Plasticity of primary somatosensory cortex paralleling sensorimotor skill recovery from stroke in adult monkeys

Effects of postlesion experience on behavioral recovery and neurophysiologic reorganization after cortical injury in primates

Previous studies have shown that after injury to the hand representation in primary motor cortex (M1), size of the spared hand representation decreased dramatically unless the unimpaired hand was restrained and monkeys received daily rehabilitative training using the impaired fingers. The goal of this study was to determine if restriction of the unimpaired hand was sufficient to retain spared hand area after injury or if retention of the spared area required repetitive use of the impaired limb. After infarct to the hand area of M1 in adult squirrel monkeys, the unimpaired hand was restrained by a mesh sleeve over the unimpaired arm. Monkeys did not receive rehabilitative training. Electrophysiologic maps of M1 were derived in anesthetized monkeys before infarct and 1 month after infarct by using intracortical microstimulation. One month after the lesion, the size of the hand representation had decreased. Areal changes were significantly smaller than those in animals in a previous study that had received daily repetitive training after infarct (p < 0.05). Areal changes were not different from those in a group of animals that received neither rehabilitative intervention nor hand restraint after injury. These results suggest that retention of hand area in M1 after a lesion requires repetitive use of the impaired hand.

Chemical network of the living human brain. Evidence of reorganization with aging

We recently described the chemical network properties of the human brain using in vivo proton magnetic resonance spectroscopy ((1)H MRS). In a separate study of aging we found increased concentration of chemicals in the prefrontal and sensorimotor cortices up to the third decade of life, and subsequent decrease of chemical concentrations in the same brain regions after the third decade between young and middle age. We anticipated that these age-dependent differences in chemical concentrations might be a reflection of the chemical network reorganization of the brain during aging. The pattern of chemical connectivity within and across brain regions for all regional chemicals, and specific patterns of chemical connectivity for each chemical type were examined for young and middle age groups using (1)H MRS and correlation analysis. For all studied ages, the dominant positive correlations occurred within brain regions and negative correlations were seen across brain regions. However, the pattern of negative chemical connectivity across brain regions was weaker in middle-aged group (F = 40.4, P < 10(-7) comparing r-values between the two age groups, ANOVA). Within brain regions, the age effects on chemical correlations were seen in the cingulate cortex (46% decrease in the middle-aged group, F = 7.2, P < 0.007) and sensorimotor cortex (SMC) (27% decrease, F = 8.9, P<0.003). Between brain regions, the age effects on chemical correlations were seen in the chemical interactions between the thalamus (433.3% increase in the middle-aged group, F = 11.7, P < 0.003), SMC (280% increase, F=20.1, P < 10(-5)), cingulate cortex (100.7% increase, F = 21.3, P < 10(-7)), and other brain regions. We found also age-differential patterns of chemical connectivity across the studied brain regions for most chemical types. The results provide evidence that normal aging is associated with reorganization of chemical network of the human brain.

Experience-dependent structural plasticity in cortex heterotopic to focal sensorimotor cortical damage

Structural plasticity following focal neocortical damage in adult rats has recently been found to be sensitive to postinjury rehabilitative training. Experience on a complex motor skills task, the acrobatic task, after unilateral lesions of the forelimb representation region of the sensorimotor cortex (FLsmc) enhanced synaptic structural changes in the cortex contralateral and homotopic to the lesions. Using tissue from this previous study, the present study examined whether a heterotopic region of the sensorimotor cortex of either hemisphere, the hindlimb representation area (HLsmc), would undergo structural changes following unilateral FLsmc lesions and whether these changes would also be sensitive to postinjury training on the acrobatic task. Stereological methods for light and electron microscopy were used to assess structural changes in lesion or sham-operated rats following 28 days of postoperative acrobatic training or simple repetitive exercise (motor controls). In the HLsmc contralateral to the lesions of rats receiving acrobatic training, there was a subtle, but significant, increase in cortical volume and in layer II/III neuropil and dendritic volume per neuron in comparison to shams. In rats receiving simple exercise after the lesions, these changes were not significantly different from shams. Acrobatic training also prevented a loss of cortical volume in the HLsmc adjacent to the lesion in comparison to shams. These data suggest that behavioral training following cortical injury facilitates structural plasticity in behaviorally relevant areas of the neocortex other than the homotopic cortex contralateral to the lesion. This structural plasticity might be relevant to the development of behavioral compensation after cortical injury.

Does the application of constraint-induced movement therapy during acute rehabilitation reduce arm impairment after ischemic stroke?

BACKGROUND AND PURPOSE

Motor dysfunction after unilateral deafferentation in primates can be overcome by restraining the unaffected limb. We asked whether a constraint-induced movement (CIM) program could be implemented within 2 weeks after stroke and whether CIM is more effective than traditional upper-extremity (UE) therapies during this period.

METHODS

Twenty-three persons were enrolled in a pilot randomized, controlled trial that compared CIM with traditional therapies. A blinded observer rated the primary end point, the Action Research Arm Test (ARA). Inclusion criteria were the following: ischemic stroke within 14 days, persistent hemiparesis, evidence of preserved cognitive function, and presence of a protective motor response. Differences between the groups were compared by using Student's t tests, ANCOVA, and Mann-Whitney U: tests.

RESULTS

Twenty subjects completed the 14-day treatment. Two adverse outcomes, a recurrent stroke and a death, occurred in the traditional group; 1 CIM subject met rehabilitation goals and was discharged before completing 14 inpatient days. The CIM treatment group had significantly higher scores on total ARA and pinch subscale scores (P:<0.05). Differences in the mean ARA grip, grasp, and gross movement subscale scores did not reach statistical significance. UE activities of daily living performance was not significantly different between groups, and no subject withdrew because of pain or frustration.

CONCLUSIONS

A clinical trial of CIM therapy during acute rehabilitation is feasible. CIM was associated with less arm impairment at the end of treatment. Long-term studies are needed to determine whether CIM early after stroke is superior to traditional therapies.

Cortical and subcortical contributions to activity-dependent plasticity in primate somatosensory cortex

After manipulations of the periphery that reduce or enhance input to the somatosensory cortex, affected parts of the body representation will contract or expand, often over many millimeters. Various mechanisms, including divergence of preexisting connections, expression of latent synapses, and sprouting of new synapses, have been proposed to explain such phenomena, which probably underlie altered sensory experiences associated with limb amputation and peripheral nerve injury in humans. Putative cortical mechanisms have received the greatest emphasis but there is increasing evidence for substantial reorganization in subcortical structures, including the brainstem and thalamus, that may be of sufficient extent to account for or play a large part in representational plasticity in somatosensory cortex. Recent studies show that divergence of ascending connections is considerable and sufficient to ensure that small alterations in map topography at brainstem and thalamic levels will be amplified in the projection to the cortex. In the long term, slow, deafferentation-dependent transneuronal atrophy at brainstem, thalamic, and even cortical levels are operational in promoting reorganizational changes, and the extent to which surviving connections can maintain a map is a key to understanding differences between central and peripheral deafferentation.

Reorganization of adult rat barrel cortex intrinsic signals following kainic acid induced central lesion

A plasticity model studying the adult rat barrel cortex intrinsic signal after a central lesion was developed. Repeated optical imaging studies of the barrel cortex of five rats were performed over variable periods of time (2 days to 6 weeks) after intracortical injection of kainic acid. The signal of the elicited principal whisker corresponding to the injected barrel in the repeat studies relocated to the perimeter of the lesion. The area of the signals of this principal whisker and of surrounding whiskers were larger in the first two weeks studies than those obtained before injection (P<0.01) resulting in increase overlapping of adjacent signals (P=0.01). Even though the signal of the PW remains relocated in the later studies (>2 weeks), all the signals returned to normal size. These findings demonstrate recovery and reorganization of sensory representation in the somatosensory cortex following a central lesion.

Environmental influence on brain-derived neurotrophic factor messenger RNA expression after middle cerebral artery occlusion in spontaneously hypertensive rats

Enriched environment significantly enhances postischemic functional outcome. We have tested the hypothesis that housing in enriched environment stimulates gene expression for brain-derived neurotrophic factor. After ligation of the middle cerebral artery in male spontaneously hypertensive rats, they were housed in individual cages for 30h, then housed either in standard cages or in an enriched environment. The rats were killed two to 30days after the ischemic event. Cryostat coronal sections through the dorsal hippocampus (Bregma -3.3) were processed for in situ hybridization using a rat-brain-derived neurotrophic factor messenger RNA antisense oligonucleotide probe. Postischemic gene expression was significantly higher in standard rats than in enriched rats in contralateral and peri-infarct cortex and in most parts of the hippocampus two, three and 12days after the ischemic event, with a trend for higher-than-baseline levels in standard rats and lower-than-baseline levels in enriched rats. At 20 and 30days the values for both groups were below baseline levels. Contrary to our hypothesis, gene expression in rats postoperatively housed in enriched environment was significantly lower than in standard rats at a time when other studies have reported hyperexcitability in the ipsilateral and contralateral cortex. Should the low messenger RNA levels correspond to low protein synthesis, this might indicate that dampening of the early postischemic hyperexcitability may be beneficial. Low levels in both groups at 20 and 30days may correspond to loss of callosal connections in the opposite hemisphere and to horizontal cortical connections in the lesioned hemisphere.

Recovery recapitulates ontogeny

Several studies support the hypothesis that after stroke, specific features of brain function revert to those seen at an early stage of development, with the subsequent process of recovery recapitulating ontogeny in many ways. Many clinical characteristics of stroke recovery resemble normal development, particularly in the motor system. Consistent with this, brain-mapping studies after an ischemic insult suggest re-emergence of childhood organizational patterns: recovery being associated with a return to adult patterns. Experimental animal studies demonstrate increased levels of developmental proteins, particularly in the area surrounding an infarct, suggesting an active process of reconditioning in response to cerebral ischemia. Understanding the patterns of similarity between normal development and stroke recovery might be of value in its treatment.

Chronic motor dysfunction after stroke: recovering wrist and finger extension by electromyography-triggered neuromuscular stimulation

BACKGROUND AND PURPOSE

After stroke, many individuals have chronic unilateral motor dysfunction in the upper extremity that severely limits their functional movement control. The purpose of this study was to determine the effect of electromyography-triggered neuromuscular electrical stimulation on the wrist and finger extension muscles in individuals who had a stroke > or = 1 year earlier.

METHODS

Eleven individuals volunteered to participate and were randomly assigned to either the electromyography-triggered neuromuscular stimulation experimental group (7 subjects) or the control group (4 subjects). After completing a pretest involving 5 motor capability tests, the poststroke subjects completed 12 treatment sessions (30 minutes each) according to group assignments. Once the control subjects completed 12 sessions attempting wrist and finger extension without any external assistance and were posttested, they were then given 12 sessions of the rehabilitation treatment.

RESULTS

The Box and Block test and the force-generation task (sustained muscular contraction) revealed significant findings (P<0. 05). The experimental group moved significantly more blocks and displayed a higher isometric force impulse after the rehabilitation treatment.

CONCLUSIONS

Two lines of evidence clearly support the use of the electromyography-triggered neuromuscular electrical stimulation treatment to rehabilitate wrist and finger extension movements of hemiparetic individuals > or =1 year after stroke. The treatment program decreased motor dysfunction and improved the motor capabilities in this group of poststroke individuals.

Early exclusive use of the affected forelimb after moderate transient focal ischemia in rats : functional and anatomic outcome

BACKGROUND AND PURPOSE

Previous work by researchers in our laboratory has shown that in the rat, the exclusive use of the affected forelimb during an early critical period exaggerates lesion volume and retards functional recovery after electrolytic lesions of the forelimb sensorimotor cortex. In the present study, we examined the effects of exclusive use of the affected forelimb after middle cerebral artery occlusion (MCAO).

METHODS

Ischemia of moderate severity was produced in male Long-Evans rats through 45 minutes of occlusion of the left middle cerebral and both common carotid arteries. Exclusive use of either the affected or unaffected forelimb was forced through immobilization of either the ipsilateral (MCAO+ipsi) or contralateral (MCAO+contra) forelimb, respectively, for 10 days in a plaster cast, or the animal was left uncasted (MCAO+nocast). Sham surgeries were performed, and animals were also casted for 10 days or left uncasted. Sensorimotor testing was performed during days 17 to 38. At the end of sensorimotor testing, cognitive performance was tested with use of the Morris water maze. In a separate experiment, temperatures and corticosterone levels were measured during the 10-day period after 45-minute ischemia and casting.

RESULTS

The MCAO+ipsi group performed worse on sensorimotor tasks than the MCAO+contra, MCAO+nocast, and sham groups. Infarct volume was significantly larger in the MCAO+ipsi group than in the sham and MCAO+contra groups but not in the MCAO+nocast group. No group differences were found with the Morris water maze, and no group differences were found in either temperature or plasma corticosterone level.

CONCLUSIONS

The exclusive use of the affected forelimb immediately after focal ischemia has detrimental effects on sensorimotor function that cannot be attributed to hyperthermia or stress.

Studies of physiology and the morphology of the cat LGN following proton irradiation

PURPOSE

We have examined the effects of proton irradiation on the histologic and receptive field properties of thalamic relay cells in the cat visual system. The cat lateral geniculate nucleus (LGN) is a large structure with well-defined anatomical boundaries, and well-described afferent, efferent, and receptive field properties.

METHODS AND MATERIALS

A 1.0-mm proton microbeam was used on the cat LGN to determine short-term (3 months) and long-term (9 months) receptive field effects of irradiation on LGN relay cells. The doses used were 16-, 40-, and 60-gray (Gy).

RESULTS

Following irradiation, abnormalities in receptive field organization were found in 40- and 60-Gy short-term animals, and in all of the long-term animals. The abnormalities included "silent" areas of the LGN where a visual response could not be evoked and other regions that had unusually large or small compound receptive fields. Histologic analysis failed to identify cellular necrosis or vascular damage in the irradiated LGN, but revealed a disruption in retinal afferents to areas of the LGN.

CONCLUSIONS

These results indicate that microbeam proton irradiation can disrupt cellular function in the absence of obvious cellular necrosis. Moreover, the area and extent of this disruption increased with time, having larger affect with longer post-irradiation periods.

Role of sensory deficits in motor impairments after injury to primary motor cortex

After a focal ischemic lesion in the hand representation of the primary motor cortex in squirrel monkeys, manual skill was mildly and transiently impaired on a reach-and-retrieval task. Performance was significantly poorer during weeks 1 and 3 post-lesion, but was normal by week 4. An unusual behavioral event was also observed after the lesion. Monkeys reached for pellets, but visually inspected the hand for the presence of the pellets, even when none were actually retrieved. This behavior, possibly indicative of a sensory deficit, was rarely observed prior to the lesion, but was observed at significantly higher levels during week one post-lesion. These results suggest that the primary motor cortex plays a significant role in somatosensory processing during the execution of motor tasks. Motor deficits heretofore identified as purely motor, may be at least partially due to a sensory deficit, or sensory-motor disconnection.

Mapping clinically relevant plasticity after stroke

After stroke, patients show a wide range in the degree of recovery. Recovery occurs on the basis of discrete physiologic events. Identifying and measuring these events will be useful for a better understanding of stroke recovery mechanisms. The most extensive experience mapping these events has been with positron emission tomography, functional magnetic resonance imaging, and transcranial magnetic stimulation. This article reviews brain mapping studies that have examined stroke recovery. Serial assessment of patients during recovery raises the need for control studies evaluating the effect of intra-subject variability over time. The clearest insights into the significance of bilateral activation during unilateral movements by the stroke-affected hand will come from studies that include bilateral electromyographic measurements. Most brain imaging studies have focused on patients with very good recovery; further study of patients with a wide range of outcomes is needed. The described brain mapping methods have complementary strengths. Insights into the biological basis of recovery may best be achieved when results are considered together. With the advent of treatments targeting stroke recovery, measurement of post-stroke restorative events may also have value as a surrogate end point in clinical trials.

A pilot study of somatotopic mapping after cortical infarct

BACKGROUND AND PURPOSE

Animal studies have described remodeling of sensory and motor representational maps after cortical infarct. These changes may contribute to return of function after stroke.

METHODS

Functional MRI was used to compare sensory and motor maps obtained in 35 normal control subjects with results from 2 patients with good recovery 6 months after a cortical stroke.

RESULTS

During finger tapping in controls, precentral gyrus activation exceeded or matched postcentral gyrus activation in 40 of 42 cases. Patient 1 had a small infarct limited to precentral gyrus. Finger tapping activated only postcentral gyrus, a pattern not seen in any control subject. During tactile stimulation of a finger or hand in controls, postcentral gyrus activation exceeded or matched precentral gyrus activation in 11 of 14 cases. Patient 2 had a small infarct limited to postcentral gyrus and superior parietal lobule. Tactile stimulation of the finger activated only precentral gyrus, a pattern not seen in any control. In both patients, activation during pectoralis contraction was medial to the site activated during finger tapping.

CONCLUSIONS

Results during finger tapping (patient 1) and finger stimulation (patient 2) may reflect amplification of a preserved component of normal sensorimotor function, a shift in the cortical site of finger representation, or both. Cortical map reorganization along the infarct rim may be an important contributor to recovery of motor and sensory function after stroke. Functional MRI is useful for assessing motor and sensory representational maps.

Brain plasticity and stroke rehabilitation. The Willis lecture

Neuronal connections and cortical maps are continuously remodeled by our experience. Knowledge of the potential capabilityof the brain to compensate for lesions is a prerequisite for optimal stroke rehabilitation strategies. Experimental focal cortical lesions induce changes in adjacent cortex and in the contralateral hemisphere. Neuroimaging studies in stroke patients indicate altered poststroke activation patterns, which suggest some functional reorganization. To what extent functional imaging data correspond to outcome data needs to be evaluated. Reorganization may be the principle process responsible for recovery of function after stroke, but what are the limits, and to what extent can postischemic intervention facilitate such changes? Postoperative housing of animals in an enriched environment can significantly enhance functional outcome and can also interact with other interventions, including neocortical grafting. What role will neuronal progenitor cells play in future rehabilitation-stimulated in situ or as neural replacement? And what is the future for blocking neural growth inhibitory factors? Better knowledge of postischemic molecular and neurophysiological events, and close interaction between basic and applied research, will hopefully enable us to design rehabilitation strategies based on neurobiological principles in a not-too-distant future.

Recovery after damage to motor cortical areas

Until recently, the neural bases underlying recovery of function after damage to the cerebral cortex were largely unknown. Recent results from neuroanatomical and neurophysiological studies in animal models have demonstrated that after cortical damage, long-term and widespread structural and functional alterations take place in the spared cortical tissue. These presumably adaptive changes may play an important role in functional recovery.

Mapping plastic brain changes after acute lesions

The combination of different mapping techniques has yielded new insights in reorganization processes after acute lesions in humans. Recent research focused not only on lesion-induced plasticity, but also on therapy-induced reorganization of the brain. Data from animal experiments has expanded our knowledge of mechanisms that underlie plastic changes.

Environmental influence on gene expression and recovery from cerebral ischemia

An emerging concept in neurobiology is that the adult brain retains a capacity for plasticity and functional reorganization throughout the life span. Experimental data from electrophysiological, morphological and behavioral studies have documented experience dependent plasticity in the intact and injured adult brain. Neuroimaging clinical studies indicate altered post stroke functional activation patterns, usually including activation of the intact hemisphere. However, there is some disagreement regarding their functional significance and longitudinal studies correlating outcome and activation pattern are needed to solve some controversies. Postoperative housing of rats in activity stimulating environment after ligation of the middle cerebral artery significantly enhances outcome. Gene expression for brain derived neurotrophic factor and Ca2+/calmodulin-dependent protein kinase II, two substances with potential role in brain plasticity, show different patterns in animals housed in standard and in enriched environment. The functional significance of altered gene expression needs to be evaluated.

Early training may exacerbate brain damage after focal brain ischemia in the rat

Early overuse of a lesioned forelimb, induced by immediate immobilization of the intact forelimb after a cortical lesion, has been reported to increase tissue damage and delay functional recovery. To investigate if early training without immobilization of the intact forelimb could increase tissue loss and reduce recovery, the middle cerebral artery was ligated distal to the striatal branches in 25 male spontaneously hypertensive rats. Control rats were housed in standard cages, training rats were transferred to larger cages allowing various activities and received additional special training 1 hour a day starting either 24 hours or 7 days after the ligation. The rats were tested on a rotating pole, in a leg placement test, and in a water maze and they were killed 6 weeks after the ligation. Delayed training resulted in the best overall performance; however, both training groups performed better than standard rats on the rotating pole. The cortical infarct volume was larger in the early training group than in the other two groups (P < .005), possibly related to increased glutamate release and peri-infarct cortical hyperexcitability.

The role of diaschisis in stroke recovery

BACKGROUND AND PURPOSE

Recovery from hemiparesis after stroke has been shown to involve reorganization in motor and premotor cortical areas. However, whether poststroke recovery also depends on changes in remote brain structures, ie, diaschisis, is as yet unresolved. To address this question, we studied regional cerebral blood flow in 7 patients (mean+/-SD age, 54+/-8 years) after their first hemiparetic stroke.

METHODS

We analyzed imaging data voxel by voxel using a principal component analysis by which coherent changes in functional networks could be disclosed. Performance was assessed by a motor score and by the finger movement rate during the regional cerebral blood flow measurements.

RESULTS

The patients had recovered (P<0. 001) from severe hemiparesis after on average 6 months and were able to perform sequential finger movements with the recovered hand. Regional cerebral blood flow at rest differentiated patients and controls (P<0.05) by a network that was affected by the stroke lesion. During blindfolded performance of sequential finger movements, patients were differentiated from controls (P<0.05) by a recovery-related network and a movement-control network. These networks were spatially incongruent, involving motor, sensory, and visual cortex of both cerebral hemispheres, the basal ganglia, thalamus, and cerebellum. The lesion-affected and recovery-related networks overlapped in the contralesional thalamus and extrastriate occipital cortex.

CONCLUSIONS

Motor recovery after hemiparetic brain infarction is subserved by brain structures in locations remote from the stroke lesion. The topographic overlap of the lesion-affected and recovery-related networks suggests that diaschisis may play a critical role in stroke recovery.

Acute reorganization of the forepaw representation in the rat SI cortex after focal cortical injury: neuroprotective effects of piracetam treatment

Immediate postlesion reorganization of the somatosensory cortical representation was examined in adult rats. Response properties of small clusters of neurons were recorded in the area of the primary somatosensory cortex (SI) devoted to the contralateral forepaw representation. Electrophysiological maps were elaborated on the basis of the sensory 'submodality' (cutaneous or noncutaneous) and the location of the peripheral receptive fields (RFs) of layer IV neurons. Recordings were made prior to, and from 1 to 12 h after, induction of a focal neurovascular lesion to the SI cortex that initially destroyed a part (8.5%) of the cutaneous representation. Moreover, the influence of an anti-ischaemic substance (piracetam) on lesion-induced changes was analysed. The main observations were: (i) a gradual outward expansion of the area of the functional lesion, which was smaller in the piracetam-treated (PT) rats than in the control, placebo-treated (PL) rats; (ii) a substantial remodelling of the spared representational zones, both in cortical sectors adjoining the site of injury and those remote from the site; (iii) a significant postlesion increase in the size of cutaneous RFs in the PT rats, but not in the PL rats; (iv) a better preservation of RF submodality and topographic organization in the PT maps than in the PL maps; and (v) a decrease in neuronal responsiveness to cutaneous stimulation which was less pronounced in the PT than in the PL rats. Our results can be ascribed to a rapid change in the balance of excitatory and inhibitory connections which leads to unmasking of subthreshold inputs converging onto cortical neurons. Our findings also indicate that acute piracetam treatment exerts a protective function on the physiological response properties of cortical neurons after focal injury.

Reorganization of sensory and motor systems in hemiplegic stroke patients. A positron emission tomography study

BACKGROUND AND PURPOSE

Cortical reorganization of motor systems has been found in recovered stroke patients. Reorganization in nonrecovered hemiplegic stroke patients early after stroke, however, is less well described. We used positron emission tomography to study the functional reorganization of motor and sensory systems in hemiplegic stroke patients before motor recovery.

METHODS

Regional cerebral blood flow (rCBF) was measured in 6 hemiplegic stroke patients with a single, subcortical infarct and 3 normal subjects with the [(15)O]H(2)O injection technique. Brain activation was achieved by passive elbow movements driven by a torque motor. Increases of rCBF comparing passive movements and rest were assessed with statistical parametric mapping. Significant differences were defined at P<0.01.

RESULTS

In normal subjects, significant increases of rCBF were found in the contralateral sensorimotor cortex, supplementary motor area, cingulate cortex, and bilaterally in the inferior parietal cortex. In stroke patients, significant activation was observed bilaterally in the inferior parietal cortex and in the contralateral sensorimotor cortex, ipsilateral prefrontal cortex, supplementary motor area, and cingulate cortex. Significantly larger increases of rCBF in patients compared with normal subjects were found bilaterally in the sensorimotor cortex, stronger in the ipsilateral, unaffected hemisphere, and in both parietal lobes, including the ipsilateral precuneus.

CONCLUSIONS

Passive movements in hemiplegic stroke patients before clinical recovery elicit some of the brain activation patterns that have been described during active movements after substantial motor recovery. Changes of cerebral activation in sensory and motor systems occur early after stroke and may be a first step toward restoration of motor function after stroke.

Are neuronal markers and neocortical graft-host interface influenced by housing conditions in rats with cortical infarct cavity?

The aim was to study if exposure to an enriched environment influenced graft-host interface and neuronal markers in neocortical grafts implanted in cortical infarct cavities 3 weeks after distal ligation of the middle cerebral artery in adult hypertensive rats. Half the rats were exposed to an enriched environment for 2 h daily 5 days a week starting 1 week after the arterial ligation. The brain was fixed by perfusion 4 weeks postgrafting. The immunoreactivity to glial fibrillary acidic protein, microtubule associated protein 2, and synaptophysin was studied in coronal paraffin-embedded sections. A distinct glial border separated the infarct cavity from the surrounding brain in sham-transplanted rats. Most grafts filled the larger part of the infarct cavity. In 8 of 18 transplants, 4 in each experimental group, part of the transplants protruded through the thin glial membrane that delineated the transplant-host interface into the adjacent host brain tissue. Microtubule associated protein 2 immunostained sections indicated bridging of dendrites in the host-transplant interface. Synaptophysin immunoreactivity was significantly higher in grafts than in contralateral cortex. However, graft morphology and neuronal marker immunoreactivity did not differ between rats housed in standard and activity stimulating cages.

Lesion-induced plasticity as a potential mechanism for recovery and rehabilitative training

Brain lesions not only cause a functional deficit in the lesion area, but also affect the structurally intact brain network connected to the lesion. In brain areas surrounding the lesion, as well as those remote from it, the structural and functional plasticity of the brain is increased because of an alteration of transmitter receptor expression and membrane properties of neurones. Within the penumbra of brain ischaemia, as well as after trauma, an additional perilesional dysfunctional zone is found that contributes to the neurological deficit. The lesion-induced plasticity can be used for adaptation, which also may restore function in the perilesional zone, if adequate rehabilitative training is performed.

Thalamic and brainstem contributions to large-scale plasticity of primate somatosensory cortex

After long-term denervation of an upper limb in macaque monkeys, the representation of the face in somatosensory cortex expands over many millimeters into the silenced representation of the hand. Various brainstem and cortical mechanisms have been proposed to explain this phenomenon. Reorganization in the thalamus has been largely ignored. In monkeys with deafferented upper limbs for 12 to 20 years, it was found that the brainstem cuneate and the thalamic ventral posterior nuclei had undergone severe transneuronal atrophy, and physiological mapping in the thalamus revealed that the face and trunk representations were adjoined while the normally small representation of the lower face had expanded comparable to the expansion in cortex. Reorganization of brainstem and thalamic nuclei associated with slow transneuronal atrophy is likely to be a progressive process. When coupled with divergence of ascending connections, it is likely to make a substantial contribution to representational changes in cortex.

Neuronal damage and plasticity identified by microtubule-associated protein 2, growth-associated protein 43, and cyclin D1 immunoreactivity after focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

An objective of therapeutic intervention after cerebral ischemia is to promote improved functional outcome. Improved outcome may be associated with a reduction of the volume of cerebral infarction and the promotion of cerebral plasticity. In the developing brain, neuronal growth is concomitant with expression of particular proteins, including microtubule-associated protein 2 (MAP-2), growth-associated protein 43 (GAP-43), and cyclin D1. In the present study we measured the expression of select proteins associated with neurite damage and plasticity (MAP-2 and GAP-43) as well as cell cycle (cyclin D1) after induction of focal cerebral ischemia in the rat.

METHODS

Brains from rats (n=28) subjected to 2 hours of middle cerebral artery occlusion and 6 hours, 12 hours, and 2, 7, 14, 21, and 28 days (n=4 per time point) of reperfusion and control sham-operated (n=3) and normal (n=2) rats were processed by immunohistochemistry with antibodies raised against MAP-2, GAP-43, and cyclin D1. Double staining of these proteins for cellular colocalization was also performed.

RESULTS

Loss of immunoreactivity of both MAP-2 and GAP-43 was observed in most damaged neurons in the ischemic core. In contrast, MAP-2, GAP-43, and cyclin D1 were selectively increased in morphologically intact or altered neurons localized to the ischemic core at an early stage (eg, 6 hours) of reperfusion and in the boundary zone to the ischemic core (penumbra) during longer reperfusion times.

CONCLUSIONS

The selective expressions of the neuronal structural proteins (MAP-2 in dendrites and GAP-43 in axons) and the cyclin D1 cell cycle protein in neurons observed in the boundary zone to the ischemic core are suggestive of compensatory and repair mechanisms in ischemia-damaged neurons after transient focal cerebral ischemia.