Abstract
Obstructive hydrocephalus is a brain disorder in which the circulation of cerebrospinal fluid (CSF) is altered in a manner that causes expansion of fluid-filled intracranial compartments particularly the ventricles. The pyramidal neurons of the sensorimotor cortex are excitatory in nature and their dendritic spines are targets of excitatory synapses. This study evaluated the effect of hydrocephalus on dendritic arborization and synaptic structure of the pyramidal neurons of the sensorimotor cortex of neonatal hydrocephalic mice. Sterile kaolin suspension (0.01 ml of 250 mg/mL) was injected intracisternally into day old mice. Control animals mice received sham injections. Pups were weighed and sacrificed on postnatal days (PND) 7, 14 and 21. Fixed brain tissue blocks were silver impregnated using a modified Golgi staining technique and immunolabeled with synaptophysin to determine dendritic morphology and synaptic integrity respectively. Data were analyzed using ANOVA at α0.05. Golgi staining revealed diminished arborization of the basal dendrites and loss of dendritic spines in the pyramidal neurons of hydrocephalic mice. Compared to age-matched controls, there was a significant reduction in the percentage immunoreactivity of anti-synaptophysin in hydrocephalic mice on PND 7 (14.26 ± 1.91% vs. 62.57 ± 9.40%), PND 14 (4.19 ± 1.57% vs. 93.01 ± 1.66%) and PND 21 (17.55 ± 2.76% vs. 99.11 ± 0.63%) respectively. These alterations suggest impaired neuronal connections that are essential for the development of cortical circuits and may be the structural basis of the neurobehavioral deficits observed in neonatal hydrocephalus.
Highlights
Hydrocephalus is a serious problem in sub-Saharan Africa (Salvador et al, 2014)
The animals were weighed weekly and assessed for the development of hydrocephalus. These mice were sacrificed on postnatal days (PND) 7, 14 and 21 and were perfused transcardially first with normal saline for 3 min to wash out the blood cells and for 15–20 min with 4% paraformaldehyde (PFA) until well fixed, using pallor of the liver and stiff muscles as an indication of good fixation
The impression obtained in the qualitative evaluation described above is supported by measurements which revealed that the mean (±standard error of mean (SEM)) length of the basal dendrites was significantly reduced in the hydrocephalic groups on PND 7 (32.09 μm ± 4.17), PND 14 (33.00 μm ± 3.63) and PND 21 (32.38 μm ± 4.84) compared to length in their age matched controls (1889 μm ± 186.70, 2466 μm ± 202.80 and 3091 μm ± 343.60, respectively; Figure 6)
Summary
Hydrocephalus is a serious problem in sub-Saharan Africa (Salvador et al, 2014). It is an incapacitating disorder (Turgut et al, 2018) affecting 0.2–3.5/1,000 healthy births (Krause et al, 2018) and is the most common neurologic disorder requiring surgery in children (Vogel et al, 2012). The dendritic spines of these neurons are the main postsynaptic target of excitatory synapses (DeFelipe, 2015) Specializations in their structure are likely to influence cortical function at the subcellular, cellular and systems levels (Jacobs and Scheibel, 2002; Elston, 2003; Spruston, 2008; Luebke, 2017). It is located in the synaptic vesicles of membranes proteins and a constituent of the family of presumptive channel protein and the most abundant synaptic vesicle protein (Grabs et al, 1994) It is unclear how the hydrocephalic process influences the development of the synaptic landscape and the larger dendritic geometry in pyramidal neurons of the sensorimotor cortex.
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