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Abstract

This chapter discusses the prenatal formation of synapses and dendritic spines in guinea-pig cortex and their postnatal changes. Electrophysiologically it has been shown that the responses of cortical neurons to sensory stimuli can be altered after exposure to abnormal environment. The chapter discusses the extent to which neuronal contacts appearing as synaptic specializations on electromicrographs or as dendritic spines in Golgi preparations are already present in the newborn guinea pig before environment can make its influence felt through sense organs. In adult animals, synapses with very prominent postsynaptic thickening are frequently seen and distinction between symmetrical and asymmetrical synapses is more difficult in prenatal animals. The dendritic spines in prenatal animals have a more delicate appearance. The chapter also explains that another postnatal change in the cortex of the guinea pig shows an increase in the number of myelineated fibers. The cortical nerve cells are interconnected by a process of growth and that learning processes only modulate the strength of the connections.