A simple, quantifiable, and accurate method for applying a noxious mechanical stimulus.

I n animals, anesthetic requirements for a supramaximal noxious stimulus are usually determined using a hemostat applied to the tail or extremity (1,2). Although a generally accepted technique, the applied force is either not stated or unknown. Furthermore, when a noxious mechanical stimulus is applied to determine neurophysiological responses (e.g., dorsal horn activity), the force is often varied and must be accurately known. We sought to determine whether spring-activated A-clamps could be used to reproducibly apply a known force. The force (F) required to deform a spring is proportional to the spring constant (k). In the case of compressing or stretching a spring a certain distance (x), F = -kx. Springs in A-clamps apply force as the result of twisting along the longitudinal axis, with the force proportional to the amount of twisting. Additionally, adjusting the area of the A-clamp in contact with the tissue can vary the force applied per unit area of tissue.