Immunofluorescence staining for 5-HT1B, (A-E), AT1(F-J), ETB (K-O), and ETA (P-T) receptors in the ischemic middle cerebral artery (MCA), cerebral microvessels (Mic.V), and surrounding brain tissue (Brain). There was a clear increase in 5-HT1B, AT1, and ETB receptor protein levels in the smooth muscle cell layer of ischemic vessels (MCA and Mic.V) as compared to vehicle control. Treatment with U0126 starting at 6 h after MCAO prevented the increase in expression of 5-HT1B, AT1 and ETB receptors in smooth muscle cells of the MCA and Mic.V but not at 12 h. The ETA receptor is normally expressed fairly strong, and expression is not upregulated in ischemia. U0126 treatment did not change the expression of ETA receptor protein in the smooth muscle cell layer. There was no significant difference in expression of receptor protein levels in control brain tissue, in ischemic brain tissue, and tissue from animals treated with U0126. Data were obtained with confocal microscopy. Scale bar, 50 μm.