Connexin36 identified at morphologically mixed chemical/electrical synapses on trigeminal motoneurons and at primary afferent terminals on spinal cord neurons in adult mouse and rat.

Morphologically mixed chemical/electrical synapses at axon terminals, with the electrical component formed by gap junctions, is common in the CNS of lower vertebrates. In mammalian CNS, evidence for morphologically mixed synapses has been obtained in only a few locations. Here, we used immunofluorescence approaches to examine the localization of the neuronally expressed gap junction forming protein connexin36 (Cx36) in relation to the axon terminal marker vesicular glutamate transporter-1 (vglut1) in the spinal cord and the trigeminal motor nucleus (Mo5) of rat and mouse. In adult rodents, immunolabeling for Cx36 appeared exclusively as Cx36-puncta, and was widely distributed at all rostro-caudal levels in most spinal cord laminae and in the Mo5. A high proportion of Cx36-puncta was co-localized with vglut1, forming morphologically mixed synapses on motoneurons, in intermediate spinal cord lamina, and in regions of medial lamina VII, where vglut1-containing terminals associated with Cx36 converged on neurons adjacent to the central canal. Unilateral transection of lumbar dorsal roots reduced immunolabeling of both vglut1 and Cx36 in intermediate laminae and lamina IX. Further, vglut1-terminals displaying Cx36-puncta were contacted by terminals labeled for glutamic acid decarboxylase65, which is known to be contained in presynaptic terminals on large-diameter primary afferents. Developmentally, mixed synapses begin to emerge in the spinal cord only after the second to third postnatal week and thereafter increase to adult levels. Our findings demonstrate that axon terminals of primary afferent origin form morphologically mixed synapses containing Cx36 in broadly distributed areas of adult rodent spinal cord and Mo5.

Phenytoin toxicity: an easily missed cause of cerebellar syndrome.

We present a series of cases of phenytoin toxicity where the diagnosis was initially missed. These patients all suffered unnecessary morbidity or investigations. The side-effects and unusual pharmacokinetics of phenytoin are discussed, as well as the array of potential drug interactions. We remind clinicians that phenytoin toxicity can easily mimic a cerebellar lesion or alcohol intoxication, and suggest that in accordance with National Institute for Clinical Excellence (NICE) guidelines phenytoin should no longer be used as a first-line treatment for epilepsy.

The "OBS" chart: an evidence based approach to re-design of the patient observation chart in a district general hospital setting.

OBJECTIVE: The primary role of the patient bedside observation chart is to make clinicians aware of the deteriorating patient. Despite this, its performance has not been scrutinised. Many versions exist with different styles of data entry but the optimal format remains elusive. This paper hypothesised that chart design measurably influences function and that redesign and standardisation would improve the detection of physiological decline by clinical staff. DESIGN: Objective evaluation of existing charts (n = 5), evidence based redesign, and re-evaluation of new chart. SETTING: 250 bed district general hospital. RESULTS: Design of existing observation charts had a significant effect on the ability of clinical staff to detect patient deterioration, with detection rates of parameters indicating physiological decline ranging from 0% to 100%. Graphical plots portrayed information better than written values for all parameters being measured except tachypnoea. No single existing chart was best for all variables. A new chart was designed, implemented with training in its use, and re-evaluated. The new chart also incorporated an early warning scoring system. There were significant improvements in the average detection rates of parameters poorly identified on existing charts: detection rates of tachypnoea and hypoxia increased by 41% (p<0.05) and 45% (p<0.05) respectively. There were also significant improvements in detection rates of tachycardia and fever by 29% (p<0.05) and 16% (p<0.05) respectively. CONCLUSION: Evidence based redesign of the patient bedside observation chart coupled with specific training in its use significantly improves the detection of patient physiological deterioration.

Risk communication related to animal products derived from biotechnology.

Previous chapters of this review have dealt with the key considerations related to the application of biotechnology in veterinary science and animal production. This article explores the theory and practice of risk communication and sets out the basic principles for good risk communication when dealing with new technologies, uncertainty, and cautious and sceptical consumers. After failure to communicate with consumers and stakeholders about the risk to human health from bovine spongiform encephalopathy (BSE) in the 1990s, Government Agencies in the United Kingdom have made significant improvements in risk communication. The official inquiry that followed the BSE crisis concluded that a policy of openness was the correct approach, and this article emphasises the importance of consultation, consistency and transparency. There are, however, many different factors that affect public perception of risk (religious, political, social, cultural, etc.) and developing effective risk communication strategies must take all of these complex issues into consideration.

Control of locomotor cycle durations.

In intact animals and humans, increases in locomotor speed are usually associated with decreases in step cycle duration. Most data indicate that the locomotor central pattern generator (CPG) shortens cycle duration mainly by shortening the durations of extensor rather than flexor phases of the step cycle. Here we report that in fictive locomotion elicited by electrical stimulation of the midbrain locomotor region (MLR) in the cat, spontaneous variations in cycle duration were due more to changes in flexor rather than extensor phase durations in 22 of 31 experiments. The locomotor CPG is therefore not inherently extensor- or flexor-biased. We coined the term "dominant" to designate the phase (flexion or extension) showing the larger variation. In a simple half-center oscillator model, experimental phase duration plots were fitted well by adjusting two parameters that corresponded to background drive ("bias") and sensitivity ("gain") of the oscillator's timing elements. By analogy we argue that variations in background drive to the neural timing elements of the CPG could produce larger variations in phase duration in the half-center receiving the lower background drive, i.e., background drive may determine which half-center is dominant. The fact that data from normal cats were also fitted well by the model indicates that sensory input and central drive combine to determine locomotor phase durations. We conclude that there is a considerable flexibility in the control of phase durations in MLR-induced fictive locomotion. We posit that this may be explained by changes in background excitation of neural timing elements in the locomotor CPG.

Candidate interneurones mediating group I disynaptic EPSPs in extensor motoneurones during fictive locomotion in the cat.

In the present study we sought to find interneurones responsible for the group I-evoked disynaptic excitation of hindlimb extensor motoneurones that occurs during fictive locomotion. Locomotion was produced by stimulation of the mesencephalic locomotor region (MLR) in decerebrate paralysed cats in which activation of ankle extensor group I afferents evoked a disynaptic excitation of motoneurones during the extension phase of fictive locomotion. Extracellular recordings were used to locate interneurones fulfilling all, or five of the six following criteria: (i) weak or no response to stimulation of extensor group I afferents in the absence of locomotion; (ii) strong group I activation during locomotion; (iii) group I activation at monosynaptic latencies; (iv) strong group I activation during only the extensor phase of locomotion; and (v) antidromic activation from the extensor motor nuclei; but (vi) no antidromic activation from rostral spinal segments. Candidate excitatory interneurones were located in mid to caudal parts of the L7 segments in areas where monosynaptic field potentials were evoked by group I afferents, within 2 mm of the stimulation site in the ventral horn from which they were antidromically activated. All were activated during extension by stimulation of group I afferents in extensor nerves. In the absence of peripheral nerve stimulation, six of the seven candidate excitatory interneurones were rhythmically active with maximal activation during the extension phase of fictive locomotion. Rhythmic activity during extension was also seen in five additional interneurones located near candidate interneurones but not activated by group I strength stimulation of the tested nerves. We suggest that the lumbosacral interneurones located in the intermediate laminae that can be activated by extensor group I afferents during the extension phase are a previously unknown population of interneurones, and may mediate group I-evoked disynaptic excitation of extensor motoneurones. Their rhythmic activity suggests that they also provide central excitatory drive to extensor motoneurones during locomotion.

Risk communication of the transmissible spongiform encephalopathies.

Previous chapters of this review have dealt with the scientific basis of assessing the risks from transmissible spongiform encephalopathies and how those risks should be managed. The author explores the theory and practice of risk communication and sets out the basic principles for good risk communication when dealing with uncertainty.

Spinal circuitry of sensorimotor control of locomotion.

During locomotion many segmental hindlimb reflex pathways serve not only to regulate the excitability of local groups of motoneurones, but also to control the basic operation of the central pattern-generating circuitry responsible for locomotion. This is accomplished through a reorganization of reflexes that includes the suppression of reflex pathways operating at rest and the recruitment during locomotion of previously unrecognized types of spinal interneurones. In addition presynaptic inhibition of transmission from segmental afferents serves to regulate the gain of segmental reflexes and may contribute to the selection of particular reflex pathways during locomotion. The fictive locomotion preparation in adult decerebrate cats has proved to be an important tool in understanding reflex pathway reorganization. Further identification of the spinal interneurones involved in locomotor-dependent reflexes will contribute to our understanding not only of reflex pathway organization but also of the organization of the mammalian central pattern generator.

State-dependent hyperpolarization of voltage threshold enhances motoneurone excitability during fictive locomotion in the cat.

Experiments were conducted on decerebrate adult cats to examine the effect of brainstem-evoked fictive locomotion on the threshold voltage (Vth) at which action potentials were initiated in hindlimb motoneurones. Measurements of the voltage threshold of the first spike evoked by intracellular injection of depolarizing ramp currents or square pulses were compared during control and fictive locomotor conditions. The sample of motoneurones included flexor and extensor motoneurones, and motoneurones with low and high rheobase currents. In all 38 motoneurones examined, action potentials were initiated at more hyperpolarized membrane potentials during fictive locomotion than in control conditions (mean hyperpolarization -8.0 +/- 5.5 mV; range -1.8 to -26.6 mV). Hyperpolarization of Vth occurred immediately at the onset of fictive locomotion and recovered in seconds (typically < 60 s) following the termination of locomotor activity. The Vth of spikes occurring spontaneously without intracellular current injection was also reduced during locomotion. Superimposition of rhythmic depolarizing current pulses on current ramps in the absence of locomotion did not lower Vth to the extent seen during fictive locomotion. We suggest that Vth hyperpolarization results from an as yet undetermined neuromodulatory process operating during locomotion and is not simply the result of the oscillations in membrane potential occurring during locomotion.The hyperpolarization of Vth for action potential initiation during locomotion is a state-dependent increase in motoneurone excitability. This Vth hyperpolarization may be a fundamental process in the generation of motoneurone activity during locomotion and perhaps other motor tasks.

Absent right precordial R waves are associated with reduced left ventricular function and poor prognosis in patients with aortic stenosis.

Right precordial Q waves can be present in patients with aortic stenosis as well as in those with anterior myocardial infarction. In order to evaluate the relationship of right precordial Q waves to left ventricular function and prognosis in patients with aortic stenosis, we studied 49 such patients with no history of myocardial infarction, by means of ECG, clinical history and echocardiography. 15 (31%) patients had Q waves in both V1 and V2 and 34 (69%) did not. There were no differences in age (77+/-9.0 years vs. 78+/-9.7), follow-up time (15+/-9.0 months vs. 18+/-10), gender (female:male 8:7 vs. 15:19), aortic valve gradient on Doppler (70.0+/-20 mmHg vs. 71+/-20) and left ventricular mass (360+/-118 g vs. 320+/-80) between the two groups (all P=NS). Left ventricular shortening fraction (22+/-9.0% vs. 28+/-8.5, P<0.05), ejection fraction (51+/-15% vs. 62+/-12, P<0.01) and circumferential fibre shortening (0.8+/-0.3 circ/s vs. 1.0+/-0.3, P<0.0s) were all significantly reduced in patients with right precordial Q waves compared to those without. During a mean follow-up of 1.5 years, 9 out of 15 (60%) patients with right precordial Q waves died compared with only 5 out of 34 (15%) patients with a normal QRS pattern died (P<0.01). In summary, a right precordial QS ECG pattern is present in nearly 1/3 patients with aortic stenosis and is associated with impaired left ventricular systolic function and adverse prognosis.

Depression of group Ia monosynaptic EPSPs in cat hindlimb motoneurones during fictive locomotion.

The effects of fictive locomotion on monosynaptic EPSPs recorded in motoneurones and extracellular field potentials recorded in the ventral horn were examined during brainstem-evoked fictive locomotion in decerebrate cats. Composite homonymous and heteronymous EPSPs and field potentials were evoked by group I intensity (<= 2T) stimulation of ipsilateral hindlimb muscle nerves. Ninety-one of the 98 monosynaptic EPSPs were reduced in amplitude during locomotion (mean depression of the 91 was to 66 % of control values); seven increased in amplitude (to a mean of 121 % of control). Twenty-one of the 22 field potentials were depressed during locomotion (mean depression to 72 % of control). All but 14 Ia EPSPs were smaller during both the flexion and extension phases of locomotion than during control. In 35 % of the cases there was < 5 % difference between the amplitudes of the EPSPs evoked during the flexion and extension phases. In 27 % of the cases EPSPs evoked during flexion were larger than those evoked during extension. The remaining 38 % of EPSPs were larger during extension. There was no relation between either the magnitude of EPSP depression or the locomotor phase in which maximum EPSP depression occurred and whether an EPSP was recorded in a flexor or extensor motoneurone. The mean recovery time of both EPSP and field potential amplitudes following the end of a bout of locomotion was approximately 2 min (range, < 10 to > 300 s). Motoneurone membrane resistance decreased during fictive locomotion (to a mean of 61 % of control, n = 22). Because these decreases were only weakly correlated to EPSP depression (r 2 = 0.31) they are unlikely to fully account for this depression. The depression of monosynaptic EPSPs and group I field potentials during locomotion is consistent with the hypothesis that during fictive locomotion there is a tonic presynaptic regulation of synaptic transmission from group Ia afferents to motoneurones and interneurones. Such a reduction in neurotransmitter release would decrease group Ia monosynaptic reflex excitation during locomotion. This reduction may contribute to the tonic depression of stretch reflexes occurring in the decerebrate cat during locomotion.

Group I disynaptic excitation of cat hindlimb flexor and bifunctional motoneurones during fictive locomotion.

The incidence of short latency excitation of motoneurones innervating flexor and bifunctional muscles evoked by group I intensity (<= 2 x threshold) electrical stimulation of hindlimb muscle nerves was investigated during fictive locomotion in decerebrate cats. Intracellular recordings were made from hindlimb motoneurones in which action potentials were blocked by intracellular diffusion of a lidocaine (lignocaine) derivative (QX-314) and fictive locomotion was evoked by electrical stimulation of the midbrain. Few motoneurones (16%) received group I-evoked oligosynaptic excitation in the absence of fictive locomotion. During fictive locomotion 39/44 (89%) motoneurones innervating ankle, knee or hip flexor muscles and 18/28 (64%) motoneurones innervating bifunctional muscles received group I-evoked oligosynaptic EPSPs. In flexor motoneurones, locomotor-dependent excitation was present in both step cycle phases but largest during flexion. In bifunctional motoneurones, EPSPs were often largest at the transition between flexion and extension phases. Activation of homonymous afferents most consistently evoked the largest locomotor-dependent excitation (amplitude up to 4.6 mV), but in some cases stimulation of heteronymous flexor or bifunctional muscle nerves evoked large EPSPs. EPSP amplitude became maximal as stimulation intensity was increased to about twice threshold. This suggests that tendon organ afferents can evoke group I EPSPs during locomotion. The EPSPs resulting from brief, small stretches of extensor digitorum longus tendons indicate that group Ia muscle spindle afferents can also evoke the group I excitation of flexors. Stimulation of extensor group I afferents did not result in excitation of flexor motoneurones. The mean latency of locomotor-dependent group I excitation in flexor and bifunctional motoneurones was 1.64 +/- 0.16 ms, indicating a path consisting of a single interneurone interposed between group I afferents and motoneurones innervating flexor and bifunctional muscles. This disynaptic excitation is analogous to that recorded in extensor motoneurones and evoked from extensor group I afferents during locomotion. Differences in the phase dependence and sources of group I excitation to flexor and extensor motoneurones during locomotion suggest the existence of separate groups of excitatory interneurones exciting flexor and extensor motoneurones. The wide distribution of group I disynaptic excitation in motoneurones innervating extensor, flexor and bifunctional muscles acting on hip, knee and ankle joints suggests that these pathways can play an important role in the reinforcement of ongoing locomotor activity throughout the limb.

Depression of muscle and cutaneous afferent-evoked monosynaptic field potentials during fictive locomotion in the cat.

1. Monosynaptic extracellular field potentials evoked by electrical stimulation of ipsilateral hindlimb nerves carrying muscle group I, II and cutaneous afferents were examined during fictive locomotion. Fifty-eight field potentials were recorded in the dorsal and intermediate laminae throughout the mid-lumbar to first sacral segments and fictive locomotion was evoked by mesencephalic locomotor region (MLR) stimulation in paralysed decerebrate cats. 2. The majority (96 %) of group I, II and cutaneous-evoked field potentials were decreased during fictive locomotion. Group I, cutaneous and dorsal group II potentials were reduced on average to about 80 % of control values. Group II field potentials recorded in the intermediate laminae were reduced to a mean of 49 % of control values. Cyclic variations in field potential amplitude between the flexion and extension phases were observed in 24 of 45 cases analysed. Of those 24 field potentials, the two group I and four cutaneous field potentials were smaller during the flexion phase. All eleven group II and the remaining seven cutaneous fields were smaller during extension. In all but two cases, these cyclic variations were smaller than the tonic depression upon which they were superimposed. 3. In 7/9 group II field potentials examined, reductions (on average to 85 % of control) began with the onset of MLR stimulation that produced tonic activity in the motor nerves before the onset of rhythmic alternating, locomotor discharges. In six of the seven cases the field potential depression increased with the establishment of fictive locomotion. This observation and the cyclic modulation of field potentials during fictive locomotion suggests that the depression was strongly linked to the operation of the spinal locomotor circuitry. 4. Depression of the monosynaptic components of the field potentials suggests a reduction in synaptic transmission from primary afferents to first-order spinal interneurones during fictive locomotion. Accordingly, the larger depression of intermediate group II field potentials may indicate a preferential reduction in transmission from group II afferents to interneurones located in intermediate spinal laminae. 5. Flexion reflexes evoked by group II and cutaneous afferents were also depressed during MLR-evoked fictive locomotion. The possibility that this depression results from a reduction in transmission from primary afferents, and in particular from group II afferents, ending on interneurones in the intermediate laminae is discussed.

Tapping into spinal circuits to restore motor function.

Motivated by the challenge of improving neuroprosthetic devices, the authors review current knowledge relating to harnessing the potential of spinal neural circuits, such as reflexes and pattern generators. If such spinal interneuronal circuits could be activated, they could provide the coordinated control of many muscles that is so complex to implement with a device that aims to address each participating muscle individually. The authors' goal is to identify candidate spinal circuits and areas of research that might open opportunities to effect control of human limbs through electrical activation of such circuits. David McCrea's discussion of the ways in which hindlimb reflexes in the cat modify motor activity may help in developing optimal strategies for functional neuromuscular stimulation (FNS), by using knowledge of how reflex actions can adapt to different conditions. Michael O'Donovan's discussion of the development of rhythmogenic networks in the chick embryo may provide clues to methods of generating rhythmic activity in the adult spinal cord. Serge Rossignol examines the spinal pattern generator for locomotion in cats, its trigger mechanisms, modulation and adaptation, and suggests how this knowledge can help guide therapeutic approaches in humans. Hugues Barbeau applies the work of Rossignol and others to locomotor training in human subjects who have suffered spinal cord injury (SCI) with incomplete motor function loss (IMFL). Michel Lemay and Warren Grill discuss some of the technical challenges that must be addressed by engineers to implement a neuroprosthesis using electrical stimulation of the spinal cord, particularly the control issues that would have to be resolved.

Neuronal basis of afferent-evoked enhancement of locomotor activity.

Activation of ankle extensor group Ia muscle spindle or Ib tendon organ afferents during locomotion can prolong and enhance hindlimb extensor motoneuron activity. A growing body of evidence suggests that these group I evoked reflexes not only compensate for a changing environment but also help shape extensor activity during normal, unperturbed locomotion. In this paper we review four mechanisms that underlie the group I evoked enhancement of ipsilateral extensor activity during locomotion. The first three are pre-motoneuronal mechanisms that are part of group I reflex pathway reorganization during locomotion. They are (1) a suppression of group I evoked nonreciprocal inhibition, (2) a release from inhibition of excitatory interneurons in disynaptic pathways from group I afferents to extensor motoneurons, and (3) longer latency excitation evoked through extensor portions of the locomotor circuitry. The fourth factor contributing to group I evoked increases in motoneuron activity during locomotion is the increase in motoneuron excitability produced by postsynaptic changes in motoneuron membrane conductances. Most results to be discussed were obtained during locomotion in decerebrate cats in which fictive locomotion was evoked by stimulation of the midbrain following neuromuscular blockade.

Group I extensor afferents evoke disynaptic EPSPs in cat hindlimb extensor motorneurones during fictive locomotion.

1. Intracellular recording from extensor motoneurones in paralysed decerebrate cats was used to examine the distribution of short-latency non-monosynaptic excitation by group I afferents during fictive locomotion produced by stimulation of the mesencephalic locomotor region (MLR). 2. During the extension but not the flexion phase of fictive locomotion, stimulation of ankle extensor nerves at 1.2-2.0 times threshold evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating hip, knee and ankle extensors. Disynaptic EPSPs were also evoked by selective activation of group Ia muscle spindle afferents by muscle stretch. 3. The central latencies of these group I-evoked EPSPs (mean, 1.55 ms) suggest their mediation by a disynaptic pathway with a single interneurone interposed between extensor group I afferents and extensor motoneurones. Disynaptic EPSPs were also evoked during periods of spontaneous locomotion following the cessation of MLR stimulation. 4. Hip extensor motoneurones received disynaptic EPSPs during extension following stimulation of both homonymous and ankle extensor nerves. Stimulation of hip extensor nerves did not evoke disynaptic EPSPs in ankle extensor motoneurones. 5. The appearance of disynaptic EPSPs during extension appears to result from cyclic disinhibition of an unidentified population of excitatory spinal interneurones and not postsynaptic voltage-dependent conductances in motoneurones or phasic presynaptic inhibition of group I afferents during flexion. 6. The reorganization of group I reflexes during fictive locomotion includes the appearance of disynaptic excitation of hip, knee and ankle extensor motoneurones. This excitatory reflex is one of the mechanisms by which group I afferents can enhance extensor activity and increase force production during stance.

Primary Sjögren's syndrome, ulcerative colitis and selective IgA deficiency.

A 24-year-old man with primary Sjögren's syndrome presented with xerophthalmia, xerostomia, and marked parotid swelling. He had a previous history of selective IgA deficiency and ulcerative colitis treated with sulphasalazine. Immunosuppression and withdrawal of sulphasalazine resulted in rapid resolution of the parotitis and disappearance of autoantibodies. A possible role for sulphasalazine in the induction of autoimmunity in this case is discussed.