Curare has a voltage-dependent blocking action on the glutamate synapse

Area of Science:

• Neuroscience
• Insect Physiology
• Molecular Biology

Background:

• Skeletal muscle innervation in insects like Orthoptera and Diptera is likely glutamatergic.
• Previous research suggests L-glutamate mimics transmitter action at insect neuromuscular junctions.
• Conflicting findings exist regarding acetylcholine antagonists blocking neurally evoked muscle potentials in insects.

Purpose of the Study:

• To analyze the action of curare on the neuromuscular junction of Tenebrio molitor larvae.
• To investigate the mechanism by which curare affects glutamatergic transmission in insect muscle.

Main Methods:

• Iontophoretic application of L-glutamate to ventral muscle fibres.
• Recording of extracellular excitatory postsynaptic potentials (e.p.s.ps).
• Analysis of curare's effect on neuromuscular transmission.

Main Results:

• L-glutamate application mimicked endogenous transmitter action, generating e.p.s.ps.
• Curare, a known acetylcholine antagonist, was found to suppress neurally evoked muscle potentials.
• Curare blocked glutamatergic transmission by acting as a postsynaptic antagonist.

Conclusions:

• Glutamatergic transmission is the primary mechanism for neuromuscular excitation in Tenebrio molitor larvae.
• Curare's action is postsynaptic antagonism of glutamate, not acetylcholine antagonism, at this junction.
• These findings clarify the role of curare and glutamate in insect neuromuscular signaling.