SBH17: Benchmark Database of Barrier Heights for Dissociative Chemisorption on Transition Metal Surfaces.

Accurate barriers for rate controlling elementary reactions on metal surfaces are key to understanding, controlling, and predicting the rate of heterogeneously catalyzed processes. While barrier heights for gas phase reactions have been extensively benchmarked, dissociative chemisorption barriers for the reactions of molecules on metal surfaces have received much less attention. The first database called SBH10 and containing 10 entries was recently constructed based on the specific reaction parameter approach to density functional theory (SRP-DFT) and experimental results. We have now constructed a new and improved database (SBH17) containing 17 entries based on SRP-DFT and experiments. For this new SBH17 benchmark study, we have tested three algorithms (high, medium, and light) for calculating barrier heights for dissociative chemisorption on metals, which we have named for the amount of computational effort involved in their use. We test the performance of 14 density functionals at the GGA, GGA+vdW-DF, and meta-GGA rungs. Our results show that, in contrast with the previous SBH10 study where the BEEF-vdW-DF2 functional seemed to be most accurate, the workhorse functional PBE and the MS2 density functional are the most accurate of the GGA and meta-GGA functionals tested. Of the GGA+vdW functionals tested, the SRP32-vdW-DF1 functional is the most accurate. Additionally, we found that the medium algorithm is accurate enough for assessing the performance of the density functionals tested, while it avoids geometry optimizations of minimum barrier geometries for each density functional tested. The medium algorithm does require metal lattice constants and interlayer distances that are optimized separately for each functional. While these are avoided in the light algorithm, this algorithm is found not to give a reliable description of functional performance. The combination of relative ease of use and demonstrated reliability of the medium algorithm will likely pave the way for incorporation of the SBH17 database in larger databases used for testing new density functionals and electronic structure methods.

Accurate Probabilities for Highly Activated Reaction of Polyatomic Molecules on Surfaces Using a High-Dimensional Neural Network Potential: CHD3 + Cu(111).

An accurate description of reactive scattering of molecules on metal surfaces often requires the modeling of energy transfer between the molecule and the surface phonons. Although ab initio molecular dynamics (AIMD) can describe this energy transfer, AIMD is at present untractable for reactions with reaction probabilities smaller than 1%. Here, we show that it is possible to use a neural network potential to describe a polyatomic molecule reacting on a mobile metal surface with considerably reduced computational effort compared to AIMD. The highly activated reaction of CHD3 on Cu(111) is used as a test case for this method. It is observed that the reaction probability is influenced considerably by dynamical effects such as the bobsled effect and surface recoil. A special dynamical effect for CHD3 + Cu(111) is that a higher vibrational efficacy is obtained for two quanta in the CH stretch mode than for a single quantum.

Gray matter differences contribute to variation in cognitive performance in Parkinson's disease.

BACKGROUND AND PURPOSE: A substantial proportion of patients with Parkinson's disease (PD) suffer from cognitive deficits, although there is a large variability in the severity of these impairments. Whilst the cognitive deficits are often attributed to monoaminergic changes, there is evidence that alterations in structural brain volume also play a role. The aim of our study was to gain more insight into the variability of cognitive performance amongst PD patients by examining the relation between regional gray matter (GM) volume and cognitive performance. METHODS: Linear regression analyses were performed between task performance and GM volume for six neuropsychological tasks within a group of 93 PD patients; they were additionally compared at a group level with matched healthy controls, using voxel-based morphometry. RESULTS: Our most important findings were positive correlations between GM volume and cognitive performance for (i) parahippocampal gyrus and verbal memory, (ii) medial temporal lobe and putamen and visuospatial memory, and (iii) middle temporal gyrus and frontal lobe and verbal fluency. In addition, decreased GM volume was found in the frontal, parietal and temporal cortices of PD patients compared with matched healthy controls. CONCLUSIONS: It is argued that the large variability in cognitive function across PD patients is partly mediated by GM volume differences in the implicated areas. Volume differences in these brain regions do not discriminate between patients and controls but explain cognitive variation within the patient population.

Sucrose metabolism in plastids.

The question whether sucrose (Suc) is present inside plastids has been long debated. Low Suc levels were reported to be present inside isolated chloroplasts, but these were argued to be artifacts of the isolation procedures used. We have introduced Suc-metabolizing enzymes in plastids and our experiments suggest substantial Suc entry into plastids. The enzyme levansucrase from Bacillus subtilis efficiently synthesizes fructan from Suc. Targeting of this enzyme to the plastids of tobacco (Nicotiana tabacum) and potato (Solanum tuberosum) plants leads to high-level fructan accumulation in chloroplasts and amyloplasts, respectively. Moreover, introduction of this enzyme in amyloplasts leads to an altered starch structure. Expression of the yeast invertase in potato tuber amyloplasts results in an 80% reduction of total Suc content, showing efficient hydrolysis of Suc by the plastidic invertase. These observations suggest that Suc can enter plastids efficiently and they raise questions as to its function and metabolism in this organelle.

Input of anterior and posterior semicircular canal interneurons encoding head-velocity to the dorsal Y group of the vestibular nuclei.

Neurons in the Y group of the vestibular nuclei are activated disynaptically from the ipsilateral VIIIth nerve and polysynaptically from the contralateral nerve. The ipsilateral anterior and posterior semicircular canals project to the Y group via interneurons in the vestibular nuclei. Candidate interneurons located in the rostrolateral corner of the superior (SVN) and in the caudal medial (MVN) vestibular nuclei were retrogradely labeled by the iontophoretic injection of biocytin into the Y group. The physiology of these interneurons named Y-group projecting neurons (YPNs) was studied in the SVN. SVN-YPNs were activated antidromically by electric pulse stimulation in the Y group. The properties of SVN-YPNs are distinct from those of SVN flocculus projecting neurons (FPNs). Namely, YPNs have a lower resting rate than FPNs, have more irregular interspike intervals, show a different phase and gain during the vestibuloocular reflex, and are located differentially within the SVN. After the injection of biocytin into the Y group, the locations of Purkinje cells that project to the Y group were confined to the vertical zones of the flocculus and ventral paraflocculus. However, mossy fibers originating in the Y group terminate in both the vertical and horizontal zones of the flocculus and ventral paraflocculus as well as in the ipsilateral nodulus.

The subdivisions of the guinea pig vestibular complex revealed by acetylcholinesterase staining.

A detailed map of the vestibular nuclear complex of the guinea pig has been established by Gstoettner and Burian (1987), using cytoarchitectonic (cresyl violet staining) and fiberarchitectonic criteria. However, the exact borders between the different subdivisions are not always evident in Nissl stained sections. In the present study, serial sections of the vestibular nuclei of the guinea pig were stained to visualize acetylcholinesterase (AChE) activity, and compared with corresponding sections stained with cresyl violet. All of the subdivisions of the vestibular nuclear complex previously described are more readily distinguished in AChE than in Nissl preparations. The AChE reactivity also shows that the medial vestibular nucleus extends more rostrally than previously described. Furthermore, it questions whether the area classically referred to as the rostral pole of the descending vestibular nucleus belongs to the descending vestibular nucleus or to the lateral vestibular nucleus (LV). Finally, a morphometric analysis performed on cresyl violet stained sections shows that (1) in the caudal LV, the neurons of the ventromedial extension are smaller than those of the dorsolateral extension and that (2) in the rostral LV, the ventromedial division contains a larger ratio of smaller neurons than the dorsolateral one.

Sucrose-specific signalling represses translation of the Arabidopsis ATB2 bZIP transcription factor gene.

The Arabidopsis bZIP transcription factor gene ATB2 has been shown previously to be expressed in a light-regulated and tissue-specific way. Here we describe the precise localization of ATB2 expression, using transgenic lines containing an ATB2 promoter-GUS reporter gene construct. The observed expression pattern suggests a role for ATB2 in the control of processes associated with the transport or utilization of metabolites. Remarkably, expression of the ATB2-GUS reporter gene construct was specifically repressed by sucrose. Other sugars, such as glucose and fructose, alone or in combination, were ineffective. Repression was observed at external sucrose concentrations exceeding 25 mM. Transcript levels of both the endogenous ATB2 gene and the ATB2-GUS reporter gene were not repressed by sucrose, suggesting that sucrose affects mRNA translation. This translational regulation involves the ATB2 leader sequence because deletion of the leader resulted in loss of sucrose repression. Our results provide evidence for a sucrose-specific sugar sensing and signalling system in plants.

Distribution of GABA, glycine, and glutamate immunoreactivities in the vestibular nuclear complex of the frog.

This study describes the localization of gamma-aminobutyric acid (GABA), glycine, and glutamate immunoreactive neurons, fibers, and terminal-like structures in the vestibular nuclear complex (VNC) of the frog by using a postembedding procedure with consecutive semithin sections at the light microscopic level. For purposes of this study, the VNC was divided into a medial and lateral region. Immunoreactive cells were observed in all parts of the VNC. GABA-positive neurons, generally small in size, were predominantly located in the medial part of the VNC. Glycine-positive cells, more heterogeneous in size than GABA-positive cells, were scattered throughout the VNC. A quantitative analysis of the spatial distribution of GABA glycine immunoreactive cells revealed a complementary relation between the density of GABA and glycine immunoreactive neurons along the rostrocaudal extent of the VNC. In about 10% of the immunolabeled neurons, GABA and glycine were colocalized. Almost all vestibular neurons were, to a variable degree, glutamate immunoreactive, and colocalization of glutamate with GABA and/or glycine was typical. GABA, glycine, or glutamate immunoreactive puncta were found in close contact to somata and main dendrites of vestibular neurons. A quantitative analysis revealed a predominance of glutamate-positive terminal-like structures compared to glycine or GABA containing profiles. A small proportion of terminal-like structures expressed colocalization of GABA and glycine or glycine and glutamate. The results are compared with data from mammals and discussed in relation to vestibuloocular and vestibulo-spinal projection neurons, and vestibular interneurons. GABA and glycine are the major inhibitory transmitters of these neurons in frogs as well as in mammals. The differential distribution of GABA and glycine might reflect a compartmentalization of neurons that is preserved to some extent from the early embryogenetic segmentation of the hindbrain.

GABAergic and glycinergic inputs to the rabbit oculomotor nucleus with special emphasis on the medial rectus subdivision.

Contradictory results have been reported about the inhibitory input to the medial rectus subdivision of the oculomotor nucleus of the cat. In the present ultrastructural study, we quantified the GABAergic and glycinergic terminals in the various subdivisions of the rabbit oculomotor nucleus with the use of post-embedding immunocytochemistry combined with retrograde tracing of horseradish peroxidase. The density of the GABAergic input to the medial rectus subdivision was as substantial as that to the other subdivisions and the postsynaptic distribution of the GABAergic and glycinergic innervation did not differ among the different oculomotor subdivisions.

A conserved histidine residue of Escherichia coli outer-membrane phospholipase A is important for activity.

Escherichia coli outer-membrane phospholipase A (OMPLA) is thought to be a member of the class of serine hydrolases, having a classical Asp-His-Ser catalytic triad [Horrevoets, A. J. G., Verheij, H. M. & de Haas, G. H. (1991) Eur. J. Biochem. 198, 247-253]. To identify the histidine residue that is important for catalytic activity, the four histidine residues in E. coli OMPLA that are conserved in other enterobacterial OMPLA enzymes were replaced by cysteine residues using PCR-directed, site-specific mutagenesis. The resulting mutant proteins were all well expressed and displayed heat modifiability, indicating that they were properly folded. Enzyme assays showed that only the His142Cys mutant protein was lacking enzymatic activity. In addition, a His142Gly mutant protein appeared to be inactive. These results show that His142 is important for the enzymatic activity of OMPLA.

Existence in the nucleus incertus of the cat of horizontal-eye-movement-related neurons projecting to the cerebellar flocculus.

1. Properties of nucleus incertus (NIC) neurons projecting to the cerebellar flocculus were studied in alert cats by using chronic unit and eye movement recording and antidromic activation. Projection of these neurons onto the flocculus was verified with retrograde transport of horseradish peroxidase after injections in the flocculus. 2. Bipolar stimulation electrodes were implanted into the "middle" zone of each flocculus because this zone is known to be involved in the control of horizontal eye movements. The dorsomedial aspect of the pontine tegmentum was explored with microelectrodes during stimulation of both flocculi. The majority of neurons antidromically activated from the flocculus were found in the caudal part of the NIC. 3. Of the 69 neurons activated from the flocculus, 44 were classified as burst-tonic (BT) neurons; 34 discharged in relation with horizontal movements of the eye, 10 in relation with vertical movements. Of the 14 remaining neurons, 6 were not related to eye movements and 8 were classified as burst neurons. The BT neurons of the NIC displayed a great sensitivity to both horizontal eye position and horizontal eye velocity. 4. This study demonstrates the presence of a new group of horizontal eye movement related BT neurons situated in the NIC. The fact that they project to the horizontal floccular zone emphasizes the importance of the functional specialization of the different Purkinje cell zones.

Zonal organization of the climbing fiber projection to the flocculus and nodulus of the rabbit: a combined axonal tracing and acetylcholinesterase histochemical study.

The localization and termination of olivocerebellar fibers in the flocculus and nodulus of the rabbit were studied with anterograde axonal transport methods [wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) and tritiated leucine] and correlated with the compartments in the white matter of these lobules delineated with acetylcholinesterase histochemistry (Tan et al. J. Comp. Neurol., 1995, this issue). Olivocerebellar fibers originating from the caudal dorsal cap travel through floccular compartments FC2 and FC4 to terminate as climbing fibers in floccular zones FZII and FZIV. Fibers from the rostral dorsal cap and the ventrolateral outgrowth traverse compartments FC1 and FC3, which are interleaved with compartments FC2 and FC4, and terminate in zones FZI and FZIII. Fibers from the rostral pole of the medial accessory olive traverse the C2 compartment and terminate in the C2 zone. FZI-III extend into the adjoining folium (folium p) of the ventral paraflocculus. The C2 zone continues across folium p into other folia of the ventral paraflocculus and into the dorsal paraflocculus. Four compartments and five zones were distinguished in the nodulus. Medial compartment XC1 contains olivocerebellar fibers from the caudal dorsal cap and subnucleus beta that terminate in the XZI zone. Olivocerebellar fibers from the rostral dorsal cap and the ventrolateral outgrowth occupy XC2 and terminate in XZII. The XC4 compartment contains fibers from both the caudal dorsal cap and from the rostral dorsal cap and the ventrolateral outgrowth. The latter terminate in a central portion of the XZIV zone. The dorsomedial cell column projects to the XZIII zone, which is present only in the dorsal part of the nodulus. The rostral medial accessory olive projects to the XZV zone, which occupies the lateral border of the nodulus. These results confirm and extend the conclusions of Katayama and Nisimaru ([1988] Neurosci. Res. 5:424-438) on the zonal pattern in the olivo-nodular projection in the rabbit. Additional observations were made on the presence of a lateral A zone (Buisseret-Delmas [1988] Neurosci. Res. 5:475-493) in the hemisphere of lobules VI and VII. Retrograde labeling of the nucleo-olivary tract of Legendre and Courville ([1987] Neuroscience 21:877-891) was observed after WGA-HRP injections into the inferior olive including the rostral dorsal cap and the ventrolateral outgrowth. The anatomical and functional implications of these observations are discussed.

Inhibitory synaptic inputs to the oculomotor nucleus from vestibulo-ocular-reflex-related nuclei in the rabbit.

Studies of the pathways involved in the vestibulo-ocular reflex have suggested that the projection from the superior vestibular nucleus to the ipsilateral oculomotor nucleus is inhibitory, whereas the medial vestibular nucleus, the abducens nucleus and the contralateral superior vestibular nucleus most likely exert excitatory effects on oculomotor neurons. In order to determine directly the termination pattern and the neurotransmitter of these afferents, we studied their input to the oculomotor nucleus in the rabbit at the light microscopic level with the use of anterograde tracing of Phaseolus vulgaris-leucoagglutinin combined with retrograde tracing of horseradish peroxidase from the extraocular muscles, and at the ultrastructural level with the use of anterograde tracing of wheatgerm-agglutinated horseradish peroxidase combined with GABA and glycine postembedding immunocytochemistry. The general ultrastructural characteristics of the neuropil and the types of boutons observed in the rabbit oculomotor nuclei are in general agreement with the descriptions for the oculomotor complex of other mammals. The superior vestibular nucleus projected bilaterally to the superior rectus and inferior oblique subdivisions, and ipsilaterally to the inferior rectus and medial rectus subdivision; the medial vestibular nucleus projected bilaterally to the medial rectus, inferior oblique, inferior rectus and superior rectus subdivisions with a strong contralateral predominance. The abducens nucleus projected contralaterally to the medial rectus subdivision. More than 90% of all the anterogradely labeled terminals from the ipsilateral superior vestibular nucleus were GABAergic. These terminals were characterized by flattened vesicles and symmetric synapses, and they contacted somata, as well as proximal and distal dendrites of motoneurons. All terminals derived from the medial vestibular nucleus the abducens nucleus and the contralateral superior vestibular nucleus were non-GABAergic. These non-GABAergic terminals showed spherical vesicles and asymmetric synapses, and they contacted predominantly distal dendrites. None of the anterogradely labeled terminals from the studied vestibular nuclei or abducens nucleus were glycinergic. The present study provides the first direct anatomical evidence that most, if not all, of the synaptic input from the superior vestibular nucleus to the ipsilateral oculomotor nucleus is GABAergic, and that the medial rectus subdivision is included in the termination area. Furthermore, it confirms that the projections from the medial vestibular nucleus, the abducens nucleus and the contralateral superior vestibular nucleus are exclusively non-GABAergic.

Visual pontocerebellar projections in the macaque.

The cerebellum plays an important role in the visual guidance of movement. In order to understand the anatomical basis of visuomotor control, we studied the projection of pontine visual cells onto the cerebellar cortex of monkeys. Wheat germ agglutinin horseradish peroxidase was injected into the dorsolateral pons two monkeys. Retrogradely labelled cells were mapped in the cerebral cortex and superior colliculus, and orthogradely labelled fibers in the cerebellar cortex. The largest number of retrogradely labelled cells in the cerebral cortex was in a group of medial extrastriate visual areas. The major cerebellar target of these dorsolateral pontine cells is the dorsal paraflocculus. There is a weaker projection to the uvula, paramedian lobe, and Crus II, and a sparse but definite projection to the ventral paraflocculus. There are virtually no projections to the flocculus. There are sparse ipsilateral pontocerebellar projections to these same regions of cerebellar cortex. In nine monkeys, we made small injections of the tracer into the cerebellar cortex and studied the location of retrogradely filled cells in the pontine nuclei and inferior olive. Injections into the dorsal paraflocculus or rostral folia of the uvula retrogradely labelled large numbers of cells in the dorsolateral region of the contralateral pontine nuclei. Labelled cells were found ipsilaterally, but in reduced numbers. Injections outside of these areas in ventral paraflocculus or paramedian lobule labelled far fewer cells in this region of the pons. We conclude that the principal source of cerebral cortical visual information arises from a medial group of extrastriate visual areas and is relayed through cells in the dorsolateral pontine nuclei. The principal target of pontine visual cells is the dorsal paraflocculus.

The rostral dorsal cap and ventrolateral outgrowth of the rabbit inferior olive receive a GABAergic input from dorsal group Y and the ventral dentate nucleus.

The dorsal cap and ventrolateral outgrowth of the inferior olive are involved in the control of eye movements. The caudal dorsal cap is predominantly involved in the horizontal optokinetic reflex; it receives most of its GABAergic input from the nucleus prepositus hypoglossi. In the present study, we determined the source of a major inhibitory input to the rostral dorsal cap and the ventrolateral outgrowth, which are the olivary subnuclei mainly involved in the "vertical" optokinetic reflexes. We studied these subnuclei in the rabbit with the use of retrograde tracing of horseradish peroxidase and anterograde tracing of wheat germ agglutinin-coupled horseradish peroxidase combined with postembedding immunocytochemistry. The ventral dentate nucleus of the cerebellum and dorsal group y project contralaterally to the rostral dorsal cap and ventrolateral outgrowth; this projection is entirely GABAergic. The terminals of this input form predominantly symmetric synapses with extraglomerular and intraglomerular dendrites; the remaining terminals are axosomatic. In addition, the dorsal cap and ventrolateral outgrowth contain significantly more crest synapses than any other olivary subnucleus. The terminals that form these crest synapses are derived from dorsal group y and/or the ventral dentate nucleus. None of the terminals in the dorsal cap or ventrolateral outgrowth was glycinergic.

Colocalization of GABA and glycine in the rabbit oculomotor nucleus.

In the present study we examined the possible colocalization of the inhibitory neurotransmitters glycine and GABA in the oculomotor nucleus of the rabbit. Serial sections were processed alternately for glycine and GABA postembedding immuno-cytochemistry. Ultrastructural analysis revealed that all terminals that showed glycine-positive immunoreactivity were also GABA positive; up to 5% of the GABA-positive terminals were also glycine positive.

Laterality in the vestibulo-cerebellar mossy fiber projection to flocculus and caudal vermis in the rabbit: a retrograde fluorescent double-labeling study.

The vestibular nuclear input into the flocculus and the uvula and nodulus of the caudal vermis was studied in rabbits by means of retrograde transport of the fluorescent tracers Fast Blue and Diamidino Yellow. Through simultaneous injection of the tracers in the homonymous lobules at either side of the midline, the distribution, the preference in laterality and the degree of collateralization of vestibulo-cerebellar neurons could be studied. The nucleus prepositus hypoglossi was included in the analysis. In the nucleus prepositus hypoglossi and in the medial vestibular nucleus 6% of the number of labeled neurons contained both tracers, against 4% in the descending vestibular nucleus. In the superior vestibular nucleus a statistically significant difference in the proportion of double-labeled neurons was found between cases with injections in the flocculus (1%) and the caudal vermis (9%). The relative distribution of single-labeled neurons projecting to either the flocculus or the caudal vermis was similar in most of the vestibular nuclei. A statistically significant preference for a projection to the flocculus in favor of one to the caudal vermis, was found for neurons in the medial vestibular nucleus and the prepositus hypoglossal nucleus. Statistically significant laterality preferences were found in the superior vestibular nucleus for the contralateral flocculus.