ESTROGEN INCREASES GAP-43 (NEUROMODULIN) MESSENGER-RNA IN THE PREOPTIC AREA OF AGED RATS

Estrogen has been shown to affect the growth, differentiation, and sur vival of brain neurons and to modulate processes involved in synapse f ormation and connectivity. These trophic effects are diminished with a ging as secretion of estrogen declines. The growth associated protein GAP-43 is found concentrated in axonal growth cones and is implicated in neuronal growth and regeneration Previous studies have established that expression of GAP-43 can be modulated by estrogen in the preoptic area of developing and adult rat brain. This study was undertaken to determine whether this estrogenic regulation of GAP-43 mRNA is retaine d in aged rat brain. Young (3 months) and aged (24 months) rats were o variectomized to remove endogenous estrogen and GAP-43 mRNA in the pre optic area was evaluated using in situ hybridization to compare estrog en and vehicle treatments between age groups. The results demonstrate an age-related decline in GAP-43 mRNA hybridization signal that can be restored to levels comparable to that seen in young animals with estr ogen treatment.