Fig. 1.

At the right, sampling of three specimens from the brainstem. The first specimen, ponto-mesencephalic, includes the upper third of the pons and the adjacent portion of mesencephalon. The second extends from the upper portion of the medulla oblongata to the adjacent caudal portion of the pons. The third specimen extends 2–3 mm above and below the obex. A fourth sample is taken from the rostral tract of spinal cord. At the left, the histological sections obtained from the specimens are represented, indicating the main nuclei and structures to be examined