ZCCHC17 knockdown phenocopies Alzheimer's disease-related loss of synaptic proteins and hyperexcitability.

ZCCHC17 is a master regulator of synaptic gene expression and has recently been shown to play a role in splicing of neuronal mRNA. We previously showed that ZCCHC17 protein declines in Alzheimer's disease (AD) brain tissue before there is significant gliosis and neuronal loss, that ZCCHC17 loss partially replicates observed splicing abnormalities in AD brain tissue, and that maintenance of ZCCHC17 levels is predicted to support cognitive resilience in AD. Here, we assessed the functional consequences of reduced ZCCHC17 expression in primary cortical neuronal cultures using siRNA knockdown. Consistent with its previously identified role in synaptic gene expression, loss of ZCCHC17 led to loss of synaptic protein expression. Patch recording of neurons shows that ZCCHC17 loss significantly disrupted the excitation/inhibition balance of neurotransmission, and favored excitatory-dominant synaptic activity as measured by an increase in spontaneous excitatory post synaptic currents and action potential firing rate, and a decrease in spontaneous inhibitory post synaptic currents. These findings are consistent with the hyperexcitable phenotype seen in AD animal models and in patients. We are the first to assess the functional consequences of ZCCHC17 knockdown in neurons and conclude that ZCCHC17 loss partially phenocopies AD-related loss of synaptic proteins and hyperexcitability.

Mitovesicles secreted into the extracellular space of brains with mitochondrial dysfunction impair synaptic plasticity.

BACKGROUND: Hypometabolism tied to mitochondrial dysfunction occurs in the aging brain and in neurodegenerative disorders, including in Alzheimer's disease, in Down syndrome, and in mouse models of these conditions. We have previously shown that mitovesicles, small extracellular vesicles (EVs) of mitochondrial origin, are altered in content and abundance in multiple brain conditions characterized by mitochondrial dysfunction. However, given their recent discovery, it is yet to be explored what mitovesicles regulate and modify, both under physiological conditions and in the diseased brain. In this study, we investigated the effects of mitovesicles on synaptic function, and the molecular players involved. METHODS: Hippocampal slices from wild-type mice were perfused with the three known types of EVs, mitovesicles, microvesicles, or exosomes, isolated from the brain of a mouse model of Down syndrome or of a diploid control and long-term potentiation (LTP) recorded. The role of the monoamine oxidases type B (MAO-B) and type A (MAO-A) in mitovesicle-driven LTP impairments was addressed by treatment of mitovesicles with the irreversible MAO inhibitors pargyline and clorgiline prior to perfusion of the hippocampal slices. RESULTS: Mitovesicles from the brain of the Down syndrome model reduced LTP within minutes of mitovesicle addition. Mitovesicles isolated from control brains did not trigger electrophysiological effects, nor did other types of brain EVs (microvesicles and exosomes) from any genotype tested. Depleting mitovesicles of their MAO-B, but not MAO-A, activity eliminated their ability to alter LTP. CONCLUSIONS: Mitovesicle impairment of LTP is a previously undescribed paracrine-like mechanism by which EVs modulate synaptic activity, demonstrating that mitovesicles are active participants in the propagation of cellular and functional homeostatic changes in the context of neurodegenerative disorders.

The 5HT2b Receptor in Alzheimer's Disease: Increased Levels in Patient Brains and Antagonist Attenuation of Amyloid and Tau Induced Dysfunction.

BACKGROUND: Background: Neurodegenerative diseases manifest behavioral dysfunction with disease progression. Intervention with neuropsychiatric drugs is part of most multi-drug treatment paradigms. However, only a fraction of patients responds to the treatments and those responding must deal with drug-drug interactions and tolerance issues generally attributed to off-target activities. Recent efforts have focused on the identification of underexplored targets and exploration of improved outcomes by treatment with selective molecular probes. Objective: As part of ongoing efforts to identify and validate additional targets amenable to therapeutic intervention, we examined levels of the serotonin 5-HT2b receptor (5-HT2bR) in Alzheimer's disease (AD) brains and the potential of a selective 5-HT2bR antagonist to counteract synaptic plasticity and memory damage induced by AD-related proteins, amyloid-ß, and tau. Methods: This work used a combination of biochemical, chemical biology, electrophysiological, and behavioral techniques. Biochemical methods included analysis of protein levels. Chemical biology methods included the use of an in vivo molecular probe MW071, a selective antagonist for the 5HT2bR. Electrophysiological methods included assessment of long-term potentiation (LTP), a type of synaptic plasticity thought to underlie memory formation. Behavioral studies investigated spatial memory and associative memory. Results: 5HT2bR levels are increased in brain specimens of AD patients compared to controls. 5HT2bR antagonist treatment rescued amyloid-ß and tau oligomer-induced impairment of synaptic plasticity and memory. Conclusions: The increased levels of 5HT-2bR in AD patient brains and the attenuation of disease-related synaptic and behavioral dysfunctions by MW071 treatment suggest that the 5HT-2bR is a molecular target worth pursuing as a potential therapeutic target.

Heart failure-induced cognitive dysfunction is mediated by intracellular Ca2+ leak through ryanodine receptor type 2.

Cognitive dysfunction (CD) in heart failure (HF) adversely affects treatment compliance and quality of life. Although ryanodine receptor type 2 (RyR2) has been linked to cardiac muscle dysfunction, its role in CD in HF remains unclear. Here, we show in hippocampal neurons from individuals and mice with HF that the RyR2/intracellular Ca2+ release channels were subjected to post-translational modification (PTM) and were leaky. RyR2 PTM included protein kinase A phosphorylation, oxidation, nitrosylation and depletion of the stabilizing subunit calstabin2. RyR2 PTM was caused by hyper-adrenergic signaling and activation of the transforming growth factor-beta pathway. HF mice treated with a RyR2 stabilizer drug (S107), beta blocker (propranolol) or transforming growth factor-beta inhibitor (SD-208), or genetically engineered mice resistant to RyR2 Ca2+ leak (RyR2-p.Ser2808Ala), were protected against HF-induced CD. Taken together, we propose that HF is a systemic illness driven by intracellular Ca2+ leak that includes cardiogenic dementia.

Re-Arranging the Puzzle between the Amyloid-Beta and Tau Pathology: An APP-Centric Approach.

After several years of research in the field of Alzheimer's disease (AD), it is still unclear how amyloid-beta (Aß) and Tau, two key hallmarks of the disease, mediate the neuropathogenic events that lead to AD. Current data challenge the "Amyloid Cascade Hypothesis" that has prevailed in the field of AD, stating that Aß precedes and triggers Tau pathology that will eventually become the toxic entity in the progression of the disease. This perspective also led the field of therapeutic approaches towards the development of strategies that target Aß or Tau. In the present review, we discuss recent literature regarding the neurotoxic role of both Aß and Tau in AD, as well as their physiological function in the healthy brain. Consequently, we present studies suggesting that Aß and Tau act independently of each other in mediating neurotoxicity in AD, thereafter, re-evaluating the "Amyloid Cascade Hypothesis" that places Tau pathology downstream of Aß. More recent studies have confirmed that both Aß and Tau could propagate the disease and induce synaptic and memory impairments via the amyloid precursor protein (APP). This finding is not only interesting from a mechanistic point of view since it provides better insights into the AD pathogenesis but also from a therapeutic point of view since it renders APP a common downstream effector for both Aß and Tau. Subsequently, therapeutic strategies that act on APP might provide a more viable and physiologically relevant approach for targeting AD.

Soluble guanylate cyclase stimulator riociguat improves spatial memory in mice via peripheral mechanisms.

Soluble guanylate cyclase (sGC) - cyclic guanosine monophosphate (cGMP) signalling is important for healthy memory function and a healthy vascular system. Targeting sGC-cGMP signalling can therefore be a potential strategy to enhance memory processes. sGC can be targeted by using agonists, such as sGC stimulator riociguat. Therefore, this study aimed to target sGC using riociguat to investigate its acute effects on memory function and neuronal plasticity in mice. The effects of riociguat on long-term memory and a biperiden-induced memory deficit model for assessing short-term memory were tested in the object location task, and working memory was tested in the Y-maze continuous alternation task. Pharmacokinetic measurements were performed within brain tissue of mice, and hippocampal plasticity measures were assessed using western blotting. Acute oral administration with a low dose of 0.03 mg/kg riociguat was able to enhance working-, short-, and long-term spatial memory. Under cerebral vasoconstriction higher doses of riociguat were still effective on memory. Pharmacokinetic measurements revealed poor brain penetration of riociguat and its metabolite M-1. Increased activation of VASP was found, while no effects were found on other memory-related hippocampal plasticity measures. Memory enhancing effects of riociguat are most likely regulated by vascular peripheral effects on cGMP signalling. Yet, further research is needed to investigate the possible contribution of hemodynamic or metabolic effects of sGC stimulators on memory performance.

Pleiotrophin, nitric oxide and glutamate AMPA receptors in chick cerebellum morphogenesis.

Avian cerebellum, a highly conserved, laminated and foliated structure, provides an excellent model for developmental studies. During the intermediate embryonic stages, granule cell progenitor proliferation and the inwards migration of post-mitotic granule cells have been implicated in the morphogenesis of cerebellar cortex cytoarchitecture and foliation. The present study questioned the spatio-temporal expression pattern of pleiotrophin, an extracellular matrix growth factor, during the morphogenesis of embryonic cerebellum, and the roles of ionotropic AMPA glutamate receptors and the diffusible neuromodulator nitric oxide (NO) in the proliferation pattern of EGL granule cell progenitors. To this end, the density of proliferating cells in the developing embryonic external granule layer (EGL) was determined following acute treatment with AMPA receptor antagonist CNQX or NO synthase inhibitor L-NAME, at embryonic stages HH38-41 (E12-E15 days), by means of BrdU immunohistochemistry and double immunofluorescence. Importantly, at earlier stages, pleiotrophin-like immunoreactivity showed high expression levels in the EGL that gradually decreased, persisting within the growing folia apices, later in development. Interestingly, blockage of AMPA receptors had no effect; while NOS inhibition resulted in transient age- and region-specific increases of EGL granule progenitor cell proliferation at earlier stages, but decreased the post-mitotic granule cells at folia apices, at a later stage HH41 (E15 day). Overall, NO had a transient anti-proliferative effect in EGL similar to mammalian cerebellum, acting as a modulator of the EGL function at different stages, suggesting its possible implication in complex processes guiding cerebellar cytoarchitecture and folia formation.

Soluble Guanylate Cyclase Stimulator Vericiguat Enhances Long-Term Memory in Rats without Altering Cerebral Blood Volume.

Vascular cognitive impairment (VCI) is characterized by impairments in cerebral blood flow (CBF), endothelial function and blood-brain barrier (BBB) integrity. These processes are all physiologically regulated by the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cGMP signaling pathway. Additionally, cGMP signaling plays an important role in long-term potentiation (LTP) underlying memory formation. Therefore, targeting the NO-sGC-cGMP pathway may be a therapeutic strategy for treating VCI. Hence, in this study we investigated whether sGC stimulator vericiguat has potential as a cognitive enhancer. The effects of vericiguat on long-term memory were measured in rats using an object location task. Due to the low brain-penetrance of vericiguat found in this study, it was investigated whether in the absence of BBB limitations, vericiguat enhanced hippocampal plasticity using an ex vivo memory acquisition-like chemical LTP model. Finally, peripheral effects were measured by means of blood pressure and cerebral blood volume. Vericiguat successfully enhanced long-term memory and increased hippocampal plasticity via enhanced translocation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors to the cell membrane, while blood pressure and cerebral blood volume were unaltered. Although the memory enhancing effects in this study are likely due to peripheral effects on the cerebral microvasculature, sGC stimulation may provide a new therapeutic strategy for treating VCI, especially when BBB integrity is reduced.

Tau is not necessary for amyloid-ß-induced synaptic and memory impairments.

The amyloid hypothesis posits that the amyloid-beta (Aß) protein precedes and requires microtubule-associated protein tau in a sort of trigger-bullet mechanism leading to Alzheimer's disease (AD) pathology. This sequence of events has become dogmatic in the AD field and is used to explain clinical trial failures due to a late start of the intervention when Aß already activated tau. Here, using a multidisciplinary approach combining molecular biological, biochemical, histopathological, electrophysiological, and behavioral methods, we demonstrated that tau suppression did not protect against Aß-induced damage of long-term synaptic plasticity and memory, or from amyloid deposition. Tau suppression could even unravel a defect in basal synaptic transmission in a mouse model of amyloid deposition. Similarly, tau suppression did not protect against exogenous oligomeric tau-induced impairment of long-term synaptic plasticity and memory. The protective effect of tau suppression was, in turn, confined to short-term plasticity and memory. Taken together, our data suggest that therapies downstream of Aß and tau together are more suitable to combat AD than therapies against one or the other alone.

Role of cyclic nucleotides and their downstream signaling cascades in memory function: Being at the right time at the right spot.

A plethora of studies indicate the important role of cAMP and cGMP cascades in neuronal plasticity and memory function. As a result, altered cyclic nucleotide signaling has been implicated in the pathophysiology of mnemonic dysfunction encountered in several diseases. In the present review we provide a wide overview of studies regarding the involvement of cyclic nucleotides, as well as their upstream and downstream molecules, in physiological and pathological mnemonic processes. Next, we discuss the regulation of the intracellular concentration of cyclic nucleotides via phosphodiesterases, the enzymes that degrade cAMP and/or cGMP, and via A-kinase-anchoring proteins that refine signal compartmentalization of cAMP signaling. We also provide an overview of the available data pointing to the existence of specific time windows in cyclic nucleotide signaling during neuroplasticity and memory formation and the significance to target these specific time phases for improving memory formation. Finally, we highlight the importance of emerging imaging tools like Förster resonance energy transfer imaging and optogenetics in detecting, measuring and manipulating the action of cyclic nucleotide signaling cascades.

Development of novel phosphodiesterase 5 inhibitors for the therapy of Alzheimer's disease.

Nitric oxide (NO) is a gaseous molecule that plays a multifactorial role in several cellular processes. In the central nervous system, the NO dual nature in neuroprotection and neurotoxicity has been explored to unveil its involvement in Alzheimer's disease (AD). A growing body of research shows that the activation of the NO signaling pathway leading to the phosphorylation of the transcription factor cyclic adenine monophosphate responsive element binding protein (CREB) (so-called NO/cGMP/PKG/CREB signaling pathway) ameliorates altered neuroplasticity and memory deficits in AD animal models. In addition to NO donors, several other pharmacological agents, such as phosphodiesterase 5 (PDE5) inhibitors have been used to activate the pathway and rescue memory disorders. PDE5 inhibitors, including sildenafil, tadalafil and vardenafil, are marketed for the treatment of erectile dysfunction and arterial pulmonary hypertension due to their vasodilatory properties. The ability of PDE5 inhibitors to interfere with the NO/cGMP/PKG/CREB signaling pathway by increasing the levels of cGMP has prompted the hypothesis that PDE5 inhibition might be used as an effective therapeutic strategy for the treatment of AD. To this end, newly designed PDE5 inhibitors belonging to different chemical classes with improved pharmacologic profile (e.g. higher potency, improved selectivity, and blood-brain barrier penetration) have been synthesized and evaluated in several animal models of AD. In addition, recent medicinal chemistry effort has led to the development of agents concurrently acting on the PDE5 enzyme and a second target involved in AD. Both marketed and investigational PDE5 inhibitors have shown to reverse cognitive defects in young and aged wild type mice as well as transgenic mouse models of AD and tauopathy using a variety of behavioral tasks. These studies confirmed the therapeutic potential of PDE5 inhibitors as cognitive enhancers. However, clinical studies assessing cognitive functions using marketed PDE5 inhibitors have not been conclusive. Drug discovery efforts by our group and others are currently directed towards the development of novel PDE5 inhibitors tailored to AD with improved pharmacodynamic and pharmacokinetic properties. In summary, the present perspective reports an overview of the correlation between the NO signaling and AD, as well as an outline of the PDE5 inhibitors used as an alternative approach in altering the NO pathway leading to an improvement of learning and memory. The last two sections describe the preclinical and clinical evaluation of PDE5 inhibitors for the treatment of AD, providing a comprehensive analysis of the current status of the AD drug discovery efforts involving PDE5 as a new therapeutic target.

Pro-cognitive effect of upregulating cyclic guanosine monophosphate signalling during memory acquisition or early consolidation is mediated by increased AMPA receptor trafficking.

BACKGROUND: Episodic memory consists of different mnemonic phases, including acquisition and early and late consolidation. Each of these phases is characterised by distinct molecular processes. Although both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are implicated in the acquisition phase, early consolidation only depends on cGMP, whereas late consolidation is mediated by cAMP. Accordingly, the cGMP-selective phosphodiesterase 5 (PDE5) inhibitor vardenafil or the cAMP-selective PDE4 inhibitor rolipram can improve memory acquisition or consolidation when applied during their respective time windows. AIMS: Considering the important role of glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) during normal memory function, we aimed to investigate whether the differential actions of these PDE inhibitors are mediated through AMPAR dynamics. METHODS: For biochemical analysis, mice were treated with either vardenafil or rolipram and sacrificed shortly after injection. For the behavioural studies, mice received either of the inhibitors during the different mnemonic phases, while their spatial memory was tested using the object location task, and they were sacrificed 24 hours later. RESULTS: Administration of either vardenafil or rolipram causes rapid changes in AMPARs. Moreover, treatment with vardenafil during the acquisition or early consolidation of spatial memory resulted in increased surface levels of AMPARs which were still augmented 24 hours after learning. Membrane levels of AMPARs were not affected anymore 24 hours after learning when rolipram was administrated at either the acquisition or late consolidation phase. CONCLUSIONS: These results suggest that dissociative molecular mechanisms could mediate the pro-cognitive function of different classes of PDE inhibitors, and in the case of vardenafil, this phenomenon could be explained by changes in AMPAR dynamics.

Synaptic and memory dysfunction induced by tau oligomers is rescued by up-regulation of the nitric oxide cascade.

BACKGROUND: Soluble aggregates of oligomeric forms of tau protein (oTau) have been associated with impairment of synaptic plasticity and memory in Alzheimer's disease. However, the molecular mechanisms underlying the synaptic and memory dysfunction induced by elevation of oTau are still unknown. METHODS: This work used a combination of biochemical, electrophysiological and behavioral techniques. Biochemical methods included analysis of phosphorylation of the cAMP-responsive element binding (CREB) protein, a transcriptional factor involved in memory, histone acetylation, and expression immediate early genes c-Fos and Arc. Electrophysiological methods included assessment of long-term potentiation (LTP), a type of synaptic plasticity thought to underlie memory formation. Behavioral studies investigated both short-term spatial memory and associative memory. These phenomena were examined following oTau elevation. RESULTS: Levels of phospho-CREB, histone 3 acetylation at lysine 27, and immediate early genes c-Fos and Arc, were found to be reduced after oTau elevation during memory formation. These findings led us to explore whether up-regulation of various components of the nitric oxide (NO) signaling pathway impinging onto CREB is capable of rescuing oTau-induced impairment of plasticity, memory, and CREB phosphorylation. The increase of NO levels protected against oTau-induced impairment of LTP through activation of soluble guanylyl cyclase. Similarly, the elevation of cGMP levels and stimulation of the cGMP-dependent protein kinases (PKG) re-established normal LTP after exposure to oTau. Pharmacological inhibition of cGMP degradation through inhibition of phosphodiesterase 5 (PDE5), rescued oTau-induced LTP reduction. These findings could be extrapolated to memory because PKG activation and PDE5 inhibition rescued oTau-induced memory impairment. Finally, PDE5 inhibition re-established normal elevation of CREB phosphorylation and cGMP levels after memory induction in the presence of oTau. CONCLUSIONS: Up-regulation of CREB activation through agents acting on the NO cascade might be beneficial against tau-induced synaptic and memory dysfunctions.

Effects of DNA methyltransferase inhibition on pattern separation performance in mice.

Enhancement of synaptic plasticity through changes in neuronal gene expression is a prerequisite for improved cognitive performance. Moreover, several studies have shown that DNA methylation is able to affect the expression of (e.g. plasticity) genes that are important for several cognitive functions. In this study, the effect of the DNA methyltransferase (DNMT) inhibitor RG108 was assessed on object pattern separation (OPS) task in mice. In addition, its effect on the expression of target genes was monitored. Administration of RG108 before the test led to a short-lasting, dose-dependent increase in pattern separation memory that was not present anymore after 48 h. Furthermore, treatment with RG108 did not enhance long-term memory of the animals when tested after a 24 h inter-trial interval in the same task. At the transcriptomic level, acute treatment with RG108 was accompanied by increased expression of Bdnf1, while expression of Bdnf4, Bdnf9, Gria1 and Hdac2 was not altered within 1 h after treatment. Methylation analysis of 14 loci in the promoter region of Bdnf1 revealed a counterintuitive increase in the levels of DNA methylation at three CpG sites. Taken together, these results indicate that acute administration of RG108 has a short-lasting pro-cognitive effect on object pattern separation that could be explained by increased Bdnf1 expression. The observed increase in Bdnf1 methylation suggests a complex interplay between Bdnf methylation-demethylation that promotes Bdnf1 expression and associated cognitive performance. Considering that impaired pattern separation could constitute the underlying problem of a wide range of mental and cognitive disorders, pharmacological agents including DNA methylation inhibitors that improve pattern separation could be compelling targets for the treatment of these disorders. In that respect, future studies are needed in order to determine the effect of chronic administration of such agents.

Preparation of Tau Oligomers After the Protein Extraction from Bacteria and Brain Cortices.

Oligomerization of soluble tau protein is attracting the attention of an increasingly larger number of scientists involved in research on Alzheimer's disease and other tauopathies. A variety of methods have been developed for the purification of proteins from biological tissues and bacterial cells. Various types of high performance liquid chromatography (HPLC) and affinity tags represent the most common techniques for isolating proteins. Here, we describe a procedure for extracting recombinant tau protein from bacterial cells, utilizing a 6×His affinity tag, or endogenous tau from brain cortices using acid extraction followed by fast protein liquid chromatography (FPLC). Additionally, we introduce a method for oligomerization based on reduction and oxidation of cysteine residues. Our preparation assures high yield of tau protein, while preserving its physiological function.

Physiological and pathological processes of synaptic plasticity and memory in drug discovery: Do not forget the dose-response curve.

The response of a biological system to an endogenous or exogenous molecule depends upon the dose. For this reason, performing dose-response curves is crucial to understand physiological and pathophysiological phenomena, and to predict the effect of a drug. Most of the studies in pharmacological research have been performed according to the classical threshold model, focusing on higher doses able to ensure a biological effect. However, recent evidences pointed out the need to investigate the effect of low doses. Indeed, several molecules behave in a hormetic fashion, i.e. low-doses stimulate whereas high-doses inhibit a biological response. This is particularly interesting in CNS, where several physiological molecules involved in neuronal transmission during learning and memory have shown a biphasic effect that might represent the link between physiology and pathology. In this review we will focus on cholinergic, glutamatergic and nitrinergic transmission, because of their central role in learning and memory and their impairment in neurodegenerative disorders such as Alzheimer's disease. Pre-clinical studies performed on healthy adult animals and aged animals, as well as transgenic animal models of AD, have suggested a biphasic DR for acetylcholine, glutamate and nitric oxide. This stresses the relevance to perform DR curves when studying the mechanisms underlying synaptic plasticity and memory, the pharmacological profile of cognitive-enhancing drugs acting on these systems, and the possibility to combine low/ineffective doses of drugs that might have additive/synergistic effects, reducing the unwanted side effects associated to the high doses.

Memory-enhancing effects of GEBR-32a, a new PDE4D inhibitor holding promise for the treatment of Alzheimer's disease.

Memory loss characterizes several neurodegenerative disorders, including Alzheimer's disease (AD). Inhibition of type 4 phosphodiesterase (PDE4) and elevation of cyclic adenosine monophosphate (cAMP) has emerged as a promising therapeutic approach to treat cognitive deficits. However, PDE4 exists in several isoforms and pan inhibitors cannot be used in humans due to severe emesis. Here, we present GEBR-32a, a new PDE4D full inhibitor that has been characterized both in vitro and in vivo using biochemical, electrophysiological and behavioural analyses. GEBR-32a efficiently enhances cAMP in neuronal cultures and hippocampal slices. In vivo pharmacokinetic analysis shows that GEBR-32a is rapidly distributed within the central nervous system with a very favourable brain/blood ratio. Specific behavioural tests (object location and Y-maze continuous alternation tasks) demonstrate that this PDE4D inhibitor is able to enhance memory in AD transgenic mice and concomitantly rescues their hippocampal long-term potentiation deficit. Of great relevance, our preliminary toxicological analysis indicates that GEBR-32a is not cytotoxic and genotoxic, and does not seem to possess emetic-like side effects. In conclusion, GEBR-32a could represent a very promising cognitive-enhancing drug with a great potential for the treatment of Alzheimer's disease.