The application of Raman microspectroscopy for the study of healthy rat brain tissue

• Three areas of the Wistar rat brain tissue with no fixation method, to arrange samples kept in artificial cerebrospinal fluid during Raman measurements, were studied.
• PCA was applied to explore the structurally sensitive lipid spectral regions, methylene stretching and the deformation vibrations range.
• The structure and molecular conformation of the hydrocarbon chains have been deduced by comparison with model unsaturated fatty acids, linoleic (LA) and docosahexaenoic acid (DHA).
• The I2930/I2880 intensity ratio shows the specificity of the lipids arrangement.

The Raman spectra of three areas of Wistar rat brain tissue: the somatosensory cortex (Sc), the dorsal lateral geniculate nucleus of the thalamus (DLG) and the cerebellar cortex (Cc), excited with 785 nm and 442 nm laser line, were obtained. The no fixation method to arrange the samples was adopted, and fresh brain scraps were kept in artificial cerebrospinal fluid during the measurement. The CH stretching vibrations region was used to probe the state of the lipids and their arrangement in the studied brain areas. The obtained spectra were discussed by analyzing differences in particular spectral regions by evaluating changes in band intensity ratios as well as using principal component analysis (PCA). The I2880/I2850 intensity ratio of the model unsaturated fatty acids, linoleic (LA) and the docosahexaenoic acid (DHA) were treated as a model of lipid composition and used for a comparison because of their similarity. The I2880/I2850 intensity ratio allowed us to investigate the differences in the microenvironment of the studied areas of the brain. The I2930/I2880 intensity ratio showed the specificity of the lipids disorder because they are a mixture of several hydrocarbon chains of different acyl region compositions. These differences were consistent with the lipid molecular architecture in the studied regions as shown in the PCA loadings plot. Some protein also seemed to differentiate the explored areas of the brain. The obtained results demonstrate that Raman spectroscopy can provide insight into healthy brain tissue composition and structure.