Dopamine autoreceptor regulation of release and uptake in mouse brain slices in the absence of D(3) receptors.

The effects of the dopamine D(3) receptor, a putative autoreceptor, have been investigated by comparing behavioral and neurochemical properties of wild-type mice and mice with a genetic deletion of the D(3) receptor. The D(3) knock-out mice were modestly hyper-responsive to a novel environment relative to wild-type mice, and, consistent with this, quantitative in vivo microdialysis revealed elevated striatal dopamine extracellular levels. The dynamic actions of autoreceptors on electrically evoked dopamine release were examined in striatal brain slices from these animals and monitored with fast scan cyclic voltammetry at carbon-fiber microelectrodes.

Behavioral and neurochemical effects of wild-type and mutated human alpha-synuclein in transgenic mice.

Human alpha-synuclein (halpha-SYN) is implicated in the Parkinson's disease phenotype (PDP) based on a variety of studies in man, animal models, and in vitro studies. The normal function of halpha-SYN and the mechanism by which it contributes to the PDP remains unclear. We created transgenic mice expressing either wild-type (hwalpha-SYN) or a doubly mutated (hm2alpha-SYN) form of halpha-SYN under control of the 9-kb rat tyrosine hydroxylase promoter.

Dopaminergic transmission in the rat striatum in vivo in conditions of pharmacological modulation.

The effects of pharmacological modulation of striatal dopaminergic neurotransmission were studied in freely mobile rats by intracerebral microdialysis and HPLC to assay dopamine and dopamine metabolite levels and the rate of dopamine synthesis, in combination with observations of stereotypical behavior. Inhibition of catechol O-methyltransferase (COMT) with tolcapone led to increases in extracellular dopamine levels only when the baseline dopamine level was elevated by administration of L-3,4-dihydroxyphenylalanine in combination with the decarboxylation inhibitor carbidopa. Increases in dopamine levels in striatal dialysates by blockade of reuptake were enhanced by inhibition of metabolic degradation of dopamine by tolcapone, a selective catechol O-methyltransferase inhibitor.

Hyperactivity, elevated dopaminergic transmission, and response to amphetamine in M1 muscarinic acetylcholine receptor-deficient mice.

Acetylcholine serves an important modulatory role in the central nervous system. Pharmacological evidence has suggested that cholinergic activity can modulate central dopaminergic transmission; however, the nature of this interaction and the receptors involved remain undefined. In this study we have generated mice lacking the M1 muscarinic acetylcholine receptor and examined the effects of M1 deletion on dopaminergic transmission and locomotor behavior.

Glutamatergic modulation of hyperactivity in mice lacking the dopamine transporter.

In the brain, dopamine exerts an important modulatory influence over behaviors such as emotion, cognition, and affect as well as mechanisms of reward and the control of locomotion. The dopamine transporter (DAT), which reuptakes the released neurotransmitter into presynaptic terminals, is a major determinant of the intensity and duration of the dopaminergic signal. Knockout mice lacking the dopamine transporter (DAT-KO mice) display marked changes in dopamine homeostasis that result in elevated dopaminergic tone and pronounced locomotor hyperactivity.

Genetic animal models: focus on schizophrenia.

The neurobiology of schizophrenia remains poorly understood. Symptoms of schizophrenia are classically thought to be associated with an imbalance of the dopaminergic system. However, the contribution of other neurotransmitters, in particular glutamate, has been increasingly appreciated.

Effects of intrastriatal infusion of D2 and D3 dopamine receptor preferring antagonists on dopamine release in rat dorsal striatum (in vivo microdialysis study).

Dopamine D2-like receptor antagonists haloperidol, spiperone, clozapine, cis -( +)- (1S,2R)-5-methoxy-1-methyl-2-(n -propylamino)tetralin, ( +)-AJ76, cis -( +)- (1S,2R)-5-methoxy-1-methyl-2-(n -di-propylamino)tetralin, ( +)-UH232, and putative D3 dopamine receptor agonist ( +/-)- 7-hydroxy-N,N-di- n -propyl-2-aminotetralin, 7-OH-DPAT, were infused via a transcerebral microdialysis probe into the dorsal striatum of freely moving rats. Local infusion of all the dopamine antagonists studied resulted in concentration-dependent increase of striatal dopamine release in vivo. Subsequent i.

Effect of acute ethanol on striatal dopamine neurotransmission in ambulatory rats.

The effect of ethanol on evoked dopamine release in the caudate putamen has been measured in behaving animals with in vivo electrochemistry. Dopamine was measured with fast-scan cyclic voltammetry in adult male rats to resolve the competing processes of dopamine uptake and release. Ethanol dose dependently decreased dopamine efflux compared with saline-treated animals: to 89% of controls with 0.

Hyperactivity and impaired response habituation in hyperdopaminergic mice.

Abnormal dopaminergic transmission is implicated in schizophrenia, attention deficit hyperactivity disorder, and drug addiction. In an attempt to model aspects of these disorders, we have generated hyperdopaminergic mutant mice by reducing expression of the dopamine transporter (DAT) to 10% of wild-type levels (DAT knockdown). Fast-scan cyclic voltammetry and in vivo microdialysis revealed that released dopamine was cleared at a slow rate in knockdown mice, which resulted in a higher extracellular dopamine concentration.

Dopamine transporter and vesicular monoamine transporter knockout mice : implications for Parkinson's disease.

One of the most valuable methods for understanding the function of a particular protein is the generation of animals that have had the gene encoding for the protein of interest disrupted, commonly known as a "quo;knockout"quo; or null mutant. By incorporating a sequence of DNA (typically encoding antibiotic resistance to aid in the selection of the mutant gene) into embryonic stem cells by homologous recombination, the normal transcription of the gene is effectively blocked (Fig. 1).

Mu-opioid receptor desensitization by beta-arrestin-2 determines morphine tolerance but not dependence.

Morphine is a powerful pain reliever, but also a potent inducer of tolerance and dependence. The development of opiate tolerance occurs on continued use of the drug such that the amount of drug required to elicit pain relief must be increased to compensate for diminished responsiveness. In many systems, decreased responsiveness to agonists has been correlated with the desensitization of G-protein-coupled receptors.

[Pharmacological modulation of dopaminergic transmission in the rat striatum in vivo].

Inhibition of catechol-0-methyltransferase (COMT) activity by Tolcapone was shown to result in increase of the striatal DA extracellular content in unrestrained rats pretreated with L-3,4-dihydroxyphenilalanine combined with Carbidopa, the decarboxylation inhibiting agent. Tolcapone enhanced the increase of the DA level in the rat striatal dialysates produced by treatment of these animals with specific DA re-uptake blocker GBR 12909. The latter elicits stereotype behaviour in rats that is substantially enhanced by tolcapone.

Mice lacking the dopamine transporter display altered regulation of distal colonic motility.

The mechanisms by which dopamine (DA) influences gastrointestinal (GI) tract motility are incompletely understood and complicated by tissue- and species-specific differences in dopaminergic function. To improve the understanding of DA action on GI motility, we used an organ tissue bath system to characterize motor function of distal colonic smooth muscle segments from wild-type and DA transporter knockout (DAT -/-) mice. In wild-type mice, combined blockade of D(1) and D(2) receptors resulted in significant increases in tone (62 +/- 9%), amplitude of spontaneous phasic contractions (167 +/- 24%), and electric field stimulation (EFS)-induced (40 +/- 8%) contractions, suggesting that endogenous DA is inhibitory to mouse distal colonic motility.

Mice lacking the norepinephrine transporter are supersensitive to psychostimulants.

The action of norepinephrine (NE) is terminated, in part, by its uptake into presynaptic noradrenergic neurons by the plasma-membrane NE transporter (NET), which is a target for antidepressants and psychostimulants. Disruption of the NET gene in mice prolonged the clearance of NE and elevated extracellular levels of this catecholamine. In a classical test for antidepressant drugs, the NET-deficient (NET-/-) animals behaved like antidepressant-treated wild-type mice.

Quantitation of in vivo measurements with carbon fiber microelectrodes.

Fast-scan cyclic voltammetry (FSCV) at carbon fiber disk microelectrodes and quantitative microdialysis were used to measure striatal concentration changes of N-acetyl-p-aminophenol (APAP, acetaminophen) following an intraperitoneal injection of 75 mg/kg APAP in rats. The goal of this work was to determine which in vitro calibration procedure, precalibration or postcalibration, gave the most accurate results when using carbon fiber microelectrodes in vivo. Voltammetric detection of APAP in vivo was complicated with normal electrodes by interference from pH changes.

Correlation between behavior and extracellular dopamine levels in rat striatum: comparison of microdialysis and fast-scan cyclic voltammetry.

Recently, fast-scan cyclic voltammetry (FSCV) has been adapted for real-time measurements of evoked dopamine (DA) release and uptake in freely moving rats. Using the advantages of this experimental design in combination with behavioral measures, we examined the effect of GBR 12909 (20 mg/kg, i.p.

Potentiated opioid analgesia in norepinephrine transporter knock-out mice.

Several studies have shown that activation of alpha(2)-adrenergic receptors (alpha(2)ARs) leads to mild analgesic effects. Tricyclic antidepressants (TCAs), such as desipramine (DMI), which block norepinephrine transporters (NETs), also produce mild antinociception. The coadministration of either alpha(2)AR agonists or TCAs with opiates produces synergistically potentiated antinociception.

Muscarinic supersensitivity and impaired receptor desensitization in G protein-coupled receptor kinase 5-deficient mice.

G protein-coupled receptor kinase 5 (GRK5) is a member of a family of enzymes that phosphorylate activated G protein-coupled receptors (GPCR). To address the physiological importance of GRK5-mediated regulation of GPCRs, mice bearing targeted deletion of the GRK5 gene (GRK5-KO) were generated. GRK5-KO mice exhibited mild spontaneous hypothermia as well as pronounced behavioral supersensitivity upon challenge with the nonselective muscarinic agonist oxotremorine.

Enhanced morphine analgesia in mice lacking beta-arrestin 2.

The ability of morphine to alleviate pain is mediated through a heterotrimeric guanine nucleotide binding protein (G protein)-coupled heptahelical receptor (GPCR), the mu opioid receptor (muOR). The efficiency of GPCR signaling is tightly regulated and ultimately limited by the coordinated phosphorylation of the receptors by specific GPCR kinases and the subsequent interaction of the phosphorylated receptors with beta-arrestin 1 and beta-arrestin 2. Functional deletion of the beta-arrestin 2 gene in mice resulted in remarkable potentiation and prolongation of the analgesic effect of morphine, suggesting that muOR desensitization was impaired.

Microdialysis studies on the action of tolcapone on pharmacologically-elevated extracellular dopamine levels in conscious rats.

To elucidate the importance of catechol-O-methyltransferase, we performed striatal microdialysis studies in conscious rats given tolcapone, an inhibitor of catechol-O-methyltransferase, together with four compounds each of which elevates the extracellular dopamine content through a different mechanism. Tolcapone itself did not alter dopamine levels in the striatal microdialysis fluid but increased DOPAC and decreased homovanillic acid levels. However, tolcapone pretreatment (30 mg/kg) multiplied the already high dopamine levels after levodopa, and less so the moderately elevated dopamine levels after GBR-12909 (at 20 mg/kg) alone, but the minor (insignificant) dopamine-elevating effects of haloperidol and (+)-U232 were not altered.