Learning deficits induced by 4 belladonna alkaloids are preferentially attenuated by tacrine.
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AIM: To examine the antagonism of tacrine on the amnesic effects of scopolamine (Sco), anisodine (AT3), atropine (Atr), and anisodamine (Ani). METHODS: Cognitive functions and locomotor activities were determined using two sessions of step-through and open-field tests, respectively. Mice were injected with one of the belladonna alkaloids (0.05-50 mumol.kg-1, i.p.) and tacrine (50 mumol.kg-1, s.c.) 30 min before the first session. RESULTS: Tacrine completely blocked the avoidance-learning deficit caused by Sco 0.5 mumol.kg-1, AT3 and Atr 5 mumol.kg-1, or Ani 50 mumol.kg-1. But tacrine partly antagonized the learning deficit induced by Sco 5-50 mumol.kg-1 or Atr and AT3 50 mumol.kg-1. The avoidance-memory deficit caused by Sco 0.05-5 mumol.kg-1 or Atr 5 mumol.kg-1 was completely or partly attenuated by tacrine, which did not antagonize the memory deficit elicited by Sco and Atr 50 mumol.kg-1, AT3 5 and 50 mumol.kg-1, and Ani 50 mumol.kg-1. During the acquisition, the locomotor activity of the mice was inhibited by tacrine. This reduction was completely antagonized by Sco 0.5-50 mumol.kg-1, AT3 5-50 mumol.kg-1, Atr 5-50 mumol.kg-1, and only partly antagonized by AT3 and Atr 0.5 mumol.kg-1 or Ani 50 mumol.kg-1. CONCLUSION: Compared with the avoidance-memory deficit, the avoidance-learning deficit caused by belladonna alkaloids is more preferentially attenuated by tacrine. (+info)
Lack of tissue glucocorticoid reactivation in 11beta -hydroxysteroid dehydrogenase type 1 knockout mice ameliorates age-related learning impairments.
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11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1) intracellularly regenerates active corticosterone from circulating inert 11-dehydrocorticosterone (11-DHC) in specific tissues. The hippocampus is a brain structure particularly vulnerable to glucocorticoid neurotoxicity with aging. In intact hippocampal cells in culture, 11beta-HSD-1 acts as a functional 11beta-reductase reactivating inert 11-DHC to corticosterone, thereby potentiating kainate neurotoxicity. We examined the functional significance of 11beta-HSD-1 in the central nervous system by using knockout mice. Aged wild-type mice developed elevated plasma corticosterone levels that correlated with learning deficits in the watermaze. In contrast, despite elevated plasma corticosterone levels throughout life, this glucocorticoid-associated learning deficit was ameliorated in aged 11beta-HSD-1 knockout mice, implicating lower intraneuronal corticosterone levels through lack of 11-DHC reactivation. Indeed, aged knockout mice showed significantly lower hippocampal tissue corticosterone levels than wild-type controls. These findings demonstrate that tissue corticosterone levels do not merely reflect plasma levels and appear to play a more important role in hippocampal functions than circulating blood levels. The data emphasize the crucial importance of local enzymes in determining intracellular glucocorticoid activity. Selective 11beta-HSD-1 inhibitors may protect against hippocampal function decline with age. (+info)
An unliganded thyroid hormone receptor causes severe neurological dysfunction.
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Congenital hypothyroidism and the thyroid hormone (T(3)) resistance syndrome are associated with severe central nervous system (CNS) dysfunction. Because thyroid hormones are thought to act principally by binding to their nuclear receptors (TRs), it is unexplained why TR knock-out animals are reported to have normal CNS structure and function. To investigate this discrepancy further, a T(3) binding mutation was introduced into the mouse TR-beta locus by homologous recombination. Because of this T(3) binding defect, the mutant TR constitutively interacts with corepressor proteins and mimics the hypothyroid state, regardless of the circulating thyroid hormone concentrations. Severe abnormalities in cerebellar development and function and abnormal hippocampal gene expression and learning were found. These findings demonstrate the specific and deleterious action of unliganded TR in the brain and suggest the importance of corepressors bound to TR in the pathogenesis of hypothyroidism. (+info)
Down syndrome and the phonological loop: the evidence for, and importance of, a specific verbal short-term memory deficit.
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Individuals with Down syndrome are thought to perform poorly on tests of verbal short-term memory, such as measures of word span or digit span. This review critically examines the evidence for a specific deficit in verbal short-term memory in Down syndrome, and outlines a range of possible explanations for such a deficit. The potential implications of a verbal short-term memory impairment for broader aspects of development are outlined, in particular with respect to vocabulary development. Possible intervention strategies, which might improve verbal short-term memory performance in Down syndrome are also considered. However, we argue that further research is needed to fully clarify the nature of a verbal short-term memory deficit in Down syndrome, before the merits of these various intervention approaches can be properly evaluated. (+info)
Learning to count: a difficult task?
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This article is concerned with the acquisition of counting skills in pupils with Down syndrome. Data from a larger survey of pupils with severe learning difficulties is explored to investigate the types of errors children make at the earliest stages of learning to count. The pattern of responding was consistent with the view that children with Down syndrome have particular difficulties in tasks utilising auditory sequential memory, in this case learning the number string. The practical implications of these findings are discussed. (+info)
Ablation of NF1 function in neurons induces abnormal development of cerebral cortex and reactive gliosis in the brain.
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Neurofibromatosis type 1 (NF1) is a prevalent genetic disorder that affects growth properties of neural-crest-derived cell populations. In addition, approximately one-half of NF1 patients exhibit learning disabilities. To characterize NF1 function both in vitro and in vivo, we circumvent the embryonic lethality of NF1 null mouse embryos by generating a conditional mutation in the NF1 gene using Cre/loxP technology. Introduction of a Synapsin I promoter driven Cre transgenic mouse strain into the conditional NF1 background has ablated NF1 function in most differentiated neuronal populations. These mice have abnormal development of the cerebral cortex, which suggests that NF1 has an indispensable role in this aspect of CNS development. Furthermore, although they are tumor free, these mice display extensive astrogliosis in the absence of conspicuous neurodegeneration or microgliosis. These results indicate that NF1-deficient neurons are capable of inducing reactive astrogliosis via a non-cell autonomous mechanism. (+info)
3,4-methylenedioxymethamphetamine (ecstasy)-induced learning and memory impairments depend on the age of exposure during early development.
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Use of 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) has increased dramatically in recent years, yet little is known about its effects on the developing brain. Neonatal rats were administered MDMA on days 1-10 or 11-20 (analogous to early and late human third trimester brain development). MDMA exposure had no effect on survival but did affect body weight gain during treatment. After treatment, body weight largely recovered to 90-95% of controls. MDMA exposure on days 11-20 resulted in dose-related impairments of sequential learning and spatial learning and memory, whereas neonatal rats exposed on days 1-10 showed almost no effects. At neither stage of exposure did MDMA-treated offspring show effects on swimming ability or cued learning. Brain region-specific dopamine, serotonin, and norepinephrine changes were small and were not correlated to learning changes. These findings suggest that MDMA may pose a previously unrecognized risk to the developing brain by inducing long-term deleterious effects on learning and memory. (+info)
General health status measures for people with cognitive impairment: learning disability and acquired brain injury.
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BACKGROUND: Currently there is a wide range of health status measures that aim to assess general health status in people with cognitive impairment. However, the validity and/or applicability to this patient group are largely unknown. This has implications for the assessment of treatment outcomes and rehabilitation, for prognostic purposes, for planning services, and for determining the benefits and adverse effects of health technologies targeted at these patient groups. OBJECTIVES: (1) To identify the general health status measures that have been validated in patients with cognitive impairment. (2) To assess the extent to which these measures have been validated. (3) To draw out the implications of the findings for the use of existing measures and for future primary research in this area. METHODS. SELECTION CRITERIA: Studies that assessed general health status in people with cognitive impairment due to acquired brain injury (traumatic brain injury, cerebro-vascular accident or multiple sclerosis (MS)) or learning disability (LD) were included in the review. Studies that used general health status instruments measuring only one general health dimension, and studies that only featured participants with cognitive impairment due to dementia were excluded. METHODS. SEARCH STRATEGY: A wide range of relevant databases were searched for studies on cognitive impairment, general health status measures, and validation of health status measures. A handsearch of general health status bibliographies was also conducted. Data were collected on the general health status measure used, the population characteristics, aims of the study, validity details, and conclusions. RESULTS: The review includes data from 71 studies, reported in 83 separate publications. In total 34 different general health status measures were described in the 83 publications, with the Sickness Impact Profile (SIP) and the Short Form-36 (SF-36) the most frequently used measures (20 and 19 studies, respectively). These studies included a total of 98 instrument validations, 52 of which definitely or probably included people with cognitive impairment. Six measures were extensively validated (quality scores ranged from 0.25 to 0.5, on a scale from 0 to 1) in studies in which more than 50% of the respondents were people with cognitive impairment. A further three measures were also validated in studies in which more than 50% of the respondents were people with cognitive impairment, but their level of validation was more limited (quality scores ranged from 0.1 to 0.2). Five measures were validated in studies in which 20-50% of the respondents were cognitively impaired, which may limit their relevance to participants with cognitive impairment (quality scores ranged from 0.1 to 0.6). The SF-36 was also validated in two studies in which 20-50% of the respondents were cognitively impaired and the quality score was 0.3. Finally, nine of the measures were only validated in studies in which less than 20% of the respondents were cognitively impaired. For these measures it was unclear whether the findings applied to people with cognitive impairment. CONCLUSIONS: Very few measures have been validated specifically for cognitively impaired respondents. Studies where at least 50% of the respondents were cognitively impaired generally showed poorer validity results compared with studies with fewer cognitively impaired persons, indicating that general health status measures designed for the general population are not automatically suitable for people with cognitive impairment. The few measures that were specifically developed for people with cognitive impairment also reported poor validity results. Therefore, there are no validated instruments available for use in cognitively impaired respondents; existing measures, specifically designed for use in these populations, should be used with caution. The most promising measure is the MS-Quality of Life Interview (MS-QLI) for MS patients. The MS-QLI was thoroughly validated in 300 MS patients and the results were good, except for the 'social function' subscale. However, only 20-50% of the respondents in this study had cognitive impairment. Most information on the validity of general health status measures was found in studies among people with LD. For these patients, six measures were found that have been validated in a populations where more than 50% of the respondents were cognitively impaired LD patients. CONCLUSIONS: (1) Existing general health status measures should be used with caution in individuals with cognitive impairments. (2) There is no evidence to indicate the most suitable general health status measure for use in economic evaluations of cognitive impairment. (3) There is little evidence to support the validity of proxy assessments in cognitively impaired populations. (ABSTRACT TRUNCATED) (+info)