Zebrafish suggested as model to test analgesics

Authors: Correia, A et
Journal: Pharmaceuticals 4, 665-680; doi:10.3390/ph4040665
Year: 2011
Where: Portugal
A nociceptor is a sensory receptor that reacts to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process is called nociception.

Three studies were carried out on different groups of zebrafish.

Study 1
1. Acetic acid injected into lips
Result: reduced activity

Study 2
1. Morphine injection
2. Acetic acid injected into lips
Result: reduced activity, but less of a reduction than Study 1

Study 3
1. Morphine injection
2. naloxone injection (known to counter the effects of morphine)
3. Acetic acid injected into lips
Result: reduced activity, similar to Study 1

The study therefore showed that pain of the acetic acid affected the behaviour of the fish. As in humans, the pain could be blocked by morphine. Again, as in humans the analgesic effect of morphine could be blocked.

"Our results suggest that a change in behavioral responses of zebrafish to acetic acid is a reasonable model to test analgesics."

"The response scales with stimulus intensity, is attenuated by morphine, and the analgesic effect of morphine is blocked with naloxone."

"Fish possess the necessary sensory components to detect a noxious stimulus and also have brain areas similar to those of higher vertebrates that respond to painful stimuli."

"The neuronal activity detected in fish brain centers such as the spine, cerebellum, tectum and telencephalon also suggests the possibility of pain perception in fish in which the dorsal telencephalon (similar to the cortex in mammals) may mediate the coordination of the pain information." "There is convincing evidence that fish possess nociceptors that react in a fashion similar to those in mammals."

"We also showed that pre-treatment with naloxone, an opioid receptor antagonist, significantly attenuated morphine antinociceptive behaviors in adult zebrafish. These results suggest an opioid receptor involvement in the morphine effect similar to mammals and amphibians."

"A change in behavioral responses of zebrafish to acetic acid is a reasonable model to test analgesics. The response scales with stimulus intensity, is attenuated by morphine in a dose-dependent manner, and the analgesic effect of morphine is blocked with naloxone."
Fish Pain