Non-pyramidal neurons in the medical bank (Clare-Bishop area) of the middle suprasylvian sulcus. A Golgi study in the cat.

The morphology and laminar distribution of non-pyramidal cells in the medial wall (the Clare-Bishop area) of the cat middle suprasylvian sulcus were studied with the rapid Golgi and Golgi-Kopsch methods. The cells are classified into three categories on the basis of their morphological features; in particular, the pattern of axonal ramifications. Class V cells with vertically oriented axonal ramification include three subtypes. Type V-1 cells are found mainly in layer II and in the upper part of layer III and have narrow axonal ramifications, less than 150 micrometer wide. Type V-2 cells are situated almost exclusively in layer III and display a pattern of axonal "cascades", less than 250 micrometer in width. The axon terminals of both of these subtypes may potentially end on apical dendrites of pyramidal cells, and both subtypes have sparsely spinous dendrites. Type V-3 cells with spinous dendrites are characterized by narrow, recurrent axonal ramifications, located mainly in layer IV. Class H cells, composed of four cell types, have horizontally oriented axons. Type H-1 cells with spine-free dendrites are situated in layers III-VI and have widely distributed axons. Type H-2 cells cells with spinous dendrites also have long axonal branches; these are distributed in all layers, but the somata are found mainly in the deeper part of layer III and layer IV. Type H-3 cells with spine-free dendrites inhabit layers I and II, and have axons mainly confined to layer II. The axons of these types (H-1, H-2 and H-3) may potentially contact somata and proximal dendrites of pyramidal cells. Type HV cells with spinous dendrites are observed chiefly in layers I and II and have axons that extend for as much as 300-400 micrometer and apparently terminate on apica dendrites of pyramidal cells. Class L cells, composed of two cell types, are characterized by a local axonal ramification less than 200 micrometer in diameter which also is likely to terminate on pyramidal cells. Type L-1 cells with spine-free dendrites are found through all cortical layers. Type L-2 cells with sparsely spinous dendrites are observed mainly in layer II and the upper part of layer III and have a bush-like axonal ramification. For assistance in the further elucidation of cortical structure at the cellular level in the C-B area, the potential contacts between the pyramidal and non-pyramidal neurons, and the relations between the neurons and corticipetal afferents; important components of the columnar and laminar organization of the cortex, are discussed.