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Density of neurons and synapses in the cerebral cortex of the mouse
Author(s) -
Schüz Almut,
Palm Günther
Publication year - 1989
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902860404
Subject(s) - neuropil , nissl body , neocortex , paraformaldehyde , biology , neuron , cerebral cortex , anatomy , synapse , synaptophysin , shrinkage , staining , neuroscience , central nervous system , chemistry , immunohistochemistry , materials science , genetics , organic chemistry , immunology , composite material
Quantitative anatomical investigations provide the basis for functional models. In this study the density of neurons and synapses was measured in three different areas (8, 6, and 17) of the neocortex of the mouse. Both kinds of measurements were made on the same material, embedded in Epon/Araldit. In order to determine the synaptic density per mm 3 , the proportion of synaptic neuropil was also measured; it was found to be 84%. The cortical volume occupied by cell bodies of neurons and glia cells amounted to 12%, that by blood vessels to 4%. The total average was 9.2 × 10 4 neurons/mm 3 and 7.2 × 10 8 synapses/mm 3 . About 11% of the synapses were of type II. The density of neurons increased with decreasing cortical thickness; thus the number of neurons under a given surface area was about constant. The synaptic density, on the other hand, was almost constant in the three areas, the number of synapses under a given cortical surface area tended, therefore, to increase with cortical thickness. The average number of synapses per neuron was 8,200, with a tendency to increase with increasing cortical thickness. Shrinkage of the tissue was also measured for various staining techniques. No shrinkage occurred during perfusion with 3.7% formaldehyde or with a solution of buffered paraformaldehyde and glutaraldehyde and during fixation in situ. Electron microscopical material showed almost no shrinkage, whereas Nissl‐preparations on paraffin‐embedded material had only 43% of their original volume. After Nissl stain on frozen sections the volume had shrunken to 68% and after Golgi impregnation and embedding in celloidin to 70%. The total volume of the neocortex was 112 mm 3 (both hemispheres together). The total number of neurons was thus 1.0 × 10 7 and the total number of synapses 8.1 × 10 10 .