Effects of vigabatrin on spontaneous locomotor activity of rats

Effects of vigabatrin (saline, 125, 250 or 500 mg/kg i.p.) on spontaneous locomotor activity in Wistar rats were investigated. There was a dose dependent decrease in amount of locomotion for doses up to 250 mg/kg. This decrease was measurable 2-4 hours after injection and still became more pronounced in the following hours. The mean velocity during the movements 2-6 hours after injection remained intact and was higher in the 500 mg/kg group. In this high dose group an abnormal posture with a hunched back and pilo-erection was observed. The decrease of the amount of motor activity with the preservation of the mean velocity in this non-stimulating procedure, suggests that the level in which the experimental procedure imposes motor activity might be an important factor when measuring effects of vigabatrin. Postscript: Immediate post injection effects were observed, equivalent to those seen in the writhing test, a pain test using hyperosmolar saline injections. These observations stress the importance of controlling the osmolarity of the injection fluids.