Sulfide silver architectonics of rat, cat, and guinea pig spinal cord. A light microscopic study with Timm's method for demonstration of heavy metals.

The distribution of heavy metals in the spinal cord of the cat, rat, and guinea pig has been studied histochemically with Timm's sulfide silver method. There was considerable variation in the degree of staining of the neuropil. The dorsal horn showed a laminar staining pattern corresponding to the cytoarchitectonic lamination. Lamina I in the cat and guinea pig was light. Lamina II in all three species was heavily stained. In the rat and guinea pig it could be subdivided in a ventral and a dorsal layer, and moreover in the rat a darkly staining borderzone abutting on lamina III was present. Lamina III, characterized by heterogeneous staining, also appeared dark, although less obvious in the guinea pig. In the ventral horn the coarser stained particles in lamina IX contrasted with the surrounding lamina. Cell staining varied between different cell groups, and within single cell populations. In the cat thoracic cord the cells in nucleus intermedio-lateralis (IL) and nucleus intercalatus (IC) stained very weakly. In Clarke's column and in the motoneuron area cells, uniform in Nissl preparations, could be seen different after Timm staining. The results are discussed in relation to other histochemical patterns, cytoarchitectonics, and terminal fields of afferents. Considerable correlation of the Timm pattern to these data was found.