Cellular organization of locus coeruleus in the rat as studied by Golgi method

The locus coeruleus (LC) of rats at different ages was studied in sections stained by the Golgi-rapid method. The LC is composed of two types of neurons, medium-sized (20mu x 35mu) and small cells (10mu x 15mu). The medium-sized cells are mainly fusiform in shape and occupy the dorso-caudal part of the nucleus, while pyramidal or multipolar cells frequently occur in the ventral part. Both types of cells bear a moderate to large number of spines on the surface of their soma, which form the main criterion for identifying the LC neurons. Though they radiate several relatively short dendrites in different directions, which bifurcate once or twice, the medio-ventral ramification is prevailing, extending beyond the limit of cells to the pontine central gray adjacent to the LC. The latter region might constitute the principal receptive sites of LC for inputs from various origins. Axons of LC neurons take their initial course either latero-rostral- or latero-caudalwards, while some axons divide dichotomously rostral- and caudalwards. Fine axon collaterals are frequently demonstrated within the LC and sometimes seem to contact with dentrites of LC neurons. Besides this, two kinds of afferents of unknown origins are observed between LC neurons. At least three kinds of small oval neurons are occasionally impregnated, though their axonal distributions cannot be demonstrated.