Structural organization of the pedunculopontine nucleus of the tegmentum of the dog midbrain.

The aim of the present work was to perform cytoarchitectonic studies of the pedunculopontine nucleus (PPN) of the tegmentum of the midbrain in dogs to define the margins of this structure and to describe its separate substructures. The Nissl and Kluver-Barrera methods and histochemical detection of NADPH-diaphorase, this being a selective marker for cholinergic neurons in the tegmentum, were used to analyze the fiber organization, the morphological types of neurons, and the neuron density in the PPN of the tegmentum. This yielded a map of this nucleus in the dog with descriptions of the margins of its component zones: the compact and the diffuse. The mesencephalic extrapyramidal part could not be discriminated from the general composition of the PPN of the tegmentum.