| Summary: | Rationale. Nicotine is often considered a ‘gateway’ drug because people typically experiment with tobacco before illicit drugs such as cocaine and amphetamine. We have shown that nicotine increases approach to reward-associated stimuli, this is referred to as ‘sign-tracking’, and that this effect persists after nicotine is discontinued. Individuals who are high in sign-tracking also show increased cocaine self-administration.
Objectives. The goal of this experiment was to determine whether nicotine enhanced sign tracking could result in greater cocaine self-administration.
Method. Rats were randomly assigned to one of 2 groups (NIC or SAL), and injected with their assigned solution (0.4 mg/kg base or placebo, respectively) 15 min before conditioning sessions. During conditioning sessions, a lever/light stimulus was inserted into the chamber for 15 s and immediately followed by sucrose delivery. Approach to the sucrose receptacle was recorded by monitoring head entries and defined as goal tracking. Contact with the lever was recorded and defined as ‘sign-tracking’. After 29 conditioning sessions, the rats were instrumented for cocaine self-administration and were shaped to respond for cocaine on the same lever that served as the CS. After 10 days of acquisition of cocaine self-administration (0.16 mg/inf), demand for cocaine was tested over 6 days using a within session procedure that increased cocaine price every 10 min.
Results. We showed increased sign-tracking, but not goal tracking in the NIC group relative to the SAL group. The NIC group also showed increased demand for cocaine during the price manipulation, but the essential value of cocaine did not differ, relative to the SAL group.
Conclusion. Our results support a gateway interpretation of substance use – when both the gateway drug (nicotine) and drug-associated rewards (the lever/light) occur together, they can promote future self-administration of illicit drugs such as cocaine.
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