The effects of lysergic acid diethylamide and mescaline-derived hallucinogens on sensory-integrative function: tactile startle.

In male Sprague-Dawley rats, hallucinogens and other psychoactive drugs were tested for their effects on the tactile startle response to air-puff stimuli. Phenylethylamine-derived compounds such as mescaline increased startle magnitudes throughout the session, suggesting increased reactivity. Indoleamine hallucinogens like LSD did not increase startle responding. LSD did increase the response to the first stimulus with more intense air-puffs and impaired habituation when the number of stimuli increased: control rats' responses decreased by 70% across the session, while LSD-treated rats' responses decreased by only 32%. These results suggest that LSD and phenylethylamine-derived hallucinogens differ in their effects on tactile startle.

Study at a glance

Abstract

Tactile startle responding by male Sprague-Dawley rats given 60 presentations of air-puff stimuli (37.5 psi) was measured after the intraperitoneal administration of graded doses of hallucinogens and other psychoactive drugs. Among the drugs tested were the indoleamine-derived compounds, lysergic acid diethylamide (LSD), N,N-dimethyltryptamine and psilocin, and the phenylethylamine-derived compounds, mescaline, 2,5-dimethoxy-4-methylamphetamine and a series of active and inactive congeners of 2,5-dimethoxy-4-methylamphetamine. All of the active phenylethylamines increased startle response magnitudes throughout the test session. This pattern of augmented startle suggests that these drugs increase reactivity. However, none of the indoleamine hallucinogens increased startle responding. Of the nonhallucinogenic drugs tested, only apomorphine increased startle responding, while clonidine significantly decreased it, and amphetamine, chlorimipramine, scopolamine and methysergide had no effect. In additional studies with LSD, it was found that LSD increased the response to only the first stimulus when more intense air-puffs were used (50 psi). Furthermore, when the number of stimuli was increased from 60 to 240 (1 hr) so that appreciable habituation was evident in controls, LSD impaired this habituation. Whereas the response magnitudes of the control group decreased by 70% across the session, the responses of LSD-treated rats decreased by only 32%. These results suggest that LSD and phenylethylamine-derived hallucinogens may differ in their effects on tactile startle responding.