Differential mechanisms in the acquisition and expression of heroin-induced place preference

✍ Scribed by Timothy H. Hand; Luis Stinus; Michel Moal

• Publisher: Springer
• Year: 1989
• Tongue: English
• Weight: 906 KB
• Volume: 98
• Category: Article
• ISSN: 0033-3158
• DOI: 10.1007/bf00442007

✦ Synopsis

These experiments examined the neurochemical mechanisms involved in the development and expression of place conditioning produced by heroin. Conditioned place preferences (CPP) lasting up to 8 weeks were obtained with doses of 50-1000 gg/kg heroin, using a regimen shown not to produce physical dependence. Naloxone pretreatment (50 gg/kg) during conditioning prevented the acquisition of heroin-induced CPP, but when given only on the test day, naloxone (50 or 1000 ~tg/kg) did not prevent the expression of heroin CPP. Clonidine disrupted the establishment of heroin CPP at 20 gg/kg, but disrupted its expression only at debilitating doses (100 and 200 lag/kg). Pimozide attenuated the acquisition (100 gg/kg) and expression (250 gg/kg) of heroin CPP. Together, these results support a role for opioid and catecholamine systems in the acquisition of heroin reinforcement, but they suggest that once heroin CPP is established, its expression in opiate-free subjects is not opiate receptor mediated and is relatively refractory to pharmacological treatments which disrupt acquisition. The data challenge the notion that the conditioned effects of opiates in drug-free animals are related to the release of endogenous opioids, and they also may help to explain why naloxone and clonidine are ineffective in the treatment of opiate addiction.