Application of calibrated forceps for assessing mechanical nociception with high time resolution in mice

In order to investigate the basic physiological mechanisms of pain and the anti-nociceptive effects of analgesics, development of pain assays in mice is critical due to the advances of genetic manipulation techniques. The von Frey hairs/Semmes-Weinstein monofilaments test (von Frey test) has long been applied to examine mechanical nociception in mice. Though the von Frey test is a well-established and standardized method, it is inappropriate to assess a rapid change in the nociceptive threshold because voluntary resting/sleeping states are necessary to examine the response. In this study, we assessed the effectiveness of calibrated forceps to determine the mechanical nociceptive threshold in mice. Repeated daily measurements of the threshold over 5 days indicated that the device obtained stable and reliable values. Furthermore, repeated measurements with 5 minute intervals revealed that the device detected the rapid change of the threshold induced by remifentanil, a short-acting μ-receptor agonist. These results indicate that the calibrated forceps are well-suited for measuring the mechanical nociceptive threshold in mice, and are useful in assessing the effects of short-acting analgesics on mechanical nociception.