Effects of intracisternal administration of insulin on the time dynamics of behavior in rats

The effects of intracisternal administration of insulin at doses of 2.5, 25, 50, and 200 ng on the behavior of rats in an open field test and elevated plus maze were studied at 45 min, 24 h, and nine days after single doses. On day 1, doses of 2.5 and 25 ng increased the probability of orientational-investigative behavior and locomotion in the open field, while doses of 50 and 200 ng, conversely, produced some tendency to decreases in investigative behavior (mainly at the dose of 50 ng). On day 2 after dosage with insulin, the tendency to increased investigative activity persisted only in rats given a dose of 25 ng of insulin, while on day 9 this was increased in all experimental animals independently of the insulin dose given. In the elevated plus maze, insulin doses of 2.5 and 200 ng decreased anxiety in rats during the first 5 min of testing on day one, while doses of 2.5 and 25 ng reduced anxiety in the second 5 min. On day 2, the level of anxiety increased (at doses of 50 and 200 ng) or tended to increase (at doses of 2.5 and 25 ng); on day 9, anxiety decreased in all experimental rats. Studies of the time dynamics of the behavior of rats showed that single doses of insulin had aftereffects in CNS structures, consisting of weakening of non-associative memory in the open field test on days 2 and 9 and increases in anxiety in the elevated plus maze on day 2, followed by weakening of anxiety on day 9.