Examination of the Gateway Hypothesis in a Rat Model

The Gateway Hypothesis is based on epidemiological data and states there is a progression of drug use from use of a softer drug (e.g., nicotine) to use of a harder drug (e.g., morphine). It has been suggested that this sequence is causal and is relevant to drug prevention policies and programs. The present experiment used an animal model to investigate whether the Gateway Hypothesis involves a causal progression. The subjects were 16 female and 16 male Sprague Dawley rats with ages comparable to late adolescence/emerging adulthood in humans. Subjects received nicotine (6 mg/kg/day) or saline for 21 days subcutaneously via osmotic minipump and were subsequently allowed to self-administer morphine intravenously for 10 days. Results did not confirm the Gateway Hypothesis. In fact, rats pre-exposed to nicotine self-administered significantly less morphine than did rats pre-exposed to saline. These findings may be relevant to future drug use prevention policies and program