Structure and dynamics of water in tendon from NMR relaxation measurements.

Nuclear magnetic relaxation times were measured in collagen tissue when varying the orientation of the fiber with respect to the static field. T1 was found to be only slightly dependent on theta, the fiber-to-field angle, but T2 was very sensitive to the orientation, with a maximum value at the magic angle. The transverse decay curves were multiexponential. Their deconvolution displayed four components; the ones that decayed most slowly were almost independent of theta, but the two fastest ones showed a strong angular dependence that was interpreted with a cross-relaxation model. Quadrupolar dips were visible in the 1/T1 dispersion curves. These dips were independent of theta, so that the magnetization transfer could also be assumed to be independent of the fiber orientation. Finally, each component was assigned to a fraction of protons localized in the macromolecular structure and characterized by particular dynamics. The model of Woessner was applied to the water molecules tightly bound into the macromolecules, which resulted in a dynamical description of this water fraction. This description is compatible with the two-sites model of Ramachandran based on x-ray diffraction and with the extensive studies of Berendsen. However, the important indications obtained from the deconvolution lead to a less static representation of the tissue.

The optokinetic reflex in the cat: modeling and computer simulation.

After a brief comparative review of the dynamic characteristics of the optokinetic reflex ( OKR ) in different species and after a brief description of the main anatomical structures involved in this reflex, a mathematical model of the OKR in the cat is presented. The experimental results obtained by Godaux and Vanderkelen (1984) in the normal and in the totally cerebellectomized cat were used to validate the model and to obtain an estimation of its parameters.