Timecourse of effects of triiodothyronine on mouse cerebellar cells cultured by two different methods.

Dissociated cells from week-old mouse cerebellum were grown on either polylysine coated coverslips or on uncoated coverslips. Polylysine coated coverslips give rise to cultures containing all of the cerebellar cell types except Purkinje cells. Use of uncoated coverslips gives rise to cultures which are depleted of granule cells because the granule cells are unable to adhere to glass without a substrate present. The uncoated coverslip cultures are therefore enriched in glial and other non-neuronal cells. Effects of triiodothyronine on each type of culture were then examined as a function of time. On coated coverslips hormone treatment caused a noticeable increase in cell clumping at 1 week, and seemed responsible for a leveling off of the decline in total high-affinity uptake of γ-aminobutyric acid, as well as for a small increase in β-alanine inhibited uptake between 2 and 3 weeks. There was no effect on the overall uptake of thymidine. On uncoated coverslips triiodothyronine treatment significantly increased the thymidine uptake at days 2 and 3, and increased the proportion of Bergmann-like to velate astrocytes at 1 week. There were, however, no significant differences in GABA uptake at any of the time points examined. We conclude that in cerebellar cultures lacking Purkinje cells, triiodothyronine affects both the rate of acquisition and the timecourse of morphological changes (possibly reflecting transformation to more differentiated states) of glial cells but not of neurons. These results are consistent with the hypothesis that, in vivo, thyroxine acts indirectly via Purkinje cells to give developmental signals to neuroblasts and/ or neurons.