REGIONAL AND SEASONAL-VARIATIONS OF RNA-SYNTHESIS IN THE BRAIN OF THEGREEN FROG, RANA-ESCULENTA

Changes of RNA synthesis were demonstrated in neurons and ependymal ce lls of the green frog Rana esculenta during annual cycle using the Mal lory's trichrome stain as histochemical marker and autoradiography. Si nce the higher affinity of the nuclei for aniline blue is consistent w ith the increase of RNA content, the increase of RNA synthesis was exp ressed as percentage of the blue stained nuclei (% BSN). Neuronal tran scription starts slowly in March or April, reaches a maximum in July a nd declines from September to November or December, depending on the b rain region. In the ependymal cells, RNA synthesis starts in March and lasts until October. Neuronal transcriptional activity is found mostl y in the glomerular layer of the olfactory bulb, in the striatum, nucl eus accumbens septi, lateral and medial septal nuclei of the telenceph alon, in the habenulae and various nuclei of the diencephalon, in the tectum opticum (particularly in the stratum griseum centrale), in the molecular layer of the cerebellum and in various nuclei of the rhomben cephalon. The transcriptional activity of the ependymal cells is quite uniform in the lateral ventricles and the fourth ventricle, while it shows regional symmetric distribution in the third ventricle. Seasonal differences in transcriptional activity appear to be independent of s easonal thermic and photoperiodic fluctuations. In fact, temperature a nd photoperiod manipulations do not modify significantly the number of active nuclei. It is likely that the increase of RNA synthesis in ner ve and ependymal cells corresponds to the resumption of neurotransmitt er biosynthesis after hibernation. The simple Mallory's trichrome stai n provides a reliable method for revealing increased transcriptional a ctivity in histological sections.