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  • 1
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Many studies have supported a genetic etiology for autism. Here we report mutations in two X-linked genes encoding neuroligins NLGN3 and NLGN4 in siblings with autism-spectrum disorders. These mutations affect cell-adhesion molecules localized at the synapse and suggest that a defect of ...
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: A 3.7-kb cDNA fragment, designated rat-XT1, was isolated from a rat whole-brain cDNA library. The nucleotide sequence of XT1 codes for a 727 amino acid protein with a calculated molecular mass of 81,139 Da and 12 putative transmembrane domains. This protein shares significant homology (28–32%) with the monoamine- (dopamine, norepinephrine, serotonin), amino acid- (taurine, proline, GABA, glycine), choline-, and betaine-, Na+/Cl−-dependent transporters. The homology is especially high within the first, second, sixth, and eighth transmembrane domains (45–75%). Thus, XT1 clearly belongs to the Na+/Cl−-dependent neurotransmitter transporter superfamily. However, XT1 may define a new subfamily of transporter because it differs structurally from other members of this family in that the extracellular loop linking transmembrane domains 7 and 8 and the C-terminal tail are significantly larger in size. Transient or stable expression of rat-XT1 failed to confer to the transfected cells the ability to transport actively any of the 〉60 established or putative neurotransmitter substances assessed. Northern blot analyses of peripheral and neural tissues demonstrated that expression of the 8-kb XT1 mRNA is essentially restricted to the nervous system. In situ hybridization demonstrated a broad but discrete localization of XT1 message in the CNS, particularly in the cerebellum (Purkinje and granular cell layers), the hippocampus (pyramidal and granular cell layers), and the thalamus and throughout the cerebral cortex. This distribution parallels that of the neurotransmitters glutamate and aspartate; however, neither of these excitatory amino acids is a substrate for transport. One noticeable exception to the codistribution of the mRNA for rat-XT1 and these excitatory neurotransmitters is the cerebellar Purkinje cell layer, in which GABAergic neurons are localized. The gene encoding for XT1 is localized to the mouse chromosome 3 in the vicinity of the locus for the mouse neurological disorder spastic (spa).
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Amplification of rat intestine mRNAs was performed by the reverse transcriptase-polymerase chain reaction (RT-PCR) using various oligonucleotide primers mainly corresponding to the translated region of the enkephalinase (EC 3.4.24.11, membrane metalloendopeptidase, MME 1) gene. In addition to the expected transcript, a shorter one was identified and its sequence indicated that it corresponds to an alternatively spliced mRNA from which exons 5–18 of MME I are deleted. It encodes a deduced 255 amino acid protein, MME II, instead of the 742 amino acid sequence of enkephalinase. The deduced structure of MME II is consistent with its being a membrane-bound, zinc-containing glycoprotein with a modified peptidase activity. MME II mRNA is also expressed, together with MME I mRNA, in brain and thyroid in a tissue-specific manner.
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 24 (1985), S. 2179-2185 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
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  • 5
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: It has recently emerged that there is a commonality in the molecular mechanisms underlying long-term neuronal changes in drug addiction and those mediating synaptic plasticity associated with learning and memory. In the hippocampus, the calcium–calmodulin-dependent protein phosphatase calcineurin plays a pivotal role in the molecular mechanisms that underlie learning and memory functions. Transgenic mice that express an active form of calcineurin specifically in forebrain structures have previously been shown to have a deficit in the transition from short- to long-term memory. Here, we investigated the involvement of calcineurin in the motivational effects of amphetamine and morphine using this line of transgenic mice (CN98). Our results showed that amphetamine and morphine did not induce conditioned place preference in calcineurin-mutant mice, whereas food remained an efficient reinforcer. In addition, behavioural sensitization to these two drugs, as measured by horizontal locomotion, was disturbed in the transgenic mice. In contrast, neither the horizontal locomotion in response to acute d-amphetamine or morphine nor the somatic signs of morphine withdrawal were affected in calcineurin mutant mice compared to their wild-type littermates. Our data indicate that calcineurin-mediated protein dephosphorylation in the hippocampus is involved in the long-term effects of drugs of abuse without influencing the motivational response to a natural reward or the physical component of opioid withdrawal. The present results emphasize the essential role of hippocampal-dependent learning and memory in the development of drug addiction.
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  • 6
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The activation of dopamine (DA) neurotransmission plays a crucial role in the behavioural responses to drugs of abuse. In particular, increased extracellular levels of DA within the mesolimbic pathway have been implicated in the rewarding and locomotor stimulatory properties of morphine. We investigated the behavioural responses to morphine in mice with a genetic disruption of the DA transporter (DAT), resulting in a constitutively high level of extrasynaptic DA. In the conditioned place preference test, DAT–/– mice exhibited a stronger rewarding response to morphine (5 mg/kg, s.c.) compared with control littermates. However, the same dose of morphine failed to increase locomotor activity in DAT–/– mice, whilst enhancing locomotion in DAT+/– and DAT+/+ animals. Morphine-induced analgesia was unaffected in mutant mice, but the behavioural expression of naloxone-induced withdrawal signs was blunted. In vivo voltammetry in the shell of the nucleus accumbens revealed that morphine was able to stimulate DA neurons in DAT–/– mice, resulting in the accumulation of higher extracellular DA levels compared with control animals. Morphine also induced a higher rate of c-fos transcription in the shell of the nucleus accumbens in mutant mice. We conclude that morphine-induced rewarding responses are firmly established in DAT mutant mice despite a DA transmission that is already tonically activated, and independently of any effect on locomotion. These particular behavioural responses to morphine may be associated with the action of the drug on DA release and c-fos expression in the shell of the nucleus accumbens of DAT–/– mice.
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  • 7
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Mice lacking the dopamine transporter (DAT) display biochemical and behavioural dopaminergic hyperactivity despite dramatic alteration in dopamine homeostasis. In order to determine the anatomical and functional integrity of the dopaminergic system, we examined the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine synthesis as well as DOPA decarboxylase and vesicular monoamine transporter. TH-positive neurons in the substantia nigra were only slightly decreased (–27.6 ± 4.5%), which can not account for the dramatic decreases in the levels of TH and dopamine that we previously observed in the striatum. TH mRNA levels were decreased by 25% in the ventral midbrain with no modification in the ratio of TH mRNA levels per cell. However, TH protein levels were decreased by 90% in the striatum and 35% in the ventral midbrain. In the striatum, many dopaminergic projections had no detectable TH, while few projections maintained regular labelling as demonstrated using electron microscopy. DOPA decarboxylase levels were not modified and vesicular transporter levels were decreased by only 28.7% which suggests that the loss of TH labelling in the striatum is not due to loss of TH projections. Interestingly, we also observed sporadic TH-positive cell bodies using immunohistochemistry and in situ hybridization in the striatum of homozygote mice, and to some extent that of wild-type animals, which raises interesting possibilities as to their potential contribution to the dopamine hyperactivity and volume transmission previously reported in these animals. In conjunction with our previous findings, these results highlight the complex regulatory mechanisms controlling TH expression at the level of mRNA, protein, activity and distribution. The paradoxical hyperdopaminergia in the DAT KO mice despite a marked decrease in TH and dopamine levels suggests a parallel to Parkinson’s disease implying that blockade of DAT may be beneficial in this condition.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 10 (1998), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The functional role of the dopamine transporter (DAT) in central dopaminergic neurotransmission was assessed further by investigating the consequences on dopamine (DA) turn-over of up- and down-regulation of this protein induced by a non-viral gene transfer approach. For this purpose, expression plasmids containing the sense or antisense coding sequence of DAT complexed with the cationic polymer, polyethylenimine (PEI), were injected into the rat substantia nigra, the brain region containing the majority of DA cell bodies. Before in vivo injection, the efficacies of the different DNA constructs were assessed by transfection studies into LLC-PK1 cells. Stereotaxic administration of the sense plasmid complexed to PEI induced, 3 days later, a significant increase in the immunoautoradiographic labelling by anti-DAT antibodies of the substantia nigra and various DA projection areas. These effects were associated with a significantly enhanced capacity of striatal synaptosomes to take up [3H]-DA and lasted up to 14 days postinjection. In contrast, 7 days after intranigral administration of the antisense plasmid complexed to PEI, we observed a significant decrease of DAT immunolabelling in the substantia nigra and [3H]-DA uptake by striatal synaptosomes. Whereas DA turnover in the striatum was unaltered 3 days after intranigral administration of the sense plasmid, it was increased 7 days after intranigral administration of the antisense construct. These data indicate that non-viral transfer of the sense or antisense coding sequence of DAT can be used as a novel approach to induce long-term changes in central DA neurotransmission.
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  • 9
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The dopamine transporter (DAT) plays a critical role in calibrating the duration and intensity of dopamine (DA) neurotransmission. Mice in which the DAT gene has been genetically deleted exhibit constitutively high levels of extrasynaptic DA and spontaneous hyperactivity. Numerous studies have characterized the adaptive molecular, physiological, and behavioural consequences of abnormal DA neurotransmission in these mice. In order to determine the genetic background contribution to these phenotypes, the DAT mutation was transferred on C57BL/6JOrl (B6) or DBA/2JOrl (D2) inbred backgrounds for more than ten generations of back-crossing to derive three B6-, D2-, and B6xD2(F1)-DAT strains. We observed that the genetic background dramatically affects phenotypes previously reported on DAT knockout (KO) mice. Depending on the genetic background, it was possible to restore survival, growth rate and ability to lactate. Interactions with the genetic background were found to modulate both quantitative and qualitative patterns of novelty-driven spontaneous hyperactivity. The paradoxical calming effect of cocaine was observed for all DAT-KO mice. However, the genetic background influenced individual threshold responses to both locomotor and rewarding effects of cocaine. These findings reveal the extent of phenotypic variation associated with the DAT mutation. They also provide concrete arguments against the assumption that the normal function of a gene can be inferred directly from its mutant phenotype.
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  • 10
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Congenital myoclonus is a widespread neurologic disorder characterized by hyperexcitability, muscular spasticity and myoclonus associated with marked reduction in neural glycine binding sites. The recessive mouse mutation spastic (spa) is a prototype of inherited myoclonus. Here we show that ...
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