Chromatin organization in frog Purkinje neurons during the annual cycle: cytochemical and ultrastructural studies.

Feulgen-DNA microdensitometric and propidium Iodide-DNA (PI-DNA) microfluorometric evaluations were made in Purkinje cells of cerebella from hibernating frogs and from active frogs. Higher Feulgen-DNA/distribution area ratios and lower PI-DNA values were found in the hibernating frog (both at high and low fluorochrome concentrations). These data indicate a higher degree of chromatin compactness. During the activity period, the Feulgen-DNA/distribution area ratios are lower and the Feulgen-DNA content is higher; the corresponding higher PI-DNA values indicate a lower degree of chromatin condensation. Histochemical and ultrastructural data show clearly different distribution patterns of chromatin and ribosomes in the two periods. The overall results underscore lower activity of neurons and a greater homogeneity within the Purkinje cell population during hibernation.