To study the Analgesic effect of morphine in mice using the Tail flick method

Aim: To study the Analgesic effect of the given drug (morphine)in mice using the Tail flick method.

Principle: Pain is an unpleasant feeling, which makes us uncomfortable and reduces physical as well as mental alertness. Although pain is also useful for us because it acts as a warning signal and it warns about something uncommon inside or outside our body. If the pain is minor it may be tolerated but if the pain becomes severe it has to be managed at the earliest.

Analgesia is defined as a state of reduced awareness of pain, and analgesics are substances that decrease pain sensation (pain–killers) by increasing the threshold to painful stimuli. The commonly used analgesics are aspirin, paracetamol(non-narcotic type), and morphine (narcotic type).

Painful reactions in experimental animals can be applying noxious (unpleasant)stimuli such as

  1. Thermal (radiant heat as a source of pain)
  2. Chemical (irritants such as acetic acid and bradykinin)
  3. Physical pressure (tail compression)

In the laboratory, commonly used procedures are the tail-flick (tail-withdrawal from the radiant heat) method using analgesiometer, the hot plate (jumping from the hot plate at 55 º C) method, and acetic acid-induced writhing.


Animals: Mice (20-25 g)

Equipment: Analgesiometer

Drugs: Morphine sulphate(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)


  1. Weigh and number the mice.
  2. Take basal reaction time to radiant heat by placing the tip (last 1-2 cm) of the tail on the radiant heat source. The tail withdrawal from the heat (flicking response) is taken as the endpoint. Normally a mouse withdraws its tail within 3-5 sec. A cut-off period of 10-12 sec is observed to prevent damage to the tail. Any animal failing to withdraw its tail in 3-5 sec is rejected from the study. Take at least 3-5 basal reaction times for each mouse at a gap of 5min to confirm the normal behavior of the animal.
  3. Inject morphine and note the reaction time at 5,15,30,60 min after the drug. As the reaction time reaches 10 sec it is considered maximum analgesia and the tail is removed from the source of heat to avoid tissue damage.
  4. Calculate the percentage increase in reaction time (index of analgesia) at each time interval.



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