Prodynorphin-derived peptides are critical modulators of anxiety and regulate neurochemistry and corticosterone.

Stress and anxiety are mainly regulated by amygdala and hypothalamic circuitries involving several neurotransmitter systems and providing physiological responses to peripheral organs via the hypothalamic-pituitary-adrenal axis and other pathways. The role of endogenous opioid peptides in this process is largely unknown. Here we show for the first time that anxiolytic parameters of explorative behavior in mice lacking prodynorphin were increased 2-4-fold in the open field, the elevated plus maze and the light-dark test. Consistent with this, treatment of wild-type mice with selective kappa-opioid receptor antagonists GNTI or norbinaltorphimine showed the same effects. Furthermore, treatment of prodynorphin knockout animals with U-50488H, a selective kappa-opioid receptor agonist, fully reversed their anxiolytic phenotype. These behavioral data are supported by an approximal 30% reduction in corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus and central amygdala and an accompanying 30-40% decrease in corticosterone serum levels in prodynorphin knockout mice. Although stress-induced increases in corticosterone levels were attenuated in prodynorphin knockout mice, they were associated with minor increases in depression-like behavior in the tail suspension and forced swim tests. Taken together, our data suggest a pronounced impact of endogenous prodynorphin-derived peptides on anxiety, but not stress coping ability and that these effects are mediated via kappa-opioid receptors. The delay in the behavioral response to kappa-opioid receptor agonists and antagonist treatment suggests an indirect control level for the action of dynorphin, probably by modulating the expression of CRH or neuropeptide Y, and subsequently influencing behavior.

Reduction of intracellular pH inhibits constitutive expression of cyclooxygenase-2 in human colon cancer cells.

Cyclooxygenase-2 (COX-2) over-expression is critically involved in tumor formation. Intracellular pH (pHi) has been shown to be alkaline in cancer cells, and to be an important trigger for cell proliferation. This study therefore analyzed the relationship between pHi and COX-2 expression. HRT-18 and Caco-2 cells cultured in medium with bicarbonate maintained a pHi of approximately 7.6, which is higher than that of non-neoplastic cells. Cells grown in bicarbonate-free medium with a pH at 6.8 showed a reduction in pHi to approximately 7.0. Importantly, reduction of pHi resulted in a complete inhibition of COX-2 mRNA and protein expression. When cells were grown in bicarbonate-supplemented medium at pH 6.8, pHi maintained at approximately 7.6 and COX-2 expression was not inhibited. Additionally, analysis utilizing protein synthesis inhibitor cycloheximide demonstrated that pHi mediated inhibition of COX-2 mRNA expression requires de novo protein synthesis of regulatory protein(s). These data strongly suggest that an alkaline pHi is an important trigger for constitutive COX-2 expression. Defining pHi-mediated mechanisms that govern the constitutive COX-2 expression may help in developing new strategies to block COX-2 over-expression in cancer cells.