Neuropeptide Y and galanin enhance the inhibitory effects of clonidine on norepinephrine release from medulla oblongata of rats.

The medulla oblongata is thought to play an important role in the central regulation of blood pressure. Neuropeptide Y (NPY) and galanin (Gal) coexist with norepinephrine (NE) and may have a functional interaction in this region. The aim of the present study was to investigate whether NPY and Gal could modulate the presynaptic neuronal mechanisms, especially the alpha-adrenoceptor function, inhibiting NE release in medulla oblongata. In slices of rat medulla oblongata, clonidine, an alpha-adrenoceptor agonist, inhibited the NE release elicited by electrical stimulation in a concentration-dependent manner. A combination of clonidine and low concentration of NPY (1 X 10(-9) mol/L) resulted in an increase in the inhibitory action of clonidine on stimulation-evoked NE release. The inhibitory action of clonidine was also potentiated by Gal (1 X 10(-8) mol/L). These results indicate the existence of the presynaptic NPY- and Gal-receptors on noradrenergic nerve terminals, which may enhance the presynaptic alpha-adrenoceptor function to inhibit NE release. This suggests a possible involvement of NPY and Gal in the regulation of sympathetic nerve activity in medulla oblongata.