Neuropeptide Y enhances the inhibitory effects of clonidine on3H-noradrenaline release in synaptosomes isolated from the medulla oblongata of the male rat

Summary In studies on superfused synaptosomes from the rat medulla oblongata, the inhibitory effects of the2-adrenergic agonist clonidine (0.1M) on potassium (15 mM K⁺) induced³H-noradrenaline (NA) release was potentiated by 20%, when neuropeptide Y was added to the system. The effect of NPY was detectable at low concentrations (1 nM) and was not dose-dependent. Neuropeptide Y alone produced no significant effects on³H-NA release. The results may indicate the existence of a presynaptic NPY receptor on the noradrenaline and/or adrenaline nerve terminals, which may enhance the presynaptic2-adrenoreceptor function to inhibit³H-NA release.