ABSTRACT
Self-administration and intracranial self-stimulation — obviously associated with feelings of pleasure — have been widely used to determine the motivational effects of drugs of abuse (Wise and Bozarth, 1982; Bozarth, 1987). These operant techniques measure the primary reinforcing processes by means of specific behavioral tasks such as lever-pressing. In the behavioral experiments discussed in the present article, the drug-induced motivational effects were assessed by place conditioning, a technique which measures the secondary reinforcing effects of drugs. In this procedure, the association that develops between the presentation of a drug and a previously neutral stimulus (e.g. differently colored compartments of a shuttle box) is evaluated. The results obtained with this paradigm for rewarding drugs are largely identical to those obtained with the self-administration paradigm technique (Spyraki, 1988; Carr, Fibinger, and Phillips, 1989). Besides the evaluation of rewarding properties, the place conditioning procedure also allows the detection of aversive (negatively reinforcing) properties of drugs, which is of particular importance when investigating the effects of opioids; a further advantage is that it uses drug-naive rats. In parallel to the conditioned behavior, the neurochemical events underlying opioid effects by means of in vivo microdialysis were studied, thus allowing the immediate correlation between behavioral and biochemical parameters.
