Abstract
Similar to hair cells in the mammalian cochlear system, mechanosensory neurons in the Central American wandering spider Cupiennius salei are strongly innervated by efferent fibers that originate from neurons whose somata are located in the central nervous system (CNS). In both the mammalian and arachnid systems, efferent fibers have been shown to co-express two or more transmitters; however, our understanding regarding co-transmission and how it affects sensory signal transduction and processing in these systems is only fragmentary. The spider model system is exceptionally suitable for this type of investigation due to the large size and easy accessibility of the sensory and efferent neurons in this system. Thus far, GABA and glutamate have been identified as the main fast-acting transmitters in efferent axons that form synaptic contacts onto sensory neurons in slit sense organs. Ultrastructural investigations suggest an abundance of neuropeptides within these peripheral synapses. In an effort to identify these peptides and conduct functional studies, we have employed immunohistochemistry to investigate whether the neuropeptide proctolin is present in neurons of the leg ganglia and in peripheral leg structures. Here, we demonstrate that ~ 73% of all neurons in the CNS of C. salei show proctolin-like immunoreactivity (proc-LIR) including the leg ganglia. We demonstrate that both strongly and weakly labeled neurons can be distinguished. The majority of proc-LIR neurons show weak labeling intensity and ~ 86.2% co-localize with glutamate. In future experiments, we plan to undertake functional studies to investigate the significance of this co-expression, which has yet to be investigated.
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Acknowledgments
The authors would like to thank Ann and Dr. David MacLaughlin for their generous donation to purchase the Zeiss Confocal microscope that was used for this study. We are grateful to Anthony Maginnis for his generous stipend to HEP and members of the Board of Trustees at Saint Michael’s College for their support to MGD and BMA.
Funding
This research was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103449 (RF-F and EES). Support was also obtained from the office of the Vice President of Academic Affairs at Saint Michael’s College.
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Senior, E.E., Poulin, H.E., Dobecki, M.G. et al. Co-expression of the neuropeptide proctolin and glutamate in the central nervous system, along mechanosensory neurons and leg muscle in Cupiennius salei. Cell Tissue Res 382, 281–292 (2020). https://doi.org/10.1007/s00441-020-03217-6
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DOI: https://doi.org/10.1007/s00441-020-03217-6