EVIDENCE FOR SPECIFIC N-TERMINAL GALANIN FRAGMENT BINDING-SITES IN THE RAT-BRAIN

The existence and widespread distribution of specific [I-125]galanin-(1-15) fragment binding sites in the rat brain was demonstrated by using [I-125]galanin-(1-15) as a radioligand in quantitative receptor autoradiographical studies. These binding sites were also present in several areas lacking or having very few [I-125]galanin-(1-29) binding sites, such as the dorsal hippocampal formation, the neocortex and the neostriatum. [I-125]Galanin-(1-15) binding sites showed a high selectivity for the fragment, since galanin-(l-15) could displace 80% of the binding whereas porcine galanin-(1-29) could only displace 30%. The binding was saturable with a K(d) of 0.63 +/- 0.02 nM and a B(max) of 15.3 +/- 1.7 fmol/mg in sections from the dorsal hippocampal formation. Thus, a new type of galanin receptor selective for N-terminal galanin fragments may exist in the rat brain.