Browsing by Author "Lira Mendieta, Matías Sebastián"

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    Binge-like Alcohol Administration Alters Decision Making in an Adolescent Rat Model: Role of N-Methyl-D-Aspartate Receptor Signaling
    (2023) Arce Olave, Camila Raquel; Mira Guzmán, Rodrigo Andrés; Lira Mendieta, Matías Sebastián; Cerpa Nebott, Waldo Francisco
    Alcohol is one of the most used legal drugs abused worldwide, and its consumption is associated with high mortality and morbidity rates. There is an increasing concern about the starting age of consumption of this drug since it has become evident that it is at younger ages. The so-called “pattern of consumption by binge” corresponds to ingesting large amounts of alcohol in a short period and is the most popular among young people. Previous studies show that alcohol causes damage in different areas, such as the hippocampus, hypothalamus, and prefrontal cortex, and adolescents are more susceptible to alcohol toxicity. Alcohol inhibits the membrane glutamate receptor, NMDA-type glutamate receptors (NMDAR). Using a binge-like alcohol administration protocol in adolescent rats (PND25), we investigate decision making through the attentional set-shifting test (ASST) and alterations in the NMDAR signaling in related areas. We observe an impairment in executive function without alterations in NMDAR abundance. However, binge alcohol changes NMDAR signaling and decreases quantity in the synapse, mainly in the hippocampus and hypothalamus. We suggest that prefrontal cortex impairment could arise from damaged connections with the hippocampus and hypothalamus, affecting the survival pathway and memory and learning process.
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    Exo70 intracellular redistribution after repeated mild traumatic brain injury
    (2021) Lira Mendieta, Matías Sebastián; Zamorano, Pedro; Cerpa Nebott, Waldo Francisco
    Abstract Background Exo70 is a subunit of the greater exocyst complex, a collection of proteins that oversees cellular membrane addition and polarized exocytosis by acting as a tethering intermediate between the plasma membrane and newly synthesized secretory vesicles. Although Exo70 function has been implicated in several developmental events including cytokinesis and the establishment of cell polarity, its role in neuropathologies is poorly understood. On the other hand, traumatic brain injury is the result of mechanical external force including contusion, fast acceleration, and expansive waves that produce temporal or permanent cognitive damage and triggers physical and psychosocial alterations including headache, memory problems, attention deficits, difficulty thinking, mood swings, and frustration. Traumatic brain injury is a critical health problem on a global scale, constituting a major cause of deaths and disability among young adults. Trauma-related cellular damage includes redistribution of N-methyl-D-aspartate receptors outside of the synaptic compartment triggering detrimental effects to neurons. The exocyst has been related to glutamate receptor constitutive trafficking/delivery towards synapse as well. This work examines whether the exocyst complex subunit Exo70 participates in traumatic brain injury and if it is redistributed among subcellular compartments Results Our analysis shows that Exo70 expression is not altered upon injury induction. By using subcellular fractionation, we determined that Exo70 is redistributed from microsomes fraction into the synaptic compartment after brain trauma. In the synaptic compartment, we also show that the exocyst complex assembly and its interaction with GluN2B are increased. Finally, we show that the Exo70 pool that is redistributed comes from the plasma membrane. Conclusions The present findings position Exo70 in the group of proteins that could modulate GluN2B synaptic availability in acute neuropathology like a traumatic brain injury. By acting as a nucleator factor, Exo70 is capable of redirecting the ensembled complex into the synapse. We suggest that this redistribution is part of a compensatory mechanism by which Exo70 is able to maintain GluN2B partially on synapses. Hence, reducing the detrimental effects associated with TBI pathophysiology.
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    Exo70 involvement on NMDAR dynamics in traumatic brain injury
    (2021) Lira Mendieta, Matías Sebastián; Cerpa Nebott, Waldo Francisco; Pontificia Universidad Católica de Chile. Facultad de Ciencias Biológicas
    El correcto funcionamiento de la sinapsis es fundamental para mantener la estabilidad neuronal. En neuropatologías como la lesión cerebral traumática (TBI), la sinapsis se altera o destruye. TBI es una condición que posee una alta incidencia a nivel mundial y es una causa importante de muertes y discapacidad. TBI se caracteriza por cambios de presión intracraneal debido a fuerzas de aceleración inducidas por el golpe, lo que genera un daño primario a nivel de tejido. El daño secundario posterior puede durar por semanas o meses, incluso años dependiendo de la gravedad del trauma. Este daño secundario es en parte mediado por glutamato al estimular receptores NMDA extrasinápticos, lo que desencadena una pérdida de función sináptica y por consiguiente alteración de conductas cognitivas y sociales. El daño mediado por el derrame de glutamato provoca una redistribución de receptores N-methyl-D-aspartic acid (NMDA) hacia sitios extrasinápticos, lo que potenciaría el daño generado por el glutamato extrasináptico. Uno de los componentes asociados a tráfico, exocitosis y mantención de los receptores de glutamato en la sinapsis es el exocisto. El exocisto es un complejo multiproteico constituido por 8 proteínas encargado de la exocitosis de membrana basolateral y de crecimiento de neuritas, así como también del tráfico y exocitosis de receptores de glutamato. A su vez, el exocisto ha sido relacionado a la disponibilidad basal de receptores de glutamato en la sinapsis y por lo tanto regula el umbral de activación de estos. A pesar de que se conoce bastante sobre el complejo exocisto a nivel celular, existe poca información que relacione al exocisto con neuropatologías. Nuestra hipótesis de trabajo es que Exo70 promueve la disponibilidad y señalización sináptica del receptor NMDA en respuesta a trauma cerebral inducido por golpe, manteniendo así procesos cognitivos. Para poner a prueba esta hipótesis se utilizó un modelo de trauma leve provocado por golpes repetitivos en ratones. Nuestros resultados demuestran que Exo70 es redistribuido hacia la sinapsis en condición TBI, donde el ensamblaje del complejo se incrementa y la interacción con GluN2B se ve favorecida. En esta tesis se logró la sobreexpresión de Exo70 en la región CA1 del hipocampo dorsal previo a la inducción de TBI, lo que nos permitió realizar ensayos conductuales, electrofisiológicos y bioquímicos que responden a la evaluación de la disponibilidad de receptores NMDA en la sinapsis. En estos experimentos encontramos que la previa sobreexpresión de Exo70 protege contra el deterioro cognitivo, acompañado de la estabilización de la transmisión glutamatérgica basal y la potenciación a largo plazo en hipocampo. Finalmente, GluN2B permanece en la sinapsis cuando Exo70 es sobre expresado, promoviendo así la señalización intracelular asociada a receptores NMDA sinápticos. Estos hallazgos revelan el papel que cumple Exo70 en la dinámica intracelular de receptores NMDA en condición de trauma cerebral y sugieren que Exo70 podría ser parte de la maquinaria de distribución sináptica de estos receptores en otras neuropatologías.
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    Inhibition of astroglial hemichannels prevents synaptic transmission decline during spreading depression
    (2024) Tichauer Calderón, Juan Enrique; Lira Mendieta, Matías Sebastián; Cerpa Nebott, Waldo Francisco; Orellana Roca, Juan Andrés; Sáez Carreño, Juan Carlos; Rovegno Echavarría, David Maximiliano
    Spreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is repetitive and produces a metabolic overload that increases secondary damage. However, the mechanisms associated with the initiation and propagation of SD are unknown. Multiple lines of evidence indicate that persistent and uncontrolled opening of hemichannels could participate in the pathogenesis and progression of several neurological disorders including acute brain injuries. Here, we explored the contribution of astroglial hemichannels composed of connexin-43 (Cx43) or pannexin-1 (Panx1) to SD evoked by high-K+ stimulation in brain slices. Results Focal high-K+ stimulation rapidly evoked a wave of SD linked to increased activity of the Cx43 and Panx1 hemichannels in the brain cortex, as measured by light transmittance and dye uptake analysis, respectively. The activation of these channels occurs mainly in astrocytes but also in neurons. More importantly, the inhibition of both the Cx43 and Panx1 hemichannels completely prevented high K+-induced SD in the brain cortex. Electrophysiological recordings also revealed that Cx43 and Panx1 hemichannels critically contribute to the SD-induced decrease in synaptic transmission in the brain cortex and hippocampus. Conclusions Targeting Cx43 and Panx1 hemichannels could serve as a new therapeutic strategy to prevent the initiation and propagation of SD in several acute brain injuries.