Dendritic spine associated exocytic/endocytic apparatus in local membrane traffic

Abstract

The dendritic spines, in spite of their small micrometer size, are apparently well endowed with an endomembrane system, as demonstrated by various ultrastructural studies. These membranous structures, visibly located at the base and also within spines of at least a subset of neurons, appear to perform roles that are akin to those classically associated with somatic membranes of the exocytic/secretory and endocytic pathways. The exact biochemical nature, compartmental identity and inter connectivity of these membrane structures, with names ranging from the spine apparatus to the recycling endosome, remains uncertain. The spine apparatus, while morphologically resembling and at least in partial membranous continuity with the smooth ER extending from the dendritic shaft, have been shown to contain some Golgi markers. It also appears to be rather specifically enriched in synaptopodin, an actin-associated protein found in telencephalic dendrites and podocytes of the kidney glomerulus. The recycling endosomes of dendritic spines are positive for somatic recycling endosome markers such as Rab11 and syntaxin 13. Interestingly, both these structures appear to function in modulating plasticity of excitatory synapses, mediating the trafficking, or recycling, of glutamate receptors to the postsynaptic plasma membrane. We briefly discuss here, with some speculative remarks, aspects of what has recently come to light about these dendritic spine exocytic/endocytic structures. © Nova Science Publishers, Inc.