Quantitative and qualitative characteristics of synapses in different layers of the auditory cortex

Abstract

The electron-microscopic examination of synapses in different layers of the cat auditory cortex was performed. 53% of them were located on dendritic spines, 37% on dendrites and 10% on neuronal soma. All synapses were separated into type I and type II according to Gray. The type I synapses amounted to 91% (69.5% were of type Ia and 21.5% of type Ib), the type II synapses constituted 9%. The type I synapses were located mainly on dendrites and dendritic spines, the type II--on neuronal soma, axon hillocks and large dendrites. 60 h after complete neuronal isolation of a portion of the auditory cortex 22.8% of synapses revealed signs of degeneration. No type II degenerating synapses were found. This indicates that they are formed by axons of intracortical neurons. Quantitative and qualitative composition of synapses in different layers of the auditory cortex is shown to be different.