How do you evaluate analgesic activity in mice?

To study the Analgesic effect of morphine against acid-inducing writhing in mice

Aim: To study the Analgesic effect of morphine against acid-inducing writhing in mice.

Principle: Painful reactions in animals may be produced by chemicals also. Intraperitoneal injection of phenyl quinone, bradykinin, or acetic acid produces a pain reaction which is characterized as a writhing response. Constriction of the abdomen, turning of the trunk (twist) and extension of the hind legs are taken as a reaction to chemically induced pain. Analgesics, both narcotic and non-narcotic types, inhibit writhing response.


Animals: Mice (25-30 g)

Drugs: Morphine sulfate (dose 5 mg/kg,sc., prepare a stock solution containing 0.5 mg/ml and inject 1 ml/100 g of body weight of mouse), acetic acid 1%v/v Inject 1 ml/100 g of body weight of the animal.


  1. Weigh and number the mice.
  2. Divide the animals into two groups, each consisting of 5 animals. Administer the appropriate volume of acetic acid solution to the first group(which serves as control), and place them individually under a glass jar for observation.
  3. Note the onset on wriths,.. Record the number of abdominal contractions, trunk twist response, and extension of hind limbs as well as the number of animals showing such response during a period of 10 min.
  4. The second group of animals injects morphine. Fifteen minutes later, administer an acetic acid solution to these animals. Note the onset and severity of the writhing response as done in step 3.
  5. Calculate the mean writhing scores in control and morphine-treated groups. Note the inhibition of pain response by morphine.



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