Functional Differentiation of Cholecystokinin-Containing Interneurons Destined for the Cerebral Cortex

Abstract

Although extensively studied postnatally, the functional differentiation of cholecystokinin (CCK)-containing interneurons en route towards the cerebral cortex during fetal development is incompletely understood. Here, we used CCKBAC/DsRed mice encoding a CCK promoter-driven red fluorescent protein to analyze the temporal dynamics of DsRed expression, neuronal identity, and positioning through high-resolution developmental neuroanatomy. Additionally, we developed a dual reporter mouse line (CCKBAC/DsRed::GAD67gfp/+) to differentiate CCK-containing interneurons from DsRed+ principal cells during prenatal development. We show that DsRed is upregulated in interneurons once they exit their proliferative niche in the ganglionic eminence and remains stably expressed throughout their long-distance migration towards the cerebrum, particularly in the hippocampus. DsRed+ interneurons, including a cohort coexpressing calretinin, accumulated at the palliosubpallial boundary by embryonic day 12.5. Pioneer DsRed+ interneurons already reached deep hippocampal layers by embryonic day 14.5 and were morphologically differentiated by birth. Furthermore, we probed migrating interneurons entering and traversing the cortical plate, as well as stationary cells in the hippocampus by patch-clamp electrophysiology to show the first signs of Na+ and K+ channel activity by embryonic day 12.5 and reliable adult-like excitability by embryonic day 18.5. Cumulatively, this study defines key positional, molecular, and biophysical properties of CCK+ interneurons in the prenatal brain.

Hypothalamic CNTF volume transmission shapes cortical noradrenergic excitability upon acute stress

“…Here, we unmask an efficient mechanism coordinated by glutamate release from CRH neurons onto ependymal cells that line the wall of the 3 rd ventricle to trigger long-range volume transmission by ciliary neurotrophic factor (CNTF) in the brain aqueductal system. Once reaching the LC, CNTF heightens NE output ( Fig 1A), as opposed to fast synaptic coupling known to evoke anxiety acutely (Zhang et al, 2017). We show the maintenance of NE excitability through CNTF-induced sequential recruitment of secretagogin (Scgn) and extracellular signal-regulated kinase 1 (Erk1) to increase tyrosine hydroxylase (TH) activity by phosphorylation for cortical NE production.…”

“…Bains, University of Calgary, Canada) were crossed with B6.Cg‐ Gt(ROSA)26Sor tm6(CAG‐ZsGreen1)Hze /J mice ( Ai6 ; JAX stock #012704 and #007906) to visualize periventricular innervation by CRH neurons (Romanov et al , 2017a,b). Scgn ‐Cre mice were developed using the BAC technology (Calvigioni et al , 2017; Z.M., F.E., and G.S., Institute of Experimental Medicine, Hungarian Academy of Sciences). When using Wistar rats, experiments were performed at 12 weeks of age.…”

“…A neural link between CRH + parvocellular cells and norepinephrinergic (NE) neurons of the locus coeruleus (LC) is of particular appeal because NE activity increases with the severity and duration of stress (Aston-Jones et al, 1996;Chowdhury et al, 2000) and NE afferents of the PFC are poised to facilitate adaptive behaviors (Uematsu et al, 2017). Recently, CRH + innervation of NE neurons has been described (Zhang et al, 2017), including at the ultrastructural level (Van Bockstaele et al, 1996). However, a monosynaptic circuit operating through excitatory CRH [i.e., CRH acting at G s protein-coupled Crhr1 and/or Crhr2 receptors (De Souza, 1995)] seems insufficient to functionally convert shortlived surges of excitability into long-lasting NE sensitization for cortical stress adaptation, particularly since neuropeptide release likely commences only upon intense burst firing (Overton & Clark, 1997).…”

A beginner’s guide to tissue clearing

“…The original version of the Sca l e method (which was extremely slow) has recently been superseded by Sca l eS, which is faster, avoids tissue expansion and preserves lipids such that lipid staining is possible (Hama et al, 2015). Examples of applications of these methods include mapping progenitors during heart morphogenesis (CUBIC (Chabab et al, 2016)), studying interneurons during brain development (CUBIC (Calvigioni et al, 2016)) and visualizing amyloid beta plaques in brains from 18-month old mice (Sca l eS (Hama et al, 2015)).…”

The DMCdrive: practical 3D-printable micro-drive system for reliable chronic multi-tetrode recording and optogenetic application in freely behaving rodents

“…300 µm thick brain sections were cut on a vibratome (Leica VT1000, Leica Microsystems). Brain sections were cleared according to a modified CUBIC clearing method 35 . Z-stack images were acquired at 10x, using a Zeiss (LSM800) confocal laser scanning microscope.…”