have thus received little attention in treatment research. Growing evidence indicates that a significant proportion of individuals with TBI demonstrate an inability to recognize affective information from the face, voice, bodily movement, and posture. Because accurate interpretation of emotion in others is critical for the successful negotiation of social interactions, effective treatments are necessary. Until recently, however, there have been no rehabilitation efforts in this area. The present review examines the literature on emotion perception deficits in TBI and presents a theoretical rationale for targeted intervention. Several lines of research relevant to the remediation of emotion perception in people with TBI are considered. These include work on emotion perception remediation with other cognitively impaired populations, current neuropsychological models of emotion perception and underlying neural systems, and recent conceptualizations of remediation processes. The article concludes with a discussion of the importance of carrying out efforts to improve emotion perception within a contextualized framework in which the day-to-day relevance of training is clear to all recipients.

Rehabilitative therapies differentially alter proliferation and survival of glial cell populations in the perilesional zone of cortical infarcts

Rehabilitative therapies after stroke are designed to improve remodeling of neuronal circuits and to promote functional recovery. Only very little is known about the underlying cellular mechanisms. In particular, the effects of rehabilitative training on glial cells, which play an important role in the pathophysiology of cerebral ischemia, are only poorly understood. Here, we examined the effects of rehabilitative therapies on proliferation and survival of distinct glial populations in the perilesional area of photochemically induced focal ischemic infarcts in the forelimb sensorimotor cortex in rats. Immediately after the infarct, one group of animals housed in standard cages received daily sessions of skilled reaching training of the impaired forelimb; a second group was transferred to an enriched environment, whereas a third control group remained in standard cages without further treatment. Functional recovery was assessed in a sensorimotor walking task. To label proliferating cells, bromodeoxyuridine (BrdU) was administered from day 2 until day 6 postinfarct. Proliferation and survival of astrocytes, microglia/macrophages, and immature and mature oligodendrocytes in the perilesional zone were immunocytochemically quantified at day 10 and 42. Using this approach, we demonstrate that enriched environment and reaching training both significantly improve functional recovery of the impaired forelimb. Furthermore, these therapies strongly reduce the proliferation of microglia/macrophages in the perilesional zone, and daily training of the impaired forelimb significantly increased the survival of newly generated astrocytes. Our data, therefore, demonstrate that rehabilitative therapies after cortical infarcts not only improve the functional recovery but also significantly influence the glial response in the perilesional zone.

Longitudinal in vivo MRI of alterations in perilesional tissue after transient ischemic stroke in rats

Spontaneous restoration of function after stroke is associated with remodelling of functional neuronal networks in and around the ischemic lesion. However, the spatiotemporal profile of structural alterations in (peri)lesional tissue in relation to post-stroke recovery of neuronal function remains largely to be elucidated. We performed neurological testing in combination with in vivo serial T(2)-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to assess functional recovery in relation to longitudinal changes in tissue integrity from 3 h up to 9 weeks after experimental unilateral stroke in rats (n=7). Subsequently, to evaluate perilesional neuronal connectivity, we conducted manganese-enhanced MRI after MnCl(2) injection in cortical tissue at the boundary of the lesion at 10 weeks post-stroke (n=5). All animals showed significant improvement of neurological function over time. Normalization of tissue T(2) and fractional diffusion anisotropy (FA) after significant subacute change was observed in cortical and subcortical lesion borderzones between 3 and 9 weeks post-stroke. Progressive FA increase above baseline levels was detected in perilesional white matter areas (n=4). In these animals particularly, significant manganese enhancement appeared within the neuronal network around the chronic lesion, including areas that were part of the lesion at day 3 post-stroke. This longitudinal multi-parametric MRI study suggests that resolution of early ischemic damage and reorganization of white matter in perilesional tissue is chronically accompanied by preservation or restoration of neuronal connectivity, which may significantly contribute to post-stroke functional recovery.

Manganese-enhanced MRI of brain plasticity in relation to functional recovery after experimental stroke

Restoration of function after stroke may be associated with structural remodeling of neuronal connections outside the infarcted area. However, the spatiotemporal profile of poststroke alterations in neuroanatomical connectivity in relation to functional recovery is still largely unknown. We performed in vivo magnetic resonance imaging (MRI)-based neuronal tract tracing with manganese in combination with immunohistochemical detection of the neuronal tracer wheat-germ agglutinin horseradish peroxidase (WGA-HRP), to assess changes in intra- and interhemispheric sensorimotor network connections from 2 to 10 weeks after unilateral stroke in rats. In addition, functional recovery was measured by repetitive behavioral testing. Four days after tracer injection in perilesional sensorimotor cortex, manganese enhancement and WGA-HRP staining were decreased in subcortical areas of the ipsilateral sensorimotor network at 2 weeks after stroke, which was restored at later time points. At 4 to 10 weeks after stroke, we detected significantly increased manganese enhancement in the contralateral hemisphere. Behaviorally, sensorimotor functions were initially disturbed but subsequently recovered and plateaued 17 days after stroke. This study shows that manganese-enhanced MRI can provide unique in vivo information on the spatiotemporal pattern of neuroanatomical plasticity after stroke. Our data suggest that the plateau stage of functional recovery is associated with restoration of ipsilateral sensorimotor pathways and enhanced interhemispheric connectivity.

Abnormal corticomotor excitability assessed in biceps brachii preceding pronator contraction post-stroke

OBJECTIVE

To assess corticomotor (CM) excitability of the antagonist biceps brachii (BB) post-stroke in preparation for pronator contraction. In healthy subjects, we previously demonstrated that prior to pronator contraction CM excitability of the antagonist BB was suppressed.

METHODS

Transcranial magnetic stimulation (TMS) was used to assess pre-contraction changes in motor evoked potential (MEP) amplitude of the BB, when BB was acting either as an antagonist or an agonist. TMS was applied 100-200ms prior to rhythmic isometric BB or pronator contractions in chronic stroke survivors and age/gender matched healthy control subjects.

RESULTS

Prior to pronator contraction, MEPs in BB were elicited in the stroke group but were absent in healthy controls indicating that CM excitability of the antagonist BB was increased post-stroke. The extent of the abnormal increase in excitability positively correlated with the extent of upper limb motor impairment.

CONCLUSIONS

Our results suggest that an alteration of cortical control mechanisms regulating motor excitability of the antagonist BB may contribute to the impairment of upper limb motor coordination post-stroke.

SIGNIFICANCE

This study offers a unique approach to study the potential for a cortical origin of post-stroke motor discoordination.

Sensorimotor deficits associated with brain tumor progression and tumor-induced brain plasticity mechanisms

The objective of this study was to investigate functional deficits and reactive peri-tumoral brain plasticity events in glioma-bearing rats. 9L gliosarcoma cells were implanted into the forelimb region of the sensorimotor cortex in Fischer rats. Control animals underwent the same operation without tumor implantation. Sensitive tests for detecting sensorimotor dysfunction, including forelimb-use asymmetry, somatosensory asymmetry, and vibrissae-evoked forelimb placing tests, were conducted. We found that tumor-bearing animals exhibited significant composite behavioral deficits on day 14 post-tumor injection compared to surgical controls. With the assistance of magnetic resonance imaging, we demonstrated a significant correlation between tumor volume and magnitude of somatosensory asymmetry, indicating that the somatosensory asymmetry test can provide an effective and efficient means to measure and predict tumor progression. Histopathological assessments were performed after the rats were sacrificed 14 days following tumor implantation. Immunostaining revealed that densities of microtubule-associated protein 2, glial fibrillary acid protein, von Willebrand factor, and synaptophysin were all significantly upregulated in the peri-tumoral area, compared to the corresponding region in surgical controls, suggesting synaptic plasticity, astrocyte activation and angiogenesis in response to tumor insult. Understanding the behavioral and bystander cellular events associated with tumor progression may lead to improved evaluation and development of new brain tumor treatments that promote, or at least do not interfere with, functional adaptation.

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.

Cognitive neural plasticity during learning and recovery from brain damage

The process of neuroplasticity is the ability of the brain to change, either in response to experience or injury. It is a vital process both during normal development and for the recovery after brain injury. Recent research has emphasized that this takes place via both local restitution as well as reorganization and compensatory reassignment. The fact that the brain can undergo such plastic changes has provided evidence for what underlies developmental brain disorders, as well as the variable response to injury at different points in the lifespan. The factors affecting plasticity and its long-term consequences may have increasing importance in exposing the pattern of changes that occur in the normal brain with aging.

Possible role of nerve growth factor in the pathogenesis of alcohol dependence

BACKGROUND

Recent studies have raised the possibility that nerve growth factor (NGF) is abnormally regulated in the central nervous system (CNS) of animal models of chronic ethanol treatment. The goals of this study were to determine whether prolonged alcohol consumption is associated with the plasma NGF levels and to assess the effect of a positive family history of alcohol dependence on plasma NGF levels in the alcohol-dependent patients.

METHODS

We used the enzyme-linked immunosorbent assay (ELISA) to determine the concentrations of peripheral NGF in patients with alcohol dependence and in a control group.

RESULTS

The plasma NGF concentrations in the alcohol-dependent patients were significantly lower than in the controls (71.9 vs 110.5 pg/mL, respectively). Moreover, the alcohol-dependent patients with positive family histories showed a greater decrease in their NGF levels than those subjects with negative family histories (64.7 vs 83.3 pg/mL, respectively).

CONCLUSIONS

Our study suggests that the NGF levels may be a trait marker for the development of alcohol dependence.

Mass-related traumatic tissue displacement and behavior: a screen for treatments that reduce [corrected] harm to bystander cells and recovery of function

In this study, we focused on a preclinical model of brain compression injury that has relevance to pathological conditions such as tumor, hematoma, blood clot, and intracerebral bony fragment. We investigated behavioral impairment as a result of rapid-onset small mass, and the factors involved in lesion formation and neuroplasticity. An epidural bead implantation method was adopted. Two sizes (1.5 mm and 2.0 mm thick) of hemisphere-shaped beads were used. The beads were implanted into various locations over the sensorimotor cortex (SMC--anterior, middle and posterior). The effects of early versus delayed bead removal were examined to model clinical neurosurgical or other treatment procedures. Forelimb and hind-limb behavioral deficits and recovery were observed, and histological changes were quantified to determine brain reaction to focal compression. Our results showed that the behavioral deficits of compression were influenced by the location, timing of compression release, and magnitude of compression. Even persistent compression by the thicker bead (2.0 mm) caused only minor behavioral deficits, followed by fast recovery within a week in most animals, suggesting a mild lesion pattern for this model. Brain tissue was compressed into a deformed shape under pressure with slight tissue damage, evidenced by pathological evaluation on hematoxylin and eosin (H&E)- and TUNEL-stained sections. Detectable but not severe behavioral dysfunction exhibited by this model makes it particularly suitable for direct assessment of adverse effects of interventions on neuroplasticity after brain compression injury. This model may permit development of treatment strategies to alleviate brain mass effects, without disrupting neuroplasticity.

Post-Traumatic Neural Depression and Neurobehavioral Recovery after Brain Injury

There are an estimated 2 million traumatic brain injuries (TBIs) each year in the United States, making the yearly incidence eight times greater than that of breast cancer and 34 times greater than HIV/AIDS. Still, it remains a "silent epidemic" because TBI results in persistent neurobehavioral impairment, without necessarily imparting a physical scar. The present review is a comparative analysis of TBI research, both basic and applied, outlining the evidence that at least one component of the brain's innate response to insult (e.g., post-traumatic neural depression) is sufficiently well understood to be the target of additional clinical studies and therapeutic strategy development.

Relationship of calpain-mediated proteolysis to the expression of axonal and synaptic plasticity markers following traumatic brain injury in mice

The role of neuronal plasticity and repair on the final functional outcome following traumatic brain injury (TBI) remains poorly understood. Moreover, the relationship of the magnitude of post-traumatic secondary injury and neurodegeneration to the potential for neuronal repair has not been explored. To address these questions, we employed Western immunoblotting techniques to examine how injury severity affects the spatial and temporal expression of markers of axonal growth (growth-associated protein GAP-43) and synaptogenesis (pre-synaptic vesicular protein synaptophysin) following either moderate (0.5 mm, 3.5 M/s) or severe (1.0 mm, 3.5 M/s) lateral controlled cortical impact traumatic brain injury (CCI-TBI) in young adult male CF-1 mice. Moderate CCI increased GAP-43 levels at 24 and 48 h post-insult in the ipsilateral hippocampus relative to sham, non-injured animals. This increase in axonal plasticity occurred prior to maximal hippocampal neurodegeneration, as revealed by de Olmos silver staining, at 72 h. However, moderate CCI-TBI did not elevate GAP-43 expression in the ipsilateral cortex where neurodegeneration was extensive by 6 h post-TBI. In contrast to moderate injury, severe CCI-TBI failed to increase hippocampal GAP-43 levels and instead resulted in depressed GAP-43 expression in the ipsilateral hippocampus and cortex at 48 h post-insult. In regards to injury-induced changes in synaptogenesis, we found that moderate CCI-TBI elevated synaptophysin levels in the ipsilateral hippocampus at 24, 48, 72 h and 21 days, but this effect was not present after severe injury. Together, these data highlights the adult brain's ability for axonal and synaptic plasticity following a focal cortical injury, but that severe injuries may diminish these endogenous repair mechanisms. The differential effects of moderate versus severe TBI on the post-traumatic plasticity response may be related to the calpain-mediated proteolytic activity occurring after a severe injury preventing increased expression of proteins required for plasticity. Supporting this hypothesis is the fact that GAP-43 is a substrate for calpain along with our data demonstrating that calpain-mediated degradation of the cytoskeletal protein, alpha-spectrin, is approximately 10 times greater in ipsilateral hippocampal tissue following severe compared to moderate CCI-TBI. Thus, TBI severity has a differential effect on the injury-induced neurorestorative response with calpain activation being one putative factor contributing to neuroregenerative failure following severe CCI-TBI. If true, then calpain inhibition may lead to both neuroprotective effects and an enhancement of neuronal plasticity/repair mechanisms post-TBI.

Local fluorouracil chemotherapy interferes with neural and behavioral recovery after brain tumor-like mass compression

In this study, we investigated the impact of intracerebral delivery of chemotherapy on functional recovery from focal cortical tissue displacement, characteristic of brain tumors. Unilateral focal brain compression was induced by epidural implantation of an inverted hemisphere-shaped bead over the sensorimotor cortex. Microinjections of a total of 1mg chemoagent fluorouracil or the same volume of saline were made into the compressed cortex. Behavioral tests of forelimb sensorimotor function were conducted during 4 weeks' observation. Rats subjected to any of the three types of lesions, saline microinjection plus cortical compression, chemoagent microinjection alone, or chemoagent microinjection combined with cortical compression, demonstrated significant behavioral deficits in several sensorimotor tasks, compared with saline-microinjected control animals. In placing tests, behavioral deficits elicited by each single treatment were worsened by combined treatment with chemoagent microinjection and focal cortical compression. Concurrently, local delivery of chemoagent into the compressed cortex induced increased cortical tissue loss, necrosis and apoptosis. These data indicate that local chemotherapy exacerbates compression-induced neurological impairment, and a model of controlled focal cortical compression may provide a valuable means to improve anti-cancer therapeutic designs with reduced deterioration of brain function.

Astrocytic changes in the hippocampus and functional recovery after cerebral ischemia are facilitated by rehabilitation training

In this study we examined whether astrocytic and basic fibroblast growth factor changes after cerebral ischemia can be influenced by rehabilitation training and if these changes are associated with functional improvement. After receiving either ischemia or sham surgery, male adult Wistar rats were assigned to one of two rehabilitation training group: complex environment housing (EC) or paired housing as controls (CON). Rats were tested in the water maze after 14 days of rehabilitation training. Results showed increased expression of reactive astrocytes (GFAP) in all ischemic animals and in the sham EC rats with a significant overall increased seen in the ischemia EC housed animals. The pattern of basic fibroblast growth factor (FGF-2) expression seen was somewhat similar to that of GFAP. Behavioral data showed that even though all animals learned to perform the water maze task over time, the ischemia CON rats took longer to learn the task while all the ischemia EC animals performed as well as the sham groups. Regression analysis showed that increased GFAP was able to explain some of the variances in the behavioral parameters in the water maze of the ischemia EC rats suggesting that the activation of astrocytes in this group probably mediated enhanced functional recovery. Lastly, it is possible that the favorable effect of astrocyte activation after cerebral ischemia was mediated by FGF-2.

Long-term gene expression changes in the cortex following cortical ischemia revealed by transcriptional profiling

Cerebral ischemia evokes changes in gene expression time-dependently after the ischemic event. Most studies on transcriptional changes following ischemia have centered on relatively early postischemic time points, and detected multiple genes relevant to neuronal cell death. However, functional outcome after ischemia depends critically on adaptations of the postischemic brain. Plasticity may derive from network-inherent changes, or from the formation of new nerve cells in the CNS. We have screened for gene expression changes up to 3 weeks following a limited photothrombotic cortical insult in the rat sensorimotor cortex by using the sensitive restriction-mediated differential display (RMDD) technique. A high number of genes were detected as induced at early or intermediate time points in the ipsi- and contralateral cortex (6 and 48 h). Unexpectedly, at the late time point examined (3 weeks), we still detected 40 genes that were changed in their expression. We further characterized the expression of two genes linked to neurogenesis (nestin and stathmin), and two genes likely involved in reconfiguring neuronal networks (semaphorin VIa and synaptotagmin IV). Conclusively, our data highlight the degree of long-term transcriptional changes in the cortex after ischemia, and provide insight into functional pathways of relevance for compensatory recovery mechanisms in neural networks.

Plastic reorganization of hippocampal and neocortical circuitry in experimental traumatic brain injury in the immature rat

The reorganization of circuitry in the immature forebrain resulting from controlled cortical impact was examined with viral transneuronal tracing. Animals injured on postnatal day (PND) 17 and sham controls from the same litters received an intracerebral injection of a recombinant strain of pseudorabies virus (PRV) into the entorhinal cortex on PND 45. Fifty hours following injection of virus the animals were perfused and infected neurons were localized immunohistochemically with antisera specific for PRV. Prior studies have demonstrated that the PRV recombinant used in this analysis moves exclusively in the retrograde direction through synaptically linked neurons. CCI induced a necrotic loss of cortex at the site of impact and variable damage to the underlying corpus callosum and rostral (dorsal) hippocampus that was not present in sham controls. Analysis of viral transport in sham controls revealed retrograde transport of virus through hippocampal and neocortical circuitry in a pattern consistent with established patterns of connectivity and topography. Injured animals exhibited preservation of topographically organized connections in both the hippocampus and neocortex. However, the magnitude of labeling in the injured hemisphere was significantly increased relative to control animals and correlated with the magnitude of the injury. The distribution of infected neurons in the contralateral uninjured hemisphere also conformed to known connections. However differences in the involvement of the corpus callosum in the injury resulted in greater variability in the number of infected neurons among cases. These data provide novel insights into trauma induced reorganization of the developing brain and add to the experimental tools that can be used to assess the basis for functional recovery in animal models of developmental traumatic brain injury.

Neural mechanisms of prefrontal cortical function: implications for cognitive rehabilitation

Understanding the role of the frontal lobes in cognition remains a challenge for neurologists and neuroscientists. It is proposed that goal-directed behavior, at the core of what we consider human, depends critically on the function of the frontal lobes, and, specifically, the prefrontal cortex (PFC). In this chapter, we put forth the hypothesis that further insight into the neural mechanisms underlying normal PFC function may ultimately help us understand the frontal-lobe syndrome, and importantly, potentially lead to effective therapeutic interventions for frontal-lobe dysfunction. Thus, the aim of this chapter is to review current hypotheses and knowledge about the neural mechanisms underlying the normal function of the PFC in cognition that could guide the development of therapeutic interventions.

Activation of neural stem and progenitor cells after brain injury

Neural stem and progenitor cells in the mammalian brain persist and are functional well into adulthood. Reservoirs for these cells are found in both the subventricular zone and the dentate gyrus of the hippocampus. It is still unclear what role these cells may play in humans during normal brain maturation. In addition, there is currently tremendous speculation regarding the potential role of these cells in providing a substrate for recovery and repair after injury. This review provides an overview of the existing data regarding how neural stem and progenitor cells respond to various types of brain injury. In particular, we focus upon their role in the dentate gyrus since this brain area provides a compelling and tractable model of how the brain may use its ability for endogenous regeneration to recover from a variety of injuries.

PolyADP-ribosylation is involved in neurotrophic activity

PolyADP-ribosylation is a transient posttranslational modification of proteins, mainly catalyzed by poly(ADP-ribose)polymerase-1 (PARP-1). This highly conserved nuclear protein is activated rapidly in response to DNA nick formation and promotes a fast DNA repair. Here, we examine a possible association between polyADP-ribosylation and the activity of neurotrophins and neuroprotective peptides taking part in life-or-death decisions in mammalian neurons. The presented results indicate an alternative mode of PARP-1 activation in the absence of DNA damage by neurotrophin-induced signaling mechanisms. PARP-1 was activated in rat cerebral cortical neurons briefly exposed to NGF-related nerve growth factors and to the neuroprotective peptides NAP (the peptide NAPVSIPQ, derived from the activity-dependent neuroprotective protein ADNP) and ADNF-9 (the peptide SALLRSIPA, derived from the activity-dependent neurotrophic factor ADNF) In addition, polyADP-ribosylation was involved in the neurotrophic activity of NGF-induced and NAP-induced neurite outgrowth in differentiating pheochromocytoma 12 cells as well as in the neuroprotective activity of NAP in neurons treated with the Alzheimer's disease neurotoxin beta-amyloid. A fast loosening of the highly condensed chromatin structure by polyADP-ribosylation of histone H1, which renders DNA accessible to transcription and repair, may underlie the role of polyADP-ribosylation in neurotrophic activity.

Ischemic preconditioning procedure induces behavioral deficits in the absence of brain injury?

Preconditioning describes a phenomenon whereby a sub-injury inducing insult can protect against a later larger injury. Thus, short-term cerebral ischemia can protect against a prolonged ischemia (ischemic preconditioning). This study examines rats undergoing ischemic preconditioning to test whether preconditioning may cause changes in behavior even though they do not cause an identifiable brain lesion. Rats had a transient (15 minutes) middle cerebral artery occlusion or a sham occlusion. Forelimb placing and forelimb use asymmetry tests were used to assess behavioral deficits. Brain histology, microglia activation, heat shock protein and ferritin levels were also examined. Ischemic preconditioning did not cause brain infarction, but induced behavioral changes. There were no significant differences between ischemic preconditioning and sham rats in the two behavioral tests at day one. However, the ischemic preconditioning group showed impaired forelimb placing at days 3, 7 and 14 (p<0.05). That group also had a significant (p<0.05) behavioral deficit in the forelimb use asymmetry test at days 3 and 7 (but not 14). Our present study demonstrated that a behavioral deficit occurred in ischemic preconditioning. This raises the question of whether induction of protective mechanisms by preconditioning stimuli necessarily involves some form of brain injury, detectable by changes in behavior though not by a lesion. This would be consistent with data suggesting that brain injury can initiate mechanisms potentially favorable to neuroplasticity and neuroprotection.

A probabilistic framework for region-specific remodeling of dendrites in three-dimensional neuronal reconstructions

Dendritic arborization is an important determinant of single-neuron function as well as the circuitry among neurons. Dendritic trees undergo remodeling during development, aging, and many pathological conditions, with many of the morphological changes being confined to certain regions of the dendritic tree. In order to analyze the functional consequences of such region-specific dendritic remodeling, it is essential to develop techniques that can systematically manipulate three-dimensional reconstructions of neurons. Hence, in this study, we develop an algorithm that uses statistics from precise morphometric analyses to systematically remodel neuronal reconstructions. We use the distribution function of the ratio of two normal distributed random variables to specify the probabilities of remodeling along various regions of the dendritic arborization. We then use these probabilities to drive an iterative algorithm for manipulating the dendritic tree in a region-specific manner. As a test, we apply this framework to a well-characterized example of dendritic remodeling: stress-induced dendritic atrophy in hippocampal CA3 pyramidal cells. We show that our pruning algorithm is capable of eliciting atrophy that matches biological data from rodent models of chronic stress.

Long-term effects of sequential cortical infarcts on scar size, brain volume and cognitive function

Focal ischemia induces long-term pathophysiological consequences in widespread brain areas. Here we analyzed long-term effects of sequential cortical lesions on brain volume and cognitive function. Rats received either single photothrombotic lesions in the forelimb sensorimotor cortex (SL) or two lesions in sequence either immediately (DL0), 2 days (DL2), 7 days (DL7), or 10 days (DL10) after the first surgery in the homotopic contralateral area. Infarct and global brain volume were measured 7 days (SL and DL2 groups) and one month (all groups) after the last period of ischemia. In the weeks following a stroke, the single lesion shrank considerably. This shrinkage was accentuated by a further lesion received either earlier or later. Thirty-one days after obtaining the second lesion, the lesion scars on both sides had a mean volume of 5.8 +/- 2.3 mm3 in DL2 as compared to 8.5 +/- 3.5 mm3 in SL-animals. In addition, there was a super-additive loss of residual brain volume by 2.2-8.0% in each hemisphere in animals with sequential lesions. In the watermaze, this loss of brain volume corresponded to a slight but significant impairment in performance. The present study revealed a complex interaction of lesions in animals with sequential strokes associated with global reduction of brain volume and cognitive impairment indicating degenerative processes beyond the lesions itself.

Repeated episodic exposure to ethanol affects neurotrophin content in the forebrain of the mature rat

Chronic exposure to ethanol can cause deficits in learning and memory. It has been suggested that withdrawal is potentially more damaging than the ethanol exposure per se. Therefore, we explored the effect of repeated episodic exposure to ethanol on key regulators of cortical activity, the neurotrophins. Rats were exposed to ethanol via a liquid diet for 3 days per week for 6-24 weeks. Control rats were pair-fed an isocaloric liquid diet or ad libitum fed chow and water. The concentrations of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were determined using enzyme-linked immunosorbant assays (ELISAs). Five telencephalic structures were examined: parietal cortex, entorhinal cortex, hippocampus, the basal nucleus, and the septal nuclei. All five areas expressed each of the three neurotrophins; BDNF was most abundant and NGF the least. The parietal cortex was susceptible to ethanol exposure, NGF and BDNF content increased, and NT-3 content fell, whereas no changes were detectable in the entorhinal cortex. In the hippocampus, the amount all three neurotrophins increased following episodic ethanol exposure. Neurotrophin content in the two segments of the basal forebrain was affected; NGF and NT-3 content in the basal forebrain was reduced and NGF and BDNF content in the septal nuclei was increased by ethanol exposure. In many cases where ethanol had an effect, the change was transient so that by 24 weeks of episodic exposure, no significant changes were evident. Thus, the effects of ethanol are site- and time-dependent. This pattern differs from changes caused by chronic ethanol exposure, hence, neurotrophins must be vulnerable to the effects of withdrawal. Furthermore, the ethanol-induced changes do not appear to fit a model consistent with retrograde regulation, rather they suggest that neurotrophins act through autocrine/paracrine systems.

Activity-regulated cytoskeleton-associated protein Arc is targeted to dendrites and coexpressed with mu-opioid receptors in postnatal rat caudate-putamen nucleus

Dendritic expression of the activity-regulated cytoskeleton-associated protein (Arc) is dramatically enhanced by increased synaptic activity in adult brain. We used immunocytochemical electron microscopy to determine whether the subcellular localization of Arc in developing dendrites corresponds to the peak period of synaptogenesis in the postnatal rat caudate-putamen nucleus (CPN). The distribution was compared with that of mu-opioid receptors (MORs), whose localization in dendritic spines closely parallels excitatory synapse formation during postnatal development (Wang et al. [2003] Neuroscience 118:695-708). Sections were processed for immunocytochemical detection of antisera against Arc or MORs at the beginning (postnatal day 15; P15) and the end (P30) of the peak period of synaptogenesis in rat CPN. At P15, immunolabeling for Arc showed a punctate distribution in the cytoplasm of dendritic shafts, some of which was associated with polyribosomes. In some spiny dendrites, Arc immunoreactivity was more intensely localized in putative spines than in their parental dendrites, whereas, in other spiny dendrites, Arc labeling was restricted in the shafts. Many dendritic shafts and spines also showed immunoreactivity for MORs, although dually labeled spines were less numerous than the shafts. At P30, the proportion of singly and dually labeled spines significantly increased from 2.0% to 7.5% and from 9.5% to 21%, respectively. Arc labeling in spines was more detectable beneath the postsynaptic density or at extrasynaptic sites on the plasma membrane. Our results suggest a correlation between Arc expression in dendritic spines during postnatal development and the onset of synaptogenesis in opioid-responsive neurons in the rat CPN.