Pannexin1 stabilizes synaptic plasticity and is needed for learning.

Pannexin 1 (Panx1) represents a class of vertebrate membrane channels, bearing significant sequence homology with the invertebrate gap junction proteins, the innexins and more distant similarities in the membrane topologies and pharmacological sensitivities with gap junction proteins of the connexin family. In the nervous system, cooperation among pannexin channels, adenosine receptors, and K(ATP) channels modulating neuronal excitability via ATP and adenosine has been recognized, but little is known about the significance in vivo. However, the localization of Panx1 at postsynaptic sites in hippocampal neurons and astrocytes in close proximity together with the fundamental role of ATP and adenosine for CNS metabolism and cell signaling underscore the potential relevance of this channel to synaptic plasticity and higher brain functions. Here, we report increased excitability and potently enhanced early and persistent LTP responses in the CA1 region of acute slice preparations from adult Panx1(-/-) mice. Adenosine application and N-methyl-D-aspartate receptor (NMDAR)-blocking normalized this phenotype, suggesting that absence of Panx1 causes chronic extracellular ATP/adenosine depletion, thus facilitating postsynaptic NMDAR activation. Compensatory transcriptional up-regulation of metabotropic glutamate receptor 4 (grm4) accompanies these adaptive changes. The physiological modification, promoted by loss of Panx1, led to distinct behavioral alterations, enhancing anxiety and impairing object recognition and spatial learning in Panx1(-/-) mice. We conclude that ATP release through Panx1 channels plays a critical role in maintaining synaptic strength and plasticity in CA1 neurons of the adult hippocampus. This result provides the rationale for in-depth analysis of Panx1 function and adenosine based therapies in CNS disorders.

Detecting copy number variations in autosomal recessive limb-girdle muscular dystrophies using a multiplex ligation-dependent probe amplification (MLPA) assay.

Pathogenic mutations in the four sarcoglycan genes, designated SGCA, SGCB, SGCD and SGCG, are responsible for a subgroup of autosomal, recessive limb-girdle muscular dystrophies (LGMD 2C-F), also called sarcoglycanopathies. For the present study, we designed a multiplex ligation-dependent probe amplification (MLPA) assay, targeting all 30 coding exons and a non-coding exon of these four genes. The assay uses synthetic probes and two colours, such that as many as 28 probes can be combined into one reaction. The set of probes was established for routine application, in order to diagnostically screen patients for large duplications or deletions. In 14 of the 94 cases (15%) tested, we detected changes in copy number. Mutations in gene SGCG accounted for 7 of the 94 cases (8%), suggesting that the size of the gene makes it vulnerable to large exonic deletions. The results suggested that all cases of sarcoglycanopathy should be screened for changes in copy number. The MLPA was shown to be a rapid, robust and reliable method to screen for copy number variations (CNVs). The present synthetic probe-approach overcomes the limitations associated with cloning procedures and is particularly applicable to a range of diseases for which the number of patients to be tested is small.

Rescue of hippocampal LTP and learning deficits in a rat model of psychosis by inhibition of glycine transporter-1 (GlyT1).

N-methyl-D-aspartate (NMDA) receptor hypofunction is believed to comprise a central factor in the cognitive symptoms of psychotic illnesses such as schizophrenia. In the MK801 model of psychosis in rats, NMDA hypofunction also occurs, and animals display a profound impairment of both hippocampus-dependent learning and synaptic plasticity. The NMDA receptor may thus comprise a useful target for therapeutic amelioration of the symptoms of psychosis. However, direct activation of the receptor could lead to disturbed synaptic information storage. One possibility, however, is to enhance NMDA receptor function indirectly through elevation of glycine levels. We investigated the effects of inhibition of the glycine transporter-1, GlyT1, on long-term potentiation (LTP) and long-term depression (LTD) in the dentate gyrus of freely behaving rats that had been treated previously with MK801. LTP, but not LTD, was impaired in MK801-treated animals. Systemic application of the GlyT1-inhibitor N[3-(4'-flurophenyl)-3-(4'-phenylphenoxy) propyl]sarcosine (NFPS) rescued LTP but had no effect on LTD in MK801-treated animals. Application of the antagonist to vehicle-treated controls resulted in a disruption of LTP but not LTD. NFPS significantly ameliorated reference memory deficits in a radial maze that occurred following MK801 treatment. NFPS-treated controls performed less well, however, than vehicle-injected controls. These data support that treatment with a glycine transporter inhibitor can ameliorate deficits in both LTP and learning that occur in a rat model of psychosis, and may therefore prove a useful strategy to address cognitive disruption in psychotic illnesses. Use of the inhibitor in healthy subjects is neither beneficial to synaptic plasticity nor hippocampus-dependent learning.