John Macdonald - Academia.edu (original) (raw)

Papers by John Macdonald

inhibiting either PKC or cell adhesion kinase ␤ [CAK␤ or Pyk2 (proline rich tyrosine kinase 2)]. ... more inhibiting either PKC or cell adhesion kinase ␤ [CAK␤ or Pyk2 (proline rich tyrosine kinase 2)]. Peptides that mimic the binding sites for either Fyn or Src on receptor for activated C kinase-1 (RACK1) also enhanced NMDAR in CA1 neurons, but their effects were blocked by Src(40 -58), implying that Src is the ultimate regulator of NMDARs. RACK1 serves as a hub for PKC, Fyn, and Src and facilitates the regulation of basal NMDAR activity in CA1 hippocampal neurons.

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 11, 2015

In Alzheimer's disease, accumulation of soluble oligomers of β-amyloid peptide is known to be... more In Alzheimer's disease, accumulation of soluble oligomers of β-amyloid peptide is known to be highly toxic, causing disturbances in synaptic activity and neuronal death. Multiple studies relate these effects to increased oxidative stress and aberrant activity of calcium-permeable cation channels leading to calcium imbalance. The transient receptor potential melastatin 2 (TRPM2) channel, a Ca(2+)-permeable nonselective cation channel activated by oxidative stress, has been implicated in neurodegenerative diseases, and more recently in amyloid-induced toxicity. Here we show that the function of TRPM2 is augmented by treatment of cultured neurons with β-amyloid oligomers. Aged APP/PS1 Alzheimer's mouse model showed increased levels of endoplasmic reticulum stress markers, protein disulfide isomerase and phosphorylated eukaryotic initiation factor 2α, as well as decreased levels of the presynaptic marker synaptophysin. Elimination of TRPM2 in APP/PS1 mice corrected these abnorma...

The Journal of neuroscience : the official journal of the Society for Neuroscience, 2001

The postsynaptic density (PSD) at excitatory dendritic synapses comprises a protein complex of gl... more The postsynaptic density (PSD) at excitatory dendritic synapses comprises a protein complex of glutamate receptors, scaffolding elements, and signaling enzymes. For example, NMDA receptors (NMDARs) are linked to several proteins in the PSD, such as PSD-95, and are also tethered via binding proteins such as alpha-actinin directly to filamentous actin of the cytoskeleton. Depolymerization of the cytoskeleton modulates the activity of NMDARs, and, in turn, strong activation of NMDARs can trigger depolymerization of actin. Myosin, the motor protein of muscular contraction and nonmuscle motility, is also associated with NMDARs and the PSD. We show here that constitutively active myosin light chain kinase (MLCK) enhances NMDAR-mediated whole-cell and synaptic currents in acutely isolated CA1 pyramidal and cultured hippocampal neurons, whereas inhibitors of MLCK depress these currents. This MLCK-dependent regulation was observed in cell-attached patches but was lost after excision to insid...

Molecular Pain, 2006

Understanding basic neuronal mechanisms hold the hope for future treatment of brain disease. The ... more Understanding basic neuronal mechanisms hold the hope for future treatment of brain disease. The 1st international conference on synapse, memory, drug addiction and pain was held in beautiful downtown Toronto, Canada on August 21-23, 2006. Unlike other traditional conferences, this new meeting focused on three major aims: (1) to promote new and cutting edge research in neuroscience;

Toxicology Letters, 1998

1. Intravenous anaesthetics, including propofol and thiopental have at least three distinct effec... more 1. Intravenous anaesthetics, including propofol and thiopental have at least three distinct effects on GABA A receptor function. 2. Low concentrations of these drugs enhance the amplitude of currents evoked by sub-saturating concentrations of GABA whereas higher concentrations directly activate the receptor in the absence of GABA. 3. Propofol and some barbiturates also decrease the rate and extent of desensitization as indicated by a prolongation in the decay of currents evoked by saturating concentrations of GABA. 4. In contrast, sedative benzodiazepines that lack general anaesthetic properties do not directly activate the GABA A receptor. 5. In addition, benzodiazepines such as midazolam, have no effect on desensitization when examined in the presence of saturating concentrations of GABA. 6. Here, we discuss the effects of intravenous general anaesthetic on desensitization of the GABA A receptor.

Toxicologic Pathology, 1990

ABSTRAC~ Sequential histologic and ultrastructural changes in juxtaglomerular apparatus (JGA) wer... more ABSTRAC~ Sequential histologic and ultrastructural changes in juxtaglomerular apparatus (JGA) were defined in"ma1e rats treated with quinapril, an inhibitor of angiotensin-converting enzyme (ACE). Doses of 0, 10, 100, and 400 mg/kg were administered daily by gavage for up to 4 weeks. Granular juxtaglomerular (JG) cells were normal or hypogranular on Day 1 at all doses and were hypergranular by Day 7 in rats given 100 and 400 mg/kg relative to age-matched controls. Histologically, JGA hypertrophy was apparent by Day 7 at all doses and was most pronounced by Day 14 in intermediate and deep cortical zones of rats given 100 and 400 mg/ kg. Ultrastructurally, hypertrophic JG cells had abundant rough endoplasmic reticulum and free ribosomes, and prominent Golgi complexes associated with numerous cytoplasmic coated vesicles. Dose-dependent increases in numbers of protogranules, altered granules, and cytoplasmic vacuoles occurred in association with decreased size and increased pleomorphism of mature secretory granules. Granule alterations included vesicular to lamellar membranous matrical inclusions, irregular patterns ofosmiophilia, matrical vacuolation, and flocculent to coarsely granular matrix of greater density than mature granules. We concluded that JG cell hypertrophy and hyperplasia occurred rapidly in response to subchronic ACE inhibition. Further, ultrastructural changes in JG cells were indicative of stimulated renin synthesis by a regulated pathway, renin secretion by exocytosis and cytoplasmic solubilization of granules, and autophagy of granules as a mechanism whereby JG cells regulate levels of stored renin under conditions of excessive stimulation.

Journal of Neuroscience, 2005

Journal of Neuroscience, 2010

The tyrosine kinase Pyk2 plays a unique role in intracellular signal transduction by linking Ca 2... more The tyrosine kinase Pyk2 plays a unique role in intracellular signal transduction by linking Ca 2+ influx to tyrosine phosphorylation, but the molecular mechanism of Pyk2 activation is unknown. We report that Pyk2 oligomerization by antibodies in vitro or overexpression of PSD-95 in PC6-3 cells induces trans-autophosphorylation of Tyr402, the first step in Pyk2 activation. In neurons, Ca 2+ influx through NMDA-type glutamate receptors (NMDAR) causes postsynaptic clustering and autophosphorylation of endogenous Pyk2 via Ca 2+ -and calmodulin-stimulated binding to PSD-95. Accordingly, Ca 2+ influx promotes oligomerization and thereby autoactivation of Pyk2 by stimulating its interaction with PSD-95. We show that this mechanism of Pyk2 activation is critical for LTP in the hippocampus CA1 region, which is thought to underlie learning and memory.

Hippocampus, 2009

Vasoactive intestinal peptide (VIP) is a 28 amino acid peptide which belongs to a superfamily of ... more Vasoactive intestinal peptide (VIP) is a 28 amino acid peptide which belongs to a superfamily of structurally related peptide hormones including pituitary adenylate cyclase-activating polypeptide (PACAP). Although several studies have identified the involvement of PACAP in learning and memory, little work has been done to investigate such a role for VIP. At least three receptors for VIP have been identified including the PACAP receptor (PAC1-R) and the two VIP receptors (VPAC receptors). VIP can activate the PAC1-R only if it is used at relatively high concentrations (e.g. 100 nM); however, at lower concentrations (e.g. 1 nM) it is selective for the VPAC receptors. Our lab has showed that PAC1-R activation signals through PKC/CAKβ/Src pathway to regulate NMDA receptors, however there is little known about the potential regulation of NMDA receptors by VPAC receptors. Our studies demonstrated that application of 1nM VIP enhanced NMDA currents by stimulating VPAC receptors as the effect was blocked by VPAC receptor antagonist [Ac-Tyr 1 , D-Phe 2 ]GRF (1-29). This enhancement of NMDA currents was blocked by both Rp-cAMPS and PKI 14-22 (they are highly specific PKA inhibitors), but not by the specific PKC inhibitor, bisindolylmaleimide I. In addition, the VIP-induced enhancement of NMDA currents was accentuated by inhibition of phosphodiesterase 4, which inhibits the degradation of cAMP. This regulation of NMDA receptors also required the scaffolding protein AKAP. In contrast, the potentiation induced by high concentration of VIP (e.g. 100 nM) was mediated by PAC1-R as well as by Src kinase. Overall, these results show that VIP can regulate NMDA receptors through different receptors and signaling pathways.

Hippocampus, 2011

The induction of long-term potentiation (LTP) of CA3-CA1 synapses requires activation of postsyna... more The induction of long-term potentiation (LTP) of CA3-CA1 synapses requires activation of postsynaptic N-methyl-D-aspartate receptors (GluNRs). At resting potential, the contribution of GluNRs is limited by their voltage-dependent block by extracellular Mg 21 . Highfrequency afferent stimulation is required to cause sufficient summation of excitatory synaptic potentials (EPSPs) to relieve this block and to permit an influx of Ca 21 . It has been assumed that this relief of Mg 21 block is sufficient for induction. We postulated that the induction of LTP also requires a Src-dependent plasticity of GluNRs. Using whole-cell recordings, LTP (GluARs) of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors-EPSCS was induced by pairing postsynaptic depolarization with presynaptic stimulation. This LTP was both GluNR and Src-dependent, being sensitive to AP-5, a GluNR selective antagonist, or to SU6656, a Src-selective inhibitor. When CNQX was used to block all GluARs, we observed a long-lasting potentiation of GluNR-mediated EPSCs. This plasticity was prevented by transiently blocking GluNRs during the induction protocol or by chelating intracellular Ca 21 . GluNRs plasticity was also prevented by bath applications of SU6656 or intracellular applications of the Src-selective inhibitory peptide, Src(40-58). It was also blocked by preventing activation of protein kinase C, a kinase that is upstream of Src-kinase-dependent regulation of GluNRs. Both GluN2A and GluN2B receptors were found to contribute to the plasticity of GluNRs. The contribution of GluNRs and, in particular, their plasticity to the maintenance of LTP was explored using AP5 and SU6656, respectively. When applied >20 min after induction neither drug influenced the magnitude of LTP. However, when applied immediately after induction, treatment with either drug caused the initial magnitude of LTP to progressively decrease to a sustained phase of reduced amplitude. Collectively, our findings suggest that GluNR plasticity, although not strictly required for induction, is necessary for the maintenance of a nondecrementing component of LTP. V V C 2010 Wiley-Liss, Inc.

Stem Cells and Development, 2009

Transplantation of neural stem/progenitor cells (NSPCs) is a promising strategy for repair of the... more Transplantation of neural stem/progenitor cells (NSPCs) is a promising strategy for repair of the diseased/ injured central nervous system (CNS); however, controlling their differentiation remains a signifi cant hurdle. This study is aimed at controlling differentiation and specifi cally at screening exogenous factors to direct NSPC differentiation into neurons in vitro. In this study, adult rat SVZ-derived NSPCs were treated with several factors and screened individually and in combination for changes in cellular morphology, neuronal marker expression, quantitative real-time qRT-PCR, and electrophysiological properties. These in vitro screens showed that of all the different treatments, dibutyryl cyclic AMP (dbcAMP) and interferon-gamma (IFN-γ) enhanced neuronal differentiation most signifi cantly compared to the 1% fetal bovine serum (FBS) controls. Importantly, the combined treatment of NSPCs with dbcAMP and IFN-γ promoted greater neuronal differentiation as refl ected by an increase in β-III tubulin expression and morphological differentiation. Interestingly, the neurons that were generated from the NSPCs in vitro in the presence of dbcAMP and IFN-γ, alone or in combination, responded to exogenous glutamate (Glu), but not gamma-aminobutyric acid (GABA), indicating that these neurons express glutamate receptors. These NSPC-derived neurons may be promising for neural regenerative strategies in the CNS.

Science, 2008

Pannexin-1 (Px1) is expressed at postsynaptic sites in pyramidal neurons, suggesting that these h... more Pannexin-1 (Px1) is expressed at postsynaptic sites in pyramidal neurons, suggesting that these hemichannels contribute to dendritic signals associated with synaptic function. We found that, in pyramidal neurons, N-methyl-d-aspartate receptor (NMDAR) activation induced a secondary prolonged current and dye flux that were blocked with a specific inhibitory peptide against Px1 hemichannels; knockdown of Px1 by RNA interference blocked the current in cultured neurons. Enhancing endogenous NMDAR activation in brain slices by removing external magnesium ions (Mg2+) triggered epileptiform activity, which had decreased spike amplitude and prolonged interburst interval during application of the Px1 hemichannel blocking peptide. We conclude that Px1 hemichannel opening is triggered by NMDAR stimulation and can contribute to epileptiform seizure activity.

Physical Therapy, 2007

a Data entries are mean (ϮSD) for 70 patients with bilateral limb lymphedema. All posttreatment v... more a Data entries are mean (ϮSD) for 70 patients with bilateral limb lymphedema. All posttreatment volumes are significantly less than corresponding pretreatment volumes (PϽ.001). Volume reductions (in milliliters and as percentage of reduction) for each leg calculated for 4-, 8-, and 12-cm segment lengths were not significantly different from each other (PϾ.5).

Neuron, 2001

nine and tyrosine kinases (Raymond et al., 1994; Smart, 1997), including the nonreceptor tyrosine... more nine and tyrosine kinases (Raymond et al., 1994; Smart, 1997), including the nonreceptor tyrosine kinase Src (Yu et al., 1997). The upregulation of NMDARs that results from activating Src has been shown to be necessary for * Programmes in Brain and Behaviour & Cell Biology inducing LTP (Lu et al., 1998), a persistent enhancement of synaptic transmission proposed as a principal cellular Hospital for Sick Children Toronto, Ontario, M5G 1X8 substrate for learning and memory (Bliss and Collingridge, 1993; Malenka and Nicoll, 1999). Numerous bio- † Department of Physiology University of Toronto chemical pathways leading to the activation of Src are known (Brown and Cooper, 1996; Della Rocca et al., Toronto, Ontario, M5S 1A8 ‡ Samuel Lunenfeld Research Institute 1997; Thomas and Brugge, 1997; Biscardi et al., 1999), but the identity of the pathway(s) responsible for en-Mt. Sinai Hospital Toronto, Ontario, M5G 1X5 hancing NMDAR function and inducing LTP is unknown. A molecular candidate for activating Src and enhanc-Canada § Department of Biochemistry ing NMDAR function is the nonreceptor tyrosine kinase, cell adhesion kinase ␤/proline-rich tyrosine kinase 2 Cancer Research Institute Sapporo Medical University (CAK␤/Pyk2) (Lev et al., 1995; Sasaki et al., 1995; Husi et al.

Molecular Pharmacology, 2003

In the hippocampus, two distinct forms of GABAergic inhibition have been identified, phasic inhib... more In the hippocampus, two distinct forms of GABAergic inhibition have been identified, phasic inhibitory postsynaptic currents that are the consequence of the vesicular release of GABA and a tonic conductance that is activated by low ambient concentrations of extracellular GABA. It is not known what accounts for the distinct properties of receptors that mediate the phasic and tonic inhibitory conductances. Moreover, the physiological role of the tonic inhibitory conductance remains uncertain because pharmacological tools that clearly distinguish tonic and phasic receptors are lacking. Here, we demonstrate that GABA A receptors that generate a tonic conductance in cultured hippocampal neurons from embryonic mice have different pharmacological properties than those in cerebellar granule neurons or pyramidal neurons in the dentate gyrus. The tonic conductance in cultured hippocampal neurons is enhanced by the benzodiazepine, midazolam, and is insensitive to the inhibitory effects of the competitive antagonist, gabazine (Յ10 M). We

Molecular Pharmacology, 2007

The mechanisms by which insulin modulates neuronal plasticity and pain processes remain poorly un... more The mechanisms by which insulin modulates neuronal plasticity and pain processes remain poorly understood. Here we report that insulin rapidly increases the function of glycine receptors in murine spinal neurons and recombinant human glycine receptors expressed in human embryonic kidney cells. Whole-cell patch-clamp recordings showed that insulin reversibly enhanced current evoked by exogenous glycine and increased the amplitude of spontaneous glycinergic miniature inhibitory postsynaptic currents recorded in cultured spinal neurons. Insulin (1 M) also shifted the glycine concentration-response plot to the left and reduced the glycine EC 50 value from 52 to 31 M. Currents evoked by a submaximal concentration of glycine

Journal of the American College of Surgeons, 2008

Journal of Neurochemistry, 2006

NMDA receptor function is modulated by both G-proteincoupled receptors and receptor tyrosine kina... more NMDA receptor function is modulated by both G-proteincoupled receptors and receptor tyrosine kinases. In acutely isolated rat hippocampal neurons, direct activation of the platelet-derived growth factor (PDGF) receptor or transactivation of the PDGF receptor by D 4 dopamine receptors inhibits NMDA-evoked currents in a phospholipase C (PLC)dependent manner. We have investigated further the ability of D 2 -class dopamine receptors to modulate NMDA-evoked currents in isolated rat prefrontal cortex (PFC). We have demonstrated that, similar to isolated hippocampal neurons, the application of PDGF-BB or quinpirole to isolated PFC neurons induces a slow-onset and long-lasting inhibition of NMDA-evoked currents. However, in contrast to hippocampal neurons, the inhibition of NMDA-evoked currents by quinpirole in PFC neurons is dependent upon D 2/3 , rather than D 4 , dopamine receptors. In PFC slices, application of both PDGF-BB and quinpirole induced a phosphorylation of the PDGF receptor at the PLCc binding and activation site, Tyr1021. The PDGF receptor kinase inhibitor, tyrphostin A9, and the D 2/3 dopamine receptor antagonist, raclopride, inhibited quinpiroleinduced Tyr1021 phosphorylation. These finding suggest that quinpirole treatment inhibits NMDAR signaling via PDGF receptor transactivation in both the hippocampus and the PFC, and that the effects of quinpirole in these regions are mediated by D 4 and D 2/3 dopamine receptors, respectively.