Circuitry and Synaptic Dysfunction in Alzheimer's Disease: A New Tau Hypothesis.

For more than five decades, the field of Alzheimer's disease (AD) has focused on two main hypotheses positing amyloid-beta (Aß) and Tau phosphorylation (pTau) as key pathogenic mediators. In line with these canonical hypotheses, several groups around the world have shown that the synaptotoxicity in AD depends mainly on the increase in pTau levels. Confronting this leading hypothesis, a few years ago, we reported that the increase in phosphorylation levels of dendritic Tau, at its microtubule domain (MD), acts as a neuroprotective mechanism that prevents N-methyl-D-aspartate receptor (NMDAr) overexcitation, which allowed us to propose that Tau protein phosphorylated near MD sites is involved in neuroprotection, rather than in neurodegeneration. Further supporting this alternative role of pTau, we have recently shown that early increases in pTau close to MD sites prevent hippocampal circuit overexcitation in a transgenic AD mouse model. Here, we will synthesize this new evidence that confronts the leading Tau-based AD hypothesis and discuss the role of pTau modulating neural circuits and network connectivity. Additionally, we will briefly address the role of brain circuit alterations as a potential biomarker for detecting the prodromal AD stage.

Activation of the anti-inflammatory reflex blocks lipopolysaccharide-induced decrease in synaptic inhibition in the temporal cortex of the rat.

Stress is a potential trigger for a number of neuropsychiatric conditions, including anxiety syndromes and schizophrenic psychoses. The temporal neocortex is a stress-sensitive area involved in the development of such conditions. We have recently shown that aseptic inflammation and mild electric shock shift the balance between synaptic excitation and synaptic inhibition in favor of the former in this brain area (Garcia-Oscos et al., 2012), as well as in the prefrontal cortex (Garcia-Oscos et al., 2014). Given the potential clinical importance of this phenomenon in the etiology of hyperexcitable neuropsychiatric illness, this study investigates whether inactivation of the peripheral immune system by the "anti-inflammatory reflex" would reduce the central response to aseptic inflammation. For a model of aseptic inflammation, this study used i.p. injections of the bacterial toxin lipopolysaccharide (LPS; 5 µM) and activated the anti-inflammatory reflex either pharmacologically by i.p. injections of the nicotinic α7 receptor agonist PHA543613 or physiologically through electrical stimulation of the left vagal nerve (VNS). Patch-clamp recording was used to monitor synaptic function. Recordings from LPS-injected Sprague Dawley rats show that activation of the anti-inflammatory reflex either pharmacologically or by VNS blocks or greatly reduces the LPS-induced decrease of the synaptic inhibitory-to-excitatory ratio and the saturation level of inhibitory current input-output curves. Given the ample variety of pharmacologically available α7 nicotinic receptor agonists as well as the relative safety of clinical VNS already approved by the FDA for the treatment of epilepsy and depression, our findings suggest a new therapeutic avenue in the treatment of stress-induced hyperexcitable conditions mediated by a decrease in synaptic inhibition in the temporal cortex.

Relación entre la sobrecarga y el índice depresivo de cuidadores primarios de pacientes con enfermedades neuromusculoesqueléticas / The relationship between the overload and the depressive index of primary caregivers of patients with neuromusculoskeletal diseases

Resumen Introducción Una enfermedad neuromusculoesquelética no solo afecta a la persona que la padece, sino que también repercute de manera directa en la familia y en particular al cuidador primario informal. Las labores de cuidado incrementan la morbilidad psicológica y el estrés de los cuidadores primarios. El objetivo del presente estudio consiste en identificar la relación entre la sobrecarga y el índice de depresión presente en los cuidadores primarios informales de pacientes con enfermedad neuromusculoesquelética. Material y Métodos Se realizó un estudio exploratorio que incluyó a 18 cuidadores primarios informales de pacientes con enfermedad neuromusculoesquelética, y que asistieron a consulta en la Unidad Universitaria de Rehabilitación de la Universidad Autónoma de Yucatán. Resultados Entre las características sociodemográficas predominaron las cuidadoras del sexo femenino (83%) con parentesco familiar con el paciente. Además, predomino entre los cuidadores primarios el estado civil casado y un nivel de estudios de licenciatura. La relación entre la sobrecarga y el índice de depresión fue elevada y significativa (r=0.72, p=0.0007). En conclusión, estos resultados sugieren que, a mayor sobrecarga producida por las labores del cuidado, mayor será el grado de afectación en el estado anímico del cuidador primario informal. Este estudio ayudará en la elaboración de un programa de intervención para prevenir la sobrecarga en cuidadoras primarias informales.

Abstract Introduction A neuromusculoskeletal disease not only affects the person who suffers it but also directly affects the family and in particular with the informal primary caregiver. Care work increases the psychological morbidity and stress of primary caregivers. The aim of the present study was to identify the relationship between overload and the rate of depression present in informal primary caregivers of patients with the neuromusculoskeletal disease. Methods An exploratory study was carried out that included 18 informal primary caregivers of patients with the neuromusculoskeletal disease, and who attended a consultation at the University Rehabilitation Unit of the Autonomous University of Yucatan. Results Among the sociodemographic characteristics, female caregivers prevailed (83%) with a family relationship with the patient. Also, primary married status and a bachelor's degree level predominated among primary caregivers. The relationship between overload and depression index was high and significant (r = 0.72, p = 0.0007). In conclusion, these results suggest that the greater the overload produced by the tasks of care, the greater the degree of involvement in the state of the informal primary caregiver. This study will help in the development of an intervention program to prevent overload in informal primary caregivers.

Prevalencia, causas y tratamiento de la depresión Mayor / Prevalence, Causes, and Treatment of Major Depression

Resumen La depresión mayor representa un problema de salud pública debido a su alta prevalencia. La etiología de la depresión es compleja ya que en ella intervienen factores psicosociales, genéticos, y biológicos. Entre los factores psicosociales, se ha observado que los primeros episodios depresivos aparecen después de algún evento estresante, y el estrés que acompaña al primer episodio produce cambios a largo plazo en la fisiología cerebral que pueden producir variaciones a nivel estructural y en el funcionamiento de diferentes áreas cerebrales. Entre los factores genéticos que intervienen en el trastorno depresivo, se ha reportado que alrededor de 200 genes están relacionados con el trastorno depresivo mayor. Dentro de los factores biológicos, existen evidencias de alteraciones a nivel de neurotransmisores, citosinas y hormonas, cuyas acciones inducen modificaciones estructurales y funcionales en el sistema nervioso central, en el sistema inmunológico y en el sistema endocrino, que incrementan el riesgo de padecer la depresión mayor. A pesar de años de estudio, las bases biológicas del trastorno depresivo mayor y el mecanismo preciso de la eficacia antidepresiva siguen siendo poco claras. El objetivo de la presente revisión es resumir las principales conclusiones de la literatura clínica y experimental en relación con la etiología del trastorno depresivo mayor.

Abstract Major depression represents a public health problem due to its high prevalence. The etiology of major depression is complex because involves psychosocial, genetic, and biological factors. Among psychosocial factors, different studies report that the first depressive episode appear after some stressful event and produces long-term changes in brain physiology. These long-lasting changes produce variations at the structural level and in the functioning of different brain areas. Among the genetic factors involved in depressive illness, it has been reported that about 200 genes are related to major depressive disorder. Within the biological factors, there is an evidence of alterations in the level of neurotransmitters, cytosine's and hormones, whose actions induces structural and functional modifications in the central nervous system, the immune system and the endocrine system, which increases the risk of suffering major depression. Despite years of study, the biological basis of major depression and precise mechanisms of antidepressant efficacy remain unclear. The objective of the present review is to summarize the main conclusions of the clinical and experimental literature regarding to the etiology of major depressive disorder.