Activation of NOS-cGMP pathways promotes stress-induced sensitization of behavioral responses in zebrafish.

Nitric oxide (NO) is a molecule involved in plasticity across levels and systems. The role of NOergic pathways in stress-induced sensitization (SIS) of behavioral responses, in which a particular stressor triggers a state of hyper-responsiveness to other stressors after an incubation period, was assessed in adult zebrafish. In this model, adult zebrafish acutely exposed to a fear-inducing conspecific alarm substance (CAS) and left undisturbed for an incubation period show increased anxiety-like behavior 24 h after exposure. CAS increased forebrain glutamate immediately after stress and 30 min after stress, an effect that was accompanied by increased nitrite levels immediately after stress, 30 min after stress, 90 min after stress, and 24 h after stress. CAS also increased nitrite levels in the head kidney, where cortisol is produced in zebrafish. CAS-elicited nitrite responses in the forebrain 90 min (but not 30 min) after stress were prevented by a NOS-2 blocker. Blocking NOS-1 30 min after stress prevents SIS; blocking NOS-2 90 min after stress also prevents stress-induced sensitization, as does blocking calcium-activated potassium channels in this latter time window. Stress-induced sensitization is also prevented by blocking guanylate cyclase activation in both time windows, and cGMP-dependent channel activation in the second time window. These results suggest that different NO-related pathways converge at different time windows of the incubation period to induce stress-induced sensitization.

Chrysin, but not flavone backbone, decreases anxiety-like behavior in animal screens.

Chrysin (5,7-dihydroxyflavone), a nutraceutical flavonoid present in diverse plants, has a backbone structure shared with the flavone backbone, with additional hydroxyl groups that confers its antioxidant properties and effects at the GABAA receptor complex. However, whether these effects are due to the hydroxyl groups is unknown. Here we report the effects of chrysin or the flavone backbone (1 mg/kg) in rats subjected to the elevated plus-maze and the locomotor activity test, as well as in the zebrafish evaluated in light/dark model. Chrysin, but not flavone, increased entries and time in the open arms of the elevated plus-maze, as well as time on white compartment of the light/dark model in zebrafish. These effects were comparable to diazepam, and were devoid of motor effects in both tests, as well as in the locomotor activity test. On the other hand, flavone decreased risk assessment in the light/dark test but increased rearing in the locomotor activity test in rats, suggesting effects threat information gathering; important species differences suggest new avenues of research. It is suggested that the specific effects of chrysin in relation to flavone include more of a mechanism of action in which in addition to its action at the GABAA/benzodiazepine receptor complex also could be involved its free radical scavenging abilities, which require specific research. Preprint: https://doi.org/10.1101/575514; Data and scripts:https://github.com/lanec-unifesspa/chrysin.