Acute ampakine treatment ameliorates age-related deficits in long-term potentiation

AMPA receptors play an important role in the biological consequences of spinal cord injury: Implications for AMPA receptor modulators for therapeutic benefit

Spinal cord injury (SCI) afflicts millions of individuals globally. There are few therapies available to patients. Ascending and descending excitatory glutamatergic neural circuits in the central nervous system are disrupted by SCI, making α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) a potential therapeutic drug target. Emerging research in preclinical models highlights the involvement of AMPARs in vital processes following SCI including breathing, pain, inflammation, bladder control, and motor function. However, there are no clinical trial data reported in this patient population to date. No work on the role of AMPA receptors in sexual dysfunction after SCI has been disclosed. Compounds with selective antagonist and potentiating effects on AMPA receptors have benefit in animal models of SCI, with antagonists generally showing protective effects early after injury and potentiators (ampakines) producing improved breathing and bladder function. The role of AMPARs in pathophysiology and recovery after SCI depends upon the time post injury, and the timing of AMPAR augmentation or antagonism. The roles of inflammation, synaptic plasticity, sensitization, neurotrophic factors, and neuroprotection are considered in this context. The data summarized and discussed in this paper document proof of principle and strongly encourage additional studies on AMPARs as novel gateways to therapeutic benefit for patients suffering from SCI. The availability of both AMPAR antagonists such as perampanel and AMPAR allosteric modulators (i.e., ampakines) such as CX1739, that have been safely administered to humans, provides an expedited means of clinical inquiry for possible therapeutic advances.

Neurobiological Mechanisms of Cognitive Decline Correlated with Brain Aging

Cognitive decline has emerged as one of the greatest health threats of old age. Meanwhile, aging is the primary risk factor for Alzheimer's disease (AD) and other prevalent neurodegenerative disorders. Developing therapeutic interventions for such conditions demands a greater understanding of the processes underlying normal and pathological brain aging. Despite playing an important role in the pathogenesis and incidence of disease, brain aging has not been well understood at a molecular level. Recent advances in the biology of aging in model organisms, together with molecular- and systems-level studies of the brain, are beginning to shed light on these mechanisms and their potential roles in cognitive decline. This chapter seeks to integrate the knowledge about the neurological mechanisms of age-related cognitive changes that underlie aging.

Modeling suggests combined-drug treatments for disorders impairing synaptic plasticity via shared signaling pathways

Genetic disorders such as Rubinstein-Taybi syndrome (RTS) and Coffin-Lowry syndrome (CLS) cause lifelong cognitive disability, including deficits in learning and memory. Can pharmacological therapies be suggested that improve learning and memory in these disorders? To address this question, we simulated drug effects within a computational model describing induction of late long-term potentiation (L-LTP). Biochemical pathways impaired in these and other disorders converge on a common target, histone acetylation by acetyltransferases such as CREB binding protein (CBP), which facilitates gene induction necessary for L-LTP. We focused on four drug classes: tropomyosin receptor kinase B (TrkB) agonists, cAMP phosphodiesterase inhibitors, histone deacetylase inhibitors, and ampakines. Simulations suggested each drug type alone may rescue deficits in L-LTP. A potential disadvantage, however, was the necessity of simulating strong drug effects (high doses), which could produce adverse side effects. Thus, we investigated the effects of six drug pairs among the four classes described above. These combination treatments normalized impaired L-LTP with substantially smaller individual drug 'doses'. In addition three of these combinations, a TrkB agonist paired with an ampakine and a cAMP phosphodiesterase inhibitor paired with a TrkB agonist or an ampakine, exhibited strong synergism in L-LTP rescue. Therefore, we suggest these drug combinations are promising candidates for further empirical studies in animal models of genetic disorders that impair histone acetylation, L-LTP, and learning.

Interactions between Tumor Cells, Neurons, and Microglia in the Glioma Microenvironment

Despite significant strides made in understanding the pathophysiology of high-grade gliomas over the past two decades, most patients succumb to these neoplasias within two years of diagnosis. Furthermore, there are various co-morbidities associated with glioma and standard of care treatments. Emerging evidence suggests that aberrant glutamate secretion in the glioma microenvironment promotes tumor progression and contributes to the development of co-morbidities, such as cognitive defects, epilepsy, and widespread neurodegeneration. Recent data clearly illustrate that neurons directly synapse onto glioma cells and drive their proliferation and spread via glutamatergic action. Microglia are central nervous system-resident myeloid cells, modulate glioma growth, and possess the capacity to prune synapses and encourage synapse formation. However, current literature has yet to investigate the potential role of microglia in shaping synapse formation between neurons and glioma cells. Herein, we present the literature concerning glutamate's role in glioma progression, involving hyperexcitability and excitotoxic cell death of peritumoral neurons and stimulation of glioma proliferation and invasion. Furthermore, we discuss instances in which microglia are more likely to sculpt or encourage synapse formation during glioma treatment and propose studies to delineate the role of microglia in synapse formation between neurons and glioma cells. The sex-dependent oncogenic or oncolytic actions of microglia and myeloid cells, in general, are considered in addition to the functional differences between microglia and macrophages in tumor progression. We also put forth tractable methods to safely perturb aberrant glutamatergic action in the tumor microenvironment without significantly increasing the toxicities of the standard of care therapies for glioma therapy.

Ampakine pretreatment enables a single brief hypoxic episode to evoke phrenic motor facilitation

Phrenic long-term facilitation (LTF) is a sustained increase in phrenic motor output occurring after exposure to multiple (but not single) hypoxic episodes. Ampakines are a class of drugs that enhance AMPA receptor function. Ampakines can enhance expression of neuroplasticity, and the phrenic motor system is fundamentally dependent on excitatory glutamatergic currents. Accordingly, we tested the hypothesis that combining ampakine pretreatment with a single brief hypoxic exposure would result in phrenic motor facilitation lasting well beyond the period of hypoxia. Phrenic nerve output was recorded in urethane-anesthetized, ventilated, and vagotomized adult Sprague-Dawley rats. Ampakine CX717 (15 mg/kg iv; n = 8) produced a small increase in phrenic inspiratory burst amplitude and frequency, but values quickly returned to predrug baseline. When CX717 was followed 2 min later by a 5-min exposure to hypoxia (n = 8; PaO2 ~45 mmHg), a persistent increase in phrenic inspiratory burst amplitude (i.e., phrenic motor facilitation) was observed up to 60 min posthypoxia (103 ± 53% increase from baseline). In contrast, when hypoxia was preceded by vehicle injection (10% 2-hydroxypropyl-β-cyclodextrin; n = 8), inspiratory phrenic bursting was similar to baseline values at 60 min. Additional experiments with another ampakine (CX1739, 15 mg/kg) produced comparable results. We conclude that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation. This targeted approach for enhancing respiratory neuroplasticity may have value in the context of hypoxia-based neurorehabilitation strategies.NEW & NOTEWORTHY A single brief episode of hypoxia (e.g., 3-5 min) does not evoke long-lasting increases in respiratory motor output after the hypoxia is concluded. Ampakines are a class of drugs that enhance AMPA receptor function. We show that pairing low-dose ampakine treatment with a single brief hypoxic exposure can evoke sustained phrenic motor facilitation after the acute hypoxic episode.

Novel Players in the Aging Synapse: Impact on Cognition

While neuronal loss has long been considered as the main contributor to age-related cognitive decline, these alterations are currently attributed to gradual synaptic dysfunction driven by calcium dyshomeostasis and alterations in ionotropic/metabotropic receptors. Given the key role of the hippocampus in encoding, storage, and retrieval of memory, the morpho- and electrophysiological alterations that occur in the major synapse of this network-the glutamatergic-deserve special attention. We guide you through the hippocampal anatomy, circuitry, and function in physiological context and focus on alterations in neuronal morphology, calcium dynamics, and plasticity induced by aging and Alzheimer's disease (AD). We provide state-of-the art knowledge on glutamatergic transmission and discuss implications of these novel players for intervention. A link between regular consumption of caffeine-an adenosine receptor blocker-to decreased risk of AD in humans is well established, while the mechanisms responsible have only now been uncovered. We review compelling evidence from humans and animal models that implicate adenosine A2A receptors (A2AR) upsurge as a crucial mediator of age-related synaptic dysfunction. The relevance of this mechanism in patients was very recently demonstrated in the form of a significant association of the A2AR-encoding gene with hippocampal volume (synaptic loss) in mild cognitive impairment and AD. Novel pathways implicate A2AR in the control of mGluR5-dependent NMDAR activation and subsequent Ca2+ dysfunction upon aging. The nature of this receptor makes it particularly suited for long-term therapies, as an alternative for regulating aberrant mGluR5/NMDAR signaling in aging and disease, without disrupting their crucial constitutive activity.

Targeting the BDNF/TrkB pathway for the treatment of tumors

Neurotrophins are a family of growth factors that regulate neural survival, development, function and plasticity in the central and the peripheral nervous system. There are four neurotrophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and NT-4. Among them, BDNF is the most studied due to its high expression in the brain. Over the past two decades, BDNF and its receptor tropomyosin receptor kinase B (TrkB) have been reported to be upregulated in a wide range of tumors. This activated signal stimulates a series of downstream pathways, including phosphoinositide 3-kinase/protein kinase B, Ras-Raf-mitogen activated protein kinase kinase-extracellular signal-regulated kinases, the phospholipase-C-γ pathway and the transactivation of epidermal growth factor receptor. Activation of these signaling pathways induces oncogenic effects by increasing cancer cell growth, proliferation, survival, migration and epithelial to mesenchymal transition, and decreasing anoikis, relapse and chemotherapeutic sensitivity. The present review summarizes recent findings to discuss the role of BDNF in tumors, the underlying molecular mechanism, targeting Trk receptors for treatment of cancers and its potential risk.

Long-term social isolation inhibits autophagy activation, induces postsynaptic dysfunctions and impairs spatial memory

. Moreover, we found that L-PWSI increased the protein expression of p-AKT/AKT, p-mTOR/mTOR and p62, whereas the protein levels of LC3B and Beclin1 were decreased indicating an inhibition in autophagy activity. Intraperitoneal injection of rapamycin significantly potentiated fEPSP slope and cognition-related proteins expression in the L-PWSI mice. These results therefore suggest that L-PWSI induces postsynaptic dysfunction by disrupting the interaction between AMPAR, NMDAR and PSD-95, and inhibit the autophagy activity which led to impaired spatial memory and cognitive function.

AMPA Receptor Trafficking in Natural and Pathological Aging

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) enable most excitatory transmission in the brain and are crucial for mediating basal synaptic strength and plasticity. Because of the importance of their function, AMPAR dynamics, activity and subunit composition undergo a tight regulation which begins as early as prenatal development and continues through adulthood. Accumulating evidence suggests that the precise regulatory mechanisms involved in orchestrating AMPAR trafficking are challenged in the aging brain. In turn dysregulation of AMPARs can be linked to most neurological and neurodegenerative disorders. Understanding the mechanisms that govern AMPAR signaling during natural and pathological cognitive decline will guide the efforts to develop most effective ways to tackle neurodegenerative diseases which are one of the primary burdens afflicting an increasingly aging population. In this review, I provide a brief overview of the molecular mechanisms involved in AMPAR trafficking highlighting what is currently known about how these processes change with age and disease. As a particularly well-studied example of AMPAR dysfunction in pathological aging I focus in Alzheimer’s disease (AD) with special emphasis in how the production of neurofibrillary tangles (NFTs) and amyloid-β plaques may contribute to disruption in AMPAR function.