A NONINVASIVE METHOD FOR STUDYING QUANTITATIVELY HEAT-EVOKED NOCIFENSIVE HINDLIMB WITHDRAWAL REFLEXES IN LIGHTLY ANESTHETIZED RATS

We have developed a noninvasive method for studying quantitatively the magnitude of hindlimb withdrawal reflexes induced by noxious heat in lightly anesthetized rats. The amplitude, latency, and duration of the hindlimb withdrawal was determined by a very small piezoceramic devic e placed on the hamstring muscle while the glabrous skin of the hindpa w was stimulated using a feedback-controlled contact thermostimulator. An increase in the amplitude and duration of the withdrawal response, concomitant with a decrease in the response latency, was found with i ncreasing stimulus temperature. The sensitivity of the method was veri fied using morphine, which produced a dose-related (3.5-7.0 mg/kg) att enuation of all these response components. The use of a piezoceramic d evice for measuring the withdrawal response provides a quantitative, n oninvasive method for evaluating the magnitude of various components o f the nocifensive withdrawal reflexes induced by noxious stimuli in li ghtly anesthetized rats.