Growth hormone (GH) increases the preference for novel locations. (A–C) Easy version of the spontaneous location recognition (SLR) task using a square box with objects placed in the corners. New objects and pseudorandomized corners were used for each trial. (B) (Upper panel) After a 3-h delay, all groups spent significantly more time with the displaced object compared to the object in the familiar location (upper panel, paired t-tests, P < 0.05). (Lower panel) Comparison of discrimination ratio revealed no group differences (ANOVA F(2,25) = 1.16, n.s., n = 8 GH, n = 8 antagonizing GH (aGH), n = 13 controls). (C) (Upper panel) Using a 24-h delay, only the GH treated animals explored the novel location significantly more than the familiar location (t(7) = 2.56, P < 0.05.). (Lower panel) The GH rats also had a significantly higher discrimination ratio than the other two groups (ANOVA F(2,26) = 3.36, P = 0.05, post-hoc contrasts t(26) = 2.59, P = 0.016, as compared to controls and animals treated with aGH. (D–F) Second variation of the SLR task, using a circular arena with three objects in the sample phase. After the delay, the location of two objects were merged into one novel location. (E,F) (Upper panels) Only the GH group tended to explore the novel object location more, but not significantly (3 h delay condition: paired t-test, t(7) = 0.12, 24 h delay condition: t-test t(7) = 0.07). (Lower panels) ANOVA of the discrimination ratio showed no significant group differences (P > 0.5).
