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A direct translaminar inhibitory circuit tunes cortical output.

ABSTRACT: Anatomical and physiological experiments have outlined a blueprint for the feedforward flow of activity in cortical circuits: signals are thought to propagate primarily from the middle cortical layer (layer 4, L4) up to L2/3 and down to the major cortical output layer (L5). Pharmacological manipulations, however, have contested this model and have suggested that L4 may not be critical for sensory responses of neurons in either superficial or deep layers. To address these conflicting models, we reversibly manipulated L4 activity in awake, behaving mice using cell type-specific optogenetics. In contrast with both prevailing models, we found that activity in L4 directly suppressed L5, in part by activating deep, fast-spiking inhibitory neurons. Our data suggest that the net effect of L4 activity is to sharpen the spatial representations of L5 neurons. Thus, we establish a previously unknown translaminar inhibitory circuit in the sensory cortex that acts to enhance the feature selectivity of cortical output.

SUBMITTER: Pluta S

PROVIDER: S-EPMC4624464 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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A direct translaminar inhibitory circuit tunes cortical output.

Pluta Scott S Naka Alexander A Veit Julia J Telian Gregory G Yao Lucille L Hakim Richard R Taylor David D Adesnik Hillel H

Nature neuroscience 20150928 11

Anatomical and physiological experiments have outlined a blueprint for the feedforward flow of activity in cortical circuits: signals are thought to propagate primarily from the middle cortical layer (layer 4, L4) up to L2/3 and down to the major cortical output layer (L5). Pharmacological manipulations, however, have contested this model and have suggested that L4 may not be critical for sensory responses of neurons in either superficial or deep layers. To address these conflicting models, we r ...[more]

PMID: 26414615

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Project description:Anti-NMDA receptor (NMDAR) encephalitis is a severe neuropsychiatric disorder associated with autoantibodies against NMDARs, which cause a variety of symptoms from prominent psychiatric and cognitive manifestations to seizures and autonomic instability. Previous studies mainly focused on hippocampal effects of these autoantibodies, helping to explain mechanistic causes for cognitive impairment. However, antibodies' effects on higher cortical network function, where they could contribute to psychosis and/or seizures, have not been explored in detail until now. Here, we employed a patient-derived monoclonal antibody targeting the NR1 subunit of NMDAR and tested its effects on in vitro cultures of rodent cortical neurons, using imaging and electrophysiological techniques. We report that this hNR1 antibody drives cortical networks to a hyperexcitable state and disrupts mechanisms stabilizing network activity such as Npas4 signaling. Network hyperactivity is in part a result of a reduced synaptic output of inhibitory neurons, as indicated by a decreased inhibitory drive and levels of presynaptic inhibitory proteins, specifically in inhibitory-to-excitatory neuron synapses. Importantly, on a single-cell level hNR1 antibody selectively impairs NMDAR-mediated currents and synaptic transmission of cortical inhibitory neurons, yet has no effect on excitatory neurons, which contrasts with its effects on hippocampal neurons. Together, these findings provide a novel, cortex-specific mechanism of antibody-induced neuronal hyperexcitability, highlighting regional specificity underlying the pathology of autoimmune encephalitis.SIGNIFICANCE STATEMENT It is increasingly appreciated that the inadvertent activation of the immune system within CNS can underlie pathogenesis of neuropsychiatric disorders. Although the exact mechanisms remain elusive, autoantibodies derived from patients with autoimmune encephalitis pose a unique tool to study pathogenesis of neuropsychiatric states. Our analysis reveals that autoantibody against the NMDA receptor (NMDAR) has a distinct mechanism of action in the cortex, where it impairs function of inhibitory neurons leading to increased cortical network excitability, in contrast to previously described hippocampal synaptic mechanisms of information encoding, highlighting brain regional specificity. Notably, similar mechanism of NMDAR-mediated inhibitory hypofunction leading to cortical disinhibition has been suggested to underlie pathology of schizophrenia, hence our data provide new evidence for common mechanisms underlying neuropsychiatric disorders.

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A direct translaminar inhibitory circuit tunes cortical output.

Publications

A direct translaminar inhibitory circuit tunes cortical output.

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