Nicotine attenuates place aversion induced by naloxone in single-dose, morphine-treated rats.

RATIONALE

Acute physical dependence refers to the withdrawal syndrome precipitated by an opioid antagonist administered several hours after either a single dose or a short-term infusion of an opioid agonist.

OBJECTIVES

We examined the mechanism of nicotine-induced attenuation of naloxone-precipitated withdrawal syndrome when used to produce an aversive motivational state in a place-conditioning paradigm.

METHODS

The effect of nicotine was investigated through place aversion induced by naloxone in morphine-pretreated rats. Additionally, the mechanism of nicotine action in this model was explored specifically in relation to the dopaminergic system through the use of dopamine receptor antagonist and agonist.

RESULTS

Place avoidance behavior was potently elicited by naloxone (0.5 mg/kg s.c.) 24 h after a single exposure to morphine (10 mg/kg s.c.). Avoidance behavior was attenuated by pretreatment with a 0.2-mg/kg dose of nicotine 15 min prior to naloxone administration. The effect of nicotine was completely blocked by mecamylamine, but not hexamethonium. The dopamine receptor antagonists haloperidol (0.05, 0.1 mg/kg, s.c.), SCH23390 (0.1 mg/kg, s.c.), raclopride (1.0 mg/kg, s.c.) and eticlopride (0.1 mg/kg, s.c.) showed effects similar to mecamylamine. Additionally, the dopamine receptor agonist apomorphine (0.03, 0.1, 0.3 mg/kg, s.c.) inhibited naloxone-induced place aversion in morphine-treated rats.

CONCLUSION

The inhibitory effect of nicotine on place aversion induced by naloxone-precipitated morphine withdrawal may involve a dopaminergic portion of the central nervous system.