Effects of Diagnostic-Level Ultrasound on Dendritic Development in the Mouse Cortex

Papp T, Ferenczi Z, Szilagyi B, Petro M, Varga A, Kókai E, Berenyi E, Olah G, Halmos G, Szucs P, Meszar Z. Ultrasound used for diagnostic imaging facilitates dendritic branching of developing neurons in the mouse cortex. Front Neurosci 2022;16:803356. doi: 10.3389/fnins.2022.803356.

Background: Ultrasound is widely used for fetal imaging, and although considered safe, its potential subtle effects on brain development remain unclear. Neuronal differentiation and dendritic arborization are influenced by both intrinsic and extrinsic mechanical factors, suggesting that exposure to diagnostic ultrasound could modulate neuronal morphology. This study examined whether short-term, high-frequency ultrasound (HFU) exposure affects developing cortical neurons in mice.

Hypothesis: This study hypothesized that a single brief exposure to diagnostic-level HFU alters neuronal morphology in the developing mouse cortex by promoting dendritic branching through mechanosensitive receptor-mediated pathways.

Methods: The authors used in utero electroporation at embryonic day 14.5 to label layer V pyramidal neurons in the mouse retrosplenial cortex with fluorescent proteins. Embryos were then exposed at E18.5 to a 10-minute, 3 MHz HFU stimulus using clinical imaging parameters. Neurons were reconstructed in three dimensions using Neurolucida from confocal image stacks, and morphometric analyses were performed. Immunohistochemistry assessed c-Fos, BDNF and TRPC4 expression, and quantitative RT-PCR examined BDNF mRNA levels.

Results: Ultrasound-treated neurons displayed a significant increase in the number of basal dendrites compared to controls, while dendrite length, branching complexity and soma size were unchanged. HFU exposure transiently elevated c-Fos immunoreactivity without altering BDNF expression, although repeated HFU stimulation increased both c-Fos and BDNF levels. GFP-positive pyramidal neurons expressed TRPC4, suggesting mechanosensitive involvement.

Conclusions: A single diagnostic-level ultrasound exposure modestly enhanced dendritic branching of developing cortical neurons, potentially via TRPC4-mediated signaling. Repeated exposure amplified molecular markers of neuronal activation, implying that even clinically relevant ultrasound intensities can subtly modulate neuronal maturation.