Cardiac responses to external sensory stimuli: a precious tool for testing insect responsiveness

That the insect heart represents an experimental model with interesting biological properties having close ultrastructural and functional similarities with the mammalian myocardium has been known since time. More recently, further elements of interest have emerged from the results of genetic and pharmacological research, on the basis of which the insect myocardium has been proposed as an experimental model with unique biological characteristics. This article describes how, in analogy with responses of the vegetative type typical of more evolved animal species, cardiac responses to stimulation of external sensory receptors occur in insects as well. The experiments described herein were performed on Phormia regina, Calliphora vomitoria, Protophormia terraenovae blowflies (Diptera: Calliphoridae), and on Heliothis virescens, Lymantria dispar, Bombyx mori and Spodoptera littoralis moths (Lepidoptera: Noctuidae). Regular cardiac activity and sensoryinduced variations were continuously monitored in restrained and intact specimens by means of electrocardiography (ECG). At the same time, sensory activity induced by olfactory or taste stimulation was electrophysiologically monitored on antennal (EAG) or labellar (tip-recording technique) sensilla. Short latencies and low threshold ranges of cardiac responses to sensory stimulation were measured, thus proving that prompt and efficient adjustments of the insect cardiocirculatory function take place in response to changes in the external environment. Although the physiological significance of these phenomena remains to be established, it may be hypothesized that they play an important role in adaptation of internal milieu conditions of the insect to chemical-physical changes in the external environment.