Clorinda Arias

Optical imaging of intrinsic signals: recent developments in the methodology and its applications

Since optical imaging (OI) of intrinsic signals was first developed in the 1980s, significant advances have been made regarding our understanding of the origins of the recorded signals. The technique has been refined and the range of its applications has been broadened considerably. Here we review recent developments in methodology and data analysis as well as the latest findings on how intrinsic signals are related to metabolic cost and electrophysiological activity in the brain. We give an overview of what optical imaging has contributed to our knowledge of the functional architecture of sensory cortices, their development and plasticity. Finally, we discuss the utility of OI for functional studies of the human brain as well as in animal models of neuropathology.

β-Amyloid neurotoxicity is exacerbated during glycolysis inhibition and mitochondrial impairment in the rat hippocampus in vivo and in isolated nerve terminals: Implications for alzheimer's disease

Abstract Senile plaques composed mainly by β-amyloid (Aβ) protein are one of the pathological hallmarks of Alzheimers disease (AD). In vitro, Aβ and its active fragment 25–35 have been shown either to be directly neurotoxic or to exacerbate the damaging effect of other neurotoxic insults. However, the attempts to replicate Aβ neurotoxicity in vivo have yielded conflicting results. One of the most consistent alterations in AD is a reduced resting glucose utilization. Important evidence suggests that impairment of brain energy metabolism can lead to neuronal damage or facilitate the deleterious effects of some neurotoxic agents. In the present study we have investigated the influence of glycolysis inhibition induced by iodoacetate, and mitochondrial impairment induced by 3-nitropropionic acid (3-NP), in the toxicity of Aβ. We have studied Aβ neurotoxicity during energy deficiency both in vivo in the dentate gyrus of the hippocampal formation and in presynaptic terminals isolated from neocortex and hippocampus. Results show that during metabolic inhibition an enhanced vulnerability of hippocampal neurons to Aβ peptide toxicity occurs, probably resulting from decreased glucose metabolism and mitochondrial ATP production. Synaptosomal response to energy impairment and Aβ toxicity was evaluated by the MTT assay. Results suggest that synapses may be particularly sensitive to metabolic perturbation, which in turn exacerbates Aβ toxicity. The present data provide experimental support to the hypothesis that certain risk factors such as metabolic dysfunction and amyloid accumulation may interact to exacerbate AD, and that metabolic substrates such as pyruvate may play a role as a therapeutic tool.

β-Amyloid peptide induces ultrastructural changes in synaptosomes and potentiates mitochondrial dysfunction in the presence of ryanodine

In Alzheimers disease (AD), loss of synapses exceeds neuronal loss and some evidence suggests a role of β‐amyloid protein (Aβ) in synaptic degeneration through a mechanism which may involve intraneuronal Ca2+ dyshomeostasis. Emerging evidence points to the participation of the internal Ca2+ stores in the pathophysiology of neurodegeneration in AD. To test the involvement of intrasynaptic Ca2+ mobilization in Aβ toxicity, we explored the role of ryanodine receptor activation in rat cortical synaptosomes taken as a model system for the central presynapses. Evaluation of synaptosomal mitochondrial redox capacity was assessed by the MTT reduction technique, and ultrastructural changes of synaptosomes after exposure to Aβ and ryanodine were evaluated by electron microscopy. Our results show that Aβ potentiates mitochondrial dysfunction in the presence of ryanodine and induces morphological changes consisting of mitochondrial swelling and intense small synaptic vesicles depletion. These changes were accompanied by a reduction in the content of synaptophysin and actin proteins. The reduction of actin immunoreactivity was reversed in the presence of a wide range caspase inhibitors, suggesting the activation of synaptic apoptotic mechanisms.

Long-term exposure to environmental enrichment since youth prevents recognition memory decline and increases synaptic plasticity markers in aging.

Aging-associated brain changes include functional alterations that are usually related with memory decline. Epidemiological reports show that a physically and intellectually active life provides a protective effect on this decline and delays the onset of several neurodegenerative diseases. The cellular mechanisms behind the behavioral-based therapies, such as environmental enrichment (EE) exposure, as a method for alleviating age-related memory impairments, are still unknown. Although some reports have shown the benefits of EE exposure in cognitive outcomes in old mice and in animals with experimental neurodegenerative conditions, the effects of lifelong animal exposure to EE have not been explored in detail. In the present work we tested in a rat model the effects of intermittent lifelong exposure since youth to EE on behavioral performance, object recognition memory and anxiety level, as well as on some morphological and biochemical markers of brain plasticity such as hippocampal neurogenesis, synaptophysin content and synaptic morphology. We found that environmental factors have a positive impact on short-memory preservation, as well as on the maintenance of synapses and in the increase in number of new generated neurons within the hippocampus during aging.

Oxidative stress promotes JNK-dependent amyloidogenic processing of normally expressed human APP by differential modification of α-, β- and γ-secretase expression

The pathogenesis of Alzheimer disease (AD) is complex and is certain to involve diverse etiological factors, but a central role has been strongly suggested for amyloid beta-protein (Abeta), based on genetic, biochemical and neurotoxicological evidence. In contrast with the well-documented effect of genetic mutations in Abeta overproduction, not much is known about the mechanisms involved in sporadic AD (SAD) which account for more than 95% of cases. Extensive data from patients and in vivo animal models indicate that oxidative stress is one of the cardinal factors most frequently associated with this neurodegenerative disease. The aim of the present study was to explore the effect of oxidative stress on the normally expressed wild-type amyloid precursor protein (APP) in human neuroblastoma cells, which represents a more physiological model of neuronal Abeta generation. Since H(2)O(2) is the main source of the highly reactive hydroxyl radical in the brain, and FeCl(2) can stimulate oxidative stress, including the formation of the hydroxyl radical from H(2)O(2), in the present work we studied the effect of these two pro-oxidant molecules on the levels and processing of human APP by alpha-, beta- and gamma-secretase, and the role of the stress-activated kinase c-jun N-terminal kinase (JNK). We provide evidence for a dual modulation of amyloid precursor protein metabolism in differentiated human neuroblastoma cells related with a down-regulation of alpha-secretase and up-regulation of gamma-secretase, and particularly of beta-secretase and also a JNK depending Abeta generation.

Role of oxidative stress on β-amyloid neurotoxicity elicited during impairment of energy metabolism in the hippocampus : Protection by antioxidants

Age-associated oxidative stress has been implicated in neuronal damage linked with Alzheimers disease (AD). In addition to the role of beta-amyloid peptide (Abeta) in the pathogenesis of AD, reduced glucose oxidative metabolism and decreased mitochondrial activity have been suggested as associated factors. However, the relationship between Abeta toxicity, metabolic impairment, and oxidative stress is far from being understood. In vivo neurotoxicity of Abeta25-35 peptide has been conflicting. However, in previous studies, we have shown that Abeta25-35 consistently induces synaptic toxicity and neuronal death in the hippocampus in vivo, when administered during moderate glycolytic or mitochondrial inhibition. In the present study, we have investigated whether enhancement of Abeta neurotoxicity during these conditions involves oxidative stress. Results show increased lipoperoxidation (LPO) when Abeta is administered in the hippocampus of rats previously treated with the glycolysis inhibitor, iodoacetate. Neuronal damage and LPO are efficiently prevented by vitamin E, while the spin trapper, alpha-phenyl-N-tert-butyl nitrone, shows partial protection. Abeta stimulates LPO in synaptosomes, but toxicity is only observed in the presence of metabolic inhibitors. Damage and LPO are efficiently prevented by vitamin E. The present results suggest an interaction between oxidative stress and metabolic impairment in the Abeta neurotoxic cascade.

Selective stimulation of neurotransmitter release from chick retina by kainic and glutamic acids.

Abstract: The excitatory action of kainic and glutamic acids in chick whole retina was demonstrated as an immediate stimulation of the release of labeled γ‐aminobutyric acid (GABA) and glycine in a superfusion system. This stimulatory effect was 3–10 times greater than that produced by a depolarizing K+ concentration; in addition, it was independent of Caz+ in the medium, but notably inhibited when Na+ was omitted from the medium. Under identical experimental conditions, neither kainic nor glutamic acid had any effect on the release of labeled dopamine or α‐aminoisobutyric acid, thus indicating that their effect is not unspecific or due to cell damage. Similar although less marked stimulation of labeled GABA and glycine release by kainic acid was obtained in subcellular retinal fractions, particularly in fraction PI, which contained photoreceptor terminals and outer segments. This stimulation was also Ca2+ independent and greatly reduced when Na+ was omitted from the medium. It is suggested that the stimulation of GABA release by kainic and glutamic acids is probably due to a Na+‐dependent, carrier‐mediated mechanism that responds to the entry of Na+ produced by the interaction of glutamic and kainic acids with retinal membranes. In cortical or striatal slices from mouse brain, these acids had a negligible stimulatory effect on GABA and dopamine release.

When astrocytes become harmful: Functional and inflammatory responses that contribute to Alzheimer's disease

A growing body of research suggests that astrocytes play roles as contributors to the pathophysiology of Alzheimers disease (AD). Several lines of evidence propose that activated astrocytes produce and release proinflammatory molecules that may be critical for the generation of amyloid-β peptide (Aβ). However, accumulating evidence indicates that Aβ may activate astrocytes, which leads to an increase in cytokines that has been suggested to be a causative factor in the cognitive dysfunction of AD; thus, a vicious circle may be created. Intrinsic inflammatory mechanisms may provide a regulatory system that is capable of influencing the neuronal microenvironment that affects neuronal survival. In this article, we address the evidence surrounding the interactions of dysfunctional astrocytes with neighboring neurons that may initiate a cascade of events that culminates with neuronal injury and the expression of the hallmark lesions of AD. Comprehensive knowledge of the molecular mechanisms underlying the participation of astrocytes in neurodegeneration could aid the development of therapies to restore proper astrocyte function that can be used in AD patients to prevent or alleviate the progression of the disease in a more efficient and comprehensive manner.

GSK3 Function in the Brain during Development, Neuronal Plasticity, and Neurodegeneration

GSK3 has diverse functions, including an important role in brain pathology. In this paper, we address the primary functions of GSK3 in development and neuroplasticity, which appear to be interrelated and to mediate age-associated neurological diseases. Specifically, GSK3 plays a pivotal role in controlling neuronal progenitor proliferation and establishment of neuronal polarity during development, and the upstream and downstream signals modulating neuronal GSK3 function affect cytoskeletal reorganization and neuroplasticity throughout the lifespan. Modulation of GSK3 in brain areas subserving cognitive function has become a major focus for treating neuropsychiatric and neurodegenerative diseases. As a crucial node that mediates a variety of neuronal processes, GSK3 is proposed to be a therapeutic target for restoration of synaptic functioning and cognition, particularly in Alzheimers disease.

Short-Term High-Fat-and-Fructose Feeding Produces Insulin Signaling Alterations Accompanied by Neurite and Synaptic Reduction and Astroglial Activation in the Rat Hippocampus

Chronic consumption of high-fat-and-fructose diets (HFFD) is associated with the development of insulin resistance (InsRes) and obesity. Systemic insulin resistance resulting from long-term HFFD feeding has detrimental consequences on cognitive performance, neurogenesis, and long-term potentiation establishment, accompanied by neuronal alterations in the hippocampus. However, diet-induced hippocampal InsRes has not been reported. Therefore, we investigated whether short-term HFFD feeding produced hippocampal insulin signaling alterations associated with neuronal changes in the hippocampus. Rats were fed with a control diet or an HFFD consisting of 10% lard supplemented chow and 20% high-fructose syrup in the drinking water. Our results show that 7 days of HFFD feeding induce obesity and InsRes, associated with the following alterations in the hippocampus: (1) a decreased insulin signaling; (2) a decreased hippocampal weight; (3) a reduction in dendritic arborization in CA1 and microtubule-associated protein 2 (MAP-2) levels; (4) a decreased dendritic spine number in CA1 and synaptophysin content, along with an increase in tau phosphorylation; and finally, (5) an increase in reactive astrocyte associated with microglial changes. To our knowledge, this is the first report addressing hippocampal insulin signaling, as well as morphologic, structural, and functional modifications due to short-term HFFD feeding in the rat.