Developmental changes in the glutamate receptor at the insect neuromuscular synapse

Developmental changes in the glutamate receptors were studied using insect (Tenebrio molitor) neuromuscular synapses. Bath-applied L-glutamate produced depolarization of the postsynaptic membrane of larva muscle, whereas in imago muscle L-glutamate produced both depolarization and hyperpolarization with conductance increase. Iontophoretically applied glutamate distinguished two types (depolarization and hyperpolarization) of receptors in the imago muscle. Quisqualic acid and ibotenic acid mimic depo- and hyper-type response by L-glutamate respectively. Kainic acid blocks the excitatory postsynaptic potentials in both larva and imago, with little effect on the resting conductance of the postsynaptic membrane. As the nerve terminal spike was abolished by kainate it is suggested that kainate mainly acts on the nerve terminal.