Effects of ethanol and nicotine coadministration on probability discounting in rats

Ethanol and nicotine are among the most widely used drugs in the USA, and their combined use is associated with increased health risks. This study aimed to investigate the acute effects of ethanol alone and in combination with nicotine on risky choice in rats using a probability-discounting task. Sprague-Dawley rats chose between a smaller, certain reinforcer (one food pellet) and a larger, probabilistic reinforcer (two food pellets). In Experiment 1, effects of acute ethanol administration were assessed. In Experiment 2, acute nicotine was administered either alone or in combination with ethanol. Ethanol was delivered via oral 'Jell-O shots' and nicotine was delivered via subcutaneous injection. Ethanol (2.0 g/kg) and nicotine (0.3 mg/kg) each increased risky choice compared with vehicle controls. The highest combined dose of ethanol (2.0 g/kg) and nicotine (1.0 mg/kg) further increased risky choice compared with the same ethanol dose paired with a lower nicotine dose (0.3 mg/kg), although there was no evidence that the combination increased risky choice beyond either drug alone. These findings highlight drug interactions that may contribute to heightened risk-taking behaviors associated with comorbid use. Future studies should explore the influence of ethanol dose, concentration, vehicle, and administration route on risky choice to further characterize these effects. This study underscores the need for basic investigations to inform interventions targeting the combined use of ethanol and nicotine.