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Mad Science 2006 : Rats’ screams of pain are recorded

Rat being injected

In a collaborative behaviour study involving the University of Nottingham and the University of Ireland, male rats were placed in a small perspex chamber that was wired up to deliver electric shocks to their feet. A special microphone was placed above the chamber to record the rats’ cries of pain.

On the first day of the experiment, a group of rats received an electric shock every minute, for 10 minutes. A day later, they were briefly anaesthetised and given an injection of formalin - a toxic chemical that causes considerable and lasting pain - into one foot. Half an hour later, the fully conscious animals were returned to the perspex chamber and observed for 15 minutes. The level of pain experienced by the rats as a result of the formalin injection was measured by the amount of time they spent flinching, and licking, biting and shaking the injected foot.

A second group of rats were not subjected to foot-shocks but were given formalin injections. When placed in the perspex chamber, this group appeared to feel the painful effects of the formalin more than the previous group but emitted fewer cries of pain.

All the rats were then killed by ‘stunning’ (this is normally achieved by a severe blow to the head) and decapitation. Their brains were studied. The researchers said that the results confirmed those of other scientists, and that further such investigations were needed.

This study was supported by the Wellcome Trust.

Ref. Finn DP, Jhaveri MD, Beckett RG, Madjd A, Kendall DA, Marsden CA, Chapman V. Neuroscience 2006; 138:1309-1317. ‘Behavioural, central monoaminergic and hypothalamo-pituitary-adrenal axis correlates of fear-conditioned analgesia in rats.’

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