A combined behavioral-physiological method for the assessment of thermal sensibility in the rat

A behavioral and physiological method has been developed to study thermal detection in the rat. Threshold temperatures signaling (1) disruption of a trained behavior (forelimb bar pressing) and (2) increased heart rate were determined using a gradually increasing thermal stimulus delivered to the hindlimb. Response thresholds for disruption of bar press activity (44.8 degrees C) and heart rate elevation (44.4 degrees C) were statistically equivalent. No differences in thresholds for either response end point were found between the left and right hindlimbs, thus validating the consistency of the technique and reproducibility of the stimulus delivery device during test periods of 3-4 weeks. Advantages of the method include the use of two independent end points that are determined objectively, performance criteria that do not rely upon motor responses from the stimulated limb and the use of quantitative descriptors that enables comparisons to be made between different test groups. The method combines behavior with cardiovascular and somatosensory function in a way that can be used for the assessment of spinal and supraspinal pathways involved in thermal detection in the unanesthetized, behaviorally active rat.