Singapore Institute for Neurotechnology SINAPSE

Singapore, Singapore

Singapore Institute for Neurotechnology SINAPSE

Singapore, Singapore
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Farooq U.,National University of Singapore | Farooq U.,Singapore Institute for Neurotechnology SINAPSE | Rajkumar R.,National University of Singapore | Rajkumar R.,Singapore Institute for Neurotechnology SINAPSE | And 7 more authors.
European Journal of Neuroscience | Year: 2013

The medial prefrontal cortex (mPFC) in the rat has been implicated in a variety of cognitive processes, including working memory and expression of fear memory. We investigated the inputs from a brain stem nucleus, the nucleus incertus (NI), to the prelimbic area of the mPFC. This nucleus strongly expresses corticotropin-releasing factor type 1 (CRF1) receptors and responds to stress. A retrograde tracer was used to verify connections from the NI to the mPFC. Retrogradely labelled cells in the NI expressed CRF receptors. Electrophysiological manipulation of the NI revealed that stimulation of the NI inhibited spontaneous neuronal firing in the mPFC. Similarly, CRF infusion into the NI, in order to mimic a stressful condition, inhibited neuronal firing and burst firing in the mPFC. The effect of concurrent high-frequency stimulation of the NI on plasticity in the hippocampo-prelimbic medial prefrontal cortical (HP-mPFC) pathway was studied. It was found that electrical stimulation of the NI impaired long-term potentiation in the HP-mPFC pathway. Furthermore, CRF infusion into the NI produced similar results. These findings might account for some of the extra-pituitary functions of CRF and indicate that the NI may play a role in stress-driven modulation of working memory and possibly other cognitive processes subserved by the mPFC. © 2013 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Kumar J.R.,National University of Singapore | Kumar J.R.,Singapore Institute for Neurotechnology SINAPSE | Rajkumar R.,National University of Singapore | Rajkumar R.,Singapore Institute for Neurotechnology SINAPSE | And 13 more authors.
British Journal of Pharmacology | Year: 2017

Relaxin-3 has been proposed to modulate emotional–behavioural functions such as arousal and behavioural activation, appetite regulation, stress responses, anxiety, memory, sleep and circadian rhythm. The nucleus incertus (NI), in the midline tegmentum close to the fourth ventricle, projects widely throughout the brain and is the primary site of relaxin-3 neurons. Over recent years, a number of preclinical studies have explored the function of the NI and relaxin-3 signalling, including reports of mRNA or peptide expression changes in the NI in response to behavioural or pharmacological manipulations, effects of lesions or electrical or pharmacological manipulations of the NI, effects of central microinfusions of relaxin-3 or related agonist or antagonist ligands on physiology and behaviour, and the impact of relaxin-3 gene deletion or knockdown. Although these individual studies reveal facets of the likely functional relevance of the NI and relaxin-3 systems for human physiology and behaviour, the differences observed in responses between species (e.g. rat vs. mouse), the clearly identified heterogeneity of NI neurons and procedural differences between laboratories are some of the factors that have prevented a precise understanding of their function. This review aims to draw attention to the current preclinical evidence available that suggests the relevance of the NI/relaxin-3 system to the pathology and/or symptoms of certain neuropsychiatric disorders and to provide cognizant directions for future research to effectively and efficiently uncover its therapeutic potential. Linked Articles: This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit © 2016 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.

Rajkumar R.,National University of Singapore | Rajkumar R.,Singapore Institute for Neurotechnology SINAPSE | Wu Y.,National University of Singapore | Wu Y.,Singapore Institute for Neurotechnology SINAPSE | And 7 more authors.
Brain Research Bulletin | Year: 2016

The nucleus incertus (NI) is a small cluster of brainstem neurons presumed to play a role in stress responses. We show that swim stress (normal water: 30min and cold water: 20min) and elevation stress robustly induced c-Fos expression in the NI and significantly suppressed long-term potentiation (LTP) in the hippocampo-medial prefrontal cortical (HP-mPFC) pathway. To examine whether activation of CRF1 receptors in the NI plays a role in the suppression of HP-mPFC LTP, antalarmin, a specific CRF1 receptor antagonist, was infused directly into the NI either before presentation of (1) elevation stress or (2) high frequency stimulation. As predicted, the intra-NI infusion of antalarmin reversed the elevation stress-induced suppression of LTP in the HP-mPFC pathway. This report suggests that the CRF1 receptor in the NI contributes to stress-related impairment in plasticity of the HP-mPFC pathway. The findings suggest that the NI-HP-mPFC is a stress responsive circuit in the rodent brain. © 2015 The Authors.

Rajkumar R.,National University of Singapore | Rajkumar R.,Singapore Institute for Neurotechnology SINAPSE | Kumar J.R.,National University of Singapore | Kumar J.R.,Singapore Institute for Neurotechnology SINAPSE | And 2 more authors.
Neurobiology of Learning and Memory | Year: 2017

Priming phenomenon, in which an earlier exposure to a stimulus or condition alters synaptic plasticity in response to a subsequent stimulus or condition, known as a challenge, is an example of metaplasticity. In this review, we make the case that the locus coeruleus noradrenergic system-medial perforant path-dentate gyrus pathway is a neural ensemble amenable to studying priming-challenge effects on synaptic plasticity. Accumulating evidence points to a tyrosine hydroxylase-dependent priming effect achieved by pharmacological (nicotine and antipsychotics) or physiological (septal theta driving) manipulations of the locus coeruleus noradrenergic system that can facilitate noradrenaline-induced synaptic plasticity in the dentate gyrus of the hippocampus. The evidence suggests the hypothesis that behavioural experiences inducing tyrosine hydroxylase expression in the locus coeruleus may be sufficient to prime this form of metaplasticity. We propose exploring this phenomenon of priming and challenge physiologically, to determine whether behavioural experiences are sufficient to prime the locus coeruleus, enabling subsequent pharmacological or behavioural challenge conditions that increase locus coeruleus firing to release sufficient noradrenaline to induce long-lasting potentiation in the dentate gyrus. Such an approach may contribute to unravelling mechanisms underlying this form of metaplasticity and its importance in stress-related mnemonic processes. © 2016 The Authors

Farooq U.,National University of Singapore | Farooq U.,Singapore Institute for Neurotechnology SINAPSE | Kumar J.R.,National University of Singapore | Kumar J.R.,Singapore Institute for Neurotechnology SINAPSE | And 4 more authors.
Physiology and Behavior | Year: 2016

Locomotion is essential for goal-oriented behavior. Theta frequency oscillations in the hippocampus have been associated with behavioral activation and initiation of movement. Recently, the nucleus incertus, a brainstem nucleus with widespread cortical and subcortical projections, has been reported to modulate the septo-hippocampal axis triggering theta activity in the hippocampus. This suggests that activation of the nucleus incertus would induce movement. In this study, we investigated the effects of electrical microstimulation of the nucleus incertus on locomotion in conscious rats. Rats chronically implanted with microelectrodes targeting the nucleus incertus were electrically stimulated while their behavior was tracked. High frequency electrical microstimulation of the nucleus incertus was sufficient to induce forward locomotion and rotation. The latencies of evoked locomotion were consistent with a role of the nucleus incertus in modulating premotor areas, possibly the septo-hippocampal axis. Electrical microstimulation of the nucleus incertus increased velocity, mobility and rotations during stimulation and post-stimulation. These results suggest that the nucleus incertus plays a role in behavioral activation and locomotion. © 2016 The Authors.

Lim E.P.,National University of Singapore | Lim E.P.,Singapore Institute for Neurotechnology SINAPSE | Lim E.P.,French Institute of Health and Medical Research | Lim E.P.,University of Paris Descartes | And 4 more authors.
Neurobiology of Learning and Memory | Year: 2017

Noradrenaline (NA), released by the locus coeruleus (LC), plays a key role in mediating the effects of stress on memory functions. The LC provides diffuse projections to many forebrain nuclei including the hippocampus, the prefrontal cortex (PFC), and the basolateral amygdala (BLA). These three structures are intricately interlinked. The hippocampal-prefrontal (H-PFC) pathway is involved in various cognitive functions. The first aim of this study was to examine the role of BLA in H-PFC plasticity by infusion of drugs to activate and inactivate the BLA and studying the effects on H-PFC long-term potentiation (LTP) in the rat in vivo. Activation of the BLA with glutamate impaired, while inactivation with muscimol augmented, H-PFC LTP. This study also aimed to demonstrate how directly applying noradrenaline and other noradrenergic agents in the BLA can affect H-PFC LTP. Noradrenaline at 1 μg/0.2 μl enhanced H-PFC LTP. Stimulating alpha-2-adrenoceptors in the BLA with clonidine enhanced LTP while blocking alpha-2 adrenoceptors with idazoxan impaired it. Propranolol, a non-selective beta antagonist, enhanced H-PFC LTP while isoprenaline, a non-selective beta agonist, decreased H-PFC LTP. These results suggest that the BLA regulates H-PFC plasticity negatively and also provide a mechanism by which noradrenaline in the BLA can affect H-PFC plasticity via alpha-2 and beta adrenoceptors. © 2016 Elsevier Inc.

Lee J.H.,National University of Singapore | Koh S.Q.,National University of Singapore | Guadagna S.,King's College London | Francis P.T.,King's College London | And 7 more authors.
Psychopharmacology | Year: 2016

Rationale: The G-protein-coupled relaxin family receptors RXFP1 and RXFP3 are widely expressed in the cortex and are involved in stress responses and memory and emotional processing. However, the identification of these receptors in human cortex and their status in Alzheimer's disease (AD), which is characterized by both cognitive impairments and neuropsychiatric behaviours, have not been reported. Objectives: In this study, we characterized RXFP receptors for immunoblotting and measured RXFP1 and RXFP3 immunoreactivities in the postmortem neocortex of AD patients longitudinally assessed for depressive symptoms. Methods: RXFP1 and RXFP3 antibodies were characterized by immunoblotting with lysates from transfected HEK cells and preadsorption with RXFP3 peptides. Also, postmortem neocortical tissues from behaviourally assessed AD and age-matched controls were processed for immunoblotting with RXFP1 and RXFP3 antibodies. Results: Compared to controls, putative RXFP1 immunoreactivity was reduced in parietal cortex of non-depressed AD patients but unchanged in depressed patients. Furthermore, putative RXFP3 immunoreactivity was increased only in depressed AD patients. RXFP1 levels in the parietal cortex also correlated with severity of depression symptoms. In contrast, RXFP1 and RXFP3 levels did not correlate with dementia severity or β-amyloid burden. Conclusion: Alterations of RXFP1 and RXFP3 may be neurochemical markers of depression in AD, and relaxin family receptors warrant further preclinical investigations as possible therapeutic targets for neuropsychiatric symptoms in dementia. © 2015 Springer-Verlag Berlin Heidelberg.

Ong W.-Y.,National University of Singapore | Tanaka K.,National University of Singapore | Dawe G.S.,National University of Singapore | Dawe G.S.,Singapore Institute for Neurotechnology SINAPSE | And 2 more authors.
Journal of Alzheimer's Disease | Year: 2013

Progress is being made in identifying possible pathogenic factors and novel genes in the development of Alzheimer's disease (AD). Many of these could contribute to 'slow excitotoxicity', defined as neuronal loss due to overexcitation as a consequence of decreased energy production due, for instance, to changes in insulin receptor signaling; or receptor abnormalities, such as tau-induced alterations the N-methyl-D-aspartate (NMDA) receptor phosphorylation. As a result, glutamate becomes neurotoxic at concentrations that normally show no toxicity. In AD, NMDA receptors are overexcited by glutamate in a tonic, rather than a phasic manner. Moreover, in prodromal AD subjects, functional MRI reveals an increase in neural network activities relative to baseline, rather than loss of activity. This may be an attempt to compensate for reduced number of neurons, or reflect ongoing slow excitotoxicity. This article reviews possible links between AD pathogenic factors such as AβPP/Aβ and tau; novel risk genes including clusterin, phosphatidylinositol-binding clathrin assembly protein, complement receptor 1, bridging integrator 1, ATP-binding cassette transporter 7, membrane-spanning 4-domains subfamily A, CD2-associated protein, sialic acid-binding immunoglobulin-like lectin, and ephrin receptor A1; metabolic changes including insulin resistance and hypercholesterolemia; lipid changes including alterations in brain phospholipids, cholesterol and ceramides; glial changes affecting microglia and astrocytes; alterations in brain iron metallome and oxidative stress; and slow excitotoxicity. Better understanding of the possible molecular links between pathogenic factors and slow excitotoxicity could inform our understanding of the disease, and pave the way towards new therapeutic strategies for AD. © 2013 - IOS Press and the authors. All rights reserved.

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