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The Journal of Neuroscience, June 1, 2003, 23(11):4625-4634
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GABA Receptors Containing Rdl Subunits Mediate Fast Inhibitory Synaptic Transmission in Drosophila Neurons
Daewoo Lee,
Hailing Su, and
Diane K. O'Dowd
Departments of Anatomy and Neurobiology, Developmental and Cell Biology,
University of California, Irvine, California 92697-1280
GABAergic inhibition in Drosophila, as in other insects and
mammals, is important for regulation of activity in the CNS. However, the
functional properties of synaptic GABA receptors in Drosophila have
not been described. Here, we report that spontaneous GABAergic postsynaptic
currents (sPSCs) in cultured embryonic Drosophila neurons are
mediated by picrotoxin-sensitive chloride-conducting receptors. A rapid
increase in spontaneous firing in response to bath application of picrotoxin
demonstrates that these GABA receptors mediate inhibition in the neuronal
networks formed in culture. Many of the spontaneous GABAergic synaptic
currents are sodium action potential independent [miniature IPSCs (mIPSCs)]
but are regulated by external calcium levels. The large variation in mIPSC
frequency, amplitude, and kinetics properties between neurons suggests
heterogeneity in GABA receptor number, location, and/or subtype. A decrease in
the mean mIPSC decay time constant between 2 and 5 d, in the absence of a
correlated change in rise time, demonstrates that the functional properties of
the synaptic GABA receptors are regulated during maturation in vitro.
Finally, neurons from the GABA receptor subunit mutant Rdl exhibit
reduced sensitivity to picrotoxin blockade of the mIPSCs and resistance to
picrotoxin-induced increases in spontaneous firing frequency. This
demonstrates that Rdl containing GABA receptors play a direct role in
mediating synaptic inhibition in Drosophila neural circuits formed in
culture.
Key words: Drosophila; GABAergic synaptic transmission; GABA receptor; Rdl receptors; development; synaptic inhibition
Received Jan. 14, 2003;
revised Mar. 11, 2003;
accepted Mar. 17, 2003.
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