Administration of amyloid beta-peptides in the rat medial septum causes memory deficits: reversal by SR 57746A, a non-peptide neurotrophic compound

Modulation of learning and memory by natural polyamines

Spermine and spermidine are natural polyamines that are produced mainly via decarboxylation of l-ornithine and the sequential transfer of aminopropyl groups from S-adenosylmethionine to putrescine by spermidine synthase and spermine synthase. Spermine and spermidine interact with intracellular and extracellular acidic residues of different nature, including nucleic acids, phospholipids, acidic proteins, carboxyl- and sulfate-containing polysaccharides. Therefore, multiple actions have been suggested for these polycations, including modulation of the activity of ionic channels, protein synthesis, protein kinases, and cell proliferation/death, within others. In this review we summarize these neurochemical/neurophysiological/morphological findings, particularly those that have been implicated in the improving and deleterious effects of spermine and spermidine on learning and memory of naïve animals in shock-motivated and nonshock-motivated tasks, from a historical perspective. The interaction with the opioid system, the facilitation and disruption of morphine-induced reward and the effect of polyamines and putative polyamine antagonists on animal models of cognitive diseases, such as Alzheimer's, Huntington, acute neuroinflammation and brain trauma are also reviewed and discussed. The increased production of polyamines in Alzheimer's disease and the biphasic nature of the effects of polyamines on memory and on the NMDA receptor are also considered. In light of the current literature on polyamines, which include the description of an inborn error of the metabolism characterized by mild-to moderate mental retardation and polyamine metabolism alterations in suicide completers, we can anticipate that polyamine targets may be important for the development of novel strategies and approaches for understanding the etiopathogenesis of important central disorders and their pharmacological treatment.

Age-Dependent Effect of β-Amyloid Toxicity on Basal Forebrain Cholinergic Neurons and Inflammation in the Rat Brain

Beta-amyloid (Aβ) accumulation, neuroinflammation, basal forebrain cholinergic loss and hippocampal degeneration are well-described pathologies associated with Alzheimer's disease (AD). However, the role that age plays in the susceptibility of the brain to these AD pathologies and the relationships between them is still not well understood. This study investigated the age-related response to intracerebroventricular injection of Aβ(25-35) in 3-, 6- and 9-month-old rats. Aβ toxicity resulted in an age-related increase in cholinergic loss and microglial activation in the basal forebrain along with neuronal loss in the hippocampal CA3 subfield. Performance in the Morris water maze revealed impairments in long-term reference memory in 6-month-old Aβ administered animals, which was not seen in 3-month-old animals. These results support a role of Aβ administration in inducing age-dependent cholinergic loss and neuroinflammation, and additionally provide evidence for a more age-appropriate model of adult-onset Aβ toxicity demonstrating pathological changes that reflect the early stages of AD pathogenesis including neuroinflammation, cholinergic loss and beginning stages of memory impairment.

Estradiol prevents olfactory dysfunction induced by A-β 25-35 injection in hippocampus

Background

Some neurodegenerative diseases, such as Alzheimer and Parkinson, present an olfactory impairment in early stages, and sometimes even before the clinical symptoms begin. In this study, we assess the role of CA1 hippocampus (structure highly affected in Alzheimer disease) subfield in the rats’ olfactory behavior, and the neuroprotective effect of 17 beta estradiol (E₂) against the oxidative stress produced by the injection of amyloid beta 25–35.

Results

162 Wistar rats were ovariectomized and two weeks after injected with 2 μl of amyloid beta 25–35 (A-β_25–35) in CA1 subfield. Olfactory behavior was evaluated with a social recognition test, odor discrimination, and search tests. Oxidative stress was evaluated with FOX assay and Western Blot against 4-HNE, Fluoro Jade staining was made to quantify degenerated neurons; all these evaluations were performed 24 h, 8 or 15 days after A-β_25–35 injection. Three additional groups treated with 17 beta estradiol (E₂) were also evaluated. The injection of A-β_25–35 produced an olfactory impairment 24 h and 8 days after, whereas a partial recovery of the olfactory behavior was observed at 15 days. A complete prevention of the olfactory impairment was observed with the administration of E₂ two weeks before the amyloid injection (A-β_25–35 24 h + E₂) and one or two weeks after (groups 8 A-β +E₂ and 15 A-β +E₂ days, respectively); a decrease of the oxidative stress and neurodegeneration were also observed.

Conclusions

Our finding shows that CA1 hippocampus subfield plays an important role in the olfactory behavior of the rat. The oxidative stress generated by the administration of A-β_25–35 is enough to produce an olfactory impairment. This can be prevented with the administration of E₂ before and after amyloid injection. This suggests a possible therapeutic use of estradiol in Alzheimer’s disease.

Na+ and K+ ion imbalances in Alzheimer's disease

Alzheimer's disease (AD) is associated with impaired glutamate clearance and depressed Na(+)/K(+) ATPase levels in AD brain that might lead to a cellular ion imbalance. To test this hypothesis, [Na(+)] and [K(+)] were analyzed in postmortem brain samples of 12 normal and 16 AD individuals, and in cerebrospinal fluid (CSF) from AD patients and matched controls. Statistically significant increases in [Na(+)] in frontal (25%) and parietal cortex (20%) and in cerebellar [K(+)] (15%) were observed in AD samples compared to controls. CSF from AD patients and matched controls exhibited no differences, suggesting that tissue ion imbalances reflected changes in the intracellular compartment. Differences in cation concentrations between normal and AD brain samples were modeled by a 2-fold increase in intracellular [Na(+)] and an 8-15% increase in intracellular [K(+)]. Since amyloid beta peptide (Aβ) is an important contributor to AD brain pathology, we assessed how Aβ affects ion homeostasis in primary murine astrocytes, the most abundant cells in brain tissue. We demonstrate that treatment of astrocytes with the Aβ 25-35 peptide increases intracellular levels of Na(+) (~2-3-fold) and K(+) (~1.5-fold), which were associated with reduced levels of Na(+)/K(+) ATPase and the Na(+)-dependent glutamate transporters, GLAST and GLT-1. Similar increases in astrocytic Na(+) and K(+) levels were also caused by Aβ 1-40, but not by Aβ 1-42 treatment. Our study suggests a previously unrecognized impairment in AD brain cell ion homeostasis that might be triggered by Aβ and could significantly affect electrophysiological activity of brain cells, contributing to the pathophysiology of AD.

Behavioural and cellular effects of exogenous amyloid-β peptides in rodents

A better understanding of Alzheimer's disease (AD) and the development of disease modifying therapies are some of the biggest challenges of the 21st century. One of the core features of AD are amyloid plaques composed of amyloid-beta (Aβ) peptides. The first hypothesis proposed that cognitive deficits are linked to plaque-development and transgenic mice have been generated to study this link, thereby providing a good model to develop new therapeutic approaches. Since later it was recognised that in AD patients the cognitive deficit is rather correlated to soluble amyloid levels, consequently, a new hypothesis appeared associating the earliest amyloid toxicity to these soluble species. The purpose of this review is to give a summary of behavioural and cellular data obtained after soluble Aβ peptide administration into rodents' brain, thereby showing that this model is a valid tool to investigate AD pathology when no plaques are present. Additionally, this method offers an excellent, efficient model to test compounds which could act at such early stages of the disease.

Effects of Hericium erinaceus on amyloid β(25-35) peptide-induced learning and memory deficits in mice

The mushroom Hericium erinaceus has been used as a food and herbal medicine since ancient times in East Asia. It has been reported that H. erinaceus promotes nerve growth factor secretion in vitro and in vivo. Nerve growth factor is involved in maintaining and organizing cholinergic neurons in the central nervous system. These findings suggest that H. erinaceus may be appropriate for the prevention or treatment of dementia. In the present study, we examined the effects of H. erinaceus on amyloid β(25-35) peptide-induced learning and memory deficits in mice. Mice were administered 10 µg of amyloid β(25-35) peptide intracerebroventricularly on days 7 and 14, and fed a diet containing H. erinaceus over a 23-d experimental period. Memory and learning function was examined using behavioral pharmacological methods including the Y-maze test and the novel-object recognition test. The results revealed that H. erinaceus prevented impairments of spatial short-term and visual recognition memory induced by amyloid β(25-35) peptide. This finding indicates that H. erinaceus may be useful in the prevention of cognitive dysfunction.

Role of the glucose-dependent insulinotropic polypeptide and its receptor in the central nervous system: therapeutic potential in neurological diseases

Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid hormone, secreted from the enteroendocrine K cells, which has insulin-releasing and extra-pancreatic actions. GIP and its receptor present a widespread distribution in the mammalian brain where they have been implicated with synaptic plasticity, neurogenesis, neuroprotection and behavioral alterations. This review attempts to provide a comprehensive picture of the role of GIP in the central nervous system and to highlight recent findings from our group showing its potential involvement in neurological illnesses including epilepsies, Parkinson's disease and Alzheimer's disease.

SR 57746A/xaliproden, a non-peptide neurotrophic compound: prospects and constraints for the treatment of nervous system diseases

Neurodegenerative disorders such as Alzheimer's disease or amyotrophic lateral sclerosis as well as peripheral neuropathies are difficult to treat due to a limited range of effective drugs. Neurotrophic growth factors promote neuronal survival and differentiation and could hence be interesting tools to treat these diseases. Their therapeutic use is limited due their short half-life, their inability to cross the BBB and potential side effects including tumor promotion. SR 57746A is a non-peptide, orally active compound that exhibits neuroprotective effects in various model systems in vitro and in vivo. SR 57746A shows--amongst other activities--agonistic activity on 5-HT(1A) receptors. Several clinical trials examined SR 57746A in patients with Alzheimer's disease, amyotrophic lateral sclerosis or chemotherapy-induced peripheral sensory neuropathy. This article reviews the preclinical and clinical data on SR 57746A and points out potential future applications of this compound. However, due to disapointing results in phase III trials, Sanofi-Aventis recently decided to discontinue the development of this drug.

Chronic psychosocial stress exacerbates impairment of cognition and long-term potentiation in beta-amyloid rat model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a degenerative disorder that leads to progressive cognitive decline. Alzheimer's disease develops as a result of over-production and aggregation of beta-amyloid (Abeta) peptides in the brain. The reason for variation in the gravity of symptoms among AD patients is unknown and might result from patient-related factors including lifestyle. Individuals suffering from chronic stress are at an increased risk for developing AD. This study investigated the effect of chronic psychosocial stress in Abeta rat model of AD.

METHODS

Psychosocial stress was induced with a rat intruder model. The rat model of AD was induced by 14-day osmotic pump infusion of a mixture of 300 pmol/day Abeta(1-40)/Abeta(1-42). The effect of chronic stress on the severity of Abeta-induced spatial learning and memory impairment was tested by three approaches: behavioral testing in the radial arm water maze, in vivo electrophysiological recording in anesthetized rat, and immunoblot analysis to determine protein levels of learning- and memory-related molecules.

RESULTS

A marked impairment of learning and memory developed when stress was combined with Abeta, more so than that caused by Abeta alone. Additionally, there was a significantly greater impairment of early-phase long-term potentiation (E-LTP) in chronically stressed/Abeta-treated rats than in either the stressed or Abeta-treated rats. This might be a manifestation of the reduction in protein levels of calcium/calmodulin-dependent protein kinase II (CaMKII) and the abnormal increase in calcineurin levels.

CONCLUSIONS

Chronic stress significantly intensified Abeta-induced deficits of short-term memory and E-LTP by a mechanism involving decreased CaMKII activation along with increased calcineurin levels.

Taking the next steps in the treatment of Alzheimer's disease: disease-modifying agents

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in the United States and the number of AD patients is increasing at an alarming rate. There is no cure for AD and the currently available treatments are symptomatic, providing only limited effects on disease pathophysiology and progression. An overwhelming need exists for therapies that can slow or halt this debilitating disease process. Disease modification in AD has been defined from patient-focused, regulatory, and neurobiological perspectives. The latter two of these perspectives rely largely on an interruption of the disease process and a clear demonstration of this interruption. As defined by Cummings, a disease-modifying treatment is a “pharmacologic treatment that retards the underlying process of AD by intervening in the neurobiological processes that constitute the pathology and pathophysiology of the disease and lead to cell death or dysfunction.” By this definition, the burden of confirmatory study is placed on any new treatment for which the claim of “disease modification” is to be made (Slide 1).

Glutamatergic synaptic depression by synthetic amyloid beta-peptide in the medial septum

The medial septum/diagonal band region, which participates in learning and memory processes via its cholinergic and GABAergic projection to the hippocampus, is one of the structures affected by beta amyloid (betaA) deposition in Alzheimer's disease (AD). The acute effects of betaA (25-35 and 1-40) on action potential generation and glutamatergic synaptic transmission in slices of the medial septal area of the rat brain were studied using current and patch-clamp techniques. The betaA mechanism of action through M1 muscarinic receptors and voltage-dependent calcium channels was also addressed. Excitatory evoked responses decreased (30-60%) in amplitude after betaA (2 microM) perfusion in 70% of recorded cells. However, the firing properties were unaltered at the same concentration. This depression was irreversible in most cases, and was not prevented or reversed by nicotine (5 microM). In addition, the results obtained using a paired-pulse protocol support pre- and postsynaptic actions of the peptide. The betaA effect was blocked by calcicludine (50 nM), a selective antagonist of L-type calcium channels, and also by blocking muscarinic receptors with atropine (5 muM) or pirenzepine (1 microM), a more specific M1-receptor blocker. We show that in the medial septal area this oligomeric peptide acts through calcium channels and muscarinic receptors. As blocking any of these pathways blocks the betaA effects, we propose a joint action through both mechanisms. These results may contribute to a better understanding of the pathophysiology at the onset of AD. This understanding will be required for the development of new therapeutic agents.

Studies of the effects of fragment (25?35) of beta-amyloid peptide on the behavior of rats in a radial maze

Decreases in cognitive functions, particularly long-term (episodic) and working memory, are among the earliest prognostic signs of Alzheimer's disease. The toxicity of beta-amyloid peptide is regarded as a major cause of neurodegeneration and cognitive impairment in this disease. The present report describes studies of the effects of intracerebroventricular administration of beta-amyloid peptide (25-35) (Abeta(25-35)) on the reproduction of a previously assimilated habit consisting of finding food in an eight-arm radial maze in rats. Abeta(25-35) was given bilaterally at doses of 15 and 30 nmol/animal seven days after preliminary training. Testing was performed 60 days after peptide administration. The results showed that Abeta(25-35) impaired working memory in rats without having any significant effect on the retention of responses. We were unable to demonstrate any relationship between memory impairment and the dose of peptide given. These data provide evidence of the ability of Abeta(25-35) to produce greater degradation of working memory function than long-term memory function.

A case for a non-transgenic animal model of Alzheimer's disease

Alzheimer's disease (AD) is associated with an early impairment in memory and is the major cause of dementia in the elderly. beta-Amyloid (Abeta) is believed to be a primary factor in the pathogenic pathway leading to dementia. Mounting evidence suggests that this syndrome begins with subtle alterations in synaptic efficacy prior to extensive neuronal degeneration and that the synaptic dysfunction could be caused by diffusible oligomeric assemblies of Abeta. This paper reviews the findings from behavioral analysis, electrophysiology, neuropathology and nootropic drug screening studies involving exogenous administration of Abeta in normal rodent brains. This non-transgenic model of amyloid pathology in vivo is presented as a complementary alternative model to transgenic mice to study the cellular and molecular pathways induced by amyloid, which in turn may be a causal factor in the disruption of cognition. The data reviewed here confirm that the diffusible form of Abeta rapidly induces synaptic dysfunction and a secondary process involving cellular cascades induced by the fibrillar form of amyloid. The time-course of alteration in memory processes implicates at least two different mechanisms that may be targeted with selective therapies aimed at improving memory in some AD patients.

Effects of Pre-Germinated Brown Rice on .BETA.-Amyloid Protein-Induced Learning and Memory Deficits in Mice

We evaluated the effects of pre-germinated brown rice (hatsuga genmai, PGR) on learning and memory and compared them with those of polished rice or cornstarch. In mice that were fed pellets of polished rice or PGR for two weeks, the learning ability in the Morris water maze test was significantly enhanced compared with mice that were fed cornstarch pellets. In the Y-maze test, the intake of food pellets for two weeks failed to affect spontaneous alternation behavior. Beta-amyloid(25-35) (Abeta(25-35): 3 nmol/mouse, i.c.v.) protein impaired spontaneous alternation behavior in mice that were fed pellets of cornstarch or polished rice. In contrast, PGR pellets prevented the Abeta(25-35)-induced impairment of spontaneous alternation behavior. These results suggest that polished rice and PGR have facilitating effects on spatial learning. In particular, it is surmised that PGR may prevent Alzheimer's disease associated with Abeta.

Single intracerebroventricular administration of amyloid-beta (25-35) peptide induces impairment in short-term rather than long-term memory in rats

Ample experimental evidence indicates that intracerebral injection or infusion of amyloid-beta peptides (Abeta) to rodents induces learning and memory impairments as well as neurodegeneration in brain areas related to cognitive function. In the present study, we assessed the effects of a single intracerebroventricular (i.c.v.) injection of aggregated Abeta fragment (25-35) at a dose of 15nmol/rat on short-term and long-term memory in rats during the 6-month post-surgery period. The results demonstrate that Abeta(25-35)-induced memory impairments in spontaneous alternation behavior in a Y-maze at 17, 36, and 180 days after the surgery as well as in a social recognition task 110 days post-surgery. Abeta(25-35) also impaired spatial memory in an 8-arm radial maze, but did not influence performance of the step-down passive avoidance task. These results suggest that Abeta(25-35) preferably induces impairments of spatial and non-spatial short-term (working) memory rather than long-term memory in rats.

Estrogen restores cognition and cholinergic phenotype in an animal model of Down syndrome

Estrogen maintains normal function of basal forebrain (BF) cholinergic neurons and estrogen replacement therapy (ERT) has therefore been proposed as a therapy for Alzheimer's disease (AD). We provide evidence to support this hypothesis in an animal model of Down syndrome (DS), a chromosome 16 segmental trisomy (Ts65Dn) mouse. These mice develop cholinergic degeneration similar to young adults with DS and AD patients. ERT has not been tested in women with DS, even though they are more likely than normosomic women to develop early menopause and AD. Female Ts65Dn and normosomic mice (11-15 months) received a subcutaneous estrogen pellet or a sham operation. After 60 days, estrogen treatment improved learning of a T-maze task and normalized behavior in the Ts65Dn mice in reversal learning of the task, a measure of cognitive flexibility. Stereological evaluation of choline acetyltransferase (ChAT) immunopositive BF neurons showed that estrogen increased cell size and total number of cholinergic neurons in the medial septum of Ts65Dn mice. In addition, estrogen increased NGF protein levels in the BF of trisomic mice. These findings support the emerging hypothesis that estrogen may play a protective role during neurodegeneration and cognitive decline, particularly in cholinergic BF neuronal systems underlying cognition. The findings also indicate that estrogen may act, at least partially, via endogenous growth factors. Collectively, the data suggest that ERT may be a viable therapeutic approach for women with DS coupled with dementia.

Alzheimer's disease through the eye of a mouse. Acceptance lecture for the 2001 Gayle A. Olson and Richard D. Olson prize

There is now ample evidence that beta-amyloid proteins decrease memory. The SAMP8 mouse (P8) develops an early decline in the ability to learn and to retain new information. The studies reviewed here suggest that this is due to overproduction of beta-amyloid. Both antibodies to beta-amyloid and specific antisense to the amyloid precursor protein reverse these deficits in the P8 mouse. This antisense can cross the blood brain barrier. It is hypothesized that the overproduction of beta-amyloid leads to a decline in Delta(9) desaturase activity with an alteration in membrane fatty acids. This results in altered membrane mobility leading to a decline in neurotransmitter activity and a decreased release of acetylcholine. This decreased cholinergic activity results in a decreased ability of the P8 mouse to learn and retain new information.

Hippocampal injections of amyloid beta-peptide 1-40 impair subsequent one-trial/day reward learning

The injection of amyloid beta-peptide (Abeta) into rat CNS has been reported to induce cellular neuropathology. The present study investigated whether multiple intrahippocampal injections of Abeta 1-40 would impair one-trial/day reward learning 14 days later. Twenty-four male Sprague-Dawley rats, 3-4 months old, were injected with either Abeta 1-40 or distilled water into seven hippocampal sites bilaterally. Ten rats received 3 nmol Abeta 1-40 in 2 microl of distilled water per injection site, while 14 rats received distilled water alone. Following a 9-day recovery period, rats were gradually food deprived to 82% of their initial body weight. Fourteen days after the intrahippocampal injection, all rats received an initial training trial and three subsequent daily retention trials. Rats receiving Abeta 1-40 were significantly impaired on the second retention trial in terms of accuracy (number of unbaited alleys entered) and on the second and third retention trials in terms of speed (reciprocal of latency to reward). Histological analysis showed that Abeta 1-40 injections produced significant neuronal loss and gliosis. Abeta 1-40 immunoreactivity persisted locally at the injection site and in macrophages 2 weeks following the hippocampal injections. These effects appear to be sequence-specific; rats receiving Abeta 1-42 with a scrambled peptide sequence did not differ significantly from rats receiving distilled water alone in retention of the learning task or degree of histological damage.

The beta-amyloid precursor protein and its derivatives: from biology to learning and memory processes

Intensive investigation towards the understanding of the biology and physiological functions of the beta-amyloid precursor protein (APP) have been supported since it is known that a 39-43 amino acid fragment of APP, called the beta-amyloid protein (Abeta), accumulates in the brain parenchyma to form the typical lesions associated with Alzheimer's disease (AD). It emerges from extensive data that APP and its derivatives show a wide range of contrasting physiological properties and therefore might be involved in distinct physiological functions. Abeta has been shown to disrupt neuronal activity and to demonstrate neurotoxic properties in a wide range of experimental procedures. In contrast, both in vitro and in vivo studies suggest that APP and/or its secreted forms are important factors involved in the viability, growth and morphological and functional plasticity of nerve cells. Furthermore, several recent studies suggest that APP and its derivatives have an important role in learning and memory processes. Memory impairments can be induced in animals by intracerebral treatment with Abeta. Altered expression of the APP gene in aged animals or in genetically-modified animals also leads to memory deficits. By contrast, secreted forms of APP have recently been shown to facilitate learning and memory processes in mice. These interesting findings open novel perspectives to understand the involvement of APP in the development of cognitive deficits associated with AD. In this review, we summarize the current data concerning the biology and the behavioral effects of APP and its derivatives which may be relevant to the roles of these proteins in memory and in AD pathology.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood-brain barrier disruption: implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood-brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor alpha and IFN-gamma mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.

Neurohypophyseal peptides and social recognition in rats

An encounter between rats results in bouts of social investigation consisting mainly of sniffing, nosing, following and grooming. The assessment of social recognition is based on the tendency of rodents to investigate unfamiliar conspecifics more intensely, than familiar ones. In the laboratory an immature conspecific is normally used as the social stimulus because the use of juveniles eliminates possible sexual and/or aggressive behaviors of the rat whose memory is assessed. When a juvenile is presented for the first time, it is intensely investigated. A second presentation shortly after the first one elicits less attention. This is not due to satiation or fatigue, since the presentation of a novel juvenile triggers the full sequence of investigation. Social recognition is defined as a specific decrease in social investigation during the second encounter of the same individual. This form of memory is short lasting (< 40 min) and based on the olfactory characteristics of the stimulus animal. Social memory is prolonged by repeated exposure to the stimulus juvenile rat and is impaired by retroactively interfering stimuli. It can be facilitated by vasopressin and derivatives as well as by several other memory facilitating compounds, and, depending on the dose, attenuated or facilitated by oxytocin and derivatives. Ethologically oriented memory tests, that are based on olfactory characteristics of the information to-be-remembered, have an advantage over 'classical' ones: they estimate behavioral patterns which are important to an animal and not only to the investigator. Social memory paradigms can reveal information about memory processes in animals that is relevant for memory deficits in humans.

Age-related toxicity to lactate, glutamate, and beta-amyloid in cultured adult neurons

The age-related susceptibility of the brain to neurodegenerative disease may be inherent in the susceptibility of individual neurons to various stressors. Neurons were isolated from embryonic, young- and old-aged rat hippocampus, cultured in serum-free medium and exposed to lactic acid, glutamate or beta-amyloid. Yields of isolated adult cells were 1 million cells/hippocampus, 12,000 cells/mg tissue, independent of age. For lactic acidosis, there was a non-significant 10% increment in killing of neuron-like cells from old rats compared to young. For glutamate, there was a 5-10% increment in killing of neuron-like cells from old rats compared to young rats and embryonic neurons. For cells exposed to the toxic fragment of beta-amyloid, A beta (25-35), toxicity was age, dose and time-dependent. Maximum toxicity in cells treated for 1 day with 25 microM A beta (25-35) was 16%, 24%, and 33% for embryonic, young and old cells. Similar results were found for A beta (1-40) (LD50 = 2 microM). These results suggest that aging imparts to individual cells an increased susceptibility to toxic substances relevant to neurodegenerative diseases.

Experimental and clinical methods in the development of anti-Alzheimer drugs

Methodology used for the development of anti-Alzheimer's disease (AD) drugs raises specific problems which are rarely examined in the literature. While the general development scheme is similar to that required for most drugs, some specific aspects must be analyzed, highly dominated by the dual goal of pharmacology, i.e., to obtain both symptomatic and etiopathogenic drugs. During preclinical studies, aged or lesioned animals are mainly useful for symptomatic drugs, whereas transgenic models or neurodegeneration-induced techniques would probably lead to etiopathogenic drugs potentially slowing down the process of AD. The first administrations of a new compound to human beings raise the question of the activity measurement techniques. Psychometry remains the most informative procedure to detect and analyze the activity of the drugs on the different components of cognition. Electrophysiology and neuroimaging need some complementary studies before they can be proposed as surrogate criteria in phase III trials. At this stage of development, American and the recently published European guidelines are of great help while insisting on long-term (6 months) placebo controlled trials with the use of the triple efficacy criterion: an objective cognition scale, a global assessment, and the opinion of the caregiver. In the long term, pharmacoepidemiology and pharmacoeconomy will have to confirm the rationale of this recent progress in the methodology of anti-AD drug development.