A device for automatic measurement of writhing and its application to the assessment of analgesic agents.

A device was developed for automatically measuring writhing in mice so as to be applied to the assessment of analgesic agents. The device was composed of a specially designed container equipped with a detector, namely, a mechanoelectro transducer for writhing. The detector was made up of units of a string, two plates, and two strain gauges. In the unit, each end of the string was connected to either of the plates to which either of the strain gauges was attached. The change in tension of the string due to writhing was converted into the mechanical strain of the plates and then the resistance change of the strain gauges. The resistance change was amplified by a Wheatstone bridge circuit that was connected to a differential amplifier, a high-pass filter, comparator(s), and a monostable multivibrator to obtain the electrical signal for writhing. Using this device, writhing was continuously measured, and evaluation of various types of analgesic agents was performed. The result suggests that this device has sufficient accuracy both for the detection of writhing and the evaluation of analgesics. It has the advantage of automatic measurement of writhing in contrast to the conventional visual observation method.