Biology subjects

Rancillac, A.

Publications and source records attributed to Rancillac, A..

5 recordsLinked to original sources

bioRxiv2026

Long-projection astrocytes challenge canonical territorial organization in the sleep-promoting VLPO

The ventrolateral preoptic nucleus (VLPO) is a key hypothalamic hub for non-rapid eye movement sleep, yet the glial architecture supporting its circuits remains poorly understood. Here, combining genetic labeling, high-resolution imaging and calcium imaging, we uncover unexpected astrocyte diversity in the VLPO. In addition to classical protoplasmic astrocytes, we identify paired "doublet" astrocytes associated with high local proliferative activity, as revealed by EdU incorporation. We further describe a population of long-projection astrocytes extending processes far beyond canonical astrocytic territories and contacting distant cells. These projections challenge the classical territorial organization of astrocytes and resemble morphologies previously thought to be restricted to hominid brains. Notably, VLPO astrocytes display robust spontaneous Ca{superscript 2} activity and a highly functionally connected network compared to astrocytes in the cortex and hippocampus. Together, these findings reveal specialized astrocyte architectures and enhanced glial network integration within a sleep-promoting nucleus. Reporting summaryBellier et al. identify three astrocyte subtypes in the sleep-promoting VLPO, including long-projection astrocytes with hominid-like morphology. They uncover marked postnatal gliogenesis, distinctive spontaneous Ca{superscript 2} dynamics, and tightly interconnected astrocytic networks, revealing region-specific astrocyte specialization and enhanced glial communication.

neuroscience↗

bioRxiv2025

Slow Intrinsic Oscillations in the Ventrolateral Preoptic nucleus

The ventrolateral preoptic nucleus (VLPO) of the hypothalamus plays a major role in the induction and consolidation of non-rapid eye movement (NREM) sleep. While VLPO neurons are heterogeneous, they often display low-threshold spikes (LTS), a feature that supports rhythmic activity. Nevertheless, rhythmic bursting in these VLPO neurons has never been observed. Here, we report that [~]12% of VLPO neurons in a large database of ex vivo patch-clamp recordings display spontaneous rhythmic bursting of action potentials. This activity occurred in putative sleep-promoting neurons, identified by inhibitory responses to noradrenaline (NA), as well as wake-active neurons that were activated by NA. Unsupervised clustering of 24 neurons based on burst properties, electrophysiological, and morphological features revealed three distinct groups: one corresponding to putative sleep-promoting neurons and two wake-active neurons with fast and slow bursting dynamics. Strikingly, membrane potential oscillations persisted in the presence of tetrodotoxin (TTX), indicating that rhythmic bursting is driven by intrinsic mechanisms rather than network activity. These findings suggest that rhythmic bursting is an intrinsic and functionally relevant mode of activity in VLPO neurons, which may contribute to sleep regulation.

neuroscience↗

bioRxiv2024

Unveiling the Functional Connectivity of Astrocytic Networks with AstroNet, a Graph Reconstruction Algorithm Coupled to Image Processing

Astrocytes form extended intercellular networks, displaying complex calcium activity. However, the specific organization of these astrocytic networks and the precise extent of their functional connectivity in different brain areas remain unexplored. To unveil the functional architecture of astrocytic networks, we developed, using a data-driven methodology, a novel algorithm called AstroNet that uses two-photon calcium imaging to map temporal correlations in activation events among neighboring astro-cytes. Our approach involves reconstructing functional astrocytic networks by organizing individual astrocyte activation events chronologically. This chronological order creates activity paths that enable the extraction of local astrocyte functional correlations. Ultimately, by tallying the occurrences of direct co-activations between pairs of cells along these pathways, we construct a graph that mirrors the underlying astrocyte functional network. By applying this method to two distinct brain regions (CA1 hippocampus and motor cortex), we identified notable differences in local network organizations in sub-regions of around 20-40 astrocytes. Specifically, the cortex exhibited a lower connectivity, while astrocytes in the hippocampus displayed stronger connections. Moreover, we found that in both regions, astrocytic networks consist of smaller, tightly connected sub-networks embedded within a larger, more loosely connected one. Altogether, our innovative method enables the identification of activation paths among astrocytes, facilitates the characterization of local network functional connectivity, and quantifies distinct connectivity patterns among astrocytes from different brain regions. This approach sheds light on the heterogeneous functional organization of astrocytic networks within the brain, pointing to region-specific astrocyte connectivity.

neuroscience↗

bioRxiv2021

Megalencephalic leukoencephalopathy with subcortical cysts is a developmental disorder of the gliovascular unit

Absence of the astrocyte-specific membrane protein MLC1 is responsible for megalencephalic leukoencephalopathy with subcortical cysts (MLC); this rare type of leukodystrophy is characterized by early-onset macrocephaly and progressive white matter vacuolation that lead to ataxia, spasticity, and cognitive decline. During postnatal development (from P5 to P15 in the mouse), MLC1 forms a membrane complex with GlialCAM (another astrocytic transmembrane protein) at the junctions between perivascular astrocytic processes (PvAPs, which along with blood vessels form the gliovascular unit (GVU)). We analyzed the GVU in the Mlc1 knock-out mouse model of MLC. The absence of MLC1 led to an accumulation of fluid in the brain but did not modify the endothelial organization or the integrity of the blood-brain barrier. From P10 onward, the postnatal acquisition of vascular smooth muscle cell contractility was altered, resulting in a marked reduction in arterial perfusion and neurovascular coupling. These anomalies were correlated with alterations in astrocyte morphology, astrocyte polarity and the structural organization of the PvAPs perivascular coverage, and poor intraparenchymal circulation of the cerebrospinal fluid (CSF). Hence, MLC1 is required for the postnatal development and organization of PvAPs and controls vessel contractility and intraparenchymal interstitial fluid clearance. Our data suggest that (i) MLC is a developmental disorder of the GVU, and (ii) PvAP and VSMC maturation defects are primary events in the pathogenesis of MLC and therapeutic targets for this disease.

neuroscience↗

bioRxiv2021

In mice and humans, the brain's blood vessels mature postnatally to acquire barrier and contractile properties

The brain dense vascular network is essential for distributing oxygen and nutrients to neural cells. The network develops during embryogenesis and leads to the formation of the endothelial blood-brain barrier (BBB). This barrier is surrounded by mural cells (pericytes and vascular smooth muscle cells (VSMCs)) and fibroblasts. Here, we compared the molecular and functional properties of brain vascular cells on postnatal day (P)5 vs. P15, via a transcriptomic analysis of purified mouse cortical microvessels (MVs) and the identification of vascular-cell-type-specific or -preferentially expressed transcripts. We found that endothelial cells (ECs), VSMCs and fibroblasts follow specific molecular maturation programs over this time period. In particular, ECs acquire P-glycoprotein (P-gP)-mediated efflux capacities. The arterial VSMC network expands, acquires contractile proteins (such as smooth muscle actin (SMA) and myosin heavy chain 11 (Myh11)) and becomes contractile. We also analyzed samples of human brain cortex from the early prenatal stage through to adulthood: the expression of endothelial P-gP increased at birth and Myh11 in VSMCs acts as a developmental switch (as in the mouse) at birth and up to the age of 2 of 5 years. Thus, in both mice and humans, the early postnatal phase is a critical period during which the essential properties of cerebral blood vessels (i.e. the endothelial efflux of xenobiotics and other molecules, and the VSMC contractility required for vessel tone and brain perfusion) are acquired and mature.

neuroscience↗