Dopamine D 4 Receptor-Deficient Mice Display Cortical Hyperexcitability

The dopamine D(4) receptor (D(4)R) is predominantly expressed in the frontal cortex (FC), a brain region that receives dense input from midbrain dopamine (DA) neurons and is associated with cognitive and emotional processes. However, the physiological significance of this dopamine receptor subtype has been difficult to explore because of the slow development of D(4)R agonists and antagonists the selectivity and efficacy of which have been rigorously demonstrated in vivo. We have attempted to overcome this limitation by taking a multidimensional approach to the characterization of mice completely deficient in this receptor subtype. Electrophysiological current and voltage-clamp recordings were performed in cortical pyramidal neurons from wild-type and D(4)R-deficient mice. The frequency of spontaneous synaptic activity and the frequency and duration of paroxysmal discharges induced by epileptogenic agents were increased in mutant mice. Enhanced synaptic activity was also observed in brain slices of wild-type mice incubated in the presence of the selective D(4)R antagonist PNU-101387G. Consistent with greater electrophysiological activity, nerve terminal glutamate density associated with asymmetrical synaptic contacts within layer VI of the motor cortex was reduced in mutant neurons. Taken together, these results suggest that the D(4)R can function as an inhibitory modulator of glutamate activity in the FC.Fil: Rubinstein, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cepeda, Carlos. University of California at Los Angeles; Estados UnidosFil: Hurst, Raymond S.. University of California at Los Angeles; Estados UnidosFil: Flores Hernandez, Jorge. University of California at Los Angeles; Estados UnidosFil: Ariano, Marjorie A.. The Chicago Medical School; Estados UnidosFil: Falzone, Tomas Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Kozell, Laura B.. Oregon Health Sciences University; Estados UnidosFil: Meshul, Charles K.. Oregon Health Sciences University; Estados UnidosFil: Bunzow, James R.. Oregon Health Sciences University; Estados UnidosFil: Low, Malcolm J.. Oregon Health Sciences University; Estados UnidosFil: Levine, Michael S.. University of California at Los Angeles; Estados UnidosFil: Grandy, David K.. Oregon Health Sciences University; Estados Unido

Effects of climate change on grassland biodiversity and productivity: the need for a diversity of models

There is increasing evidence that the impact of climate change on the productivity of grasslands will at least partly depend on their biodiversity. A high level of biodiversity may confer stability to grassland ecosystems against environmental change, but there are also direct effects of biodiversity on the quantity and quality of grassland productivity. To explain the manifold interactions, and to predict future climatic responses, models may be used. However, models designed for studying the interaction between biodiversity and productivity tend to be structurally different from models for studying the effects of climatic impacts. Here we review the literature on the impacts of climate change on biodiversity and productivity of grasslands. We first discuss the availability of data for model development. Then we analyse strengths and weaknesses of three types of model: ecological, process-based and integrated. We discuss the merits of this model diversity and the scope for merging different model types

Extreme sensitivity of myelinating optic nerve axons in a rodent model of perinatal ischemic injury

Cerebral white matter injury (WMI) is increasingly recognized as a common form of perinatal brain injury that predisposes to cerebral palsy as well as cognitive and learning disabilities. Despite the growing impact of WMI, it is unclear whether common cellular and molecular mechanisms define WMI pathogenesis in preterm and term neonates. Although numerous studies have defined a role for glial vulnerability in WMI, there has been limited study of the susceptibility of immature axons.peer-reviewe

Effects of Subthalamic Nucleus Lesions and Stimulation upon Corticostriatal Afferents in the 6-Hydroxydopamine-Lesioned Rat

Abnormalities of striatal glutamate neurotransmission may play a role in the pathophysiology of Parkinson's disease and may respond to neurosurgical interventions, specifically stimulation or lesioning of the subthalamic nucleus (STN). The major glutamatergic afferent pathways to the striatum are from the cortex and thalamus, and are thus likely to be sources of striatal neuronally-released glutamate. Corticostriatal terminals can be distinguished within the striatum at the electron microscopic level as their synaptic vesicles contain the vesicular glutamate transporter, VGLUT1. The majority of terminals which are immunolabeled for glutamate but are not VGLUT1 positive are likely to be thalamostriatal afferents. We compared the effects of short term, high frequency, STN stimulation and lesioning in 6-hydroxydopamine (6OHDA)-lesioned rats upon striatal terminals immunolabeled for both presynaptic glutamate and VGLUT1. 6OHDA lesions resulted in a small but significant increase in the proportions of VGLUT1-labeled terminals making synapses on dendritic shafts rather than spines. STN stimulation for one hour, but not STN lesions, increased the proportion of synapses upon spines. The density of presynaptic glutamate immuno-gold labeling was unchanged in both VGLUT1-labeled and -unlabeled terminals in 6OHDA-lesioned rats compared to controls. Rats with 6OHDA lesions+STN stimulation showed a decrease in nerve terminal glutamate immuno-gold labeling in both VGLUT1-labeled and -unlabeled terminals. STN lesions resulted in a significant decrease in the density of presynaptic immuno-gold-labeled glutamate only in VGLUT1-labeled terminals. STN interventions may achieve at least part of their therapeutic effect in PD by normalizing the location of corticostriatal glutamatergic terminals and by altering striatal glutamatergic neurotransmission

Down-Regulation of ZnT8 Expression in INS-1 Rat Pancreatic Beta Cells Reduces Insulin Content and Glucose-Inducible Insulin Secretion

The SLC30A8 gene codes for a pancreatic beta-cell-expressed zinc transporter, ZnT8. A polymorphism in the SLC30A8 gene is associated with susceptibility to type 2 diabetes, although the molecular mechanism through which this phenotype is manifest is incompletely understood. Such polymorphisms may exert their effect via impacting expression level of the gene product. We used an shRNA-mediated approach to reproducibly downregulate ZnT8 mRNA expression by >90% in the INS-1 pancreatic beta cell line. The ZnT8-downregulated cells exhibited diminished uptake of exogenous zinc, as determined using the zinc-sensitive reporter dye, zinquin. ZnT8-downregulated cells showed reduced insulin content and decreased insulin secretion (expressed as percent of total insulin content) in response to hyperglycemic stimulus, as determined by insulin immunoassay. ZnT8-depleted cells also showed fewer dense-core vesicles via electron microscopy. These data indicate that reduced ZnT8 expression in cultured pancreatic beta cells gives rise to a reduced insulin response to hyperglycemia. In addition, although we provide no direct evidence, these data suggest that an SLC30A8 expression-level polymorphism could affect insulin secretion and the glycemic response in vivo

CART Peptide Is a Potential Endogenous Antioxidant and Preferentially Localized in Mitochondria

The multifunctional neuropeptide Cocaine and Amphetamine Regulated Transcript (CART) is secreted from hypothalamus, pituitary, adrenal gland and pancreas. It also can be found in circulatory system. This feature suggests a general role for CART in different cells. In the present study, we demonstrate that CART protects mitochondrial DNA (mtDNA), cellular proteins and lipids against the oxidative action of hydrogen peroxide, a widely used oxidant. Using cis-parinaric acid as a sensitive reporting probe for peroxidation in membranes, and a lipid-soluble azo initiator of peroxyl radicals, 2,2′-Azobis(2,4-dimethylvaleronitrile) we found that CART is an antioxidant. Furthermore, we found that CART localized to mitochondria in cultured cells and mouse brain neuronal cells. More importantly, pretreatment with CART by systemic injection protects against a mouse oxidative stress model, which mimics the main features of Parkinson's disease. Given the unique molecular structure and biological features of CART, we conclude that CART is an antioxidant peptide (or antioxidant hormone). We further propose that it may have strong therapeutic properties for human diseases in which oxidative stress is strongly involved such as Parkinson's disease

An ultrastructural analysis of the effects of ethanol self-administration on the hypothalamic paraventricular nucleus in rhesus macaques

A bidirectional relationship between stress and alcohol exists whereby stressful events are comorbid with problematic alcohol use and prolonged alcohol exposure results in adaptations of the physiological stress response. Endocrine response to stress is initiated in the hypothalamic paraventricular nucleus (PVN) with the synthesis and release of corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Alterations in CRH and AVP following long-term alcohol exposure in rodents is well demonstrated, however little is known about the response to alcohol in primates or the mechanisms of adaptation. We hypothesized that long-term alcohol self-administration in nonhuman primates would lead to ultrastructural changes in the PVN underlying adaptation to chronic alcohol. Double-label immunogold electron microscopy was used to measure presynaptic GABA and glutamate density within synaptic terminals contacting CRH- and AVP-immunoreactive dendrites. Additionally, pituitary-adrenal hormones (ACTH, cortisol, DHEA-s and aldosterone) under two conditions (low and mild stress) were compared before and after self-administration. All hormones were elevated in response to the mild stressor independent of alcohol consumption. The presynaptic glutamate density in recurrent (i.e., intra-hypothalamic) CRH terminals was highly related to alcohol intake, and may be a permissive factor in increased drinking due to stress. Conversely, glutamate density within recurrent AVP terminals showed a trend-level increase following alcohol, but was not related to average daily consumption. Glutamate density in non-recurrent AVP terminals was related to aldosterone under the low stress condition while GABAergic density in this terminal population was related to water consumption. The results reveal distinct populations of presynaptic terminals whose glutamatergic or GABAergic density were uniquely related to water and alcohol consumption and circulating hormones

Differential electrophysiological and morphological alterations of thalamostriatal and corticostriatal projections in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a fatal genetic disorder characterized by cell death of medium-sized spiny neurons (MSNs) in the striatum, traditionally attributed to excessive glutamate inputs and/or receptor sensitivity. While changes in corticostriatal projections have typically been studied in mouse models of HD, morphological and functional alterations in thalamostriatal projections have received less attention. In this study, an adeno-associated virus expressing channelrhodopsin-2 under the calcium/calmodulin-dependent protein kinase IIα promoter was injected into the sensorimotor cortex or the thalamic centromedian-parafascicular nuclear complex in the R6/2 mouse model of HD, to permit selective activation of corticostriatal or thalamostriatal projections, respectively. In symptomatic R6/2 mice, peak amplitudes and areas of corticostriatal glutamate AMPA and NMDA receptor-mediated responses were reduced. In contrast, although peak amplitudes of AMPA and NMDA receptor-mediated thalamostriatal responses also were reduced, the areas remained unchanged due to an increase in response decay times. Blockade of glutamate reuptake further increased response areas and slowed rise and decay times of NMDA responses. These effects appeared more pronounced at thalamostriatal synapses of R6/2 mice, suggesting increased activation of extrasynaptic NMDA receptors. In addition, the probability of glutamate release was higher at thalamostriatal than corticostriatal synapses, particularly in R6/2 mice. Morphological studies indicated that the density of all excitatory synaptic contacts onto MSNs was reduced, which matches the basic electrophysiological findings of reduced amplitudes. There was a consistent reduction in the area of spines but little change in presynaptic terminal size, indicating that the postsynaptic spine may be more significantly affected than presynaptic terminals. These results highlight the significant and differential contribution of the thalamostriatal projection to glutamate excitotoxicity in HD

Time-dependent changes in GLT-1 functioning in striatum of hemi-Parkinson rats

Striatal dopamine loss in Parkinson's disease is accompanied by a dysregulation of corticostriatal glutamatergic neurotransmission. Within this study, we investigated striatal expression and activity of the glial high-affinity Na+/K+-dependent glutamate transporters, GLT-1 and GLAST, in the 6-hydroxydopamine hemi-Parkinson rat model at different time points after unilateral 6-hydroxydopamine injection into the medial forebrain bundle. Using semi-quantitative Western blotting and an ex vivo D-[H-3]-aspartate uptake assay, we showed a time-dependent bilateral effect of unilateral 6-hydroxydopamine lesioning on the expression as well as activity of GLT-1. At 3 and 12 weeks post-lesion, striatal GLT-1 function was bilaterally upregulated whereas at 5 weeks there was no change. Even though our data do not allow a straightforward conclusion as for the role of glutamate transporters in the pathogenesis of the disease, they do clearly demonstrate a link between disturbed glutamatergic neurotransmission and glutamate transporter functioning in the striatum of a rat model for Parkinson's disease. (C) 2010 Elsevier Ltd. All rights reserved