Noxious stimulation of animals by brief intense laser induced heat: Advantages to pharmacological testing of analgesics

A new technique for experimental pain inducing in animals is described. The technique, which involves brief and intense pulses of heat generated by a CO₂ laser, has several advantages over other procedures of noxious thermal stimulation. The animals do not have to be restrained, they do not adapt to the stimulation, and they respond by a rich behavioral repertoire which is related to the stimulus intensity. The usefulness of the technique in pharmacological testing of analgesics is illustrated in a preliminary study demosntrating a remarkable elevation of the thresholds to this type of noxious thermal stimulation after subcutaneous morphine injections.