Evidence for a form of adrenergic response to stress in the mollusc Crassostrea gigas

Catecholamines and pro-opiomelanocortin (POMC)derived peptides, some of the central regulators of the stress-response systems of vertebrates, are also present in invertebrates, However, studies are needed to determine how the se hormones participate in the organisation of neuroendocrine stress-respon se axes in invertebrates. Our present work provides evidence for the presen ce of an adrenergic stress-response system in the oyster Crassostrea gigas, Noradrenaline and dopamine are released into the circulation in response t o stress. Storage and release of these hormones take place in neurosecretor y cells presenting morphological and biochemical similarities with vertebra te chromaffin cells. Both in vivo and in vitro experiments showed that appl ications of the significant release of noradrenaline or dopamine. Moreover, the nicotinic antagonists hexamethonium and alpha -bungarotoxin and the mu scarinic antagonist atropine caused no significant inhibition of catecholam ine release in stressed oysters. Adrenocorticotropic hormone (ACTH) induced a significant release of noradrenaline, but the release of dopamine in res ponse to ACTH was not significant. These results suggest that, unlike that of vertebrates, the adrenergic stress-response system of oysters is not und er the control of acetylcholine and that other factors, such as the neurope ptide ACTH, might control this system.