CALRETININ IN PRETECTOCEREBELLAR AND OLIVOCEREBELLAR PROJECTIONS IN THE CHICK - IMMUNOHISTOCHEMICAL AND EXPERIMENTAL-STUDY

Calretinin (CaR) is a calcium-binding protein that is distributed exte nsively in the central nervous system. It is localized in the cell bod ies and neurites of specific neuronal populations and serves, therefor e, as a reliable anatomical marker. Some components of the pretectocer ebellar projection, which connects specific pretectal nuclei to caudal cerebellar folia, are concerned with the cerebellar control of visual reflexes. We investigated the distribution of pretectocerebellar-proj ecting neurons in relation to cells that show CaR immunoreactivity. Ce lls that project to the cerebellar cortex in the diencephalic primary visual nuclei and in other grisea, like the nucleus spiriformis medial is and the nucleus dorsofrontalis, colocalized with those that appeare d to be immunolabeled intensely with anti-CaR antiserum. To explore th e hypothesis of a common developmental origin of these pretectal cereb ellopetal neurons, we also investigated the development of CaR-immunop ositive cells in the chick pretectum and the arrival of their fibers i n the cerebellum, from 10 days of incubation (stage 36) to posthatchin g stages. Finally, we analyzed the source of CaR+ climbing fibers and found a subpopulation of CaR+ cells in the inferior olivary nucleus. O n the whole, these results suggest that there is a common developmenta l origin of pretectal cerebellopetal neurons, some of which share the property of CaR expression. The functional significance of this correl ation needs to be investigated. J. Comp. Neurol. 397:149-162, 1998. (C ) 1998 Wiley-Liss, Inc.