Differentiation of an identified sensory neuron (SR) and associated structures (CTO) in grasshopper embryos

Abstract

The differentiation of an identified sensory neuron, the grasshopper wing hinge Stretch Receptor (SR), is examined throughout embryogenesis. The morphological features of the SR axon, as it finds its path from the peripheral cell body to the CNS, and the timing of this peripheral growth were determined by intracellular injection of Lucifer yellow. The course of growth of the SR axon within the CNS and the sequence of formation of the identified branches in its characteristic central arborization were investigated by silver intensification of cobalt-stained axons. In addition, intracellular recording from the cell body of SR was used to determine the onset of electrical excitability and the characteristics of the somal action potential. A brief account of the differentiation of the closely associated wing hinge Chordotonal Organ is also given. During differentiation, the cell bodies of SR and the first wing hinge Chordotonal Organ neuron (CTN₁) extend processes and migrate posteriorly along a peripheral epithelial ridge. The cell bodies migrate up to 150 m̈m with a group of undifferentiated cells to a specific site at the posterior edge of the segment. As the SR and CTN₁ cell bodies migrate, their trailing axons stretch across the epithelial ridge. These axons form the medial body wall nerve (1D₂) that the axons of subsequent sensory neurons follow.