Postsynaptic density

The postsynaptic density (PSD) is a cytoskeletal specialization at neuronal synapses that was originally identified as an electron-dense region at the membrane of a postsynaptic neuron, as viewed by electron microscopy. PSDs are usually comprised of L-glutamate neurotransmitter receptors, their molecular scaffolding molecules, cell adhesion molecules and a diverse set of other signaling proteins. PSDs vary in size and composition among brain regions. Many of the PSD proteins contain PDZ domains.

Function
The PSD has been proposed to concentrate and organize neurotransmitter receptors to respond rapidly to neurotransmitter in the synaptic cleft. Some of the features of the PSD are similar to the neuromuscular junction and other cellular junctions, as the PSD has been modeled as a specialized cellular junction that allows for rapid, asymmetical signaling.

Structure
The structure and composition of the PSD have been the focus of numerous molecular studies of synaptic plasticity, a cellular model of learning and memory. PSDs are sized on the order of 0.25 to 0.5 micrometres in diameter and 0.025 to 0.05 micrometres in thickness, depending on the activity state of the synapse.

Composition
Many proteins in the PSD are involved in the regulation of synaptic function. Key among these, are postsynaptic density-95 (PSD95), neuroligin (a cellular adhesion molecule) NMDA receptors, AMPA receptors, calcium/calmodulin-dependent protein kinase II and actin. As protein detection technologies have increased in sensitivity, such as with improvements in mass spectroscopy techniques, more numerous proteins have been attributed to the PSD. Current estimates are greater than several hundred proteins are found at PSDs among brain regions and during different states of development and synaptic activity.

General Review

 * Ziff EB. "Enlightening the postsynaptic density." Neuron. 1997; 19(6):1163-74. NCBI Pubmed
 * Kennedy MB. "Signal-processing machines at the postsynaptic density." Science. 2000; 290(5492):750-4. NCBI Pubmed

Structure and Compostion

 * Banker G, Churchill L, Cotman CW. "Proteins of the postsynaptic density." J Cell Biol. 1974; 63(2):456-465. NCBI Pubmed
 * Cohen RS, Blomberg F, Berzins K, Siekevitz P. "The structure of postsynaptic densities isolated from dog cerebral cortex. I. Overall morphology and protein composition."  J Cell Biol. 1977; 74(1):181-203. NCBI Pubmed
 * Blomberg F, Cohen RS, Siekevitz P. "The structure of postsynaptic densities isolated from dog cerebral cortex. II. Characterization and arrangement of some of the major proteins within the structure."  J Cell Biol. 1977; 74(1):204-25. NCBI Pubmed
 * Walikonis RS, Jensen ON, Mann M, Provance DW Jr, Mercer JA, Kennedy MB. "Identification of proteins in the postsynaptic density fraction by mass spectrometry." J Neurosci. 2000; 20(11):4069-80. NCBI Pubmed
 * Peng J, Kim MJ, Cheng D, Duong DM, Gygi SP, Sheng M. "Semiquantitative proteomic analysis of rat forebrain postsynaptic density fractions by mass spectrometry."  J Biol Chem. 2004; 279(20):21003-11.  NCBI Pubmed
 * Jordan BA, Fernholz BD, Boussac M, Xu C, Grigorean G, Ziff EB, Neubert TA. "Identification and verification of novel rodent postsynaptic density proteins." Mol Cell Proteomics. 2004; 3(9):857-71.  NCBI Pubmed