Barbro B. Johansson

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.

Environment Influences Functional Outcome of Cerebral Infarction in Rats

BACKGROUND AND PURPOSE The purpose of this study was to determine whether preoperative and postoperative enrichment of the environment can enhance the functional outcome after cerebral infarction in rats. METHODS The right middle cerebral artery was ligated in adult spontaneously hypertensive male rats, and the functional outcome was studied for 12 weeks after the operation. Three groups were compared: A, rats kept in individual cages before and after the operation (n = 9); B, rats kept in individual cages before the operation but transferred to an enriched environment after the operation (n = 10); and C, rats kept in an enriched environment all the time (n = 12). The enriched environment consisted of a large cage with opportunities for various activities, but rats were not forced to do any particular tasks. RESULTS Rats kept in an enriched environment (groups B and C) performed significantly better than rats in group A in a leg-placement test, beam walking, walking on a rotating pole, and climbing. The infarct size and thalamic atrophy did not differ among the groups. CONCLUSIONS The laboratory environment is important for the functional outcome in brain ischemia. We hypothesize that an enriched environment may stimulate mechanisms that enhance brain plasticity after focal brain ischemia.

Environment, social interaction, and physical activity as determinants of functional outcome after cerebral infarction in the rat.

Rats housed in an enriched environment allowing both social interaction and physical activity improve more than rats housed in standard laboratory cages after focal brain ischemia. To determine the relative importance of social and physical activity, rats that sustained ligation of the middle cerebral artery were kept in an enriched environment with opportunities for various activities (group A), housed together in the same size of cage as group A but with no activity-stimulating equipment (group B), or housed in individual cages with a running wheel (group C). There was no significant difference in infarct size between the groups. Limb placement, climbing, balance on an inclined plane, and ability to traverse a beam and a rotating pole were repeatedly tested 2-13 weeks after the operation. During the entire postoperative period, group A performed significantly better than group C in all tests and better than group B on the rotating pole. With time they also performed significantly better than group B in limb placement, climbing, and on the inclined plane. Group B performed significantly better than group C on the inclined plane and in climbing at all times, and by 13 weeks also in the limb placement test and on the beam. Thus, social interaction was superior to wheel-running but an enriched environment allowing free physical activity combined with social interaction resulted in the best performance.

Neuronal plasticity and dendritic spines: effect of environmental enrichment on intact and postischemic rat brain.

The authors compared the influence of environmental enrichment on intact and lesioned brain, and tested the hypothesis that postischemic exposure to an enriched environment can alter dendritic spine density in pyramidal neurons contralateral to a cortical infarct. The middle cerebral artery was occluded distal to the striatal branches in spontaneously hypertensive rats postoperatively housed either in a standard or in an enriched environment. Intact rats were housed in the same environment. Three weeks later the brains were perfused in situ. The dendritic and spine morphology was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer yellow in pyramidal neurons in layers II/III and V/VI in the somatosensory cortex. In intact rats, the number of dendritic spines was significantly higher in the enriched group than in the standard group in all layers (P < 0.05). Contralateral to the infarct, pyramidal neurons in layers II/III, which have extensive intracortical connections that may play a role in cortical plasticity, had significantly more spines in the enriched group than in the standard group (P < 0.05). No difference was observed in layers V/VI. They conclude that housing rats in an enriched environment significantly increases spine density in superficial cortical layers in intact and lesioned brain, but in deeper layers of intact brain.

Plasma homocysteine in the acute and convalescent phases after stroke

BACKGROUND AND PURPOSE Stroke patients frequently manifest moderate hyperhomocysteinemia. In most published studies, plasma homocysteine was measured at least 1 month after stroke (or the interval was not reported). To determine whether plasma homocysteine concentrations change in the acute phase, we compared acute-phase values with both convalescent-phase and control values. METHODS Plasma homocysteine concentrations were measured in the acute phase (mean, 2 days after stroke onset) in 162 first-ever stroke patients aged 50 years or more (median, 75 years) and again at a median interval of 583 days (range, 460 to 645 days) after stroke onset in a subgroup of 17 patients, with values for 60 age-matched subjects serving as controls. Twenty of the control subjects were reexamined 2 to 3 years after their initial examination. RESULTS The median plasma homocysteine concentration was 13.4 mumol/L in the patient group compared with 13.8 mumol/L for control subjects (NS, Mann-Whitney U test) and increased from 11.4 mumol/L in the acute phase to 14.5 mumol/L in the convalescent phase in the subgroup of patients examined twice (P < .01, Wilcoxon signed rank test). In the 20 reexamined control subjects, no significant change over time in plasma homocysteine concentration was found. CONCLUSIONS The post-acute-phase increase in plasma homocysteine may explain why higher values were obtained for stroke patients than for control subjects in previous studies. Possible reasons for the variation in plasma homocysteine concentrations over time are (1) an acute-phase reduction secondary to a decrease in plasma albumin and (2) an increase in plasma homocysteine during the convalescent phase due to modified vitamin intake and/or lifestyle. The timing of plasma homocysteine measurements relative to stroke onset is a factor to be considered in the interpretation of results.

Enriched Environment Increases Neural Stem/Progenitor Cell Proliferation and Neurogenesis in the Subventricular Zone of Stroke-Lesioned Adult Rats

Background and Purpose— The subventricular zone in the adult brain is identified as an endogenous resource of neuronal precursors that can be recruited to adjacent lesioned areas. The hypothesis was tested that postischemic environmental enrichment might enhance subventricular zone cell genesis. Methods— A cortical infarct was induced in adult spontaneously hypertensive rats by ligating the middle cerebral artery distal to the striatal branches, after which animals were housed in either standard or enriched environment and allowed to survive for 5 weeks. The thymidine analogue bromodeoxyuridine was administered during the first postischemic week. The generation of neural stem/progenitor cells and neuronal precursors in the subventricular zone were studied with cell specific markers such as Ki67 and phosphorylated histone H3 (cell proliferation), Sox-2 (neural stem/progenitor cells), bromodeoxyuridine (slowly cycling, nonmigratory putative neural stem cells), and doublecortin (newborn immature neurons). Results— Proliferating cells in the subventricular zone were identified as chiefly neural progenitors but also putative neural stem cells and neuronal precursors. Five weeks after stroke, proliferation in the subventricular zone was lower in stroke-lesioned rats housed in standard environment compared with nonlesioned rats. Postischemic environmental enrichment normalized cell proliferation levels, increased the numbers of putative neural stem cells as assessed with bromodeoxyuridine, and increased doublecortin-positive neuroblasts, which extended in migratory chains toward the infarct. Conclusions— Enriched environment increased the neural stem/progenitor cell pool and neurogenesis in the adult subventricular zone 5 weeks after a cortical stroke. This might be of potential importance for tissue regeneration.

Effect of environmental enrichment on stress related systems in rats

The aim of this study was to test whether environmental enrichment alters the status and responsiveness of pituitary‐adrenocortical and sympathetic‐adrenomedullary hormones in rats. Previous studies have shown that rats kept in an enriched environment differ from those kept in standard cages in dendritic branching, synaptogenesis, memory function, emotionality and behaviour. In male Wistar rats kept in an enriched environment for 40 days, we studied basal concentrations of hormones, endocrine responses to 5‐HT1A challenge and responsiveness and adaptation to repeated handling. Environmental enrichment consisted of large plexiglass cages with 10 rats per cage, which contained variety of objects exchanged three times a week. Rats kept in this enriched environment had higher resting plasma concentrations of corticosterone, larger adrenals and increased corticosterone release to buspirone challenge compared to controls. Lower adrenocorticotropic hormone, corticosterone and adrenaline responses to handling were noticed in rats kept in an enriched environment. Exposure to repeated handling led to a more rapid extinction of corticosterone responses in rats kept in an enriched environment. Thus, environmental enrichment leads to pronounced changes in neuroendocrine regulation, including larger adrenals and increased adrenocortical function, which are so far considered to be indication of chronic stress.

Can sensory stimulation improve the functional outcome in stroke patients

After obtaining informed consent, we randomized 78 patients with severe hemiparesis of the left or right side within 10 days of stroke onset: 40 to a control group receiving daily physiotherapy and occupational therapy, and 38 to a group that, in addition, we treated with sensory stimulation (acupuncture) twice a week for 10 weeks. The median age was 76 years for both groups. Motor function, balance, and ADL (Barthels Index) were assessed before the start of treatment and at 1 and 3 months after stroke onset; ADL was also assessed after 12 months. We assessed the quality of life (QL) using the Nottingham Health Profile 3, 6, and 12 months after stroke onset. Patients given sensory stimulation recovered faster and to a larger extent than the controls, with a significant difference for balance, mobility, ADL, QL, and days spent at hospitals/nursing homes. Whether acupuncture per se is responsible for the differences requires further study.

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.

Functional Outcome in Rats Transferred to an Enriched Environment 15 Days After Focal Brain Ischemia

BACKGROUND AND PURPOSE The aim was to determine whether a delayed transfer to an enriched environment improves outcome after focal brain ischemia. METHODS Performance on a rotating pole, prehensile traction, limb placement, and postural reflexes were tested in 15 spontaneously hypertensive rats housed in standard laboratory cages for 2 weeks after middle cerebral artery ligation. Seven of the 15 rats were then transferred to an enriched environment, and the two groups were tested 1, 3, and 5 weeks later. RESULTS The enriched environment significantly improved pole performance, prehensile traction, and limb placement. CONCLUSIONS Delayed postoperative environmental enrichment improves outcome in experimental stroke.