Postsynaptic density (PSD) is a dynamic structure that functions as an essential device for synaptic transmission and plasticity, and is critical for normal synaptic and brain activities. Many neuropsychiatric diseases and symptoms appear to be caused by abnormalities in synapses, including PSD. Therefore, precise and detailed knowledge of PSD is valuable for understanding neuropsychiatric diseases and developing new therapies. In this paper, we searched for PSDs with lattice- or mesh-like structures by preparing PSD from rat forebrains using different detergents, brain ages, and methods for collecting the brains. We next searched for the protein components responsible for the mesh-like structure in PSD using sodium dodecyl sulfate polyacrylamide gel electrophoresis/silver staining coupled with mass spectrometry and quantitative analyses of western blotting. The results suggest that general cytoskeletal proteins, together with PSD scaffold and adaptor proteins, may play a role in the core structure of mature PSDs. In the immature PSD core, general cytoskeletal proteins, in particular actin and α-internexin, and synapse-associated protein 102 may be involved. However, Ca2+/calmodulin-dependent protein kinase II is not a major constituent of the mesh-like PSD basic structure.