Atropine increases pilocarpine-induced yawning behavior in paradoxical sleep deprived rats.

Paradoxical sleep (PS) deprivation has been suggested to induce supersensitivity of postsynaptic dopamine (DA) receptors and subsensitivity of acetylcholine (ACh) receptors. Yawning behavior is reduced after PS deprivation and is believed to result from an interaction between ACh and DA systems. Concomitant treatment of PS deprived animals with DA agonists reverses PS deprivation effects on stereotypy and aggressiveness. To examine this possibility on yawning behavior, rats were treated, during the deprivation period, with atropine, methamphetamine, haloperidol or distilled water. Following PS deprivation, rats were injected with apomorphine or pilocarpine and number of yawns was recorded. Atropine increased yawning of PS deprived rats induced by pilocarpine, but not by apomorphine. Treatment with methamphetamine and haloperidol did not change PS deprivation effect on pilocarpine- and apomorphine-induced yawning. The data suggest that reversal of PS deprivation-induced yawning inhibition is mediated distinctly by both acetylcholine and dopamine systems.