ABSTRACT
Methamphetamine (METH) addicts lose control over drug consumption despite suffering multiple adverse medicolegal consequences. To mimic the negative events associated with drug addiction in humans, we recently introduced a rat model of self-administration (SA) with response-contingent punishment on METH intake. These procedures allowed us to distinguish between two addiction-like phenotypes in rats, those that sustained METH taking despite negative consequences (shock-resistant, SR) and rats that significantly reduced their METH intake (shock-sensitive, SS). Here, we further developed our adverse consequence model and examined incubation of METH craving by measuring cue-induced drug seeking in SR and SS rats. Male Sprague-Dawley rats were trained to self-administer METH (0.1mg/kg/injection) or saline intravenously (i.v.) during twenty-two 9-h sessions that consisted of 3 separate 3-h sessions separated by 30min. Subsequently, rats were subjected to incremental footshocks during thirteen additional 9-h METH SA sessions performed in a fashion identical to the training phase. Cue-induced drug craving was then assessed at 2 and 21days after the footshock phase. All rats escalated their intake of METH, with both phenotypes showing similar drug taking patterns during SA training. In addition, rats that continued their METH intake despite negative consequences showed even greater cue-induced drug craving following withdrawal than the rats that reduced METH intake following negative consequences. Taken together, our adverse consequence-based model highlights the possibility of identifying rats by addiction-like phenotypes and subsequent vulnerability to relapse-like behaviors. The use of similar SA models should help in the development of better therapeutic approaches to treat different stages of METH addiction.
