Stimulated single-fiber electromyography in Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission. Electrodiagnosis is confirmed by an increase in compound muscle action potential amplitude during high-frequency repetitive nerve stimulation or following brief exercise. We describe the results of stimulated single-fiber electromyography in 4 patients with disorders of neuromuscular transmission: LEMS (2), LEMS/myasthenia gravis (MG) overlap (1), and MG (1). Stimulated SFEMG was performed in the extensor digitorum communis muscle with axonal intramuscular suprathreshold stimulation at low and high rates. In all 4 patients, a rate dependence of jitter was found. In LEMS and LEMS/MG, jitter and blocking improved with high stimulation rates, as compared with the opposite effect in MG. We conclude that stimulated SFEMG is a valuable technique in the diagnosis of LEMS.

Corticosteroid-responsive dominantly inherited neuropathy in childhood

We describe three children with corticosteroid-responsive inflammatory demyelinating polyneuropathy from families with dominantly inherited neuropathy. There were atypical clinical, electrophysiologic, and pathologic characteristics that suggested a coexistent inflammatory demyelinating neuropathy and that should alert the clinician to the possibility of an associated acquired, potentially treatable disorder.

Peripheral neuropathy associated with eosinophilia-myalgia syndrome

In 1989, the Centers for Disease Control recognized the existence of an epidemic illness characterized by myalgia and eosinophilia in individuals taking preparations containing L-tryptophan. We evaluated 3 patients with eosinophilia-myalgia syndrome who presented with subacute progressive neuropathies. The neuropathies were predominantly motor and maximal in the lower extremities. Two patients were confined to a wheelchair and one was ventilator-dependent and bedridden. Sensory loss predominantly involved small fiber modalities. Electrophysiological studies showed multifocal marked conduction slowing and conduction block indicating segmental demyelination, with associated axonal degeneration that was accentuated distally. Examination of sural nerve biopsy specimens demonstrated axonal degeneration in all 3 patients and perivascular infiltrates in 2. Levels of quinolinic acid, a neurotoxic metabolite of L-tryptophan, were elevated in the cerebrospinal fluid in the 2 patients in whom it was measured. The cause of the neuropathy is unknown but may include immune mechanisms or toxicity of eosinophils, L-tryptophan, its metabolic products, or contaminants within L-tryptophan preparations.

Evidence for a dipeptide porter in the lysosome membrane

Small neutral dipeptides such as Gly-Gly are known to cross the lysosome membrane rapidly. The mode of dipeptide translocation was studied, using an osmotic-protection method. Results with dipeptide analogues, such as omega-amino aliphatic acids and taurine, indicated that dipeptides do not cross the rat liver lysosome membrane by unassisted diffusion. Using seven pairs of dipeptide stereoisomers, the penetration of the L-isomer was always found to be much more rapid than that of the D-analogue. It is concluded that the lysosome membrane contains a porter that recognizes and transports L-dipeptides.

Genetic testing for neurologic diseases. A rose with thorns

Genetic testing for neurologic conditions, including HD, requires that the primary concerns of informed consent, counseling and support, and confidentiality be recognized and addressed. A safe, reliable test should be available to those who want the information and understand the limitations of the testing procedure. However, testing should be in the context of multifaceted counseling, which combines a variety of components. Safeguards for confidentiality should be assured. Predictive testing for hereditary disease emphasizes the need to focus on capabilities rather than disability. This is an extension of the larger reality that continuing advances in health care can extend the length of an individual's life and stave off death without restoring health. Certainly, new developments in molecular biology may provide new tools, but the basic ethical problems are fundamental issues independent of technology. Just as change is not necessarily progress, the application of scientific advances to health care does not automatically benefit humanity. Sensitivity to human needs is the art of applying medical technology.

Passive diffusion of non-electrolytes across the lysosome membrane

An osmotic-protection method has been used to study the permeability of rat liver lysosomes to 43 organic non-electrolytes of formula weights ranging from 62 to 1000. A lysosome-rich centrifugal fraction of rat liver homogenate was resuspended in an unbuffered 0.25 M solution of test solute, pH 7.0, and incubated at 25 degrees C for 60 min. The free and total activities of 4-methylumbelliferyl N-acetyl-beta-D-glucosaminidase were measured after incubation for 0, 30 and 60 min. Three patterns of results were seen. In pattern A the percentage free activity remained low throughout the 60 min incubation, indicating little or no solute entry into the lysosomes. In pattern B, the percentage free activity was initially low, but rose substantially during the incubation, indicating solute entry. In pattern C there was not even initial osmotic protection, indicating very rapid solute entry. The rapidity of solute entry into the lysosomes showed no correlation with the formula weight, but a perfect inverse correlation with the hydrogen-bonding capacity of the solutes. The results, which can be used to predict the ability of further compounds to cross the lysosome membrane by unassisted diffusion, are discussed in the context of metabolite and drug release from lysosomes in vivo.

Translocation of sugars into rat liver lysosomes. Evidence against a common carrier for D-glucose and D-ribose

A conflict exists in the literature concerning the mode of translocation of D-glucose and D-ribose across the lysosome membrane. The more rapid net uptake of ribose, when measured by the osmotic-protection technique, has been attributed either to its smaller size and lower hydrogen-bonding capacity, or to a lower affinity for a transport system shared by both sugars. The latency of acid beta-hexosaminidase in isolated rat liver lysosomes was measured after preincubation for periods up to 1 h in various solutions containing glucose and/or ribose, and in some cases sucrose. After confirmation of the superior osmotic protection afforded by glucose (than by ribose), it was shown that a solution 0.125 M in both glucose and ribose provided protection intermediate between that given by 0.25 M-glucose and that given by 0.25 M-ribose. This result is inconsistent with the common-carrier hypothesis.

Presymptomatic testing for Huntington's disease

Recombinant DNA technology has made possible the identification of a DNA marker for Huntington's disease (HD). In spite of limitations to a presymptomatic test based on this work, and a variety of ethical and policy concerns associated with presymptomatic testing in general, it is likely that such a testing program can and will soon be developed. Its impact needs to be carefully considered by the health care community and policymakers. A presymptomatic test for HD is sought by those at risk and should be made available with proper safeguards to protect confidentiality. Given its potential impact, testing should be offered in a setting that provides diverse and continuing support. Research institutions with a variety of counseling programs, health care professionals, HD lay organizations, and society at large can work together to develop programs that provide the support necessary for responsible, autonomous decision making.

Effects of neuronal activity on kainic acid neurotoxicity in the ventral cochlear nucleus

Kainic acid was injected into the brain stem of adult guinea pigs, and the animals were either placed in a sound reducing-chamber or stimulated with 90 dB noise. The pattern and rate of kainic acid-induced degeneration in the anteroventral cochlear nucleus (AVCN) of sound-deprived animals was similar to that in animals exposed to ambient noise [2]. The amount of degeneration was greatly increased in animals stimulated with 90 dB noise. Therefore, although decreased activity in primary auditory fibers does not protect neurons in the AVCN from kainate-induced neurotoxicity, increased auditory stimulation augments the effects of kainic acid in the cochlear nucleus.

Kainic acid injections result in degeneration of cochlear nucleus cells innervated by the auditory nerve

When kainic acid, a putative neurotoxin for neurons with glutamatergic input, is injected into the brainstem, it produces a selective pattern of degeneration in the cochlear nucleus. The rate and extent of degeneration is correlated with the distribution of the primary auditory fibers. This evidence supports the hypothesis that glutamate is the neurotransmitter for primary auditory fibers.

Iontophoretic application of opiates to the locus coeruleus

The vast majority of morphine-sensitive single units in the area examined were localized to the locus coeruleus. This corresponds well with the known distribution of the highest densities of opiate receptor sites in this region of the midbrain. The effect of iontophoretically applied morphine was a marked and prolonged depression of spontaneous activity. Levorphanol, an opiate agonist, produced an effect similar to that of morphine while comparable doses of dextrorphan, it's clinically inactive stereoisomer, did not. Naloxone and levallorphan prevented as well as reversed the depression due to application of agonists. While the units were depressed following the application of opiate agonists, the cells were still excited by the neurotransmitter acetylcholine. We conclude that (1) neuronal sensitivity to opiates has a high positive correlation with autoradiographically determined opiate receptor sites, and (2) this sensitivity to opiates is blocked by opiate antagonists and is stereospecific in nature.

Denervation supersensitivity in the cholinergic septo-hippocampal pathway: a microiontophoretic study

The purpose of this study was to determine whether denervation supersensitivity could be produced in an identified cholinergic pathway in the CNS of the rat. The mechanism for the development of this phenomenon was also explored. Cholinergic denervation of the hippocampus was accomplished by lesions of the medial septum. The response of hippocampal pyramidal cells to microiontophoretic application of acetylcholine (ACh) and carbachol in lesioned and unlesioned animals was determined by extracellular recording. There was a marked increase (6 X) in sensitivity to ACh 2-43 days following lesions. However, there was no increase in sensitivity to carbachol or glutamate. Other workers have shown that septal lesions cause a large decrease in hippocampal acetylcholinesterase (AChE) which is located mainly presynaptically. The absence of increase in sensitivity to carbachol, a cholinomimetic resistant to hydrolysis by AChE, suggests that the postlesion increase in sensitivity to ACh results from a decrease in its inactivation by AChE. A time course for the development of ACh supersensitivity was found to be similar to the time course of AChE loss previosly reported. Experiments using physostigmine, an AChE inhibitor, demonstrated that inhibition of AChE can potentiate the effects of ACh in unlesioned preparations, but not in lesioned preparations. We conclude: (1) denervation supersensitivity to ACh occurs in the septo-hippocampal pathway; and (2) the supersensitivity is probably due to decreased inactivation of ACh by AChE. The results suggest that presynaptic AChE plays a significant role in modulating the neurotransmitter function of ACh in the septo-hippocampal pathway.