Comparative anatomy of cerebellar catecholamine innervation from teleosts to mammals

The cerebellar innervation of the catecholamine (CA) neurons was experimentally investigated with histofluorescence method in the brains of the vertebrates from teleosts to mammals. In the teleosts the source for the cerebellar CA are composed of three CA neuron groups. Hypothalamic CA neuron group contributes mainly to innervation in the valvula cerebelli whose development is dependent on the high degree of the development of the lateral-line organ. CA neurons in the medulla oblongata might innervate the vestibulo-lateral lobe and corpus cerebelli. These two CA neuron groups appear to constitute the main source for the cerebellar CA, though it is certain that rhombencephalic CA neurons also send their axons to innervate the cerebellum. In the tailless amphibian which is devoid of the lateral-line nerves, cerebellar CA especially in the corpus cerebelli is supplied mainly by the rhombencephalic CA neurons which still remain in less developed stage in phylogenetic scale. In the bird, ascending CA neuron system is maintained by long axons and the anlage of locus coeruleus (LC) appear first in this class. A large number of CA nerve terminals in the cerebellum of the bird are supplied by both CA neurons of the dorsal part of the tegmentum and CA neurons disseminated in the tegmental reticular formation. In the mammals showing the highest development of the cerebellar and cerebral cortices, LC is well developed and cerebellar CA is supplied mainly by LC, though cerebellum is innervated by other CA neurons besides LC. Possible significance of the CA neurons on the development of the cerebellum in phylogeny was discussed.