A transcriptomic axis predicts state modulation of cortical interneurons

Transcriptomics has revealed that cortical inhibitory neurons exhibit a great diversity of fine molecular subtypes^1-6, but it is not known whether these subtypes have correspondingly diverse patterns of activity in the living brain. Here we show that inhibitory subtypes in primary visual cortex (V1) have diverse correlates with brain state, which are organized by a single factor: position along the main axis of transcriptomic variation. We combined in vivo two-photon calcium imaging of mouse V1 with a transcriptomic method to identify mRNA for 72 selected genes in ex vivo slices. We classified inhibitory neurons imaged in layers 1-3 into a three-level hierarchy of 5 subclasses, 11 types and 35 subtypes using previously defined transcriptomic clusters³. Responses to visual stimuli differed significantly only between subclasses, with cells in the Sncg subclass uniformly suppressed, and cells in the other subclasses predominantly excited. Modulation by brain state differed at all hierarchical levels but could be largely predicted from the first transcriptomic principal component, which also predicted correlations with simultaneously recorded cells. Inhibitory subtypes that fired more in resting, oscillatory brain states had a smaller fraction of their axonal projections in layer 1, narrower spikes, lower input resistance and weaker adaptation as determined in vitro⁷, and expressed more inhibitory cholinergic receptors. Subtypes that fired more during arousal had the opposite properties. Thus, a simple principle may largely explain how diverse inhibitory V1 subtypes shape state-dependent cortical processing.

Direct and efficient transfection of mouse neural stem cells and mature neurons by in vivo mRNA electroporation

In vivo brain electroporation of DNA expression vectors is a widely used method for lineage and gene function studies in the developing and postnatal brain. However, transfection efficiency of DNA is limited and adult brain tissue is refractory to electroporation. Here, we present a systematic study of mRNA as a vector for acute genetic manipulation in the developing and adult brain. We demonstrate that mRNA electroporation is far more efficient than DNA electroporation, and leads to faster and more homogeneous protein expression in vivo Importantly, mRNA electroporation allows the manipulation of neural stem cells and postmitotic neurons in the adult brain using minimally invasive procedures. Finally, we show that this approach can be efficiently used for functional studies, as exemplified by transient overexpression of the neurogenic factor Myt1l and by stably inactivating Dicer nuclease in vivo in adult born olfactory bulb interneurons and in fully integrated cortical projection neurons.

Time-Specific Effects of Spindle Positioning on Embryonic Progenitor Pool Composition and Adult Neural Stem Cell Seeding

The developmental mechanisms regulating the number of adult neural stem cells (aNSCs) are largely unknown. Here we show that the cleavage plane orientation in murine embryonic radial glia cells (RGCs) regulates the number of aNSCs in the lateral ganglionic eminence (LGE). Randomizing spindle orientation in RGCs by overexpression of Insc or a dominant-negative form of Lgn (dnLgn) reduces the frequency of self-renewing asymmetric divisions while favoring symmetric divisions generating two SNPs. Importantly, these changes during embryonic development result in reduced seeding of aNSCs. Interestingly, no effects on aNSC numbers were observed when Insc was overexpressed in postnatal RGCs or aNSCs. These data suggest a new mechanism for controlling aNSC numbers and show that the role of spindle orientation during brain development is highly time and region dependent.

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Randomization of the spindle orientation changes the progenitor pool composition

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Overexpression of Insc or dnLgn reduces asymmetric self-renewing division of aRGCs

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The change in embryonic progenitor pool leads to reduced seeding of adult NSCs

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Insc influences the seeding of adult NSCs in a narrow developmental time window

Characterization of 99mTc-DTPA aerosols for lung permeability studies

BACKGROUND

The interpretation of 99mTc diethylenetriamine pentaacetate (99mTc DTPA) aerosol clearance is based on the hypothesis that the 99mTc-DTPA complex is not altered by the nebulization process.

OBJECTIVES

To characterize (1) the radiochemical purity (RCP) of 99mTc-DTPA and the stability of labeling after jet nebulization, and (2) the particle size distribution of the aerosol.

METHODS

RCP and stability--the aerosol was driven by oxygen, captured on filters which were eluted and RCP was checked by thin layer chromatography. Particle size distribution--the aerosol was generated using dry air (50 psi) at three different flow rates, i.e. 3 (1 run), 6 (4 runs) and 9 l x min(-1) (4 runs). The mass median aerodynamic diameter (MMAD) and the geometric standard deviation (sigma(g)) were determined using a cascade impactor from the radioactivity counted on each stage.

RESULTS

The RCP was more than 95% in all cases. Mean MMAD (+/-SD) was 0.70 microm (+/-0.07) at 9 l x min(-1), 0.93 microm (+/-0.05) at 6 l x min(-1) (p < 0.05) and 1.50 microm at 3 l x min(-1). Mean sigma(g) (+/-SD) was 2.02 (+/-0.08) at 9 l x min(-1), 2.00 (+/-0.16) at 6 l x min(-1) and 1.90 at 3 l x min(-1).

CONCLUSION

This study demonstrates (1) that the high RCP of 99mTc-DTPA is not affected by jet nebulization, even when using oxygen at a high flow rate, and (2) that when using a flow rate between 6 and 9 l x min(-1), the MMAD remains optimal for peripheral lung deposition.