Differential effects of lysergic acid diethylamide, methysergide, and cyproheptadine on modality-specific and nonspecific sensory evoked potentials

Effects of intraocular mescaline and LSD on visual-evoked responses in the rat

The effects of mescaline and LSD on the flash-evoked cortical potential (FEP) were determined in unrestrained rats with chronically-implanted electrodes. Systemic administration of mescaline or LSD significantly attenuated the primary component of the FEP at three stimulus intensities with the greatest effect observed 60-90 minutes following drug administration. The magnitude and specificity of the effects of these agents on the primary response suggest that they produce deficits in conduction through the retino-geniculato-cortical system. The serotonin receptor antagonists, cyproheptadine and methysergide, antagonized the mescaline-induced depression of the FEP in accordance with neurochemical and behavioral evidence that mescaline acts as a partial agonist on serotonin receptors. Topical or intraocular administration of atropine antagonized the actions of systemically-administered mescaline. In addition, intraocular administration of mescaline or LSD attenuated the FEP indicative of an action of these hallucinogens on visual processing in the retina which is modulated by muscarinic receptor activity.

Inhibition of heterosensory thalamocortical evoked potentials by delta-9-tetrahydrocannabinol

The effects of delta-9-tetrahydrocannabinol on sensory activity in the thalamic intralaminar nuclei, centralis lateralis and the mesencephalic reticular formation were compared with the effects on cortical association or heterosensory systems in alpha-chloralose-anesthetized cats. The drug depressed the anterior marginal responses to multiple-modality sensory stimulation 30 min after administration of 2 mg/kg. Posterior suprasylvian responses were not significantly depressed except during 15 min postadministration. The drug did not depress sensory responses at the centralis lateralis or the mesencephalic reticular formation. Cortical responses evoked by stimulation of the latter were globally depressed by the drug. In contrast, delta-9-tetrahydrocannabinol depressed the anterior marginal response to centralis lateralis stimulation and not the posterior suprasylvian response similarly to the responses to sensory stimulation. The drug was without effect on caudate nucleus responses to stimulation of the mesencephalic reticular formation or centralis lateralis. These data demonstrate that, unlike pentobarbital, delta-9-tetrahydrocannabinol maintains heterosensory afferent activity to mesencephalic and thalamic sites and that its unique properties appear to be due, in part, to the selective disruption of heterosensory thalamocortical function.

Alteration of electrical correlates of sensory processing by tetrahydrocannabinol

The action of tetrahydrocannabinol on the function of four multimodality responsive neocortical areas was assessed in the cat. Cats, anesthetized with alpha-chloralose, were subjected to auditory, somatosensory, and two types of visual stimulation. Simultaneous evoked field potentials and multiple-unit activity were recorded. The drug produced a significant reduction in evoked field responses at the three most rostral cortical areas, whereas responses at the posterior suprasylvian gyrus were spared. There were no significant differences between sensory modalities. In addition to being the first pharmacological study to demonstrate differential drug sensitivity between these polysensory areas, these studies localized an effect of tetrahydrocannabinol. Sensory evoked multiple-unit activity showed a pattern of change after THC consistent with a reduction in activity of pyramidal output cells and a concomitant increase in interneuron activity. The action of tetrahydrocannabinol on polysensory systems is important in attention and orientation.