Inhibitory cholinergic effects on the autonomously contractile bulbus cordis branchialis of the cephalopod Sepia officinalis L

Immunohistochemical localization of two types of choline acetyltransferase in neurons and sensory cells of the octopus arm

Cholinergic structures in the arm of the cephalopod Octopus vulgaris were studied by immunohistochemistry using specific antisera for two types (common and peripheral) of acetylcholine synthetic enzyme choline acetyltransferase (ChAT): antiserum raised against the rat common type ChAT (cChAT), which is cross-reactive with molluscan cChAT, and antiserum raised against the rat peripheral type ChAT (pChAT), which has been used to delineate peripheral cholinergic structures in vertebrates, but not previously in invertebrates. Western blot analysis of octopus extracts revealed a single pChAT-positive band, suggesting that pChAT antiserum is cross-reactive with an octopus counterpart of rat pChAT. In immunohistochemistry, only neuronal structures of the octopus arm were stained by cChAT and pChAT antisera, although the pattern of distribution clearly differed between the two antisera. cChAT-positive varicose nerve fibers were observed in both the cerebrobrachial tract and neuropil of the axial nerve cord, while pChAT-positive varicose fibers were detected only in the neuropil of the axial nerve cord. After epitope retrieval, pChAT-positive neuronal cells and their processes became visible in all ganglia of the arm, including the axial and intramuscular nerve cords, and in ganglia of suckers. Moreover, pChAT-positive structures also became detectable in nerve fibers connecting the different ganglia, in smooth nerve fibers among muscle layers and dermal connective tissues, and in sensory cells of the suckers. These results suggest that the octopus arm has two types of cholinergic nerves: cChAT-positive nerves from brain ganglia and pChAT-positive nerves that are intrinsic to the arm.

The role of cholinergic networks of the anterior basal and inferior frontal lobes in the predatory behaviour of Sepia officinalis

The predatory behaviour of the cuttlefish has been the subject of a few detailed studies and can be divided into several stages: prey detection, orientation, positioning, prey-seizing, prey-manipulation and ingestion. Nevertheless, the data about its control by the CNS remain fragmentary. By injecting a cholinergic agonist (nicotine) and antagonists (alpha-bungarotoxin, mecamylamine), the implication of cholinergic networks of the anterior basal and inferior frontal lobes in the control of predatory behaviour are demonstrated. Through these cholinergic networks, the anterior basal lobe takes an important part in the orientation and positioning. The inferior frontal lobe seems to play a role in the control of brachial manipulative and buccal mass activities. The implication of cholinergic networks of the anterior basal and inferior frontal lobes in the predatory behaviour and the pharmacology of nicotinic receptors are discussed.