SUMMARY1. A study has been made of the formation of synapses in developing striated muscles which receive either a focal (the rat hemidiaphragm) or a distributed (the avian anterior latissimus dorsi) innervation using histological, ultrastructural and electrophysiological techniques.2. In the developing diaphragm only a single synaptic contact was initially established at random along the length of the short (300,um) myotubes by a single axon; in the developing ALD more than one synaptic contact could be established initially along the length of the long (2500 ,im) myotubes by axons, but the distance between these was never less than 170gm. 3. Each synapse established by the initial axonal contact in either the diaphragm or the ALD subsequently received a multiple innervation from further exploring axons in the muscles, and all such additional innervation of muscle cells was constrained to the sites of the initial synaptic contacts; this multiple innervation of synaptic sites was lost in the subsequent 4 weeks.4. It is suggested that the axon forming the initial synaptic contact on myotubes induces a property over an adjacent length of myotube which makes its membrane refractory to synapse formation over this length; this characteristic length is longer for axons forming a focal innervation than it is for those forming distributed innervation.

QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater-Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary-field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit and graphical processing unit systems. We detail the program's capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://qmcpack.org.

We outline ideas on desired properties for a new generation of effective core potentials (ECPs) that will allow valence-only calculations to reach the full potential offered by recent advances in many-body wave function methods. The key improvements include consistent use of correlated methods throughout ECP constructions and improved transferability as required for an accurate description of molecular systems over a range of geometries. The guiding principle is the isospectrality of all-electron and ECP Hamiltonians for a subset of valence states. We illustrate these concepts on a few first- and second-row atoms (B, C, N, O, S), and we obtain higher accuracy in transferability than previous constructions while using semi-local ECPs with a small number of parameters. In addition, the constructed ECPs enable many-body calculations of valence properties with higher (or same) accuracy than their all-electron counterparts with uncorrelated cores. This implies that the ECPs include also some of the impacts of core-core and core-valence correlations on valence properties. The results open further prospects for ECP improvements and refinements.

We review recent advances in the capabilities of the open source ab initio Quantum Monte Carlo (QMC) package QMCPACK and the workflow tool Nexus used for greater efficiency and reproducibility. The auxiliary field QMC (AFQMC) implementation has been greatly expanded to include k-point symmetries, tensor-hypercontraction, and accelerated graphical processing unit (GPU) support. These scaling and memory reductions greatly increase the number of orbitals that can practically be included in AFQMC calculations, increasing the accuracy. Advances in real space methods include techniques for accurate computation of bandgaps and for systematically improving the nodal surface of ground state wavefunctions. Results of these calculations can be used to validate application of more approximate electronic structure methods, including GW and density functional based techniques. To provide an improved foundation for these calculations, we utilize a new set of correlation-consistent effective core potentials (pseudopotentials) that are more accurate than previous sets; these can also be applied in quantum-chemical and other many-body applications, not only QMC. These advances increase the efficiency, accuracy, and range of properties that can be studied in both molecules and materials with QMC and QMCPACK.

The sympathetic nerve terminals of the mouse vas deferens were loaded with the calcium indicator Oregon Green 488 BAPTA‐1 by orthograde transport along the postganglionic nerves. Changes in the calcium concentration in the varicosity (Δ[Ca2+]v) were determined following single impulses, and short (5‐impulse) and long (200‐impulse) trains at 5 Hz. All varicosities showed a significant Δ[Ca2+]v in response to every single impulse. The elevated Δ[Ca2+]v declined in two phases with similar kinetics for all varicosities: a fast phase (time constant, 0.42 ± 0.05 s) and a moderate phase (3.6 ± 0.4 s). Line scanning confocal microscopy revealed that the Δ[Ca2+] of a single terminal following single impulses was smaller for the intervaricose regions than for the varicosities. Blockade of the voltage‐sensitive calcium channels with Cd2+ (in calcium‐free solution) completely blocked the Δ[Ca2+]v on stimulation. The addition of either nifedipine (10 μm), ω‐conotoxin GVIA (100 nM) or ω‐agatoxin TK (100 nm) showed that 47 ± 6% of the evoked response was mediated by N‐type calcium channels. Ryanodine (10 μm) did not significantly change the amplitude of Δ[Ca2+]v in response to short trains. Spontaneous increases in Δ[Ca2+]v were observed in individual varicosities, with coupling in the increase of Δ[Ca2+]v between varicosities. The presynaptic α2‐receptor antagonist yohimbine (10 μm) increased the amplitude of Δ[Ca2+]v in response to five impulses (5 Hz) by 54 ± 14%, while the α2‐receptor agonist clonidine (1 μm) decreased the Δ[Ca2+]v by 55 ± 4%. These results are discussed in terms of the hypotheses that the increased probability for secretion at sympathetic nerve terminals which accompanies facilitation and augmentation is due to the residual Δ[Ca2+]v remaining after the calcium influx following impulses and that noradrenaline acts presynaptically to decrease the probability of secretion by modifying calcium influx.

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SUMMARY1. The hemidiaphragm of the adult rabbit has a single band of endplates running around the middle of the muscle. A study has been made of the formation of synapses during spontaneous reinnervation of this muscle, using histological, ultrastructural and electrophysiological techniques.2. Following spontaneous reinnervation, silver-stained nerve terminals were found in association with cholinesterase-stained end-plates only in the region of the muscle corresponding to the original innervation band. 3. The regenerated nerve terminals were observed with the electronmicroscope in positions overlying or adjacent to the old synaptic folds.4. Spontaneous miniature end-plate potentials and evoked synaptic potentials were recorded only in the middle of the muscle fibres after remnervation. 5. The growth of the regenerating axons was not oriented towards the end-plate zone but followed muscle fibres and blood vessels in random directions.6. It is concluded that, in adult mammalian striated muscle, the old end-plate region is preferentially reinnervated as a consequence of some special property of the muscle fibre at this site.

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