BackgroundInvestigations following stroke first of all require information about the spatio-temporal dimension of the ischemic core as well as of perilesional and remote affected tissue. Here we systematically evaluated regions differently impaired by focal ischemia.Methodology/Principal FindingsWistar rats underwent a transient 30 or 120 min suture-occlusion of the middle cerebral artery (MCAO) followed by various reperfusion times (2 h, 1 d, 7 d, 30 d) or a permanent MCAO (1 d survival). Brains were characterized by TTC, thionine, and immunohistochemistry using MAP2, HSP72, and HSP27. TTC staining reliably identifies the infarct core at 1 d of reperfusion after 30 min MCAO and at all investigated times following 120 min and permanent MCAO. Nissl histology denotes the infarct core from 2 h up to 30 d after transient as well as permanent MCAO. Absent and attenuated MAP2 staining clearly identifies the infarct core and perilesional affected regions at all investigated times, respectively. HSP72 denotes perilesional areas in a limited post-ischemic time (1 d). HSP27 detects perilesional and remote impaired tissue from post-ischemic day 1 on. Furthermore a simultaneous expression of HSP72 and HSP27 in perilesional neurons was revealed.Conclusions/SignificanceTTC and Nissl staining can be applied to designate the infarct core. MAP2, HSP72, and HSP27 are excellent markers not only to identify perilesional and remote areas but also to discriminate affected neuronal and glial populations. Moreover markers vary in their confinement to different reperfusion times. The extent and consistency of infarcts increase with prolonged occlusion of the MCA. Therefore interindividual infarct dimension should be precisely assessed by the combined use of different markers as described in this study.

BackgroundTriggering receptor expressed on myeloid cells-2 (TREM2) is a microglial surface receptor involved in phagocytosis. Clearance of apoptotic debris after stroke represents an important mechanism to re-attain tissue homeostasis and thereby ensure functional recovery. The role of TREM2 following stroke is currently unclear.Methods and ResultsAs an experimental stroke model, the middle cerebral artery of mice was occluded for 30 minutes with a range of reperfusion times (duration of reperfusion: 6 h/12 h/24 h/2 d/7 d/28 d). Quantitative PCR (qPCR) revealed a greatly increased transcription of TREM2 after stroke. We subsequently analyzed the expression of pro-inflammatory cytokines, chemokines and their receptors in TREM2-knockout (TREM2-KO) mice via qPCR. Microglial activation (CD68, Iba1) and CD3-positive T-cell invasion were analyzed via qPCR and immunohistochemistry. Functional consequences of TREM2 knockout were assessed by infarct volumetry. The acute inflammatory response (12 h reperfusion) was very similar between TREM2-KO mice and their littermate controls. However, in the sub-acute phase (7 d reperfusion) following stroke, TREM2-KO mice showed a decreased transcription of pro-inflammatory cytokines TNFα, IL-1α and IL-1β, associated with a reduced microglial activity (CD68, Iba1). Furthermore, TREM2-KO mice showed a reduced transcription of chemokines CCL2 (MCP1), CCL3 (MIP1α) and the chemokine receptor CX3CR1, followed by a diminished invasion of CD3-positive T-cells. No effect on the lesion size was observed.ConclusionsAlthough we initially expected an exaggerated pro-inflammatory response following ablation of TREM2, our data support a contradictory scenario that the sub-acute inflammatory reaction after stroke is attenuated in TREM2-KO mice. We therefore conclude that TREM2 appears to sustain a distinct inflammatory response after stroke.

Background and Purpose-The potassium chloride cotransporter 2 (KCC2) is the main neuronal chloride extruder in the adult nervous system. Therefore, KCC2 is responsible for an inwardly directed electrochemical gradient of chloride that leads to hyperpolarizing GABA-mediated responses. Under some pathophysiological conditions, GABA has been reported to be depolarizing because of a downregulation of KCC2. This is the first study to our knowledge analyzing the expression of KCC2 after a focal cerebral ischemia. Methods-Mild and severe ischemia were induced in rats by a transient occlusion of the middle cerebral artery for 30 and 120 minutes, respectively. KCC2 mRNA and protein expression were studied in the ischemic hemisphere after different reperfusion times (2 hour, 1 day, 7 days, 30 days, 168 days) by using quantitative polymerase chain reaction, Western blotting, and immunohistological staining. Results-We found a substantial decrease of KCC2 mRNA and protein levels in the ischemic hemisphere, with a stronger downregulation of KCC2 after severe vs mild ischemia. Long-term surviving cells expressing KCC2 could be detected in the infarct core. These cells were identified as GABAergic interneurons mainly expressing parvalbumin. Conclusions-Our study revealed a substantial neuron-specific downregulation of KCC2 after focal cerebral ischemia. (Stroke.2010;41:e151-e159.)

Stroke survivors often recover from motor deficits, either spontaneously or with the support of rehabilitative training. Since tonic GABAergic inhibition controls network excitability, it may be involved in recovery. Middle cerebral artery occlusion in rodents reduces tonic GABAergic inhibition in the structurally intact motor cortex (M1). Transcript and protein abundance of the extrasynaptic GABAA-receptor complex α4β3δ are concurrently reduced (δ-GABAARs). In vivo and in vitro analyses show that stroke-induced glutamate release activates NMDA receptors, thereby reducing KCC2 transporters and down-regulates δ-GABAARs. Functionally, this is associated with improved motor performance on the RotaRod, a test in which mice are forced to move in a similar manner to rehabilitative training sessions. As an adverse side effect, decreased tonic inhibition facilitates post-stroke epileptic seizures. Our data imply that early and sometimes surprisingly fast recovery following stroke is supported by homeostatic, endogenous plasticity of extrasynaptic GABAA receptors.

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