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.
