Coleman WL, Fischl MJ, Weimann SR, Burger RM. GABAergic and glycinergic inhibition modulate monaural auditory response properties in the avian superior olivary nucleus. J Neurophysiol 105: 2405-2420, 2011. First published March 2, 2011 doi:10.1152/jn.01088.2010.-The superior olivary nucleus (SON) is the primary source of inhibition in the avian auditory brainstem. While much is known about the role of inhibition at the SON's target nuclei, little is known about how the SON itself processes auditory information or how inhibition modulates these properties. Additionally, the synaptic physiology of inhibitory inputs within the SON has not been described. We investigated these questions using in vivo and in vitro electrophysiological techniques in combination with immunohistochemistry in the chicken, an organism for which the auditory brainstem has otherwise been well characterized. We provide a thorough characterization of monaural response properties in the SON and the influence of inhibitory input in shaping these features. We found that the SON contains a heterogeneous mixture of response patterns to acoustic stimulation and that in most neurons these responses are modulated by both GABAergic and glycinergic inhibitory inputs. Interestingly, many SON neurons tuned to low frequencies have robust phase-locking capability and the precision of this phase locking is enhanced by inhibitory inputs. On the synaptic level, we found that evoked and spontaneous inhibitory postsynaptic currents (IPSCs) within the SON are also mediated by both GABAergic and glycinergic inhibition in all neurons tested. Analysis of spontaneous IPSCs suggests that most SON cells receive a mixture of both purely GABAergic terminals, as well as terminals from which GABA and glycine are coreleased. Evidence for glycinergic signaling within the SON is a novel result that has important implications for understanding inhibitory function in the auditory brainstem.GABA A receptor; sound localization; superior olivary nucleus; glycine receptor; inhibition; interaural time disparity INTERAURAL TIME DISPARITIES (ITDs) are the main cue that animals use to localize low frequency sounds. Many features of neural circuitry that process this cue are similar between birds and mammals. For example, both systems involve specialized coincidence-detecting neurons that detect the timing differences of spikes arriving from both ears. These neurons comprise the medial superior olive in mammals (Goldberg and Brown 1969;Yin and Chan 1990) and nucleus laminaris (NL) in birds (Parks and
The synapsins, an abundant and highly conserved family of proteins that associate with synaptic vesicles, have been implicated in regulating the synaptic vesicle cycle. However, it has not been determined whether synapsin directly regulates the number of docked vesicles.
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