Ontogenetic alterations in molecular and structural correlates of dendritic growth after developmental exposure to polychlorinated biphenyls.

ObjectivePerinatal exposure to polychlorinated biphenyls (PCBs) is associated with decreased IQ scores, impaired learning and memory, psychomotor difficulties, and attentional deficits in children. It is postulated that these neuropsychological deficits reflect altered patterns of neuronal connectivity. To test this hypothesis, we examined the effects of developmental PCB exposure on dendritic growth.MethodsRat dams were gavaged from gestational day 6 through postnatal day (PND) 21 with vehicle (corn oil) or the commercial PCB mixture Aroclor 1254 (6 mg/kg/day). Dendritic growth and molecular markers were examined in pups during development.ResultsGolgi analyses of CA1 hippocampal pyramidal neurons and cerebellar Purkinje cells indicated that developmental exposure to PCBs caused a pronounced age-related increase in dendritic growth. Thus, even though dendritic lengths were significantly attenuated in PCB-treated animals at PND22, the rate of growth was accelerated at later ages such that by PND60, dendritic growth was comparable to or even exceeded that observed in vehicle controls. Quantitative reverse transcriptase polymerase chain reaction analyses demonstrated that from PND4 through PND21, PCBs generally increased expression of both spinophilin and RC3/neurogranin mRNA in the hippocampus, cerebellum, and cortex with the most significant increases observed in the cortex.ConclusionsThis study demonstrates that developmental PCB exposure alters the ontogenetic profile of dendritogenesis in critical brain regions, supporting the hypothesis that disruption of neuronal connectivity contributes to neuropsychological deficits seen in exposed children

SIRT1 Is Essential for Normal Cognitive Function and Synaptic Plasticity

Conservation of normal cognitive functions relies on the proper performance of the nervous system at the cellular and molecular level. The mammalian NAD(+)-dependent deacetylase, SIRT1, impacts different processes potentially involved in the maintenance of brain integrity such as chromatin remodeling, DNA repair, cell survival and neurogenesis. Here we show that SIRT1 is expressed in neurons of the hippocampus, a key structure in learning and memory. Using a combination of behavioral and electrophysiological paradigms we analyzed the effects of SIRT1 deficiency and overexpression on mouse learning and memory as well as on synaptic plasticity. We demonstrated that the absence of SIRT1 impaired cognitive abilities, including immediate memory, classical conditioning and spatial learning. In addition, we found that the cognitive deficits in SIRT1 knockout mice were associated with defects in synaptic plasticity without alterations in basal synaptic transmission or NMDA receptor function. Brains of SIRT1-KO mice exhibited normal morphology and dendritic spine structure but display a decrease in dendritic branching, branch length and complexity of neuronal dendritic arbors. Also, a decrease in ERK1/2 phosphorylation and altered expression of hippocampal genes involved in synaptic function, lipid metabolism and myelination were detected in SIRT1-KO mice. In contrast, mice with high levels of SIRT1 expression in brain exhibited regular synaptic plasticity and memory. We conclude that SIRT1 is indispensable for normal learning, memory and synaptic plasticity in mice

Dendritic Alterations in a Tauopathy Rat Model of Alzheimer’s Disease Using PP2A Inhibition

PP2A is protein phosphatase-2A. Inhibition of PP2A (by PP2A inhibitors 1 and 2) results in hyperphosphorylation and accumulation of tau protein. Hyperphosphorylated tau is a major component of neurofibrillary tangles – a pathological hallmark of Alzheimer’s Disease (AD). Hence PP2A inhibition represents a putative new approach for a rodent model of AD. The goal of this study was to evaluate the effects of PP2A inhibition on dendritic branching in cortical pyramids in rats that wereinjected ICV with an adeno- associated virus for expression of: (1) Inhibitor 1 full length (I1 FL) (2) Inhibitor 2 full length (I2 FL) (3) Inhibitor 2 amino terminal fragment (I2 NTF) (4) GFP (Green Fluorescent Protein), Control Rat brains were subsequently Golgi stained and from coded slides randomly selected layer V pyramids were evaluated for the amount and distribution of their basilar dendritic arbor using Sholl analysis. Results showed that administration of both I2 groups (full length and amino terminal fragment) resulted in more dendritic branching than either the GFP control or the I1 full length inhibitor. Tau hyperphosphoryation by PP2A-inhibition did not result in a diminution of cortical branching. Additional studies are ongoing to further characterize the validity of this model

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy

UnlabelledArginase 1 deficiency is a urea cycle disorder associated with hyperargininemia, spastic diplegia, loss of ambulation, intellectual disability, and seizures. To gain insight on how loss of arginase expression affects the excitability and synaptic connectivity of the cortical neurons in the developing brain, we used anatomical, ultrastructural, and electrophysiological techniques to determine how single-copy and double-copy arginase deletion affects cortical circuits in mice. We find that the loss of arginase 1 expression results in decreased dendritic complexity, decreased excitatory and inhibitory synapse numbers, decreased intrinsic excitability, and altered synaptic transmission in layer 5 motor cortical neurons. Hepatic arginase 1 gene therapy using adeno-associated virus rescued nearly all these abnormalities when administered to neonatal homozygous knock-out animals. Therefore, gene therapeutic strategies can reverse physiological and anatomical markers of arginase 1 deficiency and therefore may be of therapeutic benefit for the neurological disabilities in this syndrome.Significance statementThese studies are one of the few investigations to try to understand the underlying neurological dysfunction that occurs in urea cycle disorders and the only to examine arginase deficiency. We have demonstrated by multiple modalities that, in murine layer 5 cortical neurons, a gradation of abnormalities exists based on the functional copy number of arginase: intrinsic excitability is altered, there is decreased density in asymmetrical and perisomatic synapses, and analysis of the dendritic complexity is lowest in the homozygous knock-out. With neonatal administration of adeno-associated virus expressing arginase, there is near-total recovery of the abnormalities in neurons and cortical circuits, supporting the concept that neonatal gene therapy may prevent the functional abnormalities that occur in arginase deficiency

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy

Arginase 1 deficiency is a urea cycle disorder associated with hyperargininemia, spastic diplegia, loss of ambulation, intellectual disability, and seizures. To gain insight on how loss of arginase expression affects the excitability and synaptic connectivity of the cortical neurons in the developing brain, we used anatomical, ultrastructural, and electrophysiological techniques to determine how single-copy and double-copy arginase deletion affects cortical circuits in mice. We find that the loss of arginase 1 expression results in decreased dendritic complexity, decreased excitatory and inhibitory synapse numbers, decreased intrinsic excitability, and altered synaptic transmission in layer 5 motor cortical neurons. Hepatic arginase 1 gene therapy using adeno-associated virus rescued nearly all these abnormalities when administered to neonatal homozygous knock-out animals. Therefore, gene therapeutic strategies can reverse physiological and anatomical markers of arginase 1 deficiency and therefore may be of therapeutic benefit for the neurological disabilities in this syndrome. SIGNIFICANCE STATEMENT These studies are one of the few investigations to try to understand the underlying neurological dysfunction that occurs in urea cycle disorders and the only to examine arginase deficiency. We have demonstrated by multiple modalities that, in murine layer 5 cortical neurons, a gradation of abnormalities exists based on the functional copy number of arginase: intrinsic excitability is altered, there is decreased density in asymmetrical and perisomatic synapses, and analysis of the dendritic complexity is lowest in the homozygous knock-out. With neonatal administration of adeno-associated virus expressing arginase, there is near-total recovery of the abnormalities in neurons and cortical circuits, supporting the concept that neonatal gene therapy may prevent the functional abnormalities that occur in arginase deficiency

Enrichment improves cognition in AD mice by amyloid-related and unrelated mechanisms. Neurobiol Aging;28:831-844

Abstract Lifelong cognitive stimulation is associated with a lower risk of Alzheimer's disease (AD), but causality is difficult to prove. We therefore sought to investigate the preventative potential of environmental enrichment (EE) using mice expressing both human mutant presenilin-1 and the amyloid precursor protein (PS1/PDAPP). At weaning, mice were placed into either an enriched or standard housing environment. Behavioral testing at 4.5-6 months showed that environmentally enriched PS1/PDAPP mice outperformed mice in standard housing, and were behaviorally indistinguishable from non-transgenic mice across multiple cognitive domains. PS1/PDAPP mice exposed to both environmental enrichment and behavioral testing, but not to EE alone, showed 50% less brain ␤-amyloid without improved dendritic morphology. Microarray analysis revealed large enrichment-induced changes in hippocampal expression of genes/proteins related to A␤ sequestration and synaptic plasticity. These results indicate that EE protects against cognitive impairment in AD transgenic mice through a dual mechanism, including both amyloid dependent and independent mechanisms

Developmental exposure to polychlorinated biphenyls interferes with experience-dependent dendritic plasticity and ryanodine receptor expression in weanling rats.

BackgroundNeurodevelopmental disorders are associated with altered patterns of neuronal connectivity. A critical determinant of neuronal connectivity is the dendritic morphology of individual neurons, which is shaped by experience. The identification of environmental exposures that interfere with dendritic growth and plasticity may, therefore, provide insight into environmental risk factors for neurodevelopmental disorders.ObjectiveWe tested the hypothesis that polychlorinated biphenyls (PCBs) alter dendritic growth and/or plasticity by promoting the activity of ryanodine receptors (RyRs).Methods and resultsThe Morris water maze was used to induce experience-dependent neural plasticity in weanling rats exposed to either vehicle or Aroclor 1254 (A1254) in the maternal diet throughout gestation and lactation. Developmental A1254 exposure promoted dendritic growth in cerebellar Purkinje cells and neocortical pyramidal neurons among untrained animals but attenuated or reversed experience-dependent dendritic growth among maze-trained littermates. These structural changes coincided with subtle deficits in spatial learning and memory, increased [3H]-ryanodine binding sites and RyR expression in the cerebellum of untrained animals, and inhibition of training-induced RyR upregulation. A congener with potent RyR activity, PCB95, but not a congener with negligible RyR activity, PCB66, promoted dendritic growth in primary cortical neuron cultures and this effect was blocked by pharmacologic antagonism of RyR activity.ConclusionsDevelopmental exposure to PCBs interferes with normal patterns of dendritic growth and plasticity, and these effects may be linked to changes in RyR expression and function. These findings identify PCBs as candidate environmental risk factors for neurodevelopmental disorders, especially in children with heritable deficits in calcium signaling