Monoamine oxidase in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus) and the tortoise (Clemmys japonica)

Summary

Distribution of monoamine oxidase (MAO) was histochemically determined in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus), and the tortoise (Clemmys japonica) by means of a tryptamine-tetrazolium (TNBT) method. The median eminence in all of these species gave a similar MAO reaction. The ependymal cells showed a very slight or no MAO activity. MAO-positive fibers, which extended rostro-caudally to the pars nervosa, were observed in the fiber layer of the median eminence. In the external layer of the median eminence, a large number of strongly MAO-positive fibers were identified around blood capillaries of the primary portal plexus. In the tortoise, these fibers were more conspicuous in the posterior region of the median eminence than in its anterior region. The presence of MAO-positive fibers around the portal blood capillaries suggests that a monoaminergic mechanism is functional in the regulation of the secretion of releasing factors at the level of the median eminence. MAO-positive fibers in the pars nervosa were, like in the median eminence, thickly distributed around the blood capillaries. In the pars intermedia, there were a considerable number of MAO-positive fibers among the intermedia cells and sometimes in close contact with them. These fibers appeared to innervate the pars intermedia via the pars nervosa.