Interaction between autumnal temperature-photoperiod and experimentally induced transient cold shock influences proliferative activity in the brain of an adult terrestrial heterothermic vertebrate, Rana bergeri (Günther, 1986)

It has been shown previously that in adult Rana esculenta, caught in nature, cold-shocked and brain-injured, encephalic cell proliferation is increased when capture and experiment occurred in spring and depressed when they occurred in autumn. Upon exclusive thermal stress cell proliferation appeared weak in spring and intense in autumn. The present study has investigated cold-shocked, but otherwise uninjured Rana bergeri to assess the impact of autumnal environment on encephalic cell proliferation. Lowering temperature--natural or experimental--seemed to exert a mild stimulation on the proliferative activity only in the forebrain. These results complete those previously obtained in spring and appear in substantial agreement with past reports about antithetical interactions between natural (season climate-photoperiod) and experimental (cold stimulus) environmental factors. However, the present results do not seem sufficient to explain the regenerative events described by past authors. A possible explanation of this discrepancy might be that if the spread between the autumnal environmental conditions and the entity of the cold shock is small the latter would be less effective. Alternatively, cold shock may need to be accompanied by further stimuli, such as surgical trauma (partial resection of brain tissue), to achieve extended stimulation and in the absence of those stimuli it would promote cell proliferation only in the forebrain, which is the region best provided with stand-by putative stem cells.