Scratching behavior induced by bombesin-related peptides. Comparison of bombesin, gastrin-releasing peptide and phyllolitorins.

Bombesin and 10 bombesin-related peptides were administered intracerebroventricularly to conscious and freely moving rats. All peptides tested were found to elicit excessive grooming, especially scratching behavior. Bombesin itself had the most potent and long-lasting activity in eliciting scratching behavior. Naturally occurring peptides such as neuromedin B and gastrin-releasing peptide (GRP)-(18-27) were short-acting compared with exogenous peptides such as bombesin and synthesized analogs. Two phyllolitorins, a new bombesin subfamily, were also examined in this study. [Leu8]phyllolitorin induced more scratching than [Phe8]phyllolitorin and proved to be virtually equipotent to bombesin. Corticotropin-releasing factor (CRF) and substance P induced considerable excessive grooming, but both peptides were strikingly weak in inducing scratching behavior. It is suggested that (1) scratching represents a specific behavior commonly induced by bombesin-related peptides and (2) the relative potency to induce scratching behavior reflects the metabolic stability of the peptide, e.g. endogenous versus exogenous, shorter versus longer sequences, or chemical protection of N-terminus.