A systematic review of animal based indicators of sheep welfare on farm, at market and during transport, and qualitative appraisal of their validity and feasibility for use in UK abattoirs

In the UK, it has been suggested that abattoirs are ideal locations to assess the welfare of sheep as most are slaughtered at abattoirs either as finished lambs or cull ewes. Data from abattoirs could provide benchmarks for welfare indicators at a national level, as well as demonstrating how these change over time. Additionally, feedback could be provided to farmers and regulatory authorities to help improve welfare and identify high or low standards for quality assurance or risk-based inspections. A systematic review of the scientific literature was conducted, which identified 48 animal-based indicators of sheep welfare that were categorised by the Five Freedoms. Their validity as measures of welfare and feasibility for use in abattoirs were evaluated as potential measures of prior sheep welfare on the farm of origin, at market, or during transportation to the abattoir. A total of 19 indicators were considered valid, of which nine were considered theoretically feasible for assessing sheep welfare at abattoirs; these were body cleanliness, carcass bruising, diarrhoea, skin lesions, skin irritation, castration, ear notching, tail docking and animals recorded as 'obviously sick'. Further investigation of these indicators is required to test their reliability and repeatability in abattoirs. Novel welfare indicators are needed to assess short-term hunger and thirst, prior normal behaviour and long-term fear and distress.

Veterinarians and food safety

Since the early days of veterinary science, vets have played an important part in protecting public health through controls over the safety of food of animal origin. Traditionally, public health has been treated as a topic separate from the mainstream veterinary subjects of diagnosis and treatment of animal disease. However, there is now increasing awareness of the interconnection between animal and human health, and between the work of vets in production animal practice and those in food safety and other disciplines, as Kenneth Clarke explains.

Regulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity in ovine placenta by fetal cortisol

The effect of fetal cortisol on the activity of the type 2 isoform of the enzyme, 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD2), was examined in ovine placenta and fetal kidney by measuring tissue 11 beta-HSD2 activity during late gestation when endogenous fetal cortisol levels rise and after exogenous cortisol administration to immature fetuses before the prepartum cortisol surge. Placental 11 beta-HSD2 activity decreased between 128-132 days and term (approximately 145 days of gestation) in association with the normal prepartum increase in fetal plasma cortisol. Raising fetal cortisol levels to prepartum values in the immature fetus at 128--132 days of gestation reduced placental 11 beta-HSD2 activity to term values. In contrast, 11 beta-HSD2 activity in the fetal renal cortex was unaffected by gestational age or cortisol infusion. When all the data were combined, there was an inverse correlation between the log fetal plasma cortisol level at delivery and placental 11 beta-HSD2 activity, expressed both on a weight-specific basis and per mg placental protein. Fetal cortisol therefore appears to be a physiological regulator of placental, but not renal, 11 beta-HSD2 activity in fetal sheep during late gestation. These findings have important implications, not only for glucocorticoid exposure in utero, but also for the local actions of cortisol within the placental tissues that are involved in initiating parturition in the sheep.

Ground reaction force and spatiotemporal measurements of the gait of the mouse

Measurement of ground reaction forces with force plates permits quantification of the subtle changes in movement associated with a variety of pathophysiological states. The apparatus used here permits simultaneous recording of other spatial and temporal characteristics of gait. Since the mouse is becoming increasingly important for modeling human disorders, we have recorded ground reaction forces (P) in this species. To date, we have measured the vertical component (Pz) and found it to be similar to that of other species, in that a greater Pz is exerted via the forelimb, although the areas under the force/time curves, are not different. Different points of discontinuity are seen in the forelimb and hindlimb curves, indicating differential deployment. Pz varies consistently with stance time and is consistent across the adult life of the mouse. It is suggested that the technique has potential for the study of a variety of mouse models of disease and of their therapies.

Post-weaning social isolation of rats leads to an abnormal gait

The purpose of this study was to further characterize the phenotype of rats that have experienced prolonged postweaning social isolation, a paradigm that produces changes relevant to neuropsychiatric disorders. At weaning, male Wistar rats from three litters were housed socially (n = 12) or in isolation (n = 13) for 10 weeks. Isolated rats could see, hear and smell other rats. A sophisticated analysis of gait revealed that the stride duration was increased in isolates (12%, P = 0.0024) as a result of increased stance duration (18%, P = 0.0005), but there was no difference in vertical reaction force or velocity. Adrenal glands were heavier in isolates (19%, P = 0.0047). There was no difference in cross-sectional area of the brain or lateral ventricles anywhere along the anterior-posterior axis. All experiments and analysis were performed blind to housing condition. This is the first study to demonstrate that socially isolated rats have an abnormal gait. Further analysis, including pharmacological manipulation, is needed in order to understand the nature of the abnormality.

Development and consistency of gait in the mouse

Mouse models of human disease may display developmental abnormalities or adult onset of the condition. Since many diseases are accompanied by gait disturbances, knowledge of normal gait development in the mouse and its adult characteristics might be valuable as standards against which to appraise disease progression and the efficacy of putative therapies. Assessment of the gait of mice from postnatal day (pnd) 13 to postnatal week (pnw) 80 was undertaken utilising video techniques to examine velocity, stride, stance and swing times and between pnw 29 and 80 using load cells for analysis of the vertical reaction force (P(z)) associated with limb placements. Some adult features are apparent by pnd 13, but in the hindlimb (HL) particularly, the adult pattern of relationships between stride, stance and swing are not established. Adult characteristics of forelimb (FL) deployment develop earlier than those of HL while the systems controlling HL stance develop earlier than those regulating its swing. All the features measured, however, such as the shorter stance and longer swing of FL compared to HL, are established in their adult form by pnd 24 and maintained throughout adult life. In healthy mice at pnw 80, there was no deviation from the adult pattern of gait in which P(z) transmitted via FL exceeds that via HL by around 5%. We did not detect any significant change in any other variable or in their relationships.

Bovine tuberculosis in free-ranging carnivores from Michigan

During a survey of carnivores and omnivores for bovine tuberculosis conducted in Michigan (USA) since 1996, Mycobacterium bovis was cultured from lymph nodes pooled from six coyotes (Canis latrans) (four adult female, two adult male), two adult male raccoons (Procyon lotor), one adult male red fox (Vulpes vulpes), and one 1.5-yr-old male black bear (Ursus americanus). One adult, male bobcat (Felis rufus) with histologic lesions suggestive of tuberculosis was negative on culture but positive for organisms belonging to the Mycobacterium tuberculosis complex when tested by polymerase chain reaction. All the tuberculous animals were taken from three adjoining counties where M. bovis is known to be endemic in the free-ranging white-tailed deer (Odocoileus virginianus) population. There were two coyotes, one raccoon, one red fox, and one bobcat infected in Alpena county. Montmorency County had two coyotes and one raccoon with M. bovis. Two coyotes and a bear were infected from Alcona County. These free-ranging carnivores/omnivores probably became infected with M. bovis through consumption of tuberculous deer. Other species included in the survey were opossum (Didelphis virginiana), gray fox (Urocyon cinereoargenteus), and badger (Taxidea taxus); these were negative for M. bovis.

Cryopreserved femoral vein grafts for difficult hemodialysis access

Improved survival of patients with renal failure has led to the need for complex angioaccess procedures. The use of cryopreserved femoral vein for angioaccess when prosthetic arteriovenous grafts (AVG) could not be placed, owing to infection or the loss of conventional angioaccess sites from multiple AVG failures, was prospectively evaluated. Forty-eight cryopreserved femoral vein AVGs were placed in 44 patients. Thirty-eight (82%) of the cryopreserved femoral vein AVGs were placed for infection, whereas the other 10 (18%) were placed for multiple graft failures with compromised venous outflow. Even with implantation of the cryoveins into infected patients, there were no cryopreserved femoral vein AVG infections. The 1-year primary graft patency rate was 49% and the secondary graft patency rate was 75%. During the same time interval, 68 prosthetic brachial artery-to-axillary vein AVGs were placed. The 1-year primary and secondary patency rates for the prosthetic AVGs were 65 and 78%, respectively. In this study the overall patency rate of the cryopreserved femoral vein AVGs was similar to that for the PTFE AVGs (p = 0.519). In conclusion, the cryopreserved femoral vein proved useful in difficult angioaccess cases. The lack of infection after cryovein implantation around an infected area shows promise for salvaging an angioaccess site that would otherwise have been abandoned.

Gait analysis in the mouse

The gait of the adult Swiss (Mike Flack--MF1 subtype) mouse during spontaneous walk/trot locomotion at velocities ranging from 14-43 cm s(-1) has been analysed using simultaneous video and reaction force analysis. No differences were observed between males and females. Velocity adjustments within this range are accounted for to a greater extent (>70%) by stride time decreases and to a lesser degree (<30%) by stride length increases. Equivalent stride times for fore and hindlimbs were, in the former, composed of a shorter stance and a longer swing time. Peak vertical reaction force increases with decreasing stance time, with that for the forelimb being about 5% greater than that for the hindlimb across the whole stance time range studied. The areas under the vertical reaction force curves for fore and hindlimbs are, however, not significantly different. The results are discussed in the light of in vitro work cycle studies on the properties of some of the major hindlimb locomotor mouse muscles, and with previously established data in the rat. It is concluded that the mouse shows a consistent and quantifiable gait that would allow incorporation of locomotor assessment into the evaluation of a number of pathophysiological states.

Intestinal lymphosarcoma in captive African hedgehogs

Two captive adult female African hedgehogs (Atelerix albiventris) had inappetance and bloody diarrhea for several days prior to death. Both hedgehogs had ulceration of the small intestine and hepatic lipidosis. Histopathology revealed small intestinal lymphosarcoma with metastasis to the liver. Extracellular particles that had characteristics of retroviruses were observed associated with the surface of some neoplastic lymphoid cells by transmission electron microscopy. These are the first reported cases of intestinal lymphosarcoma in African hedgehogs.

Listeria monocytogenes and Escherichia coli septicemia and meningoencephalitis in a 7-day-old llama

Listeria monocytogenes and Escherichia coli were isolated from blood collected on presentation and tissues samples taken postmortem. Listeria monocytogenes was isolated from cerebrospinal fluid collected antemortem. The importance of passive transfer of immunity, the subtlety of neurologic signs in early meningitis, and considering blood-CSF penetration in antimicrobial selection are discussed.

Gait analysis in a rat model of osteoarthrosis

Gait analysis has been undertaken in a rat model of osteoarthrosis, induced by intra-articular injection of sodium iodoacetate into the left knee. Two weeks after injection, no disturbances were recorded to the velocity of locomotion, the stride length nor the stride, stance, or swing times. However, clear and consistent reductions in the peak vertical load bearing (Pz) by the affected limb were observed of 22-29% relative to the other limbs, with the right forelimb taking the major share of extra load. This redistribution fitted well with the gait pattern of the rat, allowing Pz redistribution with minimum gait disturbance, and was still present 6 weeks later. These results are discussed in the context of the possible load sensitivity of the damage process to the gait pattern of the rat.

Differential fore- and hindpaw force transmission in the walking rat

Previous studies suggest that the stance phase of the rat stride is initiated by a soft contact period when the forepaw may engage in tactile sampling of the terrain. However, no ground reaction force measurements have yet been made during rat locomotion. In the dog and other quadrupeds a brief or nonexistent soft contact phase is observed. Therefore, forces and pressures exerted via fore and hindpaws have been measured in the spontaneously walking rat. These indicate while the hindpaw vertical reaction forces are temporally similar to those in the dog, those transmitted via the forepaw are not. At average walking velocities the forepaw soft contact time is some 4 times longer than that of the hindpaw, with values of 207 +/- 25 ms and 52 +/- 12.2 ms (mean +/- 1 SEM) respectively. These data are consistent with the idea of forepaw useage to provide tactile information of the terrain during a prolonged initial soft contact phase, while the hindpaw transmits most of the early vertical ground reaction forces.

Gait analysis in the rat as a model for the study of peripheral vascular disease

A number of problems are associated with investigation of the pathophysiology of peripheral vascular disease (PVD) in humans and unilateral ligation of the common iliac artery in the rat has been extensively used as an experimental model of PVD. However, techniques so far applied to monitor the effects of PVD on muscular function are invasive and difficult to relate to natural locomotion. The present study aimed to investigate gait during spontaneous, unforced locomotion in the animal model. No differences were observed between control and experimental rats in velocity or stride lengths. Although stride time was unchanged, its internal balance was disturbed with reduced stance, prolonged swing, for the ligated limb (LL) relative to the nonligated limb (NLL). Gait symmetry was also affected with NLL strike occurring earlier during LL stance. Analysis of footfall patterns showed a reduction of stance area and pressures exerted via LL relative to NLL. It is concluded that gait and footfall analysis could be useful for assessing limb function under natural exercise conditions.

Stimulation of locomotion in neonate rats by TRH analogue CG3703

Thyrotropin releasing hormone (TRH) and its analogues have been shown to depolarise motoneurons and stimulate cyclical motor activities such as respiration and locomotion. It has been suggested that one of its roles might be modulation of neuronal membrane excitability to release intrinsic rhythmicity. The present experiments were designed to determine whether it would initiate locomotion in the neonate rat prior to the development of spontaneous walking. It was found that the TRH analogue CG3703 did activate locomotion in 3-day-old rat pups. Quantification of various gait parameters and study of spatiotemporal footfall patterns showed the gait to be indistinguishable from the spontaneous locomotion of older pups. Possible loci of action are discussed.

Development of locomotion in the rat--spatiotemporal footfall patterns

Footfall patterns during locomotor ontogeny have been observed in Wistar rats 10-30 days old. These reveal that, even at 22 days, the paw contacts are both spatially and temporally unlike those of the adult. In the adult there is a precise presentation sequence involving early soft contact of tactile sensitive forepaw parts that may be important in tactile locomotor guidance and which is not fully established even at 22-30 days. The hindpaw contact pattern is also not yet adult-like involving a greater incidence of early toe contact. It is suggested that, only after day 15, when the forelimb is no longer the major weight-bearing limb, can it start to be developed for the fine discriminative touch required for tactile guidance of limb placement. Some further time is necessary for adult patterns to be achieved.

Analysis of walking locomotion in adult female rats undernourished as sucklings

Suckling rats were undernourished from birth by underfeeding their mothers. They were refed from 3 weeks of age. Detailed analyses were made of the walking locomotion of previously undernourished and well-fed control female rats at 10 weeks, using electronic, computer, and TV techniques. Previously undernourished rats were found to deploy shorter stride times resulting in greater forward velocities. The shorter stride times were attained by reductions in stance time, while swing time was unaffected. No changes in stride length or width were observed, and the relationships between stride time and velocity, swing, or stance times were unaffected.

Disturbance of spatiotemporal footfall contact patterns in the rat by TRH analogue CG3703

Administration of TRH or its analogues to a rat changes the dynamics of locomotion resulting in shorter stance times and causes postural disturbances, including hunched back and pelvic girdle elevation. Locomotor disturbance, induced by a variety of methods, results in changes to the footfall patterns during the stance phase of locomotion. The present work investigated whether these postural and locomotor dynamic disturbances in the CG3703 treated rat were associated with changes to the pattern of paw/floor contact during locomotion. It was found that in treated animals the area of hindpaw contact increased while that of the forepaw decreased from control values. The pattern of contact changed, with hindpaw stance being shifted towards more distal elements while in the forepaw a reduction in the deployment of proximal elements without any compensating increase in distal contact was seen. These results are discussed in the context of the effects of TRH analogues on sensory and motor processing in the CNS.

Swing time changes contribute to stride time adjustment in the walking rat

Locomotor analysis is a useful tool for assessing normal and disturbed brain function. Previous studies have indicated that, during locomotion at walking velocities, the rat adjusts its velocity by changes to stride time and length. The present work has shown that, in the Sheffield strain rat, changes in stride time are achieved by a differential deployment of its two components, stance time and swing times. During slow walking, swing time changes provide minimal contribution to stride time reductions. At above average stride frequencies, however, swing time changes become significant, providing for more than half the reduction over parts of the range.

Interactions between adrenergic systems, anaesthetic and TRH analogue induced analeptic effects on VBT transmission

Previous behavioural and electrophysiological studies have indicated an antinarcotic action of thyrotropin-releasing hormone (TRH) and its analogues in antagonizing the action of CNS depressant drugs, including baclofen and a variety of anesthetics. While beta-adrenergic receptors are implicated in the level of anaesthesia/arousal, whether the analeptic action of TRH involves adrenergic systems for its expression is uncertain. The object of the present experiments, therefore, was to examine interactions between adrenergic systems and the anti-anaesthetic effects of TRH analogue CG3703. It was found that pretreatment with the beta-block (+/-)propranolol did not abolish or reduce the ability of CG3703 to antagonize urethane-induced depression of VBT transmission. These results suggest therefore, that beta-adrenergic systems are unlikely to be involved in the anti-anaesthetic effect of the tripeptide.

TRH analogue antagonizes anaesthetic induced depression of information transfer through the ventrobasal thalamus of the rat

Previous studies have indicated an anti-narcotic action of TRH and its analogues. A major site of anaesthetic action is in the ventrobasal thalamus (VBT). The present experiments were performed to determine whether there was antagonism between anaesthetics and a TRH analogue on VBT transmission. It was found that the TRH analogue CG3703 reversed the depressant actions of the anaesthetics urethane, sodium pentobarbitone and sodium brietal on ventrobasal transmission. These actions were also observed at the cortical level but cuneate transmission was unaffected. These results are discussed in the context of modulation of information flow through VBT. In particular it is suggested that TRHergic input from the thalamic reticular nucleus may be an important regulator of VBT transmission.

Antagonism of baclofen induced reduction in ventrobasal thalamic transmission by a TRH analogue

It has been shown previously that baclofen, the GABB beta receptor agonist, reduces the excitability of ventrobasal thalamic relay neurons measured by increases in latency and decreased discharge probability, while thyrotropin releasing hormone (TRH) analogues have the opposite effects. The present experiments have shown that the excitability reducing effects of baclofen on ventrobasal transmission are antagonised by the administration of TRH analogue CG3703. These results are discussed in the context of possible GABAergic and TRHergic modulation of VBT transmission from the thalamic reticular nucleus.

Gait topography in rat locomotion

Gait topography has been quantified and normative data established for free, spontaneous locomotion in rats. The normal walking pattern has been compared for male and female rats and for three rat strains. The normal walking gait was found to be symmetrical, and measures of stride width (SW) and stride length (SL) were consistent, with coefficients of variability ranging between 10 and 21%. A study of gait ontogeny found that for both male and female rats, SL increased as a linear function of body weight, whereas SW increased curvilinearly. The results indicate that repeated measures of gait topography were not subject to interference from habituation. A sex difference in gait ontogeny was observed. The developmental pattern is similar for both sexes, but males increase both SL and SW faster than females. It is proposed that gait topography may yield valuable information in activity studies.

Abnormal locomotion in the rat after administration of a TRH analogue

Previous studies have indicated that the TRH analogue CG3703 induces changes in gross measures of motor activity. The purpose of the present study was to determine whether it affected the underlying components of the locomotor cycle, stance and swing times. It has been found that while total stride time was unaffected there was an alteration in the balance between swing and dual stance times such that treated rats used longer swing times and shorter dual stance times. For both control and treated animals dual stance time increased with stride time. However, for any particular stride time, treated animals deployed longer swing times and shorter dual stance times. Possible mechanisms for these observations are discussed.

Further studies on the effects of a thyrotropin releasing hormone analogue on locomotor activity in the rat

In these experiments, the relationship between two of the variables of locomotion, stepping frequency and velocity, after injection of the TRH analogue RX77368 (10 mg/Kg i.p.), has been studied. A shift towards higher stepping frequencies was observed, confirming previous observations. However, there was no difference between the velocities of locomotion produced by treated and control rats. In the treated rats the relationship between stepping frequency and velocity was disturbed, such that a higher stepping frequency was employed to attain any particular velocity. This was accompanied by a reduction in stride length. Possible reasons for this disturbance are discussed in terms of changes in muscle stiffness and proprioceptive reflexes.

A quantitative study of normal locomotion in the rat

Three variables of locomotion; stride length, stride frequency and velocity have been measured in forty-eight rats. Median values were found to be 11.3 cm, 2.4 Hz and 24.2 cm/sec respectively. The results are assessed both as independent variables and in terms of their interaction. It was found that the two variables used to increase velocity (stride length and stride frequency) were not deployed equally during normal walking velocities (10-50 cm/sec). It is proposed that the study of these three readily quantifiable variables, particularly the relationships between velocity and stride frequency may be useful for the evaluation of locomotion in the assessment of neuropharmacologically active agents.

TRH analogue affects information transfer through the ventrobasal thalamus

Extracellular microelectrode recordings have been made from single ventrobasal thalamic neurones in rats anaesthetised with urethane. Injection of the thyrotropin releasing hormone (TRH) analogue RX77368 (2mg/kg), produced increases in spontaneous activity and decreases in the latency of response to peripheral stimulation, together with increased production of later, rhythmic discharges. These changes were maximal between 30 and 60 minutes after injection. Decreases in latency and increases in amplitude were also observed in the evoked potential recorded from the somatosensory cortex. These results are discussed in relation to previously observed effects of TRH. Since this system is important in the planning and execution of motor acts it is suggested that modification of information flow through this system could have effects on the production of motor activity.

Potentiation of motoneurone excitability by combined administration of 5-HT agonist and TRH analogue

Motoneurone field potentials have been recorded from the lumbar region of the spinal cord, to antidromic stimulation of a ventral root, in rats anaesthetised with urethane. Injection of the thyrotropin releasing hormone (TRH) analogue RX77368 (1mg/kg) plus the 5-hydroxytryptamine (5-HT) receptor agonist 5-methoxy-N, N-dimethyl-tryptamine (5MeODMT 0.4mg/kg) resulted in a potentiation of the increase in amplitude and duration of response, compared to when the drugs were given singly. These results are discussed in the context of possible interactions between 5-HT and TRH systems.

Effects of a thyrotropin releasing hormone analogue on locomotor and other motor activity in the rat

In the present experiments, locomotion has been studied in rats after injection of TRH analogue RX77368 (10 mg/kg i.p.). The measure used was the frequency of the cyclic shifts of weight from side to side (WTF) which accompany the progress of locomotion. It therefore provides an indirect measure of stepping frequency. After injection of RX77368 there was a shift in WTFs towards higher frequencies, i.e. when the rat walked it was taking more steps per second. These results suggest that RX77368 stimulates basic motor patterns associated with locomotion. The results obtained in these experiments are compared with those obtained using different quantification methods for locomotion and there is speculation concerning the possible modes of action of RX77368 including interactions with other neurotransmitter systems.

Motoneurone excitability during antidromically evoked inhibition after administration of a thyrotrophin releasing hormone (TRH) analogue

Acute experiments have been performed in urethane anaesthetised rats to determine the effect of a TRH analogue (RX77368) on the excitability of motoneurone pools in the lumbar region of the spinal cord to paired antidromic stimuli ( interval 10ms) delivered to the ventral root, by measuring the field potentials produced. Following the response (CR) to the first stimulus (conditioning stimulus), the response (TR) to the second stimulus (test stimulus) is reduced in size. In control experiments, the greater the amplitude of CR, the smaller TR becomes. After RX77368 injection, CR progressively increases over the initial post injection period. It would be expected therefore that during this time there would be a progressive decline in TR relative to CR. It has been shown however, that over this period there is no decline of TR relative to CR. There is speculation on a possible role of putative neuromodulators such as TRH in the maintenance of control parameters during motoneurone recruitment and/or increases in discharge frequency.

Locomotion in the rat after 5-hydroxy-L-tryptophan

Previous work has shown that administration of 5HTP in amounts substantially less than those required to elicit 'serotonin syndrome' to rats pretreated witha peripheral decarboxylase inhibitor, produced increases in locomotion, measured by whole body movements. The purpose of the present work was to study the cyclic shifts of weights from side to side which underly the progress of locomotion and to see whether these change after 5HTP. From the reciprocal of the interval for one complete cycle was calculated the weight transferral frequency (WTF). The modal WTF for control and treated rats were in the ranges 1-1.49 and 2-2.49 Hz respectively, while the medians were in the ranges 2-2.49 and 2.5-2.99 Hz respectively. Testing of goodness of fit between the frequency distribution curves in control and treated animals showed significant differences. It is concluded that after 5HTP treatment, basic locomotor patterns are shifted towards higher frequencies.

Motoneurone excitability after administration of a thyrotrophin releasing hormone analogue

Recording have been made of motoneurone field potentials at vertebral level L1 to stimulation of the ventral root, in rats anaesthetized with urethane. Injection of thyrotrophin releasing hormone (TRH) analogue RX77368 (2 mg kg-1) produced an increase in the amplitude of the field potential within 1 min of injection, reaching peak amplitude of 51-69% above control values 6-12 min after injection; the duration of the elevation was 30-65 min. Arguments are presented which show that this effect is compatible with an RX77368-induced depolarization of the motoneurone, allowing the antidromic volley to invade more cell bodies.

Effect of baclofen on sensory transmission through the ventrobasal thalamic nucleus of the rat

Previous work suggests that after administration of baclofen there is a reduction in excitatory cuneothalamic transmission, while preliminary experiments in this laboratory had shown that baclofen produces lowered level of cortical activity. Since much of the corticothalamic output is inhibitory, the consequences of possible reductions in excitatory corticopetal and inhibitory corticofugal flow into the ventrobasal thalamus required investigation. Baclofen produced increased latency and decreased probability of discharge of the short-latency discharge of single ventrobasal thalamic units to peripheral stimulation. It is suggested that these observations are compatible with a decreased excitatory cuneothalamic volley. Accompanying the decline in the early discharge was a development of later rhythmic discharges at 80-100 msec intervals, lasting up to 900 msec. This type of response is also seen in decorticate rats and has the same temporal pattern as the inhibition of the response to the second of a pair of peripheral stimuli shown in rats with an intact cerebral cortex. Since baclofen produced a decline in cortical activity (N1 wave of evoked potential, synchronisation of the ECoG), is suggested that this emergence of rhythmic activity is produced by a reduction of corticothalamic inhibition.

The effects of trimethadione on pentetrazol-induced discharges of primary muscle spindle afferents from the hind limb of the rat

1 Recordings have been made from primary muscle spindle afferents in split dorsal root filaments of rats anaesthetized with urethane. 2 Injection of pentetrazol (PTZ, 10 mg/kg) produced elevated discharge in the afferents with intact efferents without any charge in tension or electrical activity of the muscle of origin. 3 This elevated discharge was found to contain elements of both gamma d and gamma s activation. 4 Trimethadione (100 mg/kg), itself produced a transient increase in discharge and effectively suppressed PTZ-induced discharges of the afferents for at least 2 h. 5 These results are discussed in the context of established effects on sensory and motor systems.

Effect of metrazol on the discharge characteristics of muscle spindle afferents from the hind limb of the rat

The nature of altered fusimotor discharge induced by subconvulsive doses of Metrazol has been investigated in deeply anaesthetized rats. Large amplitude stretching (ramp and hold or sinusoidal) of the appropriate muscle during the course of drug action shows Metrazol to have a predominant gamma d effect on primaries, and an exclusive gamma s effect on secondaries in both plantar and dorsiflexors of ankle and toes. Small amplitude stretches revealed gamma s activity which large amplitude stretching failed to show. Experiments with convulsive doses of Metrazol show that this elevated spindle discharge precedes development of electromyographic activity. It is suggested that fusimotor activity must be considered when analysing the mechanisms of Metrazol-induced seizures in non-paralysed animals.

Effect of catechol on the discharge of muscle spindle afferents from the hind limb of the rat

Previous work had shown that some of the effects of catechol could be via the fusimotor system. In order to determine the extent of fusimotor involvement, recordings have been made from muscle spindle afferents in split dorsal root filaments of anaesthetised rats. Catechol failed to excite de-efferented muscle spindles therefore eliminating many possible non-fusimotor effects. Over 80% of spindle afferents with intact efferents showed increased discharge frequency 1 min after injection, this increase often following a biphasic pattern with a pronounced pre-myoclonic burst and decline followed by a more sustained period of activity during the myoclonic phase. Analysis of spontaneous twitches or twitches evoked by ipsilateral auditory stimulation showed in addition a phasic increase in discharge suggesting alpha-gamma co-activation. Both primary and secondary afferents from many muscle groups around ankle and toes had their discharge frequencies elevated. Elevation of discharge frequencies of secondaries implies increased gamma-s activity confirmed by a decrease in dynamic index. Both gamma-d and gamma-s involvement in catechol action on primaries is suggested by dynamic index measurements. Perhaps a more continuous form of testing such as sinusoidal stretches would reveal any rapid switching between activities in the two systems.

A pharmacological study of the spontaneous convulsive activity induced by 1,2-dihydroxybenzene (catechol) in the anaesthetized mouse

1. The convulsive activity induced by catechol has been examined in anaesthetized mice either by determining the CD50 for the convulsions in drug-treated and control animals, or by studying the effects of various drugs on the total whole body activity. 2. The results indicate that catecholamines play no part in the mechanism of action of catechol. Drugs which alter cerebral catecholamine levels had no effect on the convulsions, nor did the alpha- and beta-adrenoceptor blocking drugs. 3. 5-Hydroxytryptamine (5-HT) could possibly be important, though results with drugs which either change brain 5-HT levels, or block 5-HT receptors were inconsistent. 4. gamma-Aminobutyric acid also appears not to be involved in the mechanism of action of catechol. 5. The results strongly suggest that catechol primarily activates a central cholinergic system, in that muscarinic and nicotinic receptor blocking drugs inhibit, and anticholinesterases potentiate the convulsions.

An analysis of the representation of the forelimb in the ventrobasal thalamic complex of the albino rat

1. Glass micro-electrodes have been used to record from a total of 998 units situated in the ventrobasal thalamic complex in the deeply anaesthetized albino rat. 2. Of these units 889 responded to electrical stimulation of the contralateral forelimb and fifty-one to the contralateral hind limb. The remaining units consisted of those with receptive fields on the trunk, head and those which responded to stimulation of more than one limb. Only the latter group of units showed any spontaneous activity in the absence of intentional stimulation. 2. Of the units which responded to electrical stimulation of the contralateral forelimb the receptive fields, modality and latencies of response were accurately determined for 505 units. The mean latency to supramaximal stimulation at the wrist was 4.49 (+/- 0.04 S.E. of mean) msec; and to mechanical stimulation (for 146 of these units) at the centre of the receptive field 6.58 (+/- 0.12) msec. The modalities were distributed as follows: light pressure, 391; heavy pressure, 47; hair movement, 40; claw sensitive, 15 and joint movement, 12 units. 4. The forelimb representation within the ventrobasal thalamic complex was somatotopically organized, the over-all appearance being that of an incompletely closed fist, palmar surface uppermost, thumb media, with the wrist caudal and the digital tips rostral and dorsal. 5. The central projection was distorted, some parts showing expanded representation, notably the tips of digits II and III and the medial wrist pad. Other parts were contracted, e.g. the wrist, forearm and shoulder. 6. Units with receptive fields consisting of the whole of a walking pad had shorter mean latencies, to tactile stimulation, than those whose field was a single spot on a pad. 7. Units were found to show an abolute unresponsive time to the second of a pair of identical supramaximal electrical stimuli of up to 50 msec, and a relative unresponsive time which could last up to 500 msec. The absolute unresponsive and relative unresponsive times to the second of a pair of tactile stimuli was shorter being 30 and 150 msec respectively. 8. The effect of decortication was to increase the excitability of thalamic units to peripheral stimulation both in the initial and later discharges.