The effect of insulin on the central serotonergic system of the rat

Single administration of insulin (1-3 U/kg) caused an increased response of rats to 5-methoxytryptamine (head shakes), 4 but not 16 h after the injection. Multiple insulin injections caused a dose and time-related increase in the number of head shakes. The effect was observed up to 24 h after the last insulin dose. Insulin (2 U/kg given for 3-14 days) caused an increase in the cerebral concentration of 5-hydroxyindoleacetic acid (5-HIAA) and accelerated the cerebral serotonin (5-HT) turnover. The 5-HIAA concentration was approx. twice as high as in the controls, regardless of the duration of the treatment; the degree of 5-HT turnover acceleration did not depend on the duration of the treatment, either, and was observed up to 14 days after cessation of insulin administration.