Neuroscience
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Previous work has shown an important role for neuroligins in promoting the formation of synaptic connections in cultured cells. Although neuroligins enhance both excitatory and inhibitory synapse formation, individual neuroligin isoforms have been shown to preferentially localize to either glutamatergic or GABAergic synapses. Current evidence points to an important role for both the extracellular and intracellular domains of neuroligins in their synaptic localization. ⋯ We demonstrate that knockdown of gephyrin results in a significant shift of NL2 from inhibitory to excitatory synaptic contacts, while knockdown of PSD-95 leads to a partial shift of NL2 and NL3 from excitatory to inhibitory contacts. Furthermore, analysis of specific domain deletions within the C-terminal, intracellular domain of NL2 reveals that the region between amino acids 716 and 782 is required for the normal synaptic clustering of this protein. Together, these data suggest that intracellular mechanisms are involved in the targeting of different neuroligin family members to synapses (216).
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The prefrontal cortex plays a key role in the perception of painful stimuli, including those emerging from the viscera. Colorectal distension is a non-invasive stimulus used to study visceral pain processing in the nervous system. Visceral hypersensitivity is one of the main characteristics of the functional bowel disorder irritable bowel syndrome (IBS). ⋯ However, an exaggerated cell activation was found in the prelimbic, infralimbic and rostral anterior cingulate cortices of the WKY rat compared to SD animals. No significant difference was found in caudal anterior cingulate cortex activation when the strains were compared. These results demonstrate, to our knowledge, for the first time an augmented colorectal distension-induced prefrontal cortex activity in WKY rats similar to that seen in IBS patients, further supporting the use of this strain as a model in which to study brain-gut axis dysregulation observed in IBS.
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Soluble guanylyl cyclases (sGCs) are traditionally recognized as the main molecular receptor for nitric oxide (NO), a gaseous transmitter involved in many functions of the nervous system. Some sGCs are however insensitive to NO and therefore are known as atypical. Although atypical sGCs have been shown to exist in both vertebrate and invertebrate nervous systems, our understanding of their functional role is incomplete. ⋯ The results of our in situ hybridization and RT-PCR experiments support this idea further by showing that Lym-sGCbeta3 is expressed in the osphradium, a peripheral sense organ in which oxygen-sensing neurons are located. Also of interest are our observations that many neurons in Lymnaea CNS co-express conventional and atypical sGC subunits. These data are consistent with a possible dominant negative regulatory role of atypical sGC subunits through the formation of heterodimers exhibiting low enzymatic activity.
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We previously identified KEPI as a morphine-regulated gene using subtractive hybridization and differential display PCR. Upon phosphorylation by protein kinase C, KEPI becomes a powerful inhibitor of protein phosphatase 1. To gain insights into KEPI functions, we created KEPI knockout (KO) mice on mixed 129S6xC57BL/6 genetic backgrounds. ⋯ This strategy minimized the amount of 129S6 DNA surrounding the transgene and documented the C57BL/6 origin of the Oprm1 gene in this founder and its offspring. Recombinant KEPIKO mice displayed (a) normal analgesic responses and normal locomotion after initial morphine treatments, (b) accelerated development of tolerance to analgesic effects of morphine, (c) elevated activity of protein phosphatase 1 in thalamus, (d) attenuated morphine reward as assessed by conditioned place preference. These data support roles for KEPI action in adaptive responses to repeated administration of morphine that include analgesic tolerance and drug reward.
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N-methyl-d-aspartate (NMDA) receptors (NMDARs) are highly expressed in the CNS and mediate the slow component of excitatory transmission. The present study was aimed at characterizing the temperature dependence of the kinetic properties of native NMDARs, with special emphasis on the deactivation of synaptic NMDARs. We used patch-clamp recordings to study synaptic NMDARs at layer II/III pyramidal neurons of the rat cortex, recombinant GluN1/GluN2B receptors expressed in human embryonic kidney (HEK293) cells, and NMDARs in cultured hippocampal neurons. ⋯ Ifenprodil reduced the amplitude of NMDAR-mediated EPSCs by approximately 50% but had no effect on the time course of deactivation. Analysis of GluN1/GluN2B responses indicated that the double exponential time course of deactivation reflects mainly agonist dissociation and receptor desensitization. We conclude that the temperature dependences of native and recombinant NMDAR are different; in addition, we contribute to a better understanding of the molecular mechanism that controls the time course of NMDAR-mediated EPSCs.