The Journal of Neuroscience, April 1, 1998, 18(7):2581-2591
Sensory Cells Determine Afferent Terminal Morphology in
Cross-Innervated Electroreceptor Organs: Implications for Hair
Cells
Harold
Zakon,
Ying
Lu, and
Pedro
Weisleder
Department of Zoology and Center for Developmental Biology,
Patterson Laboratory, University of Texas, Austin, Texas 78712
Type I and type II hair cells of the vestibular system are
innervated by afferents that form calyceal and bouton terminals, respectively. These cannot be experimentally cross-innervated in the
inner ear to determine how they influence each other. However, analogous organs are accessible for transplantation and
cross-innervation in the brown ghost electric fish. These fish possess
three types of electroreceptor organs. Of these, the sensory receptors
of the type I tuberous organ are S-100- and parvalbumin-positive with a
calbindin-positive afferent that forms a large calyx around the organ.
Neither the sensory receptors nor the afferents of the ampullary organs
label with these antibodies, and the afferent branches form a single
large bouton beneath each receptor cell. In controls, when cut
ampullary afferents reinnervate transplanted ampullary organs, they
have characteristic calbindin-negative terminals with large boutons.
When type I tuberous afferents reinnervate ampullary organs, receptor
cells remain S-100- and parvalbumin-negative, and the tuberous
afferents still express calbindin. The nerve terminals, however, make
large ampullary-like boutons on the receptor cells. These results
suggest that (1) afferent terminal morphology is dictated by the
receptor organ; (2) expression of calbindin by the afferent is not
suppressed by innervation of the incorrect end organ; (3) ampullary
organs generate ampullary receptor cells although innervated by
tuberous afferents; and (4) ampullary receptor cells can be trophically
supported by tuberous afferents.
Key words:
tuberous organ; ampullary organ; hair cells; vestibular; cochlear; electric fish
Copyright © 1998 Society for Neuroscience 0270-6474/98/1872581-11$05.00/0