Separation of tolerance to the behavioral effects of LSD from changes in serotonin receptor binding in cats

Nearly complete tolerance to a test dose of 50 micrograms/kg of LSD occurred within 24 h following an initial dose of 50 micrograms/kg of the drug, using limb flicking and abortive grooming as as behavioral indices in the cat. No changes in serotonin receptor binding were observed at this time. However, chronic administration of LSD (50 micrograms/kg every 12 h for 6 days) produced a significant decrease in serotonin receptor binding in both the forebrain and brainstem plus spinal cord. These data suggest that the behavioral effects of LSD and tolerance to LSD as measured here are mediated predominantly by different sites.