Innervation of the heart and aorta of Manduca sexta

Innervation of the heart and aorta of Manduca sexta was studied by using an atomic, neuronal tracing and immunocytochemical techniques. The study was u ndertaken to provide a foundation for investigating the neural mechanisms c ontrolling cardiac reversal in adults. Lateral cardiac nerves were not foun d in the larval or adult heart. The larval heart and aorta seem to lack inn ervation, but a neurohemal system for the release of a cardioactive peptide is associated with the larval alary muscles. At adult metamorphosis, this neurohemal system regresses, and, at the same time, processes grow onto the anterior aorta. These processes seem to be neurohemal and originate from t wo pairs of neurosecretory cells located in the subesophageal ganglion. Thi s system is immunoreactive to cardioactive peptides and may function, there fore, in hormonal modulation of the activity of the adult heart. Also durin g metamorphosis, synaptic innervation develops on the terminal heart chambe r, and this innervation is from axons extending through the seventh and eig hth dorsal nerves of the terminal abdominal ganglion. These axons originate from cells that have been identified as serial homologs of motor neuron-1 of other abdominal ganglia. These neurons are immunoreactive to a cardioact ive peptide, and this peptide probably modulates the synaptic innervation o f the terminal heart chamber. During metamorphosis, the target of the motor neurons-1 of the seventh and eighth segments becomes respecified from larv al skeletal muscles to the terminal chamber of the adult heart. J. Comp. Ne urol. 440:245-260, 2001. (C) 2001 Wiley-Liss, Inc.