Immature Synaptic Contacts in Human Congenital Hydrocephalus. An Electron Microscopic study

Aggelopoulos et al. [1] analyzed the synaptogenesis in the dorsal lateral geniculate nucleus of the rat and demonstrated that during the first stage, which spans the first 4 days of life, there are only a few immature synapses scattered throughout the nucleus. During the first two postnatal weeks, and particularly during the second stage, the presence of membrane specializations that resemble vacant postsynaptic endings, and in the third stage, which spans a period between days 10 and 20, beginning of myelination and by diminution of growth cones, degenerating profiles and vacant postsynaptic endings. In previous papers we have reported synaptic plasticity and synaptic degeneration in human congenital hydrocephalus [2-5]. In the present study fourteen neonate patients with age ranging from 1day neonates to 10 years infant patients were examined to characterize the presence of immature synaptic contacts in the hydrocephalic swollen brain parenchyma. Such study is basically important to study human synaptogenesis and abnormal neural microcircuits in pathological conditions.


Introduction
Aggelopoulos et al. [1] analyzed the synaptogenesis in the dorsal lateral geniculate nucleus of the rat and demonstrated that during the first stage, which spans the first 4 days of life, there are only a few immature synapses scattered throughout the nucleus.
During the first two postnatal weeks, and particularly during the second stage, the presence of membrane specializations that resemble vacant postsynaptic endings, and in the third stage, which spans a period between days 10 and 20, beginning of myelination and by diminution of growth cones, degenerating profiles and vacant postsynaptic endings. In previous papers we have reported synaptic plasticity and synaptic degeneration in human congenital hydrocephalus [2][3][4][5]. In the present study fourteen neonate patients with age ranging from 1day neonates to 10 years infant patients were examined to characterize the presence of immature synaptic contacts in the hydrocephalic swollen brain parenchyma.
Such study is basically important to study human synaptogenesis and abnormal neural microcircuits in pathological conditions.

Material and Methods
Cortical biopsies of 14 infant patients, ranging from 12 days to 10 years old, with clinical diagnosis of congenital hydrocephalus and Arnold-Chiari malformation were taken from the frontal and parietal cortical regions, and examined with the transmission electron microscope. The (Table 1)  Fourteen surgical biopsies of cortical brain parenchyma from patients with congenital hydrocephalus ranging from 12 days to 10 years old were examined with transmission electron microscopy to study immature axosomatic and axodendritic synaptic contacts. The hydrocephalic brain parenchyma was characterized as immature tissue due to the presence of microdendritic filopodia, distended extracellular spaces, and axonal and dendritic grow cones. The first group formed by earliest immature synapses were featured by close apposition of electron dense pre-and postsynaptic synaptic membrane complexes lacking synaptic cleft and pre-and postsynaptic densities. A second group displayed electron dense pre-and postsynaptic synaptic membrane complex, thin pre-and postsynaptic densities, synaptic cleft, and few synaptic vesicles. A third group consisting of immature axosomatic synapses exhibits only electron dense pre-and postsynaptic membranes and the synaptic cleft. The immature brain parenchyma showed isolated and vacant presynaptic endings, axonal and dendritic cones. These findings provide novel insights into synapse development in a pathological environment represented by the interstitial hydrocephalic edema.  Parietal cortex.
14.CMV CCH19 2 m, F Increased cranial volume, hypertensive fontanelles, deviation of gaze to the right, external rotation of both legs.
Right parietal cortex.

Results
Close examination of hydrocephalic brain parenchyma from

Discussion
In the present study we have demonstrated different stages of synaptogenesis in a brain parenchyma with interstitial hydrocephalic edema. Formation of synapses is one of the most important step in neuronal differentiation and the establishment of neuronal circuits [6]. Some immature synapses, as illustrated in figure two, contain a few clear vesicles but lack typical synaptic membrane specializations, suggesting that they are physiologically immature, as suggested by Vaca et al. [ 7]. In addition, the presence of microphilopodia in our study indicate that there is incomplete tissue maturation.
The edematous interstitial hydrocephalic edema induces abnormal synaptogenesis. Synapse formation is a complex, incompletely understood process that has received only limited investigation in man despite the importance of synaptic dysfunction in common disorders such as epilepsy and mental retardation [8].
According to Bogolepov et al. [9], the initial stage in the synapses formation is the desmosome-like junction. The second stage is whereas stable dendrites have sparser, mature synapses. In the hydrocephalic brain parenchyma we observed synaptic plasticity and degeneration [4,5].
Perisynaptic astrocytes containing glycogen granules were observed surrounding the synaptic contacts for producing energy for synaptic maturation.
In the present study we have visualized microtubules in both pre-and postsynaptic endings. According to Bodaleo et al. Maggy et al. [12] have reported in the hippocampus at birth that most glutamatergic synapses are immature and functionally "silent" either because the neurotransmitter is released in insufficient amount to activate low-affinity alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors or because the appropriate receptor system is missing or nonfunctional. In the newborn rat a brief application of nicotine at immature Schaffer collateral-CA1 connection strongly enhances neurotransmitter release and converts presynaptically silent synapses into conductive ones.
According to Vaca [7], functional cholinergic transmission occurs within minutes of contact between the growth cone and a receptive target. These early contacts contain a few clear vesicles but lack typical ultrastructural specializations and are physiologically immature.
Since differentiation depends on many antecedent developmental events, synaptogenesis can be affected by increase our understanding of the pathogenesis of conditions in which "morphology" seems normal but function is abnormal [8].
Miyazawa T and Sato [13,14] studying hippocampal synaptogenesis in hydrocephalic HTX-rats using a monoclonal antisynaptic vesicle protein antibody considered that hippocampal synaptogenesis is more resilient than that of the cerebral cortex in hydrocephalic brains. Miyazawa et al. [15] considered that despite the presence of continuous pressure due to progressive ventricular dilatation after birth, synaptogenesis in the hydrocephalic cerebral cortex may be relatively resilient.
N-cadherin, a membrane of the Ca2+-dependent cell adhesion molecule family, play essential and specific roles in morphogenesis and histogenesis, as well as in the transduction of long-range growth and differentiation signals of nerve and muscle cells [18]. N-cadherin at the level of synaptic contacts may play a critical role in maintaining nascent pre-and postsynaptic membranes in apposition, enabling incipient synapses to acquire function and contribute to long-term potentiation [19]. N-cadherin would mediate the formation of cell-cell synaptic junctions by homophilic interactions through their extracellular domains [20].
CaMKII alpha also is localized in the brain cortex and in the three-layered structure of developing cerebellar cortex contributing to stabilization of neurons and synapses during development [21].
The disc-large (DLG)-membrane-associated guanylate kinase (MAGUK) family of proteins forms a central signaling hub of the glutamate receptor complex. Among this family, some proteins regulate developmental maturation of glutamatergic synapses, a process vulnerable to aberrations, which may lead to neurodevelopmental disorders. By controlling the pace of silent synapse maturation, the opposing but properly balanced actions of PSD-93 and PSD-95 are essential for fine-tuning cortical networks for receptive field integration during developmental critical periods, and imply aberrations in either direction of this process as potential causes for neurodevelopmental disorders [22].  [23].