Central pain in a hemispherectomized patient

We have examined a hemispherectomized patient who complained of touch-evoked pricking and burning pain in her paretic hand, especially when the hand was cold. Psychophysical examination showed that for the paretic side she confused cool and warm temperatures, and confirmed that she had a robust allodynia to brush stroking that was enhanced at a cold ambient temperature. Functional magnetic resonance imaging (fMRI) showed that during brush-evoked allodynia, brain structures implicated in normal pain processing (viz. posterior part of the anterior cingulate cortex, secondary somatosensory cortex, and prefrontal cortices) were activated. The fMRI findings thus indicate that the central pain in this patient was served by brain structures implicated in normal pain processing. Possible pathophysiological mechanisms include plasticity as well as thalamic disinhibition.

Ciprofloxacin pharmacokinetics in young cystic fibrosis patients after repeated oral doses

Until recently, only compassionate use of ciprofloxacin in children with cystic fibrosis was possible despite limited pharmacokinetic data. We studied five subjects with cystic fibrosis and exacerbation of pulmonary infection. A 15 mg/kg b.i.d. regimen of oral ciprofloxacin was administered. On the 15th day, eight blood samples were collected and plasma concentrations were measured by HPLC. The actual dose administered ranged from 10 to 14 mg/kg b.i.d., due to the fixed-dosage formulation. Corresponding AUC0-12 ranged from 8.2 to 11.9 mg.h/L. Plasma concentrations were maintained above individual MICs for a median time of 12.7 h over 24 h. The median area under the inhibitory curve was 52.8, which is about half the proposed target value for ciprofloxacin in pulmonary infections with Gram-negative bacteria such as Pseudomonas aeruginosa. A higher dose, administered from a specific formulation to ensure precise dosing, must be given in order to obtain adequate concentrations in cystic fibrosis children.

Urinary excretion reflects lung deposition of aminoglycoside aerosols in cystic fibrosis

Using nebulization to deliver aminoglycosides may be of benefit in cystic fibrosis (CF) patients colonized by Pseudomonas aeruginosa. However, one problem with this route is the absence of clinical parameters allowing estimation of the mass of drug deposited in the lungs (MDL). The aim of this study was to assess whether aminoglycoside excretion in the urine reflects the MDL. Fourteen studies were performed in seven CF patients. Amikacin was mixed with albumin labelled with 99mTc and nebulized with an ultrasonic nebulizer. The MDL was determined by the mass-balance technique. Urine was collected during the 24 h following inhalation and was assayed for amikacin by fluorescence polarization immunoassay (FPIA). The mean+/-SEM MDL was 14.0+/-2.2% of the nebulizer charge. The mean+/-SEM amount of amikacin excreted in the urine was 20.9+/-4.5 mg and correlated with the MDL (r=0.93; p=0.0001). There was, however, wide intersubject variability in both deposition and excretion in the urine. Monitoring excretion of aminoglycosides in the urine allows noninvasive estimation of the mass of drug deposited in the lung in cystic fibrosis patients, which might be useful to assess the dose-response relationship in groups of patients, but intersubject variability prevents its use for individual follow-up.

Hypoxic vasoconstriction of rat main pulmonary artery: role of endogenous nitric oxide, potassium channels, and phosphodiesterase inhibition

This study investigated the influence of NO, potassium (K+) channel blockade, and the phosphodiesterase inhibitors (PDEIs) theophylline (non-selective PDEI), siguazodan (PDE3I), rolipram (PDE4I), and zaprinast (PDE5I) on rat isolated main pulmonary artery hypoxic (95% N2 and 5% CO2) vasoconstriction. Hypoxic vasoconstriction increased by 27% (p < 0.01) in the presence of the NO synthase inhibitor L-NAME (10(-4) M), and by 15% (p < 0.05) in the presence of the K(ATP) channel blocker glibenclamide (10(-6) M), without potentiation by the combination of these two drugs. Hypoxic vasoconstriction decreased by 28% (p < 0.01) in presence of the Kv,-voltage-dependent channel blocker 4-aminopyridine (10(-3) M), whereas the other K+ channel blockers, charybdotoxin (BKCa, large-conductance Ca2+-sensitive K+ channels) and apamin (SKCa, small-conductance Ca2+-sensitive K+ channels) had no effect. The nonselective PDEI theophylline induced a concentration-dependent relaxation (pD2 = 4.05, Emax = 90% [expressed as a percentage of maximal relaxation induced by papaverine 10(-4) M]). Among the selective PDEIs, siguazodan was significantly (p < 0.01) more efficient than rolipram and zaprinast (Emax values were 84%, 67%, and 58%, respectively) and significantly (p < 0.05) more potent than zaprinast (pD2 values were 6.48, 6.34, and 6.16 for siguazodan, rolipram, and zaprinast). Glibenclamide and L-NAME significantly (p < 0.05) shifted the concentration-response curve (CRC) for zaprinast to the right, and L-NAME shifted the CRC significantly to the right for siguazodan. In the presence of L-NAME, glibenclamide had no effect on the CRC of zaprinast. We conclude that (a) NO exerts a permanent inhibitory effect against hypoxic vasoconstriction that might be mediated in part by an activation of K(ATP) channels; (b) a 4-aminopyridine-sensitive K+ channel is involved in vasoconstriction under hypoxic conditions; (c) PDEs 3 and 5 are the predominant PDE isoforms in rat pulmonary artery relaxation; and (d) NO and K(ATP), but neither BK(Ca), SK(Ca), nor Kv channels, are involved in the relaxant effect of PDEIs.

Genomic organization of the dysferlin gene and novel mutations in Miyoshi myopathy

OBJECTIVE

Mutations in the skeletal muscle gene dysferlin cause two autosomal recessive forms of muscular dystrophy: Miyoshi myopathy (MM) and limb girdle muscular dystrophy type 2B (LGMD2B). The purpose of this study was to define the genomic organization of the dysferlin gene and conduct mutational screening and a survey of clinical features in 21 patients with defined molecular defects in the dysferlin gene.

METHODS

Genomic organization of the gene was determined by comparing the dysferlin cDNA and genomic sequence in P1-derived artificial chromosomes (PACs) containing the gene. Mutational screening entailed conformational analysis and sequencing of genomic DNA and cDNA. Clinical records of patients with defined dysferlin gene defects were reviewed retrospectively.

RESULTS

The dysferlin gene encompasses 55 exons spanning over 150 kb of genomic DNA. Mutational screening revealed nine novel mutations associated with MM. The range of onset in this patient group was narrow with a mean of 19.0 +/- 3.9 years.

CONCLUSION

This study confirms that the dysferlin gene is mutated in MM and LGMD2B and extends understanding of the timing of onset of the disease. Knowledge of the genomic organization of the gene will facilitate mutation detection and investigations of the molecular biologic properties of the dysferlin gene.

Calpain 3 mRNA expression in mice after denervation and during muscle regeneration

Lack of functional calpain 3 in humans is a cause of limb girdle muscular dystrophy, but the function(s) of calpain 3 remain(s) unknown. Special muscle conditions in which calpain 3 is downregulated could yield valuable clues to the understanding of its function(s). We monitored calpain 3 mRNA amounts by quantitative RT-PCR and compared them with those of α-skeletal actin mRNA in mouse leg muscles for different types of denervation and muscle injury. Intact muscle denervation reduced calpain 3 mRNA expression by a factor of 5 to 10, while α-skeletal actin mRNA was reduced in a slower and less extensive manner. Muscle injury (denervation-devascularization), which leads to muscle degeneration and regeneration, induced a 20-fold decrease in the mRNA level of both calpain 3 and α-skeletal actin. Furthermore, whereas in normal muscle and intact denervated muscle, the full-length transcript is the major calpain 3 mRNA, in injured muscle, isoforms lacking exon 6 are predominant during the early regeneration process. These data suggest that muscle condition determines the specific calpain 3 isoform pattern of expression and that calpain 3 expression is downregulated by denervation.

Cortical activation by tactile and painful stimuli in hemispherectomized patients

Hemispherectomized patients are able to perceive tactile and painful stimuli on their nonparetic as well as paretic body halves. We have used functional MRI to study the cortical mechanisms underlying this preserved somatosensory capacity. Nonpainful brushing and painful heat were applied to the skin of the legs in four hemispherectomized patients and, for comparison, in four normal subjects. Cortical activation was studied with a 1.5 T scanner using a BOLD (blood oxygen level dependent) protocol. All patients rated both the brushing and the heat pain as almost equally intense on each leg and the ratings were similar to those in normals. Brushing on the nonparetic leg activated primary and secondary somatosensory cortices (S1 and S2) in all patients, similar to findings in normals. Brushing on the paretic leg activated S1 in two patients and S2 in one of these patients. Heat pain activated S2, insular cortex and anterior cingulate cortex to a similar degree for both legs, but the activation was weaker in the patients than in the normals. For the individual patient, there was generally no obvious correlation between cortical activation as studied with the BOLD technique and psychophysical performance. The findings from tactile stimulation of the nonparetic leg, that the activation was similar to the contralateral activation in normals, suggest that tactile information processing in the hemisphere contralateral to the stimulation is independent of the corpus callosum. In contrast, the pain activation for the nonparetic leg was weaker than in normals, suggesting that pain activation in the hemisphere contralateral to the stimulation is dependent on transcallosal information processing. The latter finding was corroborated by a subnormal capacity for pain localization on the nonparetic foot in two of the patients. The findings from stimulation of the paretic leg show that areas typically involved in the processing of tactile and painful stimuli can be activated by ipsilateral pathways directly from the periphery. The tactile-evoked ipsilateral S1 activation may be due to subcortical reorganization, since it was not observed in the normal subjects.

Secondary calpain3 deficiency in 2q-linked muscular dystrophy: titin is the candidate gene

BACKGROUND

Tibial muscular dystrophy (TMD), a late-onset dominant distal myopathy, is caused by yet unknown mutations on chromosome 2q, whereas MD with myositis (MDM) is a muscular dystrophy of the mouse, also progressing with age and linked to mouse chromosome 2. For both disorders, linkage studies have implicated titin as a potential candidate gene.

METHODS

The authors analyzed major candidate regions in the titin gene by sequencing and Southern blot hybridization, and performed titin immunohistochemistry on TMD patient material to identify the underlying mutation. Western blot studies were performed on the known titin ligands in muscle samples of both disorders and controls, and analysis of apoptosis was also performed.

RESULTS

The authors identified almost complete loss of calpain3, a ligand of titin, in the patient with limb-girdle MD (LGMD) with a homozygous state of TMD haplotype when primary calpain3 gene defect was excluded. Apoptotic myonuclei with altered distribution of transcription factor NF-kB and its inhibitor IkBalpha were encountered in muscle samples of patients with either heterozygous or homozygous TMD haplotype. Similar findings were confirmed in the MDM mouse.

CONCLUSIONS

These results imply that titin mutations may be responsible for TMD, and that the pathophysiologic pathway following calpain3 deficiency may overlap with LGMD2A. The loss of calpain3 could be a downstream effect of the deficient TMD gene product. The significance of the secondary calpain3 defect for the pathogenesis of TMD was emphasized by similar calpain3 deficiency in the MDM mouse, which is suggested to be a mouse model for TMD. Homozygous mutation at the 2q locus may thus be capable of producing yet another LGMD.

Differential targeting of components of the dystrophin complex to the postsynaptic membrane

Accumulating evidence points to the participation of dystroglycan in the clustering of nicotinic acetylcholine receptors at the neuromuscular junction [Côté et al. (1999) Nature Genet., 3, 338--342]. Dystroglycan is part of a multimolecular complex, either associated with dystrophin (the dystrophin-associated protein complex) at the sarcolemma or with utrophin (the utrophin-associated protein complex) at the neuromuscular junction. Understanding the assembly of this complex at the developing synapse led us to investigate, in Torpedo electrocyte, the intracellular routing and the targeting of several of its components, including dystroglycan, syntrophin, dystrophin and dystrobrevin. We previously demonstrated that acetylcholine receptors and rapsyn, the 43-kDa receptor-associated protein at the synapse, are cotargeted to the postsynaptic membrane via the exocytic pathway [Marchand et al. (2000) J. Neurosci., 20, 521--528]. Using cell fractionation, immunopurification and immuno-electron microscope techniques, we show that beta-dystroglycan, an integral glycoprotein that constitutes the core of the dystrophin-associated protein complex localized at the innervated membrane, is transported together with acetylcholine receptor and rapsyn in post-Golgi vesicles en route to the postsynaptic membrane. Syntrophin, a peripheral cytoplasmic protein of the complex, associates initially with these exocytic vesicles. Conversely, dystrophin and dystrobrevin were absent from these post-Golgi vesicles and associate directly with the postsynaptic membrane. This study provides the first evidence for a separate targeting of the various components of the dystrophin-associated protein complex and a step-by-step assembly at the postsynaptic membrane.

In vitro and in vivo investigations on fluoroquinolones; effects of the P-glycoprotein efflux transporter on brain distribution of sparfloxacin

The role of mdr1a-encoded P-glycoprotein on transport of several fluoroquinolones across the blood-brain barrier was investigated. In vitro, P-glycoprotein substrates were selected by using a confluent monolayer of MDR1-LLC-PK1 cells. The inhibition of fluoroquinolones (100 microM) on transport of rhodamine-123 (1 microM) was compared with P-glycoprotein inhibitors verapamil (20 microM) and SDZ PSC 833 (2 microM). Subsequently, transport polarity of fluoroquinolones was studied. Sparfloxacin showed the strongest inhibition (26%) and a large polarity in transport, by P-glycoprotein activity. In vivo, using mdr1a (-/-) and wild-type mice, brain distribution of pefloxacin, norfloxacin, ciprofloxacin, fleroxacin and sparfloxacin was determined at 2, 4, and 6 h following intra-arterial infusion (50 nmol/min). Brain distribution of sparfloxacin was clearly higher in mdr1a (-/-) mice compared with wild-type mice. Sparfloxacin was infused (50 nmol/min) for 1, 2, 3 and 4 h in which intracerebral microdialysis was performed. At 4 h, in vivo recovery (dynamic-no-net-flux method) was 6.5+/-2.2 and 1.5+/-0.5%; brain(ECF) concentrations were 5.1+/-0.2 and 26+/-21 microM; and total brain concentrations were 7.2+/-0.3 and 23+/-0.3 microM in wild-type and mdr1a (-/-) mice, respectively. Plasma concentrations were similar (18.4+/-0.7 and 17.9+/-0.5 microM, respectively). In conclusion, sparfloxacin enters the brain poorly mainly because of P-glycoprotein activity at the blood-brain barrier.

Approaches to wine aroma: release of aroma compounds from reactions between cysteine and carbonyl compounds in wine

Under conditions close to those of wine, that is, low pH, aqueous medium, and low temperatures, this work examines the role of carbonyl (acetoin and acetol) and dicarbonyl (glyoxal, methylglyoxal, diacetyl, and pentane-2,3-dione) compounds associated with cysteine in the formation of odorous products. In particular, thiazole, 4-methylthiazole, 2-acetylthiazole, and trimethyloxazole and two sulfur and oxygenated heterocyclic compounds, 2-furanmethanethiol and thiophene-2-thiol, are examined. For thiophene-2-thiol, the reactional mechanism is proposed. Attempts were made to detect these compounds in wines from various origins. Certain molecules were identified for the first time in wine.

Developmental gene expression and immunohistochemical study of the human endocrine pancreas during fetal life

The development of human endocrine pancreas has been the subject of many immunohistochemical studies but very little is known at the molecular level. We have determined the patterns of gene expression of glucagon, somatostatin and pancreatic polypeptide during fetal life (16-41 weeks of gestation) using the dot-blot hybridization method. In spite of some dispersion in the mRNA levels, no progressive increase or decrease during this period of fetal life could be found, as previously observed for insulin. In keeping with these molecular data, no increase in immunostaining of the four hormones was observed, but a dispersion of endocrine cells within the exocrine tissue was noticed at 20 weeks of gestation followed by a clear differentiation of the Langerhans islets at 31 weeks. Interestingly, the mRNA levels of the four hormones were always higher in the fetal pancreas than in the adult pancreas.

[Mortality in a pediatric hospital. Six-year retrospective study]

AIMS

To define the characteristics of patients dying in a pediatric hospital, including causes and modes of death.

PATIENTS AND METHODS

This retrospective, descriptive, epidemiologic study was performed between 1 January 1990 and 31 December 1995. All patients who died in the hospital between these dates were included. Patients already dead on arrival (sudden infant death syndrome, children deceased during their transport), and those whose hospital records could not be found, were excluded.

RESULTS

A total of 375 children were studied, including 195 neonates. The sex ratio was 1.3. Ninety-one percent of deaths took place in three departments: intensive care, neurosurgery-neurology and oncology. Median duration of hospitalization was three days. The most common causes of deaths were accidents, neurologic diseases (particularly among neonates) and tumours. Analysis of modes of death revealed that 41.1% occurred following unsuccessful resuscitation, 38.8% were the result of withdrawal of life-support or a 'do not resuscitate' order and 21.6% resulted from brain death. Evolution of modes of death over the six years showed a reduction of cases with unsuccessful resuscitation, an increase in decisions of 'do not resuscitate' orders and withdrawal of life-support and no change in rates of brain death. Organs were made available for transplantation from 12 of the 81 children with brain death (14.8%).

CONCLUSION

Accidents were the most common cause of death. The distribution of deaths showed a clear increase in withdrawal or withholding of life-support care, relying on ethical decisions, which are more frequent than some years ago.

The torpedo electrocyte: a model system to study membrane-cytoskeleton interactions at the postsynaptic membrane

Many aspects of the organization of the electromotor synapse of electric fish resemble the nerve-muscle junction. In particular, the postsynaptic membrane in both systems share most of their proteins. As a remarquable source of cholinergic synapses, the Torpedo electrocyte model has served to identify the most important components involved in synaptic transmission such as the nicotinic acetylcholine receptor and the enzyme acetylcholinesterase, as well as proteins associated with the subsynaptic cytoskeleton and the extracellular matrix involved in the assembly of the postsynaptic membrane, namely the 43-kDa protein-rapsyn, the dystrophin/utrophin complex, agrin, and others. This review encompasses some representative experiments that helped to clarify essential aspects of the supramolecular organization and assembly of the postsynaptic apparatus of cholinergic synapses.

The myristoylated protein rapsyn is cotargeted with the nicotinic acetylcholine receptor to the postsynaptic membrane via the exocytic pathway

Rapsyn, a 43 kDa protein required to cluster nicotinic acetylcholine receptors (AChRs) at the neuromuscular junction, is tightly associated with the postsynaptic membrane via an N-terminal myristoylated site. Recent studies have shown that some acylated proteins associate with the exocytic pathway to become targeted to their correct destination. In this work, we used Torpedo electrocyte to investigate the intracellular routing of rapsyn compared to those of AChR and Na,K-ATPase, the respective components of the innervated and noninnervated membranes. We previously demonstrated that these latter two proteins are sorted and targeted to plasma membrane via distinct populations of post-Golgi vesicles (). Biochemical and immunoelectron microscopy analyses of various populations of post-Golgi vesicles immunopurified with magnetic beads led us to identify post-Golgi transport vesicles containing both rapsyn and AChR. These data suggest that rapsyn, as for AChR, specifically follows the exocytic pathway. Furthermore, immunogold-labeling experiments provided in situ evidence that AChR and rapsyn are cotransported in the same post-Golgi vesicles. Taken together, our observations suggest that rapsyn and AChR are cotargeted to the postsynaptic membrane.

A diagnostic fluorescent marker kit for six limb girdle muscular dystrophies

The autosomal progressive muscular dystrophies which are grouped together under the term limb girdle muscular dystrophies (LGMD) are diseases characterized by a progressive impairment of the proximal limb muscles and myopathic changes on electromyogram and muscle biopsy. Eight independent purely recessive genetic entities have been recognized in this group of diseases by genetic localization or causative gene identification. We have developed fluorescent genetic markers bracketing six of these loci (LGMD2A-LGMD2F). The marker loci were genotyped in 96 LGMD2 families leading to genetic definition of 25 of them either with a high likelihood or with a suggested localization (7 LGMD2A, 5 LGMD2B, 4 LGMD2C, 4 LGMD2D, 2 LGMD2E and 3 LGMD2F). In addition, 18 families were excluded for all six tested loci; for 45 of the 53 remaining families at least one exclusion could be demonstrated. This kit, which makes the rapid genetic testing of LGMD2 families possible, may be useful in a diagnostic process.

Studies on calpain expression during differentiation of rat satellite cells in primary cultures in the presence of heparin or a mimic compound

We have synthesized dextran derivatives called RGTAs (for regenerating agents) that were designed to mimic some of the properties of heparin or heparan sulfate to interact with and protect heparin binding growth factors. Some of these growth factors have been described to be involved in myogenesis control. In previous studies, we have shown that muscle regeneration in adults could be greatly enhanced in vivo by treatment with RGTA. Since muscle regeneration occurs through the activation of satellite cells, in the present study we have used primary cultures of rat satellite cells and treated them with the heparan sulfate analogue RGTA or heparin in order to stimulate their growth and differentiation. We also studied the effect of these substances on calpain (calcium-activated neutral proteases) expression in these cultures. Indeed, several reports, principally based on fetal myoblast cultures or myogenic cell lines, have suggested that calpains might be involved in myoblast fusion during myogenic differentiation. We therefore studied the expression of microcalpain (mu-calpain), millicalpain (m-calpain), and calpain 3 in the course of differentiation of these satellite cell cultures in the absence or in the presence of heparin or of a mimic compound (the RGTA RG1282). RGTA and heparin were shown to have a dual effect on satellite cell proliferation and differentiation: RGTA stimulated proliferation with a maximum dose effect at 1 microgam/ml. Heparin used at concentrations similar to those of RGTA was less efficient at stimulating proliferation. Both substances were shown, however, to induce precocious and enhanced differentiation of satellite cells. We showed by quantitative RT-PCR analysis that mu-calpain, m-calpain, and calpain 3 mRNAs were expressed in satellite cell cultures in proliferating myoblasts (day 3) and differentiating cultures (days 7 and 12). The level of mu-calpain mRNA was increased by a factor of 3 during differentiation of satellite cells, whereas the level of m-calpain mRNAs was slightly increased at day 12 only, and calpain 3 mRNA was slightly reduced in these differentiating cultures. Interestingly enough, RGTA and heparin, which both strongly increased differentiation, reduced the expression of the mu- and m-calpains and slightly increased that of calpain 3 in differentiating cultures. These results showed that there was no correlation between the extent of myoblast differentiation and the level of calpain expression in satellite cells grown in primary cultures and underscored the differences between these adult cells and fetal myoblasts.

Spinal opioid analgesia: how critical is the regulation of substance P signaling?

Although opioids can reduce stimulus-evoked efflux of Substance P (SP) from nociceptive primary afferents, the consequences of this reduction on spinal cord nociceptive processing has not been studied. Rather than assaying SP release, in the present study we examined the effect of opioids on two postsynaptic measures of SP release, Fos expression and neurokinin-1 (NK-1) receptor internalization, in the rat. The functional significance of the latter was first established in in vitro studies that showed that SP-induced Ca(2+) mobilization is highly correlated with the magnitude of SP-induced NK-1 receptor internalization in dorsal horn neurons. Using an in vivo analysis, we found that morphine had little effect on noxious stimulus-evoked internalization of the NK-1 receptor in lamina I neurons. However, internalization was reduced when we coadministered morphine with a dose of an NK-1 receptor antagonist that by itself was without effect. Thus, although opioids may modulate SP release, the residual release is sufficient to exert maximal effects on the target NK-1 receptors. Morphine significantly reduced noxious stimulus-induced Fos expression in lamina I, but the Fos inhibition was less pronounced in neurons that expressed the NK-1 receptor. Taken together, these results suggest that opioid analgesia predominantly involves postsynaptic inhibitory mechanisms and/or presynaptic control of non-SP-containing primary afferent nociceptors.

Human parvovirus B19 infection in organ transplant recipients

We report a 61-yr-old kidney transplant recipient with human Parvovirus B19 (HPV B19) infection presenting as a severe pancytopenia 1 month after transplantation. Bone marrow aspiration revealed severe erythroid hypoplasia with giant and dystrophic proerythroblasts. Bone marrow cells were positive for HPV B19 DNA detected by polymerase chain reaction (PCR). Pancytopenia resolved shortly after administration of intravenous immunoglobulins. Nineteen cases of HPV B19 infection in organ transplant recipients have been so far reported in the literature. Immunocompromised patients should be considered at risk from developing symptomatic HPV B19 infections. In such patients, specific anti-HPV B19 IgM and IgG antibodies may be absent or transient and therefore their negativity cannot rule out the diagnosis of HPV B19 infestation. Bone marrow smear morphological findings may suggest the diagnosis but testing for viral DNA by PCR is mandatory. Patients may spontaneously recover. However, since specific anti-viral therapy is not currently available, intravenous immunoglobulin administration appears to be the more efficacious treatment.

Developmental regulation of tyrosine phosphorylation of the nicotinic acetylcholine receptor in Torpedo electrocyte

Tyrosine phosphorylation is thought to play a critical role in the clustering of acetylcholine receptors (AChR) at the developing neuromuscular junction. Yet, in vitro approaches have led to conflicting conclusions regarding the function of tyrosine phosphorylation of AChR beta subunit in AChR clustering. In this work, we followed in situ the time course of tyrosine phosphorylation of AChR in developing Torpedo electrocyte. We observed that tyrosine phosphorylation of the AChR beta and delta subunits occurs at a late stage of embryonic development after the accumulation of AChRs and rapsyn in the membrane and the onset of innervation. Interestingly, in the mature postsynaptic membrane, we observed two populations of AChR differing both in their phosphotyrosine content and distribution. Our data are consistent with the notion that tyrosine phosphorylation of the AChR is related to downstream events in the pathway regulating AChR accumulation rather than to initial clustering events.