52 research outputs found
John Frazer
No full textJohn Frazer, Professor, trained at the Architectural Association, taught first at Cambridge University and then the AA in the 1970s and again in the '90s. He was Head of School of Design Research History and Criticism at the University of Ulster in the 1980s, he also ran a systems and design consultancy with his wife Julia (including projects for Cedric Price and Walter Segal) and was founder and chairman of Autographics software. He is currently Swire Chair Professor and Head of School of Design in Hong Kong.-----\ud
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This is a very personal perspective on a concept of universal and future significance. It is personal, both is the sense that it is an unashamedly biased view of both the significance of the project, and the nature of that significance and because the author was personally involved as one of the consultants on GENERATOR and subsequently involved Cedric Price in its educational application at the Architectural Association. GENERATOR is still very much alive and was still developing whilst this chapter was being written.\u
TCN 201 selectively blocks GluN2A-containing NMDARs in a GluN1 co-agonist dependent but non-competitive manner
No full textAntagonists that are sufficiently selective to preferentially block GluN2A-containing N-methyl-d-aspartate receptors (NMDARs) over GluN2B-containing NMDARs are few in number. In this study we describe a pharmacological characterization of 3-chloro-4-fluoro-N-[4-[[2-(phenylcarbonyl)hydrazino]carbonyl]benzyl]benzenesulphonamide (TCN 201), a sulphonamide derivative, that was recently identified from a high-throughput screen as a potential GluN2A-selective antagonist. Using two-electrode voltage-clamp (TEVC) recordings of NMDAR currents from Xenopus laevis oocytes expressing either GluN1/GluN2A or GluN1/GluN2B NMDARs we demonstrate the selective antagonism by TCN 201 of GluN2A-containing NMDARs. The degree of inhibition produced by TCN 201 is dependent on the concentration of the GluN1-site co-agonist, glycine (or d-serine), and is independent of the glutamate concentration. This GluN1 agonist-dependency is similar to that observed for a related GluN2A-selective antagonist, N-(cyclohexylmethyl)-2-[{5-[(phenylmethyl)amino]-1,3,4-thiadiazol-2-yl}thio]acetamide (TCN 213). Schild analysis of TCN 201 antagonism indicates that it acts in a non-competitive manner but its equilibrium constant at GluN1/GluN2A NMDARs indicates TCN 201 is around 30-times more potent than TCN 213. In cortical neurones TCN 201 shows only modest antagonism of NMDAR-mediated currents recorded from young (DIV 9-10) neurones where GluN2B expression predominates. In older cultures (DIV 15-18) or in cultures where GluN2A subunits have been over-expressed TCN 201 gives a strong block that is negatively correlated with the degree of block produced by the GluN2B-selective antagonist, ifenprodil. Nevertheless, while TCN 201 is a potent antagonist it must be borne in mind that its ability to block GluN2A-containing NMDARs is dependent on the GluN1-agonist concentration and is limited by its low solubility
Investigation into the destructive and adaptive responses of neural cells to stress
No full textHomeostasis within the neuro-glial unit is essential to the longevity of neurons.
Conversely, loss of homeostasis, particularly of Ca2+ levels, of redox balance and of
ATP, contribute to neuronal loss and dysfunction in many neurodegenerative and
neurological disorders. This thesis is centred on better understanding the
vulnerability of neurons to stress, as well as adaptive responses to these stresses.
Since neurodegenerative conditions associated with Ca2+, redox and bioenergetic
dyshomeostasis are often characterised by early dendritic pathology, I first studied
dendritic vs. somatic responses of primary cortical neurons to these types of
challenges in real-time. Using a wide range of genetically-encoded probes to
measure Ca2+, ATP, NADH, glutathione and glutamate, I show that dendrites are
selectively vulnerable to oxidative stress, excitotoxicity as well as to metabolic
demand induced by action potential (AP) burst activity. However, I provide evidence
that neurons undergoing energetically demanding AP burst activity can adjust their
metabolic output by increasing mitochondrial NADH production in a manner
dependent on the mitochondrial calcium uniporter (MCU), as well as increase their
capacity to buffer their intracellular redox balance. Finally, I have studied
transcriptional programs in astrocytes triggered by neurons and neuronal activity to
better understand adaptive signaling between different cell types in the neuro-glial
unit. I developed a novel system combining neurons and astrocytes from closely-related
species, followed by RNA-seq and in silico read sorting. I uncovered a
program of neuron-induced astrocytic gene expression which drives and maintains
astrocytic maturity and neurotransmitter uptake function. In addition I identified a
novel form of synapse-to-nucleus signaling, mediated by glutamatergic activity and
acutely regulating diverse astrocytic genes involved in astrocyte-neuron metabolic
coupling. Of note, neuronal activity co-ordinately induced astrocytic genes involved
in astrocyte-to-neuron thyroid hormone signaling, extracellular antioxidant defences,
and the astrocyte-neuron lactate shuttle, suggesting that this non cell-autonomous
signaling may form part of the homeostatic machinery within the neuro-glial unit
Control of anti-apoptotic and antioxidant pathways in neural cells
No full textOxidative stress is a feature of many chronic neurodegenerative diseases as well as a
contributing factor in acute disorders including stroke. Fork head class of
transcription factors (Foxos) play a key role in promoting oxidative stress-induced
apoptosis in neurons through the upregulation of a number of pro-apoptotic genes.
Here I demonstrate that synaptic NMDA receptor activity not only promotes Foxos
nuclear exclusion but also suppresses the expression of Foxo1 in a PI3K-dependent
fashion. I also found that Foxo1 is in fact, a Foxo target gene and that it is subject to
a feed-forward inhibition by synaptic activity, which is thought to result in longerterm
suppression of Foxo downstream gene expression than previously thought. The
nuclear factor (erythroid 2-related) factor 2 (Nrf2) is another transcription factor
involved in oxidative stress and the key regulator of many genes, whose products
form important intrinsic antioxidant systems. In the CNS, artificial activation of Nrf2
in astrocytes has been shown to protect nearby neurons from oxidative insults.
However, the extent to which Nrf2 in astrocytes could respond to endogenous signals
such as mild oxidative stress is less clear. The data presented herein, demonstrate for
the first time that endogenous Nrf2 could be activated by mild oxidative stress and
that this activation is restricted to astrocytes. Contrary to the established dogma, I
found that mild oxidative stress induces the astrocytic Nrf2 pathway in a manner
distinct from the classical Keap1 antagonism employed by prototypical Nrf2
inducers. The mechanism was found to involve direct regulation of Nrf2's
transactivation properties. Overall these results advance our knowledge of the
molecular mechanism(s) associated with the control of endogenous antioxidant
defences by physiological signals
Neuronal activity-dependent protection against apoptotic and oxidative insults
No full textPatterns of physiological electrical activity in the central nervous system (CNS) cause longlasting
changes in gene expression that promote neuronal survival. These changes can be
mediated by signalling pathways activated by Ca2+ influx through synaptic N-methyl DAspartate
receptors (NMDARs). Identification and study of these, and other neuroprotective
signalling pathways of the CNS, is invaluable; as this may one day lead to therapeutic
strategies against the deleterious effects of CNS injury or degeneration. The data presented
in this thesis focuses on activity-dependent neuroprotection and how it interacts with other
signalling pathways to protect against apoptotic and oxidative insults.
A previously unobserved role of activity-dependent neuroprotection in mediating the effects
of the neuropeptide PACAP is demonstrated. By promoting cAMP/PKA signalling PACAP
triggers neuronal firing activity, which is essential for the neuroprotective effects mediated
by PACAP. This firing activity cooperates with direct signalling by PKA in promoting longlasting
CREB-mediated gene expression. The molecular events associated with PACAP
mediated stimulation of CRE-dependent gene expression are presented. Investigation of the
control of neuronal antioxidant defences by neuronal activity, both on its own and in
cooperation with astrocyte-derived support, was also investigated. Neuronal activity is
demonstrated to strongly increase the capacity of the antioxidant glutathione (GSH) system,
through a program of coordinated transcriptional events. The utilisation, biosynthesis and
recycling of GSH is enhanced in neurons, leading to increased resistance against oxidative
insults. Since several GSH pathway enzyme genes are regulated by the transcription factor
Nrf2, the ability of CDDO-F3, a small molecule activator of Nrf2, to mimic the effect of
firing activity on neuronal GSH levels was examined. CDDO-F3 sustains neuronal GSH
levels and confers neuroprotection against oxidative insult. These actions are dependent on
the presence of astrocytes; whereas Nrf2 mediated regulation of GSH pathway genes is
essentially inactive in neurons. Neuronal activity and activation of the astrocytic Nrf2
pathway can cooperate, maintaining neuronal GSH levels and protecting neurons against
strong oxidative insults. Collectively this work expands our knowledge as to the molecular
mechanisms of activity-dependent neuroprotection, and how such signals may synergise with
other protective pathways to promote neuronal health
Neuroprotection from the huntingtin-repressed transcriptional coactivator PGC-1α
No full textThe transcriptional coactivator PPARgamma coactivator 1alpha (PGC-1α)
is a regulator of mitochondrial biogenesis and function and is decreased in
the striatum of patients with Huntington’s Disease (HD). HD is an
autosomal dominant neurological disorder caused by a polyglutamine
repeat in the huntingtin protein which leads to degeneration of striatal and
cortical tissues. PGC-1α undergoes targeted downregulation by mutant
huntingtin protein (mtHtt) and PGC-1α knockout mice have striatal lesions
similar to HD transgenic mice. Exogenous PGC-1α partially reverses the
toxic effects of mutant huntingtin in cultured striatal neurons while in vivo
administration of PGC-1α to the striatum in a mouse model of HD reduces
neuronal volume loss. Synaptic N-methyl-D-aspartate receptor (NMDAR)-
activity can drive the expression of PGC-1α which is neuroprotective
against oxidative and excitotoxic stress in vitro whereas extrasynaptic
NMDAR expression is increased in HD. Excessive NMDAR activity,
specifically through extrasynaptic rather than synaptic NMDARs, leads to
excitotoxic death in neurons and its regulation has been targeted in the
search for therapeutic interventions for multiple neurological disorders.
The data presented in this thesis show that the repression of PGC-1α by
mtHtt may be significant in the dysregulation of NMDARs in HD. Both
PGC-1α knockdown and mutant huntingtin are found to increase
extrasynaptic NMDAR activity and excitotoxicity in a non-additive way,
suggesting common regulatory mechanisms. Furthermore exogenous PGC-
1α expression is sufficient to reverse this increase in extrasynaptic
NMDAR currents and excitotoxicity by mtHtt. This thesis adds
mechanistic insight into previous understanding of the synergistic roles of
mtHtt, NMDAR activity and PGC-1α in HD.
Finally, we show that chronic knockout of PGC-1α in the PGC-1α(-/-)
mouse causes distinct alterations in glutamatergic signaling that do not
mimic the observation of acute knockdown of PGC-1α. We propose that
the loss of PGC-1α in a number of neurological disorders contributes to
concurrent increases in aberrant glutamate signaling and excitotoxicity in
these diseases
Extracellular Calcium Regulates Postsynaptic Efficacy through Group 1 Metabotropic Glutamate Receptors
No full textBursts of synaptic transmission are known to induce transient depletion of Ca2+ within the synaptic cleft. Although Ca2+ depletion has been shown to lower presynaptic release probability, effects on the postsynaptic cell have not been reported. In this study, we show that physiologically relevant reductions in extracellular Ca2+ lead to a decrease in synaptic strength between synaptically coupled layer 2/3 cortical pyramidal neurons. Using quantal analysis and mEPSP analysis, we demonstrate that a lowered extracellular Ca2+ produces a reduction in the postsynaptic quantal size in addition to its known effect on release probability. An elevated Mg2+ level can prevent this reduction in postsynaptic efficacy at subphysiological Ca2+ levels. We show that the calcium-dependent effect on postsynaptic quantal size is mediated by group 1 metabotropic glutamate receptors, acting via CaMKII (Ca2+/calmodulin-dependent protein kinase II) and PKC. Therefore, physiologically relevant changes in extracellular Ca2+ can regulate information transfer at cortical synapses via both presynaptic and postsynaptic mechanisms
"A Symbol of the New African": Drum magazine, popular culture and the formation of black urban subjectivity in 1950s South Africa.
No full textPhDThis thesis examines the emergence of black urban subjectivity in South Africa
during the 1950s, focussing on the ways in which popular American genres were
utilised in the construction of black urban identities that served as a means of
resistance to apartheid. At the centre of this process was Drum magazine:
founded in South Africa in 1951 , it became the largest selling magazine on the
African continent in 1956. Drum's success was due to the way in which it
enabled the relocation of black identity from the "traditional" towards the
"modern'. The 1940s gave rise to widespread migration of black South Africans
from rural to urban areas and this newly urbanised community was seeking
models of black urban identity. Yet the Nationalist government was attempting
to curtail the emergence of a black urban proletariat, which posed a threat to
white political supremacy. Through apartheid legislation black identity was
constructed as essentially tribal and rural. As a means of resisting this, urbanised
black South Africans turned to, and appropriated, readily available forms of
American culture. Drum published Americanised images and stories: gangsters,
black detectives, black comic heroes, and pulp romances. This popular material
appeared alongside some of the finest investigative journalism ever published.
While Drum magazine is widely acknowledged as having provided a platform
for the emergence of black South African writing in English, its popular content
has been dismissed by critics as apolitical escapism, imitation and capitulation to
American culture. This thesis challenges the dismissal of the popular that has
dominated analyses of Drum since the 1960s, arguing that such a position denies
the agency of local writers and audiences. My analysis reveals that American
forms were adopted in critically discerning ways and chosen for their ability to
convey local meaning and create positions from which to resist aparthei
Synaptic NMDAR activity suppresses FOXO1 expression via a cis-acting FOXO binding site:FOXO1 is a FOXO target gene
No full textActivation of gene expression by FOXO transcription factors can promote neuronal death in response to loss of trophic support, or oxidative stress. The predominant neuronal FOXOs, FOXO1 and FOXO3, promote the expression of pro-death genes, such as Fas Ligand, Bim and Txnip. Neuroprotective signals initiated by neurotrophins, growth factors or synaptic activity trigger the nuclear export of FOXOs via activation of the PI3K-Akt pathway. One key aspect of FOXO regulation is that once PI3K-Akt activity has returned to baseline, FOXOs return to the nucleus to resume the activation of their target genes. Thus, the FOXO-inhibiting capacity of the PI3K-Akt pathway is thought to be short-lived. However, we show here that synaptic NMDA receptor activity not only triggers FOXO export, but also suppresses the expression of FOXO1. Blockade of PI3K activity prevents both FOXO nuclear export and suppression of FOXO1 expression, raising the possibility that FOXO1 is itself a FOXO target gene. We found that FOXO3, and to a lesser extent FOXO1 transactivates the FOXO1 promoter via a consensus FOXO binding site (GTAAACAA), and also an upstream sequence resembling a classical FOXO-binding insulin response sequence (CAAAACAA). Activity-dependent suppression of the FOXO1 promoter is mediated through the proximal GTAAACAA sequence. Similar suppression via this site is observed by activating neuronal IGF-1 receptors by exogenous insulin. Thus, through a feed-forward inhibition mechanism, synaptic activity triggers FOXO export resulting in suppression of FOXO1 expression. These results suggest that FOXO-inactivating signals are likely to result in longer-term inhibition of FOXO target gene expression than previously thought.</p
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