Transient middle cerebral artery occlusion prevents habit formation in C57Bl/6J mice

Surgery.On D0, 27 eight weeks old male C57/Bl6J mice underwent 30-min MCAO or sham surgery. MCAO (n=11) was induced by inserting a 0.21 mm thick silicon-coated monofilament into the right common carotid artery, under 2% isoflurane anesthesia. Sham mice underwent the same procedure without filament insertion (n=16). Rotarod. In the rotarod test, mice had to stay on an accelerated rotating rod (4 to 40 rpm). Performance was averaged over three trials on D-7 (pre-surgery baseline) and on D+21. Vertical pole test. For this test, mice were place head upward on a vertical wooden pole. Both the time to turn (t-turn) and the time to reach the floor (t-total) were recorded over three trials on D-6 (pre-surgery baseline) and on D+22. Amphetamine-induced rotation. On D+25, mice were injected with damphetamine(5 mg/kg i.p.). Twenty minutes later, they were placed in a 50 x 50 cm white arena. 360° rotation behaviors were analyzed with a videotracking software (Viewpoint). Serial Order Learning. After acquisition of the operant response, food-deprived mice underwent 12 sessions of SOL in operant boxes equipped with two levers and a food-tray (Meds-Associates). At each trials, both right and left levers were available. Only the left – right lever-presses sequences were reinforced by a food reward (20 mg Noyes pellet). Other sequences were not reinforced. An 8 s inter-trial interval separated two trials. Sessions stopped once 40 rewards have been delivered or after an hour, whichever came first. Anti-NeuN immunohistochemistry. 50 μm thick brain sections were incubated overnight in primary mouse-antiNeuN IgG (Chemicon), then in secondary Horse-Anti-Mouse Biotinylated IgG (Chemicon). 3,3’-diaminobenzidine (Sigma) was used as a chromogen. Infarct volume was then calculated by multiplying the average of two successive infarct areas by the distance between them. Results