278 research outputs found
Equivariant Lefschetz maps for simplicial complexes and smooth manifolds
Let X be a locally compact space with a continuous proper action of a locally
compact group G. Assuming that X satisfies a certain kind of duality in
equivariant bivariant Kasparov theory, we can enrich the classical construction
of Lefschetz numbers to equivariant K-homology classes. We compute the
Lefschetz invariants for self-maps of finite-dimensional simplicial complexes
and of self-maps of smooth manifolds. The resulting invariants are independent
of the extra structure used to compute them. Since smooth manifolds can be
triangulated, we get two formulas for the same Lefschetz invariant in these
cases. The resulting identity is closely related to the equivariant Lefschetz
Fixed Point Theorem of Luck and Rosenberg.Comment: Minor revisions, affecting some theorem number
Rodents and humans are able to detect the odour of L-Lactate.
This is the final version of the article. Available from PLoS via the DOI in this record.L-Lactate (LL) is an essential cellular metabolite which can be used to generate energy. In addition, accumulating evidence suggests that LL is used for inter-cellular signalling. Some LL-sensitive receptors have been identified but we recently proposed that there may be yet another unknown G-protein coupled receptor (GPCR) sensitive to LL in the brain. Olfactory receptors (ORs) represent the largest family of GPCRs and some of them are expressed outside the olfactory system, including brain, making them interesting candidates for non-olfactory LL signalling. One of the "ectopically" expressed ORs, Olfr78 in mice (Olr59 in rats and OR51E2 in humans), reportedly can be activated by LL. This implies that both rodents and humans should be able to detect the LL odour. Surprisingly, this has never been demonstrated. Here we show that mice can detect the odour of LL in odour detection and habituation-dishabituation tasks, and discriminate it from peppermint and vanilla odours. Behaviour of the Olfr78 null mice and wildtype mice in odour detection task was not different, indicating that rodents are equipped with more than one LL-sensitive OR. Rats were also able to use the smell of LL as a cue in an odour-reward associative learning task. When presented to humans, more than 90% of participants detected a smell of LL in solution. Interestingly, LL was perceived differently than acetate or propionate-LL was preferentially reported as a pleasant sweet scent while acetate and propionate were perceived as repulsive sour/acid smells. Subjective perception of LL smell was different in men and women. Taken together, our data demonstrate that both rodents and humans are able to detect the odour of LL. Moreover, in mice, LL perception is not purely mediated by Olfr78. Discovery of further LL-sensitive OR might shed the light on their contribution to LL signalling in the body.This work was supported by BBSRC: BB/L019396/1, BB/K009192/1; and MRC MR/L020661/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Expression of Microbial Enzymes in Mammalian Astrocytes to Modulate Lactate Release
Astrocytes support and modulate neuronal activity through the release of L-lactate. The
suggested roles of astrocytic lactate in the brain encompass an expanding range of vital functions,
including central control of respiration and cardiovascular performance, learning, memory, executive
behaviour and regulation of mood. Studying the effects of astrocytic lactate requires tools that limit
the release of lactate selectively from astrocytes. Here, we report the validation in vitro of novel
molecular constructs derived from enzymes originally found in bacteria, that when expressed in
astrocytes, interfere with lactate handling. When lactate 2-monooxygenase derived from M. smegmatis
was specifically expressed in astrocytes, it reduced intracellular lactate pools as well as lactate release
upon stimulation. D-lactate dehydrogenase derived from L. bulgaricus diverts pyruvate towards
D-lactate production and release by astrocytes, which may affect signalling properties of lactate in
the brain. Together with lactate oxidase, which we have previously described, this set of transgenic
tools can be employed to better understand astrocytic lactate release and its role in the regulation of
neuronal activity in different behavioural contexts
Equivariant comparison of quantum homogeneous spaces
We prove the deformation invariance of the quantum homogeneous spaces of the
q-deformation of simply connected simple compact Lie groups over the
Poisson-Lie quantum subgroups, in the equivariant KK-theory with respect to the
translation action by maximal tori. This extends a result of Neshveyev-Tuset to
the equivariant setting. As applications, we prove the ring isomorphism of the
K-group of Gq with respect to the coproduct of C(Gq), and an analogue of the
Borsuk-Ulam theorem for quantum spheres.Comment: 21 page
Some Remarks on Group Bundles and C*-dynamical systems
We introduce the notion of fibred action of a group bundle on a C(X)-algebra.
By using such a notion, a characterization in terms of induced C*-bundles is
given for C*-dynamical systems such that the relative commutant of the
fixed-point algebra is minimal (i.e., it is generated by the centre of the
given C*-algebra and the centre of the fixed-point algebra). A class of
examples in the setting of the Cuntz algebra is given, and connections with
superselection structures with nontrivial centre are discussed.Comment: 22 pages; to appear on Comm. Math. Phy
The Baum-Connes Conjecture via Localisation of Categories
We redefine the Baum-Connes assembly map using simplicial approximation in
the equivariant Kasparov category. This new interpretation is ideal for
studying functorial properties and gives analogues of the assembly maps for all
equivariant homology theories, not just for the K-theory of the crossed
product. We extend many of the known techniques for proving the Baum-Connes
conjecture to this more general setting
Glio- and neuroprotection by prosaposin is mediated by orphan G-protein coupled receptors GPR37L1 and GPR37
This is the author accepted manuscript. Available on open access from Wiley via the DOI in this recordDiscovery of neuroprotective pathways is one of the major priorities for neuroscience. Astrocytes are the natural neuroprotectors and it is likely that brain resilience can be enhanced by mobilising their protective potential. Among G-protein coupled receptors expressed by astrocytes, two highly related receptors, GPR37L1 and GPR37, are of particular interest. Previous studies suggested that these receptors are activated by a peptide Saposin C and its neuroactive fragments (such as prosaptide TX14), which were demonstrated to be neuroprotective in various animal models by several groups. However, pairing of Saposin C or prosaptides with GPR37L1/GPR37 has been challenged and presently GPR37L1/GPR37 have regained their orphan status. Here we demonstrate that in their natural habitat, astrocytes, these receptors mediate a range of effects of TX14, including protection from oxidative stress. The Saposin C/GPR37L1/GPR37 pathway is also involved in the neuroprotective effect of astrocytes on neurons subjected to oxidative stress. The action of TX14 is at least partially mediated by Gi-proteins and the cAMP-PKA axis. On the other hand, when recombinant GPR37L1 or GPR37 are expressed in HEK293 cells, they are not functional and do not respond to TX14, which explains unsuccessful attempts to confirm the ligand-receptor pairing. Therefore this study identifies GPR37L1/GPR37 as the receptors for TX14, and, by extension of Saposin C, and paves the way for the development of neuroprotective therapeutics acting via these receptors.Biotechnology and Biological Sciences Research CouncilMedical Research Council (MRC
Cardioprotection evoked by remote ischaemic preconditioning is critically dependent on the activity of vagal pre-ganglionic neurones
AIMS: Innate mechanisms of inter-organ protection underlie the phenomenon of remote ischaemic preconditioning (RPc) in which episode(s) of ischaemia and reperfusion in tissues remote from the heart reduce myocardial ischaemia/reperfusion injury. The uncertainty surrounding the mechanism(s) underlying RPc centres on whether humoral factor(s) produced during ischaemia/reperfusion of remote tissue and released into the systemic circulation mediate RPc, or whether a neural signal is required. While these two hypotheses may not be incompatible, one approach to clarify the potential role of a neural pathway requires targeted disruption or activation of discrete central nervous substrate(s). METHODS AND RESULTS: Using a rat model of myocardial ischaemia/reperfusion injury in combination with viral gene transfer, pharmaco-, and optogenetics, we tested the hypothesis that RPc cardioprotection depends on the activity of vagal pre-ganglionic neurones and consequently an intact parasympathetic drive. For cell-specific silencing or activation, neurones of the brainstem dorsal motor nucleus of the vagus nerve (DVMN) were targeted using viral vectors to express a Drosophila allatostatin receptor (AlstR) or light-sensitive fast channelrhodopsin variant (ChIEF), respectively. RPc cardioprotection, elicited by ischaemia/reperfusion of the limbs, was abolished when DVMN neurones transduced to express AlstR were silenced by selective ligand allatostatin or in conditions of systemic muscarinic receptor blockade with atropine. In the absence of remote ischaemia/reperfusion, optogenetic activation of DVMN neurones transduced to express ChIEF reduced infarct size, mimicking the effect of RPc. CONCLUSION: These data indicate a crucial dependence of RPc cardioprotection against ischaemia/reperfusion injury upon the activity of a distinct population of vagal pre-ganglionic neurones
Piano Studio Recital, September 24, 2019
Carter Campbell, from the studio of Professor Kasparov
Andrei S. Johnson, from the studio of Professor Lutsyshyn
Joel Sanford, from the studio of Professor Toomey
Robert Stahl, from the studio of Professor Rayd
Astrocytes modulate baroreflex sensitivity at the level of the nucleus of the solitary tract
Maintenance of cardiorespiratory homeostasis depends on autonomic reflexes controlled by neuronal circuits of the brainstem. The neurophysiology and neuroanatomy of these reflex pathways are well understood, however, the mechanisms and functional significance of autonomic circuit modulation by glial cells remain largely unknown. In experiments conducted in male laboratory rats we show that astrocytes of the nucleus tractus solitarii (NTS), the brain area that receives and integrates sensory information from the heart and blood vessels, respond to incoming afferent inputs with [Ca2+]i elevations. Astroglial [Ca2+]i responses are triggered by transmitters released by vagal afferents, glutamate acting at AMPA receptors and 5-HT acting at 5-HT2A receptors. In conscious freely behaving animals blockade of Ca2+-dependent vesicular mechanisms in NTS astrocytes by virally driven expression of a dominant-negative SNARE protein (dnSNARE) increased baroreflex sensitivity by 70% (p<0.001). The effect of compromised astroglial function was specific to the NTS as expression of dnSNARE in astrocytes of the ventrolateral brainstem had no effect. ATP considered the principle gliotransmitter and is released by vesicular mechanisms affected by dnSNARE expression. Consistent with this hypothesis, in anesthetized rats, activation P2Y1 purinoceptors in the NTS decreased baroreflex gain by 40% (p=0.031), while blockade of P2Y1 receptors increased baroreflex gain by 57% (p=0.018). These results suggest that glutamate and 5-HT released by NTS afferent terminals trigger Ca2+-dependent astroglial release of ATP to modulate baroreflex sensitivity via P2Y1 receptors. These data add to the growing body of evidence supporting an active role of astrocytes in the brain information processing
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