2-DG UPTAKE PATTERNS RELATED TO SINGLE VIBRISSAE DURING EXPLORATORY BEHAVIORS IN THE HAMSTER TRIGEMINAL SYSTEM

Stimulation of one or several whiskers activates discrete foci through out the trigeminal (V) neuraxis. These foci contribute to patterns, co rresponding to the patterns of vibrissae, that have been directly rela ted to aggregates of cells and axon terminals in the ''barrel'' cortex . Here, we combine high-resolution, 2-deoxyglucose (2DG) mapping and c ytochrome oxidase (CO) staining to determine whether the known pattern of V primary afferent projections is sufficient to deduce the functio nal activation of their targets during exploratory behavior. Four adul t hamsters had all of their large mystacial vibrissae trimmed acutely, except for C3 on the left, and B2 and D4 on the right; in two others, the left C3 and right A1 and E4 whiskers were spared. After fasting o vernight, 2DG was injected and the animals behaved freely in the dark for 45 minutes. The brainstem, thalamus, and cortices were sectioned, then processed for both CO staining and 2DG autoradiography. Image-pro cessing microscopy was used to separate the autoradiographic silver gr ains from the histochemical staining. CO patches were patterned in a w hiskerlike fashion in the full rostrocaudal extent of V nucleus princi palis and in caudal portions of spinal V subnuclei interpolaris and ca udalis, but absent in subnucleus oralis. 2DG silver grains were denses t above those CO patches in the pattern corresponding to the active wh iskers. There were no consistent 2DG foci in subnuclei oralis or rostr al caudalis. In these same cases, prominent 2DG labeling was restricte d to the appropriate barrels in the contralateral cortex. Only one cas e, however, displayed a clear and appropriate region of heightened 2DG uptake in contralateral ventroposteromedial thalamus (VPM) and the ad jacent part of the reticular thalamic nucleus. Patterns of increased g lucose utilization with single whisker stimulation are well matched to the CO patterns that mirror distributions of neurons associated with a vibrissa in the V brainstem complex, thalamus, and cortex. Single wh iskers are represented by relatively homogeneous longitudinal columns of 2DG labeling in the V brainstem nuclei. The columns are not continu ous through the axial extent of the V brainstem complex; rather, they occur separately within principalis, interpolaris, and caudalis. While whisker columns were consistently labeled in interpolaris and caudali s in all animals, the labeling was increasingly variable in principali s, barrel cortex, and VPM, respectively. This suggests that the behavi ng animal can and does significantly modulate activity in this major, synaptically secure pathway.