The effects of delta9-tetrahydrocannabinol on action potentials in the mollusc Aplysia

The effects of delta9-tetrahydrocannabinol (delta9-THC) on action potentials were examined during intrasomatic recordings from the isolated buccal and parieto-visceral ganglia of Aplysia californica. When added to the saline solution bathing the preparation, the compound (in concentrations 10(-4) - 10(-5) M) caused a reduction in spike overshoot (15-20% of total amplitude) and increased the lability of responses to electrical stimulation. The somatic membrane appeared to be more affected than the axonal membrane. Diffusion barriers in the ganglion probably account for the high degree of variability in drug response, such that both of the characteristic changes were observed in only about 30% of the tests. This is the first report to describe effects of delta9-THC on invertebrate neurones. The results indicate that delta9-THC causes a depression in nerve cell excitability, and these data are consistent with reported effects of THC compounds in mammals.