SUCNR1 regulates insulin secretion and glucose elevates the succinate response in people with prediabetes

Pancreatic β-cell dysfunction is a key feature of type 2 diabetes, and novel regulators of insulin secretion are desirable. Here we report that the succinate receptor (SUCNR1) is expressed in β-cells and is up-regulated in hyperglycemic states in mice and humans. We found that succinate acts as a hormone-like metabolite and stimulates insulin secretion via a SUCNR1-Gq-PKC-dependent mechanism in human β-cells. Mice with β-cell-specific Sucnr1 deficiency exhibit impaired glucose tolerance and insulin secretion on a high-fat diet, indicating that SUCNR1 is essential for preserving insulin secretion in diet-induced insulin resistance. Patients with impaired glucose tolerance show an enhanced nutritional-related succinate response, which correlates with the potentiation of insulin secretion during intravenous glucose administration. These data demonstrate that the succinate/SUCNR1 axis is activated by high glucose and identify a GPCR-mediated amplifying pathway for insulin secretion relevant to the hyperinsulinemia of prediabetic states.

Automated Patch Clamp for the Detection of Tetrodotoxin in Pufferfish Samples

Tetrodotoxin (TTX) is a marine toxin responsible for many intoxications around the world. Its presence in some pufferfish species and, as recently reported, in shellfish, poses a serious health concern. Although TTX is not routinely monitored, there is a need for fast, sensitive, reliable, and simple methods for its detection and quantification. In this work, we describe the use of an automated patch clamp (APC) system with Neuro-2a cells for the determination of TTX contents in pufferfish samples. The cells showed an IC50 of 6.4 nM for TTX and were not affected by the presence of muscle, skin, liver, and gonad tissues of a Sphoeroides pachygaster specimen (TTX-free) when analysed at 10 mg/mL. The LOD achieved with this technique was 0.05 mg TTX equiv./kg, which is far below the Japanese regulatory limit of 2 mg TTX equiv./kg. The APC system was applied to the analysis of extracts of a Lagocephalus sceleratus specimen, showing TTX contents that followed the trend of gonads > liver > skin > muscle. The APC system, providing an in vitro toxicological approach, offers the advantages of being sensitive, rapid, and reliable for the detection of TTX-like compounds in seafood.

Design, synthesis, and in vitro and in vivo characterization of new memantine analogs for Alzheimer's disease

Currently, of the few accessible symptomatic therapies for Alzheimer's disease (AD), memantine is the only N-methyl-d-aspartate receptor (NMDAR) blocker approved by the FDA. This work further explores a series of memantine analogs featuring a benzohomoadamantane scaffold. Most of the newly synthesized compounds block NMDARs in the micromolar range, but with lower potency than previously reported hit IIc, results that were supported by molecular dynamics simulations. Subsequently, electrophysiological studies with the more potent compounds allowed classification of IIc, a low micromolar, uncompetitive, voltage-dependent, NMDAR blocker, as a memantine-like compound. The excellent in vitro DMPK properties of IIc made it a promising candidate for in vivo studies in Caenorhabditis elegans (C. elegans) and in the 5XFAD mouse model of AD. Administration of IIc or memantine improved locomotion and rescues chemotaxis behavior in C. elegans. Furthermore, both compounds enhanced working memory in 5XFAD mice and modified NMDAR and CREB signaling, which may prevent synaptic dysfunction and modulate neurodegenerative progression.

Pharmacological Strategies to Improve Dendritic Spines in Alzheimer's Disease

To deeply understand late onset Alzheimer's disease (LOAD), it may be necessary to change the concept that it is a disease exclusively driven by aging processes. The onset of LOAD could be associated with a previous peripheral stress at the level of the gut (changes in the gut microbiota), obesity (metabolic stress), and infections, among other systemic/environmental stressors. The onset of LOAD, then, may result from the generation of mild peripheral inflammatory processes involving cytokine production associated with peripheral stressors that in a second step enter the brain and spread out the process causing a neuroinflammatory brain disease. This hypothesis could explain the potential efficacy of Sodium Oligomannate (GV-971), a mixture of acidic linear oligosaccharides that have shown to remodel gut microbiota and slowdown LOAD. However, regardless of the origin of the disease, the end goal of LOAD-related preventative or disease modifying therapies is to preserve dendritic spines and synaptic plasticity that underlay and support healthy cognition. Here we discuss how systemic/environmental stressors impact pathways associated with the regulation of spine morphogenesis and synaptic maintenance, including insulin receptor and the brain derived neurotrophic factor signaling. Spine structure remodeling is a plausible mechanism to maintain synapses and provide cognitive resilience in LOAD patients. Importantly, we also propose a combination of drugs targeting such stressors that may be able to modify the course of LOAD by acting on preventing dendritic spines and synapsis loss.

Gambierdiscus and Fukuyoa as potential indicators of ciguatera risk in the Balearic Islands

Gambierdiscus and Fukuyoa are genera of toxic dinoflagellates which were mainly considered as endemic to marine intertropical areas, and that are well known as producers of ciguatoxins (CTXs) and maitotoxins (MTXs). Ciguatera poisoning (CP) is a human poisoning occurring after the consumption of fish or more rarely, shellfish containing CTXs. The presence of these microalgae in a coastal area is an indication of potential risk of CP. This study assesses the risk of CP in the Balearic Islands (Western Mediterranean Sea) according to the distribution of both microalgae genera, and the presence of CTX-like and MTX-like toxicity in microalgal cultures as determined by neuro-2a cell based-assay (neuro-2a CBA). Genetic identification of forty-three cultured microalgal strains isolated from 2016 to 2019 revealed that all of them belong to the species G. australes and F. paulensis. Both species were widely distributed in Formentera, Majorca and Minorca. Additionally, all strains of G. australes and two of F. paulensis exhibited signals of CTX-like toxicity ranging respectively between 1 and 380 and 8-16 fg CTX1B equivalents (equiv.) • cell^-1. Four extracts of F. paulensis exhibited a novel toxicity response in neuro-2a cells consisting of the recovery of the cell viability in the presence of ouabain and veratridine. In addition, G. australes showed MTX-like toxicity while F. paulensis strains did not. Overall, the low CTX-like toxicities detected indicate that the potential risk of CP in the Balearic Islands is low, although, the presence of CTX-like and MTX-like toxicity in those strains reveal the necessity to monitor these genera in the Mediterranean Sea.

A novel class of multitarget anti-Alzheimer benzohomoadamantane‒chlorotacrine hybrids modulating cholinesterases and glutamate NMDA receptors

The development of multitarget compounds against multifactorial diseases, such as Alzheimer's disease, is an area of very intensive research, due to the expected superior therapeutic efficacy that should arise from the simultaneous modulation of several key targets of the complex pathological network. Here we describe the synthesis and multitarget biological profiling of a new class of compounds designed by molecular hybridization of an NMDA receptor antagonist fluorobenzohomoadamantanamine with the potent acetylcholinesterase (AChE) inhibitor 6-chlorotacrine, using two different linker lengths and linkage positions, to preserve or not the memantine-like polycyclic unsubstituted primary amine. The best hybrids exhibit greater potencies than parent compounds against AChE (IC₅₀ 0.33 nM in the best case, 44-fold increased potency over 6-chlorotacrine), butyrylcholinesterase (IC₅₀ 21 nM in the best case, 24-fold increased potency over 6-chlorotacrine), and NMDA receptors (IC₅₀ 0.89 μM in the best case, 2-fold increased potency over the parent benzohomoadamantanamine and memantine), which suggests an additive effect of both pharmacophoric moieties in the interaction with the primary targets. Moreover, most of these compounds have been predicted to be brain permeable. This set of biological properties makes them promising leads for further anti-Alzheimer drug development.

Behavioral and Cognitive Improvement Induced by Novel Imidazoline I2 Receptor Ligands in Female SAMP8 Mice

As populations increase their life expectancy, age-related neurodegenerative disorders such as Alzheimer's disease have become more common. I2-Imidazoline receptors (I2-IR) are widely distributed in the central nervous system, and dysregulation of I2-IR in patients with neurodegenerative diseases has been reported, suggesting their implication in cognitive impairment. This evidence indicates that high-affinity selective I2-IR ligands potentially contribute to the delay of neurodegeneration. In vivo studies in the female senescence accelerated mouse-prone 8 mice have shown that treatment with I2-IR ligands, MCR5 and MCR9, produce beneficial effects in behavior and cognition. Changes in molecular pathways implicated in oxidative stress, inflammation, synaptic plasticity, and apoptotic cell death were also studied. Furthermore, treatments with these I2-IR ligands diminished the amyloid precursor protein processing pathway and increased Aβ degrading enzymes in the hippocampus of SAMP8 mice. These results collectively demonstrate the neuroprotective role of these new I2-IR ligands in a mouse model of brain aging through specific pathways and suggest their potential as therapeutic agents in brain disorders and age-related neurodegenerative diseases.

Pharmacological and Electrophysiological Characterization of Novel NMDA Receptor Antagonists

This work reports the synthesis and pharmacological and electrophysiological evaluation of new N-methyl-d-aspartic acid receptor (NMDAR) channel blocking antagonists featuring polycyclic scaffolds. Changes in the chemical structure modulate the potency and voltage dependence of inhibition. Two of the new antagonists display properties comparable to those of memantine, a clinically approved NMDAR antagonist.

Enantiopure Indolo[2,3-a]quinolizidines: Synthesis and Evaluation as NMDA Receptor Antagonists

Enantiopure tryptophanol is easily obtained from the reduction of its parent natural amino acid trypthophan (available from the chiral pool), and can be used as chiral auxiliary/inductor to control the stereochemical course of a diastereoselective reaction. Furthermore, enantiopure tryptophanol is useful for the syntheses of natural products or biological active molecules containing the aminoalcohol functionality. In this communication, we report the development of a small library of indolo[2,3-a]quinolizidines and evaluation of their activity as N-Methyl d-Aspartate (NMDA) receptor antagonists. The indolo[2,3-a]quinolizidine scaffold was obtained using the following key steps: (i) a stereoselective cyclocondensation of (S)- or (R)-tryptophanol with appropriate racemic δ-oxoesters; (ii) a stereocontrolled cyclization on the indole nucleus. The synthesized enantiopure indolo[2,3-a]quinolizidines were evaluated as NMDA receptor antagonists and one compound was identified to be 2.9-fold more potent as NMDA receptor blocker than amantadine (used in the clinic for Parkinson’s disease). This compound represents a hit compound for the development of novel NMDA receptor antagonists with potential applications in neurodegenerative disorders associated with overactivation of NMDA receptors.

High-fat diet-induced deregulation of hippocampal insulin signaling and mitochondrial homeostasis deficiences contribute to Alzheimer disease pathology in rodents

Global obesity is a pandemic status, estimated to affect over 2 billion people, that has resulted in an enormous strain on healthcare systems worldwide. The situation is compounded by the fact that apart from the direct costs associated with overweight pathology, obesity presents itself with a number of comorbidities, including an increased risk for the development of neurodegenerative disorders. Alzheimer disease (AD), the main cause of senile dementia, is no exception. Spectacular failure of the pharmaceutical industry to come up with effective AD treatment strategies is forcing the broader scientific community to rethink the underlying molecular mechanisms leading to cognitive decline. To this end, the emphasis is once again placed on the experimental animal models of the disease. In the current study, we have focused on the effects of a high-fat diet (HFD) on hippocampal-dependent memory in C57/Bl6 Wild-type (WT) and APPswe/PS1dE9 (APP/PS1) mice, a well-established mouse model of familial AD. Our results indicate that the continuous HFD administration starting at the time of weaning is sufficient to produce β-amyloid-independent, hippocampal-dependent memory deficits measured by a 2-object novel-object recognition test (NOR) in mice as early as 6months of age. Furthermore, the resulting metabolic syndrome appears to have direct effects on brain insulin regulation and mitochondrial function. We have observed pathological changes related to both the proximal and distal insulin signaling pathway in the brains of HFD-fed WT and APP/PS1 mice. These changes are accompanied by a significantly reduced OXPHOS metabolism, suggesting that mitochondria play an important role in hippocampus-dependent memory formation and retention in both the HFD-treated and AD-like rodents at a relatively young age.

Evaluation of okadaic acid, dinophysistoxin-1 and dinophysistoxin-2 toxicity on Neuro-2a, NG108-15 and MCF-7 cell lines

Marine dinoflagelates from the genus Dynophisis are important producers of Diarrhetic Shellfish Poisoning (DSP) toxins which are responsible for human intoxications. The present work is an approach to study the relative toxicity of DSP toxins effects on Neuro-2a, NG108-15 and MCF-7 cell-lines. Certified standards of okadaic acid (OA), dinophysistoxin-1 (DTX-1) and dinophysistoxin-2 (DTX-2) were used. Our results show that the three toxins exhibit similar cytotoxicity in Neuro-2a and NG108-15 cell lines. Conversely, MCF-7 cells were the least sensitive to these toxins. DTX-1 displayed the most toxic effect in the three tested cell lines.

Synthesis of benzopolycyclic cage amines: NMDA receptor antagonist, trypanocidal and antiviral activities

The synthesis of several 6,7,8,9,10,11-hexahydro-9-methyl-5,7:9,11-dimethano-5H-benzocyclononen-7-amines is reported. Several of them display low micromolar NMDA receptor antagonist and/or trypanocidal activities. Two compounds are endowed with micromolar anti vesicular stomatitis virus activity, while only one compound shows micromolar anti-influenza activity. The anti-influenza activity of this compound does not seem to be mediated by blocking of the M2 protein.

Prosurvival role of JAK/STAT and Akt signaling pathways in MPP+-induced apoptosis in neurons

In the present study the role of JAK/STAT and Akt in apoptosis was evaluated in cerebellar granule cells after treatment with the mitochondrial toxin MPP(+). Firstly, we evaluated the role of the prosurvival Akt pathway in MPP(+)-induced apoptosis and found that MPP(+) rapidly reduced the phosphorylation of Akt at Ser473. Since PTEN is an upstream regulator of Akt, its inhibition with bpV(pic) (1-30 μM) should activate Akt, however, it did not attenuate CGC cell death mediated by MPP(+) but protected CGC from apoptosis mediated by S/K deprivation. We also demonstrated that after the treatment with the complex I inhibitor, the expression levels of STAT1 increased and the levels of STAT3 decreased at the time points tested (0.5-8h). Meanwhile, pharmacological inhibition of the JAK/STAT pathway with AG490 (10-40 μM) was neuroprotective, probably due to its antioxidant properties, the Jak2-inhibitor-II potentiated MPP(+) neurotoxicity. Collectively, our data indicate that the treatment of CGC with the neurotoxin MPP(+) decreased two prosurvival pathways: STAT3 and Akt. Meanwhile Akt activation, using a PTEN inhibitor, did not play a prominent role in neuroprotection; loss of STAT3 could be a signal pathway involved in neuroprotection against the Parkinsonian neurotoxin MPP(+).

Sirtuin activators: designing molecules to extend life span

Resveratrol (RESV) exerts important pharmacological effects on human health: in addition to its beneficial effects on type 2 diabetes and cardiovascular diseases, it also modulates neuronal energy homeostasis and shows antiaging properties. Although it clearly has free radical scavenger properties, the mechanisms involved in these beneficial effects are not fully understood. In this regard, one area of major interest concerns the effects of RESV on the activity of sirtuin 1 (SIRT1), an NAD(+)-dependent histone deacetylase that has been implicated in aging. Indeed, the role of SIRT1 is currently the subject of intense research due to the antiaging properties of RESV, which increases life span in various organisms ranging from yeast to rodents. In addition, when RESV is administered in experimental animal models of neurological disorders, it has similar beneficial effects to caloric restriction. SIRT1 activation could thus constitute a potential strategic target in neurodegenerative diseases and in disorders involving disturbances in glucose homeostasis, as well as in dyslipidaemias or cardiovascular diseases. Therefore, small SIRT1 activators such as SRT501, SRT2104, and SRT2379, which are currently undergoing clinical trials, could be potential drugs for the treatment of type 2 diabetes, obesity, and metabolic syndrome, among other disorders. This review summarises current knowledge about the biological functions of SIRT1 in aging and aging-associated diseases and discusses its potential as a pharmacological target.

Evaluation of transcriptional activity of caspase-3 gene as a marker of acute neurotoxicity in rat cerebellar granular cells

Caspase-3 is a key protein involved in the classical apoptosis mechanism in neurons, as in many other cells types. In the present research, we describe the transcriptional activity of caspase-3 gene as a marker of acute toxicity in a primary culture model of rat cerebellar granule neurons (CGNs). CGNs were incubated for 16h in complete medium containing the chemicals at three concentrations (10, 100microM and 1mM). A total of 48 different compounds were tested. Gene transcriptional activity was determined by low-density array assays, and by single Taqman caspase-3 assays. Results from the PCR arrays showed that the caspase-3 gene was up-regulated when CGNs were exposed to neurotoxic chemicals. Significative correlations were found between the transcriptional activity of caspase-3 and the activity of some other genes related to apoptosis, cell-cycle and ROS detoxification. In our experiments, acute exposure of CGNs to well-documented pro-apoptotic xenobiotics modulated significantly caspase-3 gene expression, whereas chemicals not related to apoptosis did not modify caspase-3 gene expression. In conclusion, acute exposure of CGNs to neurotoxic compounds modulates the transcriptional activity of genes involved in the classical apoptotic pathway, oxidative stress and cell-cycle control. Transcriptional activity of caspase-3 correlates significantly with these changes and it could be a good indicator of acute neurotoxicity.

Synthesis and pharmacological evaluation of (2-oxaadamant-1-yl)amines

The synthesis of several (2-oxaadamant-1-yl)amines is reported. They were evaluated as NMDA receptor antagonists and several of them were more active than amantadine, but none was more potent than memantine. None of the tested compounds displayed antiviral activity. Two of the derivatives showed a significant level of trypanocidal activity.

Synthesis and pharmacological evaluation of several ring-contracted amantadine analogs

The synthesis of several (3-noradamantyl)amines, [(3-noradamantyl)methyl]amines, (3,7-dimethyl-1-bisnoradamantyl)amines, and [(3,7-dimethyl-1-bisnoradamantyl)methyl]amines is reported. They were evaluated against a wide range of viruses and one of them inhibited the cytopathicity of influenza A virus at a concentration similar to that of amantadine. Several of the new polycyclic amines show an interesting activity as NMDA receptor antagonists. A rimantadine analogue displayed significant trypanocidal activity. Moreover, to further characterize the pharmacology of these compounds, their effects on dopamine uptake were also assessed.

Comparisons of the influenza virus A M2 channel binding affinities, anti-influenza virus potencies and NMDA antagonistic activities of 2-alkyl-2-aminoadamantanes and analogues

The new 2-alkyl-2-aminoadamantanes and analogues 4-10 were designed and synthesized by simplification of the structure of the potent anti-influenza virus A spiranic aminoadamantane heterocycles 2 and 3. The aim of the present work was to examine the effects of bulky and extended lipophilic moieties attached to amantadine 1 on binding to the M2 channel and the resulting antiviral potency. The binding affinities of the compounds to the M2 protein of influenza virus A/chicken/Germany/27 (Weybridge strain; H7N7) were measured for the first time using an assay based on quenching of Trp-41 fluorescence by His-37 protonation, and their antiviral potencies were evaluated against the replication of influenza virus A H2N2 and H3N2 subtypes and influenza virus B in MDCK cells. Of the various 2-alkyl-2-aminoadamantanes, and analogues, spiro[piperidine-2,2'-adamantane] 3 had the strongest M2 binding and antiviral potency, which were similar those of amantadine 1. The relative binding affinities suggested that the rigid carbon framework provided by the pyrrolidine or piperidine rings results in a more favorable orientation inside the M2 channel pore as compared to large, freely rotating alkyl groups. The aminoadamantane derivatives exhibited similar NMDA antagonistic activity to amantadine 1. A striking finding was the antiviral activity of the adamantanols 4, and 6, which lack any NMDA antagonist activity.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

Changes in oxidative stress parameters and neurodegeneration markers in the brain of the senescence-accelerated mice SAMP-8

The senescence-accelerated strains of mice (SAMP) are well-characterized animal models of senescence. Senescence may be related to enhanced production or defective control of reactive oxygen species, which lead to neuronal damage. Therefore, the activity of various oxidative-stress related enzymes was determined in the cortex of 5 months-old senescence-accelerated mice prone-8 (SAMP-8) of both sexes and compared with senescence-accelerated mice-resistant-1 (SAMR-1). Glutathione reductase and peroxidase activities in SAMP-8 male mice were lower than in male SAMR-1, and a decreased catalase activity was found in both male and female SAMP-8 mice, which correlates with the lower catalase expression found by Western blotting. Nissl staining showed marked loss of neuronal cells in the cerebral cortex of five month-old SAMP-8 mice. SAMP-8 mice also had marked astrogliosis and microgliosis. We also found an increase in caspase-3 and calpain activity in the cortex. In addition, we observed morphological changes in the immunostaining of tau protein in SAMP-8, indicative of a loss of their structural function. Altogether, these results show that, at as early as 5 months of age, SAMP-8 mice have cytological and molecular alterations indicative of neurodegeneration in the cerebral cortex and suggestive of altered control of the production of oxidative species and hyper-activation of calcium-dependent enzymes.

Hyperphosphorylation of microtubule-associated protein tau in senescence-accelerated mouse (SAM)

Tau is a neuronal microtubule-associated protein found predominantly on axons. Tau phosphorylation regulates both normal and pathological functions of this protein. Hyperphosphorylation impairs the microtubule binding function of tau, resulting in the destabilization of microtubules in brain, ultimately leading to the degeneration of the affected neurons. Numerous serine/threonine kinases, including GSK-3beta and Cdk5 can phosphorylate tau. SAMR1 and SAMP8 are murine strains of senescence. We show an increase in hyperphosphorylated forms of tau in SAMP8 (senescent mice) in comparison with resistant strain SAMR1. Moreover, an increase in Cdk5 expression and activation is described but analysis of GSK3beta isoforms failed to show differences in SAMP8 in comparison to age-matched SAMR1. In conclusion, tau hyperphosphorylation occurs in SAMP-8 (early senescent) mice, indicating a link between aging and tau modifications in this murine model.

Evidence in favour of a role for peripheral-type benzodiazepine receptor ligands in amplification of neuronal apoptosis

The mitochondrial peripheral benzodiazepine receptor (PBR) is involved in a functional structure designated as the mitochondrial permeability transition (MPT) pore, which controls apoptosis. PBR expression in nervous system has been reported in glial and immune cells. We now show expression of both PBR mRNA and protein, and the appearance of binding of a synthetic ligand fluo-FGIN-1-27 in mitochondria of rat cerebellar granule cells (CGCs). Additionally, the effect of PBR ligands on colchicine-induced apoptosis was investigated. Colchicine-induced neurotoxicity in CGCs was measured at 24 h. We show that, in vitro, PBR ligands 1-(2-chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195), 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4- benzodiazepin-2-one (Ro5-4864) and diazepam (25- 50 microM) enhanced apoptosis induced by colchicine, as demonstrated by viability experiments, flow cytometry and nuclear chromatin condensation. Enhancement of colchicine-induced apoptosis was characterized by an increase in mitochondrial release of cytochrome c and AIF proteins and an enhanced activation of caspase-3, suggesting mitochondrion dependent mechanism that is involved in apoptotic process. Our results indicate that exposure of neural cells to PBR ligands generates an amplification of apoptotic process induced by colchicine and that the MPT pore may be involved in this process.

Inhibition of CDKs: a strategy for preventing kainic acid-induced apoptosis in neurons

Stimulation of ionotropic glutamate receptors are implicated in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Recently this has been demonstrated in the expression of cell cycle proteins in vulnerable neurons in Alzheimer's disease. Thus, the aim of the present study was to evaluate the expression of cell cycle proteins in cerebellar granule cells after stimulation of AMPA/KA receptors and likewise to study the neuroprotective effects of CDK inhibitors. Our results demonstrated that after a treatment with CDK inhibitors, a significant decrease in apoptotic nuclei induced by kainic acid was found in the presence of flavopiridol and 3-ATA. We concluded that CDK activation is involved, at least, in part, in the pro-apoptotic effects of kainic acid.

Neurotoxicity of amphetamine derivatives is mediated by caspase pathway activation in rat cerebellar granule cells

The neurotoxic action of the abuse drugs methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA) on cerebellar granule neurones (CGNs) culture was examined. Treatment for 48 h with METH or MDMA (1-5 mM) induced a higher decrease in viability than 24 h treatment. z.VAD.fmk (100 microM) but not MK-801 nor NBQX recovered control viability values. In both cases, cell death was characterised as apoptotic rather than necrotic by morphology cell observation. Apoptosis measured by flow cytometry indicated an increase in the hypodiploid population after 48 h treatment with METH and MDMA. Apoptosis was reverted by the presence of z.VAD.fmk (100 microM) but not by 10 microM MK-801 or NBQX. Similar results were obtained by analysing nuclear chromatine condensation. These results ruled out excitotoxic participation in amphetamine derivative-induced neurotoxicity in CGNs. Participation of radical oxygen species (ROS) was evaluated using alpha-tocopherol (1-15 microM) and cytometric studies. The co-treatment with 4 mM METH or MDMA for 48 h partially reverted neurotoxic action and apoptotic features, indicating ROS implication in CGNs death by amphetamine derivatives. Alteration of mitochondrial function induced cytochrome C (Cyt C) release after 48-h treatment with METH and MDMA (4 mM). There was also indication of caspase-3-like activation, measured by immunoanalysis and biochemically. Finally, neurodegenerative action caused by amphetamine derivatives may be prevented by using caspase inhibitors.

3-Amino thioacridone, a selective cyclin-dependent kinase 4 inhibitor, attenuates kainic acid-induced apoptosis in neurons

The mechanisms underlying selective neuronal cell death in kainic acid-mediated neurodegeneration are not fully understood. We have recently demonstrated that in cerebellar granule neurons, kainic acid induces the expression of proteins associated with cell-cycle progression. In the present study we show that 3-amino thioacridone (3-ATA), a selective cyclin-dependent kinase 4 inhibitor, attenuates kainic acid-induced apoptosis in cerebellar granule neurons. When neurons were pre-treated with 3-ATA 10 microM for 24 h, they were less susceptible to damage induced by kainic acid 500 microM, since the number of dead cells decreased significantly. In flow cytometry studies using propidium iodide staining, 3-ATA also reduced the ratio of apoptotic cells induced by kainic acid. Moreover, 3-ATA decreased the proportion of cells with a condensed nucleus from 55% to 22%. Our data suggest that the cell cycle pathway is involved in the mechanism of apoptosis mediated by kainic acid and that cyclin-dependent kinase 4 plays a prominent role in this process. 3-ATA may to prevent the apoptosis associated with neurodegenerative disorders without the over-activation of excitatory amino acid receptors.

Neuroprotective effects of (+/-)-huprine Y on in vitro and in vivo models of excitoxicity damage

We have investigated the neuroprotective effects of (+/-)-huprine Y on excitotoxic lesions in rat cerebellar granule cells (CGCs). (+/-)-Huprine Y prevented cell death induced by 100 microM glutamate, as well as, 10 microM MK-801, a NMDA receptor antagonist, in a significant manner. On the other hand, intracellular calcium increase induced by NMDA (200 microM), measured by fura-2 fluorescence, was prevented by (+/-)-huprine Y with an EC(50) of 12.44 microM, which evidences the modulatory action of this compound on NMDA-induced calcium currents. In vivo, we have studied (+/-)-huprine Y neuroprotective effects on striatal lesions induced by the subacute administration of the mitochondrial toxin 3-nitropropionic acid (3-NP, 30 mg/kg, ip, for 10 days). We have assessed that both the behavioral and the morphological consequences of the lesion were prevented by pretreatment with (+/-)-huprine Y (2.5 mg/kg/twice a day, ip). Striatal gliosis induced by 3-NP treatment was prevented by (+/-)-huprine Y pretreatment, as demonstrated by the attenuation of both the increase in [(3)H]PK 11195 specific binding indicative of microgliosis and the expression of hsp27 kDa, a chaperone expressed mainly in astrocytes. In conclusion, (+/-)-huprine Y attenuated excitotoxic-induced lesions, both in vitro and in vivo, and further evidence is provided for the potential use of this compound in the prevention of neurodegenerative disorders.

Parameters related to oxygen free radicals in erythrocytes, plasma and epidermis of the hairless rat

The following parameters related to oxygen free radicals (OFR) were determined in erythrocytes and the epidermis of hairless rats: catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), reduced (GSH) and oxidized (GSSG) glutathione, glutathione S-transferase (GST), superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS). GSH, GSSG and TBARS were also analyzed in plasma. In erythrocytes, the Pearson correlation coefficients (r) were significant (p < 0.001) between glutathione and other parameters as follows: GSH correlated negatively with GSSG (r = -0.665) and TBARS (r = -0.669); GSSG correlated positively with SOD (r = 0.709) and TBARS (r = 0.752). Plasma GSSG correlated negatively with erythrocytic thermostable GST activity (r = -0.608; p=0.001) and with erythrocytic total GST activity (r = -0.677; p < 0.001). In epidermis (p < 0.001 in all cases), GSH content correlated with GSSG (r = 0.682) and with GPx (r = 0.663); GSSG correlated with GPx (r = 0.731) and with GR (r = 0.794). By multiple linear regression analysis some predictor variables (R(2)) were found: in erythrocytes, thermostable GST was predicted by total GST activity and GSSG, GSSG content was predicted by GSH and by the GSH/GSSG ratio and GPx activity was predicted by GST, CAT and SOD activities; in epidermis, GSSG was predicted by GR and SOD activities and GR was predicted by GSSG, TBARS and GPx. It is concluded that the hairless rat is a good model for studying OFR-related parameters simultaneously in blood and skin, and that it may provide valuable information about other animals under oxidative stress.

Carnosine prevents methamphetamine-induced gliosis but not dopamine terminal loss in rats

The neuroprotective effect of carnosine, an endogenous antioxidant, was examined against methamphetamine-induced neurotoxicity in rats. Carnosine pretreatment had no effect on dopamine terminal loss induced by methamphetamine (assessed by [3H]1-(2-[diphenylmethoxy]ethyl)-4-[3-phenylpropyl]piperazine([3H]GBR 12935) binding) but prevented microgliosis (increase in [3H]1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide ([3H]PK 11195) binding) in striatum. The 27-kDa heat-shock protein (HSP27) expression was used as indicator of astroglial stress. Methamphetamine treatment induced the expression of HSP27 in striatum and hippocampus, which was inhibited by carnosine, indicating a protective effect. Carnosine had no effect on methamphetamine-induced hyperthermia. Thus, carnosine prevents the microgliosis in striatum (where we did not detect loss of serotonergic terminals by [3H]paroxetine binding) and the expression of HSP27 in all the areas, but fails to prevent methamphetamine-induced loss of dopamine reuptake sites. Therefore, carnosine inhibits only some of the consequences of methamphetamine neurotoxicity, where reactive oxygen species play an important role.

Kainic acid-induced neuronal cell death in cerebellar granule cells is not prevented by caspase inhibitors

1. We examined the role of non-NMDA receptors in kainic acid (KA)-induced apoptosis in cultures of rat cerebellar granule cells (CGCs). KA (1 - 500 microM) induced cell death in a concentration-dependent manner, which was prevented by NBQX and GYKI 52466, non-NMDA receptor antagonists. Moreover, AMPA blocked KA-induced excitotoxicity, through desensitization of AMPA receptors. 2. Similarly, KA raised the intracellular calcium concentration of CGCs, which was inhibited by NBQX and GYKI 52466. Again, AMPA (100 microM) abolished the KA (100 microM)-induced increase in intracellular calcium concentration. 3. KA-induced cell death in CGCs had apoptotic features, which were determined morphologically, by DNA fragmentation, and by expression of the prostate apoptosis response-4 protein (Par-4). 5. KA (500 microM) slightly (18%) increased caspase-3 activity, which was strongly enhanced by colchicine (1 microM), an apoptotic stimulus. However, neither Z-VAD.fmk, a pan-caspase inhibitor, nor the more specific caspase-3 inhibitor, Ac-DEVD-CHO, prevented KA-induced cell death or apoptosis. In contrast, both drugs inhibited colchicine-induced apoptosis. 5. The calpain inhibitor ALLN had no effect on KA or colchicine-induced neurotoxicity. 6. Our findings indicate that colchicine-induced apoptosis in CGCs is mediated by caspase-3 activation, unlike KA-induced apoptosis.

C-phycocyanin protects cerebellar granule cells from low potassium/serum deprivation-induced apoptosis

We tested the potential cytoprotective role of C-phycocyanin in rat cerebellar granule cell cultures. Cell death was induced by potassium and serum (K/S) withdrawal. Cell viability was studied using the neutral red assay and laser scanning cytometry with propidium iodide as fluorochrome. C-phycocyanin (1-3 mg/ml) showed a neuroprotective effect against 24 h of K/S deprivation in cerebellar granule cells. After 4 h K/S deprivation this compound (3 mg/ml) inhibited formation of reactive oxygen species, measured as 2',7'-dichlorofluorescein fluorescence, showing its scavenger capability. Pre-treatment with C-phycocyanin reduced thymidine incorporation into DNA below control values and reduced dramatically apoptotic bodies as visualized by propidium iodide, indicating inhibition of apoptosis induced by K/S deprivation. Flow cytometry studies, using propidium iodide in TritonX100 permeabilized cells, indicated that 24 h K/S deprivation acts as a proliferative signal for cerebellar granule cells, which show an increase in S-phase percentage and cells progressed into the apoptotic pathway. C-phycocyanin protected cerebellar granule cells from the apoptosis induced by deprivation. These results suggest that C-phycocyanin prevents apoptosis in cerebellar granule cells probably through the antioxidant activity. It is proposed that K/S deprivation-induced apoptosis could be due, in part, to an alteration in the cell cycle mediated by an oxidative stress mechanism.

Inhibitors of NO-synthase and donors of NO modulate kainic acid-induced damage in the rat hippocampus

The effects of nitric oxide synthase (NOS) inhibitors, N(omega)-nitro-L-arginine and 7-nitroindazole, and the NOS substrate L-arginine on kainic acid (KA)-induced microglial reactivity and stress response were studied in the hippocampus 7 and 1 days after KA, respectively. Density of peripheral-type benzodiazepine receptors was measured as an index of microglial reactivity. Histological damage in hippocampus was evaluated at 7 days by neuronal counting. KA increased the maximal number of binding sites (B(max)) versus controls. Administration of either 7-nitroindazole (25 mg/kg) or N(omega)-nitro-L-arginine (20 and 50 mg/kg) 24 hr before KA, further increased B(max). This later effect was abolished by L-arginine (1 g/kg), which given 24 hr before KA decreased B(max) to control values. Also, KA-induced HSP72 stress response was attenuated by pre-treatment with L-arginine. Histological evaluation showed reduced cell numbers in the pyramidal cell layer of the hippocampus in groups receiving KA, either alone or in combination with 7-nitroindazole. Administration of L-arginine before KA attenuated neuronal loss in CA3 but not CA1. A clear protective effect was observed, however, in CA1 and CA3, in rats receiving both L-arginine plus 7-nitroindazole before KA. The results show that the combination of a NO substrate with a NOS inhibitor reduces the neurotoxic effects of KA in the rat hippocampus. This study suggests that extremely fine regulation of NO levels in the different neural cell types can modulate excitotoxicity.

Evaluation of free radical production, mitochondrial membrane potential and cytoplasmic calcium in mammalian neurons by flow cytometry

The overexcitation of glutamate receptors is believed to be the cause of several neurodegenerative disorders. The determination of calcium fluxes, mitochondrial membrane potential (MMP) variations or the production of reactive oxygen species (ROS) in mammalian cells are usually measured during the development of potentially useful drugs that might interfere in the events induced by glutamate receptor activation. By using flow cytometry with dissociated cerebellar granule cells, we have developed a rapid and economical method to measure changes in biochemical parameters that are involved in neuronal cell death. The formation of intracellular ROS is measured using 2',7'-dichlorofluorescin diacetate (DCFH-DA). The mitochondrial membrane potential is assessed by the retention of rhodamine 123 (Rh123), a specific fluorescent cationic dye that is readily sequestered by active mitochondria, depending on their transmembrane potential. Finally, intracellular calcium increases are detected by using the calcium-selective indicator Indo-1. Cell viability is also assessed by using propidium iodide (PI) which stains DNA strands of permeabilized cells. This method might be useful for the screening of new drugs with potential neuroprotective activity, with improved cost/effectiveness ratio compared to other techniques.

In vitro and in vivo protective effect of orphenadrine on glutamate neurotoxicity

The anticholinergic drug orphenadrine is used in the treatment of Parkinson's disease. In this study we evaluate the neuroprotective effects of orphenadrine on excitotoxicity in vivo and in vitro. Orphenadrine prevented the mitochondrial and the cytoplasmic membrane potential decrease evoked by NMDA (100 microM) in rat dissociated cerebellar granule cells showing an IC50 value of 11.6 +/- 4.7 microM (mean +/- SEM, n = 5) and 13.5 +/- 2.3 microM (n = 3), respectively. Orphenadrine was able to protect cerebellar granule cell cultures from glutamate-induced neurotoxicity. Kainic acid (KA, 10 mg/kg)-induced excitotoxicity was evaluated in vivo using the microglial marker peripheral-type benzodiazepine receptor (PBR) and heat shock protein 72 (HSP72) expression in the hippocampus. The Bmax of PBR for control tissues was 589.1 +/- 40.0 fmol/mg protein (n = 4), increasing to 1692.5 +/- 51.6 fmol/mg protein (n = 5) after the KA treatment. Pretreatment with orphenadrine (10 mg/kg) blocked the KA-induced increase in PBR density. As expected, KA-administration induced the expression of HSP72 that was blocked in the orphenadrine + KA-treated rats. We demonstrate that orphenadrine, interacting at the NMDA receptor, is able to prevent the neurotoxicity mediated by activation at glutamate ionotropic receptors.

Effects of U-83836E on glutamate-induced neurotoxicity in dissociated rat cerebellar granule cells

The effects of the lazaroid compound U-83836E on the glutamate-induced production of reactive oxygen species (ROS) were studied in dissociated rat cerebellar granule cells by flow cytometry. U-83836E completely inhibited ROS production with an estimated IC50 value of 21.7 +/- 9.1 nM. However, U-83836E did not inhibit the glutamate-evoked decrease in mitochondrial membrane potential (MMP). Nevertheless, U-83836E (10 nM to 10 microM) prevented cell death induced by 10 mM of glutamate. At concentrations above 10 microM, U-83836E by itself showed slight cytotoxicity, which was significant at a 100 microM concentration. U-83836E (25 to 200 microM) also increased the cytosolic calcium levels in a concentration-dependent manner. Our results indicate that the cytotoxic effects found at micromolar concentrations of U-83836E could be explained by an increase in [Ca2+]i. Finally, since U-83836E did not prevent the MMP decrease evoked by glutamate, it is suggested that antioxidant pharmacotherapy would not be sufficient to block the neurotoxic effects of glutamate.

Assessment of the adrenergic effects of orphenadrine in rat vas deferens

The peripheral adrenergic effects of orphenadrine, an antiparkinsonian drug, have been evaluated in the rat vas deferens to investigate whether these properties are the same as those of other phencyclidine ligands. In the low micromolar range, orphenadrine enhanced electrically-evoked and exogenous noradrenaline contractile responses in the epididymal portion of rat vas deferens. It also induced spontaneous activity that was inhibited by prazosin (1 microM) but not by atropine (20 nM). It inhibited accumulation of [3H]noradrenaline in rat vas deferens (IC50 = 14.2+/-2.3 microM). Orphenadrine competitively inhibited [3H]nisoxetine binding in rat vas deferens membranes (Ki = 1.05+/-0.20 microM). It can be concluded that orphenadrine, at low micromolar concentrations, interacts with the noradrenaline reuptake system inhibiting its functionality and thus potentiating the effect of noradrenaline.

Microgliosis and down-regulation of adenosine transporter induced by methamphetamine in rats

Chronic administration of methamphetamine to rats induces neurotoxicity characterized by a loss of striatal dopaminergic terminals and reactive gliosis. Subcutaneous administration of methamphetamine in a scheduled procedure of four doses (10 mg/kg) at 2 h interval also induces a significant increase in the peripheral-type benzodiazepine receptor (PBR) density. This increase is maximum (76%) at 72 h post-treatment in the striatum and disappears at 7 days, suggesting that microglia may have a predominant role in necrosis-phagocytosis of neuronal debris rather than acting in a restorative manner. Microgliosis is not restricted to the striatum since it is also evident in cerebellum (75.4% of PBR increase) and hippocampus (37.2% of PBR increase). In the areas with high density of adenosine transporter, the microgliosis phenomenon correlates well with a decrease of this nucleoside transporter (about 39%). Although the microgliosis and the decrease in adenosine transporter could be parallel and not related events, we can speculate that when microglia are activated, a down-regulation of adenosine transporter occurs, playing a role in tissue homeostasis. With the same dosing schedule, methamphetamine induces HSP72 expression in both cytoplasmic and nuclear fractions of the striatum, cerebellum and hippocampus. This expression is also evident in the cerebral cortex, where adenosine transporter population did not show any variation.

Effect of PCP and sigma ligands on both noradrenaline- and electrically-induced contractions and on [3H]-noradrenaline uptake in rat vas deferens

1. Electrically induced contractions of the epididymal portion of rat vas deferens were potentiated in concentration-dependent manner (0.1-30 microM) by different sigma and PCP receptor ligands (PCP, TCP, (+)-MK-801, dextromethorphan and (+)-3-PPP); dextrorphan did it in a minor extent. 2. Sigma and PCP receptor ligands also potentiated the effect of noradrenaline, inducing a reduction of the noradrenaline EC50 value in the rat vas deferens. The rank order of potencies was: PCP > TCP > (+)-3-PPP > (+)-MK-801 > dextrorphan > > > dextrometorphan. 3. In contrast, haloperidol (1 microM), a sigma receptor ligand, inhibited both the neurogenic and noradrenaline-induced responses in this tissue. 4. The effect of PCP and sigma receptor ligands on noradrenaline uptake was evaluated. All compounds tested, including haloperidol, inhibited the tritiated noradrenaline incorporation to the tissue. IC50 values were in the micromolar range, between 1.09 microM for dextrophan and 18 microM for dextrometorphan. 5. It is concluded that a direct interaction with the noradrenaline uptake system is involved in the potentiating effect of some sigma and PCP receptor ligands in the epididymal portion of rat vas deferens.

Flow cytometric study of mitochondrial dysfunction after AMPA receptor activation

The effect of AMPA-receptor stimulation on MMP and on the concentration of intracellular calcium ([Ca2+]i) was studied in dissociated CGC from rat pups, by flow cytometry. In the presence of cyclothiazide, AMPA induced a sodium-independent decrease in MMP up to 30.7+/-2.5%. This effect was antagonized by CNQX and NBQX. Mepacrine and dibucaine reversed the effect of AMPA on MMP, suggesting that it is mediated by a release of arachidonic acid. AMPA alone induced a slight (about 7%) increase in [Ca2+]i. In the presence of cyclothiazide, AMPA induced a concentration-dependent [Ca2+]i increase up to 29.10+/-2.10% that was not reversed by flunarizine. This increase was similar to that observed in a Na+-free medium, and was antagonized by CNQX and NBQX, but not by MK-801. Mitochondria play a key role in the modulation of [Ca2+]i since a significant [Ca2+]i increase was found in the presence of FCCP. On the other hand, the dantrolene-sensitive calcium pools do not participate in the [Ca2+]i increase induced by stimulation of AMPA receptors. It is concluded that when AMPA-receptor desensitization is blocked, a decrease in MMP and an increase in [Ca2+]i occurs, which could be additional events to potentiate neuronal cell death induced by glutamate.

U-83836E prevents kainic acid-induced neuronal damage

The effect of kainic acid (KA) on mitochondrial membrane potential (MMP) and reactive-oxygen species (ROS) production was studied in dissociated cerebellar granule cells from rat pups. KA induced a maximum increase of 361%+/-35% in ROS production. The lazaroid compound U-83836E (at concentrations ranging from 10(-9) to 5x10(-6) M) completely inhibited this increase, with an IC50 value of 3.02+/-1.08x10(-7) M. KA also decreased the mitochondrial membrane potential (MMP), with a maximum decrease of about 30%. Absence of Na+ in the incubation medium did not significantly alter the effect of KA on MMP. As expected, the AMPA/kainate receptor antagonist NBQX inhibited the effects of KA on MMP with an IC50 value of 1.1+/-0.8 microM. However, the lazaroid U-83836E, indomethacin, nor-dihydroguaiaretic acid and L-nitroarginine all failed to inhibit the KA-induced decrease in the MMP. Finally, to assess the neuroprotective effect of U-83836E on KA-induced neurotoxicity in vivo, the increase in the peripheral-type benzodiazepine receptor density in rat hippocampus was measured. Treatment with KA increased the Bmax to 1341+/-192 fmol mg(-1). When U-83836E was coadministered with KA, the Bmax was reduced to 765+/-122 fmol mg(-1), which was not significantly different from the Bmax obtained from untreated rats (Bmax: 518+/-33 fmol mg(-1)). We conclude that treatment with the lazaroid U-83836E might be a suitable therapeutic strategy in neurodegenerative disorders.

Reactive oxygen production by glutamate agonists in dissociated cerebellar cells: a flow cytometric study

1. The effect of glutamate, N-methyl-D-aspartate (NMDA) and kainate on radical oxygen species (ROS) production and calcium influx was studied in dissociated cerebellar granule cells with the use of flow cytometry. 2. Glutamate and NMDA induced an intracellular ROS increase by an activation of NMDA receptors. 3. (+)MK-801 inhibited the effect on ROS production of both agonists (IC50 values of 1.52 +/- 0.05 and 0.71 +/- 0.02 microM, respectively). 4. (+)MK-801 inhibited the intracellular calcium increase induced by glutamate and NMDA, whereas 6-cyano-7-nitroquinoxaline-2,3-dione inhibited that induced by kainate. 5. NG-Nitro-L-arginine, but not nitrendipine, inhibited the ROS production induced by glutamate agonists. Consequently, nitric oxide synthase might play an important role in the neurotoxic process induced by excitatory amino acids.

Characterization of [3H]nisoxetine binding in rat vas deferens membranes: modulation by sigma and PCP ligands

Sigma (sigma) and phencyclidine (PCP) receptor ligands, apart from their main effects on sigma receptors and NMDA receptor-mediated neurotransmission, have been found to interact with catecholamine systems in several central and peripheral tissues. In the present study the binding profile of [3H]nisoxetine ([3H]NIS), a selective marker of the noradrenaline transporter, has been characterized in rat vas deferens membranes to further study its modulation by a number of characteristic sigma and PCP ligands. The binding of [3H]NIS was found to be of high affinity (Kd = 1.63 +/- 0.36 nM), saturable, sodium-dependent and to a single population of binding sites (nH = 1.003 +/- 0.017). The maximal binding capacity was 1,625 +/- 500 fmol/mg of protein. Kinetic experiments gave a k(+1) of 3.9 x 10(7) min(-1)M(-1) and a k(-1) of 0.005 min(-1). The [3H]NIS binding was totally inhibited, with IC50 values in the micromolar range, by all the sigma and PCP ligands tested, with the following order of potency: haloperidol > dextromethorphan > dizocilpine > dextrorphan > (+)-3-PPP > PCP > tenocyclidine. This order correlates well with that described in other tissues using [3H]desmethylimipramine. The inhibition by all these compounds, except that of (+)-3-PPP, was competitive. These results suggest that sigma and PCP ligands bind, at low micromolar concentrations, to a site in the noradrenaline transporter that is labelled by [3H]NIS.

Effect of 1-methyl-4-phenylpyridinium (MPP+) on mitochondrial membrane potential in cerebellar neurons: interaction with the NMDA receptor

The effect of MPP+, a dopaminergic neurotoxin, in mitochondrial membrane potential was investigated in dissociated cerebellar granule cells using rhodamine 123 and flow cytometry. MPP+ (1 mM) decreased the mitochondrial membrane potential by 30%. Antagonists of the NMDA receptor complex, such as MK-801 (IC50 value of 20.92 +/- 0.02 nM), 5,7-dichlorokynurenic acid (IC50 value of 6.46 +/- 1.06 microM) and D-AP5 (IC50 value of 8.29 +/- 0.63 microM), inhibited the action of MPP+. Neither NBQX, nor riluzole, nor desipramine modified the action of MPP+. Dibucaine restored the basal values of mitochondrial membrane potential altered by MPP+. Since, in the presence of NMDA, MPP+ antagonized the effect of this total agonist, it can be concluded that, in this preparation, MPP+ interacts with the NMDA receptor complex as a partial agonist. This interaction could be the result of an allosteric modulation of the NMDA receptor complex by MPP+. The decrease of mitochondrial membrane potential induced by MPP+ is antagonized by dibucaine, suggesting that this effect is mediated by an activation of phospholipase A2.

Opposite influence of the metabotropic glutamate receptor subtypes mGlu3 and -5 on astrocyte proliferation in culture

In non-synchronized, subconfluent secondary cultures of rat cortical astrocytes, the selective group-I metabotropic glutamate (mGlu) receptor agonist 3,5-dihydroxyphenylglycine (DHPG) increased [methyl-3H]-thymidine incorporation. This effect was mediated by the activation of the mGlu5 receptor, which was shown to be present by either RT-PCR or Western blot analysis. The mixed mGlu receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine reduced the increase in both intracellular Ca2+ and [methyl-3H]-thymidine incorporation produced by DHPG. In contrast, (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV), a potent and selective agonist of group-II mGlu receptors, reduced [methyl-3H]-thymidine incorporation in non-synchronized astrocyte cultures. The antiproliferative effect of DCG-IV was prevented by the selective group-II mGlu receptor antagonist (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG-IV). The opposite effect of DHPG and DCG-IV on astrocyte proliferation was confirmed in cultures deprived of serum for 48 hours and then stimulated to proliferate with either epidermal growth factor (EGF) or the metabolically stable ATP analogue adenosine 5'-(beta,gamma-imido)-triphosphate (AMP-PNP). We conclude that activation of mGlu5 receptors enhances proliferation in cultured astrocytes, whereas activation of a receptor with pharmacological characteristics similar to those of mGlu2/3 receptors reduces proliferation.