DIFFERENTIAL CHANGES IN SEROTONIN METABOLISM IN DIFFERENT BRAIN-REGIONS OF STREPTOZOTOCIN-DIABETIC RATS

Changes in serotonin metabolism were investigated in streptozotocin-in duced diabetic rats and in insulin-treated diabetic rats. Four weeks a fter streptozotocin injection, total tryptophan levels in serum were d iminished and free tryptophan, valine, isoleucine, leucine and non-ste rified fatty acids were increased. Tryptophan levels were diminished i n the midbrain and medulla pens, and serotonin levels were diminished in the above regions, cortex and hippocampus. The synthesis rate of se rotonin and 5-hydroxyindoleacetic acid decreased in midbrain, medulla pens and cortex, while only serotonin synthesis was decreased in hippo campus. Tryptophan hydroxylase activity was increased in the midbrain and medulla pens. Monoamine oxidase activity and elimination rate of 5 -hydroxyindoleacetic acid were unchanged in both control and diabetic rats. In general, the effects elicited by streptozotocin-diabetes were well reversed by insulin administration. We have found evidence that experimental diabetes produced differential regional inhibition in the serotoninergic system dynamics. Moreover, this decrease in the seroto ninergic metabolism and utilization may be originated by two causes: a substratum-dependent one, of peripheral origin, which would affect th e neuronal somas, and a substratum-independent one, which would mainly affect the synaptic terminals.