Modification of the Thermal Radiation Method for Assessing Antinociceptive Activity in the Rat

¹ From the Department of Pharmacology, Hoffmann-La Roche, Inc., Nutley, New Jersey, Aviation Medical Acceleration Laboratory, U. S. Naval Air Development Center, Johnsville, and the Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania

A modification of the thermal radiation method of measuring thresholds in rats is described which permits taking into account changes in skin temperature during measurement of antinociceptive activity. The essential measurements to be made include the intensity of the radiation stimulus, the skin temperature prior to stimulation and the exposure time. With this information available, the reaction response can then be expressed in terms of the significant variable, i.e. the skin temperature at which the reaction occurs. The variability of penetration and reflection of the nonblackened skin of the white rat is not significant; however, application of a blackening agent increases the heat absorbing power of the skin and facilitates the use of the radiation equipment. It was found that skin temperature changes following the administration of drugs represent an important factor which must be considered in the assessment of potential analgesic activity by this method.