The effect of obestatin on anxiety-like behaviour in mice

Obestatin is a 23 amino acid-peptide, derived from the same preproghrelin-gene as ghrelin. Obestatin was originally reported as a ghrelin antagonist with anorexigenic activity, but later it was proven to be involved in multiple processes including sleep, memory retention, anxiety, morphine-induced analgesia and withdrawal. In the present study, in male CFLP mice, by using computerised open field (OF) and elevated plus maze (EPM) tests we have investigated the behavioural effects of the acute intracerebroventricular (icv) administration of obestatin alone, and following ghrelin receptor blockage with [d-Lys3]-Growth Hormone Releasing Peptide-6 ([d-Lys3]- GHRP6) or corticotropin-releasing hormone (CRH) receptor 1 antagonism with antalarmin. Plasma corticosterone levels were measured for each treatment group by using chemofluorescent assay. Our results in the EPM test showed that obestatin reduced the percent of time spent in the open arms. The basal locomotor activity (ambulation distance and time, rearing and jumping) was not influenced significantly neither in the obestatin-treated groups, nor in those receiving pre-treatment with antalarmin or [d-Lys3]-GHRP6. The percentage of central ambulation distance however was decreased by obestatin, while the percentage of time spent in the central zone showed a decreasing tendency. The administration of antalarmin or [d-Lys3]-GHRP6 have both reversed the effect of obestatin on central ambulation. Plasma corticosterone levels were elevated by obestatin, which effect was antagonised by the injection of antalarmin. These are the first results to indicate that obestatin exerts anxiogenic-like effect in mice, which might be mediated through ghrelin receptor and CRH activation.