Influence of adenohypophyseal tissue on the development of the rat fascia dentata in vitro.

In hippocampal slice cultures, the mossy fibers from the dentate granule cells were previously shown by Timm staining to retain their normal connections to CA4 and CA3 pyramidal cells. While the granule cells of the suprapyramidal (hidden) blade remained in a distinct layer, the granule cells of the infrapyramidal (free) blade of the fascia dentata, however, often spread. This aberrant trait was strikingly enhanced in the presence of a co-cultured adenohypophyseal explant. This infrapyramidal blade of the fascia dentata largely disappeared as a cell layer; granule cell-like neurons, displaying a monopolar dendritic structure directed towards the pituitary, would migrate toward the hypophyseal explant, whilst their axons still functionally innervated CA3 pyramidal cells. Axon collaterals projected in the opposite direction and presumably terminated on dendrites, thus giving rise to the intense black labelling which was observed in Timm-stained preparations as a bridge connecting the two explants. The morphological alterations induced in the fascia dentata by co-cultured adenohypophysis were tissue-specific since co-cultured neurohypophysis, pineal gland and cerebellum failed to produce similar effects. These results suggest that cultured adenohypophyseal tissue is capable of releasing yet unidentified factors which apparently enhance neuronal migration.