mise à jour du
18 juillet 2002
Prog Neuro-Psychopharmacol & Biol Psychiatr
1987; 11; 223-228
Yawning: an evolutionary perspective
 A simple method for the study of yawning in man
induced by the dopamine receptor agonist, apomorphine
Samarthji Lal, A Grassino, J Thavundayil, B Dubrovsky
Douglas Hospital Research Center; Department of Psychiatry, Montreal General Hospital and Allan Memorial lnstitutt, McGill University, Quebec, Canada
A trial of subcutaneously injected apomorphine for parkinsonian
Introduction : Apomorphine (Apo), a dopamine (DA) receptor agonist in animals and man, induces yawning in both rats and humans. In rodenu the response is blocked by both typical and atypical neuroleptics which points to the involvement of DA receptors. Dose-responst curves vith Apo show a bell shaped form with induction of yawning with low doses and absence vith large doses. These findings, together with other evidence, are compatible with the view that Apo-induced yawning is mediated by stimulating DA autoreceptors and that yawning behaviour mediated by DA agouists may provide an index of central DA autoreceptor function. Whereas a large body of literature has accumulated on Apo-induced yawning in animals. Such information that is available consists of incidental observations and subjective impressions. The lack of systematic studies on Apo-induced yawing in humans is probably the consequence of the lack of a simple technique for the objective measurement of this phenomenon.
In the present paper we describe a simple, reliable and accurate method for the recording and measurement of Apo-induced yawning behaviour in man.
Methods : A pair of linearlized magnetometers was used to measure displacement of the lower jaw by attaching one sensor to the forehead below the hairline and a second sensor under the chin. The magnetometers consist of two separate wire coils about 1 cm long and 0.5 cm in diameter mounted on a flat hard plastic base. A double sticky tape vas used to fix the base to the skin. One of the coils generates a magnetic field. The second coil by moving in and out of the field (follwing the movements of the jaw) generates a current which in proportional to the distance between both coils. The output of the magnetometers was fed into a DC amplifier and displayed on a strip chart recorder. Upward deflections indicate jaw opening. Jaw opening associated with yawning could be readily identified. Other jaw movements caused by swalloving or coughing are associated with smaller, short-lived deflections. Breathing movements do not interfere vith. jaw opening. Apo HCl (0.5 mg,-sc) was administered to five healthy normal subjects aged 18-47 (3 men; 2 women) on no medication. Yawning was monitored for 15 minutes before and 60 minutes after Apo administration. Wo of the subjects also received saline placebo. The volunteers remained recumbent in the supine position throughout the recording and were asked to refrain from talking. Subjects were observed throughout the sessions and yawning and other movements of the mouth (swalloving, coughing) noted and correlated with deflections produced on the strip charts.
A complete yawn, which might consist of one or several sequential inspiratory movements, was defined as the interval between mouth opening and closure of the mouth. The tracings vere evalusted by two independent raters. The number of yawns and total yawning time was calculated. Concordance between observed yawns and recorded yawns vas assessed.
Results : Apo induced yawning in each of the five subjects. Reither subject recelving placebo yawned. Each yawn corresponded vith a major deflection on the tracing at the commencement of yawning and a return to, baseline et the end. Each subject showed 'a characteristic tracing in which individuel yawns could be easily identified by independent evaluators. Artifacte due to swallowing, coughing or talking vere readily distinguished. The number of yawn and total yawning time could easily be calculated. There was a complets concordance between the raters for the number of yawns documented on the tracing. These numbers showed complete concordance vith the number of directly observed yawns. Preliminary observations showed thât yawning ceased if sleep vas induced. The two women showed a considerably grester number of yawns and total yawning time than the three men.
Discussion : There is little information on spontaneous yawing in man. Whether a DA mechanism subserves spontaneous yawning is unknown. It is of interest that spontaneous yawning in believed to be rare in schizophrenia and Parkinson'a disease whereas there is a propensity for yawning in Huntington's chorea. In all three conditions there in evidence for a disturbance of DA function. During the development of the prenant method va observed that subjects who yawned spontaneously had an identical yawing pattern to yawning induced in the same subjects by Apo.. The present investigation shows that yawing can be objectively recorded by measuring displacement of the lower jaw in a simple, reliable manner and the data can be easily analyzed. In the rat Apo is believed to induce yawning by stimulating central DA autoreceptors. Incidental observations with domperidone suggest that au in the rat Apo-induced yawning is also mediated by an effect on DA receptors within the blood brain barrier but whether autoreceptors are involved is unknown. Apo-induced yawning may provide a relatively noninvasive approach to evaluating DA autoreceptor function in psychiatric and neurological disorders.
The anatomical site for spontaneous yawning in man in unknown but the medulla oblongata, hypothalamus and striatum have all been suggested. In animals electrical stimulation within the hypothalamus induces yawning. Apo-induced yawning in the rat may be a striatal-media ed phenomenon. The method described for measuring yawning lands itself to the investigation of the phytiological and pharmacological regulation of the dopamine system mediating Apo-induced yavning. The rapid onset of the yawning after sc administration of Apo has obvious advantages for clinical investigation. The observation that sleep inhibits yawing suggests that subjects should remain awake during the period of monitoring. The preliminary finding that yawning was more marked in the two women compared with the three men is of interest as in animals yawning is essentially a male phenomenon. Thus, the female monkey and baboon rarely yawn spontaneously. Castration of the male rhesus monkey causes a precipitous decline in yavning and testosterone administration to ovariectomized females increases yawning. Physostigmine and Apo-induced yawning are significantly grester in the male than female rat. Testosterone restores physostigmine induced yawning in castrated male rats. Our preliminary observations in humans points to a species difference.
Conclusions : Apo-induced yawning can be objectively recorded by measuring the displacement of the lower jaw. Measuring this behavioural response may provide a simple way of assessing DA autoreceptor function in psychiatric and neurological disorders.