Michael J. Gentle

Bio: Michael J. Gentle is an academic researcher from The Roslin Institute. The author has contributed to research in topics: Joint capsule & Noxious stimulus. The author has an hindex of 13, co-authored 19 publications receiving 950 citations.

Do Fishes Have Nociceptors? Evidence for the Evolution of a Vertebrate Sensory System

Abstract: Nociception is the detection of a noxious tissue-damaging stimulus and is sometimes accompanied by a reflex response such as withdrawal. Pain perception, as distinct from nociception, has been demonstrated in birds and mammals but has not been systematically studied in lower vertebrates. We assessed whether a fish possessed cutaneous nociceptors capable of detecting noxious stimuli and whether its behaviour was sufficiently adversely affected by the administration of a noxious stimulus. Electrophysiological recordings from trigeminal nerves identified polymodal nociceptors on the head of the trout with physiological properties similar to those described in higher vertebrates. These receptors responded to mechanical pressure, temperatures in the noxious range (more than 40 degrees C) and 1% acetic acid, a noxious substance. In higher vertebrates nociceptive nerves are either A-delta or C fibres with C fibres being the predominating fibre type. However, in the rainbow trout A-delta fibres were most common, and this offers insights into the evolution of nociceptive systems. Administration of noxious substances to the lips of the trout affected both the physiology and the behaviour of the animal and resulted in a significant increase in opercular beat rate and the time taken to resume feeding, as well as anomalous behaviours. This study provides significant evidence of nociception in teleost fishes and furthermore demonstrates that behaviour and physiology are affected over a prolonged period of time, suggesting discomfort.

Physiological and behavioural responses of broilers to controlled atmosphere stunning: implications for welfare

Abstract: Controlled atmosphere (gas) stunning (CAS) has the potential to improve the welfare of poultry at slaughter but there is a lack of consensus about which gas mixtures are most humane. The aim of this study was to evaluate the welfare consequences of different gas stunning approaches. Individual broilers were exposed to gas mixtures capable of inducing unconsciousness and euthanasia while their behavioural, cardiac, respiratory and neurophysiological responses were measured simultaneously. The approaches investigated included anoxia (N2 or Ar with < 2% residual O2), hypercapnic anoxia (30% CO2 in Ar, 40% CO2 in N2) and a biphasic method (40% CO2, 30% O2, 30% N2 for 60 s followed by 80% CO2 in air). Evaluation of the welfare implications of each approach centred on the likelihood of them inducing negative states or experiences during the conscious phase. Hypercapnic mixtures were associated with strong respiratory responses, while anoxic mixtures induced vigorous wing flapping. Electroencephalogram analysis using the correlation dimension (a non-linear measure of complexity) suggested that anoxic wing flapping occurred during periods in which a form of consciousness could not be excluded. Hypercapnic hyperoxygenation (biphasic approach) exacerbated respiratory responses but eliminated the possibility of vigorous behavioural responses occurring during a conscious phase. The relative importance of respiratory discomfort versus the potential to induce significant distress due to convulsive wing flapping and associated trauma is a matter for debate. We argue that respiratory discomfort is unpleasant but may be preferable to the risk of vigorous wing flapping and associated injury while conscious in poultry during CAS.

Evaluation of the effects of infrared beak trimming in broiler breeder chicks.

Abstract: Detailed behavioural observations were made of broiler breeder chicks after their beaks had been trimmed by an automated infrared treatment at one day of age or by the traditional hot-blade method at one day or seven days, or after they had been sham-trimmed or left untreated. Observations took place immediately after the treatments and at regular intervals until six weeks of age; beak length and bodyweight were also measured regularly. There were no significant effects on the behaviour of the chicks in the first hour after trimming or in the subsequent six weeks. Variability in beak length was low within the treatments and there was significant regrowth, but it was least in the birds that had been hot-blade trimmed at seven days. Both beak-trimming methods were associated with small but significant reductions in bodyweight, with the hot-blade-treated birds being more affected.

Sodium urate arthritis: effects on the sensory properties of articular afferents in the chicken

Abstract: The physiological properties of joint capsule mechanoreceptors in the ankle joint of the chicken were studied in the 3-h period immediately after intra-articular injection of microcrystal sodium urate. The electrical activity was recorded from single C- and A-delta sensory fibres dissected from the parafibular nerve. C-fibres showed high levels of spontaneous activity and receptive fields that varied from single spots 1 mm in diameter up to 4 x 4 mm. Thresholds to mechanical stimulation ranged from 0.1 to 8 g and 80% of the units responded to movement of the joint. A-delta fibres showed little spontaneous activity and receptive fields that varied from 1 mm to 9 x 1 mm. Thresholds to mechanical stimulation ranged from 0.1 to 16 g and 17% responded to joint movement. A comparison of the physiological properties of the C- and A-delta fibres in sodium urate arthritis with similar fibres in normal and monoarthritic animals indicated an increased sensitivity in the C-fibres but not in the A-delta fibres. Sensitisation was observed in the significantly increased receptive field size, decreased response thresholds, increased response to joint movement and the high level of spontaneous activity. These changes in the sensitivity of the joint capsule C-fibre receptors provides peripheral neural evidence for the pain experienced in acute gouty arthritis.

AVMA Guidelines for the Euthanasia of Animals: 2013 Edition

Abstract: 1. Clarification: The 2013 Guidelines make a distinction between euthanasia, humane killing, and slaughter, and state that neither slaughter nor humane killing is covered in the document P.68, S6.1.1. Not included among the definitions of these terms are ending the lives of healthy animals or scientific collection of animals. For clarification, whatever the term used, classification of the method, or reason given for killing animals: euthanasia, humane killing, slaughter, harvest, depopulation, scientific collection, or research-related, the Council on Accreditation’s foremost concern, in all situations, is with humane technique. The goal of humane technique is to minimize pain, distress, and the negative effect to the animal. The technique employed should result in rapid loss of consciousness followed by cardiac or respiratory arrest and, ultimately, a loss of brain function. Although complete absence of pain and distress is preferred, it is understood that it cannot always be achieved P7.13.2.

Psychological factors in chronic pain: Evolution and revolution.

Abstract: Research has demonstrated the importance of psychological factors in coping, quality of life, and disability in chronic pain. Furthermore, the contributions of psychology in the effectiveness of treatment of chronic pain patients have received empirical support. The authors describe a biopsychosocial model of chronic pain and provide an update on research implicating the importance of people’s appraisals of their symptoms, their ability to self-manage pain and related problems, and their fears about pain and injury that motivate efforts to avoid exacerbation of symptoms and further injury or reinjury. They provide a selected review to illustrate treatment outcome research, methodological issues, practical, and clinical issues to identify promising directions. Although there remain obstacles, there are also opportunities for psychologists to contribute to improved understanding of pain and treatment of people who suffer from chronic pain. The authors conclude by noting that pain has received a tremendous amount of attention culminating in the passage of a law by the U.S. Congress designating the period 2001–2011 as the “The Decade of Pain Control and Research.”

Voluntary food intake and diet selection in farm animals.

Abstract: Feeding behaviour feedback signals ruminant gastrointestinal tract metabolites and hormones central nervous control integrative theories of food intake control growth and fattening reproduction and lactation diet digestability and concentration of available energy specific nutrients affecting intake learning about food - preferences diet selection appetites for specific nutrients environmental factors affecting intake the intake of fresh and conserved grass prediction of voluntary intake. Appendices: particular features of poultry and ruminant animals outline programme to identify and store meals from the identities of animals and weights of food containers.

Current issues in fish welfare

Abstract: Human beings may affect the welfare of fish through fisheries, aquaculture and a number of other activities. There is no agreement on just how to we igh the concern for welfare of fish against the hum an interests involved, but ethical frameworks exist th at suggest how this might be approached. Different definitions of animal welfare focus on an animal's condition, on its subjective experience o f that condition and/or on whether it can lead a natu ral life. These provide different, legitimate, pers pectives, but the approach taken in this paper is to focus on welfare as the absence of suffering. An unresolved and controversial issue in discussion s about animal welfare is whether non-human animals exposed to adverse experiences such as physical injury or confinement experience what humans would call suffering. The neocortex, which in huma ns is an important part of the neural mechanism tha t generates the subjective experience of suffering, i s lacking in fish and non-mammalian animals, and it has been argued that its absence in fish indicates that fish cannot suffer. However, a strong alternative view is that complex animals with sophisticated behaviour, such as fish, probably have the capacity for suffer ing, though this may be different in degree and kind fro m the human experience of this state. Recent empirical studies support this view and show that painful stimuli are, at least, strongly avers ive to fish. Consequently, injury or experience of othe r harmful conditions is a cause for concern in term s of welfare of individual fish. There is also growing e vidence that fish can experience fear-like states a nd that they avoid situations in which they have experience d adverse conditions.