Steroid-regulated morphological plasticity in a set of identified peptidergic neurons in the moth Manduca sexta

Abstract

ABSTRACT The lateral neurosecretory cells (LNCs) in the tobacco hornworm Manduca sexta undergo a switch in neurotransmitter phenotype during pupation. Concurrent with this change in function, the LNCs undergo a major morphological reorganization. This study characterizes the morphological change and its underlying cause. In the larva, the LNC has a very compact dendritic arborization in a small volume of neuropil ipsilateral to the cell soma. In the adult moth, the LNC arborization extends through a much larger volume of neuropil, including the contralateral side of the ganglion. Using both in vivo manipulations and a single-cell culture system, we show that this change in morphology is probably triggered by two pulses of the steroid hormone 20-hydroxyecdysone (20-HE): a small commitment peak and a larger prepupal pulse. These are the same two pulses of 20-HE as those previously shown jointly to cause the change in transmitter phenotype. This work, in conjunction with a previous study on the transmitter switch, documents the orchestration of major morphological and biochemical changes in a set of identified neurons by a single hormone.