Differential phase-amplitude coupling in nucleus accumbens and orbitofrontal cortex reflects decision-making during a delay discounting task.

BACKGROUND: The impulsive choice is characterized by the preference for a small immediate reward over a bigger delayed one. The mechanisms underlying impulsive choices are linked to the activity in the Nucleus Accumbens (NAc), the orbitofrontal cortex (OFC), and the dorsolateral striatum (DLS). While the study of functional connectivity between brain areas has been key to understanding a variety of cognitive processes, it remains unclear whether functional connectivity differentiates impulsive-control decisions. METHODS: To study the functional connectivity both between and within NAc, OFC, and DLS during a delay discounting task, we concurrently recorded local field potential in NAc, OFC, and DLS in rats. We then quantified the degree of phase-amplitude coupling (PAC), coherence, and Granger Causality between oscillatory activities in animals exhibiting either a high (HI) or low (LI) tendency for impulsive choices. RESULTS: Our results showed a differential pattern of PAC during decision-making in OFC and NAc, but not in DLS. While theta-gamma PAC in OFC was associated with self-control decisions, a higher delta-gamma PAC in both OFC and NAc biased decisions toward impulsive choices in both HI and LI groups. Furthermore, during the reward event, Granger Causality analysis indicated a stronger NAc➔OFC gamma contribution in the HI group, while the LI group showed a higher OFC➔NAc gamma contribution. CONCLUSIONS: The overactivity in NAc during reward in the HI group suggests that exacerbated contribution of NAcCore can lead to an overvaluation of reward that biases the behavior toward the impulsive choice.

Predicting tearing paths in thin sheets.

This study investigates the tearing of a thin notched sheet when two points on the sheet are pulled apart. The concepts that determine the crack trajectory are reviewed in the general anisotropic case, in which the energy of the fracture depends on the fracture direction. When observed as a flat sheet a purely geometric "tearing vector" is defined through the location of the crack tip and the pulling points. Both Griffiths's criterion and the maximum energy release rate criterion (MERR) predict a fracture path that is parallel to the tearing vector in the isotropic case. However, for the anisotropic case, the application of the MERR leads to a crack path that deviates from the tearing vector, following a propagation direction that tends to minimize the fracture energy. In the case of strong anisotropy, it is more difficult to obtain an analytical prediction of the tearing trajectory. Thus, simple geometrical arguments are provided to give a derivation of a differential equation accounting for crack trajectory, according to the natural coordinates of the pulling, and in the case that the anisotropy is sufficiently weak. The solution derived from this analysis is in good agreement with previous experimental observations.

Comparing dopaminergic dynamics in the dorsolateral striatum between adolescent and adult rats: Effect of an acute dose of WIN55212-2.

During adolescence dopaminergic neurotransmission shows transient changes until reaching adulthood. The administration of CB1 agonists such as WIN55212-2 during adulthood increases dopamine extracellular levels. However, the effects of acute administration of cannabinoids on nigrostriatal dopamine neurotransmission during adolescence are not fully elucidated. The aim of this research is to compare dorsolateral striatum (DLS) dopamine (DA) dynamics and to study the effect of WIN55212-2 on DLS DA dynamics during adolescence and adulthood. No-net flux microdialysis experiments were carried out in adolescent (post-natal day 35-40) and young-adult (post-natal day 70-75) urethane-anesthetized rats. Basal DA dialysate, DA extraction fraction (Ed) and extracellular concentration of DA (Cext) in DLS were assessed after an acute injection of WIN55212-2 (1.2 mg/kg) or vehicle. An increased basal DA dialysate and DA Ed were observed during adolescence compared to adulthood. Moreover, WIN55212-2 increases DLS DA Cext rising basal DA dialysate in adulthood and decreasing DA Ed in adolescence. Our results suggest that an age-dependent mechanism underlies the effect of WIN 55212-2 on DA balance between release and uptake in DLS.

Neuroprotective effects of EpoL against oxidative stress induced by soluble oligomers of Aß peptide.

Erythropoietin is a glycoproteic hormone that regulates hematopoiesis by acting on its specific receptor (EpoR). The expression of EpoR in the central nervous system (CNS) suggests a role for this hormone in the brain. Recently, we developed a new Epo variant without hematopoietic activity called EpoL, which showed marked neuroprotective effects against oxidative stress in brain ischemia related models. In this study, we have evaluated the neuroprotective effects of EpoL against oxidative stress induced by chronic treatment with Aß. Our results show that EpoL was neuroprotective against Aß-induced toxicity by a mechanism that implicates EpoR, reduction in reactive oxygen species, and reduction in astrogliosis. Furthermore, EpoL treatment improved calcium handling and SV2 levels. Interestingly, the neuroprotective effect of EpoL against oxidative stress induced by chronic Aß treatment was achieved at a concentration 10 times lower than that of Epo. In conclusion, EpoL, a new variant of Epo without hematopoietic activity, is of potential interest for the treatment of diseases related to oxidative stress in the CNS such as Alzheimer disease.

Neuroprotective effect of a new variant of Epo nonhematopoietic against oxidative stress.

Human erythropoietin is mainly recognized for its hematopoietic function; however, by binding to its receptor (EpoR), it can activate different signaling pathways as STAT, PI3K, MAPK and RAS to increase cellular differentiation or provide neuroprotective effects, among others. A recombinant human erythropoietin variant with low glycosylation and without hematopoietic effect (EpoL) was purified from skimmed goat milk. Recombinant human erythropoietin (Epo) was obtained from CHO cell line and used as control to compare EpoL effects. Neuroprotection studies were performed in PC12 cells and rat hippocampal slices. Cells were pretreated during 1h with EpoL or Epo and exposed to oxidative agents (H2O2 or FCCP); cell viability was assayed at the end of the experiment by the MTT method. Hippocampal slices were exposed to 15min of oxygen and glucose deprivation (OGD) and the neuroprotective drugs EpoL or Epo were incubated for 2h post-OGD in re-oxygenated medium. Cell cultures stressed with oxidative agents, and pretreated with EpoL, showed neuroprotective effects of 30% at a concentration 10 times lower than that of Epo. Moreover, similar differences were observed in OGD ex vivo assays. Neuroprotection elicited by EpoL was lost when an antibody against EpoR was present, indicating that its effect is EpoR-dependent. In conclusion, our results suggest that EpoL has a more potent neuroprotective profile than Epo against oxidative stress, mediated by activation of EpoR, thus EpoL represents an important target to develop a potential biopharmaceutical to treat different central nervous system pathologies related to oxidative stress such as stroke or neurodegenerative diseases.

Xenopus as a model organism to study heterotrimeric G-protein pathway during collective cell migration of neural crest.

Collective cell migration is essential in many fundamental aspects of normal development, like morphogenesis, organ formation, wound healing, and immune responses, as well as in the etiology of severe pathologies, like cancer metastasis. In spite of the huge amount of data accumulated on cell migration, such a complex process involves many molecular actors, some of which still remain to be functionally characterized. One of these signals is the heterotrimeric G-protein pathway that has been studied mainly in gastrulation movements. Recently we have reported that Ric-8A, a GEF for Gα proteins, plays an important role in neural crest migration in Xenopus development. Xenopus neural crest cells, a highly migratory embryonic cell population induced at the border of the neural plate that migrates extensively in order to differentiate in other tissues during development, have become a good model to understand the dynamics that regulate cell migration. In this review, we aim to provide sufficient evidence supporting how useful Xenopus model with its different tools, such as explants and transplants, paired with improved in vivo imaging techniques, will allow us to tackle the multiple signaling mechanisms involved in neural crest cell migration.

ATP leakage induces P2XR activation and contributes to acute synaptic excitotoxicity induced by soluble oligomers of ß-amyloid peptide in hippocampal neurons.

Recent studies suggest that the toxic effects of Aß can be attributed to its capability to insert in membranes and form pore-like structures, which are permeable to cations and molecules such as ATP. Our working hypothesis is that Aß increases extracellular ATP causing activation of P2X receptors and potentiating excitatory synaptic activity. We found that soluble oligomers of ß-amyloid peptide increased cytosolic Ca(2+) 4-fold above control (415 ± 28% of control). Also, ATP leakage (157 ± 10% of control) was independent of extracellular Ca(2+), suggesting that ATP traveled from the cytosol through an Aß pore-mediated efflux and not from exocytotic mechanisms. The subsequent activation of P2XR by ATP can contribute to the cytosolic Ca(2+) increase observed with Aß. Additionally, we found that ß-amyloid oligomers bind preferentially to excitatory neurons inducing an increase in excitatory synaptic current frequency (248.1 ± 32.7%) that was blocked by the use of P2XR antagonists such as PPADS (Aß + PPADS: 110.9 ± 18.35%) or Apyrase plus DPCPX (Aß + inhibitors: 98.97 ± 17.4%). Taken together, we suggest that Aß induces excitotoxicity by binding preferentially to excitatory neuron membranes forming a non-selective pore and by increasing intracellular calcium by itself and through P2XR activation by extracellular ATP leading to an augmention in mEPSC activity. All these effects were blocked with a non-specific P2XR antagonist, indicating that part of the neurotoxicity of Aß is mediated by P2XR activation and facilitation of excitatory neurotransmitter release. These findings suggest that P2XR can be considered as a potential new target for the development of drugs or pharmacological tools to treat Alzheimer's disease. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.

Modulation of the neuronal network activity by P2X receptors and their involvement in neurological disorders.

ATP is a key energetic molecule, fundamental to cell function, which also has an important role in the extracellular milieu as a signaling molecule, acting as a chemoattractant for immune cells and as a neuro- and gliotransmitter. The ionotropic P2X receptors are members of an ATP-gated ion channels family. These ionotropic receptors are widely expressed through the body, with 7 subunits described in mammals, which are arranged in a trimeric configuration with a central pore permeable mainly to Ca(2+) and Na(+). All 7 subunits are expressed in different brain areas, being present in neurons and glia. ATP, through these ionotropic receptors, can act as a neuromodulator, facilitating the Ca(2+)-dependent release of neurotransmitters, inducing the cross-inhibition between P2XR and GABA receptors, and exercising by this way a modulation of synaptic plasticity. Growing evidence shows that P2XR play an important role in neuronal disorders and neurodegenerative diseases, like Parkinson's and Alzheimer's disease; this role involves changes on P2XR expression levels, activation of key pathways like GSK3ß, APP processing, oxidative stress and inflammatory response. This review is focused on the neuromodulatory function of P2XR on pathophysiological conditions of the brain; the recent evidence could open a window to a new therapeutic target.

Transition from isometric to stretching ridges in thin elastic films.

Isometric deformations in thin elastic films easily form ridges to connect large flat regions or facets. Depending on the forces applied or the boundary conditions imposed, these ridges can be isometric, with no stretching or "stretching ridges" when bending and stretching are required to relax the elastic energy. Here we study a simple configuration to observe the transition between an isometric ridge to the well-known stretching ridge observed in crumpled films, and obtain the parameters that determine the ridge type. Specifically, we show that the transversal size of a stretching ridge acts as a cutoff length scale: a ridge is isometric if its width is greater than this characteristic length.

Amphetamine sensitization is accompanied by an increase in prelimbic cortex activity.

Drug addiction is associated with dysfunction in the medial prefrontal cortex (mPFC). However, the modifications of neuronal activity in mPFC underlying the reinforcing properties of addictive drugs are still unclear. Here we carried out single-unit recording experiments to study the neuronal activity in the prelimbic (PL) cortex of anesthetized rats, after expression of locomotor sensitization to amphetamine. In control rats, an acute injection of amphetamine induced mainly an inhibitory effect on firing rate (FR) and this response was negatively correlated with the basal FR. Sensitized rats showed a higher proportion of excited neurons and the response to amphetamine was independent of basal FR. Moreover, in control rats, acute amphetamine decreased burst rate, whereas in sensitized rats acute amphetamine increased burst rate. These findings indicate that amphetamine sensitization renders mPFC neurons hyperexcitable. Taken together, these data support the hypothesis that early withdrawal is associated with an increase in the activity of the mPFC, which could strengthen the PL-Nucleus Accumbens connection, thus facilitating amphetamine-induced locomotor sensitization.

Cloning and spatiotemporal expression of RIC-8 in Xenopus embryogenesis.

RIC-8 is a highly conserved protein that promotes G protein signaling as it acts as a Guanine nucleotide Exchanging Factor (GEF) over a subset of Gα subunits. In invertebrates, RIC-8 plays crucial roles in synaptic transmission as well as in asymmetric cell division. As a first step to address further studies on RIC-8 function in vertebrates, here we have cloned a ric-8 gene from Xenopus tropicalis (xtric-8) and determined its spatiotemporal expression pattern throughout embryogenesis. The xtric-8 transcript is expressed maternally and zygotically and, as development proceeds, it shows a dynamic expression pattern. At early developmental stages, xtric-8 is expressed in the animal hemisphere, whereas its expression is later restricted to neural tissues, such as the neural tube and the brain, as well as in the eye and neural crest-derived structures, including those of the craniofacial region. Together, our findings suggest that RIC-8 functions are related to the development of the nervous system.

Historical and current perspectives of neuroactive compounds derived from Latin America.

Plants and invertebrates in Latin America have contributed to a great extent in the use, discovery and development of novel neuroactive tools. Significantly, these neuroactive drugs have proven to be particularly important for our current understanding of the physiology and pharmacology of the nervous system. In addition, these discoveries have helped to build the modern and successful pharmacological business that we know today. For example, curare helped to introduce the use of muscle relaxing agents into modern surgical techniques. The discovery of cocaine from the leaves of Peruvian coca plants was instrumental in the discovery of local anesthetics. The search and discovery for useful neuroactive compounds derived from Latin America has also been ongoing in other areas and new applications for quinine, capsaicin and epibatidine were recently described. Besides these organic compounds, several peptides produced by spiders and other invertebrates to hunt their prey also induce effects in channels and membrane receptors at very low concentrations, indicating their high potency and selectivity. It is likely that new pharmaceutics will be developed from these molecules. The interest to renew the search for new compounds is timely, since largely unexplored lands, such as the Amazon and Patagonia, hold an important number of plants and animals that contain exciting new active compounds. With the introduction of new techniques to isolate, identify and characterize the molecular targets and actions of chemical entities, together with the need for more potent and selective compounds to treat neurological conditions, it is necessary to broaden the current exploratory effort in order to find more beneficial uses.

Depolarization evokes different patterns of calcium signals and exocytosis in bovine and mouse chromaffin cells: the role of mitochondria.

This study was planned on the assumptions that different high-voltage activated calcium channels and/or the ability of mitochondria to take up Ca(2+) could be responsible for different cytosolic Ca(2+) concentrations ([Ca(2+)](c)) and catecholamine release responses in adrenal chromaffin cells of bovine and mouse species. Short K(+) pulses (2-5 s, 70 mM K(+)) increased [Ca(2+)](c) to a peak of about 1 microM; however, in bovine cells the decline was slower than in mouse cells. Secretory responses were faster in mouse but were otherwise quantitatively similar. Upon longer K(+) applications (1 min), elevations of [Ca(2+)](c) and secretion were prolonged in bovine cells; in contrast [Ca(2+)](c) in mouse cells declined three-fold faster and failed to sustain a continued secretion. Confocal [Ca(2+)](c) imaging following a 50-ms depolarizing pulse showed a similar Ca(2+) entry, but a rate of [Ca(2+)](c) increase and a maximum peak significantly higher in bovine cells; the rate of dissipation of the Ca(2+) wave was faster in the mouse. The mitochondrial protonophore CCCP (2 microm) halved the K(+)-evoked [Ca(2+)](c) and secretory signals in mouse cells, but had little affect on bovine responses. We conclude that the relative densities of L (15% in bovine and 50% in mouse) and P/Q Ca(2+) channels (50% in bovine and 15% in mouse) do not contribute to the observed differences; rather, the different intracellular distribution of Ca(2+), which is strongly influenced by mitochondria, is responsible for a more sustained secretory response in bovine, and for a faster and more transient secretory response in mouse chromaffin cells. It seems that mitochondria near the plasmalemma sequester Ca(2+) more rapidly and efficiently in the mouse than in the bovine chromaffin cell.

[Nicotinic Receptor, galantamine and Alzheimer disease]. / Receptor nicot nico, galantamina y enfermedad de Alzheimer.

Population aging has increased and will drastically increase the prevalence of Alzheimer disease. The disease develops inexorably towards a syndrome of marked cognitive impairment, accompanied of emotional alterations and profound changes of personality. The patient loses its autonomy, and requires special attention of caregivers; this leads to a decrease of the quality of life, not only of the patient but also of its caregivers and family. The reduction of the number of functional nicotinic receptors in brain keeps pace with neurological symptoms and the severity of the disease (cholinergic theory of Alzheimer disease). There is a pleyade of data and observations reinforcing the idea that improving cholinergic neurotransmission is an investment in memory. Up to now, although with limited success, this improvement has been achieved only with the reversible inhibitors of acetylcholinesterase tacrine, rivastigmine and donepezil, available in the clinic since a few years. The last approved has been galantamine that in spite of being a modest inhibitor of acetylcholinesterase, improves memory (ADAS cog test) and slows down cognitive impairment of Alzheimer patients. To explain this therapeutic effect, a second mechanism of action for galantamine has been suggested, the positive allosteric modulation of presynaptic nicotinic receptors, that will favour the release of acetylcholine and other neurotransmitters involved in memory formation. Furthermore, galantamine possesses neuroprotectant antiapoptotic effects, according to recent data from our laboratory. These effects provide new ideas and therapeutic targets that might help to find novel and efficacious treatments for patients suffering Alzheimer disease.

Receptor nicotínico, galantamina y enfermedad de Alzheimer / Nicotinic receptor, galantamine and Alzheimer disease

El envejecimiento de la población ha incrementado y continuará incrementando drásticamente la prevalencia de la enfermedad de Alzheimer. La enfermedad avanza inexorablemente hacia un cuadro de deterioro cognitivo acusado, con alteraciones emocionales y profundos cambios de personalidad. El paciente pierde su autonomía y requiere especial atención y cuidados; ello merma no sólo su calidad de vida sino también la de sus cuidadores. La reducción del número de receptores nicotínicos funcionales en el cerebro guarda relación con los síntomas neurológicos y la gravedad de la enfermedad (teoría colinérgica del Alzheimer). Existe una pléyade de datos y observaciones que refuerzan la idea de que mejorar la neurotransmisión colinérgica es invertir en memoria. Hasta ahora, aunque con éxito limitado, esta mejoría se ha logrado sólo con los inhibidores reversibles de la acetilcolinesterasa tacrina, rivastigmina y donepezilo, disponibles en clínica desde hace pocos años. El último en aparecer ha sido la galantamina, que a pesar de poseer un modesto efecto inhibidor de la acetilcolinesterasa, mejora la memoria (test ADAS-Cog) y desacelera el deterioro cognitivo de los pacientes de Alzheimer. Para explicar este efecto terapéutico se ha acudido a un segundo mecanismo de acción de la galantamina, la modulación alostérica positiva de receptores nicotínicos presinápticos, que favorecería la liberación de acetilcolina y de otros neurotransmisores implicados en la formación de memoria. Además, la galantamina posee efectos antiapoptóticos neuroprotectores, según hemos podido saber por experimentos recientes de nuestro laboratorio. Estos efectos proporcionan nuevas ideas y dianas terapéuticas que pueden ayudar a encontrar nuevos y eficaces tratamientos para los enfermos de Alzheimer (AU)

Electrochemical and spectroelectrochemical behavior of the main photodegradation product of nifedipine: the nitrosopyridine derivative.

PURPOSE: To characterize the electrochemical behavior of the photodegradation product of nifedipine, i.e., 2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridine-carboxylic acid dimethyl ester (NPD) in different electrolytic media. We also evaluated the interaction between free radicals generated from NPD and xeno/endobiotics. METHODS: Tast polarography, differential pulse polarography, and cyclic voltammetry were used for the characterization. Controlled potential electrolysis and ultraviolet-visible spectroscopy were used to generate and to detect the nitroso radical anion. RESULTS: In protic media, the NPD derivative gave a reversible well-defined peak either on Hg or glassy carbon electrodes in a reaction involving two electrons and two protons to give the hydroxylamine derivative. In mixed aqueous-organic media (pH 9) and in aprotic media, nitroso radical anion was isolated and characterized, exhibiting second-order dimerization rate constant (k2) values of 11,300 +/- 210 [Ms](-1) and 8,820 +/- 78 [Ms](-1), respectively. Reactivity of the nitroso radical anion with relevant pharmacologic targets revealed a significant interaction with the tested endo/xenobiotics (cysteamine, GSH, N-acetylcysteine, and adenine). CONCLUSIONS: Both in mixed and aprotic media, NPD generated free-radical species, the nitroso radical anion. Taking into account their respective interaction rate constants, the following tentative rank order of reactivity can be established as follows: cysteamine > N-acetylcysteine > GSH > adenine.

Trypanosoma cruzi: inhibition of parasite growth and respiration by oxazolo(thiazolo)pyridine derivatives and its relationship to redox potential and lipophilicity.

Chagas' disease constitutes a therapeutic challenge because presently available drugs have wide toxicity to the host and are generally ineffective in the chronic stages of the disease. A series of oxazolo(thiazolo)pyridene derivatives were studied on Trypanosoma cruzi epimastigote growth and oxygen consumption and their electrochemical (redox) potentials and lipophilicity. The derivatives produced different degrees of parasite growth and respiration inhibition on CL Brener, LQ, and Tulahuen strains of T. cruzi epimastigotes. Respiratory chain inhibition appears to be a determinant of the trypanosomicidal activity of these compounds, since a significant correlation between respiration and culture growth inhibition was found. A similar correlation was found, within the different structural subfamilies, between toxic effects and the ability of the compounds to be oxidized in aqueous media. The inhibition of respiration and of parasite growth in culture increases with the lipophilicity of the substituents on the oxazolopyridine nucleus. No difference in the action of these derivatives was found among the different parasite strains. It is concluded that these compounds may have a potential usefulness in the treatment of Chagas' disease.

Chronic morphine treatment and withdrawal increase extracellular levels of norepinephrine in the rat bed nucleus of the stria terminalis.

Extracellular levels of norepinephrine (NE) and glutamate (Glu) in the ventral bed nucleus of the stria terminalis (vBNST) of saline- and chronic morphine-treated rats, with or without withdrawal, were studied by means of the in vivo microdialysis technique in anesthetized rats. In addition, the tissue concentration of NE was studied at different rostrocaudal levels of the vBNST. Chronic morphine treatment significantly increased extracellular levels of NE, but not Glu, in vBNST. At 48 h after naloxone-induced morphine withdrawal there was a further significant increase in the extracellular levels of NE, but not Glu, in vBNST. The presence of UK 14304, an alpha(2)-adrenergic agonist, induced a significant decrease in NE extracellular levels in all experimental groups. In contrast, UK 14304 induced a significant decrease in Glu extracellular levels only in saline-treated rats. The results also show that the vBNST presents a rostrocaudal gradient of NE and contains 9.4% of total brain NE. The increase in NE extracellular levels in vBNST induced by chronic morphine treatment and the further increase in NE levels 48 h after naloxone-induced morphine withdrawal suggest that NE in vBNST may be involved in the pharmacological effects of chronic morphine and withdrawal.