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 (GABAA receptor) are important excitatory and inhibitory receptors in the central nervous system,respectively.Currently,cross-talk between the NMDA receptor and the GABAA 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 GABAA 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-1 were suppressed by the pre-perfusion of GABA at 100 μmol L-1,indicating cross-inhibition of NMDA receptors by activation of GABAA receptors.Moreover,we found that the currents induced by GABA at 100 μmol L-1 (IGABA) were not suppressed by the pre-perfusion of 100 μmol L-1 aspartate,but those induced by GABA at 3 μmol L-1 were suppressed,indicating concentration-dependent cross-inhibition of GABAA receptors by activation of NMDA receptors.In addition,inhibition of IGABA by aspartate was not affected by blockade of voltage-dependent Ca2+ channels with CdCl2 in a solution that contained Ca2+,however,CdCl2 effectively attenuated the inhibition of IGABA by aspartate when it was perfused in a solution that contained Ba2+ instead of Ca2+ or a solution that contained Ca2+ and 10 mmol L-1 BAPTA,a membrane-permeable Ca2+ chelator,suggesting that this inhibition is mediated by Ca2+ influx through NMDA receptors,rather than voltage-dependent Ca2+ channels.Finally,KN-62,a potent inhibitor of Ca2+/calmodulin-dependent protein kinase II (CaMKII),reduced the inhibition of IGABA by aspartate,indicating the involvement of CaMKII in this cross-inhibition.Our study demonstrates a functional interaction
CONG DanNiTANG ZhengQuanLI LongZhuHUANG YiNaWANG JunCHEN Lin
Objective The macula lagena in birds is located at the apical end of the cochlea and contains many tiny otoliths. The macula lagena is innervated and has neural projections to the brainstem, but its physiological function is still unclear. It remains disputable that it is because otoliths in the lagena are rich in elements Fe and Zn that birds can obtain geomagnetic information for homing. To clarify this issue, we carried out a study to determine whether or not otoliths in the lagena of homing pigeons are richer in magnetic elements than those in the saccule and the utricle. Methods The contents of ferromagnetic elements （Fe, Co, Ni） and other metal elements in lagenal otoliths of adult homing pigeons were precisely analyzed with inductively coupled plasma mass spectrometry （ICP-MS） of high sensitivity, and then they were compared with those in saccular and utricular otoliths （all the contents were normalized to Ca）. Results In adult homing pigeons, the contents of ferromagnetic elements （Fe, Co, Ni） in lagenal otoliths were less than 0.7% （normalized to Ca element） and were the same order in magnitude as those in saccular and utricular otoliths. The content of Fe in lagenal otoliths was not significantly different from that in utricular otoliths and was even lower than that in saccular otoliths. The content of Co in lagenal otoliths was lower than that in saccular otoliths and higher than that in utricular otoliths. The content of Ni in lagenal otoliths was not significantly different from that in saccular otoliths and was higher than that in utricular otoliths. The contents of other metal elements Na, Mg, K, Al, Mn and Pb in lagenal otoliths were not significantly different from those in utricular and saccular otoliths. The contents of metal elements Zn, Ba and Cu in lagenal otoliths were lower than those in saccular otoliths. Conclusion The contents of magnetic elements in lagenal otoliths of homing pigeons are not much higher than those in utricular and saccular otoliths, which does not s
