1. Functional Experimental Science Chapter 9 Basic Experiments of Neurobiology Experiment 2 Measurement of Pain Threshold

2. Content Experimental objectives 1 Experimental procedures 2 Precautions 3 Results 4 Discussion 5

3. Experimental Objectives Through performing the experiments, students should become familiar with different methods to measure the pain threshold in experiments and to understand at least one method in detail..

4. Experimental Methods and Procedures Tail-flick test 1 Fix loosely the rat on the plateform of tail-flick apparatus and keep the tail on the hole of radiant heat (Fig 9-5). Switch on the power source and begin to count the time with a stopwatch until the rat flicks the tail away from the hole of radiant heat. This time is called latency of tail-flick, tail-flick threshold or pain threshold. Five minutes later repeat the measurement. Repeat 3 times and calculate the average. In the case if the rat has no response until 60 sec after being stimulated, stop stimulating and take 60 sec as its pain threshold..

5. Experimental Methods and Procedures Hot-plate test 2 Put the mouse on a metallic plate. The temperature is adjusted to and maintained at (56±1) ℃. Count the time with a stopwatch until the mouse begins to lick its hind paw. This time is called latent period, i.e. pain threshold. Five minutes later repeat the measurement. Repeat 3 times and calculate the average. In the case if the mouse doesn’t lick the hind paw until 60 sec after being put on the hot-plate, take out the mouse and take 60 sec as its pain threshold.

6. Experimental Methods and Procedures Writhing test 3 In mouse after intraperitoneal injection of 0.2 ml of 0.6% acetic acid, observe and count the number of writhes which consist of abdominal constriction, hind limb extension and concave arching of the back each for 10 min. The observation continues for 60 min.

7. Experimental Procedures Formalin test 4 Give mice an intraperioneal injection with either morphine or sterile saline. Fifteen minutes later, give them 20 μl of 1% formalin normal saline solution subcutaneously via the dorsal hind paw, and place them immediately in transparent box for observation. Then, measure the amount of time that the animal spend licking the injected paw during the first 5 min.

8. Precautions Keep quiet in the laboratory. 1 0.6% acetic acid is easy to volatile, it is preferable to prepare the solution just before the experiment. 2

9. Results 1 Please list the pain threshold that you observed by time sequence.

10. Discussion Discussion the reason of the experimental failure. Based on the recorded pain threshold, analyze and discuss the mechanisms underlying the phenomena.