Pavlovian inhibitory conditioning and tolerance-reversal to scopolamine-induced adipsia in rats.

In the present experiment the effect of a conditioned inhibitory stimulus on tolerance to scopolamine-induced adipsia was evaluated. Long-Evans rats were injected with 0.6 mg/kg scopolamine bromidrate in the presence of a tone or a noise, and physiological saline with a compound tone-odor. A summation test with the compound stimulus noise-odor showed a tolerance reversal effect to scopolamine adipsic effects in tolerant subjects. This reduction of tolerance was similar to adipsia produced by the first scopolamine administration, only when the odor stimulus was present. However, the inhibitory stimulus alone has no effect upon water intake. Results confirmed that a Pavlovian conditioned inhibition procedure can reduce conditioned tolerance to a drug.