Pergamon Pharmacology Biochemistry and Behavior, Vol. 52, No. 3, pp. 485-488, 1995 Copyright 0 1995 Elsevier Science Inc. Printed in the USA. All rights reserved 0091-3057/95 $9.50 + .oo 0091-3057(95)ooo35-6 Atropine Increases Pilocarpine-Induced Yawning Behavior in Paradoxical Sleep Deprived Rats LETiCIA L. LOBO, ROBERTA DE MEDEIROS, DI?BORA C. HIPdLIDE AND SERGIO TUFIK’ Department of Psychobiology, Escola Paulista de Medicina, Rua Botucatti 862, 1 andar, Stio Paula, SP 04023-062, Brasil Received 16 June 1994 LOBO, L. L., R. DE MEDEIROS, D. C. HIPdLIDE AND S. TUFIK. Afropine increases pilocarpine-induced yuwn- ing behavior in paradoxical sleep deprived ruts. PHARMACOL BIOCHEM BEHAV 52(3) 485-488, 1995. -Paradoxical sleep (PS) deprivation has been suggested to induce supersensitivity of postsynaptic dopamine (DA) receptors and subsensitiv- ity 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. Paradoxical sleep deprivation Apomorphine Rats Yawning Atropine Methamphetamine Haloperidol Pilocarpine THE FUNCTIONAL significance of yawning is still un- known, although this behavior has been studied for the last 3 to 4 decades. Yawning can be elicited by several cholinergic (AChergic) agonists (28,32), by low doses of dopaminergic (DAergic) agonists (1 l), and by polypeptides such as o-MSH and ACTH (2,10,33). Moreover, Cower et al. (4) showed that serotonin, histamine, and noradrenaline systems play a role in modulating this behavior. Yawning has been suggested to result from a balance be- tween DAergic and AChergic systems. This conclusion is based on a study by Yamada and Furukawa (32), who showed that scopolamine, a cholinoceptor antagonist, inhibits apo- morphine-, pilocarpine-, and physostigmine-induced yawning. The neuroleptic fluphenazine, however, does not modify pilo- carpine-induced, but increases the number of physostigmine- induced yawning. In addition, sulpiride, a D, dopamine (DA) receptor blocker, inhibits apomorphine-induced, but not phy- sostigmine-induced yawning (4). Thus, yawning appears to be mediated by inhibition of DAergic system and activation of AChergic system. Paradoxical sleep (PS) deprivation induces several changes on human’s and rat’s behavior, such as increased apomor- phine-induced stereotypy and aggressive behavior in rats (26), and improvement of endogenous depression symptoms in hu- mans (9,17,23,31). It is proposed that these effects are a conse- quence of postsynaptic DA receptors supersensitivity (26), and presynaptic DA receptors and postsynaptic acetylcholine (ACh) receptors subsensitivity (27). PS deprivation also inhib- its yawning elicited by apomorphine, physostigmine, and pilo- carpine (27). Haracz and Tseng (6) showed that DA receptor supersensi- tivity resulting from neuroleptic treatment is attenuated by an acute dose of amphetamine. In addition, treatment of PS deprived animals with amphetamine and L-dopa results in re- ’ To whom requests for reprints should be addressed. E-mail: stufik.psic@epm.br 485