Synaptic properties of thalamic and intracortical inputs to layer 4 of the first- and higher-order cortical areas in the auditory and somatosensory systems.
The thalamus is an essential structure in the mammalian forebrain conveying information topographically from the sensory periphery to primary neocortical areas. Beyond this initial processing stage, "higher-order" thalamocortical connections have been presumed to serve only a modulatory role, or are otherwise functionally disregarded. Here we demonstrate that these "higher-order" thalamic nuclei share similar synaptic properties with the "first-order" thalamic nuclei. Using whole cell recordings from layer 4 neurons in thalamocortical slice preparations in the mouse somatosensory and auditory systems, we found that electrical stimulation in all thalamic nuclei elicited large, glutamatergic excitatory postsynaptic potentials (EPSPs) that depress in response to repetitive stimulation and that fail to activate a metabotropic glutamate response. In contrast, the intracortical inputs from layer 6 to layer 4 exhibit facilitating EPSPs. These data suggest that higher-order thalamocortical projections may serve a functional role similar to the first-order nuclei, whereas both are physiologically distinct from the intracortical layer 6 inputs. These results suggest an alternate route for information transfer between cortical areas via a corticothalamocortical pathway.
Lee
Charles C
CC
Department of Neurobiology, University of Chicago, Chicago, Illinois 60637, USA. clee@bsd.uchicago.edu
Sherman
S Murray
SM
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001303:Auditory Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D001931:Brain Mapping; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D013003:Somatosensory Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013788:Thalamus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione