Platelets localize to microvessels in response to cerebral ischemia and activate brain endothelium via IL-1α. CD41-positive platelets localized to ICAM-1-positive brain microvessels (Ai,Aiii) in ischemic cerebral hemispheres, but not in nonischemic, contralateral tissue (Aii) of mice exposed to focal, transient middle cerebral artery occlusion. Scale bar represents 40 μm (Ai-Aii) or 20 μm (iii). Images were acquired on a Olympus BX51 microscope using a 40×/0.75 Plan Fln objective and Texas Red/DAPI filter sets and captured using a CoolSNAP ES camera (Photometrics) through MetaVue Software (Molecular Devices; Ai-Aii) or on a Delta Vision RT (Applied Precision) restoration microscope using a 40×/1.3 Plan Apo objective and the Sedat filter set (89000, Chroma; Aiii). The images were collected using a CoolSNAP HQ (Photometrics) camera with a Z optical spacing of 0.2 μm, raw images were deconvolved using the softWoRx software (Applied Precision), and maximum intensity projections of these deconvolved images are shown (Aiii). VCAM-1 (B), ICAM-1 (C), or CXCL1 (D-E) levels in lysates (B-C) or supernatants (D-E) of MBECs after incubation with mouse WT or IL-1α/β ^−/− platelets (B-D) or rat platelets (E) were quantified by ELISA. The effects of antagonizing IL-1 actions with IL-1RA or neutralizing antibodies to IL-1α/β (or isotype controls) on the release of CXCL1 from MBECs in response to rat platelets (E) or recombinant IL-1α or IL-1β (F) were determined. B, from left to right: n = 4, 6, 4, 4, 6, 3, 5, 5, 4; C, n = 6, 8, 4, 7, 8, 3, 5, 5, 4; D, n = 3; E, n = 6, 6, 5, 4, 4, 4, 4, 3; F, n = 5, 5, 6, 6. ND indicates not detected. Data are mean ± SEM. (B-F) ***P < .001. **P < .01. *P < .05. NS indicates no significant difference versus respective buffer control.