Browsing by Subject "calcitonin gene-related peptide (CGRP)"

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    Cellular Mechanisms Mediating the Actions of Nerve Growth Factor in Sensory Neurons
    (2007-08-08T15:24:37Z) Park, Kellie Adrienne; Vasko, Michael R.
    Nerve growth factor (NGF) is a neurotrophin upregulated with injury and inflammation. Peripheral administration of NGF causes hyperalgesia and allodynia in animals. Blocking NGF signaling reverses these effects. At the cellular level, chronic exposure of sensory neurons to NGF enhances expression the neurotransmitter, calcitonin gene-related peptide (CGRP). Acute exposure to NGF increases capsaicin-evoked CGRP release from sensory neurons in culture. Thus, NGF increases peptide release from neurons by: (1) increasing expression of peptides, and/or (2) altering their sensitivity. The increase in peptide outflow by either mechanism could contribute to development of hyperalgesia and allodynia. The signaling cascades mediating the actions of NGF in sensory neurons are unclear. Therefore, experiments were designed to determine which pathways regulate changes in iCGRP content and evoked release from primary sensory neurons in culture. The Ras/MEK/ERK cascade was identified as a possible regulator of iCGRP expression in response to NGF. To test this pathway, it was manipulated in neurons by (1) expression of dominant negative or constitutively active isoforms of Ras, (2) farnesyltransferase inhibition, (3) manipulation of the RasGAP, synGAP, and (4) blocking MEK activity. When the pathway was blocked, the NGF-induced increase in iCGRP expression was attenuated. When the Ras pathway was activated, iCGRP expression increased. These data indicate that Ras, and downstream signaling kinases, MEK and ERK, regulate the NGF-induced increases in CGRP in sensory neurons. To determine which pathway(s) regulate the increase in capsaicin-evoked iCGRP release upon brief exposure to NGF, the Ras/MEK/ERK pathway was manipulated as described above, and pharmacological inhibitors of the PI3 kinase, PLC, and Src kinase pathways were used. There were no differences observed in NGF-sensitization when the Ras and PI3 kinase pathways were inhibited, suggesting these two pathways were not involved. However, when the Src kinase inhibitor PP2 was used, the NGF-induced increase in release was completely blocked. Furthermore, the PKC inhibitor, BIM, also inhibited the sensitization by NGF. This data indicate Src and PKC regulate of sensitivity of sensory neurons in response to brief exposure to NGF. Thus, there is differential regulation of iCGRP content and evoked release from sensory neurons in response to NGF.
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    SCHWANN CELLS MODULATE THE RELEASE OF CALCITONIN GENE-RELATED PEPTIDE FROM SENSORY NEURONS
    (Office of the Vice Chancellor for Research, 2012-04-13) Meadows, Rena M.; Hingtgen, Cynthia M.
    An alteration in the interaction between Schwann cells and sensory neurons may be involved in inflammatory neuropathies associated with altered sensation and pain. The release of the peptide transmitter, calcitonin gene-related peptide (CGRP), is one method to monitor the sensitivity of a subclass of primary sensory neurons involved in pain signaling. We utilized an in vitro assay to investigate the interaction between Schwann cells and sensory neurons in an inflammatory state. Schwann cells and sensory neurons were isolated from adult mouse sciatic nerve and dorsal root ganglia, respectively, and maintained in culture. Schwann cells were exposed to HEPES buffer containing the inflammatory mediators histamine, prostaglandin E2, bradykinin, and serotonin (all 10-5 M), potassium (7 mM), and at pH 7.0 for 10 minutes. After this activation, the Schwann cells were incubated in HEPES buffer alone for 1 hour. This Schwann cell-conditioned buffer (SCCB) was collected and sensory neurons were exposed to three consecutive 10 minute incubations in HEPES buffer alone or SCCB. The amount of CGRP released during each of these incubations was measured using radioimmunoassay. Incubation with SCCB elicited a seven-fold increase in the release of CGRP compared to neurons exposed to HEPES buffer alone. The release of CGRP elicited by SCCB was abolished when neurons were exposed to SCCB containing no added calcium. After treatment with the inflammatory mediators detailed above for 10 minutes, Schwann cell lysates showed a significant decrease in six cytokines, while SCCB demonstrated an increase in interleukin-6 (IL-6) as measured by a cytokine array panel. These results suggest that during inflammation, Schwann cells release substances, which directly stimulate sensory neurons, as measured by an increase in CGRP release. These findings reinforce the importance of identifying the mechanisms underlying the interaction between Schwann cells and sensory neurons to discover novel therapeutics for treating inflammatory pain.