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. 2020 Feb 6;18(2):e3000613.
doi: 10.1371/journal.pbio.3000613. eCollection 2020 Feb.

Barrel cortex VIP/ChAT interneurons suppress sensory responses in vivo

Amir Dudai  1 , Nadav Yayon  2 , Vitaly Lerner  1 , Gen-Ichi Tasaka  1 , Yair Deitcher  1 , Karin Gorfine  1 , Naomi Niederhoffer  2 , Adi Mizrahi  1 , Hermona Soreq  2 , Michael London  1
Affiliations

Barrel cortex VIP/ChAT interneurons suppress sensory responses in vivo

Amir Dudai et al. PLoS Biol. .

Abstract

Cortical interneurons expressing vasoactive intestinal polypeptide (VIP) and choline acetyltransferase (ChAT) are sparsely distributed throughout the neocortex, constituting only 0.5% of its neuronal population. The co-expression of VIP and ChAT suggests that these VIP/ChAT interneurons (VChIs) can release both γ-aminobutyric acid (GABA) and acetylcholine (ACh). In vitro physiological studies quantified the response properties and local connectivity patterns of the VChIs; however, the function of VChIs has not been explored in vivo. To study the role of VChIs in cortical network dynamics and their long-range connectivity pattern, we used in vivo electrophysiology and rabies virus tracing in the barrel cortex of mice. We found that VChIs have a low spontaneous spiking rate (approximately 1 spike/s) in the barrel cortex of anesthetized mice; nevertheless, they responded with higher fidelity to whisker stimulation than the neighboring layer 2/3 pyramidal neurons (Pyrs). Analysis of long-range inputs to VChIs with monosynaptic rabies virus tracing revealed that direct thalamic projections are a significant input source to these cells. Optogenetic activation of VChIs in the barrel cortex of awake mice suppresses the sensory responses of excitatory neurons in intermediate amplitudes of whisker deflections while increasing the evoked spike latency. The effect of VChI activation on the response was similar for both high-whisking (HW) and low-whisking (LW) conditions. Our findings demonstrate that, despite their sparsity, VChIs can effectively modulate sensory processing in the cortical microcircuit.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. VChI cortical density and VIP/ChAT colocalization.
(A) Cortex stained with ChAT primary antibody in a 30-μm–thick coronal slice (maximum intensity z-projection; Alexa 647). (B) VChI distribution across cortical depth (n = 261 cells; 3 mice). Inset: cell counts per cubic millimeter. (C) Cortex of a VIP-tdTomato mouse stained with ChAT (maximum intensity z-projection; Alexa 647). Left: tdTomato; Middle: ChAT; Right: overlay (scale: 100 μm). (D) Respective ratios of cortical ChAT+ and VIP+ neuronal populations. Left: staining data. Right: Allen Institute single-cell RNA-seq data (“Ch” = ChAT; “V” = VIP). ChAT, choline acetyltransferase; RNA-seq, RNA sequencing; VChI, VIP/ChAT interneuron; VIP, vasoactive intestinal polypeptide.
Fig 2
Fig 2. Anatomical and physiological properties of tdTomato-expressing cells in ChAT-tdTomato mice.
(A) Image of a ChAT-tdTomato mouse cortex (30-μm coronal slice). (B) Three-dimensional rendering of VChIs in a coronal slice from a ChAT-tdTomato mouse (cube 300 × 700 × 150 μm; see S1 Video). (C) Expression of ChAT in cortical tdTomato-expressing cells. Left: tdTomato; Middle: ChAT staining (Alexa 648); Right: overlay. (D) Membrane potential responses to hyperpolarizing and depolarizing current steps of a cortical tdTomato-expressing cell. (E) F-I curve of the recorded cell shown in panel D. (F) Physiological properties of the recorded cells. τm, membrane time constant; ChAT, choline acetyltransferase; F-I, frequency-current; Rin, input resistance; sp/s, spikes per second; Vrest, resting potential; Vth, threshold potential; VChI, VIP/ChAT interneuron; VIP, vasoactive intestinal polypeptide.
Fig 3
Fig 3. VChI spontaneous firing rate and reliability in response to sensory stimulation.
(A) Illustration of the experimental system: two-photon guided cell-attached recordings from VChIs in an anaesthetized ChAT-tdTomato mouse with or without whisker deflection. (B) Top left (green): following electroporation, the recorded cell is filled with Alexa 488. Top middle (red): tdTomato expression of the recorded cell. Right: overlay (mean-intensity z-stack projection; scale: 20 μm). Bottom: spontaneous cell-attached recording from a VChI. (C) Spontaneous firing rate of VChIs and Pyrs. (D) Raster plot and PSTH of a VChI and Pyr during single-whisker stimulation (grey shaded area: piezoelectric whisker stimulation). (E) Population average PSTH of recorded VChIs and Pyrs (grey horizontal bar: piezoelectric whisker stimulation). (F) Probability of evoking a spike following the onset of the whisker stimulation. ChAT, choline acetyltransferase; Isof, isoflurane; PSTH, peristimulus time histogram; Pyr, pyramidal neuron; sp/s, spikes per second; VChI, VIP/ChAT interneuron; VIP, vasoactive intestinal polypeptide.
Fig 4
Fig 4. Rabies trans-synaptic tracing from VChIs in the barrel cortex.
(A) Illustration of the experimental procedure and the distal areas innervating the VChIs in the BCtx. The identified presynaptic distal areas of the VChIs are the VPM, S2, VIS, and the BF. (B) An example image of a VChI starter cell (expressing both mCherry and GFP) located in layer 2/3. Inset: zoom-in image showing the bipolar morphology of the cell. (C) Examples of input cells (expressing GFP) from the 4 identified distal areas. (D) The CI distribution quantifying the relative number of input cells per starter cell in all identified input areas. BCtx, barrel cortex; BF, basal forebrain; ChAT, choline acetyltransferase; CI, convergence index; GFP, green fluorescent protein; RVΔG, G-deleted rabies virus; S2, secondary somatosensory cortex; VChI, VIP/ChAT interneuron; VIP, vasoactive intestinal polypeptide; VIS, primary and secondary visual areas; VPM, ventral posteromedial thalamic nucleus.
Fig 5
Fig 5. VChIs inhibit the sensory response elicited by whisker deflection.
(A) Illustration of the experimental system: cell-attached recordings are performed from putative excitatory cells in an awake, head-fixed mouse. In each trial, a piezoelectric deflection in a random amplitude (0.2, 0.6, 1.0, or 1.4 mm) is delivered to the whiskers, and optogenetic stimulation is either delivered (“On” trial) or not (“Off” trial). (B) Example of the response of a single cell to the 4 whisker deflection amplitudes in the Off and in the On trials. (C) Population average of the response of all cells to the whisker deflections in the Off and On trials. Inset: example of the sigmoidal response of a cell in which the whiskers were deflected in 19 different amplitudes. (D) The average evoked rate for each cell in the intermediate range of the sigmoidal curve. (E) Evoked rate in the Off and On trials in LW and HW trials. (F) The response of a cell to whisker deflection, sorted by the lag to the first deflection-evoked spike (grey horizontal bar: piezoelectric stimulation). (G) The latency to the first evoked spike in the On and in the Off trials across the population. ChAT, choline acetyltransferase; HW, high whisking; LW, low whisking; sp/s, spikes per second; VChI, VIP/ChAT interneuron; VIP, vasoactive intestinal polypeptide.
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Grants and funding

This research has been supported by a grant from the Israeli Science foundation (www.isf.org.il 1024/17), ELSC collaboration seed grants (elsc.huji.ac.il, M.L. & H.S.), the Einstein Foundation (www.einsteinfoundation.de, ML), and the Gatsby Charitable Foundation (http://www.gatsby.org.uk/). A.D. is an H. & S. Hoffman fellow. M.L. is a Sachs Family Lecturer in Brain Science. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.