Neuroscience
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Nociceptive primary afferents have the capacity to induce a state of increased excitability in the dorsal horn neurons of the spinal cord. It is well accepted that capsaicin-sensitive C-fibers transduce noxious stimulation and acute pain and that capsaicin-insensitive A beta-fibers are responsible for touch and innocuous sensation. It has been reported that the intrathecal (i.t.) administration of prostaglandin F(2 alpha) (PGF(2 alpha)) and ATP induces mechanical allodynia via the capsaicin-insensitive primary afferent pathway. ⋯ Immunostaining of beta-galactosidase, a reporter knocked into the endogenous FP locus in FP(-/-) mice, showed that the FP receptor was co-localized with P2X(2) and P2X(3) receptors in neurons of the spinal cord. alphabeta-Methylene ATP evoked a transient or sustained [Ca(2+)](i) increase in most of the PGF(2 alpha)-responsive cells in the deeper layer of the spinal cord, and the alphabeta-methylene ATP-evoked increase was blocked by the FP receptor antagonist AL-8810 in two-thirds of the cells. Neither PGF(2 alpha) nor alphabeta-methylene ATP induced the activation of spinal microglia. The present study demonstrates that the alphabeta-methylene ATP-evoked allodynia is mediated by the FP receptor, possibly via the functional coupling between the activation of P2X(2/3) receptors on the central terminal of capsaicin-insensitive fibers and FP receptors on spinal neurons.
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The transmembrane isoform of agrin (Tm-agrin) is the predominant form expressed in the brain but its putative roles in brain development are not well understood. Recent reports have implicated Tm-agrin in the formation and stabilization of filopodia on neurites of immature central and peripheral neurons in culture. In maturing central neurons, dendritic filopodia are believed to facilitate synapse formation. ⋯ We found that dendritic filopodia density was markedly reduced, as was synapse density along dendrites. Moreover, synapse formation was more sharply reduced on dendrites of infected neurons contacted by uninfected axons than on uninfected dendrites contacted by infected axons. The results are consistent with a physiological role for Tm-agrin in the maturation of hippocampal neurons involving positive regulation of dendritic filopodia and consequent promotion of synaptogenesis, but also suggest a role for axonal agrin in synaptogenesis.
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At the developing vertebrate neuromuscular junction, the acetylcholine receptor becomes aggregated at high density in the postsynaptic muscle membrane. Receptor localization is regulated by the motoneuron-derived factor, agrin, and requires an intracellular, scaffolding protein called rapsyn. However, it remains unclear where rapsyn binds on the acetylcholine receptor and how their interaction is regulated. ⋯ When expressed in muscle cells, rapsyn co-immunoprecipitated together with a CD4-alpha helical region chimera, independent of agrin signaling. Together, these findings demonstrate that rapsyn interacts with the acetylcholine receptor via an alpha-helical structural motif conserved between the alpha, beta and epsilon subunits. Binding at this site likely mediates the critical rapsyn interaction involved in localizing the acetylcholine receptor at the neuromuscular junction.
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The nociceptin/orphanin FQ (N/OFQ) opioid peptide receptor (NOPr) is a new member of the opioid receptor family consisting of mu, delta and kappa opioid receptors. The anti-opioid properties of its endogenous ligand, N/OFQ provide the receptor interesting potentials in symptoms and processes related to drug addiction, learning and memory, anxiety and depression, and nociception. Using target-selected N-ethyl-N-nitrosourea (ENU)-driven mutagenesis we recently generated a rat model bearing a premature stop codon in the opioid-like receptor (oprl1) gene, and here we describe the primary characterization of this novel model. ⋯ Quantitative autoradiographic mapping of mu, delta and kappa opioid receptors using [(3)H]DAMGO, [(3)H]deltorphin and [(3)H]CI-977, respectively, did not show any changes in opioid receptor binding. In conclusion, we present a novel mutant rat lacking NOPr without compensatory changes in mu, delta and kappa opioid receptors. We anticipate that this mutant rat will have heuristic value to further understand the function of NOPr.
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Chronic opiate administration alters the expression levels of the stress-responsive peptide, corticotropin-releasing factor (CRF), in the bed nucleus of the stria terminalis (BNST). This brain region contains CRF receptors that drive drug-seeking behavior exacerbated by stress. We used electron microscopy to quantitatively compare immunolabeling of the corticotropin-releasing factor receptor (CRFr) and CRF in the anterolateral bed nucleus of the stria terminalis (BSTal) of mice injected with saline or morphine in escalating doses for 14 days. ⋯ In contrast, saline and morphine treatment groups showed no significant differences in the total number of CRF-immunoreactive axon terminals, or the frequency with which these terminals contacted CRFr-containing dendrites. This suggests that morphine does not influence axonal availability of CRF in the BSTal. The results have important implications for drug-associated adaptations in brain stress systems that may contribute to the motivation to continue drug use during dependence.