NEUROMODULATORY EFFECTS OF OCTOPAMINE AGONISTS AT NEUROMUSCULAR-JUNCTIONS IN THE MEALWORM, TENEBRIO-MOLITOR L (COLEOPTERA, TENEBRIONIDAE)

The modulatory effects of biogenic amines related to octopamine were studied at the neuromuscular junctions of larvae of the mealworm, Tenebrio molitor. Intracellular recordings were made with glass microelectrodes from ventral longitudinal muscle fibers. Phenolamines (octopamine, synephrine) and catecholamines (noradrenaline, adrenaline) reversibly potentiated the amplitude of excitatory junctional potentials (EJPs), but gave no effect either in the resting membrane potentials or on the time constant of the decay phase of the EJPs. EJPs were potentiated to a greater extent by the phenolamines than by the catecholamines. Potentiation was antagonized by phentolamine. These results suggest some structural specificity in the insect octopaminergic system.