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[Lack of antidepresant-like activity of some ligands of polyamine binding sites of NMDA receptors in models of depression].

Arcain and a series of the partial modulators of polyamine binding sites of NMDA receptors (spermine- and adamantyl-containing polyamines IEM-1460, IEM-1490, IEM-1592, IEM-1755) do not display (in contrast to melipramine and memantine) antidepressant-like action in the forced swimming test and reserpine-induced depression test in rats. Compounds IEM-1460, IEM-1490, IEM-1592 increase the total time of immobilization in the Porsolt test, probably, by facilitating the development of stress-induced depression. It is supposed that the prodepressant activity of these compounds is mediated by NMDA-receptors having NR1/NR2C and NR1/NR2D subunit composition.

Animals↗

[Pharmacological treatment of vascular cognitive impairment].

Vascular dementia is second most common cause of dementia. The paper highlights the most important trends in pharmacological treatment of vascular dementia. Result of a clinical trial of some agents appears to be promising. Pentoxifyline appears to be useful in multi-infarct vascular dementia. Nimodipine produced improvement in subcortical dementia. Some other agents like ginkgo biloba, acetylocholinesterase inhibitors, memantine and other also have shown mild benefit or at least were associated with some stabilization of dementia.

Animals↗

The expert consensus guideline series. Treatment of dementia and its behavioral disturbances. Introduction: methods, commentary, and summary.

OBJECTIVES: New treatment options for dementia and its behavioral disturbances have become available since publication of The Expert Consensus Guidelines on the Treatment of Agitation in Older Persons with Dementia in 1998. While only 2 cholinesterase inhibitors, donepezil and tacrine, were available in 1998, 3 new cognitive-enhancing agents have been introduced since that time as well as several new atypical antipsychotics and antidepressants. However, there are still limited data from controlled studies to guide clinicians in choosing among these agents and sequencing and combining treatments. We therefore conducted a new survey study of expert opinion on the treatment of cognitive impairment and behavioral disturbances associated with dementia. METHODS: Based on a literature review, a 61-question survey was developed with 1,225 options. Most options were scored using a modified version of the RAND 9-point scale for rating appropriateness of medical decisions. For other options, the experts were asked to write in answers. The survey was sent to 50 North American experts on dementia, 100% of whom completed it. In analyzing responses to items rated on the 9-point scale, consensus was defined as a nonrandom distribution of scores by chi-square "goodness-of-fit" test. Based on the 95% confidence interval around the mean, we assigned a categorical rank (first line/preferred, second line/alternate, third line/usually inappropriate) to each option. Guidelines indicating preferred treatment strategies were then developed for selected clinical situations. RESULTS: For patients at risk for dementia, the experts recommended control of hypertension and diabetes. They also recommended aspirin and would consider a lipid-lowering agent in patients at risk for vascular dementia. Cholinesterase inhibitors were an option for patients with mild cognitive impairment (i.e., at risk for Alzheimer's dementia [AD]). To slow cognitive impairment in mild/moderate AD, the experts recommended a cholinesterase inhibitor alone or combined with vitamin E. Donepezil and galantamine were the preferred cholinesterase inhibitors. The experts recommended combining a cholinesterase inhibitor with a N-methyl-D-aspartate (NMDA) antagonist (e.g., memantine) if a patient with mild/moderate dementia has an inadequate response to monotherapy. Control of hypertension and diabetes was the treatment of choice, in patients with mild/moderate vascular or mixed AD/vascular dementia, with aspirin another first-line option. Cholinesterase inhibitors were also a first-line option for mild/moderate mixed AD/vascular dementia. Among nonpharmacological interventions for mild/moderate dementia, the experts recommended caregiver education, supportive therapy for caregivers, referral to day treatment, exercise programs, and respite care. For moderate/severe AD or mixed AD/vascular dementia, the experts recommended combining an NMDA antagonist with a cholinesterase inhibitor. For moderate/severe vascular or mixed AD/vascular dementia, they recommended control of hypertension and diabetes. The experts' ratings underscore the importance of nonpharmacological strategies aimed at reducing caregiver burden in more severe dementia. Management of agitation and other behavioral disturbances was another focus of this study. The experts recommended using an atypical antipsychotic for agitation associated with delirium, psychosis, aggression, or anger. They would also consider divalproex to manage anger with a risk of physical aggression. Selective serotonin reuptake inhibitors were recommended for the treatment of depression or anxiety in patients with dementia. Benzodiazepines or atypical antipsychotics were viewed as short-term options for acute anxiety. Trazodone was recommended for insomnia. The experts also gave recommendations concerning dosage levels, duration of treatment, and choice of medications for patients with different complicating conditions. CONCLUSIONS: The experts reached high levels of consensus on key steps in treating dementia and associated behavioral disturbances. Within the limits of expert opinion and with the expectation that new research data will take precedence, these guidelines may provide direction for clinicians offering care to patients with dementia.

Alzheimer Disease↗

Excitatory amino acid antagonists and the anticonvulsive activity of conventional antiepileptic drugs.

There is a great body of evidence, that excitatory amino acid antagonists, apart from their anticonvulsive properties per se, potentiate the protective activity of conventional antiepileptics against maximal electroshock-induced seizures in mice. It is worth stressing, that combinations of valproate with either CGP 37849 (a competitive NMDA antagonist) or dizocilpine (MK-801, a non-competitive NMDA antagonist), providing a 50% protection against maximal electroshock, resulted in no adverse effects, as measured in the chimney test (motor coordination) or passive avoidance task (long-term memory). On the other hand, valproate administered alone at its ED50, to protect against maximal electroshock, produced profound adverse effects. However, some NMDA antagonists (D-CPP-ene, memantine, procyclidine or trihexyphenidyl) did enhance the protection offered by common antiepileptics but these combined treatments were associated with considerable side-effects on motor coordination and long-term memory. Interestingly, ifenprodil (an antagonist of the polyamine site within the NMDA receptor complex) possessed some anticonvulsive activity against electroconvulsions but failed to enhance the antielectroshock efficacy of conventional antiepileptics. AMPA/KA receptor antagonists (NBQX and GYKI 52466), similarly to NMDA antagonists, potentiated the protective action of antiepileptic drugs against maximal electroshock and these combinations were generally devoid of unwanted effects.

Anticonvulsants↗

A multi-center 1H MRS study of the AIDS dementia complex: validation and preliminary analysis.

PURPOSE: To demonstrate the technical feasibility and reliability of a multi-center study characterizing regional levels of the brain metabolite ratios choline (Cho)/creatine (Cr) and myoinositol (MI)/Cr, markers of glial cell activity, and N-acetyl aspartate (NAA)/Cr, a marker of mature neurons, in subjects with AIDS dementia complex (ADC). MATERIALS AND METHODS: Using an automated protocol (GE PROBE-P), short echo time spectra (TE = 35 msec) were obtained at eight sites from uniformly prepared phantoms and from three brain regions (frontal white matter, basal ganglia, and parietal cortex) of normal volunteers and ADC and HIV-negative subjects. RESULTS: A random-effects model of the phantom and volunteer data showed no significant inter-site differences. Feasibility of a multi-center study was further validated by detection of significant differences between the metabolite ratios of ADC subjects and HIV-negative controls. ADC subjects exhibited significantly higher Cho/Cr and MI/Cr in the basal ganglia and significantly reduced NAA/Cr and significantly higher MI/Cr in the frontal white matter. These results are consistent with the predominantly subcortical distribution of the pathologic abnormalities associated with ADC. CONCLUSION: This is the first study to ascertain and validate the reliability and reproducibility of a short echo time (1)H-MRS acquisition sequence from multiple brain regions in a multi-center setting. It should now be possible to examine the regional effects of HIV infection in the brain in a large number of subjects and to study the metabolic effects of new therapies for the treatment of ADC in a clinical trial setting.

AIDS Dementia Complex↗

Involvement of the 5-lipoxygenase pathway in the neurotoxicity of the prion peptide PrP106-126.

Transmissible spongiform encephalopathies are characterised by the transformation of the normal cellular prion protein (PrP(C)) into an abnormal isoform (PrP(TSE)). Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can inhibit glutathione depletion and neurotoxicity induced by PrP(TSE) and a toxic prion protein peptide, PrP106-126, in vitro. NMDA receptor activation is known to increase intracellular accumulation of Ca(2+), resulting in up-regulation of arachidonic acid (AA) metabolism. This can stimulate the lipoxygenase pathways that may generate a number of potentially neurotoxic metabolites. Because of the putative relationship between AA breakdown and PrP106-126 neurotoxicity, we investigated AA metabolism in primary cerebellar granule neuron cultures treated with PrP106-126. Our studies revealed that PrP106-126 exposure for 30 min significantly up-regulated AA release from cerebellar granule neurons. PrP106-126 neurotoxicity was mediated through the 5-lipoxygenase (5-LOX) pathway, as shown by abrogation of neuronal death with the 5-LOX inhibitors quinacrine, nordihydroguaiaretic acid, and caffeic acid. These inhibitors also prevented PrP106-126-induced caspase 3 activation and annexin V binding, indicating a central role for the 5-LOX pathway in PrP106-126-mediated proapoptosis. Interestingly, inhibitors of the 12-lipoxygenase pathway had no effect on PrP106-126 neurotoxicity or proapoptosis. These studies clearly demonstrate that AA metabolism through the 5-LOX pathway is an important early event in PrP106-126 neurotoxicity and consequently may have a critical role in PrP(TSE)-mediated cell loss in vivo. If this is so, therapeutic intervention with 5-LOX inhibitors may prove beneficial in the treatment of prion disorders.

Animals↗

Neurons depend on astrocytes in a coculture system for protection from glutamate toxicity.

Glutamate can be toxic to neurons although it is a neurotransmitter. Regulation of extracellular glutamate levels is essential for prevention of glutamate neurotoxicity. Astrocytes play a major role in clearance of glutamate released by neurons. A coculture system combining cerebellar cells and astrocytes was employed to investigate the astrocytic control of glutamate toxicity. Coculture of astrocytes with cerebellar neurons enhanced uptake of glutamate by astrocytes. Inhibition of glutamate uptake in a coculture system led to death of cerebellar cells. This toxicity could be inhibited by MK801. However, in the presence of the glutamate uptake inhibitor, there was no increase in glutamate in the cultures compared to when the neurons were not cocultured. This indicated that neurons become more susceptible to glutamate toxicity in the presence of astrocytes and thus become dependent on astrocytes for prevention of glutamate toxicity. Astrocytes treated with conditioned medium from cerebellar cells did not show an increase in glutamate uptake but medium from astrocytes exposed to neuron conditioned medium was toxic to cerebellar cells. This toxicity was due to glutamate present in the medium. This suggests that a soluble factor released by neurons signals to astrocytes that neurons are present and stimulates a signal back to neurons which causes an increased sensitivity to glutamate toxicity.

Animals↗

Central nervous system expression of HIV-1 Gp120 activates the hypothalamic-pituitary-adrenal axis: evidence for involvement of NMDA receptors and nitric oxide synthase.

The impact of HIV-1 expression in the brain on the development of AIDS is unknown. In the present study, we examined the hypothalamic-pituitary-adrenal (HPA) axis in a transgenic model in which expression of the HIV-1 envelope glycoprotein gp120 induced central nervous system (CNS) damage similar to that seen in HIV-1-infected patients. Compared with nontransgenic littermates, gp120 transgenic mice showed significant increases in plasma corticosterone and adrenocorticotrophic hormone (ACTH) levels and pituitary ACTH content. To determine whether this activation of the HPA axis could be mediated by ACTH secretagogues, the effect of recombinant gp120 on the release of these factors from hypothalamic slices was investigated in vitro. Recombinant gp120 induced release of the ACTH secretagogue arginine vasopressin from nontransgenic hypothalamic slices in a calcium-dependent fashion. This effect was inhibited by antagonists of N-methyl-D-aspartate (NMDA) receptors or of nitric oxide synthase (NOS), suggesting a role for NMDA receptor stimulation and NOS activity. Further evidence for a role of free radicals was obtained from bigenic mice coexpressing gp120 and the free radical scavenger human copper/zinc superoxide dismutase which showed normal corticosterone levels. This might relate to superoxide dismutase-mediated scavenging of superoxides generated by NOS. These findings demonstrate that CNS expression of a viral envelope protein can activate the HPA axis and thereby alter peripheral levels of immunomodulatory hormones.

Adrenocorticotropic Hormone↗

Neuropharmacological studies on D145 (1,3-dimethyl-5-aminoadamantan).

The effects of D145 (1,3-dimethyl-5-aminoadamantan) and amantadine on dopaminergic mechanisms in the rat were investigated by use of pharmacological agents known to disrupt dopamine function, by placing electrolytic lesions in the dopamine-containing areas of the extrapyrimidal and mesolimbic systems and by the direct application to dopamine sensitive areas. Stereotypy and circling behaviour were used as behavioural indices of dopaminergic stimulation and apomorphine and d-amphetamine were used as standard dopaminergic agonists. In addition, the possible importance of 5-hydroxytryptamine to the dopamine effects was investigated using electrolytic lesions of the midbrain raphé nuclei. Both D145 and amantadine caused a stereotyped behaviour characterized by periodic sniffing, repetitive limb movements and biting, but the effect of amantadine was far more periodic. In addition D145, but not amantadine, caused marked hyperactivity. These behavioural effects were resistant to pretreatment with alpha-methylparatyrosine but not to combined alpha-methylparatyrosine/reserpine or low doses of haloperidol. Also, the prior administration of D145 or amantadine inhibited the development of the biting components of apomorphine and d-amphetamine stereotypy. Both D145 and amantadine caused circling behaviour in animals with asymmetric lesions of the medial raphé nucleus or unilateral lesions of the substantia nigra but the action of D145 was more intense. Bilateral electrolytic lesions placed in the extrapyrimidal (caudate-putamen, globus pallidus, substantia nigra), mesolimbic (nucleus accumbens septi, tuberculum olfactorium, nucleus interstitialis stria terminalis, nucleus amygdaloideus centralis) nuclei or the neuronal pathways supplying them showed D145 and amantadine to act in both areas although their action on the extrapyrimidal system was most marked. However, of particular note was the significantly greater involvement of the substantia nigra with the D145 effect, and the greater involvement of the D145 effect with mesolimbic function. Lesions placed in the medial and/or dorsal raphé nucleus indicated some involvement of 5-hydroxytryptamine with the actions of both D145 and amantadine. The bilateral intrastriatal application of D145 or amantadine in nialamide pretreated animals failed to induce stereotyped or hyperactive behaviour although contralateral asymmetries, which were abolished by lesions of the substantia nigra, were recorded following the unilateral intrastriatal application of D145 or amantadine in haloperidol pretreated animals.

Amantadine↗

Dopamine agonists and interaction with other neurotransmitter systems.

Studies on the interaction of two dopamine (DA) agonists (selected as most specific): apomorphine (APO) and 1,3-dimethyl-5-aminoadamantane (DMAA) with serotonin (5-HT) and noradrenaline (NA) brain systems have revealed that the drugs induce the activation of 5-HT and NA neurons in an indirect way (via primary DA stimulation). These interactions are relevant for some pharmacological effects of DA agonists.

Animals↗

Imaging the glutamatergic system in vivo--relevance to schizophrenia.

Schizophrenia is a devastating psychiatric illness. Its pathophysiology is not fully clarified. Animal data, in vitro and indirect in vivo imaging support glutamatergic N-methyl-D-aspartate (NMDA) receptor hypofunction in the disorder. A lack of suitable ligands has obstructed direct evaluation of the NMDA receptor hypofunction hypothesis of schizophrenia. Many research groups are working towards developing appropriate single-photon emission tomography and positron emission tomography ligands for the NMDA receptor. This paper briefly presents evidence for links between glutamatergic system dysfunction and schizophrenia. It reviews the radioligands to evaluate glutamatergic receptors in vivo and discusses issues in developing novel ligands for the glutamatergic system.

Brain Chemistry↗