5.3.2. Grid-shock test

(ii) M-Zone, (iii) ice-tray and (iv) ice floor. At the start, the mouse is exposed to different parts of the M-model mainly M-Zone for about 60 s, so that the mouse is sensitive of the existence of M-Zone prior to the initiation of the experiment. From the top/ceiling of the perspex box, the animal is inserted. The ice tray containing of ice block is slide onto the floor of the perspex box. When the animal is not able to bear the cold surface of ice floor, it escapes to M-Zone. The time taken by the animal to run away into the M-Zone (Flight-Zone) when placed on the ice-floor is called endurance time. This time is recorded with the help of a stopwatch. In general, mice take about 4–6 s to escape into the M-Zone to evade ice floor. Separate groups of animals are pretreated with narcotics such as butorphanol (partial opioid agonist, 2 mg/kg, s. c), tramadol (opioid agonist, 5 mg/kg, s. c), pentazocine (10 mg/kg, s. c) and non-narcotic analgesics such as ketoprofen (non-selective COX inhibitor, 5 mg/kg, p. o), diclofenac (non-selective COX inhibitor, 15 mg/kg, i. p) and meloxicam (preferential COX-2 inhibitor, 5 mg/kg, s. c) to determine their effect on endurance time. This time is recorded at 0, 15, 30, 45, 60, 120 and 180 min after

In this test, an increasing amount of pressure is applied to a punctiform area on the hind paw or, far less frequently, on the tail. The tail or paw is wedged between a plane surface and a blunt point mounted on top of a system of cog wheels with a cursor that can be moved in the direction of length of a graduated beam [66]. When the pressure increases, following step wise reactions occurs, i.e. the reflex removal of the paw or a complex movement of the animal to free its captured limb and at last a vocal response is noticed. Randall and Selitto with the aim of enhancing the sensitivity of the test offer comparison of thresholds seen with an inflamed paw

The key method for the study of pain in animal models is the assessment of mechanosensitivity. This is frequently executed with the use of von-Frey filaments in an up-down testing model. This is the most commonly used method for measuring pain in animals described by Vivancos [68] for mechanosensitivity testing in rodents. Though, in this method, animals are getting a changeable amount of stimuli which may direct the animals in distinctive groups getting diverse testing experiences that affect their subsequent responses. In order to standardize the measurement of mechano-sensitivity, a simplified up-down method (SUDO) for reckoning paw withdrawal threshold (PWT) with von-Frey filaments has been developed that uses

Progressively escalating strength of electrical stimuli can be applied in range (lasting for some milliseconds) through subcutaneous electrodes positioned in the tail of the mouse or the rat. One can see the following: when such slowly increasing intensities of electrical stimuli are

administration of the standard drugs [65].

330 Pain Relief - From Analgesics to Alternative Therapies

5.2.1. Strain gauges

and with a healthy paw [67].

5.2.2. von-Frey filaments

5.2. Pain-state models using mechanical stimuli

a constant number of five stimuli per test [69].

5.3. Pain-state models using electrical stimuli

5.3.1. Electrical stimulation of the tail

Approximately weighing of 18–20 g of male mice is put into the clear plastic chambers. The floor of box spaced about 1 mm apart is wired firmly with stainless steel wire. In the form of square wave pulses, the stimulus is given 30 cycles/s with a period of 2 ms/pulse. By escalating shock intensities, the mice gasp, show a frightening reaction, increase movement or effort to jump. Pain threshold response is defined as the behaviour correctly reflected on the oscilloscope by marked vacillation of the displayed pulse. Prior to administration of the test drug the pain thresholds are find out in each individual mouse twice at 15, 30, 60, 90 and 120 min subsequent dosing [71].

#### 5.3.3. Stimulation of the tooth pulp

In this method, electric current is applied to stimulate the tooth-pulp of the animal. Pain symbol is exhibited as biting, chewing, licking and head flicking.

Rabbits of either sex are used as animal model. Thiopental 15 mg/kg or fentanyl-citrate 0.2 mg/kg i.v. produces anaesthesia. A high-speed dental drill is used to create pulp chambers in the lateral margins of the two front upper incisors.

Rectangular current with a frequency of 50 Hz for 1 s is applied. The 0.2-mA electrical current produces the phenomenon of licking [72].
