An automated, high-capacity method for measuring jumping latencies on a hot-plate

A high-capacity automated apparatus for conducting analgetic screening in mice with an entirely objective endpoint is described. A thermostatically controlled hot-plate apparatus is interfaced with a minicomputer for recording jump latencies, which appear to reflect an affective component of pain. In a model experiment, morphine and naloxone were tested at four temperatures and at four times during the day. As expected, latencies were temperature-dependent, with no significant diurnal variation. The apparatus records latencies to both first and tenth jumps, providing a gross estimate of possible motor depressant effects. Morphine significantly increased latencies to first jump, but did not alter the time between first and tenth jumps, suggesting that motor depression did not occur.