GABAB receptor-mediated presynaptic inhibition of glutamatergic transmission in the inferior colliculus.
Whole-cell patch clamp recordings were made from ICC neurons in brain slices of 9-16 day old rats. Postsynaptic currents were evoked by electrical stimulation of the lemniscal inputs. Excitatory postsynaptic currents (EPSCs) were isolated pharmacologically by blocking GABA(A) and glycine receptors. EPSCs were further dissected into AMPA and NMDA receptor-mediated responses by adding the receptor antagonists, APV and CNQX, respectively. The internal solution in the recording electrodes contained CsF and TEA to block K(+) channels that might be activated by postsynaptic GABA(B) receptors. The modulatory effects of GABA(B) receptors on EPSCs in ICC neurons were examined by bath application of the GABA(B) receptor agonist, baclofen, and the antagonist, CGP 35348. The amplitudes of EPSCs in ICC neurons were reduced to 34.4+/-3.2% of the control by baclofen (5-10 microM). The suppressive effect by baclofen was concentration-dependent. The reduction of the EPSC amplitude was reversed by CGP35348. The ratio of the 2nd to 1st EPSCs evoked by paired-pulse stimulation was significantly increased after application of baclofen. These results suggest that glutamatergic excitation in the ICC can be modulated by presynaptic GABA(B) receptors. In addition, baclofen reduced NMDA EPSCs more than AMPA EPSCs. The GABA(B) receptor-mediated modulation of glutamatergic excitation in the ICC provides a likely mechanism for preventing overstimulation and/or regulating the balance of excitation and inhibition involved in processing auditory information.
Sun
Hongyu
H
Institute of Neuroscience, Carleton University, Ottawa, Ont., Canada K1S 5B6.
Ma
Chun Lei
CL
Kelly
Jack B
JB
Wu
Shu Hui
SH
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials; D058786:GABA-B Receptor Agonists; D066298:In Vitro Techniques; D007245:Inferior Colliculi / Q000502:physiology*; D009433:Neural Inhibition; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000502:physiology*; D018080:Receptors, GABA-B / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission
D058786:GABA-B Receptor Agonists; D018091:Receptors, AMPA; D018080:Receptors, GABA-B; D016194:Receptors, N-Methyl-D-Aspartate; D001418:Baclofen