Acetylcholine Release and Choline Uptake by Cuttlefish (Sepia officinalis) Optic Lobe Synaptosomes

M Alexandra Nunes,Yves Dunant,Virgília S Silva,J Miguel Cordeiro,António Sykes,Sofia Santos,Fernando Morgado,Paula P Gonçalves,Paulo Neves

doi:10.2307/25066654

M Alexandra Nunes, Yves Dunant + Show 7 more

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https://doi.org/10.2307/25066654

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Abstract

Acetylcholine (ACh), which is synthesized from choline (Ch), is believed to hold a central place in signaling mechanisms within the central nervous system (CNS) of cuttlefish (Sepia officinalis) and other coleoid cephalopods. Although the main elements required for cholinergic function have been identified in cephalopods, the transmembrane translocation events promoting the release of ACh and the uptake of Ch remain largely unsolved. The ACh release and Ch uptake were quantitatively studied through the use of in vitro chemiluminescence and isotopic methods on a subcellular fraction enriched in synaptic nerve endings (synaptosomes) isolated from cuttlefish optic lobe. The ACh release evoked by K+ depolarization was found to be very high (0.04 pmol ACh.s(-1).mg(-1) protein). In response to stimulation by veratridine, a secretagogue (a substance that induces secretion) that targets voltage-gated Na+ channels, the release rate and the total amount of ACh released were significantly lower, by 10-fold, than the response induced by KCl. The high-affinity uptake of choline was also very high (31 pmol Ch.min(-1).mg(-1) protein). The observed ACh release and Ch uptake patterns are in good agreement with published data on preparations characterized by high levels of ACh metabolism, adding further evidence that ACh acts as a neurotransmitter in cuttlefish optic lobe.

Highlights

Tional anatomy of the cuttlefish nervous system has been well illustrated, including investigation by electrical stimulation [1, 2], much less information is available on signaling mechanisms within the neural networks of cephalopods [3]
The cuttlefish optic lobe comprises an outer granule cell layer, a neurophil layer, an inner granule cell layer, and numerous clusters of cell bodies separated by areas of nerve fibers and synaptic areas [5]
It has been shown that ACh catabolism increases in the optic lobes as a response to memory formation with a long-term retention delay [8]

Summary

Introduction

Tional anatomy of the cuttlefish nervous system has been well illustrated, including investigation by electrical stimulation [1, 2], much less information is available on signaling mechanisms within the neural networks of cephalopods [3]. These major processes of cholinergic function, by analyzing the time-course of ACh release and Ch uptake and by comparing the effect of two secretagogues, KCl and veratridine, in pinched-off nerve terminals (synaptosomes) from cuttlefish optic lobes.

Results

Conclusion