Apical dendritic spines and axonic terminals in the bipyramidal neurons of the dorsomedial cortex of lizards (Lacerta).

Gold-toned bipyramidal neurons of the dorsomedial cortex of Lacerta have been studied using light and electron microscopy. The spines have been classified as stubby, mushroom-shaped or thin. Thin and mushroom-shaped spines are only found on proximal and intermediate dendritic segments, whereas stubby spines are found on distal dendritic segments. A Timm's method modification for electron microscopy (sulphide-osmium procedure) has been used. Timm-positive axonal endings usually synapse on thin and mushroom-shaped spines, whereas Timm-negative axonal endings usually synapse on stubby spines. Timm-positive afferents and their post-synaptic spines on bipyramidal neurons of Lacerta's dorsomedial cortex are compared with the corresponding elements on pyramidal neurons of the CA3 region of the hippocampus of mammals, on the basis of several histochemical and morphological studies. The possibility that these two neuronal types may be homologous is discussed.