pVHL suppresses Akt/ß-catenin-mediated cell proliferation by inhibiting 14-3-3ζ expression.

The mechanisms controlling degradation of cytosolic ß-catenin are important for regulating ß-catenin co-transcriptional activity. Loss of von Hippel-Lindau protein (pVHL) has been shown to stabilize ß-catenin, increasing ß-catenin transactivation and ß-catenin-mediated cell proliferation. However, the role of phosphoinositide 3-kinase (PI3K)/Akt in the regulation of ß-catenin signaling downstream from pVHL has never been addressed. Here, we report that hyperactivation of PI3K/Akt in cells lacking pVHL contributes to the stabilization and nuclear accumulation of active ß-catenin. PI3K/Akt hyperactivation is facilitated by the up-regulation of 14-3-3ζ and the down-regulation of 14-3-3ε, 14-3-3η and 14-3-3θ. Up-regulation of 14-3-3ζ in response to pVHL is important for the recruitment of PI3K to the cell membrane and for stabilization of soluble ß-catenin. In contrast, 14-3-3ε and 14-3-3η enhanced PI3K/Akt signaling by inhibiting PI3K and PDK1, respectively. Thus, our results demonstrated that 14-3-3 family members enhance PI3K/Akt/ß-catenin signaling in order to increase proliferation. Inhibition of Akt activation and/or 14-3-3 function strongly reduces ß-catenin signaling and decreases cell proliferation. Thus, inhibition of Akt and 14-3-3 function efficiently reduces cell proliferation in 786-0 cells characterized by hyperactivation of ß-catenin signaling due to pVHL loss.

Impaired 2-AG Signaling in Hippocampal Glutamatergic Neurons: Aggravation of Anxiety-Like Behavior and Unaltered Seizure Susceptibility.

BACKGROUND: Postsynaptically generated 2-arachidonoylglycerol activates the presynaptic cannabinoid type-1 receptor, which is involved in synaptic plasticity at both glutamatergic and GABAergic synapses. However, the differential function of 2-arachidonoylglycerol signaling at glutamatergic vs GABAergic synapses in the context of animal behavior has not been investigated yet. METHODS: Here, we analyzed the role of 2-arachidonoylglycerol signaling selectively in hippocampal glutamatergic neurons. Monoacylglycerol lipase, the primary degrading enzyme of 2-arachidonoylglycerol, is expressed at presynaptic sites of excitatory and inhibitory neurons. By adeno-associated virus-mediated overexpression of monoacylglycerol lipase in glutamatergic neurons of the mouse hippocampus, we selectively interfered with 2-arachidonoylglycerol signaling at glutamatergic synapses of these neurons. RESULTS: Genetic modification of monoacylglycerol lipase resulted in a 50% decrease in 2-arachidonoylglycerol tissue levels without affecting the content of the second major endocannabinoid anandamide. A typical electrophysiological read-out for 2-arachidonoylglycerol signaling is the depolarization-induced suppression of excitation and of inhibition. Elevated monoacylglycerol lipase levels at glutamatergic terminals selectively impaired depolarization-induced suppression of excitation, while depolarization-induced suppression of inhibition was not significantly changed. At the behavioral level, mice with impaired hippocampal glutamatergic 2-arachidonoylglycerol signaling exhibited increased anxiety-like behavior but showed no alterations in aversive memory formation and seizure susceptibility. CONCLUSION: Our data indicate that 2-arachidonoylglycerol signaling selectively in hippocampal glutamatergic neurons is essential for the animal's adaptation to aversive situations.

Cannabinoid CB1 receptor in dorsal telencephalic glutamatergic neurons: distinctive sufficiency for hippocampus-dependent and amygdala-dependent synaptic and behavioral functions.

A major goal in current neuroscience is to understand the causal links connecting protein functions, neural activity, and behavior. The cannabinoid CB1 receptor is expressed in different neuronal subpopulations, and is engaged in fine-tuning excitatory and inhibitory neurotransmission. Studies using conditional knock-out mice revealed necessary roles of CB1 receptor expressed in dorsal telencephalic glutamatergic neurons in synaptic plasticity and behavior, but whether this expression is also sufficient for brain functions is still to be determined. We applied a genetic strategy to reconstitute full wild-type CB1 receptor functions exclusively in dorsal telencephalic glutamatergic neurons and investigated endocannabinoid-dependent synaptic processes and behavior. Using this approach, we partly restored the phenotype of global CB1 receptor deletion in anxiety-like behaviors and fully restored hippocampus-dependent neuroprotection from chemically induced epileptiform seizures. These features coincided with a rescued hippocampal depolarization-induced suppression of excitation (DSE), a CB1 receptor-dependent form of synaptic plasticity at glutamatergic neurons. By comparison, the rescue of the CB1 receptor on dorsal telencephalic glutamatergic neurons prolonged the time course of DSE in the amygdala, and impaired fear extinction in auditory fear conditioning. These data reveal that CB1 receptor in dorsal telencephalic glutamatergic neurons plays a sufficient role to control neuronal functions that are in large part hippocampus-dependent, while it is insufficient for proper amygdala functions, suggesting an unexpectedly complex circuit regulation by endocannabinoid signaling in the amygdala. Our data pave the way to a better understanding of neuronal networks in the context of behavior, by fine-tuned interference with synaptic transmission processes.

A Molecular Approach of Caloric Restriction and Vitamins for Cancer Prevention.

Each year, cancer claims the lives of around 10.0 million people worldwide. Food components have been shown to alter numerous intracellular signaling events that frequently go awry during carcinogenesis. Many studies suggest that dietary behaviors involving the consumption of antioxidant-rich foods, as well as caloric restriction, may play an important role in cancer prevention. Gene expression patterns, such as genetic polymorphisms, can influence the response to food components by altering their specific action on targets, as well as absorption, metabolism, and distribution, among other things. This review discusses two significant cancer prevention techniques: a vitamin-rich diet and caloric restriction. It also discusses the possible molecular interactions between the two dietary strategies and the first clues of a probable synergy that would come from combining caloric restriction with antioxidant use. Caloric restriction diets have positive effects on life expectancy and enable avoidance of age-related illnesses. As a result, this manuscript is based on the degenerative nature of cancer and intends to shed light on the biochemical features of not just calorie restriction but also vitamins. Both are thought to have an effect on oxidative stress, autophagy, and signaling pathways involved in energy metabolism and mitochondrial functions.

Probiotics and Prebiotics as a Therapeutic Strategy to Improve Memory in a Model of Middle-Aged Rats.

Aging is associated with morphological, physiological and metabolic changes, leading to multiorgan degenerative pathologies, such as cognitive function decline. It has been suggested that memory loss also involves a decrease in neurotrophic factors, including brain-derived neurotrophic factor (BDNF). In recent years, microbiota has been proposed as an essential player in brain development, as it is believed to activate BDNF secretion through butyrate production. Thus, microbiota modulation by supplementation with probiotics and prebiotics may impact cognitive decline. This study aimed to evaluate the effects of probiotics and prebiotics supplementation on the memory of middle-aged rats. Sprague-Dawley male rats were randomized in four groups (n = 13 per group): control (water), probiotic (E. faecium), prebiotic (agave inulin), symbiotic (E. faecium + inulin), which were administered for 5 weeks by oral gavage. Spatial and associative memory was analyzed using the Morris Water Maze (MWM) and Pavlovian autoshaping tests, respectively. Hippocampus was obtained to analyze cytokines [interleukin (IL-1ß) and tumor necrosis factor (TNF-α)], BDNF and γ-aminobutyric acid (GABA) by enzyme-linked immunosorbent assay (ELISA). Butyrate concentrations were also evaluated in feces. The symbiotic group showed a significantly better performance in MWM (p < 0.01), but not in Pavlovian autoshaping test. It also showed significantly lower concentrations of pro-inflammatory cytokines (p < 0.01) and the reduction in IL-1ß correlated with a better performance of the symbiotic group in MWM (p < 0.05). Symbiotic group also showed the highest BDNF and butyrate levels (p < 0.0001). Finally, we compared the electrophysiological responses of control (n = 8) and symbiotic (n = 8) groups. Passive properties of CA1 pyramidal cells (PCs) exhibited changes in response to the symbiotic treatment. Likewise, this group showed an increase in the N-methyl-D-aspartate receptor (NMDA)/AMPA ratio and exhibited robust long-term potentiation (LTP; p < 0.01). Integrated results suggest that symbiotics could improve age-related impaired memory.

Programmed and induced phenotype of the hippocampal granule cells.

Certain neurons choose the neurotransmitter they use in an activity-dependent manner, and trophic factors are involved in this phenotypic differentiation during development. Developing hippocampal granule cells (GCs) constitutively express the markers of the glutamatergic and GABAergic phenotypes, but when development is completed, the GABAergic phenotype shuts off. With electrophysiological, single-cell reverse transcription-PCR and immunohistological techniques, we show here that short-term (24 h) cultures of fully differentiated adult glutamatergic GCs, which express glutamate, VGlut-1 (vesicular glutamate transporter) mRNA, calbindin, and dynorphin mRNA, can be induced to reexpress the GABAergic markers GABA, GAD67 (glutamate decarboxylase 67 kDa isoform), and VGAT (vesicular GABA transporter) mRNA, by sustained synaptic or direct activation of glutamate receptors and by activation of TrkB (tyrosine receptor kinase B) receptors, with brain-derived neurotrophic factor (BDNF) (30 min). The expression of the GABAergic markers was prevented by the blockade of glutamate receptors and sodium or calcium channels, and by inhibitors of protein kinases and protein synthesis. In hippocampal slices of epileptic rats and in BDNF-treated slices from naive rats, we confirmed the appearance of monosynaptic GABAA receptor-mediated responses to GC stimulation, in the presence of glutamate receptors blockers. Accordingly, GC cultures prepared from these slices showed the coexpression of the glutamatergic and GABAergic markers. Our results demonstrate that the neurotransmitter choice of the GCs, which are unique in terms of their continuing birth and death throughout life, depends on programmed and environmental factors, and this process is neither limited by a critical developmental period nor restricted by their insertion in their natural network.

Plasticity of the GABAergic phenotype of the "glutamatergic" granule cells of the rat dentate gyrus.

The "glutamatergic" granule cells of the dentate gyrus transiently express a GABAergic phenotype when a state of hyperexcitability is induced in the adult rat. Consequently, granule cell (GC) activation provokes monosynaptic GABAergic responses in their targets of area CA3. Because GABA exerts a trophic action on neonatal CA3 and mossy fibers (MF) constitute its main input, we hypothesized that the GABAergic phenotype of the MF could also be transiently expressed early in life. We addressed this possibility with a multidisciplinary approach. Electrophysiological recordings in developing rats revealed that, until day 22-23 of age, glutamate receptor antagonists block the excitatory response evoked in pyramidal cells by GCs, isolating a fast metabotropic glutamate receptor-sensitive GABAergic response. In a clear-cut manner from day 23-24 of age, GC activation in the presence of glutamatergic antagonists was unable to evoke synaptic responses in CA3. Immunohistological experiments showed the presence of GABA and GAD67 (glutamate decarboxylase 67 kDa isoform) in the developing GCs and their MF, and, using reverse transcription-PCR, we confirmed the expression of vesicular GABA transporter mRNA in the developing dentate gyrus and its downregulation in the adult. The GABAergic markers were upregulated and MF inhibitory transmission reappeared when hyperexcitability was induced in adult rats. Our data evidence for the first time a developmental and activity-dependent regulation of the complex phenotype of the GC. At early ages, the GABAergic input from the MF may add to the interneuronal input to CA3 to foster development, and, in the adult, it can possibly protect the system from enhanced excitability.

Psychological impact of sociodemographic factors and medical conditions in older adults during the COVID-19 pandemic in Mexico / Impacto psicológico de factores sociodemográficos y condiciones médicas en adultos mayores durante la pandemia de COVID-19 en México

Abstract Introduction Older adults are not only at a higher medical risk during the COVID-19 pandemic, but they may also be a group particularly vulnerable to mental health diminishing. Objective To analyze the effect of some sociodemographic factors (sex and age) and medical conditions (diabetes and hypertension) on mental health and concerns about COVID-19 in a sample of older adults. Method A non-probabilistic sample of 2,992 older adults (37.7% men and 62.3% women) was selected, with an average age of 70.45 years (SD = 7.31). Participants were given the Impact of Event Scale-6 (IES-6), the Patient Health Questionnaire (PHQ-9), the Generalized Anxiety Disorder-7 (GAD-7), a questionnaire of concerns about COVID-19, and a sociodemographic questionnaire. Participants' answers were captured via Google Forms. Results The results showed that women had greater concerns about COVID-19 than men. The findings in general showed significant effects, with women showing higher scores in depressive symptoms, anxiety, and greater stress generated in addition by the impact of the event. Differences concerning event-related stress and depression were found in relation to subgroups by age. Discussion and conclusion These finding could serve for the planning and development of strategies that provide attention to the mental health of this population group.

Resumen Introducción Los adultos mayores no sólo presentan un mayor riesgo médico durante la pandemia de COVID-19, sino que también pueden ser particularmente vulnerables a la disminución de la salud mental. Objetivo Analizar el efecto de algunos factores sociodemográficos (sexo y edad) y condiciones médicas (diabetes e hipertensión) sobre la salud mental y las preocupaciones sobre COVID-19 en una muestra de adultos mayores. Método Se seleccionó una muestra no probabilística de 2,992 adultos mayores (37.7% hombres y 62.3% mujeres), con una edad promedio de 70.45 años (DE = 7.31). Los participantes recibieron la Estala de Impacto de Evento-6, el Cuestionario de Salud del Paciente-9, el Trastorno de Ansiedad Generalizada-7, un cuestionario de preocupaciones sobre COVID-19 y un cuestionario sociodemográfico. Resultados Las mujeres presentaron mayores preocupaciones por COVID-19 que los hombres. Las respuestas de los participantes se capturaron en Google Forms. Resultados En general, los hallazgos mostraron efectos significativos, siendo las mujeres quienes presentaron puntuaciones más altas en síntomas depresivos y ansiedad, así como mayor estrés asociado a evento. Además, se encontraron efectos diferenciados por subgrupos de edad en relación con estrés asociado a evento y síntomas depresivos. Discusión y conclusión Estos hallazgos pudieran ser útiles para planificar y desarrollar estrategias que brinden atención a la salud mental de este grupo de población.

Desarrollo Positivo en Jóvenes Involucrados en Voluntariado y su Relación con las Neuronas Espejo / Positive Development in Young People Involved in Volunteering and Its Relation to Mirror Neurons / Desenvolvimento Positivo em Jovens Envolvidos em Voluntariado e sua Relação com os Neurônios Espelho

Resumen En este estudio se analizó el efecto del desarrollo positivo sobre la contribución en jóvenes, y se identificaron las diferencias entre los jóvenes que han realizado actividades de voluntariado y los que no las han realizado; además se analizó la activación de las neuronas espejo. Participaron 121 universitarios, 28.9% hombres y 71.1% mujeres, con una media de edad de 21.51 años. Se utilizó la escala de Desarrollo Positivo en Adolescentes y de Contribución, además de un instrumento conformado por dos conjuntos de estímulos visuales. Los resultados corroboraron el efecto de las 5 c's sobre la contribución y se encontraron diferencias significativas en la escala de carácter y en dos dimensiones de contribución, donde los jóvenes que realizan actividades de voluntariado puntuaron más alto que aquellos que no las realizan. Se comprobó que existe activación en la zona correspondiente a las neuronas espejo, lo cual se relaciona con procesos empáticos. Se concluye que existe una relación entre las actividades de voluntariado y el desarrollo positivo en jóvenes universitarios.

Abstract The study analyzed the effect of positive development on contribution in young people and identified the differences between those who have done volunteer work and those who have not. It also studied the activation of the mirror neurons system. Participants were 121 university students, 28.9% male and 71.1% female, with an average age of 21.51. The Positive Youth Development Scale and the Contribution Scale were used, in addition to an instrument made up of two sets of visual stimuli. The results confirmed the effect of the 5 Cs on the contribution dimension and significant differences were found in the character scale and in two dimensions of contribution, in which young people who do volunteer work got higher scores than those who do not. The study confirmed that there was activation in the zone corresponding to the mirror neurons system, which is related to empathetic processes, and concluded that there was a relation between volunteering activities and the positive development of university students.

Resumo Neste estudo, foi analisado o efeito do desenvolvimento positivo sobre a contribuição em jovens e foram identificadas as diferenças entre os jovens que realizaram atividades de voluntariado e os que não as realizaram; além disso, foi analisada a ativação dos neurônios espelho. Participaram 121 universitários, 28.9 % homens e 71.1% mulheres, com uma média de idade de 21.51 anos. Foi utilizada a Escala de Desenvolvimento Positivo em Adolescentes e de Contribuição, ainda de um instrumento conformado por dois conjuntos de estímulos visuais. Os resultados corroboraram o efeito das 5 c's sobre a contribuição e foram verificadas diferenças significativas na escala de caráter e em duas dimensões de contribuição, em que os jovens que realizam atividades de voluntariado pontuaram mais alto que aqueles que não as realizam. Foi comprovado que existe ativação na zona correspondente aos neurônios espelho, o que está relacionado com processos empáticos. Conclui-se que existe uma relação entre as atividades de voluntariado e o desenvolvimento positivo em jovens universitários.

IFNγ-induced suppression of ß-catenin signaling: evidence for roles of Akt and 14.3.3ζ.

The proinflammatory cytokine interferon γ (IFNγ ) influences intestinal epithelial cell (IEC) homeostasis in a biphasic manner by acutely stimulating proliferation that is followed by sustained inhibition of proliferation despite continued mucosal injury. ß-Catenin activation has been classically associated with increased IEC proliferation. However, we observed that IFNγ inhibits IEC proliferation despite sustained activation of Akt/ß-catenin signaling. Here we show that inhibition of Akt/ß-catenin-mediated cell proliferation by IFNγ is associated with the formation of a protein complex containing phosphorylated ß-catenin 552 (pß-cat552) and 14.3.3ζ. Akt1 served as a bimodal switch that promotes or inhibits ß-catenin transactivation in response to IFNγ stimulation. IFNγ initially promotes ß-catenin transactivation through Akt-dependent C-terminal phosphorylation of ß-catenin to promote its association with 14.3.3ζ. Augmented ß-catenin transactivation leads to increased Akt1 protein levels, and active Akt1 accumulates in the nucleus, where it phosphorylates 14.3.3ζ to translocate 14.3.3ζ/ß-catenin from the nucleus, thereby inhibiting ß-catenin transactivation and IEC proliferation. These results outline a dual function of Akt1 that suppresses IEC proliferation during intestinal inflammation.

Breve historia sobre la marihuana en Occidente / A brief history of marijuana in the western world

La marihuana es una sustancia con una extensa y controvertida historia. A lo largo del tiempo, esta planta, y desde hace más de 5.000 años, ha sido utilizada para diferentes fines, que van desde el uso lúdico y recreativo, pasando por un medio de relajación y meditación, hasta su uso en el tratamiento de varias enfermedades o el alivio de procesos vinculados a cierto tipo de malestares. Aunque se supuso que la marihuana tenía su origen en Mesoamérica, ahora se sabe que es sólo una leyenda urbana de poca credibilidad y que sus orígenes los podemos registrar en referencias médicas chinas datadas alrededor del año 2737 a. de C. Si bien esta planta no tiene un origen mesoamericano, sí ha generado interés en el mundo, y sobre todo en México. Es en este país donde el uso del cannabis ha ido desde intereses textiles y medicinales hasta el consumo lúdico, pasando por su venta libre, la prohibición por presiones políticas y sociales, su tolerancia y, recientemente, su despenalización para uso lúdico y medicinal. Desgraciadamente existen pocas referencias de la historia de esta planta en México, por lo que ha sido de nuestro interés presentar algunos datos sobre las generalidades de la marihuana, una breve historia en el mundo, el desarrollo de la despenalización en Norteamérica, sus usos medicinales y su paso por México hasta nuestros días

Marijuana is a substance with a long and controversial history. At different times in its history, which goes back over 5,000 years, this plant has been used for different purposes, ranging from recreational and leisure to its use in the treatment of several diseases or to offer relief in processes that entail a certain type of malaise, and including its consideration as a means of relaxation and meditation. Although it was supposed that the roots of marijuana lay in Central America, it is now known that this is but an urban legend with little credibility and that its origins can be found recorded in Chinese medical references dating back to the year 2737 BC. Although this plant was not originally from Central America, it has aroused interest around the world, and above all in Mexico. It is in this country where the use of cannabis has gone from applications in textiles and medicine to its free sale, the bans on its use due to political and social pressures, its tolerance and, recently, its decriminalisation for recreational and medicinal use. Unfortunately there are few references on the history of this plant in Mexico, and thus we have considered it interesting to present some data about the generalities of marijuana, a brief history in the world, the development of decriminalisation in North America, its medicinal uses and its course through Mexico to the present day

Short-term adaptation of conditioned fear responses through endocannabinoid signaling in the central amygdala.

The cannabinoid receptor type 1 (CB1) and the central nucleus of the amygdala (CeA) are both known to have crucial roles in the processing of fear and anxiety, whereby they appear to be especially involved in the control of fear states. However, in contrast to many other brain regions including the cortical subregions of the amygdala, the existence of CB1 in the CeA remains enigmatic. In this study we show that CB1 is expressed in the CeA of mice and that CB1 in the CeA mediates short-term synaptic plasticity, namely depolarization-induced suppression of excitation (DSE) and inhibition (DSI). Moreover, the CB1 antagonist AM251 increased both excitatory and inhibitory postsynaptic responses in CeA neurons. Local application of AM251 in the CeA in vivo resulted in an acutely increased fear response in an auditory fear conditioning paradigm. Upon application of AM251 in the basolateral nucleus of the amygdala (BLA) in an otherwise identical protocol, no such acute behavioral effects were detected, but CB1 blockade resulted in increased fear responses during tone exposures on the subsequent days. Moreover, we observed that the efficacy of DSE and DSI in the CeA was increased on the day following fear conditioning, indicating that a single tone-shock pairing resulted in changes in endocannabinoid signaling in the CeA. Taken together, our data show the existence of CB1 proteins in the CeA, and their critical role for ensuring short-term adaptation of responses to fearful events, thereby suggesting a potential therapeutic target to accompany habituation-based therapies of post-traumatic symptoms.

GABA actions in hippocampal area CA3 during postnatal development: differential shift from depolarizing to hyperpolarizing in somatic and dendritic compartments.

Gamma-aminobutyric acid type A receptor (GABA(A)-R) activation leads to depolarization of pyramidal cells during the first postnatal week and produces hyperpolarization from the second week. However, immunohistochemical evidence has suggested that during the second and third postnatal weeks the NKCC1 cotransporter relocates from the soma to the dendrites of CA3 pyramidal cells. We hypothesized that this leads to depolarizing responses in apical dendrites. Here we show that the activation of GABA(A)-R in the distal dendrites of CA3 pyramidal cells at P15 by restricted application of muscimol or synaptic activation by stimulation of interneurons in stratum radiatum (SR) causes depolarizing postsynaptic potentials (PSPs), which are blocked by NKCC1 cotransporter antagonists. By contrast, activation of proximal GABA(A)-R by muscimol application or by stimulation of interneurons in s. oriens (SO) leads to hyperpolarizing PSPs. Activation of the dentate gyrus (DG) in the presence of glutamatergic blockers evokes hyperpolarizing responses during the second postnatal week; however, the reversal potential of the DG-evoked inhibitory (I)PSPs is more depolarized than that of IPSPs evoked by activation of SO interneurons. Despite the shift of GABA action from depolarizing to hyperpolarizing, DG-evoked field potentials (f-PSPs) recorded in s. lucidum/radiatum (SL/R) do not change in polarity until the third week. Current source density analysis yielded results consistent with depolarizing actions of GABA in the dendritic compartment. Our data suggest that GABAergic input to apical dendrites of pyramidal cells of CA3 evokes depolarizing PSPs long after synaptic inhibition has become hyperpolarizing in the somata, in the axon initial segments and in basal dendrites.

Tonic modulation of inhibition by dopamine D4 receptors in the rat hippocampus.

Dopaminergic pathways have been recognized to play a critical role in cognition and emotion. Dopamine D2 and D4 receptors are the target for most common antipsychotics and their activation, particularly those in the medial temporal lobe structures, has been associated with their beneficial actions. The entorhinal cortex, which is the cortical area most consistently and severely affected in schizophrenia constitutes the main input to the hippocampus. Since the D4 receptor is highly concentrated in the hippocampus, and the effects of the selective activation of D4 receptors on the input/output function of the hippocampal formation are poorly understood, we sought to investigate the role of these receptors in the synaptic transmission and paired-pulse inhibition from the perforant path to area CA1 and the dentate gyrus. The D4 receptor antagonist, clozapine, translated paired-pulse inhibition into paired-pulse potentiation in both perforant path targets. By contrast, the D2/D3 antagonist quinpirole had no effect. The blockade of the D2/3 receptors with sulpiride, and of D1/5 receptors with SCH-23390, has no effect on paired-pulse inhibition, suggesting that these receptors are not involved in feedforward inhibition in these hippocampal areas. Interestingly, the perfusion of the D4 selective antagonist, L-745,870 (Patel et al., 1997: J Pharmacol Exp Ther 283:636-647) during the blockade of D2/3 and D1/5 receptors produces a reversible decrease in paired-pulse inhibition in CA1, but not in the DG. Our results show that endogenous DA tonically modulates feedforward inhibition in area CA1 and the dentate gyrus through the activation of D4 receptors located in the interneuronal population of these hippocampal regions. Since activation of the D4 receptor inhibits GABA release and GABAergic synaptic transmission, we suggest that the perforant path stimulates interneurons that have the D4 receptor and that, in turn, contact other interneurons that synapse onto pyramidal cells. (c) 2004 Wiley-Liss, Inc.

Activity-dependent induction of multitransmitter signaling onto pyramidal cells and interneurons of hippocampal area CA3.

The granule cells of the dentate gyrus (DG) are considered to be glutamatergic, but they contain glutamic acid decarboxylase, gamma-amino butyric acid (GABA), and the vesicular GABA transporter mRNA. Their expression is regulated in an activity-dependent manner and coincides with the appearance of GABAergic transmission from the mossy fibers (MF) to pyramidal cells in area CA3. These data support the hypothesis that MF are able to release glutamate and GABA. Following the principle that a given neuron releases the same neurotransmitter(s) onto all its targets, we here demonstrate the emergence, after a generalized convulsive seizure, of MF GABAergic signaling sensitive to activation mGluR-III onto pyramidal cells and interneurons of CA3. Despite this, excitation overrides inhibition in interneurons, preventing disinhibition. Furthermore, on blockade of GABA and glutamate ionotropic receptors, an M1-cholinergic depolarizing signal is also revealed in both targets, which postsynaptically modulates the glutamatergic and GABAergic fast neurotransmission. The emergence of these nonglutamatergic signals depends on protein synthesis. In contrast to cholinergic responses evoked by associational/commissural fibers activation, cholinergic transmission evoked by DG stimulation is only observed after seizures and is strongly depressed by the activation of mGluR-II, whereas both are depressed by M2-AChR activation. With immunohistological experiments, we show that this cholinergic pathway runs parallel to the MF. Thus seizures compromise a delicate balance of excitation and inhibition, on which a complex interaction of different neurotransmitters emerges to counteract excitation at pre- and postsynaptic sites. Particularly, MF GABAergic inhibition emerges to exert an overall inhibitory action on CA3.

Synaptic plasticity: Understanding the neurobiological mechanims of learning and memory: part I

Uno de los fenómenos más interesantes dentro del campo de la neurobiología, es el fenómeno de la plasticidad cerebral relacionada con los eventos de aprendizaje y el procesamiento del fenómeno de memoria. De hecho, estos fenómenos neurobiológicos empezaron a ser estudiados desde principios de siglo. Remotamente, el fenómeno de plasticidad cerebral en relación con el desarrollo y aprendizaje de las conductas fue ya concebido y cuestionado desde hace más de dos centurias. Sin embargo, desde hace cuatro décadas, múltiples evidencias experimentales han demostrado que tanto la experiencia o el entrenamiento en la ejecución de tareas operantes aprendidas, inducen cambios plásticos en la fisiología neuronal, incluyendo los cambios neuroquímicos y moleculares que se requieren para consolidar una memoria a largo plazo. Asimismo, diversos procedimientos experimentales han demostrado que la experiencia diferencial, el entrenamiento y el aprendizaje de conductas o la experiencia informal, producen cambios mensurables en el cerebro de los mamíferos. Más aún, la neuropsicología ha considerado desde hace varias décadas que diferentes tipos de memoria pueden ser localizados en diferentes circuitos neuronales en distintas áreas de la corteza cerebral. Sin embargo, los estudios recientes han demostrado que los sistemas de memoria están distribuidos en circuitos neuronales corticales específicos. Por ejemplo, los mismos sistemas corticales que procesan la percepción sensorial y la función motora, son los mismos sustratos neurales que se emplean para procesar los fenómenos de memorización. El fenómeno de la memoria y el aprendizaje es resultado de la actividad fisiológica repetitiva de millones de neuronas que, ensambladas en circuitos neuronales específicos, conllevan al reforzamiento de las conexiones sinápticas involucradas y a los cambios de plasticidad sináptica que se requieren para establecer estos fenómenos neurobiológicos. El fenómeno de potenciación a largo plazo, o LTP, es un evento neurofisiológico que resulta del incremento en el reforzamiento de la transmisión sináptica, que puede perdurar en las regiones cerebrales estudiadas desde horas a días. El modelo de LTP quizá representa el modelo funcional experimental más viable para entender las bases celulares del aprendizaje y la memoria en el SNC de los mamíferos, incluyendo el cerebro de los humanos.

Synaptic plasticity: understanding the neurobiological mechanisms of learning and memory: part II

Uno de los fenómenos más nteresantes dentro del campo de la neurobiología, es el fenómeno de la plasticidad cerebral relacionada con los eventos de aprendizaje y el procesamiento del fenómeno de memoria. De hecho, estos fenómenos neurobiológicos empezaron a ser estudiados desde principios de siglo. Remotamente, el fenómeno de plasticidad cerebral en relación con el desarrollo y aprendizaje de las conductas fue ya concebido y cuestionado desde hace más de dos centurias. Sin embargo, desde hace cuatro décadas, múltiples evidencias experimentales han demostrado que tanto la experiencia o el entrenamiento en la ejecución de tareas operantes aprendidas, inducen cambios plásticos en la fisiología neuronal, incluyendo los cambios neuroquímicos y moleculares que se requieren para consolidar una memoria a largo plazo. Asimismo, diversos procedimientos experimentales han demostrado que la experiencia diferencial, el entrenamiento y el aprendizaje de conductas o la experiencia informal, producen cambios mensurables en el cerebro de los mamíferos. Más aún, la neuropsicología ha considerado desde hace varias décadas que diferentes tipos de memoria pueden ser localizados en diferentes circuitos neuronales en distintas áreas de la corteza cerebral. Sin embargo, los estudios recientes han demostrado que los sistemas de memoria están distribuidos en circuitos neuronales corticales específicos. Por ejemplo, los mismos sistemas corticales que procesan la percepción sensorial y las función motora, son los mismos sustratos neurales que se emplean para procesar los fenómenos de memorización. El fenómeno de la memoria y el aprendizaje es resultado de la actividad fisiológica repetitiva de millones de neuronas que, ensambladas en circuitos neuronales específicos, conllevan al reforzamiento de las conexiones sinápticas involucradas y a los cambios de plasticidad sináptica que se requieren para establecer estos fenómenos neurobiológicos. El fenómeno de potenciación a largo plazo, o LTP, es un evento neurofisiológico que resulta del incremento en el reforzamiento de la transmisión sináptica, que puede perdurar en las regiones cerebrales estudiadas desde horas a días. El modelo de LTP quizá representa el modelo funcional experimental más viable para entender las bases celulares del aprendizaje y la memoria en el SNC de los mamíferos, incluyendo el cerebro de los humanos.