The effects of L-glutamic acid, glutamate agonists, acetylcholine and several drugs of excitatory post-synaptic potentials at the neuromuscular junction of the larval mealworm, Tenebrio molitor Linne (Coleoptera: Tenebrionidae)

The effects of L-glutamic acid, quisqualic acid, L-aspartic acid, acetylcholine, curare, atropine, chlordimeform, nereistoxin, fenitrothion and fenitroxon on EPSP at the neuromuscular junction of the larval mealworm, Tenebrio molitor, were studied using a microelectrode technique. Applications of L-glutamic acid, quisqualic acid and L-aspartic acid suppressed 50% of EPSP at concentrations of 4.2×10-5 M, 2.3×10-5 M and 1.2×10-3 M and evoked a depolarization of muscle membrane with this EPSP reduction. However, acetylcholine at 2×10-3 M did not suppress EPSP but evoked a depolarization of the muscle membrane. Atropine, curare, nereistoxin and chlordimeform at a concentration of about 2×10-3 M suppressed 50% of EPSP. From a pharmacological aspect these results suggest that L-glutamic acid is an excitatory transmitter at the insect neuromuscular junction, because L-glutamic acid and quisqualic acid, its agonist, revealed the effect at forty and eight-fold lower concentrations than other drugs, respectively.