Analysis of Brain Tissue by FT-IR Microspectroscopy

Biological specimens contain a vast array of cell types, cell layers, extracellular materials, and other components that are structurally and functionally interrelated. Although the histological relationship of each of these constituents has been documented for most mammalian tissues, the chemical relationships between constituents has largely gone unexplored. Fourier transform infrared (FT-IR) spectroscopy can be a powerful tool for analyzing the chemical composition and molecular interactions of biological materials. Analyses of biological materials, however, have been conducted primarily on homogenized and/or purified samples. As a consequence of these limitations, the distribution and concentration of functional groups within different regions of biological tissues have not been appreciated. Several recent technological developments have enabled an FT-IR spectrometer to be combined with microscope optics. This integrated instrument, called an FT-IR microspectrometer, is capable of collecting good quality spectra from small regions of tissues down to a 10 μm × 10 μm square. Spectra collected along a grid pattern can be combined to generate contour or three-dimensional maps that represent the concentration and distribution of functional groups across a tissue. This is important because it permits a correlation of the spatial concentration of chemical functional groups with tissue histology. Analyses can be performed on normal tissue or tissues with unique properties, i.e., developmental or pathological tissues. This review will focus on FT-IR microspectroscopic investigations of normal biological tissue. Particular attention will be given to one example of FT-IR microspectroscopic analysis: white matter of brain tissue. This region was chosen because its infrared profile is very different from other brain regions, and thus it provides a clear illustration of the information that can be obtained by FT-IR microspectroscopy. This review is intended for the spectroscopist who is interested in applying his or her expertise to biological questions as well as to the biologist who is looking for new ways to obtain chemical information about his or her area of study.