Growth Hormone (GH) plays an important role in young animals promoting growth and development but its secretion decreases in adulthood, a fact which has been considered to be in part responsible of the degenerative changes observed in aged individuals. Accordingly, the GH replacement therapy has successfully used in rats to revert many biochemical, histological and anatomical traits associated to old age, improving skin structure, vascular endothelia, immune system and causing a powerful neuronal rescue after hipoxy-ischemic lesions in the hippocampus of rats older than 20 months. However, the functional consequences of the GH replacement remain largely unexplored.

The present reports aims at recording the effect of acute and chronic GH administration (2 mg/k b.w/24 h) in the learning and motor capacity of old (24 months) and young (12 weeks) Wistar rats. Young and old saline controls were also studied. All animals were tested for place learning in a 8 arms radial maze and for motor coordination in a rota-rod. Perfomance was tested just after the first GH injection, to record acute effects of GH and after four weeks of GH administration to record the chronic effects.

Both acute and chronic injections of GH caused significant effects in young and old animals, although the maximal effects were observed after chronic GH administration in old animals which reached performance levels similar to those of young injected with saline. The results confirm the usefulness of GH replacement to recover the age associated behavioural deficits observed in cognitive and motor capabilities.

Supported by SAF2007-66878-CO2-02 from Spanish MEC.