The Journal of Neuroscience, May 15, 2002, 22(10):3929-3938
In Vivo Imaging of Functional Inhibitory Networks on
the Mauthner Cell of Larval Zebrafish
Masaharu
Takahashi1,
Madoka
Narushima1, and
Yoichi
Oda1, 2
1 Laboratory of Neuroscience, Division of Biophysical
Engineering, Graduate School of Engineering Science, Osaka
University, and 2 Precursory Research for Embryonic Science
and Technology, Osaka 560-8531, Japan
Noninvasive in vivo calcium imaging was used to
observe and characterize inhibitory circuitry in intact larval
zebrafish. In the teleost hindbrain, the inhibitory network onto the
major pair of reticulospinal neurons known as Mauthner cells (M-cells) has been described in detail. There are three sources of inhibition onto M-cells: recurrent inhibition mediated by an ipsilateral collateral of the M-cell axon, feedforward inhibition driven by sensory
afferents, and reciprocal inhibition between bilaterally opposed
M-cells. To visualize these inhibitions, M-cells were retrogradely
loaded with the calcium indicator calcium green dextran. Recurrent
inhibition attenuated the Ca2+ response associated
with an action potential in M-cells. Whole-cell recording revealed
recurrent IPSCs, the conductance of which may underlie the shunting
effect on action potentials and the attenuation of the
Ca2+ signal in M-cells. Blocking synaptic
transmission within the recurrent network abolished both the
Ca2+ signal attenuation and the IPSCs. Electrical
stimulation of the otic vesicle to activate VIII nerve afferents
resulted in feedforward suppression of antidromically evoked test
Ca2+ responses in the contralateral M-cell.
Orthodromic activation of M-cells produced a reciprocal reduction of
the test Ca2+ response in the contralateral M-cell.
Thus, in the present study, we visualized the three types of inhibition
and demonstrated that they are functional at 4 d after
fertilization. The use of noninvasive techniques to image inhibition
in vivo suggest the plausibility of studying the
hypothesis previously tested in adult goldfish that use-dependent
changes in inhibitions underlie sound conditioning in escape behavior.
Key words:
Mauthner cell; confocal Ca2+ imaging; zebrafish larva; local inhibitory circuits; glycinergic synapse; recurrent IPSCs
Copyright © 2002 Society for Neuroscience 0270-6474/02/22103929-10$05.00/0
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