Chronic [D-Ala(2)]-growth hormone-releasing hormone administration attenuates age-related deficits in spatial memory

The age-related decline in growth hormone is one of the most robust endocri ne markers of biological aging and has been hypothesized to contribute to t he physiological deficits observed in aged animals. However, there have bee n few studies of the impact of this hormonal decline on brain aging In this study the effect of long-term subcutaneous administration of [D-Ala(2)]-gr owth hormone-releasing hormone (GHRH) on one measure of brain function, mem ory, was investigated. Animals were injected daily with 2.3 mu g of [D-Ala( 2)]-GHRH or saline from 9 to 30 months of age, and the spatial learning and reference memory of animals were assessed by using the Morris water maze a nd compared with those of 6-month-old animals. Results indicated that spati al memory decreased with age and that chronic [D-Ala(2)]-GHRH prevented thi s age-related decrement (24%) improvement in the annulus-40 time and 23% im provement in the number of platform crossings compared with saline treated, age-matched controls; p < .05 each). No changes were noted in sensorimotor performance. [D-Ala(2)]-GHRH attenuated the age-related decline in plasma concentrations of Insulin-like growth factor-1 (IGF-1) (p < .05). These dat a suggest that growth hormone and IGF-1 have important effects on brain fun ction, that the decline in growth hormone and IGF-1 with age contributes to impairments in reference memory, and that these changes can be reversed by the chronic administration of GHRH.