In reply

Abstract

In reply: We appreciate the comments presented by Kolbitsch et al. about our recent publication (2). Regarding the impact level, the position of the pressure transducer of the Yamaki fluid percussion device(6) is different from that of other fluid percussion devices (1,3,4). To record an accurate pressure pulse, the fluid flushing outlet and the transducer of our device were positioned close to the piston, both being perpendicular to the direction of the piston (6). In the study, two rats died without recovering from apnea after trauma. The impacts they received were 8.6 and 9.8 atm. Other MFP animals received impacts of 5.5 to 6.2 atm. From the previous experiments, we have data indicating that the impact has to be at least 3.5 atm to induce diffuse axonal injury in rats. We used stronger impact to surely produce diffuse axonal injury in the study. Kolbitsch et al. showed their para-MFP model that included cortical and subcortical lesions. This model may be similar to our lateral fluid percussion model but different from our MFP model. The intensity and duration of an impact are important factors in fluid percussion trauma, as Kolbitsch et al. indicated. The Yamaki fluid percussion device is able to produce a high-intensity impact in a short duration (within 10 ms). We have illustrated the pressure pulse in a previous publication(6). The pressure pulse is different from the one presented by Kolbitsch et al. We need a short-duration, high-intensity impact to produce diffuse axonal injury by MFP. A behavioral evaluation correlated with histological findings was published in a recent issue of Brain Research(5). We know animal examinations can be performed with a clinical MRI scanner. However, animal studies using a clinical MRI scanner in a hospital are not usually approved in Japan. So, we use an experimental magnetic resonance apparatus for experimental research. Tarumi Yamaki Yoshihiro Iwamoto Nobukuni Murakami Kyoto, Japan