Ontogeny of the behavioral effects of lysergic acid diethylamide in cats

Hallucinogens recruit specific cortical 5-HT(2A) receptor-mediated signaling pathways to affect behavior

Hallucinogens, including mescaline, psilocybin, and lysergic acid diethylamide (LSD), profoundly affect perception, cognition, and mood. All known drugs of this class are 5-HT(2A) receptor (2AR) agonists, yet closely related 2AR agonists such as lisuride lack comparable psychoactive properties. Why only certain 2AR agonists are hallucinogens and which neural circuits mediate their effects are poorly understood. By genetically expressing 2AR only in cortex, we show that 2AR-regulated pathways on cortical neurons are sufficient to mediate the signaling pattern and behavioral response to hallucinogens. Hallucinogenic and nonhallucinogenic 2AR agonists both regulate signaling in the same 2AR-expressing cortical neurons. However, the signaling and behavioral responses to the hallucinogens are distinct. While lisuride and LSD both act at 2AR expressed by cortex neurons to regulate phospholipase C, LSD responses also involve pertussis toxin-sensitive heterotrimeric G(i/o) proteins and Src. These studies identify the long-elusive neural and signaling mechanisms responsible for the unique effects of hallucinogens.

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.