Raman study of brain functions in live mice and rats: A pilot study

Raman spectra of brain tissues of live mice and rats were successfully obtained using a miniaturized Raman probe. The use of a ball lens hollow fiber Raman probe and a background-free electronically tuned Ti:sapphire laser enabled the measurement of high-quality Raman spectra in the fingerprint region and high-wavenumber region at exactly the same measurement point at the same time. The measurements were performed on the animal under anesthesia by sodium pentobarbital, after inhalation of diethyl ether (DE) vapor, and after euthanasia. The obtained spectra in the high-wavenumber region suggest that water concentration and water cluster conformation change with changes in the condition of the animal, and the change shows site dependency in the brain. In the frontal cortex, a minor increase in the water cluster of a specific conformation was observed by the inhalation of DE vapor. On the other hand, water concentration decreased after the animal was euthanized. In the olfactory lobes, the water concentration increased both after DE vapor inhalation and after euthanasia. No major spectral change was observed in the fingerprint region, suggesting that the functions of the water molecule are independent of other molecules. The study results demonstrate the high viability of Raman spectroscopy for studying brain function in live experimental animals.