Neurotransmitters of cephalopods

• Published in: Invertebrate neuroscience 1996-09, Vol.2 (2), p.95-114
• Main Author: Messenger, J. B.
• Format: Article
• Language: English
• Subjects: Cephalopoda; Marine
• ISSN: 1354-2516; 1439-1104
• DOI: 10.1007/BF02214113

ACh, dopamine, noradrenaline, 5-HT, L-glutamate, and GABA are widely distributed in cephalopods and probably all function as neurotransmitters; octopamine also occurs and at one site is known to act as a neuromodulator. Several peptides are also present, as well as nitric oxide synthase. In the brain and sense organs cholinergic, aminergic, serotonergic and glutamatergic systems seem to be the most important. ACh is also active in the gut, vascular system and some body muscles: it is generally inhibitory. The ACh receptors are similar to the vertebrate nicotinic type. The catecholamines are important in the gut and vascular system: they are generally excitatory. The NA receptors are like the alpha -adrenergic subtype of vertebrates, but the nature of the DA and OA receptors is less certain. 5-HT is important in the gut but is endogenous in some chromatophore nerves and acts on receptors that seem like the vertebrate 5-HT sub(1) type. L-glutamate is an excitatory transmitter at the chromatophore (and probably at other) nerve-muscle junctions and is an extremely strong candidate for being the excitatory transmitter at the squid giant synapse. There are NMDA receptors on Schwann-cells but the receptors on neurons and muscles are like the vertebrate kainate type. Little is known about the mode of action of cephalopod peptides; nor has it ever been shown that they co-exist with conventional transmitters in these animals. The structure of one (FMRFamide) receptor has been elucidated, but apart from this nothing is known of the molecular biology of receptors in cephalopods.