Effects of delta 9-tetrahydrocannabinol on cat spinal motoneurons

The influence of delta 9-tetrahydrocannabinol (delta 9-THC) on cat spinal motoneurons was investigated with intracellular recording techniques in order to identify possible mechanisms of action of the drug's central excitatory and depressant properties. delta 9-THC increased the amplitude of the excitatory postsynaptic potentials (EPSPs) and decreased the amplitude of the inhibitory postsynaptic potentials (IPSPs); these excitatory effects do not appear to be the result of changes in the afferent input. However, an observed increase in membrane resistance may account for, or contribute to, the enhanced EPSPs. The cannabinoid also concomitantly caused depression, as evidenced by a rise in the firing threshold for the motoneuron action potential. The responses of the motoneuron to the drug suggest synaptic sites and mechanisms of action.