On the apparent nonadhesive nature of axospinous dendritic synapses

Synaptosome preparations are rich in synaptic sacs with adherent fragments of postsynaptic membrane and it has been hypothesized that pre- and postsynaptic membranes are strongly adherent across the synaptic cleft. Scanning electron microscopy of tissue specimens subject to preliminary tearing reveals synaptic terminals on neuronal cell bodies and dendrites as well as pits in the plasma membrane from which other terminals have been avulsed. However, neither synaptic terminals nor membrane pits were seen on dendrite spines in our material. These observations support the notion of adhesion between pre- and postsynaptic membranes but suggest an absence of such adhesiveness between the elements of the axospinous synapse, fitting well with recent conceptions about spine lability and the rapid making and breaking of axospinous synapses.