Effects of monoterpenoids on 36Cl- uptake of ventral nerve cords in the American cockroach

Monoterpenoids and their derivatives showed good insecticidal activities in the previous studies, but the mechanisms of their action as natural pesticides are not known yet. In this research, modulation effects on 36Cl- uptake of ventral nerve cords in the American Cockroach of five monoterpenoids (pulegone, thymol, carvacrol, alpha-terpineol, and linalool) were studied in order to understand the reason of the toxicity of these monoterpenoids pesticides. In these five monoterpenoids, thymol, carvacrol, and pulegone at concentrations of 500 µM and 1 mM increased the 36Cl- uptake induced by 1 µM GABA dramatically. The potentiation of the Cl- uptake can be inhibited by 10 µM picrotoxin, which is a specific inhibitor to the insect’s GABA receptor. The other two monoterpenoids, alpha-terpineol and linalool, showed no effects on the 36Cl- uptake induced by 1 µM GABA. The increasing of the 36Cl- uptake showed that thymol, carvacrol, and pulegone are all positive allosteric modulators for the American Cockroach’s GABA receptor.