[Anatomic demonstration of axon collaterals of the periaqueductal gray formation and the ventrobasal thalamic nuclei of both sides].

In 4 adult cats the left and right thalamic nucleus VPM have been injected with fluorescent substances, Evans Blue and Fast Blue in order to ascertain whether PAG cells send bifurcated axons to the thalamic nuclei of both sides. The results confirm previous studies on the PAG-VPM connections performed in this laboratory by using HRP technique, and demonstrate, within the PAG, the presence of a good number of double-labeled cells (stained by both E.B. and F.B.) intermingled with single-labeled cells, stained either by E.B. or F.B. The double-labeled cells might represent the anatomical substrate of a possible bilateral analgesic mechanism in the trigeminal region.