Effects of reserpine and p-chloroamphetamine on 5-HT metabolism and release in the cerebral ganglia of Inachis io (Lepidoptera).

There have been few pharmacological studies of serotonergic system dynamics in insects. A more precise knowledge of the response of serotonergic neurons to drugs will contribute to understanding of the role of this neurotransmitter in insect behaviour. The present work was carried out to study several aspects of serotonin (5-HT) metabolism and release in an insect, the butterfly Inachis io. The effects of a single intra-abdominal injection of reserpine (30 pg/insect) or p-chloroamphetamine (50 microg/insect) on cerebral ganglia 5-HT metabolism and release were studied. After reserpine injection a depletion of 5-HT stores concomitant with an increase in N-acetylserotonin levels was observed, but not significant alteration of extraneuronal 5-HT release was observed. Administration of p-chloroamphetamine (PCA) induced extraneuronal 5-HT release, together with inhibition of its reuptake. Finally, a single injection of p-chloroamphetamine in reserpine-treated insects was able to induce new release of 5-HT. Reserpine interferes with the vesicular storage of 5-HT, but does not affect the process of neuronal release, while PCA induces the synaptic release of 5-HT and inhibits its reuptake. These effects are similar to those observed in mammals.