Cognitive impairment in asymptomatic carotid artery stenosis is associated with abnormal segments in the Circle of Willis

OBJECTIVE

Our group has previously demonstrated that patients with asymptomatic carotid artery stenosis (ACAS) demonstrate cognitive impairment. One proposed mechanism for cognitive impairment in patients with ACAS is cerebral hypoperfusion due to flow-restriction. We tested whether the combination of a high-grade carotid stenosis and inadequate cross-collateralization in the Circle of Willis (CoW) resulted in worsened cognitive impairment.

METHODS

Twenty-four patients with high-grade (≥70% diameter-reducing) ACAS underwent carotid duplex ultrasound, cognitive assessment, and 3D time-of-flight magnetic resonance angiography (MRA). The cognitive battery consisted of nine neuropsychological tests assessing four cognitive domains: learning and recall, attention and working memory, motor and processing speed, and executive function. Raw cognitive scores were converted into standardized T-scores. A structured interpretation of the MRA images was performed with each segment of the CoW categorized as being either normal or abnormal. Abnormal segments of the CoW were defined as segments characterized as narrowed or occluded due to congenital aplasia or hypoplasia, or acquired atherosclerotic stenosis or occlusion. Linear regression was used to estimate the association between the number of abnormal segments in the CoW, and individual cognitive domain scores. Significance was set to p<0.05.

RESULTS

The mean age of the patients was 66.1 + 9.6 (mean + SD) years and 79.2% (n=19) were male. A significant negative association was found between the number of abnormal segments in the CoW and cognitive scores in the learning and recall (β = -6.5, p = 0.01), and attention and working memory (β = -7.0, p = 0.02) domains. There was a trend suggesting a negative association in the motor and processing speed (β = -2.4, p = 0.35) and executive function (β = -4.5, p = 0.06) domains that did not reach significance.

CONCLUSION

In patients with high-grade ACAS, the concomitant presence of increasing occlusive disease in the CoW correlates with worse cognitive function. This association was significant in the learning and recall and attention and working memory domains. While motor and processing speed and executive function also declined numerically with increasing abnormal segments in the CoW, the relationship was not significant. Since flow restriction at a carotid stenosis compounded by inadequate collateral compensation across a diseased CoW worsens cerebral perfusion, our findings support the hypothesis that cerebral hypoperfusion underlies the observed cognitive impairment in patients with ACAS.

A critical review of cognitive behavioural therapy for hoarding disorder: How can we improve outcomes?

Psychological treatment for hoarding problems has historically been associated with poor outcomes. When treated as a subgroup of obsessive-compulsive disorder, individuals with hoarding beliefs were less likely to respond to treatment than individuals exhibiting other obsessive-compulsive beliefs and behaviours. When treated as its own disorder using cognitive behavioural therapy, individuals report approximately 25% improvement in symptoms on average. However, less than a third of people experience clinically meaningful change. Further, changes in functioning and quality of life are not routinely assessed. In this paper, we review the current conceptualization and treatment of hoarding problems to shed light on how treatment for hoarding disorder may be improved. Utilizing a harm reduction approach before administering treatment may be important to ensure the safety of individuals. Research should test whether treatment outcomes improve by including strategies that enhance a client's interpersonal functioning and ability to regulate emotions (i.e., based on dialectal behaviour therapy and mentalization-based treatments), especially while discarding and organizing belongings. We should also use modern learning theory to improve the delivery of exposure activities.

Determinants of object choice and object attachment: Compensatory consumption in compulsive buying-shopping disorder and hoarding disorder

BACKGROUND AND AIMS

Individuals who meet criteria for compulsive buying-shopping disorder (i.e., acquiring problems only) or hoarding disorder (i.e., acquiring and discarding problems) may acquire possessions to compensate for unmet belonging needs, but may do so in different ways. Those with compulsive buying-shopping disorder may acquire objects that they believe will relieve the distress associated with unmet belonging needs (e.g., objects that distract or comfort), whereas those with hoarding disorder may acquire objects that they believe achieve belonging needs (e.g., objects that have interpersonal connotations). Accordingly, this study examined whether a belongingness threat would drive individuals who excessively acquire possessions to choose a human-like object (person-shaped tea holder) or a comfort item (box of chamomile tea).

METHODS

One hundred seventy-five participants (57 self-reported excessive acquiring only; 118 self-reported excessive acquiring and difficulty discarding) recalled a time when they either felt supported or unsupported by a significant other before choosing an object to take home with them. Participants rated how anthropomorphic and comforting the objects were as well as how attached they became to their chosen object.

RESULTS

Unsupported individuals were more likely to acquire the comfort item than supported individuals; however, individuals with both acquiring and discarding problems were more likely to acquire the human-like item than those with an acquiring problem only. Comfort and anthropomorphism ratings predicted object choice and attachment.

DISCUSSIONS AND CONCLUSION

The current findings extend the Compensatory Consumer Behavior Model to include what factors determine strategy choice and object attachment.

Corrigendum to: Environmental enrichment strategies for nursery piglets and efficacy for maintaining interest

Context Animals in situations of stress and constant fear exhibit unwanted behaviours for production. Pigs that are afraid of humans tend to associate any management as stressful. The use of environment enrichment for pigs may help to alleviate anxiety and fear, and hence reduce unwanted behaviours during handling. However, provision of appropriate enrichment presents challenges such as the rapid loss of interest in objects by animals. Aims The present study evaluated the effects of different environmental enrichment strategies on the behaviour of pigs at the nursery stage, maintenance of animal interest in the enrichment objects, and their reflexes when faced with emotionally negative situations. Methods Piglets (n = 425) were assigned in a completely randomised design with five treatments and five replicates per treatment (17 animal per replicate). The treatments employed were: control, no enriching objects in the environment; WB, wooden box with popcorn and wood shavings; PT, objects made of plastic tubing; WB and PT concurrently; and WB or PT on alternate days. Behavioural observations were made over 10 days for 8 h each day, divided into four periods of 2 h. Piglets from enriched (n = 10) and non-enriched (n = 10) environments were subjected to three fear tests (human approach, novel object and novel arena). Key results No significant (P &gt; 0.05) effect was found for the type of enrichment provided or strategy adopted (concurrent vs alternating) on the time piglets interacted with the enrichment objects. Animals kept in an environment with no stimulus had higher frequency (P P P Conclusions The use of enrichment objects in the rearing environment of piglets at the nursery stage reduced undesirable behaviours, suggesting reduced fear and anxiety, and may therefore improve their psychological wellbeing. Implications Use of enrichment objects during rearing may have implications for alleviation of chronic stress, which leads to constant release of cortisol, an immune suppressor hormone that reduces the health status of the batch and hence production indices.

Environmental enrichment strategies for nursery piglets and efficacy for maintaining interest

Context Animals in situations of stress and constant fear exhibit unwanted behaviours for production. Pigs that are afraid of humans tend to associate any management as stressful. The use of environment enrichment for pigs may help to alleviate anxiety and fear, and hence reduce unwanted behaviours during handling. However, provision of appropriate enrichment presents challenges such as the rapid loss of interest in objects by animals. Aims The present study evaluated the effects of different environmental enrichment strategies on the behaviour of pigs at the nursery stage, maintenance of animal interest in the enrichment objects, and their reflexes when faced with emotionally negative situations. Methods Piglets (n = 425) were assigned in a completely randomised design with five treatments and five replicates per treatment (17 animal per replicate). The treatments employed were: control, no enriching objects in the environment; WB, wooden box with popcorn and wood shavings; PT, objects made of plastic tubing; WB and PT concurrently; and WB or PT on alternate days. Behavioural observations were made over 10 days for 8 h each day, divided into four periods of 2 h. Piglets from enriched (n = 10) and non-enriched (n = 10) environments were subjected to three fear tests (human approach, novel object and novel arena). Key results No significant (P &gt; 0.05) effect was found for the type of enrichment provided or strategy adopted (concurrent vs alternating) on the time piglets interacted with the enrichment objects. Animals kept in an environment with no stimulus had higher frequency (P &lt; 0.05) of undesirable behaviours than those with enrichment, regardless of enrichment type or strategy adopted. Piglets reared without enrichment, when isolated in a new environment, had higher frequency of behaviours such as defecating, urinating and attempting escape, as well as more and longer vocalisation events (P &lt; 0.05). Piglets reared in an enriched environment had higher frequency and duration of interaction with a new object, as well as shorter latency time for the first contact with the object (P &lt; 0.05). Conclusions The use of enrichment objects in the rearing environment of piglets at the nursery stage reduced undesirable behaviours, suggesting reduced fear and anxiety, and may therefore improve their psychological wellbeing. Implications Use of enrichment objects during rearing may have implications for alleviation of chronic stress, which leads to constant release of cortisol, an immune suppressor hormone that reduces the health status of the batch and hence production indices.

Why are caffeinated alcoholic beverages especially risky?

PURPOSE

Evidence suggests that people drink more alcohol and experience more adverse alcohol-related consequences (ARCs) on occasions when they also consume caffeine. The current study examined whether this increase in risk is a result of caffeine attenuating the subjective effects of alcohol intoxication (i.e., the masking hypothesis).

METHODS

Undergraduate students (n = 148) reported their drinking patterns using a modified Timeline Followback approach. For each recalled drinking occasion, alcohol consumption, caffeine consumption, perceived blood alcohol concentration, and ARCs were assessed. Generalized linear mixed models were used to examine the influence that alcohol and caffeine consumption had on perceived intoxication and the experience of ARCs.

RESULTS

At the occasion level, greater caffeine consumption was associated with increased consumption of alcohol and increased ARCs. There was also a significant curvilinear relationship between the amount of alcohol consumed and perceived intoxication, such that the more alcohol was consumed on each occasion the less each additional drink increased perceived intoxication. Increased caffeine consumption weakened the association between alcohol consumption and perceived intoxication and it also weakened the association between alcohol consumption and ARCs. Specifically, the weakest relationship between ARCs and alcohol consumption existed at the highest level of caffeine consumption (240+ mg). Caffeine increased subjective intoxication.

CONCLUSIONS

These findings do not support the masking hypothesis. Caffeine was strongly associated with ARCs when consumed at high doses and this effect does not appear to be the result of drinking more alcohol or underestimating one's blood alcohol content. Efforts to reduce caffeinated alcohol beverage use are greatly needed.

Scared and surrounded by clutter: The influence of emotional reactivity

BACKGROUND

Home visits can improve treatment outcomes for hoarding disorder, but factors influencing the success of home visits remain unknown. As home visits expose individuals to clutter and fear, the present study examined the effect that fear and emotional reactivity have on the relationship between clutter and discarding behaviour.

METHODS

Participants with at least subclinical discarding problems (n = 143) were asked to save or discard personal possessions of varying value following an emotional induction that took place in either a tidy or cluttered context. Participants also completed questionnaires assessing hoarding severity, emotional state, and emotional reactivity, as defined by one's sensitivity, persistence, and intensity of reactions to emotional stimuli.

RESULTS

As expected, participants discarded more items in the presence of clutter and when feeling fearful. However, emotional reactivity moderated the relations between environmental context, acute emotional state, and discarding. Low sensitivity, low persistence, and high emotional intensity negatively influenced discarding in the cluttered context. When feeling fearful, low dispositional emotional intensity negatively influenced discarding in the tidy context.

LIMITATIONS

Individuals in the tidy environment reported higher levels of fear and anxiety than individuals in the cluttered environment after the fear induction. These differences could have contributed to the difference noted between the two contexts when examining the effect of emotional intensity tendencies.

CONCLUSIONS

Providing treatment in an environment more representative of the cluttered home can improve discarding or at the very least give therapists a more accurate picture of what clients do in the context that matters most.

Anxious attachment and excessive acquisition: The mediating roles of anthropomorphism and distress intolerance

Background and aims Most individuals with hoarding disorder (HD) are prone to excessively acquiring new possessions. Understanding the factors that contribute to this collecting behavior will allow us to develop better treatment approaches for HD. The aim of this study was to test our assumption that an anxious attachment style is associated with a tendency to anthropomorphize comforting objects and an inability to tolerate distress, which in turn leads to excessive acquisition. Methods A total of 361 participants with subclinical to clinical acquisition problems (77.8% female) completed a series of self-report measures. Results As expected, greater anxious attachment was related to greater distress intolerance and stronger tendencies to anthropomorphize inanimate objects. In turn, greater distress intolerance and anthropomorphism were related to more excessive buying and greater acquisition of free items. Examination of the pathways and indirect effects showed support for double mediation rather than serial mediation, as distress intolerance did not predict anthropomorphism. Discussion and conclusion These novel findings, if replicated, suggest that adding treatment modules that target improving distress tolerance and reducing anthropomorphism to standard treatment for HD may lead to further reductions in excessive acquiring.

The autoregulation of the microcirculation

The paper reviews August Krogh's contribution to capillary physiology stressing his formulation of useful new concepts such as "tissue cylinder model", capillary intermittency and the intimate matching of capillary perfusion and cellular metabolism. Looked upon from a control theory viewpoint. Krogh was very early in considering the microcirculation as an autoregulated system with tissue oxygen tension as the controlled parameter. Recent work on Krogh's theories is briefly summarized.

Effect of aerobic training in patients with spinal and bulbar muscular atrophy (Kennedy disease)

OBJECTIVE

We examined the effect of aerobic exercise in patients with spinal and bulbar muscular atrophy (SBMA). SBMA is caused by a defect androgen receptor. This defect causes motor neuron death, but considering the important function of androgens in muscle, it is possible that muscle damage in SBMA also occurs independently of motor neuron damage.

METHODS

Eight patients with SBMA engaged in regular cycling exercise for 12 weeks. Maximum oxygen uptake (Vo(2max)), maximal work capacity (W(max)), muscle morphology, citrate synthase (CS) activity, body composition, EMG, static strength measurements, lung function, plasma proteins, and hormones were evaluated before and after training. Evaluation of improvements in activities of daily living (ADL) was conducted after training.

RESULTS

W(max) increased by 18%, and CS activity increased by 35%. There was no significant change in Vo(2max) or any of the other variables examined before and after training, and the patients with SBMA did not feel improvements in ADL.

CONCLUSIONS

Frequent, moderate-intensity aerobic conditioning is of little beneficial effect in patients with spinal and bulbar muscular atrophy (SBMA). High levels of plasma creatine kinase and muscle regeneration indicate a primary myopathic affection, which, in parallel with the motor neuron deficiency, may attenuate the response to exercise training in patients with SBMA.

Reduced reciprocal inhibition is seen only in spastic limbs in patients with neurolathyrism

If reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity as has been suggested in several studies, the inhibition is expected to be impaired in spastic, but not in normal muscles. Patients with neurolathyrism offer a possibility of testing this prediction since the spastic symptoms in these patients are restricted to the lower extremities only. Three patients with neurolathyrism were tested. Their data were compared with 15 age-matched healthy subjects. All patients showed signs of spasticity in the legs. Two patients had normal voluntary muscle force in the lower extremities and one had decreased force. No clinical abnormalities were found in the upper extremities. Reciprocal inhibition between ankle dorsiflexor and plantarflexor muscles was absent in all patients, whereas the inhibition between wrist extensor and flexor muscles was present and of normal size and latency. These findings are consistent with the hypothesis that reduced reciprocal inhibition plays a causal role in the pathophysiology of spasticity.

The spinal pathophysiology of spasticity--from a basic science point of view

Spasticity is a term, which was introduced to describe the velocity-sensitive increased resistance of a limb to manipulation in subjects with lesions of descending motor pathways. This distinguishes spasticity from the changes in passive muscle properties, which are often seen in these patients, but are not velocity-sensitive. Increased excitability of the stretch reflex is thus a central component of the definition of spasticity. This review describes changes in cellular properties and transmission in a number of spinal reflex pathways, which may explain the increased stretch reflex excitability. The review focuses mainly on results derived from the use of non-invasive electrophysiological techniques, which have been developed during the past 20-30 years to investigate spinal neuronal networks in human subjects, but work from animal models is also considered. The reflex hyperexcitability develops over several months following the primary lesion and involves adaptation in the spinal neuronal circuitries caudal to the lesion. In animal models, changes in cellular properties (such as 'plateau potentials') have been reported, but the relevance of these changes to human spasticity has not been clarified. In humans, numerous studies have suggested that reduction of spinal inhibitory mechanisms (in particular that of disynaptic reciprocal inhibition) is involved. The inter-subject variability of these mechanisms and the lack of objective quantitative measures of spasticity have impeded disclosure of a clear causal relationship between the alterations in the inhibitory mechanisms and the stretch reflex hyperexcitability. Techniques which make such a quantitative measure possible as well as longitudinal studies where development of reflex excitability and changes in the inhibitory mechanisms are followed over time are in great demand.

Reciprocal inhibition and corticospinal transmission in the arm and leg in patients with autosomal dominant pure spastic paraparesis (ADPSP)

The pathophysiological mechanisms underlying the development of spasticity are not clear, but the excitability of the disynaptic reciprocal inhibitory pathway is affected in many patients with spasticity of different origin. Patients with genetically identified autosomal dominant pure spastic paraparesis (ADPSP) develop spasticity and paresis in the legs, but usually have no symptoms in the arms. Comparison of the spinal and supraspinal control of the legs and arms in these patients may therefore provide valuable information about the pathophysiology of spasticity. In the present study, we tested the hypothesis that one of the pathophysiological mechanisms of spasticity in these patients is abnormal corticospinal transmission and that this may lead to decreased reciprocal inhibition. Ten patients and 15 healthy age-matched control subjects were investigated. The patients were all spastic in the legs (with hyperactive tendon reflexes, increased muscle tone and Babinski sign), but had no neurological symptoms in the arms (except for one patient). Disynaptic reciprocal Ia inhibition of flexor carpi radialis (FCR) and soleus (SOL) motoneurons was measured (as the depression of the background FCR and SOL EMG activity and as the short latency inhibition of the FCR and SOL H-reflex evoked by radial and peroneal nerve stimulation). In addition, the latency of motor evoked potentials (MEPs) in the FCR muscle and the tibialis anterior (TA) muscle was measured. In the patients, the mean reciprocal inhibition was normal in the arms, while it was significantly decreased in the leg compared with the healthy subjects. In the patients, the average latency of MEPs in the FCR muscle was normal, while the latency to the MEP in TA muscle was significantly longer than that found in healthy subjects. Four patients, however, differed from the other patients by having significant reciprocal inhibition in the leg and a significantly shorter latency of TA MEPs than found in the other patients. The six patients without reciprocal inhibition in the leg instead had significant short latency facilitation of the SOL H-reflex and a longer TA MEP latency than seen in the healthy subjects and in the four patients with retained reciprocal inhibition. These findings support the hypothesis that disynaptic reciprocal inhibition and short latency facilitation are involved in the development of spasticity and, furthermore, they suggest a positive correlation between impairment of corticospinal transmission and decrease of reciprocal inhibition/appearance of reciprocal facilitation.

Appearance of reciprocal facilitation of ankle extensors from ankle flexors in patients with stroke or spinal cord injury

The purpose of the present study was to investigate the pathophysiological role of reciprocal facilitation between antagonistic motoneuron pools in spasticity. The soleus H-reflex was conditioned by prior stimulation of the peroneal nerve in 15 healthy subjects, six hemiplegic patients and 11 spinal cord injured (SCI) patients. The hemiplegic patients were tested from soon after the onset of hemiplegia and up to 2 years later. Whereas stimulation of the peroneal nerve produced short-latency inhibition of the soleus H-reflex in healthy subjects, it produced facilitation in spastic SCI and hemiplegic patients. This facilitation was demonstrated to have a low threshold compatible with activation of group I afferents and was most likely mediated by an oligosynaptic (reciprocal) excitatory pathway. The facilitation appeared in parallel with the development of hyperactive Achilles tendon reflexes, which was the only clinical finding that could be correlated positively with the facilitation. It is suggested that the appearance of reciprocal excitation plays a role in the pathophysiology of spasticity.

Corticospinal transmission to leg motoneurones in human subjects with deficient glycinergic inhibition

Normal coordinated movement requires that the activity of antagonistic motoneurones may be depressed at appropriate times during the movement. Both glycinergic and GABAergic inhibitory mechanisms participate in this control. Patients with the major form of hyperekplexia (hereditary startle disease) have impaired inhibition of spinal motoneurones from local glycinergic interneurones and represent an ideal opportunity for studying the role of glycinergic inhibition in the control of antagonistic muscles. In the present study we investigated whether impaired glycinergic inhibition affects the corticospinal control of antagonistic spinal motoneurones in 10 patients with hyperekplexia and whether there are mechanisms that may compensate for the lack of glycinergic inhibition. In healthy subjects transcranial magnetic stimulation (TMS) produced a short-latency inhibition of the soleus H-reflex at rest and during tonic dorsiflexion. This inhibition, which has been shown to be mediated by spinal (glycinergic) inhibitory interneurones, was absent in all four patients in whom this experiment was performed. This confirms that glycinergic transmission is impaired in the patients. During voluntary dorsiflexion subthreshold TMS produced a depression of the ongoing EMG activity in the tibialis anterior (TA) muscle in both healthy subjects and all of the six tested patients. This is consistent with the idea that this EMG depression is caused by activation of cortical (GABAergic) inhibitory interneurones. Cross-correlation analysis revealed normal short-term synchronization of TA motor units accompanied by coherence in the 8-12 Hz and 18-35 Hz frequency bands in the 10 patients. As in healthy subjects, 8-12 Hz coherence accompanied by decreased tendency to discharge synchronously (de-synchronization) was found in recordings from the antagonistic TA and soleus muscles in 2 of the 10 patients. This suggests that glycinergic inhibition is not responsible for de-synchronization of antagonistic motor units, but that other GABAergic-inhibitory mechanisms must be involved. We propose that such mechanisms may compensate for the lack of glycinergic reciprocal inhibition in the hyperekplectic patients and explain why voluntary movements are not more severely affected.

Neurophysiological studies in malignant disease with particular reference to involvement of peripheral nerves

Neurological and neuromuscular disorders are frequent complications in patients with neoplasms and may involve the neuromuscular system, including motor and sensory nerve cell bodies, axons, myelin, neuromuscular transmission and muscle alone or in combination. Electrophysiological studies are of value in delineating the type, degree and extent of involvement, and may be of assistance in pointing towards the underlying cause: paraneoplastic factors, treatment with chemotherapy or radiation or metastatic infiltration. Though some electrophysiological features may be characteristic of certain syndromes, they rarely can stand alone but require clinical, pathological, radiological, and laboratory studies to obtain a diagnosis. Even in cases where such studies are obtained, a final diagnosis may only be ascertained during follow up, since the neuromuscular disorders frequently occur before the neoplasm is detected.

Patients with the major and minor form of hyperekplexia differ with regards to disynaptic reciprocal inhibition between ankle flexor and extensor muscles

The aim of the present study was to investigate the contribution of reciprocal inhibition to muscle tone by examining the transmission in the reciprocal inhibitory pathway in patients with a known defect in the glycine receptor. The study was performed in eight patients with hereditary hyperekplexia, six with the major form and two with the minor form of the disease. A mutation in the alpha1-subunit of the glycine receptor had been demonstrated in the patients with the major form, whereas no mutation was seen in the patients with the minor form. Disynaptic reciprocal inhibition, which is presumed to be mediated by glycine, was not seen in the patients with the major form of the disease, while it could be evoked in the patients with the minor form of the disease. Presynaptic inhibition, which is presumed to be mediated by GABA, was seen in both types of patients. It is concluded that the major form of hereditary hyperekplexia is associated with impaired transmission in glycinergic reciprocal inhibitory pathways. The findings demonstrate the importance of reciprocal inhibition for the muscle tone in man, and it is suggested that the impaired reciprocal inhibition seen in patients with a defect in the glycine receptor may contribute to the increased muscle stiffness that is observed in these patients.

Accumulation of cardiolipin and lysocardiolipin in fibroblasts from Tangier disease subjects

Tangier disease (TD) is an inherited disorder of lipid metabolism characterized by very low high density lipoprotein (HDL) plasma levels, cellular cholesteryl ester accumulation and reduced cholesterol excretion in response to HDL apolipoproteins. Molecular defects in the ATP binding cassette transporter 1 (ABCA1) have recently been identified as the cause of TD. ABCA1 plays a key role in the translocation of cholesterol across the plasma membrane, and defective ABCA1 causes cholesterol storage in TD cells. Not only cholesterol efflux, but also phospholipid efflux was shown to be impaired in TD cells. By use of thin layer chromatography, high performance liquid chromatography and time-of-flight secondary ion mass spectrometry, we characterized the cellular phospholipid content in fibroblasts from three homozygous TD patients. The cellular content of the major phospholipids was not found to be significantly altered in TD fibroblasts. However, the two phospholipids cardiolipin and lysocardiolipin, which make up minute amounts in normal cells, were at least 3-5-fold enriched in fibroblasts from TD subjects. A structurally closely related phospholipid (lysobisphosphatidic acid) has recently been shown to be enriched in Niemann-Pick type C, another lipid storage disorder. Altogether these data may indicate that the role of these phospholipids is a regulatory one rather than that of a bulk mediator of cholesterol solubilization in sterol trafficking and efflux.

Non-herbal nutritional supplements-the next wave: a comprehensive review of risks and benefits for the C-L psychiatrist

The continuing popularity of complementary medicine has led to the frequent appearance of new products in the marketplace. Non-herbal supplements are now a popular choice for patients seeking relief from a variety of medical conditions. As with herbal medicines, there are concerns about the safety of these products in those with physical illness. Clearly, consultation-liaison psychiatrists will encounter patients using non-herbal products or inquiring about them. This article seeks to provide knowledge about the risks and benefits of non-herbal supplements that consultation-liaison psychiatrists are likely to encounter.

Modulation of presynaptic inhibition and disynaptic reciprocal Ia inhibition during voluntary movement in spasticity

The aim of the study was to investigate whether impaired control of transmission in spinal inhibitory pathways contributes to the functional disability of patients with spasticity. To this end, transmission in the pathways mediating disynaptic reciprocal Ia inhibition and presynaptic inhibition was investigated in 23 healthy subjects and 20 patients with spastic multiple sclerosis during ankle dorsiflexion and plantar flexion. In healthy subjects, but not in spastic patients, the soleus H reflex was depressed at the onset of dorsiflexion (300 ms rise time, 20% of maximal voluntary effort). At the onset of plantar flexion, the soleus H reflex was more facilitated in the healthy subjects than in the patients. The H reflex increased more with increasing level of tonic plantar flexion and decreased more with dorsiflexion in the healthy subjects than in the spastic patients. Transmission in the disynaptic Ia reciprocal inhibitory pathway from ankle dorsiflexors to plantar flexors was investigated by conditioning the soleus H reflex by previous stimulation of the common peroneal nerve (conditioning-test interval 2-3 ms; stimulation intensity 1.05 times the motor response threshold). At the onset of dorsiflexion, stimulation of the common peroneal nerve evoked a significantly larger inhibition than at rest in the healthy subjects but not in the spastic patients. At the onset of plantar flexion the inhibition decreased in the healthy subjects, but because only weak inhibition was observed at rest in the patients it was not possible to determine whether a similar decrease occurred in this group. There were no differences in the modulation of inhibition during tonic plantar flexion and dorsiflexion in the two populations. Presynaptic inhibition of Ia afferents terminating on soleus motor neurones was evaluated from the monosynaptic Ia facilitation of the soleus H reflex evoked by femoral nerve stimulation. Femoral nerve facilitation was decreased at the onset of dorsiflexion and increased at the onset of plantar flexion in the healthy subjects and patients, but the changes were significantly greater in the healthy subjects. There was no difference between the two populations in the modulation of presynaptic inhibition during tonic plantar flexion and dorsiflexion. It is suggested that the abnormal regulation of disynaptic reciprocal inhibition and presynaptic inhibition in patients with spasticity is responsible for the abnormal modulation of stretch reflexes in relation to voluntary movement in these patients. Lack of an increase in reciprocal inhibition and presynaptic inhibition at the onset of dorsiflexion may be responsible for the tendency to elicitation of unwanted stretch reflex activity and co-contraction of antagonistic muscles in patients with spasticity.

The effect of baclofen on the transmission in spinal pathways in spastic multiple sclerosis patients

OBJECTIVES

To measure the effect of baclofen on the transmission in different spinal pathways to soleus motoneurones in spastic multiple sclerosis patients.

METHODS

Baclofen was administered orally in 14 and intrathecally in 8 patients. H(max)/M(max), presynaptic inhibition by biceps femoris tendon tap of femoral nerve stimulation, depression of the soleus H-reflex following previous activation of the Ia afferents from the soleus muscle (i.e. postactivation depression), disynaptic reciprocal Ia inhibition of the soleus H-reflex and the number of backpropagating action potentials in primary afferents, which may be a sign of presynaptic inhibition, were examined.

RESULTS

Baclofen depressed the soleus H(max)/M(max) ratio significantly following oral and intrathecal baclofen. None of the two tests of presynaptic inhibition, or the postactivation depression or the disynaptic reciprocal Ia inhibition of the soleus H-reflex were affected by baclofen administration. Also the action potentials of the primary afferents were unchanged during baclofen administration.

CONCLUSIONS

The antispastic effect of baclofen is not caused by an effect on the transmitter release from Ia afferents or on disynaptic reciprocal Ia inhibition. One possible explanation of the depression of the H-reflex by baclofen is suggested to be a direct depression of motoneuronal excitability.

High expression of MHC I in the tibialis anterior muscle of a paraplegic patient

A long-term paraplegic man presented exclusively (>99%) myosin heavy chain I (MHC I) in the tibialis anterior muscle (TA). This was coupled to a slow speed of contraction, a high resistance to fatigue, and a rapid resynthesis of phosphocreatine after an electrically evoked fatiguing contraction when compared with the TA muscles of 9 other paraplegic individuals. In contrast, the MHC composition of his vastus lateralis, gastrocnemius, and soleus muscles was that expected of a muscle from a spinal cord injured individual. This information may be of clinical importance in terms of the expected morphological and functional adaptations of skeletal muscle to different types of electrical stimulation therapy.

Amplitude of the maximum motor response (Mmax) in human muscles typically decreases during the course of an experiment

It was shown that the amplitude of the soleus Mmax and Hmax responses decreases in the course of long-lasting H-reflex studies. The peak-to-peak amplitudes of the Mmax and Hmax responses in the soleus muscle (and the Mmax in the tibialis anterior muscle and small hand muscles) were measured repeatedly for 1-3 h in 20 subjects. 3-5 Mmax responses and 5-10 Hmax responses were elicited about every 3 min while the subject was at rest. Decreases in the soleus Mmax response of up to 50.5% (mean 20.5% SEM 2.2) and of the soleus Hmax of up to 49.7% (mean 19.1% SEM 3.7) in relation to the amplitudes measured at the beginning of the experiment were seen in 17 subjects. In 3 subjects no Mmax amplitude decrease was seen. The maximum decrease was reached between 10 and 100 min (mean 44.2 min SEM 4.3). An Mmax amplitude decrease was also seen in the tibialis anterior muscle and in two small hand muscles. In some subjects the decrease of the Mmax response seemed to be initiated by the infrequent supramaximal stimulations. The possible causes for this amplitude reduction, as well as the methodological consequences of these findings for H-reflex studies and fatigue studies, are briefly discussed.

[Diagnosis of polyneuropathies]

The accurate diagnosis of peripheral neuropathy is important with respect to the therapeutic possibilities and limitations, which are especially relevant in immune-mediated polyneuropathies. These polyneuropathies may be axonal or demyelinating and have an acute or chronic course, and they may be difficult to distinguish from non-treatable neuropathies on clinical grounds. Efforts have been made to establish clinical, neurophysiological, morphological, biochemical, immunological and molecular biological criteria to attain specific diagnosis. This has shown heterogeneity not only within the treatable neuropathies, which may have implications for the treatment. It has also been shown that hereditary or diabetic polyneuropathy may have features which respond to immunosuppressive treatment. Molecular biology studies have revealed markers for the diagnosis of hereditary neuropathy, and have in some instances also delineated the gene product.

Changes in transmission across synapses of Ia afferents in spastic patients

The transmission across synapses of Ia afferents on spinal motor neurons was investigated in 30 healthy subjects and 25 spastic multiple sclerosis patients. Slow passive stretch (17 degrees/s of the soleus muscle evoked a pronounced depression of the soleus Hoffmann reflex (H-reflex) lasting for more than 10 s in the healthy subjects. This depression was less pronounced and had a shorter duration in the spastic patients. A tap applied to the biceps femoris tendon also produced an inhibition of the soleus H-reflex, which was larger in the healthy subjects than in the spastic patients. This inhibition only lasted for 300-400 ms. Finally, stimulation of the femoral nerve (FN) produced a facilitation of the soleus H-reflex, which was larger in the spastic patients than in the healthy subjects. The inhibition of the H-reflex evoked by the biceps femoris tendon tap is known to be caused by presynaptic inhibition of the Ia afferents, which mediate the reflex. The facilitation of the soleus H-reflex produced by FN stimulation has also been shown to be influenced by changes in presynaptic inhibition. The increased facilitation from the FN and the decreased inhibition from the biceps femoris tendon tap onto the soleus H-reflex in spastic patients are thus both compatible with a deficient presynaptic inhibition in these subjects. The long lasting depression of the reflex evoked by a previous slow stretch of the soleus muscle is most likely caused by a decrease of the probability of transmitter release from the Ia afferents. The decrease of this depression in spastic patients suggests that mechanisms other than presynaptic inhibition may contribute to changes in the efficiency of transmission across the synapses of Ia afferents in spastic patients and thus contribute to the exaggeration of stretch reflexes seen in these patients.

Central control of reciprocal inhibition during fictive dorsiflexion in man

The size of the soleus Hoffmann reflex (H-reflex) was measured in six healthy human subjects before and after transmission in the common peroneal nerve (CPN) was blocked reversibly by local injection of lidocaine. It was found that the H-reflex at rest increased after the block. When the subjects attempted to perform a dorsiflexion while the CPN was blocked ("fictive dorsi flexion"), the soleus H-reflex was strongly depressed. Stimulation of the CPN proximal to the block elicited a short-latency inhibition of the soleus H-reflex, which was probably mediated by reciprocal Ia interneurones. This inhibition never increased during dorsiflexion relative to rest prior to the CPN block, but after the block a significant increase in inhibition was seen during fictive dorsiflexion in three subjects. Stimulation of the femoral nerve (FN) elicited a short-latency monosynaptic Ia facilitation of the soleus H-reflex. This facilitation was found to decrease during dorsiflexion relative to rest before the block as well as during fictive dorsiflexion after the block. The decrease in the H-reflex during fictive dorsiflexion demonstrates that although an increased Ia-afferent feedback via the gamma-loop may contribute to reciprocal inhibition when transmission in the CPN is intact, a noticeable, centrally mediated inhibition may occur in the absence of this feedback. It is suggested that this inhibition is caused by central facilitation of interneurones mediating disynaptic Ia inhibition as well as interneurones mediating presynaptic inhibition of Ia afferents.

Central control of disynaptic reciprocal inhibition in humans

The disynaptic pathway from muscle spindle Ia afferents to motoneurones of the antagonist muscle is one of the best studied pathways in the spinal cord. Early animal studies--mainly in the cat--have provided a detailed knowledge of the pathway itself and of the integration of segmental and supraspinal convergence at the interneuronal level. Although this knowledge was used to formulate hypotheses on the function of the pathway during natural movements, the reduced animal preparation limited the possibilities of testing these ideas. However, such information has more recently been obtained from human subjects by using indirect electrophysiological techniques. In most of these experiments the disynaptic Ia inhibition was demonstrated as a short-latency depression of a monosynaptic test reflex (H-reflex) following a conditioning stimulation of the antagonist nerve. Changes in the size of this depression during voluntary tasks were then taken as evidence of a central regulation of the pathway. It has for example been demonstrated in this way that the brain regulates the Ia inhibitory interneurones in parallel with their corresponding motoneurones during extension-flexion movements, but not during co-contraction of antagonistic muscles. The importance of the central control of the pathway has also been emphasized by the finding of a disordered regulation of its activity in patients with lesions of the brain. This may possibly contribute to the inappropriate co-contraction of antagonistic muscles observed in some of these patients. It seems reasonable to expect that this kind of experiment in the future may contribute significantly to the knowledge of the central control of spinal motor mechanisms.

Disynaptic reciprocal inhibition of ankle extensors in spastic patients

The soleus Hoffmann-reflex (H-reflex) was conditioned by a preceding stimulation of the common peroneal nerve in 74 healthy control subjects and 39 patients with spasticity in the lower extremities due to multiple sclerosis. At a conditioning-test interval of 1-3 ms a decrease of the size of the soleus H-reflex was seen in the healthy subjects. The decrease was most likely caused by disynaptic reciprocal Ia inhibition (Crone et al., 1987). In the spastic patients a similar short-latency inhibition was rarely seen. On the contrary, in several patients a facilitation was seen at a conditioning-test interval of 3-4 ms. A short-latency inhibition as pronounced as in healthy subjects was seen in four patients. These four patients did not differ from the other patients regarding the degree of spasticity or any other clinical parameter. However, they all used an external peroneal nerve stimulator daily as a walking aid. It is suggested that the lack of short-latency reciprocal inhibition reflects a deficient control of the interneurons which mediate this inhibitory spinal mechanism between antagonistic muscles in man. This might contribute to the pathophysiology of spasticity and it might be related to the frequent occurrence of co-contraction of functionally antagonistic muscles during gait in spastic patients. The existence of a pronounced reciprocal inhibition in patients receiving frequent stimulation of the peroneal nerve may suggest that regular activation of peripheral nerves is of importance for the maintenance of the activity in spinal pathways.

Reciprocal inhibition in man

Reciprocal inhibition is the automatic antagonist alpha motor neurone inhibition which is evoked by contraction of the agonist muscle. This so-called natural reciprocal inhibition is a ubiquitous and pronounced phenomenon in man and must be suspected of playing a major role in the control of voluntary movements. The spinal pathways underlying this inhibitory phenomenon were studied. The disynaptic reciprocal Ia inhibitory pathway between the tibial anterior muscle and the soleus alpha motor neurones was identified and described in man. It was shown that the inhibition can be evoked in most healthy subjects at rest, but the degree of inhibition varies considerably from one subject to another. It was concluded that it corresponds to the disynaptic reciprocal Ia inhibitory pathway which has been extensively described in animal experiments. The disynaptic reciprocal inhibition was shown to increase during the dynamic phase of a dorsiflexion movement of the foot, but not during the tonic phase. However, when the peripheral afferent feedback from the contracting muscle was blocked by ischaemia, an increase of the inhibition was revealed also during the tonic phase of the dorsiflexion. The concealment of this increase during unrestrained peripheral feedback from the muscle was thought to be due to the post-activation depression mechanism; a mechanism which was described further and which probably involves reduced transmitter release at Ia afferent terminals as a result of previous activation of these afferent fibers. Hence the hypothesis was supported that alpha motor neurones and the corresponding inhibitory interneurones, which project reciprocal inhibition to the antagonist motor neurones, are activated in parallel during voluntary contraction of agonist muscles. An additional reciprocal inhibitory mechanism, the long latency reciprocal inhibition, was described between the tibial anterior muscle and the soleus alpha motor neurones. It was shown to be evoked by group I afferent activity and it was seen at a conditioning-test interval of 3-6 msec. It was initiated by supraspinal pathways and it was seen only during dorsiflexion of the foot. The pathway underlying this inhibitory mechanism is unknown, but it was suggested that it was mediated by a propriospinal pathway. The possible contribution to reciprocal inhibition of presynaptic inhibition of soleus Ia afferent fibers was studied by an indirect method. It was concluded that this presynaptic inhibition was increased during even slight dorsiflexion of the foot and that the increase was mainly dependent upon the peripheral afferent input from the contracting muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

H-reflexes are smaller in dancers from The Royal Danish Ballet than in well-trained athletes

The size of the maximal H-reflex (Hmax) was measured at rest and expressed as a percentage of the maximal M-response (Mmax) in 17 untrained subjects, 27 moderately trained subjects, 19 well-trained subjects and 7 dancers from the Royal Danish Ballet. The Hmax/Mmax was significantly larger in the moderately and well-trained subjects than in the untrained subjects but smaller in the ballet dancers. It is therefore suggested that both the amount and the type of habitual activity may influence the excitability of spinal reflexes.

Central facilitation of Ia inhibition during tonic ankle dorsiflexion revealed after blockade of peripheral feedback

Recent studies have reported that no increase of the disynaptic reciprocal inhibition can be observed during tonic voluntary dorsiflexion of the foot as compared to rest, when the size of the control H-reflex is kept constant. Other studies have, however, shown that a voluntary contraction evokes a strong and long-lasting depression of the synaptic transmission from Ia afferents to motoneurones, most likely secondary to activation of these afferents during the contraction (post-activation depression). It was thought that this effect could also interfere with the demonstration of a central facilitation of the reciprocal inhibition during movement. The amount of disynaptic Ia reciprocal inhibition from the pretibial flexors to the soleus H-reflex was therefore estimated in normal human subjects at rest and during voluntary tonic dorsiflexion before, during and after blocking the peripheral feedback from the investigated muscles. It was observed that the reciprocal inhibition measured during dorsiflexion increased during occlusion of the blood supply to the leg, reaching a maximum of inhibition after 30 min of ischaemia. After release of the ischaemia the inhibition gradually decreased to its pre-ischaemic level. It is therefore suggested that the brain facilitates transmission in the Ia disynaptic reciprocal pathway during tonic voluntary dorsiflexion of the foot, but that this facilitation is normally not observed due to a post-activation depression following the peripheral feedback activation during the movement.

Sensitivity of monosynaptic test reflexes to facilitation and inhibition as a function of the test reflex size: a study in man and the cat

In parallel experiments on humans and in the cat it was investigated how the sensitivity of monosynaptic test reflexes to facilitation and inhibition varies as a function of the size of the control test reflex itself. In man the monosynaptic reflex (the Hoffmann reflex) was evoked in either the soleus muscle (by stimulation of the tibial nerve) or the quadriceps muscle (by stimulation of the femoral nerve). In the decerebrate cat monosynaptic reflexes were recorded from the nerves to soleus and medial gastrocnemius muscles; they were evoked by stimulation of the proximal ends of the sectioned L7 and S1 dorsal roots. Various excitatory and inhibitory spinal reflex pathways were used for conditioning the test reflexes (e.g. monosynaptic Ia excitation, disynaptic reciprocal inhibition, cutaneous inhibition, recurrent inhibition, presynaptic inhibition of the Ia fibres mediating the test reflex). It was shown that the additional number of motoneurones recruited in a monosynaptic test reflex by a constant excitatory conditioning stimulus was very much dependent on the size of the test reflex itself. This dependency had the same characteristic pattern whatever the conditioning stimulus. With increasing size of the test reflex the number of additionally recruited motoneurones first increased, then reached a peak (or plateau) and finally decreased. A similar relation was also seen with inhibitory conditioning stimuli. The basic physiological factors responsible for these findings are discussed. Finally, the implications for the interpretation of experiments in man with the H-reflex technique are considered.

News From the Alveoli

Recent studies show that the alveolar epithelium performs solute-coupled fluid transport in the direction from the alveolar spaces to lung interstitial fluid. Na+-K+-ATPase plays a prime role for assuring the "dry" character of the alveoli.

Methodological implications of the post activation depression of the soleus H-reflex in man

A long lasting inhibition (greater than 8 s) of the soleus Hoffmann reflex (H-reflex) was evoked by a preceding soleus H-reflex, by a brief voluntary ankle flexor or extensor muscle contraction or by a tap applied to the Achilles tendon. The time course of this long lasting inhibition was similar in all these cases, suggesting that the same spinal mechanism is involved. Furthermore, it was shown that the post-activation depression may interfere with the determination of inhibitory or facilitatory effects on the H-reflex. It is stressed that when the onset of inhibitory or facilitatory effects on the soleus H-reflex is to be determined in relation to start of an ankle movement, either very long stimulus intervals (greater than 8 s) must be used, or the onset must be determined in relation to a reference value of the soleus H-reflex, which may be influenced by the long lasting inhibitory effect, but not yet by the succeeding muscle contraction.

Spinal mechanisms in man contributing to reciprocal inhibition during voluntary dorsiflexion of the foot

1. The inhibition of the soleus Hoffmann reflex (H reflex) during voluntary dorsiflexion of the foot--henceforth referred to as 'natural' reciprocal inhibition--was found to be initiated 50 ms before the onset of the EMG activity in the tibialis anterior muscle and to increase gradually during a ramp-and-hold dorsiflexion. There was a positive correlation between strength of tonic dorsiflexion and amount of 'natural' reciprocal inhibition. 2. The change of activity in the disynaptic and a long-latency group Ia inhibitory pathway and the change in presynaptic inhibition of the Ia fibres mediating the soleus H reflex were tested separately during ramp-and-hold dorsiflexion as well as during tonic dorsiflexion of the foot, and the results were compared with the development of the 'natural' reciprocal inhibition of the unconditioned soleus H reflex. 3. The disynaptic group I inhibition of soleus motoneurones was increased, as compared to rest, during the dynamic phase of a ramp-and-hold dorsiflexion movement, but the inhibition generally did not increase during tonic dorsiflexion of the foot. 4. The long-latency group I inhibition was seen only during dorsiflexion of the foot. It appeared around 50 ms before tibial anterior EMG activity and there was a positive correlation between strength of tonic dorsiflexion and amount of this long-latency inhibition. 5. Presynaptic inhibition of Ia afferents terminating on soleus motoneurones was estimated by an indirect method. The increase of presynaptic inhibition started soon after the onset of the ramp-and-hold dorsiflexion, and gradually became more pronounced during the ramp phase. The amount of presynaptic inhibition was positively correlated with strength of tonic dorsiflexion. 6. It is concluded that all investigated mechanisms may contribute to the 'natural' reciprocal inhibition and it seems that the different pathways are used differentially during different types of movement.

Growth of colorectal carcinoma cells: regulation in vitro by gastrin, pentagastrin and the gastrin-receptor antagonist proglumide

The growth-regulating effects of pentagastrin, gastrin and the gastrin-receptor antagonist proglumide were investigated in three established cell lines derived from human colorectal carcinomas in vitro and after transplantation into nude mice. In vitro a significant increase of cell growth in the SW 403 cell line incubated with pentagastrin or gastrin was observed. In the Lovo cell line this effect was only detected after synchronization of cell growth. Pentagastrin and gastrin had no effect on the growth of the Ls 174 T cell line. Proglumide reduced cell proliferation in all three cell lines as well as in the L929S cell line derived from fibroblasts, which served as control. After transplantation into nude mice all tumor cell lines increased, Lovo and Ls 174 T as undifferentiated tumor, SW 403 as differentiated. Pentagastrin increased and proglumide decreased growth in SW 403 tumors, whereas no effect was observed on Ls 174 T and Lovo tumors. We therefore conclude that growth of some colorectal carcinomas is regulated by gastrin, but that the effect of proglumide is unspecific rather than related to blockage of gastrin receptors. The growth-regulating effect of gastrin could be due to tumor differentiation.

Cellular effects of beta-adrenergic and of cAMP stimulation on potassium transport in rat alveolar epithelium

Alveolar fluid absorption is greatly enhanced by cAMP and by beta-adrenergic agonists via an increase in Na+ transport. Little is known about K+ homeostasis under these circumstances. We studied K+ transport across alveolar epithelium in isolated perfused rat lungs stimulated either by dibutyryl-cAMP or isoproterenol. K+ fluxes and the apparent permeability of 86Rb across the epithelium (alveoli to plasma) were interpreted according to a model involving two types of cells, B and L, distinguished by the location of Na+-K+-ATPases (basal and luminal). Water is considered to be absorbed by B cells in a solute-coupled process energized by a basolateral Na+-K+-ATPase that is stimulated by isoproterenol and cAMP. K+ transport out of the alveoli is due to the activity of a Na+-K+-ATPase located in the apical membrane of L cells. In the present study net transport rate of K+ was -0.5 +/- 0.15 nmol/s, n = 20 (out of alveoli) in control conditions. When the epithelium was stimulated by dibutyryl-cAMP (10(-4) mol/l) net absorption of K+ reversed to net 'secretion' into alveoli (3.2 +/- 0.31 nmol/s), fluid absorption was not stimulated. K+ 'secretion' was abolished by apical Ba2+, indicating it was due to opening of apical K+ channels. Basolateral ouabain reversed net K+ 'secretion' to net absorption indicating that K+ entry into alveoli was dependent on activity of B cell basolateral Na+-K+-ATPase (masking simultaneous K+ removal by apical L cell Na+-K+-pump). When larger concentrations of dibutyryl-cAMP (10(-3) mol/l) or when isoproterenol were used to stimulate the epithelium there was a tripling of fluid absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Maintained changes in motoneuronal excitability by short-lasting synaptic inputs in the decerebrate cat

1. During investigation of the tonic stretch reflex in the unanaesthetized decerebrate cat we observed that a short train of impulses in Ia afferents from the soleus muscle (or its synergists) may cause a prolonged activity in the soleus muscle as judged by EMG and tension recordings. This excitability increase, which outlasted the stimulus train, could stay virtually constant during long periods (even minutes), but could be terminated at any time by a train of impulses in, for example, the peroneal nerve. 2. Gradation of the strength of stimulation and the duration of the train of impulses show that the amount of maintained excitability increase depends-within some limits-on the total amount of Ia impulses. 3. In paralysed preparations a short train of impulses in Ia afferents from any part of the triceps surae, caused a maintained increase of the efferent activity in the nerves to triceps surae and a maintained increase of the triceps surae monosynaptic test reflex. These experiments demonstrate the existence of a central mechanism (in the spinal cord and/or the brain stem), which is responsible for the maintained excitability increase seen in motoneurones to the homonymous and synergic muscles. 4. In acute spinal preparations it was not possible to demonstrate any long-lasting excitability increase by a train of Ia impulses. Following intravenous administration of the serotonin precursor 5-hydroxytryptophan, mimicking the tonic activity of these pathways in the decerebrate state, it was again possible to elicit the long-lasting excitability increase by a train of impulses in Ia afferents. A subsequent I.V. injection of methysergide (a serotonin receptor blocker) abolished the long-lasting excitability increase. This set of experiments demonstrates that the basic mechanism responsible for the maintained excitability increase is located at segmental level, and involves serotonergic systems. 5. It was demonstrated that activation of several ipsilateral and crossed reflex pathways by trains of impulses in cutaneous or high-threshold muscle afferents could trigger a maintained excitability increase of those motoneurone pools which were activated by the stimulation. Trains of stimuli to facilitatory regions in the brain stem could also cause a long-lasting excitability increase of motoneurones. Furthermore, activation of all reflex pathways which mediate postsynaptic inhibition to a motor nucleus (including recurrent inhibition via Renshaw cells) could terminate the prolonged excitability increase of that particular motor nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Presynaptic inhibition of sympathetic fibers participating in vasodilatation in response to K+-induced contraction of frog skeletal muscle

Experiments were performed on an autoperfused transparent frog muscle (m. cutaneus pectoris) with the purpose of elucidating possible mechanisms of functional hyperaemia. The diameter of a primary arteriole was followed before and after a K+-induced contracture lasting 20 s. The vasodilatation following this period of activity was expressed as the diameter change relative to the maximal possible diameter increase. The results emphasize adenosine as an important substance participating in vasodilatation in active skeletal muscle, its effect possibly being presynaptic (prejunctional) inhibition of sympathetic vasoconstrictor fibers to arteriolar smooth muscle (sympathetic uncoupling), in addition to the well-known direct effect (relaxation) on vascular smooth muscle cells. The presence of a strong resting sympathetic tone was demonstrated by local application of phentolamine (7.1 X 10(-5) M) that led to a large diameter increase. The purinoceptor blocking agent, 8-phenyltheophylline (8-PTP) invariably attenuated post-contraction vasodilatation, the adenosine transport inhibitor dipyridamole (10(-5) M) increased the hyperaemia response. Lack of sympathetic arteriolar tone during hyperaemia was demonstrated by the absence of a dilatory effect of phentolamine applied in the post-contraction period. Conversely, blockage of purinoceptors by 8-PTP during and after the contracture allowed sympathetic discharge to continue as verified by application of phentolamine, now leading to further vasodilatation. We suggest that presynaptic inhibition of sympathetic nerve endings by adenosine participates in vasodilatation in frog skeletal muscle.

Apical sodium-sugar transport in pulmonary epithelium in situ

The presence of an apical sodium-coupled transport system for D-glucose in lung alveolar epithelial cells has been demonstrated in lungs instilled with Ringer's fluid and perfused with either blood or Ringer's fluid (Basset et al. (1987) J. Physiol. 384, 325-345). The direction of transport is from alveoli towards interstitium. The characteristics of the system were evaluated in similar preparations by use of sugar analogues such as alpha-methyl-glucopyranoside, 2-deoxyglucose, 3-O-methylglucose and L-glucose. The main finding was the presence of a transport system for alpha-methylglucopyranoside and 2-deoxyglucose in the apical cell membrane. This system was unaffected by phloretin. Both alpha-methylglucopyranoside and 2-deoxyglucose transports were inhibited by phloridzin and by the presence of glucose (10(-2) mol.l-1). Competition was demonstrated between D-glucose and alpha-methylglucopyranoside or 2-deoxyglucose, but not for 3-O-methylglucose or L-glucose. 3-O-Methylglucose was cleared as slowly as L-glucose. The results comply partly with those known from intestinal epithelium and kidney proximal tubular epithelium, but the handling of 3-O-methylglucose was different. The relative transport rates of Na+ and glucose are compatible with a Na+: glucose coupling ratio larger than one.

Potassium transport across rat alveolar epithelium: evidence for an apical Na+-K+ pump

1. Experiments were performed on rat lungs into which various solutions were instilled whilst the lungs were perfused with either whole blood or Ringer solution. Instillation of ion-free glucose solution led to a net flux of fluid and ions into the alveolar spaces. K+ ions entered faster than Na+ ions and reached a concentration about twice that in the perfusate. Ouabain in the perfusate (basolateral side) prevented the rise in alveolar K+ concentration above that in the perfusate, indicating a transcellular pathway. Ba2+ in the instillate (apical side) hindered the entry of K+ into alveoli, suggesting the presence of apical K+ channels. 2. When Ringer solution was instilled, K+ was continuously removed from the alveoli and the K+ concentration in the instillate remained constant or decreased slightly depending on the rate of fluid absorption. The net K+ efflux from alveoli to blood was 0.23 pmol/(cm2 s). When Ba2+ was added to the instillate the net K+ efflux increased to 0.36 pmol/(cm2 s). Apical ouabain reversed the K+ flux resulting in a net K+ flux of 0.19 pmol/(cm2 s) into the alveoli. This suggests the presence of an Na+-K+-ATPase located in the apical membrane of some alveolar cells. 3. The K+ transport from instillate (Ringer solution) to perfusate was traced by means of 86Rb which was added to the instillate. Ouabain in the instillate did not affect fluid absorption but reduced the apparent 86Rb permeability by 50% although the paracellular permeability (estimated with [3H]mannitol) was unaffected. This also indicates the presence of an apical Na+-K+-ATPase. When ouabain was added to the perfusate, the apparent 86Rb permeability doubled. These findings indicate that recirculation of 86Rb (and K+) occurs due to the activity of both apical and basolateral Na+-K+-ATPases. 4. When ouabain was placed on both sides of the epithelium, preventing transcellular transport, the passive 86Rb permeability was 10.3 x 10(-8) cm/s (assuming an alveolar surface area of 5000 cm2). This value agrees with the passive permeabilities for mannitol, Na+ and Cl- suggesting that the paracellular pathway acts as a water-filled neutral channel. 5. We conclude that K+ is 'secreted' into the alveoli and is also removed from the alveoli, both processes being energized by Na+-K+-ATPases placed on the basolateral and apical sides, respectively. It is likely that two functionally different cell types exist in the alveolar membrane. One type ('B cell') has a Na+-K+-ATPase located at the basolateral membrane and K+ channels situated luminally.(ABSTRACT TRUNCATED AT 400 WORDS)