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Cephalopod NeurobiologyNeuroscience Studies in Squid, Octopus and Cuttlefish$
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N. Joan Abbott, Roddy Williamson, and Linda Maddock

Print publication date: 1995

Print ISBN-13: 9780198547907

Published to Oxford Scholarship Online: March 2012

DOI: 10.1093/acprof:oso/9780198547907.001.0001

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Neurotransmitters of squid chromatophores

Neurotransmitters of squid chromatophores

Chapter:
(p.369) 22 Neurotransmitters of squid chromatophores
Source:
Cephalopod Neurobiology
Author(s):

C. J. Cornwell

J. B. Messenger

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198547907.003.0255

Squid chromatophores expand as a result of the contraction of a set of 15–25 radial muscles set around a sac containing pigment granules. Running along the surface of each radial muscle are excitatory nerve fibres that arise directly from cells lying in the brain. Squids change colour by expanding and retracting the chromatophores. Axons from cell bodies within the brain directly innervate the chromatophore radial muscles. When the nerves are active, the radial muscles contract and the chromatophore expands; when they are inactive, energy stored in the elastic sac causes the chromatophores to retract as the muscles relax. Expansion of the chromatophores reveals more pigment and thus alters the quality of light reflected from the skin: the change in area of pigment exposed, from fully retracted to fully expanded, can be 80-fold or more. Squids use their chromatophores primarily for concealment, in particular for countershading and to provide effective camouflage. This chapter presents evidence in support of the hypothesis that l-glutamate may be an excitatory transmitter at the neuromuscular junctions on the radial. The hypothesis has been confirmed by the application of a series of newly developed specific glutamate receptor agonists to the skin of the small loliginid squid, Alloteuthis subulata. This small, coastal species was studied with comparatively large chromatophores, whose skin is peculiar in that the dermis can be easily removed to allow access of drugs, antibodies, and stains. A series of experiments show that glutamate and non-N-methyl-d-aspartic acic receptor agonists elicit chromatophore expansion when topically applied to Alloteuthis skin.

Keywords:   squid chromatophores, neurotransmitters, l-glutamate, neuromuscular, Alloteuthis subulata, countershading

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