Yawning is a phylogenetically old, stereotypedevent that occurs alone or associated with stretchingand/or penile erection in humans, in animals fromreptiles to birds and mammals, under differentconditions. Several neurotransmitters and neuro-peptides are involved in its control at the central level.One of these at the level of the paraventricularhypothalamic nucleus (PVHN) is nitric oxide (NO).First, NO synthase inhibitors injected into thishypothalamic nucleus prevent yawning induced bydopamine agonists, oxytocin or N-methyl-D-asparticacid (NMDA), Which induce yawning by activating Yawning is a phylogenetically old, stereotypedevent that either alone or associated with stretching and / or penile erection in humans, in animals fromreptiles to birds and mammals, under different conditions. Several Neurotransmitters and neuro-peptides are involved in its control at the central level. One of of these at the level of the paraventricular hypyphaemic nucleus (PVHN) is nitric oxide (NO). First, NO synthase inhibitors injected into this hyphaemic nucleus prevent yawning induced by dopamine agonists, oxytocin or N-methyl-D-aspartic acid activating