Lewis (LEW) and Fischer (F344) inbred strains show several neurochemical and behavioral differences relevant for drug addiction. Thus LEW are more impulsive and have a lower D2 receptor binding in striatal areas than F344. The aim of this study was to evaluate the influence of early pre-exposure to Δ9-THC on heroin self-administration (SA) and reinstatement in adulthood. On the 6th postnatal (PN) week rats were administered twice a day with increasing doses of Δ9-THC (2,4,8 mg/kg, i.p.) for three consecutive days. In adulthood (10th PN week), LEW and F344 rats were trained to acquire heroin SA under Fixed Ratio (FR) schedule of responding. In Exp-I, after FR sessions rats underwent extinction and reinstatement phases, while in Exp-II, after acquisition, they were allowed to self-administer heroin under Progressive Ratio (PR) schedule. In both experiments LEW rats showed higher responding and faster acquisition of heroin self-administration as compared to F344 rats. Moreover, adolescent exposure of LEW rats to Δ9-THC resulted in a faster increase of responding when switching ratio schedule from FR-1 to FR-3 and FR-5, and greater responding on the active hole during reinstatement, compared to control LEW rats as well as to F344 (Exp-I). These results suggest that adolescent Δ9-THC pre-exposure differentially affects heroin reinforcement in adulthood in a strain-related way.
Influence of Δ9-THC exposure in Lewis and Fischer 344 adolescent rats on heroin self-administration in adulthood
SCIFO, ANDREA;LECCA, DANIELE;VALENTINI, VALENTINA;
2013-01-01
Abstract
Lewis (LEW) and Fischer (F344) inbred strains show several neurochemical and behavioral differences relevant for drug addiction. Thus LEW are more impulsive and have a lower D2 receptor binding in striatal areas than F344. The aim of this study was to evaluate the influence of early pre-exposure to Δ9-THC on heroin self-administration (SA) and reinstatement in adulthood. On the 6th postnatal (PN) week rats were administered twice a day with increasing doses of Δ9-THC (2,4,8 mg/kg, i.p.) for three consecutive days. In adulthood (10th PN week), LEW and F344 rats were trained to acquire heroin SA under Fixed Ratio (FR) schedule of responding. In Exp-I, after FR sessions rats underwent extinction and reinstatement phases, while in Exp-II, after acquisition, they were allowed to self-administer heroin under Progressive Ratio (PR) schedule. In both experiments LEW rats showed higher responding and faster acquisition of heroin self-administration as compared to F344 rats. Moreover, adolescent exposure of LEW rats to Δ9-THC resulted in a faster increase of responding when switching ratio schedule from FR-1 to FR-3 and FR-5, and greater responding on the active hole during reinstatement, compared to control LEW rats as well as to F344 (Exp-I). These results suggest that adolescent Δ9-THC pre-exposure differentially affects heroin reinforcement in adulthood in a strain-related way.
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