Galanin attenuates basal and antidepressant drug-induced increase of extracellular serotonin and noradrenaline levels in the rat hippocampus.

Galanin is co-localized with classical neurotransmitters, such as acetylcholine, serotonin (5-HT) and noradrenaline (NA) in neurons or in brain regions implicated in cognitive and affective behaviour. In the present study, the effects of galanin on extracellular 5-HT and NA levels in the rat hippocampus were measured by in vivo microdialysis under basal conditions and following systemic administration of antidepressant drugs. Galanin (1.5 nmol i.c.v.) reduced basal 5-HT and NA levels to 65% and 86% of controls, respectively. Galanin (0.5 and 1.5 nmol i.c.v.) dose-dependently attenuated the elevation of 5-HT concentrations induced by imipramine and citalopram (10 mg/kg i.p., each) from 350% to 312% and from 230% to 160%, respectively. Galanin at 1.5 nmol transiently attenuated the effect of desipramine-induced (10 mg/kg i.p.) increase in extracellular NA levels from a maximal increase of 389-296% of the predrug levels. It is concluded that intraventricularly administered galanin attenuated both basal 5-HT and NA release and antidepressant drug-induced accumulation of extracellular 5-HT and NA levels most likely via a predominant inhibitory action on serotonergic and noradrenergic neurons in the raphe and locus coeruleus, respectively. These results further emphasize a possible role of galanin in regulation of 5-HT and NA neurotransmission in depressive states and during the course of antidepressant therapy.