Monoaminergic regulation of hemocyte activity

Biogenic amines have previously been shown to enhance both phagocytosis and nodule formation in insects. We analyzed the effect of octopamine on the locomotory behavior, polarity, and cytoskeleton of hemocytes from the greater wax moth, Galleria mellonella. Octopamine (5 × 10^-6 M) induced an initial, transient increase in locomotory rate of exomigrating plasmatocytes in vitro, and this effect was abolished by phentolamine, a general β-adrenergic antagonist. Within 5 min exposure to octopamine, hemocytes exhibited increased protrusive activity. After 15 min exposure, a higher proportion of plasmatocytes assumed lamellar and unipolarized shapes associated with movement, and granulocytes produced extensive, bulboustipped filopodia. Morphological changes were reflected in alterations of the hemocyte cytoskeleton and were consistent with changes in the relative concentrations of F- and G-actin. Our data suggest that octopamine affects hemocyte behavior in vitro, and may therefore modulate hemocyte mobilization in response to stress.