Abstracts

Rationale: West syndrome is an age-specific epileptic encephalopathy manifesting with infantile spasms (IS), as well as dismal neurodevelopmental and epilepsy outcomes. A wide variety of etiologies -structural, metabolic, genetic- have been implicated in West syndrome. The association of ARX (aristaless related homeobox, X-linked) gene mutations with West syndrome, causing defects in GABAergic interneuron migration, suggested that impaired GABAergic interneuron migration or function, called "interneuronopathy", could be a potential etiopathogenic mechanism. To investigate further the pathogenesis of West syndrome, we have established the multiple-hit rat model, a nongenetic animal model of IS, induced by acquired structural lesions. We investigate whether interneuronopathy is also a feature of IS caused by acquired etiologies. We specifically focused on parvalbumin-immunoreactive (PRV-ir) GABAergic interneurons, because these comprise almost half of the GABAergic cortical interneuronal population, and investigated whether their number is abnormal in the cerebral cortex of multiple-hit rats. Methods: Postnatal day (PN) 3 Sprague-Dawley male rats were injected with right intracerebral injections of Doxorubicin and Lipopolysaccharide followed by systemic p-chlorophenylalanine on PN5 (herein called DLP rats). Pups were monitored daily for neurodevelopmental milestones and spasms. On PN20, rats were transcardially perfused; brains were frozen for histology. PN20 male control rats were also used. Coronal brain cryosections (40m) were stained with a primary mouse anti-PRV antibody (SIGMA, St Louis, MO). PRV-ir cells (cells/mm3) from all layers of both sensorimotor cortices and cortical volumes were counted in 8 DLP and 7 control rats, blindly to treatment allocation. Median test was used for statistical comparisons. Results: Cortical thickness of DLP rats was mildly reduced to 91.8% of controls (P=0.0553) in the left sensory cortex, but severely reduced to 57.2% of controls in the right sensory cortex (P=0.01). The densities of PRV-ir interneurons were significantly reduced in the left sensory cortex of DLP rats (median=1006.94 cells/mm3) compared to controls (median=1973.27 cells/mm3) (P=0.0062), whereas there were no remarkable differences in the right cortex. Conclusions: The differences in the reduction of the PRV-ir cell densities and thickness in the right and left sensory cortices of DLP rats indicate a preferential loss of PRV-ir interneurons contralateral to the induced lesion. Ipsilaterally, the induced lesion is however not cell-type specific, manifesting as severe cortical diminishing. These data suggest that interneuronopathy can be a characteristic of IS due to acquired structural lesions. Funding: Funded by the Department of Defense W81XWH-13-1-0180 grant, a CURE (Infantile Spasms Initiative grant), NINDS NS091170 grant, the Heffer family and Segal family foundations, and the Abbe Goldstein/Joshua Lurie and Laurie Marsh/ Dan Levitz families.