Δ⁹-Tetrahydrocannabinol and the hippocampus: Effects on CA1 field potentials in rats

The effects of Δ⁹-tetiahydrocannabinol (THC) on ortho- and antidromically elicited CA1 field potentials were observed in locally anesthetized rats and in rats anesthetized with urethane. THC augmented amplitudes of population EPSP's as well as orthodromic and antidromic population spikes from pyramidal cells in locally anesthetized animals. Latencies to peak amplitude of these responses were increased. Conditioning-test shock experiments revealed that THC also depressed recurrent inhibition probably mediated by basket cells. In animals under urethane anesthesia THC enhanced test responses, but failed to augment population responses to the conditioning stimulus. It was concluded that THC enhanced postsynaptic excitatory processes but attenuated recurrent inhibition. Urethane anesthesia completely blocked the postsynaptic excitatory effect of THC but had little apparent influence on THC's disinhibitory action.