Comparative anatomy of the locus coeruleus. II. Organization and projection of the catecholamine containing neurons in the upper rhombencephalon of the frog, Rana catesbiana.

The organization and projection of the catecholamine (CA) containing neurons in the upper rhombencephalon were experimentally investigated with histofluorescence method in the brain of the bullfrog, Rana catesbiana. A small number of catecholamine containing neurons are located in the upper rhombencephalon. These neurons do not send ascending fibers to contribute CA projection to the forebrain, but give rise to relatively short axons to innervate the cerebellum and neighbouring reticular formation. Judging from their anatomical aspects, it seems that the structure homologous to the mammalian locus coeruleus is not present in the amphibian brain.