Maturation of Post-Synaptic Densities in Chicken Forebrain

Abstract

To study maturational events at CNS synapses we have compared some morphological and biochemical properties of synaptic junctions from 2 day and adult chicken forebrain. In this period the thickness of the average post synaptic density (PSD) doubled while the length did not change. In the same period the amount of the protein which is the major component of mature PSDs (mPSDp) increased almost 3 fold. These results suggest a direct correlation between the thickness of a PSD and the amount of mPSDp it contains. Cyclic AMP-and calcium plus calmodulin-stimulated protein phosphorylation increased in synaptic junctions during this period and the relative incorporation into some protein species changed with maturation. Except for the case of the mPSDp, whose phosphorylation appears to be substrate limited, the maturational changes in protein phosphorylation could be explained by an increase in protein substrate or protein kinase or both. These results suggest that the PSD is first established as a basic protein structure containing little or no mPSDp and that subsequent maturational events add specific structural (e.g. mPSDp) or functional (e.g. kinases, phosphoproteins) to this basic structure.