Regional and ultrastructural distribution of the α8 integrin subunit in developing and adult rat brain suggests a role in synaptic function

Abstract

Integrins are heterodimeric cell adhesion molecules comprised of α and β subunits that have been implicated in the regulation of neuronal migration, differentiation, and process outgrowth. They mediate both cell-extracellular matrix and cell-cell interactions. The integrin α8β1 is a receptor for fibronectin, tenascin, and vitronectin that has been localized to axonal tracts and several types of non-neuronal cells in chick embryos and to smooth muscle cells in adult mammalian tissues. In this report, we describe the distribution of the α8 subunit in the developing and adult mammalian brain. By light microscopy, α8 labeling in the rat brain was found predominantly in neurons. It was primarily localized within perikarya and dendrites, but was also observed in certain fiber tracts. α8 immunoreactivity was most concentrated in the olfactory bulb, hippocampal formation, substantia nigra, ventral tegmental area, and superior olivary complex, but was also found at moderate levels in several regions including layer 5 of the cerebral cortex. α8 labeling was detected as early as E16, peaked in most areas during the first 3 postnatal weeks, and persisted in the adult. Electron microscopic analysis of the adult hippocampal formation revealed a striking concentration of α8 immunoreactivity in the spines and postsynaptic densities of dendrites. These results suggest that α8 is involved in the regulation of axonal and dendritic growth of some neurons in the developing central nervous system (CNS) and provide ultrastructural evidence that integrins may participate in the formation, maintenance, or plasticity of synapses. © 1996 Wiley-Liss, Inc.