Co-expression of the neuropeptide proctolin and glutamate in the central nervous system, along mechanosensory neurons an
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Co-expression of the neuropeptide proctolin and glutamate in the central nervous system, along mechanosensory neurons and leg muscle in Cupiennius salei Elizabeth E. Senior 1 & Hailee E. Poulin 1 & Madison G. Dobecki 1 & Bradley M. Anair 1 & Ruth Fabian-Fine 1 Received: 17 January 2020 / Accepted: 7 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
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. Keywords Efferent innervation . Synaptic circuits . Co-transmission . Neuropeptide . Central American wandering spider
Introduction Efferent innervation of mechanosensory receptor cells has been described in a variety of sensory organs in both vertebrate and invertebrate species. Examples include a variety of organs such as (1) crustacean stretch receptors (Elekes and Florey 1987a, b), (2) sideline organs of fishes (Wagner and Schwartz 1996), (3) hair cells in the mammalian cochlear system (Rabbitt and Brownell 2011; Schrott-Fischer et al., 2007), (4) scorpion peg sensilla (Gaffin and Brownell 1997), and (5) mechano- and chemosensory hair sensilla, slit sensilla, and proprioceptors in the Central American wandering spider Cupiennius salei (Fabian-Fine et al. 1999). * Ruth Fabian-Fine [email protected] 1
Department of Biology, Saint Michael’s College, One Winooski Park, Colchester, VT 05349, USA
Electrophysiological findings suggest that
