Long-term potentiation in the inferior colliculus studied in rat brain slice

The purpose of this study is to determine whether long-term potentiation (LTP) can be induced in the central nucleus of the inferior colliculus (ICC) by electrical stimulation of the lateral lemniscus. If LTP can be induced, is it mediated by N-methyl-D-aspartate (NMDA) and/or other receptors? Brain slices of the ICC were obtained from 14-35 day old Wistar rats. The field potentials were recorded from the ICC after GABAergic and glycinergic inhibition was suppressed. Following tetanic stimulation (50 Hz, 20 s), the amplitude of the response was increased to about 146% of control response for at least 30 min. LTP was observed in about 78% of the cases tested. Induction of LTP in the ICC required activation of both NMDA and gamma-aminobutyric acid (GABA)(B) receptors. GABAergic inhibitory postsynaptic potentials (IPSPs) were blocked by the GABA(A) receptor antagonist, but not by the GABA(B) receptor antagonist. The IPSPs were decreased by the GABA(B) receptor agonist, baclofen. The intrinsic postsynaptic membrane properties were not affected by baclofen. These results suggest that GABAergic inhibition in the ICC is mediated only by GABA(A) receptors, but that it is modulated by presynaptic GABA(B) receptors. The GABA(B) receptors in the ICC may suppress GABAergic inhibition and promote induction of LTP.