Parvalbumin immunoreactivity during the development of the cerebellum of the rainbow trout.

The distribution of parvalbumin immunoreactivity in the developing cerebellum of the rainbow trout was studied by using a specific monoclonal antibody and the avidin-biotin peroxidase method. Parvalbumin immunoreactivity was absent during the embryonic development of the cerebellum. The first immunoreactive elements, identified by their localization and posterior morphological evolution as immature Purkinje cells, appeared at 6 days posthatching in the presumptive corpus cerebelli and lobus vestibulolateralis. The labeling extended throughout the cerebellum following a caudorostral gradient, and in 21 days alevins, parvalbumin immunoreactive Purkinje cells were also observed in the valvula cerebelli. The appearance of parvalbumin-immunostaining in the Purkinje cells was not simultaneous; the labeling was observed initially in the cell body, extending gradually to the dendritic branches and finally to the axon. From 1 year onwards, parvalbumin immunoreactive terminal puncta from the Purkinje cell axons were observed surrounding the cell bodies of eurydendroid cells, that were parvalbumin immunonegative in all developmental stages studied. The spatio-temporal pattern of parvalbumin immunoreactivity in the rainbow trout cerebellum is different to previous observations in the cerebellum of amniotes.