Effects of urinary pH on the behavioral responses of squirrel monkeys to nicotine

The present study evaluated the behavioral effects of nicotine under conditions that manipulated urinary pH. The effects of nicotine were examined on the responding of squirrel monkeys under a multiple fixed-interval, fixed-ratio schedule of stimulus-shock termination when nicotine was administered alone or together with the gastric administration of an acidifier (ammonium chloride) or an alkalinizer (sodium bicarbonate). Responding under the FI schedule was increased markedly across a range of doses of nicotine (0.02-0.20 mg/kg). Responding under the FR was increased to a lesser extent by the lower doses of nicotine (0.02-0.05 mg/kg) and was decreased by doses of nicotine that increased responding under the FI (0.10-0.20 mg/kg). Generally, administration of the acidifier attenuated the effects of nicotine while administration of the alkalinizer potentiated those effects. These findings support the argument that changes in cigarette smoking under conditions that alter urinary pH involve nicotine per se. In addition, a new interpretation of the relationship between urinary pH and cigarette smoking is offered.