Region-specific microglial alterations in the acoustic startle circuit in Shank3 mice

Autism spectrum disorder (ASD) encompasses a diverse range of neurodevelopmental conditions characterized by variations in social interactions, stereotyped behaviors, and sensory processing differences. Altered tactile and auditory sensory processing is among the most frequently observed phenotypes in ASD animal models, particularly in Shank3 gene knockout rodents. Previous research has focused extensively on neural activity associated with Shank3 deficiency and sensory dysregulation, but the role of glial cells, especially microglia, has been largely overlooked. Microglia, the central nervous system's primary immune cells, are crucial for regulating neural activity throughout development and adulthood. To address this gap, we used immunofluorescence microscopy to examine microglial morphology, density, and the fluorescence intensity of IBA1 and CD68 in adult Shank3 knockout and wild type mice, focusing on brain regions primarily involved in the acoustic startle circuit, while including the somatosensory cortex as a control region. We examined six brain regions involved in auditory and tactile sensory processing: the somatosensory cortex, central nucleus of the amygdala (CeA), caudal pontine reticular nucleus (PnC), reticulotegmental nucleus (RtTg), inferior colliculus(IC), and cochlear nucleus (CN). Our findings showed a 39% increase in IBA1 expression in the CeA (p = 0.01) and a 13% increase in microglial density in the PnC (p = 0.02). However, we found no evidence of robust microglial activation, as indicated by the absence of morphological changes or alterations in CD68 expression across the examined regions. These results indicate that moderate microglial alterations in the Shank3 mouse model may be circuit-dependent rather than a global phenomenon across all sensory modalities, warranting further investigation into the interplay between glial cells and sensory circuit dysfunction.