Ultrastructure of growth cones in the cerebellar cortex of the neonatal rat and cat.

Abstract

The ultrastructure of axonal and dendritic growth cones has been examined in the cerebellar cortex of 7 days old rats and 12 days old cats. The unique feature is a bulge of the perikaryon surface or a varicosity of the growing tip of nerve processes. These cone-like areas contain large amounts of tubular smooth surfaced endoplasmic reticulum (SR) and large vacuoles. They are further characterized by filopodia (Tennyson, 1970) with a fibrillary matrix. Early cell contacts with synaptic membrane specializations are described between filopodia of mossy fiber endings and dendritic growth cones of granular cells. Synaptic vesicles appear early in synaptogenesis. While both vesicles and SR tubules are confined to separate areas of the axonal growth cone it was found that a common affinity to the ZIO staining agent exists. In contrast, the neurofilaments and microtubular components as well as the growth cone vacuoles remain consistently ZIO negative.