A neuroimmunoregulatory-like mechanism responding to stress in the marine bivalve Mytilus edulis.

Mytilus edulis has been the subject of recent studies to determine whether the relationship between the immune and nervous systems seen in vertebrates also exists in invertebrates. In the present study the effects of experimentally induced "stressful" stimuli on immunoactive hemocytes were studied in this mollusc. This subpopulation of invertebrate blood cells, resembling vertebrate granulocytes, has been previously shown to produce and react to opioid peptides. Their activation, like that of vertebrate immunocytes, expresses itself in distinctive conformational changes preceding cellular mobilization. The cellular response to "stress" observed is the same as that to the administration of exogenous mammalian opioid peptides. This strongly suggests that under the conditions of stressful stimuli, the immune/defense system can be altered by endogenous neuropeptides. The involvement of opioids in neuroimmunoregulatory phenomena appears to have a long evolutionary history.