SYSTEMIC ADMINISTRATION OF ATIPAMEZOLE, AN ALPHA(2)-ANTAGONIST, CAN REDUCE SCOPOLAMINE-INDUCED HYPERACTIVITY IN RATS

The present study investigated whether an alpha(2)-adrenoceptor antago nist (atipamezole) can influence hyperactivity induced by the systemic administration of scopolamine. In the water maze (WM) task, scopolami ne (scop) 0.25 mg/kg treatment significantly increased swimming speed during the acquisition phase of this task. Atipamezole (ati) 30 mu g/k g slightly reduced swimming speed both in saline-and in scop-treated r ats. Ati 300 mu g/kg slightly reduced swimming speed in saline-treated rats, and it prevented the scop-induced increase in swimming speed, b ecause ati300-scop treated rats swam more slowly than the saline-salin e group. In addition, ati 300 mu g/kg reduced the total distance swum in scop-treated rats during a free swim trial (the platform was remove d from the pool) performed 1 day after the acquisition phase of the WM test, even though it did not affect this parameter when administered alone. In the open arena task, which assessed the ambulation of rats w hen the pool was covered with a solid floor, scopolamine dose-dependen tly increased locomotor activity. The rats ambulated more when treated with scop 0.50 mg/kg compared to vehicle treatment, whereas the effec t of scop 0.25 mg/kg treatment did not reach significance. In a test i nvestigating the effects of ati 300 mu g/kg and scop 0.50 mg/kg given singly or combined, the rats ambulated more during both ati 300 mu g/k g and scop 0.50 mg/kg treatments given alone, but when combined, the r ats ambulated less than during scop-saline treatment even though this was more than during control (saline-saline) treatment. These results indicate that the systemic administration of an alpha(2)-antagonist ca n reduce hyperactivity induced by scopolamine.