Narcoleptic canines display periodic leg movements during sleep.

Periodic leg movements during sleep (PLMS) is a high prevalent sleep disorder of unknown etiology. The disease is pharmacologically treated with dopaminergic agonists (i.e. D2/D3 agonists) and opiates. Periodic leg movements during sleep often occur in narcoleptic patients. We observed that narcoleptic canines, like narcoleptic humans, also exhibit jerky, unilateral or bilateral slow leg movements during sleep. The movements in dogs are characterized by repetitive dorsiflexions of the ankle, lasting 0.5-1.5 s, and occur at regular intervals of 3-20 s, thus showing similarities to PLMS in humans. The observation that D2/D3 agonists aggravate cataplexy in narcoleptic dogs suggests that altered dopaminergic regulation in canine narcolepsy may play a critical role in both cataplexy and PLMS. Our canines may therefore be an invaluable resource in PLMS research.