Embryonic development of identified neurons: origin and transformation of the H cell.

We describe the origin and the transformation of a single neuron, the H cell, which assumes two different roles during grasshopper embryogenesis. The H cell originates from the single cell division of midline precursor 3 (MP3). In the metathoracic (T3) segment, the H cell first appears as one of a pair of central pioneer fibers and later transforms into an unpaired identified neuron. During the course of its transformation, the H cell loses its original morphology and acquires new morphological and physiological properties. The H cell acquires many of the same phenotypes as the first progeny of the median neuroblast (MNB); the processes of the first MNB progeny contact the soma of the H cell and these cells are electrically coupled prior to the H cell transformation.