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

Mescaline and LSD reduce the primary component of the flash-evoked cortical potential in rats, with the strongest effect 60-90 minutes after injection, suggesting impaired signal transmission through the visual pathway from retina to cortex. Serotonin receptor antagonists cyproheptadine and methysergide block mescaline's effect, supporting evidence that mescaline acts as a partial serotonin receptor agonist. Atropine, whether applied topically or injected into the eye, also blocks systemically administered mescaline. Direct injection of mescaline or LSD into the eye similarly attenuates the evoked potential, indicating these hallucinogens affect retinal visual processing through muscarinic receptor modulation.

Study at a glance

Abstract

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.