The effect of morphine on the development rate of flies (Diptera: Calliphoridae, Sarcophagidae) reared on rabbit carcasses containing this drug and its implications to postmortem interval estimates

Insects can prove to be a valuable tool in the estimation of PMI in the investigation of homicides, suicides, and other unattended human deaths, in the absence of tissues and body fluids. Aim: The current study aimed to determine morphine concentration in the second, third feeding, third post-feeding instars, and puparial skin of four forensically important flies; Lucilia sericata (Meigen), Chrysomya albiceps (Wiedemann), Chrysomya megacephala (Fabricius) (Calliphoridae), and Sarcophaga argyrostoma (Robineau-Desvoidy) (Sarcophagidae) and to evaluate its effect on the rate and pattern of development of these flies. Materials and methods: Three female domestic rabbits, Oryctolagus cuniculus (L.) each weighing 2.5 kg received dosages of 7.5, 15, and 30 mg of morphine over a 3-h period via left ear artery perfusion. For each trial, one other rabbit, weighing 2.5 kg, was used as a control. Morphine was detected in larval instars and puparial skin using ready to use RIA kit. Results: All blood and tissue samples obtained from the rabbits receiving dosages of morphine were positive for the drug. Morphine concentrations for rabbit R2 were 1.2 to 2.6 times greater than those for rabbit R1, and concentrations for rabbit R3 were 1.4 to 3.1 times greater than those for rabbit R2. For each rabbit, morphine concentration in second, third feeding and third post-feeding instars, and puparial skin for all four species, were less than those detected in the tissues. The highest levels of morphine were recorded in the feeding third instars of Chr. megacephala R3 colony, whereas the lowest level of this drug was detected in the feeding third instars of S. argyrostoma R1 colony. Estimations of larval age for L. sericata, Chr. albiceps, Chr. megacephala and S. argyrostoma based on mean length can be significantly in error if presence of morphine in the tissues is not considered. This error can be as great as 24, 27, 6 and 21 h respectively. Conclusion: In cases of badly decomposed and/or skeletonized remains, analyses of collected carrion-feeding insects, may provide the most accurate qualitative sources of toxicological information.

Evidence that the contraction-induced rapid hyperemia in rabbit masseter muscle is based on a mechanosensitive mechanism, not shared by cutaneous vascular beds

Several mechanisms have been hypothesized to contribute to the rapid hyperemia at the onset of exercise. The aim of the present study was to investigate the role played by the mechanosensitivity of the vascular network. In 12 anesthetized rabbits blood flow was recorded from the exclusively muscular masseteric artery in response to brief spontaneous contractions (BSC) of the masseter muscle, artery occlusion (AO), muscle compression (MC), and muscle stretch (MS). Activation of masseter muscle was monitored by electromyography (EMG). Responses to AO were also recorded from the mostly cutaneous facial and the central ear arteries. Five animals were also tested in the awake condition. The hyperemic response to BSC (peak amplitude of 394 ± 82%; time to peak of 1.8 ± 0.8 s) developed with a latency of 300–400 ms from the beginning of the EMG burst and 200–300 ms from the contraction-induced transient flow reduction. This response was neither different from the response to AO (peak amplitude = 426 ± 158%), MC, and MS ( P = 0.23), nor from the BSC response in the awake condition. Compared with the masseteric artery, the response to AO was markedly smaller both in the facial (83 ± 18%,) and in the central ear artery (68 ± 20%) ( P < 0.01). In conclusion, the rapid contraction-induced hyperemia can be replicated by a variety of stimuli affecting transmural pressure in muscle blood vessels and is thus compatible with the Bayliss effect. This prominent mechanosensitivity appears to be a characteristic of muscle and not cutaneous vascular beds.