AMPA receptor-induced intracellular calcium response in the paraventricular nucleus is modulated by nitric oxide: calcium imaging in a hypothalamic organotypic cell culture model

A microfluidic bubble perfusion device for brain slice culture

Ex vivo brain slice cultures are utilized as analytical models for studying neurophysiology. Common approaches to maintaining slice cultures include roller tube and membrane interface techniques. The rise of organ-on-chip technologies has demonstrated the value of microfluidic perfusion culture systems for sampling and analysis of complex biology under well-controlled in vitro or ex vivo conditions. A number of approaches to microfluidic brain slice culture have been developed, however these typically involve complex design, fabrication, or operational parameters in order to meet the high oxygen demands of brain slices. Here, we present proof-of-principle for a novel approach to microfluidic brain slice culture. In this system, which we term a microfluidic bubble perfusion device, principles of droplet microfluidics were employed to generate droplets of perfusion media dispersed between bubbles of carbogen gas, and brain tissue slices were perfused with the resulting monodispersed droplets and bubbles. The challenge of tissue immobilization in the flow system was addressed using a two-part cytocompatible carbohydrate-based tissue adhesive. Best practices are discussed for perfusion chamber designs that maintain segmented flow throughout the course of perfusion. Control of droplet and bubble volumes was possible across the range of ca. 4-15 μL, bubble generation frequency was well controlled in the range ca. 1-7 bubbles per min, and bubble duty cycle was well controlled across the range ca. 20-80%. Murine hypothalamic tissue slices containing the suprachiasmatic nuclei were successfully maintained for durations of 8-10 hours, with tissue remaining viable for the duration of perfusion as assessed by Ca²⁺ imaging and propidium iodide (PI) staining.

Dehydroevodiamine·HCl enhances cognitive function in memory-impaired rat models

Progressive memory impairment such as that associated with depression, stroke, and Alzheimer's disease (AD) can interfere with daily life. In particular, AD, which is a progressive neurodegenerative disorder, prominently features a memory and learning impairment that is related to changes in acetylcholine and abnormal β-amyloid (Aβ) deposition in the brain. In the present study, we investigated the effects of dehydroevodiamine·HCl (DHED) on cognitive improvement and the related mechanism in memory-impaired rat models, namely, a scopolamine-induced amnesia model and a Aβ_1-42-infused model. The cognitive effects of DHED were measured using a water maze test and a passive avoidance test in the memory-impaired rat models. The results demonstrate that DHED (10 mg/kg, p.o.) and Donepezil (1 mg/kg, p.o.) ameliorated the spatial memory impairment in the scopolamine-induced amnestic rats. Moreover, DHED significantly improved learning and memory in the Aβ_1-42-infused rat model. Furthermore, the mechanism of these behavioral effects of DHED was investigated using a cell viability assay, reactive oxygen species (ROS) measurement, and intracellular calcium measurement in primary cortical neurons. DHED reduced neurotoxicity and the production of Aβ-induced ROS in primary cortical neurons. In addition, similar to the effect of MK801, DHED decreased intracellular calcium levels in primary cortical neurons. Our results suggest that DHED has strong protective effects against cognitive impairments through its antioxidant activity and inhibition of neurotoxicity and intracellular calcium. Thus, DHED may be an important therapeutic agent for memory-impaired symptoms.

Glutamate-induced ATP synthesis: relationship between plasma membrane Na+/Ca2+ exchanger and excitatory amino acid transporters in brain and heart cell models

It is known that glutamate (Glu), the major excitatory amino acid in the central nervous system, can be an essential source for cell energy metabolism. Here we investigated the role of the plasma membrane Na(+)/Ca(2+) exchanger (NCX) and the excitatory amino acid transporters (EAATs) in Glu uptake and recycling mechanisms leading to ATP synthesis. We used different cell lines, such as SH-SY5Y neuroblastoma, C6 glioma and H9c2 as neuronal, glial, and cardiac models, respectively. We first observed that Glu increased ATP production in SH-SY5Y and C6 cells. Pharmacological inhibition of either EAAT or NCX counteracted the Glu-induced ATP synthesis. Furthermore, Glu induced a plasma membrane depolarization and an intracellular Ca(2+) increase, and both responses were again abolished by EAAT and NCX blockers. In line with the hypothesis of a mutual interplay between the activities of EAAT and NCX, coimmunoprecipitation studies showed a physical interaction between them. We expanded our studies on EAAT/NCX interplay in the H9c2 cells. H9c2 expresses EAATs but lacks endogenous NCX1 expression. Glu failed to elicit any significant response in terms of ATP synthesis, cell depolarization, and Ca(2+) increase unless a functional NCX1 was introduced in H9c2 cells by stable transfection. Moreover, these responses were counteracted by EAAT and NCX blockers, as observed in SH-SY5Y and C6 cells. Collectively, these data suggest that plasma membrane EAAT and NCX are both involved in Glu-induced ATP synthesis, with NCX playing a pivotal role.

Cardiovascular responses to ATP microinjected into the paraventricular nucleus are mediated by nitric oxide and NMDA glutamate receptors in awake rats

We hypothesize that a local ATP-NO-NMDA glutamate receptor interaction in the paraventricular nucleus (PVN) modulates the baseline mean arterial pressure and heart rate in unanaesthetized rats. The microinjection of α,β-methylene ATP [methyl ATP; 0.06, 0.12 and 1.2 nmol (100 nl)(-1)] into the PVN caused pressor and tachycardiac responses. Cardiovascular responses evoked by methyl ATP [0.12 nmol (100 nl)(-1)] in the PVN were blocked by pretreatment with the ganglion blocker pentolinium (5 mg kg(-1) i.v.). Also, responses to the injection of methyl ATP [0.12 nmol (100 nl)(-1)] into the PVN were reduced by pretreatment with the selective P2 purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid [0.5 nmol (100 nl)(-1)], the neuronal NO synthase inhibitor N(ω)-propyl-l-arginine [0.04 nmol (100 nl)(-1)] or the selective NMDA glutamate receptor antagonist LY235959 [2 nmol (100 nl)(-1)]. In addition, an injection of the NO donor sodium nitroprusside [27 nmol (100 nl)(-1)] into the PVN caused similar cardiovascular responses to those observed after methyl ATP, which were blocked by local pretreatment with LY235959. Therefore, the present results suggest that cardiovascular responses evoked by methyl ATP in the PVN involve a local production of NO, which promotes local glutamate release and activation of NMDA receptors that are probably located in pre-autonomic parvocellular neurons, leading to sympathetic nervous system stimulation.

Regulation of arterial pressure by the paraventricular nucleus in conscious rats: interactions among glutamate, GABA, and nitric oxide

The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic and neuroendocrine regulation. Experiments in anesthetized animals and in vitro indicate an interaction among gamma-aminobutyric acid (GABA), nitric oxide (NO), and glutamate in the PVN. The cardiovascular role of the PVN and interactions of these neurotransmitters in conscious animals have not been evaluated fully. In chronically instrumented conscious rats, mean arterial pressure (MAP) and heart rate (HR) responses to microinjections (100 nl) in the region of the PVN were tested. Bilateral blockade of ionotropic excitatory amino acid (EAA) receptors (kynurenic acid, Kyn) in the PVN produced small but significant decreases in MAP and HR. GABA_A receptor blockade (bicuculline, Bic), and inhibition of NO synthase [(NOS), N-(G)-monomethyl-L-arginine, L-NMMA] each increased MAP and HR. The NO donor sodium nitroprusside (SNP) produced depressor responses that were attenuated by Bic. NOS inhibition potentiated both pressor responses to the selective EAA agonist, N-methyl-D-aspartic acid (NMDA), and depressor responses to Kyn. Increases in MAP and HR due to Bic were blunted by prior blockade of EAA receptors. Thus, pressor responses to GABA blockade require EAA receptors and GABA neurotransmission contributes to NO inhibition. Tonic excitatory effects of glutamate in the PVN are tonically attenuated by NO. These data demonstrate that, in the PVN of conscious rats, GABA, glutamate, and NO interact in a complex fashion to regulate arterial pressure and HR under normal conditions.

Glutamatergic neurotransmission in a mouse model of Niemann-Pick type C disease

Niemann-Pick Type C Disease (NPCD) is a progressive neurodegenerative disorder characterized by accumulation of free cholesterol, sphingomyelin, glycosphingolipids (GSLs) and sphingosine in lysosomes, mainly due to a mutation in the NPC1 gene. One of the main symptoms in NPCD patients is hyperexcitability leading to epileptic activity, however, the pathophysiological basis of this neural disorder is not yet well understood. Here we studied the excitatory neurotransmission in the hippocampus of BALB/c NPC1NIH (NPC1-/-) mice, a well-described animal model of the disease. We report that hippocampal field potential population spike (fPS), as well as paired pulse ratio, is enhanced in NPC1-/- with respect to Wild Type (WT). To evaluate the contribution of glutamate receptor activity in the enhanced fPS observed in mutant mice, we recorded slices treated with glutamate receptor agonists alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and Kainate (KA). We found that a prolonged application of KA and AMPA in NPC1-/- mice do not induce the dramatic decrease of synaptic transmission observed in WT hippocampal slices suggesting a functional impairment of presynaptic KA receptors and an imbalance of AMPA receptor exo/endocytosis. In line with electrophysiological data, we also found notable differences in calcium influx during KA and AMPA bath application in NPC1-/- hippocampal culture as compared with WT. Nevertheless in synaptosomal membranes, Western Blot analysis didn't reveal any modification in protein expression levels of KA and AMPA receptor subunits. All together these data indicate that in mutant mice the hyperexcitability, that is at the basis of the insurgence of seizures, might be due to the enhanced glutamatergic neurotransmission caused by an altered KA and AMPA receptor functioning.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Inhibition of nitric oxide synthase in the paraventricular nucleus prevents the hyperthermia-induced reduction of mesenteric blood flow in rats

Increasing body core temperature reflexly decreases mesenteric blood flow (MBF), and the hypothalamic paraventricular nucleus (PVN) plays an essential role in this response. Nitric oxide (NO) is involved in temperature regulation and is concentrated within the PVN. The present study investigated whether NO in the PVN contributes to the cardiovascular responses elicited by hyperthermia. Anesthetized rats were microinjected bilaterally in the PVN (100 nl/side) with saline or NG-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor (100 or 200 nmol/100 nl) ( n = 5/group). Body core temperature was then elevated from 37°C to 39°C, and blood pressure (BP), heart rate (HR), MBF, and mesenteric vascular conductance (MVC) were monitored. In separate groups, l-NAME (200 nmol) ( n = 5) or saline ( n = 5) was microinjected in the PVN, but body core temperature was not elevated. In control rats, increasing body core temperature resulted in no marked change of BP but an increase in HR and significant decreases in MBF (15%) and MVC. Pretreatment with 100 nmol l-NAME did not affect the responses. In contrast, 200 nmol l-NAME prevented the normal reduction in MBF and MVC but did not significantly affect the BP and HR responses. In rats in which body core temperature was not increased, l-NAME reduced MBF by 19%. The present results suggest that endogenous NO in the PVN is important in mediating the reduction of MBF induced by hyperthermia. In the absence of hyperthermia, however, endogenous NO in the PVN may play a role in maintaining mesenteric vasodilation.

Modulation of arterial pressure by P2 purinoceptors in the paraventricular nucleus of the hypothalamus of awake rats

In the present study we evaluated the role of purinergic mechanisms in the PVN on the tonic modulation of the autonomic function to the cardiovascular system as well on the cardiovascular responses to peripheral chemoreflex activation in awake rats. Guide-cannulae were bilaterally implanted in the direction of the PVN of male Wistar rats. Femoral artery and vein were catheterized one day before the experiments. Chemoreflex was activated with KCN (80 μg/0.05 ml, i.v.) before and after microinjections of P2 receptors antagonist into the PVN. Microinjection of PPADS, a non selective P2X antagonist, into the PVN (n=6) produced a significant increase in the baseline MAP (99±2 vs 112±3 mmHg) and HR (332±8 vs 375±8 bpm) but had no effect on the pressor and bradycardic responses to chemoreflex activation. Intravenous injection of vasopressin receptors antagonist after microinjection of PPADS into the PVN produced no effect on the increased baseline MAP. Simultaneous microinjection of PPADS and KYN into the PVN (n=6) had no effect in the baseline MAP, HR or in the pressor and bradycardic responses to chemoreflex activation. We conclude that P2 purinoceptors in the PVN are involved in the modulation of baseline autonomic function to the cardiovascular system but not in the cardiovascular responses to chemoreflex activation in awake rats.

Interferon-gamma directly induces neurotoxicity through a neuron specific, calcium-permeable complex of IFN-gamma receptor and AMPA GluR1 receptor

Interferon-gamma (IFN-gamma) is a proinflammatory cytokine that plays a pivotal role in pathology of diseases in the central nervous system (CNS), such as multiple sclerosis. However, the direct effect of IFN-gamma on neuronal cells has yet to be elucidated. We show here that IFN-gamma directly induces neuronal dysfunction, which appears as dendritic bead formation in mouse cortical neurons and enhances glutamate neurotoxicity mediated via alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) receptors but not N-methyl-D-aspartate receptors. In the CNS, IFN-gamma receptor forms a unique, neuron-specific, calcium-permeable receptor complex with AMPA receptor subunit GluR1. Through this receptor complex, IFN-gamma phosphorylates GluR1 at serine 845 position by JAK1.2/STAT1 pathway, increases Ca(2+) influx and following nitric oxide production, and subsequently decreases ATP production, leading to the dendritic bead formation. These findings provide novel mechanisms of neuronal excitotoxicity, which may occur in both inflammatory and neurodegenerative diseases in the CNS.