MOLECULAR COMPARTMENTATION EXPRESSED IN CEREBELLAR CULTURES IN THE ABSENCE OF NEURONAL-ACTIVITY AND NEURON-GLIA INTERACTIONS

The purpose of the study was to determine if zebrin compartmentation d eveloped in permanently isolated cerebellar cultures, in the presence of agents that block neuronal activity and in the absence of myelinati on and astrocytic ensheathment of Purkinje cells. Parasagittally orien ted organotypic cultures derived from newborn mice and carefully under cut at explantation to exclude extracerebellar afferents were subjecte d to three conditions: 1) Some were maintained in standard nutrient me dium; 2) some were chronically exposed to tetrodotoxin and elevated le vels of magnesium to block neuronal activity; and 3) some were exposed to cytosine arabinoside for the first 5 days in vitro (DIV) to destro y granule cells and oligodendrocytes and functionally compromise astro cytes, so that the astrocytic survivors did not ensheath Purkinje cell s. Cultures fixed as whole-mount preparations were reacted with antibo dy to zebrin II. Cultures that were cryostat sectioned were dually rea cted with antibody to zebrin II and calbindin. Groups of zebrin(+) and zebrin(-) Purkinje cells were evident after 14 DIV in all of the expe rimental conditions, indicating that zebrin compartmentation developed 1) in isolated cerebellar explants, 2) in the absence of neuronal act ivity, and 3) in the absence of neuron-glia interactions such as myeli nation and glial ensheathment of Purkinje cell somata and dendrites. T hese results are consistent with the concept that expression of the ze brin+ and zebrin(-) phenotypes is an intrinsic property of Purkinje ce lls. The fact that zebrin expression seems to depend on an intrinsic p rogram of differentiation in Purkinje cells suggests some role for zeb rin compartmentation in cerebellar function. (C) 1995 Wiley-Liss, Inc.