Environment temperature affects cell proliferation in the spinal cord and brain of juvenile turtles

The spinal cords and brains--comprising dorsal cortex (DC), medial cortex (MC) and diencephalon (Dien)--of juvenile turtles acclimated to warm temperature [27-30 degrees C; warm-acclimated turtles (WATs)] revealed higher density values of bromodeoxyuridine-labeled cells (BrdU-LCs) than those acclimated to a cooler environment [5-14 degrees C; cold-acclimated turtles (CATs)]. Both populations were under the influence of the seasonal daily light-dark rhythms. Pronounced differences between WATs and CATs (independent t-test; confidence level, P<0.01) were found in the central area of the spinal gray matter and in the ependymal epithelium lining the brain ventricles. Forebrain regions (DC, MC and Dien) also revealed significant differences between WATs and CATs (independent t-test; confidence level, P<0.01-0.05). Unexplored biological clocks that may be affecting cell proliferation were equalized by performing paired experiments involving one WAT and one CAT. Both animals were injected on the same day at the same time and both were sacrificed 24 h later. These experiments confirmed that a warm environment increased cell proliferation in the CNS of turtles. Double- and triple-labeling experiments involving anti-BrdU antibody together with anti-glial protein antibodies revealed that temperature modulates not only cell populations expressing glial markers but also other cells that do not express them. As expected, in the case of short post-injection (BrdU) surviving time points, no cells were found colabeling for BrdU and NeuN (neuronal marker). The probable direct effect of temperature on the cell division rate should be analyzed together with potential indirect effects involving increased motor activity and increased food intake. The fate of the increased BrdU-LCs (death, permanence as progenitor cells or differentiation following neuronal or glial lines) remains a matter for further investigation. Results are discussed in the light of current opinions concerned with post-natal neurogenesis in vertebrates.