mise à jour du
26 février 2006
Europ J Pharmacol
1985; 117; 395-396
Intraventricular oxytoxin induces yawning
and penile erection in rats
Argiolas A , Melis MR, Gessa GL
Institute of Pharmacology, University of Cagliari, Italy
Department of neuroscience Cagliari University Italy
Tous les travaux de MR Melis & A Argiolas 
Tous les travaux de M Eguibar & G Holmgren


The stretching and yawning syndrome (SYS) is a complex behaviour specifically induced by the central administration of ACTH-MSH peptides. Recently we have found that ACTH activity in rat hypothalamus is represented by a heterogeneous population of peptides rather than by a unique peptide.
During an attempt to identify the hypothalamic forms of ACTH capable of inducing SYS, we discovered a peptide which did not show ACTH-like bioactivity and immunoreactivity, but induced yawning and penile erection in rats. Amino acid and sequence analysis showed the peptide to be oxytocin. Since experimental evidence indicates that oxytocin acts as a neuropeptide in the central nervous system, we further characterized the oxytocin effect on yawning and penile erection. Male Sprague Dawley rats (250-300 g) were used.
A stainless steel guide cannula was implanted chronically into a lateral ventricle 3 days before the experiments (coordinates: 1 mm anterior to bregma, 1.5 mm lateral to midline and 2 mm ventral to dura, Pellegrino and Cushman, 1971). Oxytocin was dissolved in saline and injected intraventricularly (i.c.v.) in a volume of 10µ l.
As shown in table 1, yawning and penile erection were induced by a dose ox oxytocin as low as 5 ng in 60% of the animals treated. The most effective doses were 20 and 60 ng. The 120 and 1200 ng doses were ineffective in agreement with previous studies.
Moreover, the oxytocin effect was prevented by the antimuscarinic agent atropine (10 mg/kg i.p.), but not by methylatropine (10 mg/kg i.p.) or the opiate antagonist naloxone (1 mg/kg i.p.).
It is not yet known whether or not the oxytocin-induced and the ACTH-MSH peptide-induced yawning and penile erection are mediated by similar mechanisms (i.e. ACTH-MSH peptides released by oxytocin in some brain area or vice versa) and why the high doses of oxytocin were ineffective. However, two important features distinguish the oxytocin-induced yawning and penile erection from those induced by ACTH-MSH peptides: (1) the doses of oxytocin that induce yawning and penile erection (5-60 pmol) are much lower than those of ACTH-MSH peptides that are active at doses of 1-2 nmol; and (2) oxytocin-induced yawning and penile erection begin 8-10 min after i.c.v. injection of the peptide, while a lag of 25-30 min is always observed after i.c.v. injection of ACTH-MSH peptides before the start of SYS and sexual behaviour (Bertolini and Gessa, 1981).
Although further experiments are necessary to clarify the mechanism and the site(s) of action of oxytocin, the present results suggest that oxytocin plays a crucial role in the expression of yawning and penile erection in rats and provide further evidence that oxytocin acts as a neuropeptide in the central nervous system.