Abstracts

Rationale: Cortical dysplasia (CD) is a malformation of cortical development that leads to disorganization of cortical layers and neuronal abnormalities. These abnormalities are frequently associated with medically-refractory focal-onset epilepsy in children (Pasquier et al., 2020). However, the temporal evolution of CD and their posterior epileptogenicity are still unknown, to a good extent due to their great variability in location, extension, and subtlety while trying to identify them via neuroimaging (Bernasconi, et al., 2011). Here we present a longitudinal description of macroscopic and microscopic changes during CD development in carmustine-treated rats.

Methods: The experimental protocol was based on a previously described rodent model that induces a diffuse CD (Benardette, 2002). Six pregnant Sprague-Dawley rats were injected with 1,3-bis-chloroethyl-nitrosurea (BCNU, also known as carmustine) (n = 3) or saline solution (Control ; n=3) at embryonic day 15. Their offspring (n=16 for each of the Control and BCNU groups) were scanned in-vivo at post-natal days 30, 60, 120, and 150 using a preclinical 7 T scanner. To visualize brain morphology, T2-weighted images were acquired with spatial resolution of 0.117 x 0.117 x 1.00 mm³. To assess microstructural characteristics, four animals (two each group) were sacrificed for each time point and used for immunofluorescent evaluations of the somatosensory cortex and dorsal hippocampus using layer-specific antibody Foxp2 (1:2000; usually present in neocortical layer VI ) and neuronal marker NeuN (1:350). Large field-of-view mosaics were acquired at 10X magnification with an Apotome-Zeiss microscope.

Results: Longitudinal T2-weighted images (Figure 1) show the evolution of hippocampal atrophy and concomitant enlargement of lateral ventricles, with progressive atrophy mostly evident from P60 onwards, with P30 appearing relatively normal._x000D_  _x000D_ Immunofluorescence with Foxp2 and NeuN (Figure 2) shows an abnormal arrangement of neurons in layers V and VI of the somatosensory cortex of BNCU animals. NeuN showed clear hippocampal atrophy with pyramidal cell dispersion in CA3 and abnormal morphology and neuronal dispersion of the dentate gyrus.

Conclusions: Our results suggest that CD is very subtle in the early stages of development, yet progresses over time to frank macroscopic and microscopic abnormalities in this animal model. The temporal evolution of morphologic changes of CD should be taken into consideration for the development of better diagnostic tools for the detection of CD in humans.

Funding: UNAM-DGAPA (IN2044720). We thank Nydia Hernández-Ríos, Ericka de Los Ríos, Juan Ortiz-Retana, Gema Martínez, Mirelta Regalado, and Leopoldo González-Santos for their technical assistance.