Monoamine levels in the brain of adult male grasshoppers and cockroaches and their modification by pyrethroid insecticides

High-performance liquid chromatography with electrochemical detection was used to measure 5-hydroxytryptamine and dopamine levels in the cerebral ganglia of grasshoppers ( Melanoplus sanguinipes) and cockroaches ( Periplaneta americana) exposed to pyrethroid insecticides. The synthetic pyrethroid, deltamethrin, caused an increase in dopamine concentration in both grasshoppers and cockroaches and 5-hydroxytryptamine concentrations in cockroaches. These increases were observed at low doses where uncoordinated movement rather than rapid prostration was observed. The pyrethroid permethrin had no effect on amine levels in the grasshopper. In addition, amine levels in the grasshopper appear to be dependent on the age of the adult, with higher levels found in older animals. The 5-hydroxytryptamine metabolites N-acetyl-5-hydroxytryptamine and 5-hydroxyindoleacetic acid were not detected.