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 developed in permanently isolated cerebellar cultures, in the presence of agents that block neuronal activity and in the absence of myelination and astrocytic ensheathment of Purkinje cells. Parasagittally oriented organotypic cultures derived from newborn mice and carefully undercut at explantation to exclude extracerebellar afferents were subjected to three conditions: 1) Some were maintained in standard nutrient medium; 2) some were chronically exposed to tetrodotoxin and elevated levels of magnesium to block neuronal activity; and 3) some were exposed to cytosine arabinoside for the first 5 days in vitro (DIV) to destroy granule cells and oligodendrocytes and functionally compromise astrocytes, so that the astrocytic survivors did not ensheath Purkinje cells. Cultures fixed as whole-mount preparations were reacted with antibody to zebrin II. Cultures that were cryostat sectioned were dually reacted with antibody to zebrin II and calbindin. Groups of zebrin+ and zebrin- Purkinje cells were evident after 14 DIV in all of the experimental conditions, indicating that zebrin compartmentation developed 1) in isolated cerebellar explants, 2) in the absence of neuronal activity, and 3) in the absence of neuron-glia interactions such as myelination and glial ensheathment of Purkinje cell somata and dendrites. These results are consistent with the concept that expression of the zebrin+ and zebrin- phenotypes is an intrinsic property of Purkinje cells. The fact that zebrin expression seems to depend on an intrinsic program of differentiation in Purkinje cells suggests some role for zebrin compartmentation in cerebellar function.