Summary: 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 hyper tensive rats. Control rats were housed in standard cages, train ing rats were transferred to larger cages allowing various ac tivities and received additional special training I hour a day starting either 24 hours or 7 days after the ligation. The rats Activation and training starts early after stroke onset in most stroke centers today. Evaluations of stroke units have confirmed that early mobilization reduces second ary complications and mortality and promotes long-term functional outcome (Stroke Unit Trialists ' Collaboration, 1997a,b; lndreavik et aI. , 1997). To what extent it im proves specific motor functions is less clear. Optimal time windows for specific rehabilitation interventions af ter stroke have not been defined.That experience and training can promote adaptive plasticity in the healthy brain as well as after brain le sions has been shown in many clinical and experimental studies (Rosenzweig, 1984;Jenkins and Merzenich, 1987;Pons, 1988;Bach-y-Rita, 1990;Kaas, 1991; Pas cual-Leone and Torres, 1993;Schieber, 1995; Seitz et Received December 9, 1998; final revision received February 3, 1999; accepted February 3, 1999. Supported by grants from the Swedish Medical Research Council (project 14X-4968), the Bank of Sweden Tercentenary Foundation, the Swedish Heart and Lung Foundation. the Swedish Association for the Neurologically Disabled, and the Swedish Stroke Foundation.Address correspondence and reprint requests to Dr. Barbro B. Johansson, Section for Experimental Neurology, Wallenberg Neurosci ence Center, University Hospital, S-22 1 85 Lund, Sweden.Abbreviations used: MCA, middle cerebral artery; NMDA, N methyl-D-aspartate. 997were 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; how ever, 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.

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To investigate whether rat hippocampal neurogenesis varies with strain and gender, the authors examined proliferating progenitor cells and their progeny in young male and female Sprague-Dawley (SD) and spontaneously hypertensive rats (SHR) using the thymidine analog bromodeoxyuridine (BrdU) combined with immunohistochemistry for the neuronal marker Calbindin D28k and glial fibrillary acidic protein. Rats were given 7 consecutive daily BrdU injections and were killed 1 day or 4 weeks later to allow for discrimination between proliferation and cell survival. Stereologic analysis of the numbers of BrdU-immunoreactive cells in the dentate gyrus revealed both a strain difference with significantly higher cell proliferation and net neurogenesis in SHR than in SD and a gender difference with males from both strains producing significantly more cells than their female counterparts. Whereas the number of progenitors four weeks after BrdU injections was still significantly greater in male than in female SHRs, resulting in a greater net neurogenesis in the male, the number of BrdU-immunoreactive cells did not differ between male and female SD rats, suggesting a greater survival of newly generated cells in the dentate gyrus in female than in male SD rats. No sex or strain difference was observed in the relative ratio of neurogenesis and gliogenesis.

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