haut de page



mise à jour du 23 janvier 2003
 Pharmacol Biochem Behav 1985;22(1):31-5
télécharger pdf de cet article
Association of spontaneous and dopaminergic induceed yawning and penile erections in the rat
Holmgren B, Urba-Holmgren R, Trucios N, Zermeno M, Eguibar JR
Departamento de Ciencias Fisiologicas, Instituto de Ciencias, Universidad Autonoma de Puebla, Puebla, Mexico
Tous les travaux de MR Melis & A Argiolas 
Tous les travaux de M Eguibar & G Holmgren


Early reports on the stretching and yawning syndrome (SYS) induced in rats by intracisternal injections of ACTH and MSH were soon followed by others which described that intraventricular or intracerebral administration of ACTH or MSH also produced signs of sexual excitement (penile erection (for the sake of brevity we will use the expression penile erection to describe a behavioral pattern which, in the rat, may also include genital grooming, pelvic thrusts or ejaculation and licking of the genitalia in the male, lordotic posture in the female), not only in rodents but also in other mammals. Different pharmacological evidence suggesting an association between yawning and sexual excitement began with work by Baraldi and Benassi-Benelli and Mogilnicka and Klimek demonstrating that systemic administration of apomorphine (APO) and other dopamine (DA) agonists elicits both yawning and penile erections in the rat.

Systematic observation of spontaneous and pharmacologically induced yawning and penile erections in a line of Sprague-Dawley rats selectively bred in our laboratory to establish a high incidence of yawning has led us to suggest that yawning and penile erection are correlated even in the normal spontaneously behaving animal. As reasonable parallelism exists between the elicitation or inhibition of yawning and penile erections by drugs acting through DA pathways, we further suggest that dopaminergic mechanisms operate in the regulation or modulation of these two behavioral patterns. [...]


A strict correlation between spontaneous yawning and penile erections was certainly difficult to establish in Wistar rats, because of the low frequency of these behavioral patterns. In that strain of rats spontaneous yawning has, according to different authors average frequencies within a range from 0,1 to 2 yawns/hr. For penis erection, an occurrence of 30% and an average frequency of 0,3 erections/hr were reported by Bertolini et al, from experiments in which the animals were observed during two hours. Their data show a yawning occurrence of the order of 60%, with an average frequency of 1.5 yawns/hr. The progress made in our laboratory, in the selective breeding of a 'frequent yawning' line of Sprague-Dawley rats has allowed us to demonstrate that penile erection frequency increased linearly from around 0.4 erections/hr in the group of nonyawning rats, to 2 erections/hr in the group that had an average spontaneous frequency within a range from 26 to 30 yawns/hr. This correlation suggests that some common underlying factors may participate in the regulation of these two behavioral patterns. For Bertolini et al, when both behavioral patterns occur under physiological conditions, they might be elicited by an endogenous peptide closely related to CRF, and containing the peptide sequence required for eliciting stretching, yawning and sexual stimulation.

The very similar dose-effect curves obtained by us for yawning and penile erection, when elicited with two DA agonists (APO and bromocriptine) and their equivalent depression in frequency by the selective presynaptic DA antagonist, metoclopramide strongly suggest that penile erection and yawning are both under dopaminergic control. In relation to yawning, which is also elicited in rats by cholinomimetic drugs, physostigmine or pilocarpine, a hypothetical model of its central control mechanism has been proposed, which includes a dopaminergic inhibitory-cholinergic excitatory link. Low doses of APO or other dopaminergic agonists, by activating presynaptic DA autoreceptors would inhibit DA release and thus disinhibit the cholinergic neurones exciting yawning. Wood et al have proposed that septalhippocampal cholinergic neurones are involved in the specific SYS elicited by intraventricular injection of MSH or ACTH. It is therefore tempting to suggest, as Yamada and Furukawa implicitly do, that the dopaminergiccholinergic link in yawning might involve the DA pathway ascending from the A1O mesencephalic cell group to the limbic region and the septal-hippocampal cholinergic neurones. It seems interesting to recall that Passouant et al had observed yawning in cats during the post-discharge period following electrical stimulation of the hippocampus.

With respect to genital function, consistent results from MacLean and coworkers (as reviewed by MacLean showed that electrical stimulation of several sites in the limbic areas, leading to the buildup of high-voltage potentials or after discharges in the hippocampus, are generally accompanied by penile erection. In later experiments done with Kinnard, MacLean found that depositing a-MSH or ACTH in solid form in the septo-preoptic region of the squirrel monkey resulted in recurrent episodes of stretching, yawning, scratching of the body and full penile erections which, in about three hours, could reach a frequency of twice per minute.

The reviewed evidence points strongly to the existence of some common regulating or modulating elements interrelating, under certain physiological or experimental circumstances two behavioral patterns as different as yawning and penile erection. The complex neural circuitry interconnecting the different structures of the limbic brain may offer neuroanatomical sites for this interaction. Common modulating influences seem also important. Hormones such as testosterone, or a particular polypeptide sequence contained in a-MSH and ACTH facilitate both yawning and penile erection. Tonic changes in neurotransmitter influences, as exerted by the ascending mesolimbic pathway or other DA pathways, may inhibit or disinhibit these behavioral patterns.

The most recent report by Serra et al that hypophysectomy in rats prevents yawning and penile erections induced by apomorphine is quite a strong argument in favor of their hypothesis that both behavioral effects are mediated by pituitary hormones. They suggest that activation of DA autoreceptors in the hypothalamo-hypophyseal DA neurones by low doses of apomorphine might remove an inhibitory control on MSH relcase, the hormone reaching target areas in the brain by retrograde portal flow. This hypothesis appears very attractive because it offers a unifying explanation of the elicitation of yawning and penile erections by so different substances as the common polypeptide sequence contained in a-MSH and ACTH, and DA agonists.

Involvement of 5-HT1c-receptors in drug-induced penile erections in rats H Berendsen