The Somatostatin 2A Receptor Is Enriched in Migrating Neurons during Rat and Human Brain Development and Stimulates Migration and Axonal Outgrowth

The neuropeptide somatostatin has been suggested to play an important role during neuronal development in addition to its established modulatory impact on neuroendocrine, motor and cognitive functions in adults. Although six somatostatin G protein-coupled receptors have been discovered, little is known about their distribution and function in the developing mammalian brain. In this study, we have first characterized the developmental expression of the somatostatin receptor sst2A, the subtype found most prominently in the adult rat and human nervous system. In the rat, the sst2A receptor expression appears as early as E12 and is restricted to post-mitotic neuronal populations leaving the ventricular zone. From E12 on, migrating neuronal populations immunopositive for the receptor were observed in numerous developing regions including the cerebral cortex, hippocampus and ganglionic eminences. Intense but transient immunoreactive signals were detected in the deep part of the external granular layer of the cerebellum, the rostral migratory stream and in tyrosine hydroxylase- and serotonin- positive neurons and axons. Activation of the sst2A receptor in vitro in rat cerebellar microexplants and primary hippocampal neurons revealed stimulatory effects on neuronal migration and axonal growth, respectively. In the human cortex, receptor immunoreactivity was located in the preplate at early development stages (8 gestational weeks) and was enriched to the outer part of the germinal zone at later stages. In the cerebellum, the deep part of the external granular layer was strongly immunoreactive at 19 gestational weeks, similar to the finding in rodents. In addition, migrating granule cells in the internal granular layer were also receptor-positive. Together, theses results strongly suggest that the somatostatin sst2A receptor participates in the development and maturation of specific neuronal populations during rat and human brain ontogenesis

Implanted neurosphere-derived precursors promote recovery after neonatal excitotoxic brain injury

International audienceBrain damage through excitotoxic mechanisms is a major cause of cerebral palsy in infants. This phenomenon usually occurs during the fetal period in human, and often leads to lifelong neurological morbidity with cognitive and sensorimotor impairment. However, there is currently no effective therapy. Significant recovery of brain function through neural stem cell implantation has been shown in several animal models of brain damage, but remains to be investigated in detail in neonates. In the present study, we evaluated the effect of cell therapy in a well-established neonatal mouse model of cerebral palsy induced by excitotoxicity (ibotenate treatment on postnatal day 5). Neurosphere-derived precursors or control cells (fibroblasts) were implanted into injured and control brains contralateral to the site of injury, and the fate of implanted cells was monitored by immunohistochemistry. Behavioral tests were performed in animals that received early (4 h after injury) or late (72 h after injury) cell implants. We show that neurosphere-derived precursors implanted into the injured brains of 5-day-old pups migrated to the lesion site, remained undifferentiated at day 10, and differentiated into oligodendrocyte and neurons at day 42. Although grafted cells finally die there few weeks later, this procedure triggered a reduction in lesion size and an improvement in memory performance compared with untreated animals, both 2 and 5 weeks after treatment. Although further studies are warranted, cell therapy could be a future therapeutic strategy for neonates with acute excitotoxic brain injury

The Regulatory Machinery of Neurodegeneration in In Vitro Models of Amyotrophic Lateral Sclerosis

Neurodegenerative phenotypes reflect complex, time-dependent molecular processes whose elucidation may reveal neuronal class-specific therapeutic targets. The current focus in neurodegeneration has been on individual genes and pathways. In contrast, we assembled a genome-wide regulatory model (henceforth, “interactome”), whose unbiased interrogation revealed 23 candidate causal master regulators of neurodegeneration in an in vitro model of amyotrophic lateral sclerosis (ALS), characterized by a loss of spinal motor neurons (MNs). Of these, eight were confirmed as specific MN death drivers in our model of familial ALS, including NF-κB, which has long been considered a pro-survival factor. Through an extensive array of molecular, pharmacological, and biochemical approaches, we have confirmed that neuronal NF-κB drives the degeneration of MNs in both familial and sporadic models of ALS, thus providing proof of principle that regulatory network analysis is a valuable tool for studying cell-specific mechanisms of neurodegeneration

Pitfalls in the quest of neuroprotectants for the perinatal brain

Sick preterm and term newborns are highly vulnerable to neural injury, and thus there has been a major search for new, safe and efficacious neuroprotective interventions in recent decades. Preclinical studies are essential to select candidate drugs for clinical trials in humans. This article focuses on ‘negative’ preclinical studies, i.e. studies where significant differences cannot be detected. Such findings are critical to inform both clinical and preclinical investigators, but historically they have been difficult to publish. A significant amount of time and resources is lost when negative results or nonpromising therapeutics are replicated in separate laboratories because these negative results were not shared with the research community in an open and accessible format. In this article, we discuss approaches to strengthen conclusions from negative preclinical studies and, conversely, to reduce false-negative preclinical evaluations of potential therapeutic compounds. Without being exhaustive, we address three major issues in conducting and interpreting preclinical experiments, including: (a) the choice of animal models, (b) the experimental design, and (c) issues concerning statistical analyses of the experiments. This general introduction is followed by synopses of negative data obtained from studies of three potential therapeutics for perinatal brain injury: (1) the somatostatin analog octreotide, (2) an AMPA/kainate receptor antagonist, topiramate, and (3) a pyruvate derivative, ethyl pyruvate

Necroptosis Drives Motor Neuron Death in Models of Both Sporadic and Familial ALS

Most cases of neurodegenerative diseases are sporadic, hindering the use of genetic mouse models to analyze disease mechanisms. Focusing on the motor neuron (MN) disease amyotrophic lateral sclerosis (ALS), we therefore devised a fully humanized coculture model composed of human adult primary sporadic ALS (sALS) astrocytes and human embryonic stem-cell-derived MNs. The model reproduces the cardinal features of human ALS: sALS astrocytes, but not those from control patients, trigger selective death of MNs. The mechanisms underlying this non-cell-autonomous toxicity were investigated in both astrocytes and MNs. Although causal in familial ALS (fALS), SOD1 does not contribute to the toxicity of sALS astrocytes. Death of MNs triggered by either sALS or fALS astrocytes occurs through necroptosis, a form of programmed necrosis involving receptor-interacting protein 1 and the mixed lineage kinase domain-like protein. The necroptotic pathway therefore constitutes a potential therapeutic target for this incurable disease

Regional, cellular and subcellular localization of sst2A receptor immunoreactivity on sagittal (A–H) and coronal (I–K) sections of the rat mesencephalon and diencephalon between E14 and E18.

<p>A) At E16, intense sst2A receptor immunoreactivity is observed in the substantia nigra (SN; boxed area) and along the medial forebrain bundle (mfb; arrowhead). B–B″) At E16, the sst2A receptor (red in B, B″) and tyrosine hydroxylase (TH) (green in B′, B″) immunoreactivities extensively overlap both in the SN and in emerging processes of the mfb. C–C″) At E18, sst2A receptor immunoreactivity is dramatically decreased in both the SN and the mfb. D–D″) High magnification microscopic images illustrate numerous sst2A receptor-immunoreactive fibers (red in D,D′) in the mfb at E16. Some of them are TH-positive (green in D′,D″) (arrowheads). E–E″) Some sst2A receptor-immunolabeled axons (red in E, E″) of the mfb express 5-HT (green in E′, E″) (arrowheads). F,G) Pre-embedding immunogold immunohistochemistry of the sst2A receptor in the mfb at E16 illustrates very high density of immunoparticles in axons (F) and growth cone-like structures (G). Note that although the majority of immunoparticles are intracellular, some are found associated to the plasma membrane. H) At E14, intense sst2A receptor immunolabeling is observed on sagittal sections in the developing hypothalamus (boxed area). I) Illustration of receptor immunoreactivity on coronal section at the level of hypothalamic area at E16. Note the receptor immunoreactivity in the caudal ganglionic eminence (CGE) (arrow). J,K) J represents magnification of boxed area in I. At high magnification, sst2A receptor immunoreactivity is found at the periphery of numerous hypothalamic neurons. III, third ventricle; HA, hypothalamic area. Scale bars: A, 500 µm; B–B″, C–C″, 50 µm; D–D″, E–E″, J, 20 µm; F, G, 1 µm; H, 250 µm; I, 200 µm; K, 10 µm.</p

Regional, cellular and subcellular distribution of sst2A receptor immunoreactivity on coronal sections of the rat telencephalon at E16 and E18.

<p>A,B) Intense sst2A receptor immunoreactivity is detected at E16 in the post-mitotic areas of the lateral ganglionic eminence (LGE) and the caudal ganglionic eminence (CGE) (B). Note the presence of sst2A receptor immunoreactivity in the cortex (cx) and hippocampus (hi). C represents magnification of boxed area in B and illustrates that the sst2A receptor immunoreactivity is found in cell bodies and short processes in the CGE. D,E) Pre-embedding immunogold immunohistochemistry of the sst2A receptor in the CGE illustrates that high density of immunoparticles are localized intracellularly. However, sst2A receptor-immunoreactive particles are also found in association with the plasma membrane (arrowheads in D). Note that in a neuronal process the majority of the immunoparticles are membrane-associated (arrowheads in E). F represents magnification of the boxed area in A. Numerous cells are immunoreactive for sst2A in the LGE. G represents high magnification of the area labeled with an arrow on A and illustrates that fibers are also sst2A receptor-immunolabeled. H,I) High magnification confocal microscopic analysis in the CGE demonstrates redistribution of receptors upon agonist stimulation. In control conditions, sst2A receptor immunoreactivity outlines the periphery of cells (H). Forty minutes after agonist administration, receptor immunoreactivity is confined to small puncta in the cytoplasm (I). J,K) At E18, intense sst2A receptor immunoreactivity is observed in the dorso-medial part of the caudate-putamen in rostral (J) and caudal (K) sections close to the ventricular surface. Scattered sst2A receptor immunoreactivity is also evident in the medial part of the developing caudate-putamen (asterisk). L represents magnification of boxed area on J. The sst2A receptor immunoreactivity is observed in large number of cells and their short processes in the dorsal caudate-putamen. Note the lack of sst2A receptor immunoreactivity in the subventricular zone (SVZ). M,N are high magnifications from the area labeled with asterisk on J. The sst2A receptor is expressed in neuronal perikarya and processes in the medial part of the caudate-putamen. Scale bars: A, B, 200 µm; C, F, G, L, 20 µm; D, 500 nm; E, 250 nm; H, I, M, N, 10 µm; J, K, 500 µm.</p