Fourier transform infrared spectroscopic analysis of rat brain microsomal membranes modified by dietary fatty acids: Possible correlation with altered learning behavior

We measured the Fourier transform infrared spectra of brain microsomal membranes prepared from rats fed under two dietary oil conditions with and without brightness-discrimination learning tasks: one group fed α-linolenate deficient oil (safflower oil) and the other group fed the sufficient oil (perilla oil) from mothers to off-spring. The infrared spectra of microsomes under the two dietary conditions without the learning task showed no significant difference in the range 1000-3000 cm^-1. Only after the learning task were the infrared spectral differences noted between the microsomal membranes from both groups. Spectral differences were observed mainly in the absorption bands of fatty acid ester at around 1730 cm^-1 (sn-2 position), those of phosphate and oligosaccharides in the range of 1050-1100 cm^-1, and a band at around 1145 cm^-1. The infrared band of fatty acid ester at the sn-2 position in the microsomal membrane shifted to a longer wavenumber position in the perilla oil group than in the safflower oil group, suggesting a difference between both groups in hydrogen bonding of the fatty acid ester with water. A band observed at 1055 cm^-1 and a small band at around 1145 cm^-1 in the second derivative spectrum decreased in intensity in the perilla oil group after learning task. These bands were assigned mainly to the oligosaccharide C-O bond in hydroxyl groups that might interact with some other membrane components. These results suggest changes in hydration of membrane surface and modification in oligosaccharide environment (removal or modification) of microsomes, which may be correlated in part with dietary oil-induced changes in learning performance.