Changes in Neuronal Density of the Sensorimotor Cortex and Neurodevelopmental Behaviour in Neonatal Mice with Kaolin-Induced Hydrocephalus

<b><i>Introduction:</i></b> Hydrocephalus is a disorder in which the circulation of cerebrospinal fluid is altered in a manner that leads to its accumulation in the ventricles and subarachnoid space. Its impact on the neuronal density and networks in the overlying cerebral cortex in a time-dependent neonatal hydrocephalic process is largely unknown. We hypothesize that hydrocephalus will affect the cytoarchitecture of the cerebral cortical mantle of neonatal hydrocephalic mice, which will in turn modify sensorimotor processing and neurobehaviour. <b><i>Objective:</i></b> The purpose of this study is to probe the effect of hydrocephalus on 3 developmental milestones (surface righting reflex, cliff avoidance reflex, and negative geotaxis) and on cortical neuronal densities in neonatal hydrocephalic mice. <b><i>Methods:</i></b> Hydrocephalus was induced in 1-day-old mice by intracisternal injection of sterile kaolin suspension. The pups were tested for reflex development and sensorimotor ability using surface righting reflex (PND 5, 7, and 9), cliff avoidance (PND 6), and negative geotaxis (PND 10 and 12) prior to their sacrifice on PND 7, 14, and 21. Neuronal density and cortical thickness in the sensorimotor cortex were evaluated using atlas-based segmentation of the neocortex and boundary definition in 4-μm paraffin-embedded histological sections with hematoxylin and eosin as well as cresyl violet stains. <b><i>Results:</i></b> Surface righting and cliff avoidance activities were significantly impaired in hydrocephalic pups but no statistically significant difference was observed in negative geotaxis in both experimental and control pups. The neuronal density of the sensorimotor cortex was significantly higher in hydrocephalic mice than in age-matched controls on PND 14 and 21 (373.20 ± 21.54 × 10⁻⁶ μm² vs. 157.70 ± 21.88 × 10⁻⁶ μm²; 230.0 ± 44.1 × 10⁻⁶ μm² vs. 129.60 ± 3.72 × 10⁻⁶ μm², respectively; <i>p</i> &#x3c; 0.05). This was accompanied by reduction in the cortical thickness (µm) in the hydrocephalic mice on PND 7 (2,409 ± 43.37 vs. 3,752 ± 65.74, <i>p</i> &#x3c; 0.05), PND 14 (2,035 ± 322.10 vs. 4,273 ± 67.26, <i>p</i> &#x3c; 0.05), and PND 21 (1,676 ± 33.90 vs. 4,945 ± 81.79, <i>p</i> &#x3c; 0.05) compared to controls. <b><i>Conclusion:</i></b> In this murine model of neonatal hydrocephalus, the quantitative changes in the cortical neuronal population may play a role in the observed changes in neurobehavioural findings.