Axonal pathways in the brain-retrocerebral neuroendocrine complex of Manduca sexta (L.) (Lepidoptera: Sphingidae)

Abstract

Axonal pathways of the various neurosecretory cell groups in the brain of larvae and pupae of Manduca sexta were studied, using a cobalt diffusion and precipitation technique. Five groups of cells were found to send axons to each retrocerebral complex. Axons from the fused nervi corporis cardiaci I and II arise from 2 ipsilateral dorsomedial groups, a controlateral anteromedial group, and a controlateral dorsolateral group. Axons from the NCC III arise from a group of ipsilateral tritocerebral neurosecretory cells. All of the cell groups sending axons through the NCC I+II innervate the corpus allatum. By contrast, only a few of the axons making up the NCC I+II appear to terminate in the corpora cardiaca (CC). The tritocerebral cells send axons to the CC only. Extensive migration of neurosecretory cells takes place during metamorphosis. The dorsomedial cells of the larva migrate laterad to become the lateral neurosecretory cells of the pupa and adult. The anteromedial cells of the larva migrate dorsad to become the medial neurosecretory cells of the pupa and adult.