Figure 2.

Effect of ghrelin administration (2.0mg/kg, s.c.) and Ghrelin receptor (Ghr-R) knockout (KO) during mild stress (air-puff in one corner) in a social home-cage environment (Intellicage system). (a-c) Ghrelin decreased latency to reenter any corner after a visit to the air-puff punished corner (calculated as the mean time after first and second visit to punished corner to next visit to any corner) (a) and increased total number of visits (b) and nosepokes (c) to any corner during 1 hour of air-puff punishment in 1 of 4 corners in the Intellicage system, indicating a stress-attenuating effect of ghrelin (n=10). (d-e) Ghr-R KO decreased total number of visits (d) and nosepokes (e) during 6 hours of air-puff punishment in 1 of 4 corners in the Intellicage system, supporting that ghrelin protects against acute stress (n=7). We chose to analyze the effect of ghrelin during 1 hour after administration because of the short half-life of ghrelin. In contrast, since the Ghr-R KO and WT mice received no injections, we chose to analyze a longer period to see a baseline behavioral effect (6 hours). Asterisks indicate statistical significance in unpaired Student’s t test (*P≤.05).