Growing evidence suggests that certain psychiatric diseases such as schizophrenia and developmental disorders such as autism may involve subtle changes in specific neuronal cell-types. GABAergic interneurons that express the calcium-binding protein parvalbumin (PV) are one such cell-type, with PV-cells comprising about ~50% of all GABAergic interneurons and therefore being ~1 out of every 10 neurons in the brain. How does the number and distribution of PV-cells throughout the brains of mouse models of these disorders differ as a function of disease state? To address this question in the most unbiased manner, eFLASH whole hemisphere or whole brain labeling can be performed using LifeCanvas Technologies’ SmartLabel rapid immunohistochemistry device. Following SHIELD tissue preservation and optical clearing via delipidation in SmartClear II Pro, this intact mouse brain hemisphere was immunolabeled in only ~24 hours using just 20 µg of anti-PV antibody.
By refractive index matching the hemisphere and then imaging it in just ~30 minutes using LifeCanvas’s SmartSPIM light-sheet microscope, single-cell resolution data of the entire sample is acquired in one contiguous image volume, enabling holistic analysis of the tissue. Compared to cutting tissue into hundreds of thin sections and then imaging only those discrete regions of interest (ROIs) thought important to interrogate a specific hypothesis, unbiased study of the whole organ helps counteract spotlight biases and creates fertile ground where novel and unexpected discoveries can take place. By co-staining for additional cell-type markers and then analyzing the image data by aligning it to a reference atlas and quantifying number of PV-positive cells per brain region with automated cell-detection algorithms, a powerful pipeline to molecularly phenotype tissues can be created. With this approach, new insight into mouse models of these disorders could be obtained by investigating potential changes in the density and laminar & regional patterning of these cells, as well as changes in their co-expression of markers of neuronal activation (e.g., immediate early genes) or cell health (e.g., oxidative stress markers). Importantly, by performing these analyses and assessing the effects of candidate pharmacological interventions aimed at treating these conditions on a brain-wide basis, a much more complete picture than can be obtained from using only thin sections of tissue can be considered.
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