Joseph J. McArdle

Neurons Derived From Human Mesenchymal Stem Cells Show Synaptic Transmission and Can Be Induced to Produce the Neurotransmitter Substance P by Interleukin‐1α

Mesenchymal stem cells (MSCs) exhibit immune‐suppressive properties, follow a pattern of multilineage differentiation, and exhibit transdifferentiation potential. Ease in expansion from adult bone marrow, as well as its separation from ethical issues, makes MSCs appealing for clinical application. MSCs treated with retinoic acid resulted in synaptic transmission, based on immunostaining of synaptophysin and electrophysiological studies. In situ hybridization indicated that the neurotransmitter gene preprotachykinin‐I was expressed in these cells. However, translation of this gene only occurred after stimulation with interleukin (IL)‐1α. This effect was blunted by costimulation with IL‐1 receptor antagonist. This study reports on the ability of MSCs to be transdifferentiated into neurons with functional synapses with the potential to become polarized towards producing specific neurotransmitters.

Advances in neurobiology of the neuromuscular junction: implications for the anesthesiologist.

THE mammalian neuromuscular junction (NMJ) is one of the most studied and best understood synapses. Recent work has brought forth new information as to development, maturation, and function of this fundamental synapse, both in health and disease. The healthy function of the NMJ underlies one important measurement of the response to general anesthetics, immobility. “Neuromuscular blockers” acting directly at the NMJ are used as a component of many balanced anesthetic techniques, and the health of the NMJ profoundly influences anesthetic technique. For these reasons, it is imperative that anesthesiologists be aware of new developments in the field. The normal development, maturation, and function of the NMJ are discussed. Diseases of the NMJ are also reviewed with emphasis on new etiologic, pathologic, and treatment-oriented information.

Complex end-plate potentials at the regenerating neuromuscular junction of the rat

Intracellular recordings of end-plate potentials (epps) were made in cut fiber preparations of reinnervating extensor digitorum longus muscles at various times after crushing the deep peroneal nerve. Beginning at 9 days after nerve crush, reinnervation was associated with the presence of multi-peaked epps. The percentage of fibers having such complex epps increased from 9% at 10 days to a maximum of 31% at 18 days. The complex epps could be fractionated into distinct peaks of different latencies by varying the intensity of nerve stimulation. Complex epps were also found in nerve muscle preparations that had been blocked with MgCl2 or d-tubocurarine. In the presence of elevated MgCl2 and lowered CaCl2, the component peaks of complex epps failed separately. Similar complex epps were not found in control muscles. It is suggested that mammalian muscle fibers are multi-innervated during the early stages of reinnervation.

Molecular aspects of the trophic influence of nerve on muscle

1. Opening comments 2. The acetylcholine receptor system 2.

Low-affinity sulfonylurea binding sites reside on neuronal cell bodies in the brain.

The antidiabetic sulfonylurea drugs bind to sites associated with an ATP-sensitive potassium (Katp) channel on cell bodies and terminals of neurons which increase their firing rates or transmitter release when glucose concentrations rise or sulfonylureas are present. High-affinity sulfonylurea binding sites are concentrated in areas such as the substantia nigra (SN) where glucose and sulfonylureas increase transmitter release from GABA neurons. But there is a paucity of high-affinity sites in areas such as the hypothalamic ventromedial nucleus (VMN) where many neurons increase their activity when glucose rises. Here we assessed both high- and low--affinity sulfonylurea binding autoradiographically with 20 nM [3H]glyburide in the presence of absence of Gpp(NH)p. Neurotoxin lesions with 6-hydroxydopamine (6-OHDA), 5,7-dihydroxytryptamine (5,7-DHT) and ibotenic acid were used to elucidate the cellular location of the two sites in the VMN, SN and locus coeruleus (LC). In the VMN, 25% of the sites were of low affinity. Neither 6-OHDA nor 5,7-DHT affected [3H]glyburide binding, while ibotenic acid reduced the number of VMN neurons and abolished low-affinity without changing high-affinity binding. In cell-attached patches of isolated VMN neurons, both 10 mM glucose and 100 microM glyburide decreased the open probability of the Katp channel suggesting that the low-affinity binding site resides on these neurons. In the SN pars reticulata, ibotenic acid reduced the number of neurons and high-affinity [3H]glyburide binding was decreased by 20%, while 6-OHDA had no effect. In the SN pars compacta, both 6-OHDA and ibotenic acid destroyed endogenous dopamine neurons and selectivity ablated low-affinity binding. In the LC, 6-OHDA destroyed norepinephrine neurons and abolished low-affinity binding. These data suggest that low-affinity sulfonylurea binding sites reside on cell bodies on VMN, SN dopamine and LC norepinephrine neuron cell bodies and that high-affinity sites may be on axon terminals of GABA neurons in the SN.

Severe botulism after focal injection of botulinum toxin

We report a 34-year-old woman who developed clinical botulism after the cosmetic use of an unapproved botulinum toxin type A. Electrophysiologic findings demonstrated complete denervation with complete electrical silence. She had a lengthy recovery but was able to ambulate by discharge.

Phosphorylation modulates the activity of the ATP-sensitive K+ channel in the ventromedial hypothalamic nucleus.

Regulation of the ATP-sensitive K+ (K-ATP) channel was examined in cell-attached and inside-out membrane patches of freshly isolated neurons from the ventromedial hypothalamic nucleus (VMN) of 7-14 day old male Sprague-Dawley rats. When inside-out patches were exposed to symmetrical K+, the reversal potential was -2.85 +/- 1.65 mV, the single channel conductance 46 pS, and the total conductance varied as a multiple of this value. Glucose (10 mM) reversibly inhibited channel activity in cell-attached preparations by 81%. In the presence of 0.1 mM ADP, 10, 5, and 1 mM ATP reversibly inhibited VMN K-ATP channels in inside-out patches by 88, 83, and 60%, respectively. This inhibition was not dependent on phosphorylation since 5 mM AMPPNP, the non-hydrolyzable analog of ATP, reversibly inhibited channel activity by 67%. Relatively high concentrations of glibenclamide (100 microM) also reversibly inhibited VMN K-ATP channel activity in cell attached and inside-out patches by 67 and 79%, respectively. Finally, the non-specific kinase inhibitor H7 (200 microM) decreased channel activity by 53% while the non-specific phosphatase inhibitor microcystin (250 nM) increased channel activity by 218%. These data suggest that while the inhibitory effect of ATP is not phosphorylation dependent, phosphorylation state is an important regulator of the VMN K-ATP channel.

Cocaine depresses GABAA current of hippocampal neurons.

Although blockade of dopamine re-uptake and the resulting elevation of excitatory agonists is commonly thought the primary mechanism of cocaine-induced seizures, it is possible that other neurotransmitters such as gamma-aminobutyric acid (GABA) are involved. To examine this possibility, the effects of cocaine on the whole cell GABA current (IGABA) of freshly isolated rat hippocampal neurons were investigated with the patch-clamp technique. Preincubation or acute application of cocaine reversibly suppressed IGABA. The IC50 was 127 microM when cocaine was applied before the application of GABA. The concentration-response relations of cocaine in various GABA concentrations revealed that cocaine inhibited IGABA non-competitively. This effect of cocaine appeared to be independent of voltage. The present study suggests that the GABA receptor/channel complex is also a target for cocaines action. The suppression of IGABA may contribute to cocaine-induced seizures.

Essential roles of the acetylcholine receptor γ-subunit in neuromuscular synaptic patterning

Formation of the vertebrate neuromuscular junction (NMJ) takes place in a stereotypic pattern in which nerves terminate at select sarcolemmal sites often localized to the central region of the muscle fibers. Several lines of evidence indicate that the muscle fibers may initiate postsynaptic differentiation independent of the ingrowing nerves. For example, nascent acetylcholine receptors (AChRs) are pre-patterned at select regions of the muscle during the initial stage of neuromuscular synaptogenesis. It is not clear how these pre-patterned AChR clusters are assembled, and to what extent they contribute to pre- and post-synaptic differentiation during development. Here, we show that genetic deletion of the AChR γ-subunit gene in mice leads to an absence of pre-patterned AChR clusters during initial stages of neuromuscular synaptogenesis. The absence of pre-patterned AChR clusters was associated with excessive nerve branching, increased motoneuron survival, as well as aberrant distribution of acetylcholinesterase (AChE) and rapsyn. However, clustering of muscle specific kinase (MuSK) proceeded normally in theγ -null muscles. AChR clusters emerged at later stages owing to the expression of the AChR epsilon-subunit, but these delayed AChR clusters were broadly distributed and appeared at lower level compared with the wild-type muscles. Interestingly, despite the abnormal pattern, synaptic vesicle proteins were progressively accumulated at individual nerve terminals, and neuromuscular synapses were ultimately established in γ-null muscles. These results demonstrate that the γ-subunit is required for the formation of pre-patterned AChR clusters, which in turn play an essential role in determining the subsequent pattern of neuromuscular synaptogenesis.

Identification of residues at the α and ε subunit interfaces mediating species selectivity of Waglerin-1 for nicotinic acetylcholine receptors

Waglerin-1 (Wtx-1) is a 22-amino acid peptide that is a competitive antagonist of the muscle nicotinic receptor (nAChR). We find that Wtx-1 binds 2100-fold more tightly to the α-ε than to the α-δ binding site interface of the mouse nAChR. Moreover, Wtx-1 binds 100-fold more tightly to the α-ε interface from mouse nAChR than that from rat or human sources. Site-directed mutagenesis of residues differing in the extracellular domains of rat and mouse ε subunits indicates that residues 59 and 115 mediate the species difference in Wtx-1 affinity. Mutation of residues 59 (Asp in mouse, Glu in rat ε) and 115 (Tyr in mouse, Ser in rat ε) converts Wtx-1 affinity for the α-ε interface of one species to that of the other species. Studies of different mutations at position 59 indicate both steric and electrostatic contributions to Wtx-1 affinity, whereas at position 115, both aromatic and polar groups contribute to affinity. The human nAChR also has lower affinity for Wtx-1 than mouse nAChR, but unlike rat nAChR, residues in both α and ε subunits mediate the affinity difference. In human nAChR, polar residues (Ser-187 and Thr-189) confer low affinity, whereas in mouse nAChR aromatic residues (Trp-187 and Phe-189) confer high affinity. The overall results show that non-conserved residues at the nAChR binding site, although not crucial for activation by ACh, govern the potency of neuromuscular toxins.