The Journal of Neuroscience, October 15, 2001, 21(20):8129-8135
Primordial Rhythmic Bursting in Embryonic Cochlear Ganglion
Cells
Timothy A.
Jones,
Sherri M.
Jones, and
Kristina C.
Paggett
Department of Surgery, Division of Otolaryngology, University of
Missouri School of Medicine, Columbia, Missouri 65212
This study examined the nature of spontaneous discharge patterns in
cochlear ganglion cells in embryonic day 13 (E13) to early E17 chicken
embryos (stages 39-43). Neural recordings were made with glass
micropipettes. No sound-driven activity was seen for the youngest
embryos (maximum intensity 107 dB sound pressure level). Ganglion cells
were labeled with biotinylated dextran amine in four embryos. In two
animals, primary afferents projected to hair cells in the middle region
along the length of the basilar papilla in which, in one cell, the
terminals occupied a neural transverse position and, in the other, a
more abneural location. Statoacoustic ganglion cells showing no
spontaneous activity were seen for the first time in the chicken. The
proportion of "silent" cells was largest at the youngest stages
(stage 39, 67%). In active cells, mean spontaneous discharge rates
[9.4 ± 10.4 spikes (Sp)/sec; n = 44] were
lower than rates for older embryos (19 ± 17 Sp/sec) (Jones and
Jones, 2000). Embryos at stages 39-41 evidenced even lower rates
(4.2 ± 5.0 Sp/sec). The most salient feature of spontaneous activity for stages 39-43 was a bursting discharge pattern in >75%
of active neurons (33 of 44). Moreover, in 55% of these cells, there
was a clear, slow, rhythmic bursting pattern. The proportion of cells
showing rhythmic bursting was greatest at the youngest stages (39-42)
and decreased to <30% at stage 43. Rate of bursting ranged from 1 to
54 bursts per minute. The presence of rhythmic bursting in cochlear
ganglion cells at E13-E17 provides an explanation for the existence of
such patterns in central auditory relays. The bursting patterns may
serve as a patterning signal for central synaptic refinements in the
auditory system during development.
Key words:
functional ontogeny; bird; spontaneous activity; embryonic development; primary afferents; chicken; audition; hearing
Copyright © 2001 Society for Neuroscience 0270-6474/01/21208129-07$05.00/0
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