Catecholaminergic System of the Medulla Oblongata of the Amur Bitterling (Bony Fishes, Family Cyprinidae)

Abstract

Catecholaminergic (CA-ergic) systems in the medulla of the Amur bitterling (Rhodeus sericeus) were studied using immunohistochemical labeling of tyrosine hydroxylase (ТН), the main enzyme of catecholamine synthesis. The peculiarities of localization of medullary neurons, morphology of the dendrites, and trajectories of the axon projections in the medulla of the Amur bitterling allow us to differentiate three groups of ТН-positive neurons, namely interfascicular cells, units related to the lobus vagus, and cells localized within the area postrema. Interfascicular medullary neurons form a longitudinal column of multipolar cells with broadly branching dendrites localized on both sides with respect to the midline. Neurons of the second group are smaller than interfascicular cells; their dendrites form branchings within the reticular formation and lobus vagus. On apical parts of the cells of the second group, there are branched processes directed toward the clearance of the cerebral ventricle. The third group consists of bipolar ТН-positive cells; their density of distribution is maximal near the area postrema. Terminal axon fields of medullary CA-ergic neurons in the Amur bitterling are connected with sensory systems of the medulla. In the periventricular region of this cerebral zone, we found phenotypically immature forms of the cells, highly immunopositive processes, and elements of radial glia expressing ТН. We hypothesize that, in fishes, dopamine functions as an inductor of development (morphogenetic factor) and is involved in postembryonal neurogenesis in matrix zones of the brain.