Relationships between seasonal (spring, summer, autumnal) thermal variations and cell proliferation in heterothermic vertebrates, as revealed by PCNA expression in the brain of adult Podarcis sicula

Abstract

Among the literature reports on the possible effects of the seasonal cycle, made of temperature and photoperiod variations, on spontaneous proliferation in the brain of adult fresh water, earth-dwelling Anamnia and heterothermic Amniota, one autoradiographic study was conducted on experimentally brain injured and normal Rana esculenta, collected in the wild in spring and in autumn, and another immunohistochemical study was conducted on brain injured Podarcis hispanica caught in nature in summer. To expand that knowledge an immunohistochemical investigation has been performed on brain of normal adult Podarcis sicula captured in the wild in spring, summer and autumn with the aim to analyse exclusively the seasonal (temperature and photoperiodic) cycle impact on latent spontaneous proliferation. Cycling cells have been labeled for PCNA. The results show that the cycling cells are rare in spring, in intermediate numbers in summer and frequent in autumn. Therefore environmental conditions affect the proliferative capacity of the cells in stand-by, that are typically mainly positioned in some telencephalic areas: the zonae germinativae latero-dorsales, medio-dorsales and ventrales. An investigation on the winter aspect was purposely omitted, since such lack of cycling cells in winter was already known from previous literature reports. With the present findings the time course of proliferation of putative brain stem cells - as demonstrated by immunolabeling for PCNA - is assessed in lizard for the whole year.