Opposite effects of [Leu13,Pro34]Npy and Npy13-36 on hypnotic response to α2-adrenoceptor agonist dexmedetomidine microinjected into rat locus coeruleus

Neuropeptide Y is colocalised with noradrenaline in the locus coeruleus (LC). This study evaluated the effects of neuropeptide Y (NPY) Y-1 and Y-2 receptor agonists on the hypnotic response to alpha(2)-agonist dexmedetomidine following the unilateral microinjection of these drugs into the vicinity of the locus coeruleus (LC). Dexmedetomidine alone (1 mu g) induced a loss of righting reflex and sleep in all animals. [Leu(31),Pro(34)]NPY (10 pmol) lengthened, whereas NPY13-36 (100 pmol) shortened the time of latency to sleep. The duration of sleep was shortened in rats pretreated with [Leu(31),Pro(34)]NPY. These data demonstrate that the hypnotic effect to dexmedetomidine in the LC can be modulated differentially by Y-1 and Y-2 receptor-selective agonists and provide additional evidence for NPY/alpha(2)-adrenoceptor interaction in this brain area.