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Query: UMLS:C0751295 (memory loss)
 3,619 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The case of HM, a man with intractable epilepsy who became amnesic following bilateral medial temporal lobe surgery nearly half a century ago has instigated ongoing research and theoretical speculation on the nature of memory and the role of the hippocampus. Neuropsychological testing showed that although HM had extensive anterograde memory loss he could still acquire motor and cognitive skills implicitly, but could not remember the context of this learning. This has lead to declarative and procedural descriptions of the memory process. Cholinergic and monoaminergic neurotransmitter systems have also been implicated in the memory process and anticholinergic drugs traditionally have been associated with impairment of declarative memory. The cholinergic hypothesis of Alzheimer's disease is a classic example of an application of these neuropharmacological findings. In schizophrenia, preattentive deficits have been amply demonstrated by unconscious priming studies. Memory processes are also impaired in these patients. Dopamine, glutamate and even cholinergic dysfunction has been implicated in the clinical picture of schizophrenia. The present paper will attempt to bring together both the anatomical and pharmacological data from these disparate fields of research under a cohesive theory of cognition and memory. A hypothesis is presented for an inverse relationship between monoaminergic and cholinergic systems in the modulation of implicit (unconscious) and explicit (conscious) cognitive processes. It is postulated that muscarinic cholinergic receptors and monoaminergic systems facilitate unconscious and conscious processes, respectively, and they disfacilitate conscious and unconscious processes, respectively (the purported inverse relationship). In fact, the muscarinic and monoaminergic modulations of a neural network are proposed to be finely balanced such that, if, the activity of one receptor system is modified then this by necessity has effects on the other system. It takes into account receptor subtypes and their effects mediated through excitatory and inhibitory G-protein complexes. For example, m1/D2 and D1/m4 paired receptor subtypes, colocalized on separate neurons would have opposing functional effects. A theory is then presented that the critical underlying pathophysiology of schizophrenia involves a hypofunctional muscarinic cholinergic system, which induces abnormal facilitation of monoaminergic subsystems such as dopamine (e.g., a decrease in m1R function would potentiate D2R function). This extends the idea of an inverted U function for optimal monoaminergic concentrations. Not only would this impair unconscious preattentive processes, but according to the hypothesis, explicit cognition as well including memory deficits and would underlie the mechanism of psychosis. Contrary to current thinking a different view is also presented for the role of the hippocampus in the memory process. It is postulated that long-term explicit memory traces in the neocortex are laid down by phasic coactivation of forebrain projecting monoaminergic systems above some basal firing rate, such as the rostral serotonergic raphe, which projects diffusely to the cortex and according to a modified Hebbian principle. This is the proposed principal function of the hippocampal theta rhythm. The phasic activation of the cholinergic basal forebrain is mediated by projections from a separate cortical structure, possibly the lateral prefrontal cortex. Phasic muscarinic receptor activation is proposed to strengthen implicit memory traces (at a synaptic level) in the neocortex. Thus, the latter are spared by medial temporal surgery explaining the dissociation of explicit from implicit memory.
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PMID:Neuropharmacology of cognition and memory: a unifying theory of neuromodulator imbalance in psychiatry and amnesia. 1630 Sep 5

Ten patients treated with electroconvulsive therapy (ECT) for depressive illness received anesthesia with either etomidate or ketamine. Three patients received both etomidate and ketamine anesthesia for ECT during separate episodes of depression. Patients anesthetized with ketamine for ECT had significantly less impairment of short-term memory function than did patients who received ECT with etomidate anesthesia. All patients who received both anesthetics for ECT during 2 different episodes had less memory loss during ECT with ketamine than with etomidate. These results show the importance of studying the effects of all anesthetic agents used during ECT on cognitive functions. The results imply that the effect of ECT on memory may be largely caused by effects mediated by glutamate at N-methyl-d-aspartate receptors and suggest that N-methyl-d-aspartate antagonists may offer protection from memory dysfunction during ECT.
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PMID:Ketamine appears associated with better word recall than etomidate after a course of 6 electroconvulsive therapies. 1680 24

Glycolysis and glycogenolysis are involved in memory processing in day-old chickens and, aside from the provision of energy for neuronal and astrocytic energy metabolism these pathways enable astrocytes to supply neurones with precursor for transmitter glutamate by glucose-based de novo synthesis. We have previously shown that memory processing for bead discrimination learning is dependent on glycolysis; however, the metabolic inhibitor used, iodoacetate, inhibits pyruvate formation from both glucose and glycogen. At specific time points after training transient reductions in brain glycogen content occur, mirrored by increases in glutamate/glutamine content. In the present study, we used intracerebral injection of a glycogen phosphorylase inhibitor, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB), which does not affect glucose breakdown, to evaluate the role of glycogen metabolism in memory consolidation. Dose-dependent inhibition of learning occurred when DAB was administered at specific time periods in relation to training: (i) 5 min before training, (ii) around 30 min posttraining, and (iii) 55 min posttraining. After injection at either of the two earlier periods, memory disappeared after consolidation 30 min postlearning, and after injection 55 min after learning memory was absent at 70 min. The memory loss caused by early administration could be prevented after training by central injection of the glutamate precursor glutamine or the astrocyte-specific substrate acetate together with aspartate, substituting for pyruvate carboxylation. Thus, glycogenolysis is essential for learning in this paradigm and, aside from energy supply considerations, we suggest that an important role for glycogenolysis is to provide neurones with glutamine as the precursor for neuronal glutamate and GABA.
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PMID:Inhibition of glycogenolysis in astrocytes interrupts memory consolidation in young chickens. 1681 64

In addition to its definitive pathological characteristics, neuritic plaques and neurofibrillary tangles, Alzheimer's disease (AD) brain exhibits regionally variable neuronal loss and synaptic dysfunction that are likely to underlie the symptomatic memory loss and language abnormalities. A number of mechanisms that could give rise to this localized damage have been proposed, amongst which excitotoxicity figures prominently. This is the process, well attested in experimental systems, whereby brain cells are excited to death by the pathophysiological action of the brain's most-abundant excitatory transmitter, glutamate. Glutamate transmission is mediated by a range of ionotropic and metabotropic receptors which, when activated, can lead to depolarization and increased intracellular Ca2+ ion concentration in the cells on which they are located. The action of glutamate is terminated by its removal from these receptor sites by transport into nearby cells, most commonly perisynaptic astrocytes. There it is converted to physiologically inert glutamine and shuttled back to excitatory nerve terminals. Malfunctions in components of the glutamate-glutamine cycle could result in a self-perpetuating neuronal death cascade mediated by glutamate. The approval by the FDA of an ionotropic glutamate receptor antagonist to treat late-stage AD has led to renewed interest in the contribution of altered glutamatergic neurotransmission to disease pathogenesis. This review encompasses those aspects of glutamate-glutamine cycling that are altered in AD.
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PMID:Glutamate-glutamine cycling in Alzheimer's disease. 1714 74

Bead discrimination learning in day-old chicken was inhibited by bilateral injection into the intermediate medial mesopallium (IMM), a homolog of the mammalian brain cortex, of the poorly metabolized enantiomer of L-lactate, D-lactate. The window of vulnerability extended from 10 min before training to 20 min after training. Unilateral injection 10 min before training inhibited only in the left IMM, whereas 10 min after training injection was only inhibitory if made into the right hemisphere. The pre-training administration caused memory loss from the earliest time tested whereas memory was maintained for another 20 min when D-lactate was injected 10 min post-training. The ability of acetate, an astrocyte-specific substrate, injected into the IMM to counteract the inhibitory effect was tested. Following D-lactate injection 10 min before training, rescue of memory immediately after training was achieved by acetate as long as aspartate, an oxaloacetate precursor, was also present. This suggests that pyruvate carboxylation is necessary for net synthesis of glutamate, which is known to occur at this time [Gibbs, M.E., Lloyd, H.G.E., Santa, T., Hertz, L., 2007. Glycogen is a preferred glutamate precursor during learning in 1-day-old chick: biochemical and behavioral evidence. J. Neurosci. Res., 85, 3326-3333]. However, acetate alone rescued memory 20 min post-training (following d-lactate injection 10 min after training), indicating that pyruvate at this time is used for energy production, consistent with memory inhibition by dinitrophenol. These findings suggest that D-lactate acts by inhibiting uptake of L-lactate into astrocytes (an extracellular effect) or metabolism of pyruvate in astrocytic mitochondria (an intracellular effect). An apparent lag phase between the administration of d-lactate and its inhibition of learning favors the latter possibility. Thus, under the present experimental conditions D-lactate acts as an astrocytic metabolic inhibitor rather than as an inhibitor of neuronal L-lactate uptake, as has occasionally been suggested. Analogously, a rare reversible neurological syndrome with memory deficits, D-lactate encephalopathy, may mainly or exclusively be due to astrocytic malfunction.
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PMID:Inhibition of astrocytic energy metabolism by D-lactate exposure impairs memory. 1806 42

After infection with RML murine scrapie agent, transgenic (tg) mice expressing prion protein (PrP) without its glycophosphatidylinositol (GPI) membrane anchor (GPI(-/-) PrP tg mice) continue to make abundant amounts of the abnormally folded disease-associated PrPres but have a normal life span. In contrast, all age-, sex-, and genetically matched mice with a GPI-anchored PrP become moribund and die due to a chronic progressive neurodegenerative disease by 160 days after RML scrapie agent infection. We report here that infected GPI(-/-) PrP tg mice, although free from progressive neurodegenerative disease of the cerebellum and extrapyramidal and pyramidal systems, nevertheless suffer defects in learning and memory, long-term potentiation, and neuronal excitability. Such dysfunction increases over time and is associated with an increase in gamma aminobutyric acid (GABA) inhibition but not loss of excitatory glutamate/N-methyl-d-aspartic acid. Enhanced deposition of abnormally folded infectious PrP (PrPsc or PrPres) in the central nervous system (CNS) localizes with GABAA receptors. This occurs with minimal evidence of CNS spongiosis or apoptosis of neurons. The use of monoclonal antibodies reveals an association of PrPres with GABAA receptors. Thus, the clinical defects of learning and memory loss in vivo in GPI(-/-) PrP tg mice infected with scrapie agent may likely involve the GABAergic pathway.
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PMID:Scrapie-induced defects in learning and memory of transgenic mice expressing anchorless prion protein are associated with alterations in the gamma aminobutyric acid-ergic pathway. 1866 94

We describe neuronal density, neuroplasticity and vascular remodelling and their association with spatial memory in young (4-6 months), middle-aged (9-11 months) and aged (18-20 months) rats of both genders. The neuronal density was reduced in the hippocampus of middle-aged and aged rats, particularly in male rats. However the loss of spatial memory investigated using the Morris water maze, T-maze and 8-radial arm maze tests was found only in the aged groups. The data suggested a pre-symptomatic period of pathological brain aging. Surprisingly, the middle-aged groups showed an elevation of glutamate-decarboxylase immunoreactive neurons in the hippocampus and the striatum, an increase of dopamine output in the striatum and enhanced vascular remodelling in the hippocampus when compared with the young and, in some cases, aged groups. Together, the data suggest that the loss of neurons during midlife may stimulate and enhance neuronal plasticity and vascular remodelling. These compensatory responses to initial neuronal degeneration may play a role in delaying impending memory loss during the pre-symptomatic period of pathological brain aging.
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PMID:Correlation of cellular changes and spatial memory during aging in rats. 1876 Oct 81

One of the crucial events in the pathogenesis of neurodegenerative disorders linked with dementia-like Alzheimer's Disease (AD) is the disturbance in neurotransmission based on progressive deficit of neuromediators that is manifested by marked decrease in cognitive behavior, loss of memory and inability to learn as a result of impairment in synaptic plasticity of neurons. In this study we have used a new complex of proteoglycans of embryonic genesis (PEG) created by Prof. L. Mkrtchyan, as a possible therapeutic approach that can rescue neurons from further degeneration caused by beta-amyloid (Abeta). We attempt to reveal the biochemical (determination of neuroactive amino acids such as glutamate, GABA, taurine, glycine and aspartate) changes and behavior on Y-maze and avoidance/exploratory activity on elevated plus-maze task in rats' brain after modeling Alzheimer's disease by i.c.v. injection of Abeta25-35. Furthermore, in this study we analyzed the neuroprotective properties of PEG. Under the influence of PEG the concentration of all investigated amino acids both in cerebral cortex and hippocampus (except striatum changes) increased. In the present study we demonstrated that bilateral i.c.v. injection of aggregated Abeta25-35 in dosage 30nmol/rat resulted in impairment in spatial alternation behavior. Both preliminary (single) and double injection of PEG showed constant improvement of spatial memory after the first trial up to 90 days after i.c.v. injection of aggregated Abeta25-35. Our findings suggest that proteoglycans of embryonic genesis in neurodegenerative state show an expressed regulatory-protective effect.
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PMID:Effects of beta-amyloid on behavioral and amino acids spectrum in rats' brain and their modulation by embryonic proteins. 1912 56

Domoic acid is a potent neurotoxin that is naturally produced by several diatom species of the genus Pseudo-nitzschia. The toxin acts as a glutamate agonist and is excitotoxic in the vertebrate central nervous system and other glutamate receptor-rich organs. Human exposure to domoic acid occurs via the consumption of contaminated shellfish that have accumulated the toxin while filter feeding on toxigenic phytoplankton during blooms. The first reported human domoic acid poisoning event occurred in Canada in 1987 during which clinical signs of acute toxicity such as gastrointestinal distress, confusion, disorientation, memory loss, coma and death were observed. The illness was named amnesic shellfish poisoning (ASP) and due to effective seafood monitoring programs there have been no documented ASP cases since 1987. However, domoic acid poisoning has a significant effect on marine wildlife and multiple poisoning events have occurred in marine birds and mammals over the last few decades. Currently, domoic acid producing diatom blooms are thought to be increasing in frequency world wide, posing an increasing threat to wildlife and human health. Of particular concern are the potential impacts of long-term low-level exposure in "at risk" human populations. The impacts of repetitive low-level domoic acid exposure are currently unknown. This review provides a basic description of the mechanism of action of domoic acid as well as a synthesis of information pertaining to domoic acid exposure routes, toxin susceptibility, and the importance of effective monitoring programs. The importance of investigating the potential human health impacts of long-term low-level domoic acid exposure in "at risk" human populations is also discussed.
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PMID:Domoic acid and human exposure risks: a review. 1950 88

The present study investigated an ethanol extract of the aerial part of Aralia cordata Thunb. (Araliaceae) for possible neuroprotective effects on neurotoxicity induced by amyloid beta (Abeta) protein (25 - 35) in cultured rat cortical neurons and antidementia activity in mice. Exposure of cultured cortical neurons to 10 muM Abeta(25 - 35) for 36 h induced neuronal apoptotic death. At 1 - 10 mug/ml, A. cordata inhibited neuronal death, elevation of intracellular calcium ([Ca(2+)](i)), glutamate release into the medium, and generation of reactive oxygen species (ROS) induced by Abeta(25-35) in primary cultures of rat cortical neurons. Memory loss induced by intracerebroventricular injection of ICR mice with 15 nmol Abeta(25-35) was inhibited by chronic treatment with A. cordata (50 and 100 mg/kg, p.o. for 7 days) as measured by a passive avoidance test, and corresponding reductions were observed in brain cholinesterase activity and neuronal death measured histologically in the hippocampal region. Oleanolic acid isolated from A. cordata also inhibited neuronal death, elevation of [Ca(2+)](i), glutamate release, and generation of ROS induced by Abeta(25-35) in cultured rat cortical neurons, suggesting that the neuroprotective effect of A. cordata may be, at least in part, attributable to this compound. From these results, we suggest that the antidementia effect of A. cordata is due to its neuroprotective effect against Abeta(25-35)-induced neurotoxicity and that A. cordata may have a therapeutic role in preventing the progression of Alzheimer's disease.
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PMID:Aralia cordata protects against amyloid beta protein (25-35)-induced neurotoxicity in cultured neurons and has antidementia activities in mice. 1976 45


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