Impact of climate on thermal rhythm in pastoral sheep

The effects of environmental conditions on temperature rhythms were investigated in ewe lambs at pasture. Two groups of 20 lambs had heart rate (HR), vaginal temperature (T(v)), ear-canal temperature (T(c)) and ear-pinna temperature (T(p)) monitored continuously for 3 days. Climatic conditions were recorded at the same time and Temperature Humidity Index (THI) calculated. One group experienced fine clear weather for the 3 days, the other group experienced 2 days of heavy rain. During periods of fine weather, the daily rhythm for T(v) and T(c) was monophasic. However, heavy rain and a constant THI reduced the amplitude of the recorded temperature rhythms. Daily T(v) and T(c) patterns correlated strongly with THI, with a phase lag of 2 h. Peak T(v) and T(c) were at approximately 17:00 h each day. Mean maximum daily amplitudes were approximately 1.3 degrees C for T(v) and T(c). Mean T(v) was 39.3+/-0.1 and 39.6+/-0.1 for weeks 1 and 2, respectively, while mean T(c) was 38.9+/-0.1 and 39.2+/-0.1. Changes in T(v) and T(c) were closely correlated. We conclude that climate has a major effect on body temperature rhythms.

Measuring of extracellular cortisol and corticotropin-releasing hormone in the amygdala using immunosensor coupled microdialysis

A method is described for the measurement of cortisol or corticotropin-releasing hormone (CRH) from the brain, within, or in the dialysate of, a microdialysis probe using an antibody-linked assay. Polyclonal antibodies for either cortisol or CRH provide a specificity of measurement. These antibodies are affixed on a platinum electrode within the probe. Determination of bound cortisol or CRH is performed via an indirect assessment of competitive ligand also bound, and conjugated to HRP. This is activated and measured as current change. These probes were used for extracellular measurements in the amygdala, a limbic brain region, of sheep. Direct measurement in vivo compared favorably to the use of either the immunosensor or standard RIA techniques on dialysate emerging from a classical microdialysis probe, suggesting that the method could be used directly in-vivo. This is the first report in literature of rapid on-line measurement of CRH and cortisol from a discrete brain area. The probes have fast response times (>90% of maximum response within 30 s of start of analysis), high sensitivity (<0.1 pg/ml for CRH) and can acquire data every 2 min. They are stable in-vivo (>72 h) and regenerable, offering on-line measurement, with rapid time resolution, of neurohumoral substances.

Patterns of weaning and adult response to stress

Early environmental effects including variation in maternal care, can modify hypothalamic-pituitary-adrenal (HPA) axis function. One of the more overt early effects, involving maternal care, is weaning restraint. In this study the effects of different patterns of weaning, in the rat (Rattus norvegicus), on both adult response to restraint stress and to dexamethasone administration were examined. Animals that as pups experienced a gradual lengthening time of separation from the mother, between 21 and 30 days of postnatal age (completely separated on 30 days), showed lower levels of systemic corticosterone and glutamate in the sensory cortex in response to restraint stress than seen in other groups. These animals also showed greater suppression of corticosterone by dexamethasone than did animals abruptly removed from the mother at 21 days of age. Animals left in the cage with the mother until either 30 or 40 days of age showed the greatest levels of corticosterone and glutamate in the sensory cortex in response to the stress and the least suppression by dexamethasone. These results suggest that changes in maternal contact at time of weaning can influence adult responsiveness to stress.

Maternal behaviour in sheep (Ovis aries) following administration of opioid agonists

AIMS

As kappa(kappa)-opioids have marked effects on pain threshold in sheep during oestrus, late pregnancy and after birth, a study was undertaken to determine if kappa -opioids also had other roles during these states.

METHODS

Opioid agonists (GR89696, DAMAGO) were administered into either the lateral hypothalamus (LH) or amygdala of non-pregnant sheep (n = 5) or pregnant sheep (n = 15) in late pregnancy (n = 5) within 12 h of birth (n = 5) or in the third week after birth (n = 5). Cortisol, behavioural and electrocardiographic responses to an auditory stimulus were assessed with and without drug administration, as was feed consumption and suckling events.

RESULTS

In non-pregnant sheep, DAMAGO injected into either the LH or amygdala had little effect on the response to the auditory stimulus but when injected into the LH did decrease food consumption. GR 89696 had no obvious effects. In late pregnancy, cortisol and heart rate responses to the auditory stimulus were significantly reduced compared to the non-pregnant animals irrespective of treatment. This was also the case in the third week after birth. Immediately post-partum cortisol responses were closer to that seen in the non-pregnant animal. In late pregnancy and both post-partum periods, GR 89696 in the LH significantly increased feed consumption while DAMAGO had no significant effects. GR 89696 injected into the amygdala reduced the behavioural response to the auditory stimulus in late pregnancy and both post-partum periods.

CONCLUSION

Changes in sensitivity to opioids occur in both the amygdala and LH with pregnancy and after birth. These may influence maternal behaviours and feed intake.

Influence of mouse position on muscular activity in the neck, shoulder and arm in computer users

Anecdotal reports of shoulder and arm discomfort related to computer mouse use are common. The aim of this study of ten subjects was to examine the influence of mouse position, relative to the keyboard, on shoulder and arm muscular activity and working posture. Surface electromyography and the Rapid Upper Limb Assessment were used to determine the differences in muscle activity and posture during an editing task in each of three mouse positions. Significantly less anterior (p = 0.01) and middle (p = 0.03) deltoid electromyographic activity was demonstrated when the computer mouse was positioned adjacent to a keyboard without a numeric pad when compared to performance of an identical task with the mouse adjacent to a standard keyboard. Electromyographic activity in trapezius muscle did not differ between mouse positions. Working posture of right handed mouse users is improved by removal of the numeric keypad.

Monitoring on-line of extracellular gamma-amino-4-butyric acid using microdialysis coupled to immunosensor analysis

A method is described for the measurement of gamma-amino-4-butyric acid (GABA) within a microdialysis probe using an antibody-linked assay. A monoclonal antibody for GABA provides the specificity of measurement and these antibodies are affixed on a working platinum electrode within the probe. Determination of bound GABA is performed via an indirect assessment of competitive ligand also bound, and conjugated to horseradish peroxidase which is activated and measured as current change. Using this probe directly for extracellular measurements in the somatosensory cortex of sheep compared favorably to the use of this probe on dialysate emerging from a classical microdialysis probe suggesting that it could be used directly in vivo. The probe has a fast response time (> 90% of maximum response within 30 s of start of analysis) and high sensitivity (< 0.5 mumol/l) and can acquire data every 2 min. It is stable over a period of time in vivo (> 48 h) and is regenerable. The probe design offers on-line measurement, with rapid time resolution of substances not amenable to enzyme-based amperometric measurement.

Oxytocin and prolactin suppress cortisol responses to acute stress in both lactating and non-lactating sheep

Cortisol response to stress appears to differ between lactating and non-lactating animals. Lactating (14 d post partum) and non-lactating sheep were fitted with probes so that drugs and hormones could be infused directly into the posterior pituitary and paraventricular nucleus of the hypothalamus. The animals were also fitted with instruments to allow monitoring of heart rate, body temperature and blood cortisol levels. Their reactions to a source of acute stress (a barking dog) were then followed, with or without drug and hormone manipulation. Results in both lactating and non-lactating animals indicated shortcomings in the use of cortisol as a stress indicator. Infusing prolactin and oxytocin into either the posterior pituitary or the paraventricular nucleus of the hypothalamus suppressed cortisol responsiveness to stress in both lactating and non-lactating animals (the latter to a greater extent). In the absence of drugs, lactating animals had a slightly higher basal level of cortisol and a lower cortisol response to stress than their non-lactating counterparts. Despite suppression of cortisol responses, with or without drugs, other indicators of stress still changed with the presence of a barking dog, suggesting the complexity of control involved in stress responses.

Real-time measurements of corticosteroids in conscious animals using an antibody-based electrode

An electrochemical immunosensor for real-time determination of corticosteroids, a group of steroidal hormones, is reported. The sensor measures competitive binding of endogenous corticosteroid and a corticosteroid-peroxidase conjugate with antibodies, immobilized on a platinum electrode, by monitoring of peroxidase activity. The electrode is encased within a dialysate membrane, which separates the electrode environment from the sampled fluid, allowing corticosteroid to equilibrate across the membrane. This permits measurements to be made in vivo. The small size of the probe (350 microns D) allows implantation into tissue or circulatory systems. The electrode was viable for 200 to 400 sequential measurements and at least 48 h in vivo. Detection sensitivity is 0.2 to 0.6 microgram/100 ml of cortisol or corticosterone. The results suggest the possibility of monitoring hormones in real-time within the blood or organ systems of conscious animals.

Real-time extracellular measurement of neurotransmitters in conscious sheep

Measurements of neurotransmitters in conscious animals have been restrictive in real-time. The use of specific enzymes within an amperometric probe, based upon a microdialysis membrane, may overcome some of these problems. I report the use of such a probe, with different perfusions of enzymes, to allow real-time measurement of glutamate, catecholamines and indoleamines, in conscious animals. At an adjacent site microdialysis sample collections were made concurrently and neurotransmitters measured in the dialysate. Both probes were positioned within the somatosensory cortex. Values obtained by amperometric probes were similar to those in dialysate samples for glutamate, catecholamines and indoleamines during basal and stimuli related collections. Amperometric measurements showed higher peak concentrations and better time resolution than dialysate sampling. This reflects sampling differences. Application of external stimuli increased extracellular concentrations of glutamate, catecholamines and indoleamines, in both forms of sampling. Dopamine measurements did not correlate well between the two forms of sampling. This may reflect the non-specificity of the enzyme (dopamine-beta-hydroxylase) used in the amperometric probe. This combination, of microdialysis and amperometry, offers a useful tool for real-time neurotransmitter studies in vivo.

Social behaviour in sheep relates to behaviour and neurotransmitter responses to nociceptive stimuli

Sheep in the field display differences in social behaviour. These differences allow a division into three social groups with distinct behavioural occurrences and frequencies. The behavioural and neurotransmission responses of each of these groups to aversive stimuli were compared. Behavioural responses were seen to both forelimb electric shocks and thermal heating of the nose in all groups. These responses changed with stimulus repetition in a group-dependent manner. Microdialysis probe studies of neurotransmitter release in the somatosensory cortex indicated neurotransmitter responses to stimuli in all animals that varied with both animal group and stimulus repetition. Group 1 animals, aggressive and socially active, showed increases in gamma amino-4-butyric acid (GABA) with initial stimulus presentation; this increased with stimulus repetition. Behavioural responses to the stimuli decreased with repetition and nonstimulus-related behaviours, during the course of the experiment, increased. Both of these appeared dependent upon GABA. Group 2 animals, moderately aggressive and socially active, released opioid-like peptides (OLP) upon initial exposure to stimuli but, with repetition, switched to using GABA. Group 3 animals, nonaggressive and socially inactive, released OLP with initial and repeat stimuli. In groups 2 and 3, both GABA and OLP appear to reduce stimulus-related behaviour, but OLP appeared to also reduce nonstimulus-related behaviour and GABA increased these. Changes were independent of animal liveweight. Glutamate was released in response to stimuli in all 3 groups and, with repetition, fell in groups 1 and 2 but increased in group 3. An animal's social behaviour and status may predict its response to a stimulus.

Changes in the release of amino acid neurotransmitters in the brains of calves and sheep after head-only electrical stunning and throat cutting

In calves aged two to five months, throat cutting resulted in an increase in the concentration of the amino acid neurotransmitters glutamate and aspartate in the brain. Electrical head-only stunning by itself also increased the concentrations of these two neurotransmitters. The levels induced by stunning resulted in a seizure state characterised by epileptiform-like activity in the electroencephalograph. Combing head-only stunning with throat cutting within 10 seconds of the stun had a synergistic effect upon glutamate and aspartate, increasing their concentration by a greater amount and more quickly than either procedure on its own. An irreversible loss of brain function also occurred more quickly than after throat cutting alone. The administration of glutamate and aspartate receptor antagonists before the throat cutting lengthened the time to the loss of brain function in a dose dependent manner. Similar changes were observed in sheep but they occurred much more quickly than in cattle.

Electroencephalographic studies on the nape shooting of sheep

The implications of shooting animals in the area of the occipito-atlantal junction was evaluated in three sheep by recording changes in the EEG activity. In one sheep, a shot which entered the occipito-atlantal junction and fractured the first cervical vertebra failed to produce insensibility. In contrast, a shot in another sheep which struck the occipital condyles of the skull resulted in loss of cortical evoked responses, the presence of high amplitude low frequency activity and ultimately all loss of brain activity. These results provide evidence that shooting through the vertebral column does not necessarily transmit sufficient percussive forces to higher brain regions to produce immediate insensibility. This has important implications for the humane destruction of animals, particularly, as in the case of cetaceans, where the occipito-atlantal junction or a high neck position is a recommended target area.

Contribution of amino acid transmitters to epileptiform activity and reflex suppression in electrically head stunned sheep

In sheep, administration of a combination of zolazepam and tiletamine hydrochloride resulted in a dose dependent reduction in the duration of epileptic activity induced by an electric stun applied to the head. The compound also lengthened the normal period of reflex suppression that occurs after a stun. Excitatory amino acid receptor antagonists (2-amino-7-phosphonoheptanoic and 2-amino-5-phosphonovaleric acids) also reduced the duration of epileptic activity following an electric stun. These drugs did not alter the time of pedal and ear pinch reflex suppression. Administration of bicuculline (a gamma amino-4-butyric acid [GABA] receptor antagonist) reduced the period of stun induced reflex suppression and increased seizure duration. Administration of a GABA receptor agonist, baclofen, increased the duration of reflex suppression. The results suggest that the development of epileptiform-like activity following application of an electric current to the head is dependent upon excitatory amino acid receptors. The reflex suppression that also arises following an electric stun is contributed to by the activation of GABA receptor mechanisms.

Electrophysiological responses of the fetus to hypoxia and asphyxia

To study the effect of transient hypoxia on neural function in utero, we examined brainstem auditory and somatosensory evoked potentials in chronically instrumented fetal sheep subject to altered maternal inspired gases. Moderate hypoxia without acidosis for 1 h, in 10 fetuses (fetal arterial pH = 7.37 +/- 0.03, PaO2 = 1.4 +/- 0.27 kPa) caused a transient depression of the later components of the evoked potentials. These recovered within 1 h. However, in 6 fetuses exposed to a second, acidotic, insult 2 days later, associated with a higher inspired PCO2 (fetal pH = 7.25 +/- 0.05, PaO2 = 1.17 +/- 0.28 kPa), there was greater impairment of the later components of the evoked potentials, with significant changes still observable 72 h later. In 4 fetuses a non-acidotic hypoxia was repeated instead and in these fetuses no persisting deficit was seen. These data suggest that there is a narrow threshold between a degree of intrauterine hypoxaemia associated with no sequelae and an insult causing persistent cerebral impairment, and that even mild acidosis may contribute to this.

Excitatory amino acid projections to the periaqueductal gray in the rat: a retrograde transport study utilizing D[3H]aspartate and [3H]GABA

The afferents to the periaqueductal gray utilizing excitatory amino acid transmitters have been described in rat brain by autoradiography following microinfusion and retrograde transport of D[3H]aspartate. Parallel experiments employing injections of [3H]GABA established that the retrograde labelling found with D[3H]aspartate was transmitter-selective. Following infusion of D[3H]aspartate, perikaryal labelling was found in nine subcortical areas, particularly infralimbic and cingulate cortices, with a predominance of ipsilateral labelled perikarya. Heaviest cortical labelling was localized in perirhinal cortex, in an extensive band of cells adjoining the rhinal sulcus. The hypothalamus contained the heaviest perikaryal labelling within brain: D[3H]aspartate labelled cells in 11 hypothalamic and mammillary nuclei. Intense bilateral labelling was obtained in ventromedial hypothalamus, although the number of perikarya was lower contralaterally. D[3H]Aspartate also produced heavy ipsilateral labelling of perikarya in posterior hypothalamus. Labelling patterns in cortex and hypothalamus were precise and topographic, and [3H]GABA never labelled cells in these regions. Other telencephalic and diencephalic areas containing prominent, retrogradely labelled cells were the lateral septum, amygdala, zona incerta and lateral habenula. The relative density of labelled cells in mesencephalic areas was much lower than that found in cortex and hypothalamus, although D[3H]aspartate labelled a moderate number of perikarya in the inferior colliculus and cuneiform nucleus. A smaller number of heavily labelled cells was found in the parabrachial nuclei, Kolliker-Fuse nucleus and laterodorsal tegmental nucleus. Only occasional labelled perikarya were observed in the myencephalon. Low densities of labelled cells were found after the injection of [3H]GABA into the periaqueductal gray, and the only regions in which a small number of perikarya were labelled by both [3H]GABA and D[3H]aspartate were the dorsal raphe and parabrachial nuclei. Overall, the retrograde transport of D[3H]aspartate revealed a complex topographic and convergent network of afferent pathways to the periaqueductal gray likely to utilize an excitatory amino acid transmitter. Our findings confirm the selectivity of this neurochemical mapping technique and provide evidence that hypothalamic, habenular, subthalamic and cuneiform afferents to the periaqueductal gray utilize an acidic amino acid as their transmitter. They also confirm that corticofugal afferents to periaqueductal gray utilize an excitatory amino acid.

The effects on central dopamine function of chronic L-dopa (methyl ester hydrochloride) treatment of mice

Mice were treated for 28 days with drinking water containing L-DOPA methyl ester hydrochloride (DME) plus carbidopa, carbidopa alone, or with the vehicle. All mice were then given the vehicle for 1 day and behavioural and biochemical assessments made on the 29th day. On average, mice consumed between 181 and 302 mg/kg of DME (expressed as the base) each day. In behavioural experiments DME- and carbidopa-treated mice were subsensitive to the locomotor stimulating effects of apomorphine, after their pretreatment with reserpine plus alpha-methyl-p-tyrosine to remove endogenous stores of dopamine and to stop its synthesis. Even mice pretreated for only one day with chronic DME or carbidopa displayed some subsensitivity to apomorphine challenge, but the effect was more marked the longer the chronic treatment. Other mice were chronically treated for 28 days with alpha-methylDOPA or vehicle, and these mice when challenged with apomorphine after dopamine depletion (as described above), were also markedly subsensitive to the locomotor activating effects of apomorphine. There were no changes in sensitivity of drug-treated mice to the hypothermic effects of apomorphine, to the stereotypy-inducing effects of apomorphine or d-amphetamine, or to the locomotor activating effects of L-DOPA itself or to bromocriptine. There were, however, some changes in the basal grooming behaviour of both DME- and carbidopa-treated mice, and in their response to SKF38393 challenge. Striatal binding studies with [3H]-spiperone and [3H]-SCH23390 indicated that there were no marked changes in Kd or Bmax of either D-1 or D-2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)