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Biomedical subjects

M J Gentle

Publications and source records attributed to M J Gentle.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ankle joint (artc. intertarsalis) receptors in the domestic fowl.

The physiological responses of joint capsule sensory receptors in the ankle joint of the chicken were studied by recording the electrical activity from single sensory afferent nerve fibres dissected from the parafibular nerve. All units included in this study were sensitive to mechanical stimulation of the joint capsule and were classified with respect to nerve conduction velocity, receptive field size and response threshold. Rapidly adapting mechanoreceptors formed 23% of the receptors present in the sample and responded to the mechanical probe by giving a single response or a short burst of activity at the onset of stimulation. The majority of units identified showed a slowly adapting response and on the basis of conduction velocity were divided into group IV (CV 2.5 m/s), group III (CV 2.5-20 m/s) and those units conducting over 20 m/s. Group IV units had single spot-like receptive fields and mechanical thresholds ranging from 0.6 to 60 g. Group III units could be divided into two groups based on receptive field size. One group had spot-like receptive fields 1-2 mm in diameter, whereas in the other group the receptive fields were larger (over 2 x 3 mm). The large receptive field units had significantly faster conduction velocities, lower mechanical thresholds and steeper stimulus-response curves than small receptive field units. In response to movement of the joint very few of the receptors, whether rapidly or slowly adapting, were found to be excited by moving the joint by hand in the middle of its physiological range. The physiological properties of these avian mechanoreceptive fine afferent units suggest that while some are activated by normal joint movement and non-noxious local mechanical stimulation of the joint capsule, others have nociceptive functions. The receptors present in the ankle joint were correlated with the anatomical structures found in the avian joints and their physiological properties compared and contrasted to the joint receptors found in mammals.

Action Potentials↗
PubMed1991

The onset of pain related behaviours following partial beak amputation in the chicken.

The number of pecks delivered by birds to an attractive visual stimulus was measured before and again 6, 26 and 32 h after partial beak amputation. There was a significant reduction in the number of pecks by birds 26 h after amputation but not at 6 h after. This reduction was considered to be a quantitative measure of pain related guarding behaviour. The results indicated the presence of a pain-free period immediately following amputation which may last in some birds for as long as 26 h.

Amputation, Surgical↗
PubMed1991

Physiological and behavioural responses associated with feather removal in Gallus gallus var domesticus.

Electroencephalographic, cardiovascular and behavioural parameters were examined in Gallus gallus var domesticus in response to feather removal. The progressive removal of feathers resulted in marked changes in the bird's behaviour from an alert agitated response following the initial removals to periods of crouching immobility following successive removals. During the periods of immobility the birds showed a high amplitude low frequency EEG pattern and successive removals resulted in a progressive increase in the total duration of this activity in the two minutes after removal. The heart rate response to feather removal was variable whereas the blood pressure always increased and this increase was followed by a gradual return to pre-stimulus levels. There were no consistent cardiovascular responses related to the immobility. It was concluded that feather removal is likely to be painful to the bird and feather removal by flockmates can be categorised as a welfare problem.

Animals↗
PubMed1989

Cutaneous sensory afferents recorded from the nervus intramandibularis of Gallus gallus var domesticus.

The responses of single sensory afferent nerve fibres were recorded from small nerve bundles of the intramandibular nerve of the chicken following thermal and mechanical stimulation of the beak. Thermoreceptors, nociceptors and mechanoreceptors were identified and their responses characterized. Of the thermoreceptors identified 11 units were classified as cold receptors, which responded to cooling the receptive field by increasing the discharge rate and had conduction velocities in the range 0.83 to 4.4 m/s. Only one warm unit was identified. Two classes of nociceptors were identified: mechano-thermal (polymodal) nociceptors and high threshold mechanical nociceptors. The discharge characteristics and stimulus-response curves of both types were described. While the mechano-thermal nociceptors were exclusively C-fibres (c.v. 0.4 to 1.86 m/s), the high threshold mechanoreceptors contained both C and A delta fibres (c.v. 1 to 5.5 m/s). Thermal response thresholds for the mechano-thermal units ranged from 41 to 50 degrees C with mechanical thresholds of 2 to over 50 g. Mechanical thresholds for the high threshold units ranged from 5 to over 50 g. The mechanoreceptors were either slowly or rapidly adapting. The pattern of response together with stimulus-response curves were presented for the slowly adapting units. Conduction velocities of the slowly adapting units varied from 0.7 to 20 m/s and mechanical threshold from 0.1 to 2 g. On the basis of their response to a vibrating, and a ramp-and-hold mechanical stimulus, the rapidly adapting units were divided into Herbst and Grandry units with only the Herbst units responding accurately to the vibrating stimulus. Both units had fibres conducting in the 50 m/s range with thresholds in the 0.1 to 10 g range. The results are discussed in relation to the receptors found in other avian species and mammalian peripheral sensory afferents.

Action Potentials↗
PubMed1989

Physiological changes during tonic immobility in Gallus gallus var domesticus.

Physiological parameters were examined in the hen in response to the induction of tonic immobility (TI). The induction of TI was associated with EEG arousal, low shank temperature and elevated heart rate. However, shortly after the adoption of TI, the EEG showed a predominantly slow-wave deactivated pattern, muscle tone fell and sympathetic nervous activity was reduced, as indicated by declining heart rate and peripheral vasodilation. Core temperature remained constant at 42 degrees C throughout the immobility response. Several instances of EEG-behavioural dissociation were observed. The results are discussed in terms of "cut-off" and waning of the induced fear state.

Animals↗
PubMed1989

Opioid modulation of feeding and drinking in fowls.

1. D-ala2-methionine enkephalinamide (DME), the stable analogue of met-enkephalin (an opioid agonist), stimulated food intake of immature hens in the first 30 min after intracerebroventricular injection (2 and 8 micrograms/kg), but had no effect on either food or water intake when injected intravenously (15 and 60 micrograms/kg). 2. Naloxone (an opioid antagonist) had no effect on food intake after either intracerebroventricular (50 and 200 micrograms/kg) or intravenous (1 and 4 mg/kg) injection, but inhibited water intake in the second 30 min after intravenous injection. 3. Water intake was not measured after the intracerebroventricular injections of DME and naloxone. 4. Both feeding and drinking were inhibited in a dose-related way in the 7 h after intramuscular injection of nalmefene (0.2, 0.4, 0.8 and 1.6 mg/kg), a more potent and longer-lasting antagonist than naloxone. 5. These data are compared with published results from similar work with birds and mammals. It is concluded that central release of endogenous opioids may reinforce both feeding and drinking in fowls, but whereas opioid blockage affects feeding more than drinking in pigeons and quail, the opposite appears to be the case in fowls.

Animals↗
PubMed1988

Neural consequences of partial toe amputation in chickens.

The extent of the damage inflicted on the hallux was determined in a group of detoed, newly hatched, male broiler-breeder chicks obtained from a commercial hatchery. Healing and neural regeneration were very rapid and after 22 days the stump had a complete epidermal and dermal covering with the dermis being well supplied with both nerves and blood vessels. Some regenerating nerve bundles became trapped in scar tissue and formed small terminal neuromas which persisted over the 60-day observation period. These results are discussed in relation to partial beak amputation and their welfare implications.

Amputation, Surgical↗
PubMed1988

Physiological and behavioural responses of the domestic hen to hypoxia.

Physiological and behavioural responses of adult hens and chicks were monitored in atmospheric and increasingly hypoxic conditions to investigate whether anoxic killing was a suitable alternative method for use in the slaughter industry. All birds were placed in a perspex box for easy observation and nitrogen gas was slowly administered when subjecting birds to anoxic conditions. When subjected to decreasing oxygen concentration adult birds slowly became unconscious, without showing any signs of distress, until respiratory failure supervened. Chicks showed similar results but loss of motor control was observed while still conscious which might cause some distress. Further investigations are suggested to alleviate this problem.

Animal Welfare↗
PubMed1987

Oral lesions in the chicken: behavioural responses following nociceptive stimulation.

The behaviour of normal birds and birds with ulcerated buccal lesions was described following oral stimulation with Acetylcholine chloride (ACh) and Bradykinin (BK). Both groups of birds showed normal oral behaviour but a number of birds with oral lesions showed a behaviour pattern which had been previously seen in our laboratory following nociceptive stimulation. The birds remained motionless in a crouch-like stance with the head pulled into the body and a significantly reduced number of alert head movements. The onset and duration of this immobility response was compared with reports of pain in humans in the blister-base test using similar concentrations of ACh and BK. It was concluded that nocifensive responses of the chicken fulfil many of the requirements for the definition of pain in animals.

Acetylcholine↗
PubMed1987

Central distribution and efferent origins of facial nerve branches in the chicken.

The central afferent distribution and the origins of visceromotor and somatomotor components of greater superficial petrosal (GSP), chorda tympani (CT), and hyomandibular (Hy) branches of the facial nerve were analyzed by the transganglionic and retrograde transport of horseradish peroxidase. Labelled sensory afferent fascicles of the GSP collected dorsomedial to the spinal trigeminal complex and passed caudally as the tractus solitarius. Fine-grain terminal fields were evident in ipsilateral n. sensorius n. facialis, nuclei ventrolateralis anterior (Vla), centralis anterior and presulcalis anterior of the solitary complex, and n. glossopharyngei et n. motorius dorsalis nervi vagi (n. IX-X). Minor contralateral projections to these nuclei occasionally were observed. CT sensory afferents exhibited similar ipsilateral projections, and specifically, the projection to Vla was qualitatively sparser than that from the GSP. Small multipolar and spindle-shaped somata of visceromotor n. salivatorius were labelled retrogradely from the GSP and CT. Large, oval somatomotor cells of the three subdivisions of the facial motor nucleus were labelled retrogradely from Hy, with no evidence of sensory afferent or visceromotor connections.

Afferent Pathways↗
PubMed1986

Central afferent connections and origin of efferent projections of the facial nerve in the chicken (Gallus gallus domesticus).

The central afferent connections and origin of efferent projections of the facial nerve in the adult domestic chicken were studied by anterograde and retrograde transport of horseradish peroxidase from the geniculate ganglion. Ipsilateral afferent projections were traced caudal to the level of entrance of the facial nerve and into tractus solitarius (TS), located dorsomedial to the spinal trigeminal nuclear complex. At several rostrocaudal levels in the medulla, fibers exited from TS and terminated in n. sensorius N. facialis (SVII), and nn. ventrolateralis anterior (Vla) and intermedius anterior (Ia) solitarii. Some axons were followed to n. presulcalis anterior (Pas) solitarii. A separate component terminated in subnucleus interpolaris (ip) of n. descendens nervi trigemini or its medially adjacent reticular formation either by exiting from TS or coursing caudally through the trigeminal complex from entering facial rootlets. Another diffuse component of facial axons ascended dorsally and rostrally from the level of entrance of the facial nerve; these projections dissipated in the pons--some on the dorsomedial border of n. principalis N. trigemini (PrV). Ipsilateral efferent projections were traced through the main genu of the facial nerve to retrogradely labelled somata of pars dorsalis (FMd), pars intermedia (FMi), and pars ventralis (FMv) of n. motorius nervi facialis. A separate group of smaller, multipolar, and spindle-shaped cells (8-25 microns) wedged between n. olivaris superioris (OS) and the caudal end of FMv, rostrally, and extending caudally in ventrolateral medulla were labelled. These small cells contrast with the larger (21-45 microns), oval, round, and multipolar somata of FMv and may correspond, in part, to a parasympathetic n. salivatorius (Sal).

Afferent Pathways↗
PubMed1986

Tissue resistivities and current pathways and their importance in pre-slaughter stunning of chickens.

The failure of commercial pre-slaughter electrical stunning to stun effectively all birds may be, in part, a result of the current following slightly different paths through the tissues of different birds. Resistivity can be used to predict current pathways, and methods are presented for determining the resistivity of a tissue in freshly-killed or anaesthetized adult fowls. A variety of tissues were tested including comb, skeletal muscle, epithelium, brain, skull bone, heart and liver. The resistivity of a particular tissue varied little between birds, with the exception of skull bone in which resistivity differed markedly from bird to bird. This variation in skull bone resistivity may explain why some birds are inadequately stunned, since in these individuals the current density in the brain is likely to be insufficient to induce an adequate epileptic seizure.

Abattoirs↗
PubMed1986

The bill tip organ of the chicken (Gallus gallus var. domesticus).

At the tip of the lower beak of the chicken there were found 15-20 specialised dermal papillae containing large numbers of mechanoreceptors. The Merkel or Grandry corpuscles were situated distally in the papillae and at the papillae base was a collection of Herbst corpuscles. The apex of the papillae, under the scanning electron microscope, appeared as a row of shallow pits on the surface of the beak just inside the mouth. These papillae resemble similar structures seen in other birds and are probably necessary for fine tactile discrimination.

Animals↗
PubMed1986

Aetiology of food-related oral lesions in chickens.

Brown Leghorn chickens fed on a mash diet developed ulcerated oral lesions with extensive epithelial erosion and large colonies of bacteria. Some birds had lesions by six weeks old and by 30 weeks oral lesions were present in all birds fed on a mash diet. These lesions occur infrequently in birds fed a pelleted diet and the relatively extensive lesions shown by birds on a mash diet heal quickly (in many cases within two weeks) when the birds are transferred to a pelleted diet. The cause of the lesion is unknown but there was no evidence for food impaction, mechanical damage to the epithelium, specific dietary constituents or blocked salivary ducts. The lesions may be due to poor oral hygiene which results from the lack of mechanical stimulation of the oral epithelium to which fine particles of mash adhere.

Animal Feed↗
PubMed1986

Neuroma formation following partial beak amputation (beak trimming) in the chicken.

Branches of the trigeminal nerve, which innervates the beak in the chicken, were damaged after partial beak amputation (beak trimming) and degeneration in the nerve extended from 2 to 3 mm proximal to the cut stumps. Within 10 days the damaged nerves showed regeneration and axon sprouts had been formed. This neural regeneration was rapid so that by 20 to 30 days bundles of regenerating fibres were present and neuromas formed adjacent to the scar tissue of the stump of the beak. These neuromas became more extensive over the 70 day observation period.

Amputation, Surgical↗
PubMed1985

Neuroma formation and abnormal afferent nerve discharges after partial beak amputation (beak trimming) in poultry.

Following partial amputation of the beak recordings were taken of the electrical activity from single afferent fibers of the intramandibular nerve. A total of 192 single afferent fiber units were isolated of which 47 were classified as nociceptors, with an abnormal pattern of discharge, and 89 were abnormal spontaneously active units. Following amputation neuromas were developing by 15 days after surgery and they were well formed by 20 to 30 days. The presence of neuromas together with abnormal spontaneous activity originating from them raise serious welfare questions concerning beak trimming.

Animals↗
PubMed1985

Olfaction and behavioral modification in domestic chicks (Gallus domesticus).

Olfactory responsiveness in the female domestic chick was examined in a series of experiments. Individually-housed chicks preferred the familiar soiled substrate from their own home box to that soiled by a strange conspecific and to clean wood litter when placed in an otherwise novel Y maze. An artificial odorant present during the development of group-reared chicks subsequently proved attractive in an otherwise novel and potentially frightening situation. Chicks reared with one of two aromatic oils subsequently discriminated between them and preferred the familiar oil when both were present in the test box. The preferences are likely acquired because naive, one-day-old chicks reacted similarly to wood litter treated with either water or oil. Presence of a familiar rearing odor also reduced fear of a novel open field. In contrast to controls, chicks whose nostrils were blocked prior to rearing with an aromatic oil showed no subsequent preference for this odorant. The present results suggest that domestic chicks can regulate their behavior in response to olfactory cues though trigeminal chemoreception may also be involved.

Animals↗