Relationships between seasonal thermal variations and cell proliferation in heterothermic vertebrates, as revealed by PCNA expression in the brain of adult Rana bergeri (Günther, 1986).

The cyclic variations of temperature with seasons, which are accompanied by variations in photoperiod, can activate proliferation in stem cells which survive in various organs and tissues of adult vertebrates, both poikilo- (aquatic and terrestrial) and homeothermic (male songbirds and Mammals). In the brain of these organisms such stem cells are mainly placed in the ependymal and/or sub-ependymal layers. To assess the influence of environmental temperature on the proliferative activity of those cells, an immunocytochemical investigation has been carried out on the brain of normal adult Rana bergeri, taken from the wild in late autumn and immediately submitted to observation. The results were compared with those of previous investigations on the same animal species, caught in their habitat in late autumn as in this study, but housed in standard laboratory environment for several days before beginning the experiments. I have now observed a widespread reduction in proliferation. This finding discordance is reasonably imputable to the former stay of the specimens in a thermostable environment during the previous investigations and appears in agreement with what is known from the literature for comparable experimental conditions, suggesting that a stay for days in a thermally stable, warm environment can counteract the anti-proliferative effect of exposition to the late autumn climate.