A serial-section study of perforated synapses in rat neocortex

Abstract

The morphology of perforated synapses in the molecular layer of rat parietal cortex has been studied in 28-day-old animals. Of the perforated synapses analyzed, 92% were axospinous and of these all had asymmetrical contacts. A spinule was present in 20% of them, and 63% had a negative curvature (concave with respect to the presynaptic terminal) overall. Up to 95% of perforated synapses had one or more negatively-curved segments. The perforated synapses studied were characterized by postsynaptic densities (PSD) with a mean length of 581 nm, compared with 233 nm for non-perforated synapses. A study of over 100 serially sectioned synapses demonstrated that, in perforated synapses, the PSD and perforations often had a highly irregular shape and arrangement, the site of the perforation frequently projected into the presynaptic terminal, and coated evaginations of membrane, or coated vesicles, were sometimes found at the site of a perforation or towards the periphery of perforated PSDs. Preliminary reconstructions of perforated synapses suggest that, for descriptive purposes, three types can be recognized. Criteria are formulated for determining, on the basis of a study of single sections, which non-perforated profiles belong to perforated synapses.

Probabilistic fluorescence-based synapse detection

“…For excitatory synapses, the expected density is 0.9 synapses μ m 3 ± 0.15 μ m 3 . For inhibitory synapses, the expected density is 0.1 synapses μ m 3 ± 0.05 μ m 3 [28] [29]. The first row shows the relationship between density and the threshold for each dataset, while the second row shows the average density of all the datasets as a function of the threshold.…”

Perforated axospinous synapses with multiple, completely partitioned transmission zones: Probable structural intermediates in synaptic plasticity

“…In some of these studies, postsynaptic dendritic spines of perforated synapses were observed to exhibit spinules (Spacek and Hartmann, 1983;Calverley and Jones, 1987;Harris and Stevens, 1989;Lisman and Harris, 1993). Spinule or miniature spine has been defined as a small or tiny projection that emerges from the postsynaptic spine head at a discontinuity in the perforated PSD; because it is devoid of PSD and invaginates the presynaptic axon terminal, it can be seen in cross-sections as a double membrane, circular (or oval) profile placed unattached within the terminal (Westrum and Blackstad, 1962;Tarrant and Routtenberg, 1977;Calverley and Jones, 1990).…”

“…Previous work has shown that perforated synapses are morphologically heterogeneous and may be further subdivided into three subtypes characterized by a fenestrated, horseshoeshaped, or segmented PSD (Peters and Kaiserman-Abramof, 1969;Cohen and Siekevitz, 1978;Spacek and Hartmann, 1983;Calverley and Jones, 1987;Geinisman et al, 1987, 41 7 1991b, 1992a, 1992b). The data of the present study extend these observations.…”

Effect of Chronic L-Dopa or Melatonin Treatments after Dopamine Deafferentation in Rats: Dyskinesia, Motor Performance, and Cytological Analysis

“…The number of perforated synapses was determined considering the following characteristics according to Calverley and Jones [35]: the site of the perforation projects into the presynaptic terminal, the active zone has one or more negatively curved components, which are separated by a central region of the active zone that projects into the presynaptic terminal, and the presynaptic density is in close association to the spine apparatus or an extension of it.…”