Morphological plasticity of dendrites in adult brain

Deafferentation of certain brain regions in adult animals results in (1) the disappearance of degenerating axon terminals and (2) in the temporary persistence of vacant postsynaptic sites. These postsynaptic sites were shown to be re-supplied by sprouted axon terminals of intact axons. It is described in this paper, that in brain regions (e.g. cerebellar cortex, lateral geniculate nucleus) where axonal sprouting of local elements or of persisting afferent axons is negligible or absent, synaptic reorganization occurs via the active participation of postsynaptic dendritic and somatic elements of surviving local nerve cells. The dendrites may develop two types of reaction upon deafferentation (1) formation of presynaptic specializations along their otherwise "classical" postsynaptic membrane, resulting in the formation of new, dendro-dendritic synapses and (2) the "adaptive" (structural) reduction in size of denervated nerve cell dendritic arbor, leading to a relative increase in density of the surviving (though non-sprouting) afferent axon terminals. A partial functional recovery in both cases is also demonstrated.