The chromatic and motor effects of neurotransmitter injection in intact and brain-lesionedOctopus

Abstract

Various neurotransmitters were injected into the blood supplying the brain ofOctopus vulgarisand the effects, particularly on the chromatophores, were observed.l-glutamate, GABA, dopamine, noradrenaline and octopamine caused expansion of the chromatophores and darkening of the skin; ACh caused retraction of the chromatophores and paling; 5HT caused differential expansion and retraction: mottling. These responses, which are neurally mediated, were particularly well defined for ACh and 5HT and the effects of these drugs were studied in more detail. The paling effect of ACh was mimicked by nicotine but not muscarine and was partially antagonized by tubocurarine. The mottling induced by 5HT was transiently antagonized by methysergide maleate, as was ink-ejection and defaecation. Brain lesions to localize the sites of action of ACh and 5HT suggest that they act at the level of the sub-oesophageal lobes to control the chromatophores, but that 5 HT may act at the level of the optic lobe to control inking and defaecation. These results are related to the pharmacology and histochemistry of the cephalopod brain and to the organization of the chromatophore control system.