Analysis of gastrocnemius compound muscle action potential in rat after death: significance for the estimation of early postmortem interval

The estimation of postmortem interval is of great importance in forensic medicine. Changes in the properties of excitable tissue provide another possible means by which the time of death can be estimated. This paper reports the monitorization of the compound action potentials recorded from gastrocnemius muscle by means of sciatic nerve stimulation in rats before and after death. The sciatic nerve was stimulated using rectangular impulses of 0.1ms duration and intensities ranged between 1 and 100mA while the rat was alive. Subsequently, the rat was killed by cervical dislocation. The similar measurement procedure was performed at the moment of death and every 5min after sequentially. There was a progressive decline in amplitude values that began 10min after death. The decrease in the amplitude of the compound muscle action potentials (CMAP) was most prominent especially when elicited with lower stimulus intensities. The mean area of the CMAPs also began to decrease beginning from 15min after death. Fifteen minutes after death, the motor latencies began to prolong. Thirty-five minutes after death, the decline in amplitude and area of mean CMAP was most prominent as the mean motor latency. At the 40th minute, most of the CMAPs were unelicitable. During the early postmortem interval, these amplitude, area and motor latency alterations decrease in the amplitude and area, prolongation of motor latency seems to be well correlated with each other and this was statistically significant. These findings are discussed as possible basis of a forensic method for postmortem interval estimation.