Interestingly, none of the three so far cloned receptor subtypes have been found to bind galanin(3-29) with any significant affinity. This N-terminally truncated galanin analogue was reported by Wynick et al. to replace 125I-Bolton-Hunter-labelled galanin with high affinity in membranes of rat pituitary, and to act as a galanin agonist on prolactin secretion from the pituitary (Wynick et al. 1993). The same peptide was also reported to have affinity for galanin receptors in rat jejunal preparations (Rossowski et al. 1990). This points at the presence of a galanin N-terminus-independent receptor, which is yet to be cloned.
Recently, another potential galanin receptor subtype was suggested in a paper by Xu et al. (Xu et al. 1999). This receptor was found in neurones in the CA3 area of the hippocampus, as shown with electrophysiological recordings. These neurones responded with hyperpolar-ization to galanin(1-15), but not to full-length galanin, galanin(1-16), or D-Trp2-galanin, which indicates the possible existence of a galanin(1-15)-selective hippocampal galanin receptor.
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