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Min Zhuo (born 1964) is a pain neuroscientist at the University of Toronto in Canada. [1] He is the Michael Smith Chair in Neuroscience and Mental Health as well as the Canada Research Chair in Pain and Cognition and a Fellow of the Royal Society of Canada. Zhou was hosted in 2017-2018 as a guest professor at the pharmacology institute at Heidelberg University, Heidelberg.
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At the age of 16, Zhuo was admitted to the University of Science and Technology of China in Hefei — graduating in 1985. He obtained his PhD at the University of Iowa in Professor Jerry Gebhart's laboratory. In 1992, Zhuo joined Eric Kandel's laboratory at Columbia University where he showed CO-cGMP as key messengers for presynaptic LTP. [2] In 1995, Zhuo spent one year in Richard Tsien's laboratory at Stanford University. In 1996, Zhuo moved to Washington University in St. Louis and focused on pain plasticity in the spinal cord and cortex. He showed that 'smart' mice suffered more pain, [3] GluN2B and AC1 are novel therapeutic targets for treating chronic pain [4] [5] In 2003, he moved to the University of Toronto, and identified NB001 as a selective inhibitor for AC1. [6] He co-established two online journals, Molecular Pain and Molecular Brain . In 2009, he was elected to Fellow of the Royal Society of Canada.
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Born in 1964 in Xiapu, a seaside town in Fujian, China, Zhuo grew up inspired by the mountain villages and scenery. He started painting with the help of his mother and planned to pursue a career in art — perhaps as a teacher. It was not until later in life that he became interested in pursuing a career in science. In 1980, he was accepted into the University of Science and Technology of China in Hefei, from which he graduated in 1985. From there he went on to the Chinese Academy of Sciences, Shanghai Branch where his work focused mainly on the basic mechanism of acupuncture and pain.
In 1988, Zhuo joined Jerry Gebhart's laboratory at the University of Iowa as a visiting student. He then joined the graduate program as a PhD student. Using integrative pharmacological, electrophysiological, and behavioral methods, he discovered a novel descending facilitatory modulation of spinal nociceptive transmission from the RVM. [7] [8] [9] [10] [11] [12] Descending facilitation has a general impact on spinal sensory transmission, inducing sensory inputs from cutaneous and visceral organs. Recent studies found that descending facilitation is likely activated or to be up-regulated in chronic pain conditions, providing basic evidence for inhibiting descending facilitation to help to relieve chronic pain. [13]
In 1992, Zhuo graduated from University of Iowa with PhD degree in pharmacology. The same year, he joined Eric Kandel's laboratory at Columbia University. During this time, Zhuo worked on hippocampal plasticity and showed that carbon monoxide (CO), together with nitric oxide (NO), may serves as retrograde messengers in hippocampal LTP. [14] [15] Together with Dr. Yinhe Hu, he further discovered that soluble guanylyl clcyaes (sGC) and cGMP-dependent protein kinase (PKG) act downstream from these diffusible messengers. [16] Recent genetic studies confirm the importance of PKGs in central plasticity. [17] [18] [19] In 1995, after being offered an independent faculty job at Washington University in St. Louis, Zhuo joined Richard Tsien’s laboratory in Stanford for one year. While at Stanford, Zhuo mastered whole-cell patch-clamp techniques and was the first one to show that direct patching of dendrites in isolated hippocampal neuronal preparations. Together with Ege Kavalali and Haruhiko Bito, they published together a key study on voltage-gated calcium channels in neuronal dendrites (or called dendrosomes). [20]
After finishing his postdoctoral training, Zhuo started his own laboratory in 1996, at Washington University in St. Louis. He decided to combine his knowledge of pain and synaptic plasticity of hippocampal memory, and explored possible changes in spinal cord dorsal horn. [21] With the research assistance of Ms Ping Li, he identified silent synapses in spinal cord dorsal horn, and provided key synaptic mechanisms for possible recruitment of such silent nociceptive pathways in chronic pain conditions. [22] [23] It also provided synaptic mechanism for G protein coupled pathways in the facilitatory modulation of spinal sensory transmission. He further demonstrated that the interaction between AMPA receptor and PDZ proteins is critical, and inhibiting such interaction provide analgesic effects in animal model of chronic pain. [24] He is the founding member of Washington University Pain center, and acted as chief for basic research until he left for Toronto in 2003.
While working in St. Louis, Zhuo collaborated on a project with Professor Guosong Liu of MIT and Joe Tsien of Princeton University, where they discovered that enhancing NMDA NR2B receptors in the forebrain neurons enhanced LTP in the hippocampus. More importantly, such enhancement is selective, since LTD is not affected in the same mice. This work provides direct evidence that enhancing LTP can increase learning capacity. [25] Because NMDA NR2B (GluN2B) is developmentally regulated, Zhuo decided to explore whether or not there is any evolutionary disadvantage to being 'smart'. Zhuo found that NR2B expression lead to the enhancement of chronic pain. [26] These genetic and behavioral studies provide the first direct evidence that forebrain NMDA receptors play important roles in persistent pain.
In 2003, Zhuo moved to University of Toronto in Canada as EJLB-Michael Smith Chair in Neuroscience and mental health and Canada Research Chair (CRC). [27] In Toronto, Zhuo decided to focus on synaptic plasticity in the anterior cingulate cortex, a key cortical region for pain, and has mapped the signalling pathways for LTP and LTD in the ACC. [28] The discovery of LTP in pain-related cortex provides direct evidence for pathological mechanism of chronic pain as well as pain-related emotional disorders. Before these discoveries, most of academic and pharmaceutical investigators mainly focused on DRG and spinal cord when searching for new treatments for chronic pain.
Upregulation of AMPARs and/or the increase of presynaptic release are known to contribute to synaptic potentiation and behavioural learning, while postsynaptic NMDA receptors are not significantly affected. Unlike in learning and memory, Zhuo found that cortical synapses and circuits are undergoing dramatic changes after peripheral never injury. In addition to postsynaptic AMPARs, Min found that NMDA receptors are significantly increased in the ACC as well as insular cortex. Inhibiting NMDA NR2B receptors in these brain areas produced significant analgesic effects in animal models of neuropathic pain. [29] [30] [31] Positive feedback mechanisms at synaptic and circuit levels are proposed to explain why chronic pain is long-lasting and difficult to treat. [32]
Between the time in St Louis and Toronto, Zhuo identified calcium stimulated adenylyl cyclase subtype 1 as being a key enzyme for triggering injury-related LTP in the ACC. [33] [34] Using gene knockout mice lacking AC1, he discovered that AC1 is critical for ACC LTP (including early- and late-phase LTP). While acute pain responses are normal in AC1 knockout mice, behavioral responses to peripheral injection of two inflammatory stimuli, formalin and complete Freund's adjuvant as well as nerve injury were reduced or abolished. Considering AC1 is highly expressed in neurons including the ACC, Zhuo proposed that AC1 acts as a key drug target for inhibiting chronic pain related plasticity in the brains. [35] Unlike other targets, learning-related hippocampal LTP and behavioral learning and memory are not affected by AC1 gene deletion.
To search selective inhibitors for AC1, Zhuo has carried out rational drug design and chemical screening, and has a lead candidate AC1 inhibitor, NB001, which is relatively selective for AC1 over other adenylate cyclase isoforms. Using a variety of behavioral tests and toxicity studies, NB001, when administered intraperitoneally or orally, was found to have an analgesic effect in animal models of neuropathic pain, without any apparent side effects. The study thus shows that AC1 could be a productive therapeutic target for neuropathic pain and describes a new agent for the possible treatment of neuropathic pain. [36]
A dendritic spine is a small membrane protrusion from a neuron's dendrite that typically receives input from a single axon at the synapse. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. Most spines have a bulbous head, and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a single neuron can contain hundreds to thousands of spines. In addition to spines providing an anatomical substrate for memory storage and synaptic transmission, they may also serve to increase the number of possible contacts between neurons. It has also been suggested that changes in the activity of neurons have a positive effect on spine morphology.
In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons. The opposite of LTP is long-term depression, which produces a long-lasting decrease in synaptic strength.
The N-methyl-D-aspartatereceptor (also known as the NMDA receptor or NMDAR), is a glutamate receptor and predominantly Ca2+ ion channel found in neurons. The NMDA receptor is one of three types of ionotropic glutamate receptors, the other two being AMPA and kainate receptors. Depending on its subunit composition, its ligands are glutamate and glycine (or D-serine). However, the binding of the ligands is typically not sufficient to open the channel as it may be blocked by Mg2+ ions which are only removed when the neuron is sufficiently depolarized. Thus, the channel acts as a "coincidence detector" and only once both of these conditions are met, the channel opens and it allows positively charged ions (cations) to flow through the cell membrane. The NMDA receptor is thought to be very important for controlling synaptic plasticity and mediating learning and memory functions.
In neurophysiology, long-term depression (LTD) is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress.
AP5 is a chemical compound used as a biochemical tool to study various cellular processes. It is a selective NMDA receptor antagonist that competitively inhibits the ligand (glutamate) binding site of NMDA receptors. AP5 blocks NMDA receptors in micromolar concentrations.
Hyperalgesia is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.
Neuropathic pain is pain caused by a lesion or disease of the somatosensory nervous system. Neuropathic pain may be associated with abnormal sensations called dysesthesia or pain from normally non-painful stimuli (allodynia). It may have continuous and/or episodic (paroxysmal) components. The latter resemble stabbings or electric shocks. Common qualities include burning or coldness, "pins and needles" sensations, numbness and itching.
Schaffer collaterals are axon collaterals given off by CA3 pyramidal cells in the hippocampus. These collaterals project to area CA1 of the hippocampus and are an integral part of memory formation and the emotional network of the Papez circuit, and of the hippocampal trisynaptic loop. It is one of the most studied synapses in the world and named after the Hungarian anatomist-neurologist Károly Schaffer.
Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response. Sensitization often is characterized by an enhancement of response to a whole class of stimuli in addition to the one that is repeated. For example, repetition of a painful stimulus may make one more responsive to a loud noise.
Metaplasticity is a term originally coined by W.C. Abraham and M.F. Bear to refer to the plasticity of synaptic plasticity. Until that time synaptic plasticity had referred to the plastic nature of individual synapses. However this new form referred to the plasticity of the plasticity itself, thus the term meta-plasticity. The idea is that the synapse's previous history of activity determines its current plasticity. This may play a role in some of the underlying mechanisms thought to be important in memory and learning such as long-term potentiation (LTP), long-term depression (LTD) and so forth. These mechanisms depend on current synaptic "state", as set by ongoing extrinsic influences such as the level of synaptic inhibition, the activity of modulatory afferents such as catecholamines, and the pool of hormones affecting the synapses under study. Recently, it has become clear that the prior history of synaptic activity is an additional variable that influences the synaptic state, and thereby the degree, of LTP or LTD produced by a given experimental protocol. In a sense, then, synaptic plasticity is governed by an activity-dependent plasticity of the synaptic state; such plasticity of synaptic plasticity has been termed metaplasticity. There is little known about metaplasticity, and there is much research currently underway on the subject, despite its difficulty of study, because of its theoretical importance in brain and cognitive science. Most research of this type is done via cultured hippocampus cells or hippocampal slices.
Ca2+
/calmodulin-dependent protein kinase II is a serine/threonine-specific protein kinase that is regulated by the Ca2+
/calmodulin complex. CaMKII is involved in many signaling cascades and is thought to be an important mediator of learning and memory. CaMKII is also necessary for Ca2+
homeostasis and reuptake in cardiomyocytes, chloride transport in epithelia, positive T-cell selection, and CD8 T-cell activation.
Opioid-induced hyperalgesia (OIH) or opioid-induced abnormal pain sensitivity, also called paradoxical hyperalgesia, is an uncommon condition of generalized pain caused by the long-term use of high dosages of opioids such as morphine, oxycodone, and methadone. OIH is not necessarily confined to the original affected site. This means that if the person was originally taking opioids due to lower back pain, when OIH appears, the person may experience pain in the entire body, instead of just in the lower back. Over time, individuals taking opioids can also develop an increasing sensitivity to noxious stimuli, even evolving a painful response to previously non-noxious stimuli (allodynia). This means that if the person originally felt pain from twisting or from sitting too long, the person might now additionally experience pain from a light touch or from raindrops falling on the skin.
Neuromedin U is a neuropeptide found in the brain of humans and other mammals, which has a number of diverse functions including contraction of smooth muscle, regulation of blood pressure, pain perception, appetite, bone growth, and hormone release. It was first isolated from the spinal cord in 1985, and named after its ability to cause smooth muscle contraction in the uterus.
Glutamate [NMDA] receptor subunit epsilon-2, also known as N-methyl D-aspartate receptor subtype 2B, is a protein that in humans is encoded by the GRIN2B gene.
Coincidence detection is a neuronal process in which a neural circuit encodes information by detecting the occurrence of temporally close but spatially distributed input signals. Coincidence detectors influence neuronal information processing by reducing temporal jitter and spontaneous activity, allowing the creation of variable associations between separate neural events in memory. The study of coincidence detectors has been crucial in neuroscience with regards to understanding the formation of computational maps in the brain.
The wide dynamic range (WDR) neuron was first discovered by Mendell in 1966. Early studies of this neuron established what is known as the gate control theory of pain. The basic concept is that non-painful stimuli block the pathways for painful stimuli, inhibiting possible painful responses. This theory was supported by the fact that WDR neurons are responsible for responses to both painful and non-painful stimuli, and the idea that these neurons could not produce more than one of these responses simultaneously. WDR neurons respond to all types of somatosensory stimuli, make up the majority of the neurons found in the posterior grey column, and have the ability to produce long range responses including those responsible for pain and itch.
Kaang Bong-Kiun is a South Korean professor of neuroscience in the Department of Biological Sciences of Seoul National University. He is a fellow of the Korean Academy of Science and Technology and co-director of the IBS Center for Cognition and Sociality with Changjoon Justin Lee.
Early long-term potentiation (E-LTP) is the first phase of long-term potentiation (LTP), a well-studied form of synaptic plasticity, and consists of an increase in synaptic strength. LTP could be produced by repetitive stimulation of the presynaptic terminals, and it is believed to play a role in memory function in the hippocampus, amygdala and other cortical brain structures in mammals.
Sandra M. Garraway is a Canadian-American neuroscientist and assistant professor of physiology in the Department of Physiology at Emory University School of Medicine in Atlanta, Georgia. Garraway is the director of the Emory Multiplex Immunoassay Core (EMIC) where she assists researchers from both academia and industry to perform, analyze, and interpret their multiplexed immunoassays. Garraway studies the neural mechanisms of spinal nociceptive pain after spinal cord injury and as a postdoctoral researcher she discovered roles for both BDNF and ERK2 in pain sensitization and developed novel siRNA technology to inhibit ERK2 as a treatment for pain.
Epigenetics of chronic pain is the study of how epigenetic modifications of genes affect the development and maintenance of chronic pain. Chromatin modifications have been found to affect neural function, such as synaptic plasticity and memory formation, which are important mechanisms of chronic pain. In 2019, 20% of adults dealt with chronic pain. Epigenetics can provide a new perspective on the biological mechanisms and potential treatments of chronic pain.