Source: Poirier-83

Brain Res Bull 1983 Sep;11(3):371-397 Comparative morphology of the substantia nigra and ventral tegmental area in the monkey, cat and rat. Poirier LJ, Giguere M, Marchand R Four types of neurons were identified in the substantia nigra (SN) of the monkey, cat, and rat. The compacta-type neurons, characterized by unevenly distributed and intensely stained Nissl substance, display many shapes and sizes. The reticulata-type neurons, characterized by the presence of discrete Nissl bodies, are triangular or round. The intermediary-type neurons contain less intensely stained but more diffusely distributed Nissl substance. These triangular or fusiform neurons have thinner processes than the compacta- and reticulata-type cells. The globular-type neurons, characterized by a high nuclear/cytoplasmic ratio, are much smaller than the three other types of SN neurons. The total number of neurons of the SN, which is much greater in the macaque (n=73,508) than in the cat (n=38,366) and the rat (n=22,532), is comprised mainly of the compacta type neurons (n=62,624; 22,323; and 9.925 in the three species, respectively). The reticulata-type neurons are more abundant in the cat, and the intermediary and globular types are more numerous in the rat. The compacta-type neurons have a particular distribution in each species. The ventral tegmental area (VTA) contains numerous globular-type neurons and a number of compacta-like or transitional type neurons which constitute the foyer pediculaire of the central linear nucleus and the paranigral nucleus. The rostral linear nucleus is unique to the cat brain.