Application of autoradiographic analysis of 2-deoxyglucose in the study of locomotion

Trace amounts of [14C]2-deoxyglucose (2-DG) were used to detect regions of the brainstem involved in forelimb stepping in thalamic and low spinal cats. Under ether anesthesia, cats were transected at the stereotaxic A12 level and T10 segment. Two hours later, 50 microCi/kg of 2-DG was infused i.v. and one of 4 procedures was followed: 3 cats stepped on a motor-drive treadmill (Stepping), 3 were kept in a stationary standing position (Rigidity), 2 were anesthetized with sodium pentobarbital (Anesthetized), and 2 were stimulated in the mesencephalic locomotor region (MLR-induced). Absolute optical densities of the autoradiograms corresponding to identified anatomical structures of the brainstem were generally in the following order: Stepping greater than Anesthetized greater than MLR-induced greater than Rigidity. The 2-DG uptake relative to the pyramidal tract (2-DG ratio) also was compared for each of the 4 experimental procedures. In the Stepping cats, the 2-DG ratio was highest in the vestibular nuclei, periaqueductal gray, red nucleus and thalamic nuclei. In the Rigid cats, the 2-DG ratio was highest in the medial vestibular nucleus and subthalamic and thalamic nucleus. These findings suggest that the 2-DG tracer method can be useful in associating neural structures with specific kinds of motor functions within a cat. This is particularly true when using the relative activities of different neural structures and in comparing specific neural structures across cats under different experimental conditions when the amount of 2-DG infused is standardized and the optical densities of the autoradiograms are calibrated to a specific level of 2-DG.