vasoactive-intestinal-peptide and 2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline

Higher-order thalamic nuclei, such as the posterior medial nucleus (POm) in the somatosensory system or the pulvinar in the visual system, densely innervate the cortex and can influence perception and plasticity. To systematically evaluate how higher-order thalamic nuclei can drive cortical circuits, we investigated cell-type selective responses to POm stimulation in mouse primary somatosensory (barrel) cortex, using genetically targeted whole-cell recordings in acute brain slices. We find that ChR2-evoked thalamic input selectively targets specific cell types in the neocortex, revealing layer-specific modules for the summation and processing of POm input. Evoked activity in pyramidal neurons from deep layers is fast and synchronized by rapid feedforward inhibition from GABAergic parvalbumin-expressing neurons, and activity in superficial layers is weaker and prolonged, facilitated by slow inhibition from GABAergic neurons expressing the 5HT3a receptor. Somatostatin-expressing GABAergic neurons do not receive direct input in either layer and their spontaneous activity is suppressed during POm stimulation. This novel pattern of weak, delayed, thalamus-evoked inhibition in layer 2 suggests a longer integration window for incoming sensory information and may facilitate stimulus detection and plasticity in superficial pyramidal neurons.

Topics: Animals; Channelrhodopsins; Excitatory Amino Acid Antagonists; Inhibitory Postsynaptic Potentials; Mice; Mice, Inbred C57BL; Nerve Net; Neural Pathways; Parvalbumins; Piperidines; Potassium Channel Blockers; Pyramidal Cells; Quinoxalines; Receptors, Serotonin, 5-HT3; Sodium Channel Blockers; Somatosensory Cortex; Somatostatin; Tetrodotoxin; Thalamic Nuclei; Vasoactive Intestinal Peptide

Cortical inhibitory neurons contact each other to form a network of inhibitory synaptic connections. Our knowledge of the connectivity pattern underlying this inhibitory network is, however, still incomplete. Here we describe a simple and complementary interaction scheme between three large, molecularly distinct interneuron populations in mouse visual cortex: parvalbumin-expressing interneurons strongly inhibit one another but provide little inhibition to other populations. In contrast, somatostatin-expressing interneurons avoid inhibiting one another yet strongly inhibit all other populations. Finally, vasoactive intestinal peptide-expressing interneurons preferentially inhibit somatostatin-expressing interneurons. This scheme occurs in supragranular and infragranular layers, suggesting that inhibitory networks operate similarly at the input and output of the visual cortex. Thus, as the specificity of connections between excitatory neurons forms the basis for the cortical canonical circuit, the scheme described here outlines a standard connectivity pattern among cortical inhibitory neurons.

Topics: Animals; Biomarkers; Channelrhodopsins; Female; Genes, Reporter; Inhibitory Postsynaptic Potentials; Interneurons; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nerve Tissue Proteins; Neural Inhibition; Optogenetics; Organophosphorus Compounds; Parvalbumins; Patch-Clamp Techniques; Photic Stimulation; Principal Component Analysis; Pyramidal Cells; Quinoxalines; Recombinant Fusion Proteins; Somatostatin; Synaptic Transmission; Vasoactive Intestinal Peptide; Visual Cortex