Physiological Investigations into the Heart Function of Arthropods

Perfusion of the isolated heart of Periplaneta americana with caffeine, digitalin, acetylcholine, nicotine and lobeline shows that the pacemaker of this heart is different from the “ myogenic centre ” of the vertebrate heart. The action of strychnine, morphine and apomorphine on this heart preparation affords evidence of the existence of a neurogenic pacemaker. This pacemaker is stimulated by suitable concentrations of acetylcholine, nicotine, lobeline and pilocarpine, while it is inhibited by atropine. Acetylcholine and tetraethyl pyrophosphate show a synergistic action. Atropine and tetraethyl pyrophosphate, like acetylcholine and curare, show an antagonistic action. These results prove that the neurogenic pacemaker possesses cholinergic properties. Adrenaline stimulates the insect heart and ergotamine inhibits it, thus suggesting that the insect heart probably also has adrenergic properties. On the basis of the present work and the results obtained by other investigators, a theory is put forward that the heart mechanism of most arthropods consists of a neurogenic pacemaker with adrenergic properties, controlled by a cholinergic accelerating nerve. This mechanism bears some resemblance to the sympathetic nerve system of vertebrates. Rotenone strongly counteracts the action of acetylcholine, tetraethyl pyrophosphate, nicotine, lobeline, pilocarpine and digitalin on the insect heart. Its point of action, however, remains obscure at the moment. The opposing action of rotenone and tetraethyl pyrophosphate is an indication that a combination of these insecticides for pest control is not to be recommended.