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The objective of this study was to evaluate the changes in electroencephalographic (EEG) power spectrum in response to decapitation of anaesthetized rats, in order to assess the nociception or otherwise of this procedure. Ten young adult male Sprague-Dawley rats were anaesthetized with halothane in oxygen and anaesthesia was maintained at a stable concentration of halothane between 1.20% and 1.25%. The rat's head and neck were placed through the opening of a small animal guillotine so that the blade of the guillotine was positioned over the atlanto-occipial joint of the rat's neck. The EEG was recorded in a five-electrode montage, bilaterally. After recording a 15 min baseline the rat was decapitated by swiftly pressing the guillotine blade and the EEG recording was continued until the signal was isoelectric on both channels. Changes in the median frequency (F50), 95% spectral edge frequency (F95) and total power of the EEG (Ptot) were used to investigate the effects of decapitation. During the first 15 s following decapitation, there were significant increases in the F50 and F95, and a decrease in the Ptot compared with baseline values. There was a clear window of time immediately following decapitation where changes in the EEG frequency spectrum were obvious; these changes in the EEG indices of nociception could be attributed as responses generated by the rat's cerebral cortex following decapitation.Keywords rat, electroencephalogram, euthanasia, welfare, nociception Several different methods of euthanasia have been proposed for use in laboratory animals in biomedical research (e.g. injectable anaesthesia, decapitation, cervical dislocation, CO 2 asphyxiation, etc.). 1Decapitation has the advantage that it has no effect on subsequent analytical procedures.2 This is not the case with chemical methods such as a drug overdose. Despite its common use, the humaneness of decapitation of conscious animals is debatable.2-5 The question of whether brain activity continues after decapitation and, if so, for how long, has been considered essential for determining the acceptability of this procedure. These questions have been addressed in a number of studies involving different animal species including rats.2,6-10 Studies utilizing electroencephalographic (EEG) recordings have been used to map the brain following decapitation. Conversion from high voltage slow activity to low voltage fast activity (LVFA) and desynchronization, a shift in EEG activity toward high frequency, have been reported as typical EEG responses following the decapitation of conscious animals. These changes in EEG activity persist between 8 and 29 s in all species after decapitation 5 and, are followed by the onset of isoelectric EEG.Interpretation of these post-decapitation EEG changes in terms of conscious arousal and potential pain perception, and as a response to noxious stimulation, has not been simple. Other studies have demonstrated that LVFA pattern EEG activity can be seen during rapid eye movement sleep/anaesthesia and also during an...

BackgroundThe objective of this study was to compare the changes in the electroencephalogram (EEG) in response to noxious stimuli with tail flick and hot plate responses of rats administered opiorphin.MethodsFemale Sprague -Dawley rats (n = 8 per group) randomly received intravenous (IV) injection of morphine (1 mg/kg,) or opiorphin (2 mg/kg,) or saline (0.5 ml,) in each of the three testing methods (EEG, tail flick and hot plate). Each type of test (n = 24 per test) was conducted in different population of rats on separate occasions. The tail flick and hot plate latencies were recorded until 5 min after test drug administration to conscious rats. The EEG was recorded in anaesthetised rats subjected to noxious thermal and electrical stimuli after test drug administration. At the end of 5 min in each of the testing methods rats were administered naloxone subcutaneously (SC) (1 mg/kg) and the test procedure was repeated.ResultsThere was no significant increase in the median frequency and spectral edge frequency (F50 & F95) of EEG, indicators of nociception, of morphine and opiorphin groups after noxious stimulation. Noxious stimuli caused a significant increase in both F50 and F95 of the saline group. An injection of naloxone significantly increased the F50, thus blocking the action of both opiorphin and morphine. There was a significant increase in the tail flick latency after administration of opiorphin and morphine as compared to the baseline values. Rats of morphine group spent significantly longer on the hot plate when compared to those of the opiorphin and saline groups. There was no significant difference in the hot plate latencies of opiorphin and saline groups.ConclusionThe results of this study suggest that the analgesic effect of opiorphin occurs at the spinal level and it is not as effective as morphine at supraspinal level. It may be due to rapid degradation of opiorphin or limited ability of opiorphin to cross the blood brain barrier or a higher dose of opiorphin is required for its action in the brain. Pharmacokinetic/pharmacodynamics studies along with in vivo penetration of opiorphin in the cerebrospinal fluid are required for further evaluation of opiorphin analgesia.Electronic supplementary materialThe online version of this article (10.1186/s12883-018-1047-y) contains supplementary material, which is available to authorized users.

Tramadol and morphine administered pre-operatively provided an equal degree of post-operative analgesia in dogs after ovariohysterectomy. A combination of pre-operative low-dose morphine and post-operative tramadol produced better post-operative analgesia than either drug administered alone pre-operatively. Administration of analgesics pre- and post-operatively could result in improved post-operative well-being of ovariohysterectomised dogs.

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