J Neurophysiol (December 1, 2002). 10.1152/jn.00928.2001
Submitted on 9 November 2001
Accepted on 21 August 2002

Differential Dependence of LTD on Glutamate Receptors in the Auditory Cortical Synapses of Cortical and Thalamic Inputs

Department of Neurophysiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan

Kudoh, Masaharu, Masashi Sakai, and Katsuei Shibuki. Differential Dependence of LTD on Glutamate Receptors in the Auditory Cortical Synapses of Cortical and Thalamic Inputs. J. Neurophysiol. 88: 3167-3174, 2002. Pyramidal neurons in the auditory cortex (AC) receive glutamatergic inputs from the medial geniculate body (MGB inputs) and other pyramidal neurons (pyramidal inputs). We found that the induction of long-term depression (LTD) in supragranular layers was only partially suppressed by 50 µM D-()-2-amino-5-phosphonovalerate (APV), an antagonist of N-methyl-D-aspartate (NMDA) receptors (NMDARs), and 500 µM (+)--methyl-4-carboxyphenylglycine (MCPG), an antagonist of metabotropic glutamate receptors (mGluRs). However, LTD was not observed in the mixture of APV and MCPG. We hypothesized that the mixed dependence of LTD on glutamate receptors could be attributed to the heterogeneity of MGB inputs and pyramidal inputs. To test this hypothesis, the angle of slicing and other recording conditions were adjusted so that postsynaptic potentials were recorded in normal slices, but not in the slices prepared from the rats with MGB lesion. In these experiments, LTD was suppressed by MCPG alone. The conditions were adjusted to minimize the contribution of MGB inputs in field potentials. In these experiments, the induction of LTD was suppressed by APV alone. Interestingly, the induction of LTD was partially suppressed by 20 µM nifedipine, a blocker of L-type Ca²⁺ channels, in the slices prepared from the rats with MGB lesions, but not in normal slices. These findings suggest that the induction of LTD requires activation of mGluRs in the synapses of MGB inputs and of NMDARs in the synapses of pyramidal inputs.