Associative tolerance to nicotine's analgesic effects: studies on number of conditioning trials and corticosterone



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Texas A&M University


This study examined the number of conditioning trials necessary to produce associative nicotine tolerance and the changes in corticosterone levels during the procedures. Six independent groups of rats (N = 355) were run through tolerance acquisition procedures for 1, 5, or 10 conditioning sessions. Treatment groups were comprised of animals that received nicotine-environment pairings, animals that received nicotine explicitly unpaired with the drug administration environment, and control groups that received either saline throughout or no treatment. Three of the groups were tested for nicotine-induced analgesia using the tail-flick and hot-plate assays, and three groups were blood sampled after either nicotine or saline injection. Pairing of environment with nicotine produced greater tolerance for rats after 5 conditioning sessions in the tail flick and after 10 conditioning sessions in the hot-plate. Corticosterone levels were elevated in all rats given nicotine. Rats that received the nicotine-environment pairing showed a conditioned release of corticosterone in response the environment after both 5 and 10 conditioning sessions.