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J Neurophysiol (July 1, 2009). doi:10.1152/jn.00186.2009
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Submitted on March 3, 2009
Revised on June 26, 2009
Accepted on June 28, 2009

P2 receptor-mediated signaling in spherical bushy cells of the mammalian cochlear nucleus

Ivan Milenkovic1*, Ilka Rinke1, Mirko Witte1, Beatrice Dietz2, and Rudolf Rübsamen3

1 Institute of Biology II
2 University of Leipzig
3 Institute of Biology II, University of Leipzig

* To whom correspondence should be addressed. E-mail: mili{at}uni-leipzig.de.

Purinoreceptors of the P2 family contribute strongly to signaling in the cochlea, but little is known about the effects of purinergic neurotransmission in the central auditory system. Here we examine P2 receptor-mediated signaling in the large spherical bushy cells (SBCs) of Mongolian gerbil around the onset of acoustically evoked signal processing (P9-14). Brief ATP{gamma}S application evoked inward current, membrane depolarization, and somatic Ca2+ signals. Moreover, ATP{gamma}S changed the SBCs firing pattern from phasic to tonic, when the application was synchronized with depolarizing current injection. This bursting discharge activity was dependent on [Ca2+]i and PKC activity, and is presumably caused by modulation of low-threshold K+ conductance. Activation of P2Y1 receptors could not evoke these changes per se, thus it was concluded that the involvement of P2X receptors seems to be necessary. Ca2+ imaging data revealed that both P2X and P2Y1 receptors mediate Ca2+ signals in SBCs where P2Y1 receptors most likely activate the PLC-IP3 pathway and release Ca2+ from internal stores. Immunohistochemical staining confirmed the expression of P2X2 and P2Y1 receptor proteins in SBCs providing additional evidence for the involvement of both receptors in signal transduction in these neurons. Purinergic signaling might modulate excitability of SBCs and thereby contribute to regulation of synaptic strength. Functionally, the increase in firing rate mediated by P2 receptors could reduce temporal precision of the postsynaptic firing, e.g. phase locking , which has an immediate effect on signal processing related to sound localization. This might provide a mechanism for adaptation to the ambient acoustic environment.







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