Effects of cocaine on neuromuscular transmission in the lobster

In vitro electrophysiological techniques were used on an excitatory neuromuscular junction of a walking-limb stretcher muscle of the lobster in order to define the pharmacology of cocaine on a glutamatergic synapse. Cocaine reduced the amplitudes of the excitatory and the miniature junction potentials, as well as the mean quantum content of the muscle fiber. The effect on mean quantum content points to a presynaptic site of action of the drug, and the effect on miniature junctional potential suggests a postsynaptic site of action of the drug. In addition, cocaine shifted the concentration-depolarization curve for glutamate to the right, demonstrating a postsynaptic depression of the response to glutamate. Cocaine exerted no effect on the resting membrane potential or the effective membrane resistance of the muscle fibers. The data indicate that the drug concomitantly exerted pre- and postsynaptic depression of a glutamatergic junction.