Cross-talk between NMDA and GABA^sub A^ receptors in cultured neurons of the rat inferior colliculus

Neuronal ion channels of different types often do not function independently but will inhibit or potentiate the activity of other types of channels, a process called cross-talk. The N-methyl-D-aspartate receptor (NMDA receptor) and the γ-aminobutyric acid type A receptor (GABA^sub A^ receptor) are important excitatory and inhibitory receptors in the central nervous system, respectively. Currently, cross-talk between the NMDA receptor and the GABA^sub A^ receptor, particularly in the central auditory system, is not well understood. In the present study, we investigated functional interactions between the NMDA receptor and the GABA^sub A^ receptor using whole-cell patch-clamp techniques in cultured neurons from the inferior colliculus, which is an important nucleus in the central auditory system. We found that the currents induced by aspartate at 100 μmol L^sup -1^ were suppressed by the pre-perfusion of GABA at 100 μmol L^sup -1^, indicating cross-inhibition of NMDA receptors by activation of GABA^sub A^ receptors. Moreover, we found that the currents induced by GABA at 100 μmol L^sup -1^ (I ^sub GABA^) were not suppressed by the pre-perfusion of 100 μmol L^sup -1^ aspartate, but those induced by GABA at 3 μmol L^sup -1^ were suppressed, indicating concentration-dependent cross-inhibition of GABA^sub A^ receptors by activation of NMDA receptors. In addition, inhibition of IGABA by aspartate was not affected by blockade of voltage-dependent Ca^sup 2+^ channels with CdCl^sub 2^ in a solution that contained Ca^sup 2+^, however, CdCl^sub 2^ effectively attenuated the inhibition of I ^sub GABA^ by aspartate when it was perfused in a solution that contained Ba^sup 2+^ instead of Ca^sup 2+^ or a solution that contained Ca^sup 2+^ and 10 mmol L^sup -1^ BAPTA, a membrane-permeable Ca^sup 2+^ chelator, suggesting that this inhibition is mediated by Ca^sup 2+^ influx through NMDA receptors, rather than voltage-dependent Ca^sup 2+^ channels. Finally, KN-62, a potent inhibitor of Ca^sup 2+^/calmodulin-dependent protein kinase II (CaMKII), reduced the inhibition of I ^sub GABA^ by aspartate, indicating the involvement of CaMKII in this cross-inhibition. Our study demonstrates a functional interaction between NMDA and GABA^sub A^ receptors in the inferior colliculus of rats. The presence of cross-talk between these receptors suggests that the mechanisms underlying information processing in the central auditory system may be more complex than previously believed.[PUBLICATI