scholarly journals Energy state alters regulation of proopiomelanocortin neurons by glutamatergic ventromedial hypothalamus neurons: pre- and post-synaptic mechanisms

2021 ◽  
Author(s):  
Andrew R. Rau ◽  
Shane T Hentges
Keyword(s):  
Food Intake ◽  
Ampa Receptors ◽  
Energy State ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Ventromedial Hypothalamus ◽  
Information Encoding ◽  
Glutamatergic Neurons ◽  
Conditional Deletion ◽  
Inhibit Food Intake

To maintain metabolic homeostasis, motivated behaviors are driven by neuronal circuits that process information encoding the animal's energy state. Such circuits likely include ventromedial hypothalamus (VMH) glutamatergic neurons that project throughout the brain to drive food intake and energy expenditure. Targets of VMH glutamatergic neurons include proopiomelanocortin (POMC) neurons in the arcuate nucleus which, when activated, inhibit food intake. While an energy-state-sensitive, glutamate circuit between the VMH and POMC neurons has been previously indicated, the significance and details of this circuit have not been fully elucidated. This, the goal of the present work was to add to the understanding of this circuit. Using a knockout strategy, the data show that the VMH glutamateàPOMC neuron circuit is important for the inhibition of food intake. Conditional deletion of the vesicular glutamate transporter (VGLUT2) in the VMH results in increased bodyweight and increased food intake following a fast in both male and female mice. Additionally, the targeted blunting of glutamate release from the VMH resulted in an approximately 32% reduction in excitatory inputs to POMC cells suggesting that this circuit may respond to changes in energy state to affect POMC activity. Indeed, we found that glutamate release is increased at VMH-to-POMC synapses during feeding and POMC AMPA receptors switch from a calcium-permeable state to a calcium-impermeable state during fasting. Collectively, these data indicate that there is an energy-balance-sensitive VMH-to-POMC circuit conveying excitatory neuromodulation onto POMC cells at both pre- and post-synaptic levels, that may contribute to maintaining appropriate food intake and body mass.

Viewing the ventromedial hypothalamus from the adrenal gland

1984 ◽  
Vol 246 (1) ◽  
pp. R1-R12 ◽  
Author(s):  
M. F. Dallman
Keyword(s):  
Circadian Rhythm ◽  
Insulin Secretion ◽  
Food Intake ◽  
Adrenal Gland ◽  
Ventromedial Hypothalamus ◽  
Adrenocortical Function ◽  
Suprachiasmatic Nuclei ◽  
Inhibit Food Intake ◽  
Dose Dependent

The relationships among food intake, insulin secretion, and adrenocortical function are reviewed. It is hypothesized that a major role of structures in, or passing through, the ventromedial hypothalamus is to inhibit food intake, insulin secretion, and adrenocortical function during the day (in the nocturnally active rat) and that this activity is normally driven by elements within the suprachiasmatic nuclei. Lesions of the ventromedial hypothalamus of rats result in nonrhythmic food intake, hyperinsulinemia, nonrhythmic adrenocortical function, and obesity. Adrenalectomy prevents or reverses the effects of lesions of the ventromedial hypothalamus on food intake, insulin secretion, and obesity, and corticosteroid replacement restores them. Because the actions of corticosteroids are both time- and dose-dependent, it is proposed that the effects of the tonic levels of corticosteroids observed after lesions of the ventromedial hypothalamus are to augment the hyperphagia, hyperinsulinemia, and substrate flow into fat to a greater extent than would occur if there were a normal circadian rhythm in adrenocortical function.

scholarly journals Expression mechanisms underlying long-term potentiation: a postsynaptic view

2003 ◽  
Vol 358 (1432) ◽  
pp. 721-726 ◽  
Author(s):  
Roger A. Nicoll
Keyword(s):  
Nmda Receptor ◽  
Ampa Receptors ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Long Term Potentiation ◽  
Receptor Activation ◽  
Covalent Modification ◽  
Term Potentiation ◽  
Expression Mechanism

This review summarizes the various experiments that have been carried out to determine if the expression of long-term potentiation (LTP), in particular N -methyl-D-aspartate (NMDA) receptor-dependent LTP, is presynaptic or postsynaptic. Evidence for a presynaptic expression mechanism comes primarily from experiments reporting that glutamate overflow is increased during LTP and from experiments showing that the failure rate decreases during LTP. However, other experimental approaches, such as monitoring synaptic glutamate release by recording astrocytic glutamate transporter currents, have failed to detect any change in glutamate release during LTP. In addition, the discovery of silent synapses, in which LTP rapidly switches on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function at NMDA-receptor-only synapses, provides a postsynaptic mechanism for the decrease in failures during LTP. It is argued that the preponderance of evidence favours a postsynaptic expression mechanism, whereby NMDA receptor activation results in the rapid recruitment of AMPA receptors as well as a covalent modification of synaptic AMPA receptors.

scholarly journals POMC neurons functional heterogeneity relies on mTORC1 signaling

2020 ◽  
Author(s):  
Nicolas Saucisse ◽  
Wilfrid Mazier ◽  
Vincent Simon ◽  
Elke Binder ◽  
Caterina Catania ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Energy State ◽  
Glutamate Release ◽  
Negative Energy ◽  
Gabaergic Neurotransmission ◽  
Cannabinoid Type 1 Receptor ◽  
Melanocyte Stimulating Hormone ◽  
Conditional Deletion ◽  
Mtorc1 Signaling ◽  
Pharmacological Blockade

AbstractHypothalamic Pro-opiomelanocortin (POMC) neurons are classically known to trigger satiety. However, they encompass heterogeneous subpopulations whose functions are unknown. Here we show that POMC neurons releasing GABA, glutamate or both neurotransmitters possess distinct spatial distribution, molecular signatures and functions. Functional specificity of these subpopulations relies on the energy sensor mechanistic Target of Rapamycin Complex 1 (mTORC1), since pharmacological blockade of mTORC1, by mimicking a cellular negative energy state, simultaneously inhibited POMC/glutamatergic and activated POMC/GABAergic neurons. Chemogenetics and conditional deletion of mTORC1 then demonstrated that mTORC1 blockade in POMC neurons causes hyperphagia. This is due to decreased POMC-derived anorexigenic α-melanocyte-stimulating hormone and the recruitment of POMC/GABAergic neurotransmission, which is restrained by cannabinoid type 1 receptor signaling. Genetic inhibition of glutamate release from POMC neurons also produced hyperphagia, recapitulating the phenotype caused by mTORC1 blockade. Altogether, these findings pinpoint the molecular mechanisms engaged by POMC neurons to oppositely control feeding, thereby challenging conventional views about their functions.

scholarly journals Cortical and raphe GABAA, AMPA receptors and glial GLT-1 glutamate transporter contribute to the sustained antidepressant activity of ketamine

2020 ◽  
Author(s):  
Thu Ha Pham ◽  
Céline Defaix ◽  
Thi Mai Loan Nguyen ◽  
Indira Mendez-David ◽  
Laurent Tritschler ◽  
...  
Keyword(s):  
Ampa Receptors ◽  
Forced Swim Test ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Antidepressant Activity ◽  
Gaba Release ◽  
Nmda Receptor Antagonist ◽  
Post Dose ◽  
Rapid Responses

ABSTRACTAt sub-anaesthetic doses, ketamine, a non competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has demonstrated remarkable and rapid antidepressant (AD) efficacy in patients with treatment-resistant depression (TRD). However, its mechanism of action of ketamine is not fully understood. Since comorbid depression and anxiety disorders often occur, GABAergic/inhibitory and glutamatergic/excitatory drug treatments may be co-administered in these patients. Information regarding this combination is critical to establish efficacy or treatment restrictions to maximize translation from animal models to TRD patients, effectiveness and safety. To assess the specific role of excitatory/inhibitory neurotransmission in the medial prefrontal cortex-raphe nuclei (mPFC-DRN) circuit in the sustained antidepressant-like activity (AD) of ketamine (at t24h post dose), AMPA-R antagonist (intra-DRN) and GABAA-R agonist (intra-mPFC) were co-administered with ketamine (intra-mPFC). Twenty-four hours later, responses in the forced swim test (FST) and neurochemical consequences on extracellular mPFC glutamate, GABA and 5-HT levels were measured in BALB/cJ mice. Intra-DRN NBQX prevented the sustained AD-like activity of ketamine evidenced by decreases in FST swimming duration and blunted cortical 5-HText and Gluext. Intra-mPFC muscimol blocked ketamine AD-like activity and its effects on cortical 5-HText. Moreover, a selective glutamate transporter GLT-1 inhibitor, dihydrokainic acid (DHK) locally perfused into the mPFC produced an AD-like activity at t24h associated with robust increases in mPFC 5-HText, Gluext and GABAext. Thus, the sustained AD-like activity of ketamine is triggered by AMPA-R activation in the DRN and 5-HT - glutamate release in the mPFC, but limited by GABAA-R activation - GABA release in the mPFC. The local blockade of GLT-1 in the mPFC also mimics the rapid responses of ketamine, thus highlighting the role of neuronal-glial adaptation in these effects. These results also suggests the need to test for the concomitant prescription of ketamine and BZD to see whether its sustained antidepressant activity is maintained in TRD patients.

scholarly journals Role of Ventromedial Hypothalamus in Sucrose-Induced Obesity on Metabolic Parameters

2021 ◽  
pp. 097275312110057
Author(s):  
Archana Gaur ◽  
G.K. Pal ◽  
Pravati Pal
Keyword(s):  
Insulin Resistance ◽  
Weight Gain ◽  
Food Intake ◽  
Ventromedial Hypothalamus ◽  
Female Rats ◽  
Metabolic Parameters ◽  
Male Rats ◽  
Significant Weight Gain ◽  
The Metabolic Syndrome

Background: Obesity is because of excessive fat accumulation that affects health adversely in the form of various diseases such as diabetes, hypertension, cardiovascular diseases, and many other disorders. Our Indian diet is rich in carbohydrates, and hence the sucrose-induced obesity is an apt model to mimic this. Ventromedial hypothalamus (VMH) is linked to the regulation of food intake in animals as well as humans. Purpose: To understand the role of VMHin sucrose-induced obesity on metabolic parameters. Methods: A total of 24 adult rats were made obese by feeding them on a 32% sucrose solution for 10 weeks. The VMH nucleus was ablated in the experimental group and sham lesions were made in the control group. Food intake, body weight, and biochemical parameters were compared before and after the lesion. Results: Male rats had a significant weight gain along with hyperphagia, whereas female rats did not have a significant weight gain inspite of hyperphagia. Insulin resistance and dyslipidemia were seen in both the experimental and control groups. Conclusion: A sucrose diet produces obesity which is similar to the metabolic syndrome with insulin resistance and dyslipidemia, and a VMH lesion further exaggerates it. Males are more prone to this exaggeration.

scholarly journals Excitotoxic Mechanisms of Ischemic Injury in Myelinated White Matter

2007 ◽  
Vol 27 (9) ◽  
pp. 1540-1552 ◽  
Author(s):  
Selva Baltan Tekkök ◽  
ZuCheng Ye ◽  
Bruce R Ransom
Keyword(s):  
White Matter ◽  
High Performance ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Ischemic Injury ◽  
Glucose Deprivation ◽  
Kainate Receptors ◽  
Adult Mice ◽  
Direct Exposure ◽  
Glutamate Receptor Agonist

Axonal injury and dysfunction in white matter (WM) are caused by many neurologic diseases including ischemia. We characterized ischemic injury and the role of glutamate-mediated excitotoxicity in a purely myelinated WM tract, the mouse optic nerve (MON). For the first time, excitotoxic WM injury was directly correlated with glutamate release. Oxygen and glucose deprivation (OGD) caused duration-dependent loss of axon function in optic nerves from young adult mice. Protection of axon function required blockade of both α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate receptors, or removal of extracellular Ca2+. Blockade of N-methyl-D-aspartate receptors did not preserve axon function. Curiously, even extended periods of direct exposure to glutamate or kainate or AMPA failed to induce axon dysfunction. Brief periods of OGD, however, caused glutamate receptor agonist exposure to become toxic, suggesting that ionic disruption enabled excitotoxic injury. Glutamate release, directly measured using quantitative high-performance liquid chromatography, occurred late during a 60-mins period of OGD and was due to reversal of the glutamate transporter. Brief periods of OGD (i.e., 15 mins) did not cause glutamate release and produced minimal injury. These results suggested that toxic glutamate accumulation during OGD followed the initial ionic changes mediating early loss of excitability. The onset of glutamate release was an important threshold event for irreversible ischemic injury. Regional differences appear to exist in the specific glutamate receptors that mediate WM ischemic injury. Therapy for ischemic WM injury must be designed accordingly.

Opponent vesicular transporters regulate the strength of glutamatergic neurotransmission in a C. elegans sensory circuit

2021 ◽  
Author(s):  
Jung-Hwan Choi ◽  
Lauren Bayer Horowitz ◽  
Niels Ringstad
Keyword(s):  
Synaptic Vesicles ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Synaptic Function ◽  
Functional Coupling ◽  
Glutamate Signaling ◽  
C Elegans ◽  
Vesicular Transporters ◽  
Chemical Synapses

At chemical synapses, neurotransmitters are packaged into synaptic vesicles that release their contents in response to depolarization. Despite its central role in synaptic function, regulation of the machinery that loads vesicles with neurotransmitters remains poorly understood. We find that synaptic glutamate signaling in a C. elegans chemosensory circuit is regulated by antagonistic interactions between the canonical vesicular glutamate transporter EAT-4/VGLUT and another vesicular transporter, VST-1. Loss of VST-1 strongly potentiates glutamate release from chemosensory BAG neurons and disrupts chemotaxis behavior. Analysis of the circuitry downstream of BAG neurons shows that excess glutamate release disrupts behavior by inappropriately recruiting RIA interneurons to the BAG-associated chemotaxis circuit. Our data indicate that in vivo the strength of glutamatergic synapses is controlled by regulation of neurotransmitter packaging into synaptic vesicles via functional coupling of VGLUT and VST-1.

scholarly journals Ischemic Preconditioning Reveals that GLT1/EAAT2 Glutamate Transporter is a Novel PPARγ Target Gene Involved in Neuroprotection

2007 ◽  
Vol 27 (7) ◽  
pp. 1327-1338 ◽  
Author(s):  
Cristina Romera ◽  
Olivia Hurtado ◽  
Judith Mallolas ◽  
Marta P Pereira ◽  
Jesús R Morales ◽  
...  
Keyword(s):  
Nervous System ◽  
Ischemic Preconditioning ◽  
Transcriptional Activity ◽  
Target Gene ◽  
Glutamate Uptake ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Glutamate Transport ◽  
Extracellular Glutamate ◽  
Pparγ Agonist

Excessive levels of extracellular glutamate in the nervous system are excitotoxic and lead to neuronal death. Glutamate transport, mainly by glutamate transporter GLT1/EAAT2, is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels in the central nervous system. We recently showed that neuroprotection after experimental ischemic preconditioning (IPC) involves, at least partly, the upregulation of the GLT1/EAAT2 glutamate transporter in astrocytes, but the mechanisms were unknown. Thus, we decided to explore whether activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ, known for its antidiabetic and antiinflammatory properties, is involved in glutamate transport. First, we found that the PPARγ antagonist T0070907 inhibits both IPC-induced tolerance and reduction of glutamate release after lethal oxygen-glucose deprivation (OGD) (70.1% ± 3.4% versus 97.7% ± 5.2% of OGD-induced lactate dehydrogenase (LDH) release and 61.8% ± 5.9% versus 85.9% ± 7.9% of OGD-induced glutamate release in IPC and IPC + T0070907 1 μmol/L, respectively, n = 6 to 12, P < 0.05), as well as IPC-induced astrocytic GLT-1 overexpression. IPC also caused an increase in nuclear PPARγ transcriptional activity in neurons and astrocytes (122.1% ± 8.1% and 158.6% ± 22.6% of control PPARγ transcriptional activity, n = 6, P < 0.05). Second, the PPARγ agonist rosiglitazone increased both GLT-1/EAAT2 mRNA and protein expression and [3H]glutamate uptake, and reduced OGD-induced cell death and glutamate release (76.3% ± 7.9% and 65.5% ± 15.1% of OGD-induced LDH and glutamate release in rosiglitazone 1 μmol/l, respectively, n = 6 to 12, P < 0.05). Finally, we have identified six putative PPAR response elements (PPREs) in the GLT1/EAAT2 promoter and, consistently, rosiglitazone increased fourfold GLT1/EAAT2 promoter activity. All these data show that the GLT1/EAAT2 glutamate transporter is a target gene of PPARγ leading to neuroprotection by increasing glutamate uptake.

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