Effect of delta 9-tetrahydrocannabinol on synaptic transmission in the electric eel electroplaque.

When the innervated membrane of the electric eel electroplaque is exposed to concentrations of delta 9-tetracannabinol of 50 to 100 microM synaptic transmission is blocked in approximately 30 minutes. During the block, the chemosensitivity of the innervated membrane to cholinergic agonists remains unaltered. Direct stimulation of the innervated membrane after synaptic transmission had failed did not elicit any postsynaptic membrane action potentials. The passing of hyperpolarizing currents across the electroplaque caused the nerve terminals which innervate the electroplaque to produce subthreshold potentials which resemble endplate potentials with a prolonged falling phase. With further incubation in the tetrahydrocannabinol solution the subthreshold potentials decreased in size and eventually disappeared. These results indicate that delta 9-tetrahydrocannabinol does not affect the acetylcholine-mediated membrane permeability changes, but instead, reduces the excitability of nonsynaptic membrane of both the pre- and postsynaptic elements.