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Activation of presynaptic GABAB receptors modulates GABAergic and glutamatergic inputs to the medial geniculate body

2011; Elsevier BV; Volume: 280; Issue: 1-2 Linguagem: Inglês

10.1016/j.heares.2011.05.018

1878-5891

Bin Luo, Haitao Wang, Yanyan Su, S. H. Wu, Lin Chen,

Memory and Neural Mechanisms

The medial geniculate body (MGB) receives ascending inputs from the inferior colliculus and descending inputs from the auditory cortex. In the present study, we intended to determine whether activation of presynaptic GABAB receptors modulates GABAergic and glutamatergic inputs to the MGB with whole-cell patch-clamp recordings in brain slices of the rat. To evoke a synaptic response, we electrically stimulated the ascending and descending inputs to MGB neurons with bipolar electrodes placed on the brachium of the inferior colliculus and the superior thalamic radiation. To isolate presynaptic mechanisms, we blocked the effects of postsynaptic GABAB receptors by filling recording electrodes with the internal solution containing cesium and QX-314. The activation of presynaptic GABAB receptors by exogenous agonist was shown to modulate synaptic inputs to the MGB as demonstrated by that (1) baclofen, a GABAB receptor agonist, reversibly suppressed both inhibitory postsynaptic currents (IPSCs) and excitatory postsynaptic currents (EPSCs) and this suppressive effect could be blocked by CGP35348, a GABAB receptor antagonist, (2) baclofen significantly increased the ratio of IPSCs or EPSCs elicited by paired-pulse stimulation, and (3) baclofen depressed EPSCs and IPSCs in response to repetitive stimulation. The activation of presynaptic GABAB receptors by endogenously released GABA was shown to modulate the synaptic transmission as demonstrated by that CGP55845, another GABAB receptor antagonist, increased the ratio of IPSCs to paired-pulse stimulation in young (P8-10) rats, although not in juvenile (P15-18) rats. Our study provides electrophysiological evidence for the presence of functional presynaptic GABAB receptors in the MGB and suggests an age-dependent role of these receptors in the synaptic transmission in this central auditory region.