Associative and behavioral tolerance to the analgesic effects of nicotine in rats: tail-flick and paw-lick assays.

RATIONALE

Theories of drug tolerance differentiate between associative and behavioral (instrumental) drug tolerance. However, there is little research comparing these two forms of drug tolerance beyond alcohol and morphine.

OBJECTIVE

We examined the time course development of associative and behavioral tolerance to the analgesic effects of nicotine.

METHODS AND RESULTS

Associative tolerance was investigated by giving independent groups of rats one, five, 15, ten or 20 administrations of nicotine either explicitly paired or unpaired with a distinctive context. Associative tolerance, assessed in the tail flick, developed more rapidly and reached greater magnitude when nicotine and distinctive context were explicitly paired than when they were unpaired. This effect was evidenced after the fifth conditioning session and was maintained through the tenth, 15th, and 20th sessions. Contextual tolerance, assessed in the hot plate, was first evident after ten sessions. However, this effect disappeared safter 15 and 20 sessions. A second study examined the acquisition of behavioral tolerance to the disruptive effects of nicotine on the hot-plate response. Animals that practiced the test response while drugged developed greater tolerance than animals receiving as much nicotine and hot-plate practice but with these two conditions explicitly unpaired. This effect was evident in two different environments but did not generalize to the tail-flick test.

CONCLUSIONS

The findings suggest that contextual tolerance to drug effects is test specific, with tail-flick responses depending on cue-associative tolerance processes and hot-plate responses requiring procedures that allow the animal to practice the test response while drugged.