Effects of pre-exposure and coadministration of CP 55,940 on behavioural sensitization to cocaine in Lewis and Wistar rats

Chapters 2, 3 and 4 may help to explain why Lewis rats are the only rat strain so far tested to show a rewarding effect of ∆ 9-THC on MFB self-stimulation (Lepore et al., 1996a). The present chapter provides research on a behavioural assay of the addictive potential of cannabis. Furthermore, it provides an animal model of the "gateway hypothesis " , that is, the notion that prior exposure to cannabis increases an individual's vulnerability to using other drugs of abuse (Robinson & Berridge, 1993) (see section 1.7.). Sensitization of mesolimbic DA efflux during repeated intermittent exposure to drugs of abuse has been hypothesized to be a key neural adaptation underlying the development of pathological drug craving (Robinson & Berridge, 1993; Stewart & Badiani, 1993). The most widely used behavioural index of such sensitization is the progressively greater locomotor activity response elicited in rats and mice to repeated administration of drugs of abuse. As discussed in section 1.7., recent studies support the involvement of behavioural sensitization in increasing the drug-seeking behaviour 1999a,b). This is significant because associative learning of cues related to drug use is thought to be responsible for the cognitive and behavioural phenomena exhibited by drug abusers that are associated with drug craving and relapse (O'Brien, Childress,