Topographic, morphologic and developmental characterization of the nucleus loci coerulei in the chicken. A Golgi and fluorescence-histochemical study.

Golgi- and fluorescence-histochemical studies in the chicken shown the presence of a sharply delimited group of aminergic neurons beneath the floor of the fourth ventricle at the mesen-metencephalic boundary. According to the observations reported in other avian species a homology can be established between the mammalian locus coeruleus (LC) and this fluorescent cell mass of the chicken brainstem. Golgi studies revealed an isodendritic pattern of ramification of the neurons in this nucleus. In addition, a developmental study on the morphological maturation of the LC in the chick embryo was carried out by means of the histochemical-fluorescence method for biogenic amines and the rapid Golgi method. The time of the first onset of catecholamine synthesis and storage has been shown to correspond to the 9th day of incubation (stage HH 35), just when these cells display a well-established and peculiar dendritic pattern. All maturational events in the LC of the chick embryo thus occur earlier than in the fetal rat brain, the prenatal development of which is accomplished in a period of comparable length.