Role of bombesin (BN)-like peptides/receptors in emotional behavior by comparison of three strains of BN-like peptide receptor knockout mice.

Bombesin (BN)-like peptides are involved in the regulation of a wide variety of behaviors, such as spontaneous activity and feeding. We assessed the role of BN-like peptides/receptors in emotional and/or anxiety-related behavior using three strains of knockout mice, each deficient in a single BN-like peptide receptor (gastrin-releasing peptide receptor, bombesin receptor subtype-3, or neuromedin B receptor). Two representative behavioral paradigms, the light-dark (L-D) box test and the elevated plus maze test, were chosen for this purpose. In these two tests, the level of anxiety can be measured as the preference for exploring the light box, or the length of time spent in the open arms, respectively. By conventional parameters, the only significant finding was that BRS-3-deficient mice exhibited a longer duration of remaining in the open arms compared to the wild-type cohort (P < 0.01). However, analyses of risk assessment behavior revealed that BRS-3-deficient mice exhibited increased 'stretched attend posture' behavior (P < 0.01, compared to wild-type mice in both the L-D box and elevated plus maze tests) while NMB-R-deficient mice exhibited decreased behavior (P < 0.05, compared to wild-type mice in both tests). These results suggest that BN-like peptides/receptors may play a role in modulating emotion including some forms of anxiety (e.g., risk assessment behavior). Further, we found that the type of emotional behavior to which each of the peptide/receptor pathways contributes can be clearly specified.