RESUMO
Rat behaviour in the open field and elevated plus-maze was analyzed in rats after intracysternal administration of 2.5, 25, 50 and 200 ng of insulin in 45 min, 24 hrs and on the 9th day after single injection. Dose-dependent changes in 45 min occurred in both behavioural tests: insulin in low doses (2.5 and 25 ng) increased probability of locomotion and investigative activity in open field, while insulin in high doses (50 and 200 ng) did not alter locomotor activity and showed tendency to weakening of the investigative behavior (especially in the dose of 50 ng). Tendency was found in 24 hrs to increase probability of investigative behavior in open field after injection of 25 ng of insulin, although on the 9th day after insulin administration this behaviour increased in all experimental groups for all used doses. Insulin in the doses 2.5 and 200 ng decreased anxiety in elevated plus-maze in 45 min during the first five min; the doses 2.5 and 25 ng at the second five min exerted the same effect. In 24 hrs, the anxiety level increased for the doses 50 and 200 ng, and there was a tendency for an increase in the doses 2.5 and 25 ng; anxiety was decreased on the 9th day for all used doses of insulin. Thus, single insulin administration induced weakness of non-associative memory in open field on the day 2 and day 9 as well as increase of anxiety level on the day 2 and decrease of anxiety level on the day 9 in elevated plus-maze.