Amylovis-201 enhances physiological memory formation and rescues memory and hippocampal cell loss in a streptozotocin-induced Alzheimer's disease animal model.

Alzheimer's disease is the most common neurodegenerative disease, and its treatment is lacking. In this work, we tested Amylovis-201, a naphthalene-derived compound, as a possible therapeutic candidate for the treatment of AD. For this purpose, we performed three experiments. In the first and third experiment, animals received a bilateral administration of streptozotocin and, starting 24 h after injection, a daily dose of Amylovis-201 (orally), for 17 days or for the whole time of the experiment respectively (28 days), after which learning and memory, as well as the number of hippocampal dentate gyrus cells, were assessed. In the second experiment, healthy animals received a single dose of Amylovis-201, 10 min or 5 h after the learning section to assess whether this substance could promote specific mechanisms involved in memory trace formation. Our data show that, administration of a single dose of Amylovis-201, 10 min after the end of training, but not at 5 h, produces a prolongation in memory duration, probably because it modulates specific mechanisms involved in memory trace consolidation. Furthermore, daily administration of Amylovis-201 to animals with bilateral intracerebroventricular injection of STZ produces a reduction in the loss of the hippocampus dentate gyrus cells and an improvement in spatial memory, probably because Amylovis-201 can interact with some of the protein kinases of the insulin signaling cascade, also involved in neural plasticity, and thereby halt or reverse some of the effects of STZ. Taking to account these results, Amylovis-201 is a good candidate for the therapeutic treatment of AD.

Learning induces EPO/EPOr expression in memory relevant brain areas, whereas exogenously applied EPO promotes remote memory consolidation.

Memory and learning allow animals to appropriate certain properties of nature with which they can navigate in it successfully. Memory is acquired slowly and consists of two major phases, a fragile early phase (short-term memory, <4 h) and a more robust and long-lasting late one (long-term memory, >4 h). Erythropoietin (EPO) prolongs memory from 24 to 72 h when animals are trained for 5 min in a place recognition task but not when training lasted 3 min (short-term memory). It is not known whether it promotes the formation of remote memory (≥21 days). We address whether the systemic administration of EPO can convert a short-term memory into a long-term remote memory, and the neural plasticity mechanisms involved. We evaluated the effect of training duration (3 or 5 min) on the expression of endogenous EPO and its receptor to shed light on the role of EPO in coordinating mechanisms of neural plasticity using a single-trial spatial learning test. We administered EPO 10 min post-training and evaluated memory after 24 h, 96 h, 15 days, or 21 days. We also determined the effect of EPO administered 10 min after training on the expression of arc and bdnf during retrieval at 24 h and 21 days. Data show that learning induces EPO/EPOr expression increase linked to memory extent, exogenous EPO prolongs memory up to 21 days; and prefrontal cortex bdnf expression at 24 h and in the hippocampus at 21 days, whereas arc expression increases at 21 days in the hippocampus and prefrontal cortex.

A unique erythropoietin dosage induces the recovery of long-term synaptic potentiation in fimbria-fornix lesioned rats.

Synapses can experience long-term enhancements in its efficacy transmission in an activity-dependent manner (LTP, Long-Term Potentiation). This could contribute to store the living experiences in memory. Consequently, loss of synaptic plasticity can lead to failures in memory encoding and storage. Hence, finding ways to restore synaptic function can help restore learning and memory ability. Erythropoietin (EPO) has shown beneficial effects in the brain as a neuroprotector, improving affected learning, memory, and synaptic plasticity among other. In the present study, using the fimbria-fornix lesion model, we address the question whether the administration of erythropoietin restores the synaptic capacity to produce long-lasting increases in their transmission efficiency. A series of experiments was designed in which a control group of healthy young animals and one of injured young animals were formed. A subgroup of injured animals was injected with EPO or the vehicle in which the EPO is diluted (Veh). EPO or Veh was administered 15 min before LTP induction. Our data show that EPO produces a recovery in LTP in the group of fimbria-fornix lesioned animals, which show a severe impairment in the maintenance of LTP. Furthermore, LTP in the injured animals that received EPO was similar to that of the healthy control animals. LTP is widely accepted as a cellular mechanism of memory. Restoring LTP by EPO might be a potential tool for the treatment of memory disturbing diseases like Alzheimers disease. Ongoing clinical trials are evaluating a potential therapeutic effect of low sialic acid-EPO (NeuroEPO) on degenerative diseases.

Basolateral amygdala stimulation plus water maze training restore dentate gyrus LTP and improve spatial learning and memory.

Synaptic plasticity is a key mechanism of neural plasticity involved in learning and memory. A reduced or impaired synaptic plasticity could lead to a deficient learning and memory. On the other hand, besides reducing hipocampal dependent learning and memory, fimbria-fornix lesion affects LTP. However, we have consistently shown that stimulation of the basolateral amygdala (BLA) 15 min after water maze training is able to improve spatial learning and memory in fimbria fornix lesioned rats while also inducing changes in the expression of plasticity-related genes expression in memory associated brain regions like the hippocampus and prefrontal cortex. In this study we test that hypothesis: whether BLA stimulation 15 min after water maze training can improve LTP in the hippocampus of fimbria-fornix lesioned rats. To address this question, we trained fimbria-fornix lesioned rats in water maze for four consecutive days, and the BLA was bilaterally stimulated 15 min after each training session.Our data show that trained fimbria-fornix lesioned rats develop a partially improved LTP in dentated gyrus compared with the non-trained fimbria-fornix lesioned rats. In contrast, dentated gyrus LTP in trained and BLA stimulated fimbria-fornix lesioned rats improved significantly compared to the trained fimbria-fornix lesioned rats, but was not different from that shown by healthy animals. BLA stimulation in non-trained FF lesioned rats did not improve LTP; instead produces a transient synaptic depression. Restoration of the ability to develop LTP by the combination of training and BLA stimulation would be one of the mechanisms involved in ameliorating memory deficits in lesioned animals.

Alzheimer's Disease, Neural Plasticity, and Functional Recovery.

Alzheimer's disease (AD) is the most common and devastating neurodegenerative condition worldwide, characterized by the aggregation of amyloid-ß and phosphorylated tau protein, and is accompanied by a progressive loss of learning and memory. A healthy nervous system is endowed with synaptic plasticity, among others neural plasticity mechanisms, allowing structural and physiological adaptations to changes in the environment. This neural plasticity modification sustains learning and memory, and behavioral changes and is severely affected by pathological and aging conditions, leading to cognitive deterioration. This article reviews critical aspects of AD neurodegeneration as well as therapeutic approaches that restore neural plasticity to provide functional recoveries, including environmental enrichment, physical exercise, transcranial stimulation, neurotrophin involvement, and direct electrical stimulation of the amygdala. In addition, we report recent behavioral results in Octodon degus, a promising natural model for the study of AD that naturally reproduces the neuropathological alterations observed in AD patients during normal aging, including neuronal toxicity, deterioration of neural plasticity, and the decline of learning and memory.

Amygdala stimulation ameliorates memory impairments and promotes c-Fos activity in fimbria-fornix-lesioned rats.

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits.

[18F]Amylovis as a Potential PET Probe for ß-Amyloid Plaque: Synthesis, In Silico, In vitro and In vivo Evaluations.

BACKGROUND: Alzheimer's disease (AD) is the most common form of dementia. Neuroimaging methods have widened the horizons for AD diagnosis and therapy. The goals of this work are the synthesis of 2-(3-fluoropropyl)-6-methoxynaphthalene (5) and its [18F]-radiolabeled counterpart ([18F]Amylovis), the in silico and in vitro comparative evaluations of [18F]Amylovis and [11C]Pittsburg compound B (PIB) and the in vivo preclinical evaluation of [18F]Amylovis in transgenic and wild mice. METHODS: Iron-catalysis cross coupling reaction, followed by fluorination and radiofluorination steps were carried out to obtain 5 and 18F-Amylovis. Protein/Aß plaques binding, biodistribution, PET/CT Imaging and immunohistochemical studies were conducted in healthy/transgenic mice. RESULTS: The synthesis of 5 was successful obtained. Comparative in silico studies predicting that 5 should have affinity to the Aß-peptide, mainly through π-π interactions. According to a dynamic simulation study the ligand-Aß peptide complexes are stable in simulation-time (ΔG = -5.31 kcal/mol). [18F]Amylovis was obtained with satisfactory yield, high radiochemical purity and specific activity. The [18F]Amylovis log Poct/PBS value suggests its potential ability for crossing the blood brain barrier (BBB). According to in vitro assays, [18F]Amylovis has an adequate stability in time. Higher affinity to Aß plaques were found for [18F]Amylovis (Kd 0.16 nmol/L) than PIB (Kd 8.86 nmol/L) in brain serial sections of 3xTg-AD mice. Biodistribution in healthy mice showed that [18F]Amylovis crosses the BBB with rapid uptake (7 %ID/g at 5 min) and good washout (0.11±0.03 %ID/g at 60 min). Comparative PET dynamic studies of [18F]Amylovis in healthy and transgenic APPSwe/PS1dE9 mice, revealed a significant high uptake in the mice model. CONCLUSION: The in silico, in vitro and in vivo results justify that [18F]Amylovis should be studied as a promissory PET imaging agent to detect the presence of Aß senile plaques.

EPO induces changes in synaptic transmission and plasticity in the dentate gyrus of rats.

Erythropoietin has shown wide physiological effects on the central nervous system in animal models of disease, and in healthy animals. We have recently shown that systemic EPO administration 15 min, but not 5 h, after daily training in a water maze is able to induce the recovery of spatial memory in fimbria-fornix chronic-lesioned animals, suggesting that acute EPO triggers mechanisms which can modulate the active neural plasticity mechanism involved in spatial memory acquisition in lesioned animals. Additionally, this EPO effect is accompanied by the up-regulation of plasticity-related early genes. More remarkably, this time-dependent effects on learning recovery could signify that EPO in nerve system modulate specific living-cellular processes. In the present article, we focus on the question if EPO could modulate the induction of long-term synaptic plasticity like LTP and LTD, which presumably could support our previous published data. Our results show that acute EPO peripheral administration 15 min before the induction of synaptic plasticity is able to increase the magnitude of the LTP (more prominent in PSA than fEPSP-Slope) to facilitate the induction of LTD, and to protect LTP from depotentiation. These findings showing that EPO modulates in vivo synaptic plasticity sustain the assumption that EPO can act not only as a neuroprotective substance, but is also able to modulate transient neural plasticity mechanisms and therefore to promote the recovery of nerve function after an established chronic brain lesion. According to these results, EPO could be use as a molecular tool for neurorestaurative treatments.

Erythropoietin Promotes Neural Plasticity and Spatial Memory Recovery in Fimbria-Fornix-Lesioned Rats.

BACKGROUND: Erythropoietin (EPO) upregulates the mitogen activated protein kinase (MAPK) cascade, a central signaling pathway in cellular plastic mechanisms, and is critical for normal brain development. OBJECTIVE: We hypothesized that EPO could modulate the plasticity mechanisms supporting spatial memory recovery in fimbria-fornix-transected animals. METHODS: Fimbria-fornix was transected in 3 groups of rats. Seven days later, EPO was injected daily for 4 consecutive days within 10 minutes after training on a water maze task. RESULTS: Our results show that EPO injections 10 minutes after training produced a substantial spatial memory recovery in fimbria-fornix-lesioned animals. In contrast, an EPO injection shortly after fimbria-fornix lesion surgery does not promote spatial-memory recovery. Neither does daily EPO injection 5 hours after the water maze performance. EPO, on the other hand, induced the expression of plasticity-related genes like arc and bdnf, but this effect was independent of training or lesion. CONCLUSIONS: This finding supports our working hypothesis that EPO can modulate transient neuroplastic mechanisms triggered by training in lesioned animals. Consequently, we propose that EPO administration can be a useful trophic factor to promote neural restoration when given in combination with training.

Hippocampal neurotrophins after stimulation of the basolateral amygdala, and memory improvement in lesioned rats.

PURPOSE: To investigate a possible role of neurotrophins in the memory improving effect of stimulating the basolateral amygdala. METHODS: The BDNF and NGF levels were measured in the hippocampus of fimbria-fornix lesioned male rats after four days of training in the water maze and stimulation of the basolateral amygdala. RESULTS: The behavioral results confirm that daily post-training stimulation of the amygdala improves the learning abilities of the lesioned animals. BDNF increased in lesioned and trained animals, but stimulating the basolateral amygdala induces a significantly greater increase. NGF showed a slight (but significant) increase in fimbria-fornix lesioned and trained animals, but stimulating the amygdala does not produce a further increase. In separate groups of animals we measured the levels of both neurotrophins in acute experiments, after 2 and 24 hours of stimulating the amygdala. BDNF was significantly increased at both times, while NGF showed again only slight increases (significant at 24 h). CONCLUSIONS: These results suggest that the BDNF response to amygdala stimulation might be of functional importance in the observed learning improvement. The changes in NGF are most likely due to the accumulation of this protein after removal of the septal axons.

Novelty exposure overcomes foot shock-induced spatial-memory impairment by processes of synaptic-tagging in rats.

Novelty processing can transform short-term into long-term memory. We propose that this memory-reinforcing effect of novelty could be explained by mechanisms outlined in the "synaptic tagging hypothesis." Initial short-term memory is sustained by a transient plasticity change at activated synapses and sets synaptic tags. These tags are later able to capture and process the plasticity-related proteins (PRPs), which are required to transform a short-term synaptic change into a long-term one. Novelty is involved in inducing the synthesis of PRPs [Moncada D, et al. (2011) Proc Natl Acad Sci USA 108:12937-12936], which are then captured by the tagged synapses, consolidating memory. In contrast to novelty, stress can impair learning, memory, and synaptic plasticity. Here, we address questions as to whether novelty-induced PRPs are able to prevent the loss of memory caused by stress and if the latter would not interact with the tag-setting process. We used water-maze (WM) training as a spatial learning paradigm to test our hypothesis. Stress was induced by a strong foot shock (FS; 5 × 1 mA, 2 s) applied 5 min after WM training. Our data show that FS reduced long-term but not short-term memory in the WM paradigm. This negative effect on memory consolidation was time- and training-dependent. Interestingly, novelty exposure prevented the stress-induced memory loss of the spatial task and increased BDNF and Arc expression. This rescuing effect was blocked by anisomycin, suggesting that WM-tagged synapses were not reset by FS and were thus able to capture the novelty-induced PRPs, re-establishing FS-impaired long-term memory.