Photoacoustic histology of oxidative stress-induced hippocampal cell death in a mouse brain

Photoacoustic microscopy (PAM), an emerging biomedical imaging technology, has demonstrated the label-free imaging capability to visualize biomolecules with the aid of superior optical contrast in them. Especially employing ultraviolet (UV) laser at the wavelength of 266 nm, we have developed an UV-PAM. Unlike conventional histology methods such as frozen and formalin-fixed paraffin-embedded (FFPE) sections, UV-PAM can illustrate cell nuclei by utilizing superior light absorption of DNA/RNA without time consuming procedures. In-vitro experiments were conducted to evaluate the spatial resolutions of the developed system. The measured lateral resolution was 1.3 μm, and axial resolution was 62.2 μm. Then we performed ex-vivo experiments using frozen sections of mouse brain to demonstrate the imaging capability of UVPAM as a rapid histology tool. Oxidative stress induced by kainic acid (KA) was monitored using UV-PAM, which is considered as a significant cause for epileptic neuronal brain damage. We have shown the apoptotic feature resulted from the KA-induced hippocampal cell death in a mouse brain section. In contrast to the brain section of the control mouse model, the substantial nuclear marginalization of hippocampal cell death was illustrated in the vulnerable neurons of the CA1 and CA3 regions on the KA-treated mouse with PA imaging. In addition, the PA histologic results were evidenced by the corresponding HE stained images on both the control and the KA-treated mouse, showing similar hippocampal cell death. The PA histologic results could also provide its potential application for use in the monitoring of the morphological changes observed in astrocytes including hypotrophy, hyperplasia, and neoplasia. Further, it might be a beneficial histologic tool for treatment monitoring of neurodegenerative diseases such as acute traumatic brain injury and neuroprotective effects of treatments on the diseases.