Evidence that age-induced decline in memory retention is delayed in growth hormone resistant GH-R-KO (Laron) mice

Although the role of growth hormone (GH) in aging is controversial, the recent production of GH-R-KO mice may provide a means for elucidating its importance. Using the inhibitory avoidance learning task as a measure of cognitive aging, the present study compared learning and retention in young and old GH-R-KO mice and their normal siblings. Results for the old normal animals agreed with the current literature, in that the ability of old animals to retain learned information declined over time. However, retention in the old GH-R-KO mice did not decline between the 24-h, 7-day and 28-day retention tests and did not differ from young animals. To determine whether performance differences seen in the old normal vs. old GH-R-KO groups were due to locomotor behavior or emotionality, both groups were tested in the elevated-plus maze. Results showed that the normal and GH-R-KO mice did not differ in number of open or closed arms entered, time spent in closed or open arms or time taken to first enter an open arm. Thus, it was concluded that inhibitory avoidance performance was not affected by differences of locomotor activity or emotionality, and that the absence of GH signaling may be associated with improved long-term memory in aging mice.