A barrel-related interneuron in layer 4 of rat somatosensory cortex with a high intrabarrel connectivity.
Synaptic connections between identified fast-spiking (FS), parvalbumin (PV)-positive interneurons, and excitatory spiny neurons in layer 4 (L4) of the barrel cortex were investigated using patch-clamp recordings and simultaneous biocytin fillings. Three distinct clusters of FS L4 interneurons were identified based on their axonal morphology relative to the barrel column suggesting that these neurons do not constitute a homogeneous interneuron population. One L4 FS interneuron type had an axonal domain strictly confined to a L4 barrel and was therefore named "barrel-confined inhibitory interneuron" (BIn). BIns established reliable inhibitory synaptic connections with L4 spiny neurons at a high connectivity rate of 67%, of which 69% were reciprocal. Unitary IPSPs at these connections had a mean amplitude of 0.9 ± 0.8 mV with little amplitude variation and weak short-term synaptic depression. We found on average 3.7 ± 1.3 putative inhibitory synaptic contacts that were not restricted to perisomatic areas. In conclusion, we characterized a novel type of barrel cortex interneuron in the major thalamo-recipient layer 4 forming dense synaptic networks with L4 spiny neurons. These networks constitute an efficient and powerful inhibitory feedback system, which may serve to rapidly reset the barrel microcircuitry following sensory activation.
Department of Cell Physiology, Max Planck Institute of Medical Research, Jahnstr. 20, D-69120 Heidelberg, Germany Current address: Section of Cardiovascular Medicine, Boston University Medical Center, 88 East Newton Street, Boston, MA 02118, USA.
Christian
C
Koelbl
Department of Cell Physiology, Max Planck Institute of Medical Research, Jahnstr. 20, D-69120 Heidelberg, Germany Current address: Structure of Neocortical Circuits Group, Max Planck Institute of Neurobiology, Am Klopferspitz 18, D-82152 Martinsried, Germany.
Moritz
M
Helmstaedter
Institute for Neuroscience and Medicine, INM-2, Research Centre Jülich, Leo-Brandt-Str., D-52425 Jülich, Germany Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Pauwelstr. 30, D-52074 Aachen, Germany Jülich-Aachen Research Alliance, Translational Brain Medicine (JARA-Brain), D-52074, Aachen, Germany.
Joachim
J
Lübke
Institute for Neuroscience and Medicine, INM-2, Research Centre Jülich, Leo-Brandt-Str., D-52425 Jülich, Germany Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Pauwelstr. 30, D-52074 Aachen, Germany Jülich-Aachen Research Alliance, Translational Brain Medicine (JARA-Brain), D-52074, Aachen, Germany.
Dirk
D
Feldmeyer
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D019706:Excitatory Postsynaptic Potentials; D053444:Inhibitory Postsynaptic Potentials; D007395:Interneurons / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D009474:Neurons / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013003:Somatosensory Cortex / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000648:ultrastructure
GABAergic interneuron; barrel cortex; fast-spiking; layer 4; spiny stellate cell