MR microscopy of multicomponent diffusion in single neurons

This study examines multicomponent diffusion in isolated single neurons and discusses the implications of the results for macroscopic water diffusion in tissues. L7 Aplysia neurons were isolated and analyzed using a 600 MHz Bruker wide-bore instrument with a magnetic susceptibility-matched radiofrequency microcoil. Using a biexponential fit, the apparent diffusion coefficients (ADCs) from the cytoplasm (with relative fraction) were 0.48 +/- 0.14 x 10(-3) mm2 x s(-1) (61 +/- 11%) for the fast component, and 0.034 +/- 0.017 x 10(-3) mm2 x s(-1) (32 +/- 11%) for the slow component (N = 10). Diffusion in the nucleus appears to be primarily monoexponential, but with biexponential analysis it yields 1.31 +/- 0.32 x 10(-3) mm2 x s(-1) (89 +/- 6%) for the fast component and 0.057 +/- 0.073 x 10(-3) mm2 x s(-1) (11 +/- 6%) for the slow (N = 5). The slow component in the nucleus may be explained by cytoplasmic volume averaging. These data demonstrate that water diffusion in the cytoplasm of isolated single Aplysia neurons supports a multiexponential model. The ADCs are consistent with previous measurements in the cytoplasm of single neurons and with the slow ADC measurement in perfused brain slices. These distributions may explain the multiple compartments observed in tissues, greatly aiding the development of quantitative models of MRI in whole tissues.