VPT 321: Veterinary Neuropharmacology (2+1)

PROCEDURE

Analgesiometer

• The nichrome wire is heated to a temperature of 55 degree celcius which can be adjusted by milliampere gauge on the instrument which is usually adjusted up to 2.5 mA on the instrument.  In order to maintain this temperature the nichrome wire is surrounded by a double jacketed inlet and outlet through free water flow in and out continuously.
• The rats are the animal of choice for this experiment.  Six rats are weighed and sex of the animal is recorded and markings are also made for easy identification.
• The rat is restrained in a rat holder made of stainless steel which is closed at both ends.  At one end it is provided with holes on the lid through with free air flows in for the rat to respire.  At the other end of the lid a slit is provided on the lid for the tail to protrude out.  Once everything has been set the base of the tail is placed on the nichrome wire and the time at which it is placed is noted.  The end point of the reaction time is the flick of the tail.  Hence, the time at which the tail is flicked from the nichrome wire is noted.  The difference in the timing gives the reaction time.
• The animal is then injected with the drug at a dose rate of body weight i.p.  After 30 minutes the same procedure is followed and the following timings are recorded and the reaction time is calculated.  An increase of 7 sec in reaction times after administration of drug is indicated for its analgesic effect.  Usually it is not advisable to keep the tail of the rat on the nichrome wire for more than 15 seconds (cut off time) to avoid injury to tail.