Resistance of morphine-seeking behaviour in rats to pharmacological and behavioural ‘treatments’

Abstract

OPIATE addicts may be treated by the controlled prescription of an opioid drug such as methadone^1,2; such ‘replacement’ therapy aims to meet the addict's need for his drug and so to reduce self-administration. Treatment with antagonists is an alternative; this treatment is designed to diminish the efficacy of any self-administered opiate by ‘blockading’ the receptors with substances such as naloxone or naltrexone³. A third method of treatment involves behavioural aversion procedures, which aim to suppress the actions culminating in drug-taking by associating them with unpleasant stimuli, such as electric shocks or apomorphine-induced nausea. It is extremely difficult to assess the efficacy of these methods in human addicts, and laboratory tests in dependent animals offer one means of comparision. We describe here tests of three conceptually different procedures, each reflecting one of the approaches described above. The dependence behaviour was oral self-administration of morphine solutions (morphine HCl 0.5 mg ml⁻¹) by rats which had previously learned to drink such solutions in preference to water⁴.