GALANIN-(1-15), BUT NOT GALANIN-(1-29), MODULATES 5-HT1A RECEPTORS IN THE DORSAL HIPPOCAMPUS OF THE RAT-BRAIN - POSSIBLE EXISTENCE OF GALANIN RECEPTOR SUBTYPES

The aim of the present study was to evaluate whether galanin-(1-29) and galanin-(1-15) can modulate the 5-hydroxytryptamine(1A) (5-HT1A) receptors using [H-3]8-OH-2-(di-n-propylamino)-tetralin ([H-3]8-OH-DPAT) as a radioligand. Membrane preparations of the dorsal hippocampus, an area having the recently described [I-125]galanin-(1-15) fragment binding sites, but having very few porcine [I-125]galanin-(1-29) binding sites, were used. Galanin-(1-15) produced a concentration-dependent increase in the K-d value of [H-3]8-OH-DPAT with a maximum effect of approximately 65% at 3 nM of galanin-(1-15), whereas galanin-(1-29) had no effect. This increase of the K-d value of [H-3]8-OH-DPAT could be completely counteracted by the putative galanin antagonist M35 (1 nM). The B-max values of [H-3]8-OH-DPAT were not affected in any experiment. In conclusion, the present results give further evidence for the existence of a galanin receptor subtype mainly recognizing N-terminal galanin fragments, also having the ability to reduce the affinity of 5-HT1A receptors.