Glutamatergic inhibition in sensory neocortex.
In the mammalian brain, glutamate and gamma-aminobutyric acid are considered major excitatory and inhibitory neurotransmitters, respectively. However, we have found evidence that glutamate can also act as a postsynaptic inhibitory neurotransmitter in layer 4 of the neocortex. Using whole-cell recordings from layer 4 neurons in slice preparations from the mouse visual, auditory, and somatosensory cortices, we found that metabotropic glutamate receptor (mGluR) agonists (ACPD, APDC, and DCG IV) elicit a robust, long-lasting hyperpolarization that is abolished by the group II mGluR antagonist, MCCG. This response largely involves a K(+) conductance mediated by G-protein activity and GIRK channels. Furthermore, electrical and photostimulation of the intracortical inputs to layer 4 elicits a similar hyperpolarization that is blocked by group II mGluR antagonists. This novel inhibition mediated by group II mGluRs may be an unappreciated mechanism for refining cortical receptive fields in layer 4 and may enable synaptic gain control during periods of high activity.
Lee
Charles C
CC
Department of Neurobiology, University of Chicago, Chicago, IL 60637, USA. clee@bsd.uchicago.edu
Sherman
S Murray
SM
D000704:Analysis of Variance; D000818:Animals; D001303:Auditory Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D055724:Electrophysiological Phenomena; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000502:physiology*; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018091:Receptors, AMPA / Q000502:physiology; D018079:Receptors, GABA / Q000502:physiology; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013003:Somatosensory Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D014793:Visual Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018091:Receptors, AMPA; D018079:Receptors, GABA; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C108822:metabotropic glutamate receptor 2; D018698:Glutamic Acid; D002118:Calcium