Nerve dependency of developing and mature sensory receptor cells.

Old and recent data concerning development of sensory cells and trophic interdependency of sensory neurons and sensory cells is reviewed for the ear, the lateral line system, the electroreceptive system, and the taste system. All sensory neurons originate from placodes. However, only most ear, lateral line and electrosensory cells derive from placodes, while the taste sensory cell originate locally. All sensory cells apparently are nerve independent for their formation, and at least sensory cells in the ear and the taste system share the neurotrophic support for their specific sensory neurons. Later, most of these sensory cells appear to depend, to a variable degree, on some innervation for maintenance. While the molecular nature of the signal cascade from sensory cells to sensory neurons is known in at least two systems, nothing is known about the molecular nature of the signal cascade from the sensory neurons back to the sensory cells.