Stereological methods for quantitating synapses
Abstract
Chemical transmission in the nervous system occurs between nerve cells at junctions called synapses. Morphologically, synapses can be recognized under standard transmission EM, using a variety of staining methods, by three distinctive features as shown in Figure 1: a) a presynaptic profile (A) containing synaptic vesicles clustered at the presynaptic membrane; b) a cleft of 150-300 Å in width separating the pre- and post-synaptic profiles; and c) a postsynaptic profile (B) with an area of increased electron density (between black arrows) or postsynaptic density. Within the last few years, changes in the number and complexity of synapses have been shown to occur in the cortex of animals raised in enriched environments (Turner and Greenough, 1983) and may underlie some of the deficits in learning and memory which occur during aging.