Chlorpyrifos (CPF), an organophosphorus insecticide is known to cause ill health in non-target animals by inducing oxidative stress. In this study influence of cold stress (15°C and 20°C) and age as modulating factors on CPF induced oxidative stress was addressed to assess age-related differences and vulnerability in central nervous system of rats. The results indicated an interaction with age and cold exposure resulting in marked decreased activity levels of SOD (P \ 0.05), CAT (P \ 0.05), GPx (P \ 0.05), GST (P \ 0.05) followed by increased MDA (P \ 0.05) and decreased GSH levels (P \ 0.05). The ANOVA and Post-hoc analysis showed that antioxidant enzymes decreased significantly (P \ 0.05) on CPF exposure. Moreover synergistic action of CPF and cold stress at 15°C caused higher inhibition on comparison with CPF and cold stress alone and together at 20°C indicating the extent of peroxidative damage in discrete regions of CNS. Further this study showed young individuals to be more sensitive than adults.

Mitochondrial dysfunction and consequent energy depletion are the major causes of oxidative stress resulting to bring alterations in the ionic homeostasis causing loss of cellular integrity. Our previous studies have shown the age-associated interactive effects in rat central nervous system (CNS) upon co-exposure to chlorpyrifos (CPF) and cold stress leading to macromolecular oxidative damage. The present study elucidates a possible mechanism by which CPF and cold stress interaction cause(s) mitochondrial dysfunction in an age-related manner. In this study, the activity levels of Krebs cycle enzymes and electron transport chain (ETC) protein complexes were assessed in the isolated fraction of mitochondria. CPF and cold stress (15 and 20 °C) exposure either individually or in combination decreased the activity level of Krebs cycle enzymes and ETC protein complexes in discrete regions of rat CNS. The findings confirm that cold stress produces significant synergistic effect in CPF intoxicated aging rats. The synergism between CPF and cold stress at 15 °C caused a higher depletion of respiratory enzymes in comparison with CPF and cold stress alone and together at 20 °C indicating the extent of deleterious functional alterations in discrete regions of brain and spinal cord (SC) which may result in neurodegeneration and loss in neuronal metabolic control. Hence, co-exposure of CPF and cold stress is more dangerous than exposure of either alone. Among the discrete regions studied, the cerebellum and medulla oblongata appears to be the most susceptible regions when compared to cortex and SC. Furthermore, the study reveals a gradual decrease in sensitivity to CPF toxicity as the rat matures.

Reactive oxygen species are generated as a result of a number of physiological and pathological processes which can promote multiple forms of oxidative damage including protein oxidation, and thereby influence the function of a diverse array of cellular processes. In our previous study we have reported that co-exposure to chlorpyrifos and cold stress in aging rats markedly influence the toxic outcome as a result of oxidative stress. In the present study, key neurochemical/enzymes were measured in order to evaluate the macromolecular alterations in response to experimentally co-induced chlorpyrifos and cold stress (15 and 20°C) either concurrently or individually in vivo for 48 h in discrete regions of brain and spinal cord of different age group rats. CPF and cold stress exposure either individually or in combination substantially increased the activity/levels of protein carbonyls, AST, ALT and decreased protein thiols, DNA, RNA and total proteins in discrete regions of CNS. Overall, the effects of co-exposure were appreciably different from either of the exposures. However, synergistic-action of CPF and cold stress at 15°C showed higher dyshomeostasis in comparison with CPF and cold stress alone and together at 20°C indicating the extent of oxidative macromolecular damage in discrete regions of brain and spinal cord. Furthermore, the present study demonstrates that macromolecular oxidative damage is highly pronounced in neonates and juveniles than the young adults.

The adverse effects produced by chlorpyrifos (CPF) or cold stress alone in humans and animals are well documented, but there is no information available relating to the consequences of their co- exposure in an age-related manner. In this study, effects of sublethal doses of CPF were carried out in vivo, for 48 h to assess the biochemical perturbations in relation to interactions with cold stress (15°C and 20°C) in different age group rat CNS. A positive interaction of CPF with age of animal and cold exposure was observed resulting in marked decrease in the activity levels of AChE (P<0.05), ChAT (P<0.05), Na+, K+-ATPase (P<0.05), Ca2+-ATPase (P<0.05), and Mg2+-ATPase (P<0.05). The ANOVA and posthoc analysis showed that regulatory enzymes decreased significantly (P<0.05) on CPF exposure. Overall, the effect of co-exposure was appreciably different from either of the exposures. Synergistic interaction of CPF and cold stress at 15°C showed higher inhibition in comparison with CPF and cold stress alone and together at 20°C. Further, this study reveals that young animals are significantly vulnerable and sensitive than adults.