Synaptic plasticity and synaptic degeneration in human congenital hydrocephalus

Cortical biopsies of 13 infant patients with clinical diagnosis of congenital hydrocephalus, Arnold-Chiari malformation, and postmeningitis hydrocephalus were examined with transmission electron microscopy to study the synaptic plasticity and synaptic degenerative changes in hydrocephalic edema. The immature cortical neuropil of different cortical regions showed swollen nerve cell processes separated by enlarged extracellular space. Isolated and swollen presynaptic endings with few or numerous synaptic vesicles, disruption of limiting plasma membrane, and absent postsynaptic partners were also observed. Activated flat and invaginated axodendritic and axospinodendritic asymmetric synaptic contacts showed synaptic vesicles anchored to the presynaptic membrane, and short or large synaptic active zones. The swollen and degenerated synaptic contacts, including axosomatic synapses exhibited enlargement of few synaptic vesicles and lack of pre- and postsynaptic densities. Synaptic disassembly was observed in elevated intracranial pressure- hydrocephalus. Megaspines making multiple asymmetric synaptic junctions were also distinguished. Phagocytic astrocytes engulfed the degenerated synapses. The potential role of hydrocephalic edema and ischemia, oxidative stress, increased calcium concentration, activation of N-methyl D-aspartate receptors, and disturbance of ion homeostasis are discussed in relation with the observed synaptic plasticity and synaptic degenerative changes.