Jukka Jolkkonen

Glibenclamide enhances neurogenesis and improves long-term functional recovery after transient focal cerebral ischemia

Glibenclamide is neuroprotective against cerebral ischemia in rats. We studied whether glibenclamide enhances long-term brain repair and improves behavioral recovery after stroke. Adult male Wistar rats were subjected to transient middle cerebral artery occlusion (MCAO) for 90 minutes. A low dose of glibenclamide (total 0.6 μg) was administered intravenously 6, 12, and 24 hours after reperfusion. We assessed behavioral outcome during a 30-day follow-up and animals were perfused for histological evaluation. In vitro specific binding of glibenclamide to microglia increased after pro-inflammatory stimuli. In vivo glibenclamide was associated with increased migration of doublecortin-positive cells in the striatum toward the ischemic lesion 72 hours after MCAO, and reactive microglia expressed sulfonylurea receptor 1 (SUR1) and Kir6.2 in the medial striatum. One month after MCAO, glibenclamide was also associated with increased number of NeuN-positive and 5-bromo-2-deoxyuridine-positive neurons in the cortex and hippocampus, and enhanced angiogenesis in the hippocampus. Consequently, glibenclamide-treated MCAO rats showed improved performance in the limb-placing test on postoperative days 22 to 29, and in the cylinder and water-maze test on postoperative day 29. Therefore, acute blockade of SUR1 by glibenclamide enhanced long-term brain repair in MCAO rats, which was associated with improved behavioral outcome.

Constraint-Induced Movement Therapy Overcomes the Intrinsic Axonal Growth–Inhibitory Signals in Stroke Rats

Background and Purpose— Constraint-induced movement therapy (CIMT) improves functional outcome in patients with stroke possibly through structural plasticity. We hypothesized that CIMT could enhance axonal growth by overcoming the intrinsic growth–inhibitory signals, leading eventually to improved behavioral performance in stroke rats. Methods— Focal cerebral ischemia was induced by intracerebral injection of endothelin-1. Adult Wistar rats were divided into a sham-operated group, an ischemic group, and an ischemic group treated with CIMT. CIMT started at postoperative day 7 and continued for 3 weeks. Biotinylated dextran amine was injected into the contralateral sensorimotor cortex at postoperative day 14 to trace crossing axons at the cervical spinal cord. The expressions of Nogo-A, Nogo receptor, RhoA, and Rho-associated kinase in the peri-infarct cortex, and the expressions of biotinylated dextran amine, growth associated protein-43, synaptophysin, vGlut1, and postsynaptic density-95 in the denervated spinal cord were measured by immunohistochemistry and Western blots. Behavioral recovery was analyzed at postoperative days 29 to 32. Results— Infarct volumes were not different between groups after stroke. CIMT significantly increased the length and the number of midline crossings of contralateral corticospinal axons to the denervated cervical spinal cord. CIMT significantly decreased the expressions of Nogo-A/Nogo receptor and RhoA/Rho-associated kinase in the peri-infarct cortex, and increased the expressions of growth associated protein-43, synaptophysin, vGlut1, and postsynaptic density-95 in the denervated cervical spinal cord. Behavioral performances assessed by the beam-walking test and the water maze test were improved significantly by CIMT. Conclusions— CIMT promoted poststroke synaptic plasticity and axonal growth at least partially by overcoming the intrinsic growth–inhibitory signaling, leading to improved behavioral outcome.

Cell-Based Therapies and Functional Outcome in Experimental Stroke

Document S1. The Search Strategy with Inclusion and Exclusion Criteria and Two TablesxDownload (.14 MB ) Document S1. The Search Strategy with Inclusion and Exclusion Criteria and Two Tables

Overexpression of APP provides neuroprotection in the absence of functional benefit following middle cerebral artery occlusion in rats

Cerebral ischaemia leads to a transient accumulation of β‐amyloid precursor protein (APP) and β‐amyloid (Aβ) peptides adjacent to the ischaemic lesion. There is conflicting evidence that APP/Aβ fragments may either enhance neuronal plasticity or be neurotoxic. The aim of the current study was to assess the effect of overexpression of human APP in rats on functional recovery following cerebral ischaemia. Adult APP‐overexpressing (hAPP695 Tg) rats subjected to transient middle cerebral artery occlusion (MCAO) had significantly smaller infarct volumes than non‐transgenic littermates, yet did not perform better on a series of sensorimotor or learning tests during a 6‐month follow‐up period. In fact, transgenic animals were found to be significantly more impaired in both the beam‐walking and Morris water maze tests following MCAO. Immunohistochemistry showed human Aβ‐positive staining in the cortex and hippocampus of APP transgenic rats. The present data suggest that while overexpression of APP in rats may provide some histological neuroprotection in the event of cerebral ischaemia, this does not translate into significant functional recovery.

Experimental approaches to study functional recovery following cerebral ischemia

Valid experimental models and behavioral tests are indispensable for the development of therapies for stroke. The translational failure with neuroprotective drugs has forced us to look for alternative approaches. Restorative therapies aiming to facilitate the recovery process by pharmacotherapy or cell-based therapy have emerged as promising options. Here we describe the most common stroke models used in cell-based therapy studies with particular emphasis on their inherent complications, which may affect behavioral outcome. Loss of body weight, stress, hyperthermia, immunodepression, and infections particularly after severe transient middle cerebral artery occlusion (filament model) are recognized as possible confounders to impair performance in certain behavioral tasks and bias the treatment effects. Inherent limitations of stroke models should be carefully considered when planning experiments to ensure translation of behavioral data to the clinic.

Stromal cell-derived factor-1 and its receptor CXCR4 in adult neurogenesis after cerebral ischemia.

Stromal cell-derived factor-1 was originally found as a chemoattractant for immune cells. Later it was shown that stromal cell-derived factor-1 and its specific receptor CXCR4 were widely expressed in the developing and mature brains. They participate in a variety of physiological and pathological processes including brain development, angiogenesis, neurodegeneration and neurogenesis. Stromal cell-derived factor-1/CXCR4 plays a particularly important role in adult neurogenesis through mediating the proliferation of neurogenitors, regulating the migration, differentiation, as well as functional integration of newborn neurons into existing networks. After stroke, adult neurogenesis in both the subventricular zone and subgranular zone is robustly increased and stromal cell-derived factor-1 and matrix metalloproteinases are released by damaged tissue. Stromal cell-derived factor-1 promotes the proliferation of neuroblasts and their migration to injured areas. However, the majority of the neuroblasts produced after stroke undergo apoptosis and only a few differentiate and survive in the long-term. The interaction of stromal cell-derived factor-1 and matrix metalloproteinases may contribute to the unfavorable local microenvironment diminishing the survival of newborn neurons. Stromal cell-derived factor-1/matrix metalloproteinases and their downstream pathways may provide a new target for the treatment of stroke.

Gait Impairment in a Rat Model of Focal Cerebral Ischemia

The availability of proper tests for gait evaluation following cerebral ischemia in rats has been limited. The automated, quantitative CatWalk system, which was initially designed to measure gait in models of spinal cord injury, neuropathic pain, and peripheral nerve injury, is said to be a useful tool for the study of motor impairment in stroke animals. Here we report our experiences of using CatWalk XT with rats subjected to transient middle cerebral artery occlusion (MCAO), during their six-week followup. Large corticostriatal infarct was confirmed by MRI in all MCAO rats, which was associated with severe sensorimotor impairment. In contrast, the gait impairment was at most mild, which is consistent with seemingly normal locomotion of MCAO rats. Many of the gait parameters were affected by body weight, walking speed, and motivation despite the use of a goal box. In addition, MCAO rats showed bilateral compensation, which was developed to stabilize proper locomotion. All of these interferences may confound the data interpretation. Taken together, the translational applicability of CatWalk XT in evaluating motor impairment and treatment efficacy remains to be limited at least in rats with severe corticostriatal infarct and loss of body weight.

Cognitive Impairment with Vascular Impairment and Degeneration

Ischemic stroke is a leading cause of death and cognitive impairment worldwide. However, the mechanisms of progressive cognitive decline following brain ischemia are not yet certain. Ongoing interest in cerebrovascular diseases research has provided data showing that Alzheimers proteins and other factors may be involved in the pathogenesis of gradual ischemic brain injury. Thus, both focal and global brain ischemia in rodents produces a stereotyped pattern of selective neuronal degeneration, which is just the same as in Alzheimers type dementia. Data from animal models and clinical studies of ischemic stroke have demonstrated an increase in expression and processing of amyloid precursor protein (APP) to a neurotoxic form of oligomeric β-amyloid peptide (Aβ) and hyperphosphorylation of tau protein. The authors of this review are using advances in methods and technologies to study cerebrovascular diseases and this review examines the hypothesis that pathological mechanisms common to both brain ischemia and Alzheimers dementia are contributing to cognitive impairment and brain ischemia-related dementia.

Increased Neurogenesis Contributes to the Promoted Behavioral Recovery by Constraint-Induced Movement Therapy after Stroke in Adult Rats

1 Department of Neurology, The First Hospital of China Medical University, Shenyang, China 2 Department of Obstetrics and Gynecology, The First Hospital of China Medical University, Shenyang, China 3 Department of Dermatology, The First Hospital of China Medical University, Shenyang, China 4 Key Laboratory of Immunodermatology, Ministry of Health, Ministry of Education, Shenyang, China 5 Department of Cardiology, Shengjing Hospital of China Medical University, Shenyang, China 6 Institute of Clinical Medicine, Neurology, University of Eastern Finland, Kuopio, Finland

Time for a neurorestorative therapy in stroke.

Stroke remains one of the main causes of death and disability worldwide. The aging of the population is likely to result in a dramatic increase in the burden of stroke. Thus, it is not surprising that the pharmaceutical industry has invested much money in the development of pharmacotherapies for ischemic stroke. Promising experimental data, however, have almost consistently failed to produce a clinically effective neuroprotective or neurorestorative drug. Only intravenous recombinant tissue plasminogen activator (rtPA) has been approved for the treatment of acute ischemic stroke. Many pharmaceutical companies have scaled down their stroke programs and despite the unmet need, activity in the field is almost frozen. Trafermin, a recombinant form of human basic fibroblast growth factor (bFGF), is a good example of a translational failure in neuroprotection. However, trafermin may also promote neuronal plasticity after cerebral insults. Thus, clinical trials with trafermin in stroke are warranted but should be based on neuronal restoration rather than acute neuroprotection.