The dendron and episodic neuropeptide release

Many neuromuscular and central synapses exhibit activity-dependent plasticity. The sustained high-frequency firing needed to elicit some forms of plasticity are similar to those often required to release neuropeptides. We wanted to determine if neuropeptide release could contribute to post-tetanic potentiation (PTP) and chose neuromuscular synapses in buccal muscle I3a to explore this issue. This muscle is innervated by two motor neurons (termed B3 and B38) that show PTP in response to tetanic stimulation. B3 and B38 use glutamate as their fast transmitter but express different modulatory neuropeptides. B3 expresses FMRFamide, a neuropeptide that only slightly increases its own excitatory junction potentials (EJPs). B38 expresses the small cardioactive peptide (SCP), a neuropeptide that dramatically increases its own EJPs. It was our hypothesis that SCP released from B38's terminals during tetanic stimulation mediated a component of PTP for B38. Because no antagonist to SCP currently exists, we used several indirect approaches to test this hypothesis. First, we studied the effects of increasing stimulation frequency during the tetanus or lowering temperature on PTP. Both of these changes are known to dramatically increase SCP release. We found that increasing the frequency of stimulation increased PTP for both neurons; however, the effects were larger for B38. Decreasing the temperature tended to reduce PTP for B3, while increasing PTP for B38. These results were consistent with known properties of SCP release from B38. Next we selectively superfused the neuromuscular synapses with exogenous SCP to determine if this would occlude the effects of SCP released from B38 during a tetanus. We found that exogenous SCP dramatically reduced PTP for B38 but had little effect on PTP for B3. Thus our results support the hypothesis that physiological stimulation of B38 elicits PTP that is predominantly dependent on the release of SCP from its own terminals. They also demonstrate that the mechanisms underlying PTP can be very different for two motor neurons innervating the same target muscle.

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Selective Expression of a SNARE-Cleaving Protease in Peripheral Sensory Neurons Attenuates Pain-Related Gene Transcription and Neuropeptide Release

International Journal of Molecular Sciences ◽

10.3390/ijms22168826 ◽

2021 ◽

Vol 22 (16) ◽

pp. 8826

Author(s):

Wanzhi Wang ◽

Miaomiao Kong ◽

Yu Dou ◽

Shanghai Xue ◽

Yang Liu ◽

...

Keyword(s):

Chronic Pain ◽

Sensory Neurons ◽

Transient Receptor Potential ◽

Safety Concern ◽

Unmet Need ◽

Nociceptive Neurons ◽

Neuropeptide Release ◽

Selective Expression ◽

Peripheral Sensory Neurons ◽

Peripheral Sensory

Chronic pain is a leading health and socioeconomic problem and an unmet need exists for long-lasting analgesics. SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) are required for neuropeptide release and noxious signal transducer surface trafficking, thus, selective expression of the SNARE-cleaving light-chain protease of botulinum neurotoxin A (LCA) in peripheral sensory neurons could alleviate chronic pain. However, a safety concern to this approach is the lack of a sensory neuronal promoter to prevent the expression of LCA in the central nervous system. Towards this, we exploit the unique characteristics of Pirt (phosphoinositide-interacting regulator of TRP), which is expressed in peripheral nociceptive neurons. For the first time, we identified a Pirt promoter element and cloned it into a lentiviral vector driving transgene expression selectively in peripheral sensory neurons. Pirt promoter driven-LCA expression yielded rapid and concentration-dependent cleavage of SNAP-25 in cultured sensory neurons. Moreover, the transcripts of pain-related genes (TAC1, tachykinin precursor 1; CALCB, calcitonin gene-related peptide 2; HTR3A, 5-hydroxytryptamine receptor 3A; NPY2R, neuropeptide Y receptor Y2; GPR52, G protein-coupled receptor 52; SCN9A, sodium voltage-gated channel alpha subunit 9; TRPV1 and TRPA1, transient receptor potential cation channel subfamily V member 1 and subfamily A member 1) in pro-inflammatory cytokines stimulated sensory neurons were downregulated by viral mediated expression of LCA. Furthermore, viral expression of LCA yielded long-lasting inhibition of pain mediator release. Thus, we show that the engineered Pirt-LCA virus may provide a novel means for long lasting pain relief.

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