Presynaptic irregularity and pacemaker inhibition

It is known (e.g., Perkel et al., 1964) that when a pacemaker neuron elicits IPSP's in another, there are domains called paradoxical segments where in the steady-state i) faster inhibitory discharges determine faster inhibited ones, and ii) pre- and postsynaptic spikes are locked in an invariant forward-and-backward positioning in time, spikes alternating in the ratios 1:1 (1 pere for 1 postsynaptic), 1:2, 2:1..., that are also the slopes of the synaptic rate-transformation. The present project examined the matter further in the inhibitory synapse upon the crayfish tonic stretch receptor neuron, confirming the above. In addition it showed that locking and alternation existed also in the segments interposed between the 1:2, 1:1 and 2:1 paradoxical segments, even though they were not as marked and apparent, and that when tests were close to each other their order became influential and hysteresis-like phenomena appeared. The main finding was that paradoxical rate-relations, locking and alternation persisted when the presynaptic train was irregularized up to interval coefficients of variation of around 0.20 (Figs. 2–5). Therefore, both phenomena may not simply be laboratory curiosities, but also have a role in natural operation where probably a substantial population of neurons exhibits that kind of irregularity. As presynaptic irregularity increased, the paradoxical segment slopes and widths decreased and locking and alternation became less clear-cut. With CV's of about 0.20, only a relatively narrow 1:1 paradoxical segment with about O slope and little locking and alternation remained (Figs. 2b, 3g, 4right, 5third row). With larger CV's, the rate relation decreased monotonically and there was no locking nor alternation (Figs. 2e, 3h, 5bottom row). The postsynaptic discharge was more regular and had fewer changes in the number of presynaptic spikes per post-synaptic interval within paradoxical segments (particularly in their centers) than in segments interposed between them (left vs. right-hand columns in Figs. 5, 6; Fig. 7): the contrast, remarkable for regular stimuli, attenuated as variability increased. The following conclusions are relevant to coding of spike trains across a synapse with IPSP's. i) With fairly regular discharges, the same postsynaptic rate may result from several presynaptic ones (e.g., may result from rates in the 1:1 and 2:1 paradoxical segments and in the interposed one, Fig.2): in some cases but not others, the precise presynaptic rate can be identified on the basis of postsynaptic CV's, interval histograms and cycle slips. ii) A small rate change in a regular presynaptic discharge will have very different postsynaptic consequences depending on where it happens: if across a paradoxical-interposed boundary, for instance, it will cause remarkable rate, pattern and correlation changes. iii) The trans-synaptic mapping of variability involves an increase for the more regular presynaptic discharges and a decrease for the more irregular ones. iv) The postsynaptic discharge was slower with IPSP's than without in most cases; however, when the control discharge was weak or absent, IPSP's accelerated it. Results are relevant also to the operation of periodically performing systems that involve neuronal correlates, indicating that it is necessary in every case to ask whether zigzag relations and locking occur. The delay function plots the arrival time of an IPSP (or IPSP burst) relative to the last postsynaptic spike, i.e., the phase ( in Fig. 1b), against the interval lengthening produced, i.e., the delay (). In all cases, most points clustered around a straight line (Fig. 8), whose slope and ordinate intercept were in the 0.43–0.87 and the 0.02–0.52 ranges, respectively, for single IPSP's. The slope reflects how the IPSP effectiveness depends on when it arrives in the cycle; the intercept reflects the IPSP effectiveness. Large phases often showed aberrant points whose ordinates were either large (and having special formal implications), or very small (perhaps reflecting conduction and synaptic delays), or clustered around a second straight segment with a large negative slope (when spontaneous rates were low) (Fig. 8c). Delay functions for widely separated pairs of IPSP's could be multi-valued, points clustering around 2 or 3 parallel straight lines. A mathematical model of pacemaker inhibitory synaptic interactions (Segundo, 1979) agreed with this embodiment insofar as some postulated properties are concerned (e.g., regular discharge, interval lengthening by IPSP's, linear delay functions with slopes around 0.7) and as to the main aspects of the preparation's behavior (i.e., zigzag rate relations and locking), but not in terms of some aspects of the postulates (e.g., interval variability, rebound) or behavior (e.g., segment boundaries, jitter in the locking, and hysteresis). The model was judged to be on the balance satisfactorily realistic.Supported by funds from the Brain Research Institute, UclaSupported by FAPESP (Sao Paulo, Brazil)     

A model of excitatory synaptic interactions between pacemakers. Its reality,its generality,and the principles involved

This is a model of the steady-state influence of one pacemaker neuron upon another across a synapse with EPSP's. Its postulates require firstly the spontaneous regularity of both cells, whose intervals are E and N, respectively. In addition, they require a special shortening or negative delay of the interspike interval by one or more EPSP's, with a V-shaped dependence of the delay on the position or phase of the EPSP's in the interval; the minimum of the delay function corresponds to the earliest EPSP arrival phase () that triggers a spike immediately. Finally, they impose on the variables certain bounds. The model's behavior has two main features. The first is a zig-zag relationship with an overall increasing trend between the steady-state pre- and post-synaptic discharge intensities (Fig. 7). The zig-zag is formed predominantly, if not exclusively, by segments with positive slopes that are rational fractions. Passage from one such segment to others is negatively-sloped (paradoxical), involving staggered positively-sloped segments whose details are unclear for weak presynaptic discharges and discontinuities for intense discharges. The same postsynaptic intensity may result from several presynaptic ones; the maximum postsynaptic intensity may reflect refractoriness, or the earliest instants of immediate triggering. The second main feature is the locking of the discharges in an invariant forward and backward temporal relation. With at most one EPSP per postsynaptic spike, locking is always present. If the presynaptic interval E is in the closed {rN+,(r+1)N} range, locking is 1:r+1, either stable at a greater-than- phase or unstable at a smaller one; arrivals at integral multiples of N do not affect the postsynaptic intensity. If E is in {rN, rN+} (r>0), locking is at other ratios (e.g., 2:3) and less apparent. With more than one EPSP per spike, when E is below bounds that depend on the interspike interval and the point of earliest triggering, locking happens in the simple s:1 ratio (s=2,3, ...) and is stable; when E is above those bounds, there are E ranges where locking is in other ratios (e.g., 3:2) and ranges where behavior is unclear. The validity of any model is based jointly upon an a priori judgment as to whether postulates depart reasonably little from nature, and upon an a posteriori experimental comparison of modelled and real behaviors. The model's domain of applicability depends on the specific embodiment, each of the latter tolerating characteristically each departure. The present model will be evaluated in the crayfish stretch-receptor neuron (Diez-Martínez et al., in preparation). The model is applicable to any physical system that complies with its postulates, and evidence compatible with this notion is available in many disparate fields. It illustrates the modelling path to a scientific proposition, other paths being inference from experimentation, or deduction from premises acceptable at other approach levels (in this case, for example, from that of synaptic mechanisms). The periodicity postulates set this model within the category of those for oscillators. The notion of an oscillator has a far broader applicability than appears at first sight, since all physically realizable systems have some predominant output frequency, i.e., to a certain extent are oscillators.Supported by funds from the Brain Research Institute, UCLASupported by FAPESP (Sao Paulo, Brazil). Present address: Esc. Politecnica, Dee, University of Sao Paulo, Cid. Univ., CP 8174 Sao Paulo, S.P., Brazil     

Special somatic spine synapses in the ciliary ganglion of the chick

Summary Somatic spine synapses modified with postsynaptic electron opaque materials were found in the axo-somatic ciliary ganglion synapse of the chick.A part of the postsynaptic cell body protrudes into the presynaptic calyciform ending as a somatic spine with about 1 in length and 0.15 in diameter, and forms the so-called synaptic complex with presynaptic process. Moreover, conspicuous electron opaque materials can be seen in the central axis of the spine, except for its end portion. Sometimes, these opaque materials are seen as arrayed dots.The morphological characteristics of the somatic spine synapses in this study are quite similar to that found in the habenula and interpeduncular nuclei of the cat (Milhaud and Pappas, 1966). the biological significance of which is obscure at present.This work was supported in part by grant from the Education Ministry of Japan.     

Electron microscopy of taste buds of the rat

Summary The taste buds of the circumvallate papillae have been examined by electron microscopy in OsO₄-fixed, PTA stained material or after KMnO₄ fixation. The microvilli of the receptor cells have terminal dilatations which presumably give an increased surface area for transduction. The extracellular spaces at the necks of the receptor cells near the bases of the microvilli are interrupted by closed contacts.The synapses have a well defined synaptic cleft suggesting a chemical rather than an electrical mode of transmission. Synaptic membrane specialisations differ from the membrane thickenings of other types of synapse. Presynaptic dense projections are present but there is no well define postsynaptic thickening. Vesicles occur in both pre- and postsynaptic components, but it is debatable whether or not they should be termed synaptic vesicles. Acknowledgements. We are indebted to Professor J. Z. Young, F. R. S., for his stimulating support, and to Mr. S. Waterman for skilled photography.     

Ultrastructure of motor nerve terminals on different types of muscle fibers in the atlantic hagfish (Myxine glutinosa,L.)

Summary White and intermediate parietal muscle fibers of Myxine are innervated focally at one end. Most synaptic vesicles are empty. These terminals also contain 1–2% large 800–1.100 Å dense-core vesicles. Red fibers of parietal and craniovelar muscle are innervated in a distributed fashion, and the presynaptic profiles contain a higher number of large dense-core vesicles (averaging 9% and 15%, respectively; up to 37%). For all terminals the synaptic gap is 450–600 Å wide, and postsynaptic folds are absent.Empty synaptic vesicles exist as round or elongated profiles. The proportion of elongated profiles increases by formation from round ones when increasing the molarity of the buffer in the aldehyde fixative. Furthermore, the proportion of elongated vesicle profiles in terminals on Myxine white fibers at different buffer molarities, is identical with that in mammalian motor terminals at similar molarities. On this basis the significance and mode of formation of elongated vesicle profiles is discussed. The conclusion is made that the susceptibility of flattening depends on the osmotic pressure of the vesicle contents once the aldehyde has influenced the vesicle membrane.The different vesicle populations in terminals on different types of muscle fibers are significant. Terminals on red fibers probably contain serotonin (5-HT) either as sole transmitter or in addition to acetylcholine.The author is indebted to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supply of hagfishes, and to Mrs. Jorunn Line Vaaland for expert technical assistance.     

Synaptic organization of the cabbage looper moth ocellus

Summary Chemical and electronic synapses are present in the ocellar synaptic region of the moth, Trichoplusia ni. The chemical synapses all appear to be of the conventional type. Four different chemical synaptic contacts were observed: Receptor cell axons presynaptic to receptor cell axons, receptor cell axons presynaptic to 1st order interneurons, 1st order interneurons presynaptic to receptor cell axons, and 1st order interneurons presynaptic to 1st order interneurons. Two different types of contact made by electronic synapes were observed: Contacts between receptor cell axons and 1st order interneurons, and contacts between 1st order interneurons. The significance of this synaptic arrangement for the generation of on and off responses in the 1st order interneurons is discussed.Supported by NSF Grant BMS 75-07645 and by the VPI & SU Research Division     

\4 integrin expression onin vitro andin vivo metastatic variants of lewis lung carcinoma

The expression of 4, 6, and 1 integrin subunits has been investigated on somein vitro andin vivo murine metastatic variants derived from Lewis lung carcinoma (3LL). By the use of monoclonal antibodies which recognizes different epitopes of 6, 1, and 4 subunits we demonstrate that 6 and 1 subunits are expressed in all metastatic variants of 3LL irrespective of their metastatic potential, whereas 4 subunit is expressed only in highly metastasizing cells of 3LL. Northern blots of different metastatic variants probed with 1 and 4 subunits demonstrate thata) significant amounts of 1 mRNA were detected in all metastatic variants of 3LL;b) mRNA corresponding to the described entire coding sequence of 4 subunit is expressed only on highly metastasizing cells of 3LL. We conclude that 4 subunit is specifically expressed in highly metastasizig cells of 3LL while is undetectable in lower metastasizing ones.     

Vacant postsynaptic densities on supraoptic dendrites of adult rats diminish in number with chronic stimuli

Summary In earlier ultrastructural studies of the supraoptic nucleus in adult rats we noted free and incompletely covered postsynaptic densities (collectively referred to here as vacant postsynaptic densities) on dendritic shafts. Free postsynaptic densities have been reported in other parts of the central nervous system of normal rodents. We investigated the possibility that physiological activation of the supraoptic cells, which produces changes in many aspects of their morphology, would alter the incidence of the free or incompletely covered postsynaptic densities on dendrites in the supraoptic basal dendritic zone. The cells of the supraoptic nucleus are activated to increase cell firing and secretion of oxytocin and/or vasopressin in response to dehydration, gestation, and lactation. We have examined: (i) untreated virgin females; (ii) untreated males; (iii) 24 h water-deprived males; (iv) prepartum (21st day of gestation) females; (v) postpartum females (on the day of parturition); (vi) lactating females (14 days of suckling); (vii) mothers 10 days after weaning their pups; (viii) females given 2% saline to drink (dehydrated) for 10 days; and females or males given 2% saline to drink for 10 days, then given tap water for (ix) 2 or (x) 5 weeks to allow rehydration. Only long-term activation of the supraoptic nucleus by lactation or by drinking saline for 10 days brought about significant decreases in the percentage of dendrites with vacant postsynaptic densities. These densities did not reappear in saline treated rats which had been rehydrated for 2 weeks, but did return in both the 5-week rehydration and the 10-day postweaning groups. Short-term activation of the supraoptic nucleus, such as occurs at parturition or in acute dehydration, did not affect the vacant postsynaptic densities. Analysis of semiserial thin sections indicated that presynaptic elements facing the incompletely covered postsynaptic densities contain predominantly clear round vesicles and also that apparently free postsynaptic densities were usually at least partially contacted by a presynaptic ending in adjacent sections.     

Crayfish stretch-receptor organs: Effects of length-steps with and without perturbations

Isolated slowly and fast adapting stretch receptor organs (SROs) of crayfish were submitted to step-like length changes separated by prolonged stations with constant lengths. At times they were perturbed by a small-amplitude, fast length variation representing natural pertubations and referred to as jitter. Stimulus cycles depended on the sequence of lengths and on whether jitter was present. First-order afferent discharges were recorded from the dorsal nerve. Firing intensity, measured by the rate over bins of about 1 s, was displayed along ongoing time. Quantification involved estimation of cycle histograms, and trend tests for fully adapted discharges and preparation stability. The behaviour perturbed by jitter differed quantitatively in both organs from that without jitter, apart from more intense and irregular firing. Differences were also qualitative in the rapidly adapting organ (RAO), that jitter kept firing almost unccasingly and changed from a transient detector to a tonic receptor. Jitter effects varied with background stretch. The slowly adapting organ (SAO) and the perturbed RAO behaved quite similarly and exhibited features of lead-lag linear systems that implied joint sensitivity to length and velocity, like lively accelerations after stretches and lively slowings after relaxations with subsequent adaptation to steady discharges. Shortenings provided as important stimuli as lengthenings. At constant lengths, discharges eventually reached full adaptation: full adaptation cannot be proven experimentally, but can be accepted in practice using statistically sound and physiologically pragmatic criteria. When fully adapted, the SAO and the perturbed RAO had length-dependent discharges. Both SROs exhibited also prominent non-linear features besides the expected limiter behavior. Responses to symmetric stimuli were asymmetric: e.g. lengthenings produced greater rate changes and more durable transients than shortenings. The coding from steady lengths to fully-adapted discharges was multivalued (except in the unperturbed RAO): discharges were more or less intense depending on whether the particular length had been reached through lengthening or shortening, respectively (hysteresis). The anatomical and physiological reasons for many of these linear or nonlinear features are not yet identified fully. Discharge profiles deviated (in mean squared error) from the corresponding stimuli less with jitter than without. This happened, in spite of increased fluctuations in successive bins, because of reductions in transient effects and in delays to full adaptation. Length identification on the basis of the afferent discharges was improved by jitter, because of the above and because of reduction of the multivaluedness. The consequences of this more faithful representation are contingent on the neuronal analyzer to which the discharges are presented. The issues discussed, like full adaptation, multivaluedness, and the implications of the perturbations are relevant to mechanoreceptors in general, and even to all receptors.The authors acknowledge gratefully the generous support of the Fogarty Center of the National Institutes of Health (USA) and of the Fundación E. Rodríguez Pascual (España). The cooperation of the Instituto de Conservación de la Naturaleza was indispensable     

Rhizogenesis in stem discs of Malus pumila rootstock M9 “Jork”: I. Hormonal and environmental effects on root induction and callus formation

To establish a protocol suited for the molecular characterization of root induction the influences of explant position, etiolation state and orientation as well as temperature and light intensity on root and callus formation were investigated. Depending on these factors stem discs of Malus incubated on indole-3-butyric acid containing medium and subsequently on hormone-free medium regenerated roots and callus of filamentous and smooth texture to a varying extent. Concentration and incubation duration of indole-3butyric acid strongly affected rooting and the production of smooth callus. Moreover smooth callus was profuse at the low light levels applied during rooting. Rooting efficiency decreased and filamentous callus increased between 19°C and 25°C. Explants close to the shoot apex displayed reduced rooting efficiency and profuse filamentous callus. There was a strong effect of explant orientation on root and filamentous callus formation.Abbrevations IBA indole-3-butyric acid - IAA indole-3-acetic acid - BA 6-benzylaminopurine - MS Murashigeand Skoog - rts roots - rt rooted - rtd rooted discs     

Cholinergische Synapsen im Oberschlundganglion der Waldameise (Formica lugubris Zett.)

Summary The corpora pedunculata of the wood ant (Formica lugubris Zett.) consist of two sharply defined layers: The perikaryon layer and the subjacent neuropil. Synaptic endings are found exclusively in the neuropil. The synapses consist of a central, presynaptic end knob of 1.2–2.5 diameter and a relatively large number of surrounding postsynaptic processes of 0.3–1.1 diameter. These junctions are analogous to axodendritic synapses of the vertebrates. The presynaptic process contains mitochondria and a multitude of light vesicles (300–600 Å diameter). Larger vesicles 700–1000 Å with a dark center are seen more rarely. The synaptic cleft has a diameter of approximately 130 Å and varies somewhat with different fixation methods. With glutaraldehyde-osmium fixation, this relatively wide gap is maintained only in circumscribed areas of the junction, while in adjacent areas it tends to contract and an external compound membrane is formed. The postsynaptic region is characterized by the presence of a subsynaptic network which is revealed only by suitable fixation methods. This and the persistent synaptic cleft are the main structural differentiations found in junctional areas thus far.Cholinesterase is located with the aid of thiolacetic acid (Barnett) and Eserin control studies. The enzyme is found in the cytoplasm immediately adjacent to the pre- and postsynaptic membranes. In two thirds of our observations the reaction is far more concentrated postsynaptically than presynaptically. In one third, the distribution is reversed. Only an insignificant amount of cholinesterase is present within the synaptic cleft. There is no evidence that cholinesterase is evenly distributed along the entire junctional region. In contrast, only small circumscribed areas show a positive reaction and these coincide with the extent of the synaptic cleft and the subsynaptic network. Such areas seem to correspond to the active junctional areas.

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Unterstützt durch einen Kredit (Nr.2575) des Schweizer Nationalfonds für Wissenschaftliche Forschung.

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Herrn Prof. Dr. W. Bargmann zum 60. Geburtstag gewidmet.     

Zum Feinbau der Synapsen im Zentralnervensystem der Insekten

Zusammenfassung Die Feinstruktur der Synapsen im Insekten-Neuropil (Formica lugubris Zett.) wurde genauer untersucht. Dabei gelang der Nachweis von axo-axonischen Synapsen sowohl in Simplex-Form als auch in Dyaden-Stellung (wie in der Retina der Wirbeltiere). Diese Dyaden sind durch eine T-förmige präsynaptische dense projection gekennzeichnet. Die hellen synaptischen Bläschen reagieren positiv auf die Zinkjodid-Osmium-Färbung. Die PTA-Blockfärbung macht die Synapsen im Insekten-Neuropil besonders augenfällig. Zwei extreme Architekturtypen des Neuropils konnten nachgewiesen werden: eine mit vorherrschenden präsynaptischen Endigungen und die andere mit einer Vielzahl postsynaptischer Elemente, welche vereinzelte präsynaptische Endkolben umgeben.

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On the fine structure of synapses in the central nervous system of insects

Summary The fine structure of synapses in the neuropil of insect (Formica lugubris Zett.) ganglia has been further investigated. The presence of axo-axonic junctions is demonstrated in simplex form as well as in so-called dyades resembling the ones in vertebrate retina. These dyades are characterized by a T-shaped presynaptic dense projection. The clear synaptic vesicles react positively to zinc iodide osmium stain. The efficiency of PTA block staining for the demonstration of synaptic junctions in the insect neuropil is remarkable. Two extreme architectural patterns of neuropil are described: one in which the presynaptic profiles prevail and the opposite in which a few large presynaptic end bulbs are surrounded by a vast number of postsynaptic elements.

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Mit Unterstützung durch den Schweizerischen Nationalfond für wissenschaftliche Forschung (Nr. 3807) sowie der Hartmann-Müller-Stiftung für medizinische Forschung in Zürich.     

Pacemaker synaptic interactions: Modelled locking and paradoxical features

This communication describes a model for two pacemaker (i.e., regularly firing) nerve cells, such that one elicits IPSP's in the other. The assumptions involve essentially a linear dependence (delay function) of the postsynaptic interval lengthening (or delay) produced by the IPSP's on the position (or phase) with respect to the preceding spike of the latter's arrival. When the number of IPSP's in an interval increases, both the slope and intercept of the delay function increase, the former remaining under 2 and the latter unboundedly. Assumptions are more or less close to the actual biological reality, or are made for convenience. A recurrence equation for the phase can be calculated, as well as an expression for the locking phase (see below). Plots of postsynaptic vs presynaptic firing intensity averaged over steady conditions, e.g. of mean rates or intervals, are formed by a sequence of relatively broadparadoxical segments exhibiting positive slopes 1, 2, 1/2, 3, 1/3, ..., indicating that inhibited discharges are made more intense by those increases in inhibitory arrivals. These segments are separated by narrower intercalated segments where behavior is unclear except for a large overall negative slope, indicating that inhibited discharges are weakened markedly by other increases in inhibitory arrivals. Across the successive paradoxical segments that correspond to more and more intense presynaptic discharges (i.e., to higher rates or shorter intervals), postsynaptic intensities, though overlapping in part, become weaker and weaker. At the extremes, when the presynaptic discharge is very weak, or very intense, the postsynaptic cell tends to its natural undisturbed firing, or to not firing at all, respectively. The pre- and postsynaptic discharges inevitably achieve eventually an invariant relation, i.e., will lock at a constant phase, regardless of the phase of the first IPSP arrival. The characteristics of this behavior (e.g., the rate bounds of the paradoxical segments, or the magnitude of the locked phase) depend on such givens as presynaptic and postsynaptic pacemaker rates or intervals, and as the slope or intercept of the delay function.     

Between beanbag genetics and natural selection

The encounter between the Darwinian theory of evolution and Mendelism could be resolved only when reductionist tools could be applied to the analysis of complex systems. The instrumental reductionist interpretation of the hereditary basis of continuously varying traits provided mathematical tools which eventually allowed the construction of the Modern Synthesis of the theory of evolution.When genotypic as well as environmental variance allow the isolation of parts of the system, it is possible to apply Mendelian reductionism, that is , to treat the phenotypic trait as if ti causally determined by discrete genes for the trait. howeverm such a beanbag genetics approach obscures the system's eye-view. The concept of heritability, defined as the proportion of the total phenotypic variance due to (additive) hereditary variation, asserts that genetic elements have discrete effects; but by relating to the genotypic variance, it avoids the trap of reffering to genes for characters.     

The effects of pyridine nucleotides on the activity of a calcium-activated nonselective cation channel in the rat insulinoma cell line,CRI-G1

The activity of a calcium-activated nonselective (Ca-NS⁺) channel in a rat insulinoma cell line (CRI-G1) is inhibited by pyridine nucleotides in excised patches. The effects of all four pyridine nucleotides tested, -NAD⁺, -NADH, -NADP⁺ and -NADPH were very similar when tested at 0.1 mm, and at 1 mm the phosphorylated forms, -NADP⁺ and -NADPH, appeared to be slightly more potent than -NAD⁺ and -NADH. All the pyridine nucleotides tested reduced both the open state probability of the channel and the number of functional channels observed in a single patch.The application of -NAD⁺, but not of the other nucleotides tested, to the cytoplasmic surface of isolated inside-out patches from CRI-G1 cells opened a novel nonselective cation channel (the -NAD⁺-NS⁺ channel). The activity of this new channel is calcium sensitive and may also be inhibited by AMP.     

A DFT investigation of conformational geometries and interconversion equilibria of phenylthiosemicarbazone and its complexation with zinc

The geometrical structures of phenylthiosemicarbazone (HAPhTSC) conformers have been obtained by geometry optimizations using density functional theory (DFT) calculations at the B3LYP/6-31G(d) and B3LYP/6-311G(d,p) levels of theory. Six thioamino and 24 thioimino tautomers of HAPhTSC have been found. Six tautomerization reactions between thioamino and thioimino tautomers occurring via transition states and their corresponding activation energies have been obtained. Conformational pathways for tautomerizations and interconversions of HAPhTSC conformers have been presented. Tautomerization between the most stable species of thioamino (Atttcc) and its thioimino (Itttcct) tautomer is an endothermic reaction, H⁰=18.17 kcal mol^–1 and its log K=–13.74, at 298.15 K. Thermodynamic quantities of tautomerizations, interconversions of HAPhTSC conformers and their equilibrium constants are reported. The geometry of the zinc complex with HAPhTSC, found as a Zn(HAPhTSC)₂Cl₂ structure, has been obtained using B3LYP/6-31G(d) calculations. Binding of the Zn(HAPhTSC)₂Cl₂ complex is an exothermic and spontaneous reaction.Figure Conformational notation defined as a name consisting of a letter A for a thioamino tautomer followed by c for cis or t for trans isomerism of five dihedral angles of (C4-C3-C2-N3), (C3-C2-N3-N2), (C2-N3-N2-C1), (N3-N2-C1-N1) and (N2-C1-N1-H2), serially, or a letter I for b thioimino tautomer followed by c for cis or t for trans isomerism of six dihedral angles of (C4-C3-C2-N3), (C3-C2-N3-N2), (C2-N3-N2-C1), (N3-N2-C1-N1), (N2-C1-N1-H2) and (N2-C1-S-H1), serially.Electronic Supplementary Material Supplementary material is available for this article at     

Some peculiar synaptic complexes in the first visual ganglion of the fly,Musca domestica

Summary In the lamina ganglionaris, the first optic ganglion of the fly, the inventory of cell types as well as the patterns of their connections are well known from light microscopic investigations. Even the synaptic contacts are known with relative completeness. However, the structural details visible on electron micrographs are very difficult to interpret in functional terms. This paper concentrates on two aspects: 1) the synaptic complex between a retinula cell axon and four postsynaptic elements, arranged in a constant elongated array (it is suggested that all synapses in which the retinula cell is presynaptic are of this kind), and 2) the gnarl complex in which a presynaptic specialization in one neuron is separated from another neuron by a complicated glial invagination. The participation of glia at postsynaptic sites seems to be quite common in this ganglion. Occasionally it seems that a glia cell is the only postsynaptic partner facing a presynaptic specialization within a neuron.