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

Although the role of growth hormone (GH) in aging is controversial, the rec ent production of GH-R-KO mice may provide a means for elucidating its impo rtance. Using the inhibitory avoidance learning task as a measure of cognit ive aging, the present study compared learning and retention in young and o ld GH-R-KO mice and their normal siblings. Results for the old normal anima ls agreed with the current literature, in that the ability of old animals t o 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 retenti on tests and did not differ from young animals. To determine whether perfor mance 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 elevate d-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 arm s or time taken to first enter an open arm. Thus, it was concluded that inh ibitory avoidance performance was not affected by differences of locomotor activity or emotionality, and that the absence of GH signaling may be assoc iated with improved longterm memory in aging mice. (C) 2001 Elsevier Scienc e Inc. All rights reserved.