Samote, here is what I can find so for on the physical mechanism for tolerance to LSD:
Tolerance (defined as a decrease in responsiveness to a drug after repeated administration) to the behavioral effects of hallucinogens occurs in humans. At present, the precise mechanism of behavioral tolerance is unclear. In this study, we established a behavioral model of LSD tolerance and examined whether behavioral tolerance is related to altered serotonin receptor signaling. Rats were trained to discriminate 0.06 mg/kg LSD from saline in a two-lever drug discrimination paradigm. Two groups of animals were assigned to either chronic saline treatment or chronic LSD treatment. For chronic treatment, rats were injected s.c. once per day with either 130 g/kg LSD or saline for 5 days. Rats were tested on either saline or 0.06 mg/kg LSD, 24 hrs after the last chronic injection. Following chronic LSD treatment, the choice behavior of animals tested on LSD was reduced from 85% to 51% while no differences were found between the two groups tested on vehicle. In another group of rats receiving the identical chronic LSD paradigm, LSD (5 nM) stimulated [35S]GTPS binding, an index of G-protein coupling, was measured in rat brain by autoradiography. After chronic LSD, a significant reduction in LSD stimulated [35S]GTPS binding was observed in the medial prefrontal cortex (vehicle-treated; 81% above basal vs. LSD-treated; 40% above basal). These results indicate that adaptive changes in LSD stimulated serotonin receptor signaling may mediate behavioral tolerance to LSD.
http://sfn.scholarone.com/itin2003/...=126&abstract_id=13904&p_num=576.14&is_tech=0
Tolerance (defined as a decrease in responsiveness to a drug after repeated administration) to the behavioral effects of hallucinogens occurs in humans. At present, the precise mechanism of behavioral tolerance is unclear. In this study, we established a behavioral model of LSD tolerance and examined whether behavioral tolerance is related to altered serotonin receptor signaling. Rats were trained to discriminate 0.06 mg/kg LSD from saline in a two-lever drug discrimination paradigm. Two groups of animals were assigned to either chronic saline treatment or chronic LSD treatment. For chronic treatment, rats were injected s.c. once per day with either 130 g/kg LSD or saline for 5 days. Rats were tested on either saline or 0.06 mg/kg LSD, 24 hrs after the last chronic injection. Following chronic LSD treatment, the choice behavior of animals tested on LSD was reduced from 85% to 51% while no differences were found between the two groups tested on vehicle. In another group of rats receiving the identical chronic LSD paradigm, LSD (5 nM) stimulated [35S]GTPS binding, an index of G-protein coupling, was measured in rat brain by autoradiography. After chronic LSD, a significant reduction in LSD stimulated [35S]GTPS binding was observed in the medial prefrontal cortex (vehicle-treated; 81% above basal vs. LSD-treated; 40% above basal). These results indicate that adaptive changes in LSD stimulated serotonin receptor signaling may mediate behavioral tolerance to LSD.
http://sfn.scholarone.com/itin2003/...=126&abstract_id=13904&p_num=576.14&is_tech=0