Modulation of Norepinephrine Release by Galanin in Rat Medulla Oblongata

Galanin, a 29-amino acid peptide, is widely distributed in both the central and peripheral nervous systems and is colocalized with catecholamines, although its physiological significance remains to be elucidated. In the present study we investigated the regulatory mechanisms of galanin on norepinephrine release in rat medulla oblongata. In slices of medulla oblongata of Sprague-Dawiey rats, galanin inhibited the stimulation-evoked [3H] norepinephrine release in a concentration-dependent manner (fractional release ratio during electrical stimulation: control 0.937±0.043, mean±SEM, n=6; galanin lxlO"7 M 0.501 ±0.037, n=6, p<0.05; and galanin 1x10" ' M 0.299±0.018 n=6, p<0.05). Galanin potentiated inhibition of [3H] norepinephrine release by the o^-agonists (UK 14,304 and clonidine). The blockade of <*,-adrenergic receptors by RX 781094 diminished the inhibition of norepinephrine release by galanin. Pretreatment of pertussis toxin, which interferes with the coupling of inhibitory guanoslne triphosphate-binding proteins to adenjiate cyclase, significantly attenuated the suppressive effects of galanin on norepinephrine release. In slices of medulla oblongata obtained from spontaneously hypertensive rats (SHR), the inhibitory effect of galanin on norepinephrine release was significantly less than in those from age-matched Wistar-Kyoto rats. These results show that galanin might inhibit the stimulation-evoked norepinephrine release in rat medulla oblongata, at least partially mediated by ofe-adrenergic receptor