The Subventricular Zone En-face: Wholemount Staining and Ependymal Flow

The walls of the lateral ventricles contain the largest germinal region in the adult mammalian brain. The subventricular zone (SVZ) in these walls is an extensively studied model system for understanding the behavior of neural stem cells and the regulation of adult neurogenesis. Traditionally, these studies have relied on classical sectioning techniques for histological analysis. Here we present an alternative approach, the wholemount technique, which provides a comprehensive, en-face view of this germinal region. Compared to sections, wholemounts preserve the complete cytoarchitecture and cellular relationships within the SVZ. This approach has recently revealed that the adult neural stem cells, or type B1 cells, are part of a mixed neuroepithelium with differentiated ependymal cells lining the lateral ventricles. In addition, this approach has been used to study the planar polarization of ependymal cells and the cerebrospinal fluid flow they generate in the ventricle. With recent evidence that adult neural stem cells are a heterogeneous population that is regionally specified, the wholemount approach will likely be an essential tool for understanding the organization and parcellation of this stem cell niche

Perineuronal Net Formation and the Critical Period for Neuronal Maturation in the Hypothalamic Arcuate Nucleus

In leptin-deficient ob/ob mice, obesity and diabetes are associated with abnormal development of neurocircuits in the hypothalamic arcuate nucleus (ARC)1, a critical brain area for energy and glucose homoeostasis2,3. Because this developmental defect can be remedied by systemic leptin administration, but only if given before postnatal day 28, a critical period for leptin-dependent development of ARC neurocircuits has been proposed4. In other brain areas, critical-period closure coincides with the appearance of perineuronal nets (PNNs), extracellular matrix specializations that restrict the plasticity of neurons that they enmesh5. Here we report that in humans and rodents, subsets of neurons in the mediobasal aspect of the ARC are enmeshed in PNN-like structures. In mice, these neurons are densely packed into a continuous ring that encircles the junction of the ARC and median eminence, which facilitates exposure of ARC neurons to the circulation. Most of the enmeshed neurons are both γ-aminobutyric acid-ergic and leptin-receptor positive, including a majority of Agouti-related-peptide neurons. Postnatal formation of the PNN-like structures coincides precisely with closure of the critical period for maturation of Agouti-related-peptide neurons and is dependent on input from circulating leptin, because postnatal ob/ob mice have reduced ARC PNN-like material that is restored by leptin administration during the critical period. We conclude that neurons crucial to metabolic homoeostasis are enmeshed in PNN-like structures and organized into a densely packed cluster situated circumferentially at the ARC–median eminence junction, where metabolically relevant humoral signals are sensed

Axonal Control of the Adult Neural Stem Cell Niche

SUMMARYThe ventricular-subventricular zone (V-SVZ) is an extensive germinal niche containing neural stem cells (NSC) in the walls of the lateral ventricles of the adult brain. How the adult brain’s neural activity influences the behavior of adult NSCs remains largely unknown. We show that serotonergic (5HT) axons originating from a small group of neurons in the raphe form an extensive plexus on most of the ventricular walls. Electron microscopy revealed intimate contacts between 5HT axons and NSCs (B1) or ependymal cells (E1) and these cells were labeled by a transsynaptic viral tracer injected into the raphe. B1 cells express the 5HT receptors 2C and 5A. Electrophysiology showed that activation of these receptors in B1 cells induced small inward currents. Intraventricular infusion of 5HT2C agonist or antagonist increased or decreased V-SVZ proliferation, respectively. These results indicate that supraependymal 5HT axons directly interact with NSCs to regulate neurogenesis via 5HT2C

Transcriptomic analysis links diverse hypothalamic cell types to fibroblast growth factor 1-induced sustained diabetes remission

n rodent models of type 2 diabetes (T2D), sustained remission of hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1), and the mediobasal hypothalamus (MBH) was recently implicated as the brain area responsible for this effect. To better understand the cellular response to FGF1 in the MBH, we sequenced >79,000 single-cell transcriptomes from the hypothalamus of diabetic Lepob/ob mice obtained on Days 1 and 5 after icv injection of either FGF1 or vehicle. A wide range of transcriptional responses to FGF1 was observed across diverse hypothalamic cell types, with glial cell types responding much more robustly than neurons at both time points. Tanycytes and ependymal cells were the most FGF1-responsive cell type at Day 1, but astrocytes and oligodendrocyte lineage cells subsequently became more responsive. Based on histochemical and ultrastructural evidence of enhanced cell-cell interactions between astrocytes and Agrp neurons (key components of the melanocortin system), we performed a series of studies showing that intact melanocortin signaling is required for the sustained antidiabetic action of FGF1. These data collectively suggest that hypothalamic glial cells are leading targets for the effects of FGF1 and that sustained diabetes remission is dependent on intact melanocortin signaling

Epithelial organization of the adult neural stem cell niche

The adult mammalian brain, for all of its complexity, develops from a single cell layered epithelium of neural stem cells. These stem cells are retained in the epithelium lining the embryonic brain ventricles throughout development. Postnatally however, this germinal epithelium is replaced by postmitotic multiciliated ependymal cells. Neural stem cells are retained in the adult brain, but they are displaced from the ventricular epithelium and it is generally thought that they do not maintain epithelial properties. In this dissertation, I challenge this notion. Using a wholemount imaging technique that allows en-face examination of the ventricular walls, I show that the adult brain lateral ventricle is lined by a mixed neuroepithelium of multiciliated ependymal cells and adult neural stem cells (type B cells). Type B cells have very small ventricle-contacting apical surfaces observed only in neurogenic niches of the adult ventricular system. At their apical surface, B cells extend a primary cilium into the ventricle and are surrounded by ependymal cells, forming pinwheel structures that appear as repeating units across the neuroepithelium. Type B cells also contain a previously unidentified long basal process ending on blood vessels. These adult neural stem cells therefore display apical-basal polarity. En-face analysis of the ventricular walls also reveals a third cell type in the ventricular epithelium, which I call E2 cells. These cells are bi-ciliated with a novel basal body structure containing elaborate lateral extensions. Finally, in addition to apical-basal polarity, the adult ventricular epithelium has planar polarity evident in the polarized beating of ependymal cilia, which propels cerebrospinal fluid through the ventricular system and is essential to normal brain function. I describe two reliable anatomical correlates to ependymal planar polarity: the rotational orientation of basal bodies and their translational position on the apical surface of ependymal cells. I show that this planar polarity does not require ependymal cilia. Altogether, this work reveals the epithelial organization of the adult neural stem cell niche, characterized by the apical surfaces of stem cells surrounded by ependymal cells in unique pinwheel structures

Microvascular Decompression of the Trigeminal Nerve with Petrous Sling Technique: Surgical Video

The retrosigmoid approach for microvascular decompression of the trigeminal nerve (TN) is an established and highly effective technique for the treatment of trigeminal neuralgia due to vascular compression. It is common to place a pledget or other cushion material between the source of vascular compression, typically the superior cerebellar artery (SCA), and the TN after vessel mobilization and decompression. A previous study demonstrated the use of a tentorial sling on the SCA to maintain decompression of the TN, with encouraging results

Microvascular Decompression of the Trigeminal Nerve with Petrous Sling Technique: Surgical Video.

The retrosigmoid approach for microvascular decompression of the trigeminal nerve (TN) is an established and highly effective technique for the treatment of trigeminal neuralgia due to vascular compression. It is common to place a pledget or other cushion material between the source of vascular compression, typically the superior cerebellar artery (SCA), and the TN after vessel mobilization and decompression. A previous study demonstrated the use of a tentorial sling on the SCA to maintain decompression of the TN, with encouraging results