Postsynaptic membrane and spine apparatus: proximity in dendritic spines.

We have reported previously that at dendritic spine synapses, the spine apparatus is associated with the synaptic spinule. In this report this association is shown, in serial thin sections, to involve intimate physical proximity between the postsynaptic density and membranous structures that are part of, or extend from, the spine apparatus itself. Because of the variegated shapes of synaptic spinules, the spine apparatus-postsynaptic density relation suggests participation in membrane distribution or synaptic remodeling phenomena.