The cytoarchitecture of the inferior colliculus in the cat. A stereological approach

The present study gives an histometric analysis of cells in the different subdivisions of the inferior colliculus. The use of principles and methods of stereology allows the definition of various cellular parameters, i.e. nuclear and cell volume, nuclear and cell profile areas, nuclear diameter, volume proportion of perikaryon, nuclear/cytoplasmic volume ratio and nuclear packing density. Our data confirm the existence of at least 3 parts in the inferior colliculus of the cat, namely: the ventral, the dorso-medial and the lateral parts. We furnish the various parameters which permit the characterisation of cells in these different parts. The dorso medial part or region appears to be composed of numerous cells characterized by their small volume and their high nuclear/cytoplasmic volume ratio. The ventral region seems to be distinguished by its scattered cells, characterized by their large volume and their low nuclear/cytoplasmic volume ratio, whereas the lateral region appears as an intermediate one with scattered cells of low volume. It seems notable that these cytoarchitectonic subdivisions fit well with the functional subdivision since the dorsomedial region receives cortical fibres, the ventral region receives cochlear fibres and the lateral region receives both cortical and cochlear fibres.