POSTMORTEM ELECTRICAL CONDUCTIVITY CHANGES OF DICENTRARCHUS LABRAX SKELETAL MUSCLE: ROOT MEAN SQUARE (RMS) PARAMETER IN ESTIMATING TIME SINCE DEATH

The estimation of postmortem interval (PMI) is a critically important investigative tool in some animal death investigations, and nowadays it represents a major challenge for veterinary pathologists globally [1]. Investigations on the electrical properties of tissues have been of great scientific interest for decades and several practical applications have been proposed [2]. Since the electrical properties of tissues are strongly dependent 􏰂on􏰃􏰄􏰅􏰆􏰃􏰇􏰃􏰈􏰉􏰊 􏰍􏰎 􏰏􏰐􏰍􏰊􏰑􏰉􏰃morphological and 􏰊􏰒􏰇􏰇􏰓􏰔 􏰉􏰍􏰑􏰒􏰈􏰄􏰉functional cells' integrity􏰑􏰕 􏰋 􏰉and intra-and extracellular conductivities, electric impedance spectroscopy techniques have been explored to predict carcass decomposition and estimate PMI [3, 4]. However, the most relevant, quantitative parameter in approximating PMI has not been recognized so far. The present study investigated the electrical conductivity changes in skeletal muscles of sea bass specimens (Dicentrarchus labrax; n=18) (approval no. 037/2019) kept at different room temperatures (15°C; 20°C; 25°C) during a 24-hour postmortem period, using a signal generator/oscilloscope system as innovative technology. After 10-days acclimatization, fish were euthanized (1 fish/day) and blood was sampled to assess haematological profile and serum concentration of electrolytes. Signal was applied to each specimen by placing 2 electrodes in the epaxialis/hypaxialis skeletal muscles, behind the operculum. The oscilloscope was used to record the input and output signals, measured by 2 electrodes at 10 cm of distance. The Root Mean Square (RMS) voltage value, detected by the oscilloscope, was recorded every 15 minutes for 24 hours. The resulting time series were statistically analysed using MATLAB. The time evolution of the RMS signal in the 24h postmortem underwent the same qualitative behaviour for all specimens. In particular, after a short period during which the RMS signal decreased, the RMS values increased until they reached a maximum and subsequently decreased progressively over time, returning to the initial value. A strong linear correlation (r>0.978) was obtained among all RMS time series, confirming that the above time behavior was applied to all animals. Regression analysis was applied to deduce the mathematical peak function which best describes the aforementionated trend of the RMS values over the 24 hours (r2>0.86). Interestingly, the time at which the maximum of the RMS value was reached strongly depended on room temperature, ranging from 6 hours in fish kept at 25.0°C to 12-14 hours at 15.0°C. The use of a signal generator/oscilloscope system has proved to be a promising technology in studying the dielectrical properties of muscle during early PMI, with the advantage of being a fast, non-destructive and inexpensive method. Of course, further electrical and theoretical investigations will be required to standardize and validate this technology before moving from the laboratories to the field applications.