Infusions of 6-hydroxydopamine into the nucleus accumbens abolish the analgesic effect of amphetamine but not of morphine in the formalin test.
The effects of bilateral infusions of 6-hydroxydopamine into the nucleus accumbens on analgesia produced by D-amphetamine and morphine were examined, in separate experiments, in the formalin test in rats. The lesions in the two experiments were not significantly different and dopamine in the nucleus accumbens, olfactory tubercle and striatum was depleted to 21.1%, 40.3% and 65.0% of control values, respectively. D-Amphetamine (0.75 and 2.0 mg/kg) and morphine (3.0 and 6.0 mg/kg) attenuated the response to formalin in unlesioned control rats. The analgesic effect of amphetamine was severely reduced by 6-hydroxydopamine lesions, and the residual analgesia was correlated with the amount of dopamine in the nucleus accumbens, but not with dopamine levels in the olfactory tubercle or striatum. Lesions also attenuated the locomotor stimulant effect of amphetamine. The analgesic effect of morphine was not altered by 6-hydroxydopamine infusions, nor was there any correlation between the analgesic effect of morphine and dopamine concentration in the nucleus accumbens, olfactory tubercle or striatum. The results indicate that the dopamine innervation of the nucleus accumbens is not critical for the analgesic effect of morphine but plays a major role in the analgesic effect of amphetamine.
Clarke
P B
PB
Department of Pharmacology and Therapeutics, McGill University, Montreal, Que., Canada.
Franklin
K B
KB
D000700:Analgesics / Q000037:antagonists & inhibitors*; D000818:Animals; D003913:Dextroamphetamine / Q000037:antagonists & inhibitors*; D004298:Dopamine / Q000502:physiology; D005557:Formaldehyde; D006892:Hydroxydopamines / Q000008:administration & dosage*; D007263:Infusions, Parenteral; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors*; D009043:Motor Activity / Q000187:drug effects; D009714:Nucleus Accumbens / Q000187:drug effects*; D010146:Pain / Q000188:drug therapy*; D051381:Rats
D000700:Analgesics; D006892:Hydroxydopamines; D005557:Formaldehyde; D009020:Morphine; D003913:Dextroamphetamine; D004298:Dopamine