Classical conditioning of oxidative DNA damage in rats.

This study investigated whether the formation of 8-hydroxydeoxyguanosine (8-OH-dG), a known oxidative DNA modification relevant to carcinogenicity, can be classically conditioned to a novel taste in order to clarify the possible role of the central nervous system (CNS) or psychological stress on cancer initiation via a classical conditioning mechanism. Male Wistar rats underwent one or two conditioned taste aversion (CTA) experiments in which ferric nitrilotriacetate (Fe-NTA), which has renal toxicity and can induce renal cell carcinoma, served as a visceral unconditioned stimulus (US), and a saccharin solution (SAC) was used as a conditioned stimulus (CS). The 8-OH-dG levels in the group conditioned with the combination of SAC and Fe-NTA significantly increased as compared to those of the uncombined groups by two repeats of the conditioning procedure (P=0.013). The rats that showed a painful response at the Fe-NTA administration had significantly higher values of 8-OH-dG than those without pain (P=0. 003). These results not only provide the first evidence regarding classical conditioning of oxidative DNA damage using the CTA procedure, but also suggest the involvement of the CNS and psychological stress in the pathogenesis of cancer via oxidative DNA damage.