User:Millencolin/spine apparatus

The spine apparatus (SA) is a specialized form of endoplasmic reticulum (ER) that is found inside dendritic spines. Is consits of a series of stacked discs that are thought to be connected to each other and to the dendritic system of ER-tubules. Associated with the SA is the protein synaptopodin which has originally been described in podocytes of the kidney.

Morphology
In CA1 pyramidal cells of the hippocampus, a spine apparatus is found in about 20% of all dendritic spines The SA is mostly found in large mushroom-shaped spines which are thought to carry strong synapses. Not all spiny cells form a SA: Purkinje cells of the cerebellum, for example, have many dendritic spines, but no spine apparatus.

Function
Dendritic spines contain ryanodine receptors and IP3 receptors, ion channels that are capable of releasing calcium from the endoplasmic reticulum. Therefore, it has long been speculated that the spine apparatus might been involved in calcium signaling inside the spine. A knockout mouse lacking synaptopodin provided the first evidence for an involvement of the spine apparatus in synaptic plasticity. These mice, which had no spine apparatus, had impaired long-term potentiation in the hippocampus and also deficits in spatial learning.