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Increased amphetamine-induced hyperactivity and reward in mice overexpressing the dopamine transporter.

ABSTRACT: The dopamine transporter (DAT) plays a key role in the regulation of dopaminergic signaling wherein it controls both the spatial and temporal actions of dopamine. Here we evaluated the behavioral and neurochemical consequences of increased DAT function by generating DAT transgenic mice (DAT-tg) that overexpress the transporter. These mice were generated by pronuclear injection of a bacterial artificial chromosome containing the mouse DAT locus, yielding an anatomical expression pattern of DAT-tg identical to WT. In DAT-tg mice there is a 3-fold increase in the levels of total and membrane-expressed DAT, but synaptic plasma membrane fractions of DAT-tg mice show only a 30% increase in transporter levels. Functional studies reveal that in the DAT-tg animals there is a 50% increase in the rate of dopamine (DA) uptake resulting in extracellular levels of DA that are decreased by approximately 40%. Behaviorally, DAT-tg animals display similar locomotor stimulation when treated with DAT blockers such as GBR12909, methylphenidate, and cocaine. However, these mice demonstrate markedly increased locomotor responses to amphetamine compared with WT animals. Furthermore, compared with controls, there is a 3-fold greater increase in the amount of DA released by amphetamine in DAT-tg mice that correlates with the 3-fold increase in protein expression. Finally, DAT-tg animals show reduced operant responding for natural reward while displaying preference for amphetamine at much lower doses (0.2 and 0.5 mg/kg) than WT mice (2 mg/kg). These results suggest that overexpression of DAT leads to a marked increase in sensitivity to psychomotor and rewarding properties of amphetamine.

SUBMITTER: Salahpour A

PROVIDER: S-EPMC2393812 | biostudies-other | 2008 Mar

REPOSITORIES: biostudies-other

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Increased amphetamine-induced hyperactivity and reward in mice overexpressing the dopamine transporter.

Salahpour Ali A Ramsey Amy J AJ Medvedev Ivan O IO Kile Brian B Sotnikova Tatyana D TD Holmstrand Ericka E Ghisi Valentina V Nicholls Peter J PJ Wong Ling L Murphy Karen K Sesack Susan R SR Wightman R Mark RM Gainetdinov Raul R RR Caron Marc G MG

Proceedings of the National Academy of Sciences of the United States of America 20080317 11

The dopamine transporter (DAT) plays a key role in the regulation of dopaminergic signaling wherein it controls both the spatial and temporal actions of dopamine. Here we evaluated the behavioral and neurochemical consequences of increased DAT function by generating DAT transgenic mice (DAT-tg) that overexpress the transporter. These mice were generated by pronuclear injection of a bacterial artificial chromosome containing the mouse DAT locus, yielding an anatomical expression pattern of DAT-tg ...[more]

PMID: 18347339

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Project description:The excitatory amino acid transporter EAAT3 plays an important role in the neuronal uptake of glutamate regulating the activation of glutamate receptors. Polymorphisms in the gene-encoding EAAT3 have been associated with obsessive-compulsive disorder (OCD), although the mechanisms underlying this relationship are still unknown. We recently reported that mice with increased EAAT3 expression in forebrain neurons (EAAT3 g lo /CMKII) display behavioral and synaptic features relevant to OCD, including increased grooming, higher anxiety-like behavior and altered cortico-striatal synaptic function. The dopamine neurotransmitter system is implicated in ritualistic behaviors. Indeed, dopaminergic neurons express EAAT3, and mice lacking EAAT3 exhibit decreased dopamine release and decreased expression of the dopamine D1 receptor. Moreover, EAAT3 plays a role on the effect of the psychostimulant amphetamine. As such, we sought to determine if the OCD-like behavior in EAAT3 g lo /CMKII mice is accompanied by altered nigro-striatal dopaminergic transmission. The aim of this study was to analyze dopamine transmission both in basal conditions and after an acute challenge of amphetamine, using behavioral, neurochemical, molecular, and cellular approaches. We found that in basal conditions, EAAT3 g lo /CMKII mice performed more grooming events and that they remained in phase 1 of the grooming chain syntax compared with control littermates. Administration of amphetamine increased the number of grooming events in control mice, while EAAT3 g lo /CMKII mice remain unaffected. Interestingly, the grooming syntax of amphetamine-control mice resembled that of EAAT3 g lo /CMKII mice in basal conditions. Using in vivo microdialysis, we found decreased basal dopamine levels in EAAT3 g lo /CMKII compared with control mice. Unexpectedly, we found that after acute amphetamine, EAAT3 g lo /CMKII mice had a higher release of dopamine compared with that of control mice, suggesting that EAAT3 overexpression leads to increased dopamine releasability. To determine postsynaptic effect of EAAT3 overexpression over dopamine transmission, we performed Western blot analysis of dopaminergic proteins and found that EAAT3 g lo /CMKII mice have higher expression of D2 receptors, suggesting a higher inhibition of the indirect striatal pathway. Together, the data indicate that EAAT3 overexpression impacts on dopamine transmission, making dopamine neurons more sensitive to the effect of amphetamine and leading to a disbalance between the direct and indirect striatal pathways that favors the performance of repetitive behaviors.

Project description:AimAttention-deficit/hyperactivity disorder is a heterogeneous neurobiological disorder that is characterized by inattention, impulsivity, and an increase in motor activity. Although methylphenidate has been used as a medication for decades, unknown is whether methylphenidate treatment can cause drug dependence in patients with attention-deficit/hyperactivity disorder. This study investigated the reward-enhancing effects of methylphenidate using intracranial self-stimulation in an animal model of attention-deficit/hyperactivity disorder, dopamine transporter knockout mice.MethodsFor the intracranial self-stimulation procedures, the mice were trained to nosepoke to receive direct electrical stimulation via an electrode that was implanted in the lateral hypothalamus. After the acquisition of nosepoke responding for intracranial self-stimulation, the effects of methylphenidate on intracranial self-stimulation were investigated.ResultsIn the progressive-ratio procedure, dopamine transporter knockout mice exhibited an increase in intracranial self-stimulation compared with wild-type mice. Treatment with 5 and 10 mg/kg methylphenidate increased intracranial self-stimulation responding in wild-type mice. Methylphenidate at the same doses did not affect intracranial self-stimulation responding in dopamine transporter knockout mice. We then investigated the effects of high-dose methylphenidate (60 mg/kg) in a rate-frequency procedure. High-dose methylphenidate significantly decreased intracranial self-stimulation responding in both wild-type and dopamine transporter knockout mice.ConclusionsThese results suggest that low-dose methylphenidate alters the reward system (ie, increases intracranial self-stimulation responding) in wild-type mice via dopamine transporter inhibition, whereas dopamine transporter knockout mice do not exhibit such alterations. High-dose methylphenidate appears to suppress intracranial self-stimulation responding not through dopamine transporter inhibition but rather through other mechanisms. These results support the possibility that methylphenidate treatment for attention-deficit/hyperactivity disorder does not increase the risk of drug dependence, in attention-deficit/hyperactivity disorder patients with dopamine transporter dysfunction.

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Increased amphetamine-induced hyperactivity and reward in mice overexpressing the dopamine transporter.

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Increased amphetamine-induced hyperactivity and reward in mice overexpressing the dopamine transporter.

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