Biogenic amines evoke heartbeat reversal in larvae of the sweet potato hornworm, Agrius convolvuli

Abstract

The sweet potato hornworm, Agrius convolvuli, possesses a pair of anterior cardiac nerves innervating the dorsal vessel. The anterior cardiac nerves branch off the visceral nerve that arises posteriorly from the frontal ganglion. Heartbeat reversal from anterograde heartbeat to posterograde heartbeat is triggered by the anterior cardiac nerves. Application of octopamine (OA) during the anterograde heartbeat phase reverses the anterograde heartbeat to the posterograde heartbeat, while application of OA during the phase of posterograde heartbeat accelerates heartbeat. The heartbeat reversal from anterograde heartbeat to posterograde heartbeat evoked by stimuli applied to the visceral nerve is blocked by application of the octopaminergic antagonists, phentolamine and chlorpromazine. The results suggest that OA may be a neurotransmitter for the anterior cardiac nerve. The alary muscle of the second segment receives excitatory innervation from the posterior cardiac nerve and from the nerve which extends from the second abdominal ganglion. Activation of the alary muscle results in acceleration of posterograde heartbeat. Other neurotransmitters, besides OA, may take part in the resultant acceleration.