Volume 23, Issue 1

As a constitutively active kinase, glycogen synthase kinase 3 (GSK3) is a kinase which regulates body metabolism by phosphorylation of glycogen synthase (GS) and other substrates. Considerable evidence suggests that GSK3 is involved in the common pathology underlying Alzheimer’s disease (AD) and type 2 diabetes mellitus (T2DM). The overexpression or overactivation of GSK3 could induce a series of pathological changes, most of which are hallmarks of AD and T2DM. Therefore, GSK3 could be a novel target to treat these two age-dependent diseases. The inhibition of this kinase can prevent the aggregation of β-amyloid (Aβ) and hyperphosphorylation of tau protein. GSK3 inhibition can also be a promising strategy to ameliorate neurodegenerative developments. Its potential association with memory formation has been shown in electrophysiological and behavioral experiments. The neuroprotective effects of novel drugs developed to treat T2DM, glucagon-like peptide 1 (GLP-1) and its long-lasting analogs, have a possible link to GSK3 modification. Recent investigations of the interaction between the phosphatidylinositol 3 kinase (PI3K) signaling pathway and the protective effect of novel GPL-1 receptor agonist geniposide on PC12 cells support this theory.

Huntington’s disease (HD) is a neurodegenerative genetic disorder caused by an expansion of CAG repeats in the HD gene encoding for huntingtin (Htt), resulting in progressive death of striatal neurons, with clinical symptoms of chorea, dementia and dramatic weight loss. Metabolic and mitochondrial dysfunction caused by the expanded polyglutamine sequence have been described along with other mechanisms of neurodegeneration previously described in human tissues and animal models of HD. In this review, we focus on mitochondrial and metabolic disturbances affecting both the central nervous system and peripheral cells, including mitochondrial DNA damage, mitochondrial complexes defects, loss of calcium homeostasis and transcriptional deregulation. Glucose abnormalities have also been described in peripheral tissues of HD patients and in HD animal and cellular models. Moreover, there are no effective neuroprotective treatments available in HD. Thus, we briefly discuss the role of creatine and coenzyme Q10 that target mitochondrial dysfunction and impaired bioenergetics and have been previously used in HD clinical trials.

PI3K activation is the starting point of signaling pathways relaying on changes in the phosphorylation levels of membrane phosphoinositides. These pathways have been involved in several neuronal processes, including cellular growth and survival, differentiation, neuroprotection, dendritic growing, and synaptic plasticity among others. Recent data from Drosophila and rodents have demonstrated an unexpected role of PI3K controlling synapse number that lead to functional and behavioral effects. In the short-term, PI3K is also required for maintaining AMPA receptor clustering at the postsynaptic membranes. We review here the PI3K roles regulating synapse number and functionality.

The spike timing of spatially tuned cells throughout the rodent hippocampal formation displays a strikingly robust and precise organization. In individual place cells, spikes precess relative to the theta local field potential (6–10 Hz) as an animal traverses a place field. At the population level, theta cycles shape repeated, compressed place cell sequences that correspond to coherent paths. The theta phase precession phenomenon not only has afforded insights into how multiple processing elements in the hippocampal formation interact, but is also believed to facilitate hippocampal contributions to rapid learning, navigation, and lookahead. However, theta phase precession is not unique to the hippocampus, suggesting that insights derived from hippocampal phase precession could elucidate processing in other structures. In this review, we consider the implications of extrahippocampal phase precession in terms of mechanisms and functional relevance. We focus on phase precession in the ventral striatum (vStr), a prominent output structure of the hippocampus in which phase precession systematically appears in the firing of reward-anticipatory ‘ramp’ neurons. We outline how ventral striatal phase precession can advance our understanding of behaviors thought to depend on interactions between the hippocampus and the vStr, such as conditioned place preference and context-dependent reinstatement. More generally, we argue that phase precession can be a useful experimental tool in dissecting the functional connectivity between the hippocampus and its outputs.

The activity-dependent neuronal modification is important for many aspects of adaptive behavior and brain development. Very often, neurological disorders are associated with the alteration of neural signaling pathways that are required for activity-triggered cellular events. Mounting evidence has implicated the role of cyclic AMP (cAMP)-cAMP-dependent protein kinase (PKA)-ERK1/2-cAMP-responsive element-binding protein (CREB) cascade in numerous brain functions such as learning and memory. Ca 2+ -stimulated type 1 and type 8 adenylyl cyclases (AC1 and AC8) are unique enzymes that couple activity-dependent calcium influx to the activation of cAMP signaling. Here, we summarize some direct evidence to support that Ca 2+ -stimulated cAMP signaling regulates molecular and cellular substrates of neuronal adaptation. Specifically, the function of AC1 and AC8 in synaptic functions, such as long-term potentiation, long-term depression, and depotentiation, has been examined by using genetic deletion and overexpression approaches. Consistent with the current hypothesis, the Ca 2+ -stimulated cAMP production through AC1 and AC8 is required for the activity-dependent activation of the ERK1/2-CREB cascade. We further describe the phenotypes of AC1/AC8 mutant mice in memory formation and other adaptive brain functions. The findings may suggest Ca 2+ -stimulated AC as therapeutic target for the treatment of mental retardation, pain, addiction, anxiety, depression, and neurodegeneration.

The endoplasmic reticulum (ER), an important cellular organelle in eukaryotic cells, becomes dysfunctional following exposure to harmful stimuli. These stimuli can cause the ER stress response, which induces cell apoptosis due to changes in ER protein levels such as glucose-regulated protein. Current studies indicate that ER stress is closely related to the occurrence and development of neurodegenerative disorders, e.g., prion diseases. The pathogenic agent known as the misfolded prion protein may cause an imbalance in ER homeostasis and commit the neuron to a pathway of apoptosis; however, the specific mechanisms are still under intensive investigation. This review summarizes current research investigating the relationship between ER stress and prion diseases. These findings will aid in the development of novel strategies for diagnosis and therapies for prion and other neurodegenerative diseases.

Cognitive functions involve not only cortical but also subcortical structures. Subcortical sources, however, contribute very little to magnetoencephalographic (MEG) and electroencephalographic (EEG) signals because they are far from external sensors and their neural architectonic organization often makes them electromagnetically silent. Estimating the activity of deep sources from MEG and EEG (M/EEG) data is thus a challenging issue. Here, we review the influence of geometric parameters (location/orientation) on M/EEG signals produced by the main deep brain structures (amygdalo-hippocampal complex, thalamus and some basal ganglia). We then discuss several methods that have been utilized to solve the issues and localize or quantify the M/EEG contribution from deep neural currents. These methods rely on realis­tic forward models of subcortical regions or on introducing strong dynamical priors on inverse solutions that are based on biologically plausible neural models, such as those used in dynamic causal modeling (DCM) for M/EEG.

Cognitive impairment, a core feature of schizophrenia, has been suggested to arise from a disturbance of gamma oscillations that is due to decreased neurotransmission from the parvalbumin (PV) subtype of interneurons. Indeed, PV interneurons have uniquely fast membrane and synaptic properties that are crucially important for network functions such as feedforward inhibition or gamma oscillations. The causes leading to impairment of PV neurotransmission in schizophrenia are still under investigation. Interestingly, NMDA receptors (NMDARs) antagonism results in schizophrenia-like symptoms in healthy adults. Additionally, systemic NMDAR antagonist administration increases prefrontal cortex pyramidal cell firing, apparently by producing disinhibition, and repeated exposure to NMDA antagonists leads to changes in the GABAergic markers that mimic the impairments found in schizophrenia. Based on these findings, PV neuron deficits in schizophrenia have been proposed to be secondary to (NMDAR) hypofunction at glutamatergic synapses onto these cells. However, NMDARs generate long-lasting postsynaptic currents that result in prolonged depolarization of the postsynaptic cells, a property inconsistent with the role of PV cells in network dynamics. Here, we review evidence leading to the conclusion that cortical disinhibition and GABAergic impairment produced by NMDAR antagonists are unlikely to be mediated via NMDARs at glutamatergic synapses onto mature cortical PV neurons.

Cortisol has major impacts upon a range of physiological homeostatic mechanisms and plays an important role in stress, anxiety and depression. Although traditionally described as being solely synthesised via the hypothalamic-pituitary-adrenal (HPA) axis, recent animal and human studies indicate that cortisol may also be synthesised via a functionally-equivalent ‘peripheral’ HPA-like process within the skin, principally within hair follicles, melanocytes, epidermal melanocytes and dermal fibroblasts. Current data indicate that basal levels of cortisol within hair vary across body regions, show diurnal variation effects, respond to the onset and cessation of environmental stressors, and may demonstrate some degree of localisation in those responses. There are conflicting data regarding the presence of variability in cortisol concentrations across the length of the hair shaft, thus challenging the suggestion that hair cortisol may be used as a historical biomarker of stress and questioning the primary origin of cortisol in hair. The need to comprehensively ‘map’ the hair cortisol response for age, gender, diurnal rhythm and responsivity to stressor type is discussed, plus the major issue of if, and how, the peripheral and central HPA systems communicate.

No abstract available