Fig. 8. Expression of Hsp70 mRNA in isolated lateral choroid plexus (CP) following +10°C heat shock or zinc exposure in the presence and absence of trimethylamine oxide (TMAO). Levels of Hsp70 mRNA were compared in non-treated and stressed lateral CP tissues obtained from the same shark. +10°C heat stress: tissue segments were incubated in medium with and without TMAO at 13.5°C for 7.5 h () or at 23.5°C for 1 h then 13.5°C for 1.5 h (+10°C). Zinc exposure/recovery: tissue segments were incubated at 13.5°C in medium with and without TMAO for 7.5 h without zinc (No Zn) or with 50 µmol l^–1 ZnSO₄ for 6 h then without zinc for an additional 1.5 h (Zn/Rec). Relative levels of hsp70 mRNA in non-treated and stressed tissues were analyzed by semi-quantitative RT-PCR. Shown here is an EtBr-stained 1.5% agarose gel on which aliquots of PCR products from representative sets of heat-stressed and zinc-exposed tissue, along with a DNA ladder, were electrophoresed; N=2–3 for each experiment.