Must-Read Neural Circuit Papers in March 2018

Encoding of danger by parabrachial CGRP neurons

Have you read these neuroscience papers related to neural circuits published in March 2018? These must-read research papers look at a breadth of behaviors, including the encoding of danger, itch, pain, head motion, foraging, memory, and visual responses (in the auditory cortex, no less!) Check them out!

1. Encoding of danger by parabrachial CGRP neurons by

Carlos A. Campos, Anna J. Bowen, Carolyn W. Roman & Richard D. Palmiter. Nature.

The parabrachial nucleus (PBN) lies deep at the border of midbrain and hindbrain, and is essentially part of the pons. Here they showed using Inscopix nVista in vivo calcium imaging that CGRP (calcitonin gene-related peptide) neurons in the PBN relay sensory signals that contribute to satiation and pain-induced fear behaviour across modalities. This suggests parabrachial neurons in mice interpret the feeling of fullness with negative valence and contributes to feeding cessation.

Read more here

2. Circuit dissection of the role of somatostatin in itch and pain by Jing Huang, Erika Polgár, Hans Jürgen Solinski, Santosh K. Mishra, Pang-Yen Tseng, Noboru Iwagaki, Kieran A. Boyle, Allen C. Dickie, Mette C. Kriegbaum, Hendrik Wildner, Hanns Ulrich Zeilhofer, Masahiko Watanabe, John S. Riddell, Andrew J. Todd & Mark A. Hoon. Nature Neuroscience.

Employing optogenetics, chemogenetics, pharmacology and cell-specific ablation methods with conditional genetic knockouts, they delineated roles for somatostatin in itch and pain sensation.

Read more here and here

3. A three-dimensional single-cell-resolution whole-brain atlas using CUBIC-X expansion microscopy and tissue clearing by Tatsuya C. Murakami, Tomoyuki Mano, Shu Saikawa, Shuhei A. Horiguchi, Daichi Shigeta, Kousuke Baba, Hiroshi Sekiya, Yoshihiro Shimizu, Kenji F. Tanaka, Hiroshi Kiyonari, Masamitsu Iino, Hideki Mochizuki, Kazuki Tainaka & Hiroki R. Ueda. Nature Neuroscience.

Toward a single-cell-resolution mouse brain atlas, they develop a fluorescent-protein-compatible, intensive tissue-clearing method combined with a tissue expansion protocol, CUBIC-X, which enables seamless imaging of the whole mouse brain at subcellular resolution. This opens up a great opportunity for a global analysis of gene expression and neural circuitry.

Read more here and watch a video here

4. A Circuit for Integration of Head- and Visual-Motion Signals in Layer 6 of Mouse Primary Visual Cortex by Mateo Vélez-Fort, Edward F. Bracey, Sepiedeh Keshavarzi, Charly V. Rousseau, Lee Cossell, Stephen C. Lenzi, Molly Strom, Troy W. Margrie. Neuron.

They show that head-velocity signals are physiologically separate in the brain in layer 6 (L6) principal neurons in mouse primary visual cortex (V1). They receive a diffuse, vestibular-mediated synaptic input that signals the angular velocity of horizontal rotation.

Read more here and here

5. Volitional Modulation of Primary Visual Cortex Activity Requires the Basal Ganglia by Ryan M. Neely, Aaron C. Koralek, Vivek R. Athalye, Rui M. Costa, Jose M. Carmena. Neuron.

They demonstrate that cortico-basal ganglia circuits play a general role in learning to produce cortical activity that leads to desirable outcomes in a brain-machine interface task. They had previously shown that a brain-machine interface controlled by neurons in the primary motor cortex also requires cortico-striatal plasticity in order for animals to learn a novel neuroprosthetic action. Here they asked whether neurons in the primary visual cortex “could be instrumentally conditioned to produce arbitrary modulations of ongoing spike activity, and whether this abstract form of learning was dependent on the basal ganglia.” It was, which has important implications for understanding how the striatum shapes cortical responses.

Read more here and here

6. Divergent midbrain circuits orchestrate escape and freezing responses to looming stimuli in mice by Congping Shang, Zijun Chen, Aixue Liu, Yang Li, Jiajing Zhang, Baole Qu, Fei Yan, Yaning Zhang, Weixiu Liu, Zhihui Liu, Xiaofei Guo, Dapeng Li, Yi Wang & Peng Cao. Nature Communications.

It’s been shown that superior colliculus (SC) neurons expressing parvalbumin (PV+) may be a key neuronal subtype to trigger stereotyped defensive behaviors (“A parvalbumin-positive excitatory visual pathway to trigger fear responses in mice”.) Here they systematically examined the roles of these neurons and their divergent downstream pathways in visually triggered defensive behaviors. Their data “indicate that the SC PV+ neurons orchestrate these dimorphic defensive behaviors with two divergent tectofugal visual pathways.”

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7. Activation of serotonin neurons promotes active persistence in a probabilistic foraging task by Eran Lottem, Dhruba Banerjee, Pietro Vertechi, Dario Sarra, Matthijs oude Lohuis & Zachary F. Mainen. Nature Communications.

Contrary to the hypothesis that a major function of 5-HT is to promote behavioral inhibition, they show that optogenetic activation of dorsal raphe nucleus 5-HT neurons increases foraging behavior (nose pokes) in a way that demonstrates persistence. The authors say these results contradict the behavioral inhibition hypothesis and support the notion that 5-HT promotes waiting by enhancing persistence in the face of uncertainty and delay.

Read more here and here

Dentate granule cell recruitment of feedforward inhibition governs engram maintenance

8. Dentate granule cell recruitment of feedforward inhibition governs engram maintenance and remote memory generalization by Nannan Guo, Marta E Soden, Charlotte Herber, Michael TaeWoo Kim, Antoine Besnard, Paoyan Lin, Xiang Ma, Constance L Cepko, Larry S Zweifel & Amar Sahay. Nature Medicine.

“These studies exemplify a connectivity-based strategy that targets a molecular brake of feedforward inhibition in DG–CA3 and may be harnessed to decrease time-dependent memory generalization in individuals with PTSD and improve memory precision in aging individuals.”

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9. Visual Information Present in Infragranular Layers of Mouse Auditory Cortex by Ryan J. Morrill and Andrea R. Hasenstaub. Journal of Neuroscience.

This is a good reminder how much we’re still figuring out about what distinct circuits in the primary sensory areas do, and here they show that, in mouse auditory cortex, the more mysterious deeper layers represent a locus of cross-modal convergence, containing many units responsive to visual stimuli. They “suggest that this visual signal conveys the presence and timing of a stimulus rather than specifics about that stimulus, such as its orientation. These results shed light on both how and what types of cross-modal information is integrated at the earliest stages of sensory cortical processing.”

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10. The logic of single-cell projections from visual cortex by Yunyun Han, Justus M. Kebschull, Robert A. A. Campbell, Devon Cowan, Fabia Imhof, Anthony M. Zador & Thomas D. Mrsic-Flogel. Nature.

They show that instead of a one neuron – one target area mapping hypothesis, individual neurons in the visual cortex target multiple areas in parallel. They used two anterograde anatomical approaches, whole-brain fluorescence-based axonal tracing and high-throughput DNA sequencing of genetically barcoded neurons (MAPseq), to map the long-range axonal projection patterns of individual neurons in the mouse primary visual cortex. Needless to say, this is fundamental connectivity knowledge.

Read more here and here and here

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