Differential gene expression in the striatum of mice with very low expression of the vesicular monoamine transporter type 2 gene

Vivo-morpholinos induced transient knockdown of physical activity related proteins

Physical activity is associated with disease prevention and overall wellbeing. Additionally there has been evidence that physical activity level is a result of genetic influence. However, there has not been a reliable method to silence candidate genes in vivo to determine causal mechanisms of physical activity regulation. Vivo-morpholinos are a potential method to transiently silence specific genes. Thus, the aim of this study was to validate the use of Vivo-morpholinos in a mouse model for voluntary physical activity with several sub-objectives. We observed that Vivo-morpholinos achieved between 60–97% knockdown of Drd1-, Vmat2-, and Glut4-protein in skeletal muscle, the delivery moiety of Vivo-morpholinos (scramble) did not influence physical activity and that a cocktail of multiple Vivo-morpholinos can be given in a single treatment to achieve protein knockdown of two different targeted proteins in skeletal muscle simultaneously. Knocking down Drd1, Vmat2, or Glut4 protein in skeletal muscle did not affect physical activity. Vivo-morpholinos injected intravenously alone did not significantly knockdown Vmat2-protein expression in the brain (p = 0.28). However, the use of a bradykinin analog to increase blood-brain-barrier permeability in conjunction with the Vivo-morpholinos significantly (p = 0.0001) decreased Vmat2-protein in the brain with a corresponding later over-expression of Vmat2 coincident with a significant (p = 0.0016) increase in physical activity. We conclude that Vivo-morpholinos can be a valuable tool in determining causal gene-phenotype relationships in whole animal models.

VMAT2-Deficient Mice Display Nigral and Extranigral Pathology and Motor and Nonmotor Symptoms of Parkinson's Disease

Dopamine is transported into synaptic vesicles by the vesicular monoamine transporter (VMAT2; SLC18A2). Disruption of dopamine storage has been hypothesized to damage the dopamine neurons that are lost in Parkinson's disease. By disrupting vesicular storage of dopamine and other monoamines, we have created a progressive mouse model of PD that exhibits catecholamine neuron loss in the substantia nigra pars compacta and locus coeruleus and motor and nonmotor symptoms. With a 95% reduction in VMAT2 expression, VMAT2-deficient animals have decreased motor function, progressive deficits in olfactory discrimination, shorter latency to behavioral signs of sleep, delayed gastric emptying, anxiety-like behaviors at younger ages, and a progressive depressive-like phenotype. Pathologically, the VMAT2-deficient mice display progressive neurodegeneration in the substantia nigra (SNpc), locus coeruleus (LC), and dorsal raphe (DR) coupled with α-synuclein accumulation. Taken together, these studies demonstrate that reduced vesicular storage of monoamines and the resulting disruption of the cytosolic environment may play a role in the pathogenesis of parkinsonian symptoms and neurodegeneration. The multisystem nature of the VMAT2-deficient mice may be useful in developing therapeutic strategies that go beyond the dopamine system.

Oscillation development for neurotransmitter-related genes in the mouse striatum

The aims of this study were to determine (i) whether striatal neuropeptides (dynorphin, enkephalin 1, substance P, cholecystokinin) and dopamine receptors 1 and 2 (D1r and D2r) are regulated by the molecular clock; and (ii) when their oscillations start after birth. Twenty-four-hour mRNA oscillations of these genes were evaluated in the mouse striatum at early postnatal stage (postnatal day 3), preweaning stage (postnatal day 14), and adult (postnatal day 60). At P3, no daily oscillations were observed. A significant time effect was present for D2r, dynorphin, and enkephalin 1 at P14, and for all genes except D1r, at P60. In conclusion, circadian expression of these neurotransmitter-related genes develops in the mouse striatum after birth gradually.

Effect of genetic SSTR4 ablation on inflammatory peptide and receptor expression in the non-inflamed and inflamed murine intestine

The recently suggested pivotal role of somatostatin (SOM) receptor 4 (SSTR4) in inflammation and nociception in several non-intestinal organs and in gastrointestinal (GI) physiology, necessitates exploration of the role of SSTR4 in GI pathophysiology. Therefore, the role of SSTR4 in GI activity was explored by investigating the effects of SSTR4 deficiency on intestinal motility, smooth muscle contractility and on the expression of SSTRs and neuropeptides in the healthy and Schistosoma mansoni-infected murine small intestine. Functional experiments revealed no differences in intestinal motility or smooth muscle cell contractility between wild-type and SSTR4 knockout (SSTR4^–/–) mice in physiological conditions. As revealed by multiple immunofluorescent labellings, RT-PCR and quantitative real time RT-PCR (qPCR), genetic deficiency of SSTR4 considerably altered the expression of SOM and SSTRs in non-inflamed and inflamed conditions, affecting both extrinsic and intrinsic components of the intestinal innervation, along with SSTR expression in several non-neuronal cell types. Moreover, substance P and calcitonin gene-related peptide expression were significantly elevated in SSTR4^–/– mice, confirming the modulatory role of SSTR4 on intestinal pro-inflammatory neuropeptide expression. These data suggest that SSTR4 plays a previously unexpected modulatory role in the regulation of intestinal SSTR expression. Moreover, in addition to the recently described inhibitory effects of SSTR4 on the neuronal release of pro-inflammatory peptides, SSTR4 appears also to be involved in the neuronal expression of both pro- and anti-inflammatory peptides in the murine small intestine.

Protective actions of the vesicular monoamine transporter 2 (VMAT2) in monoaminergic neurons

Vesicular monoamine transporters (VMATs) are responsible for the packaging of neurotransmitters such as dopamine, serotonin, norepinephrine, and epinephrine into synaptic vesicles. These proteins evolved from precursors in the major facilitator superfamily of transporters and are among the members of the toxin extruding antiporter family. While the primary function of VMATs is to sequester neurotransmitters within vesicles, they can also translocate toxicants away from cytosolic sites of action. In the case of dopamine, this dual role of VMAT2 is combined-dopamine is more readily oxidized in the cytosol where it can cause oxidative stress so packaging into vesicles serves two purposes: neurotransmission and neuroprotection. Furthermore, the deleterious effects of exogenous toxicants on dopamine neurons, such as MPTP, can be attenuated by VMAT2 activity. The active metabolite of MPTP can be kept within vesicles and prevented from disrupting mitochondrial function thereby sparing the dopamine neuron. The highly addictive drug methamphetamine is also neurotoxic to dopamine neurons by using dopamine itself to destroy the axon terminals. Methamphetamine interferes with vesicular sequestration and increases the production of dopamine, escalating the amount in the cytosol and leading to oxidative damage of terminal components. Vesicular transport seems to resist this process by sequestering much of the excess dopamine, which is illustrated by the enhanced methamphetamine neurotoxicity in VMAT2-deficient mice. It is increasingly evident that VMAT2 provides neuroprotection from both endogenous and exogenous toxicants and that while VMAT2 has been adapted by eukaryotes for synaptic transmission, it is derived from phylogenetically ancient proteins that originally evolved for the purpose of cellular protection.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Notch regulation of progenitor cell behavior in quiescent and regenerating auditory epithelium of mature birds

Unlike mammals, birds regenerate auditory hair cells (HCs) after injury. During regeneration, mature non-sensory supporting cells (SCs) leave quiescence and convert into HCs, through non-mitotic or mitotic mechanisms. During embryogenesis, Notch ligands from nascent HCs exert lateral inhibition, restricting HC production. Here, we examined whether Notch signaling (1) is needed in mature birds to maintain the HC/SC pattern in the undamaged auditory epithelium or (2) governs SC behavior once HCs are injured. We show that Notch pathway genes are transcribed in the mature undamaged epithelium, and after HC injury, their transcription is upregulated in the region of highest mitotic activity. In vitro treatment with DAPT, an inhibitor of Notch activity, had no effect on SCs in the undamaged epithelium. Following HC damage, DAPT had no direct effect on SC division. However, after damage, DAPT caused excessive regeneration of HCs at the expense of SCs, through both mitotic and non-mitotic mechanisms. Conversely, overexpression of activated Notch in SCs after damage caused them to maintain their phenotype and inhibited HC regeneration. Therefore, signaling through Notch is not required for SC quiescence in the healthy epithelium or to initiate HC regeneration after damage. Rather, Notch prevents SCs from regenerating excessive HCs after damage.

Reduced vesicular storage of dopamine exacerbates methamphetamine-induced neurodegeneration and astrogliosis

The vesicular monoamine transporter 2 (VMAT2) controls the loading of dopamine (DA) into vesicles and therefore determines synaptic properties such as quantal size, receptor sensitivity, and vesicular and cytosolic DA concentration. Impairment of proper DA compartmentalization is postulated to underlie the sensitivity of DA neurons to oxidative damage and degeneration. It is known that DA can auto-oxidize in the cytosol to form quinones and other oxidative species and that this production of oxidative stress is thought to be a critical factor in DA terminal loss after methamphetamine (METH) exposure. Using a mutant strain of mice (VMAT2 LO), which have only 5-10% of the VMAT2 expressed by wild-type animals, we show that VMAT2 is a major determinant of METH toxicity in the striatum. Subsequent to METH exposure, the VMAT2 LO mice show an exacerbated loss of dopamine transporter and tyrosine hydroxylase (TH), as well as enhanced astrogliosis and protein carbonyl formation. More importantly, VMAT2 LO mice show massive argyrophilic deposits in the striatum after METH, indicating that VMAT2 is a regulator of METH-induced neurodegeneration. The increased METH neurotoxicity in VMAT2 LO occurs in the absence of any significant difference in basal temperature or METH-induced hyperthermia. Furthermore, primary midbrain cultures from VMAT2 LO mice show more oxidative stress generation and a greater loss of TH positive processes than wild-type cultures after METH exposure. Elevated markers of neurotoxicity in VMAT2 LO mice and cultures suggest that the capacity to store DA determines the amount of oxidative stress and neurodegeneration after METH administration.