Methylphenidate-Induced Increases in Vesicular Dopamine Sequestration and Dopamine Release in the Striatum: The Role of Muscarinic and Dopamine D2 Receptors

Abstract

Methylphenidate (MPD) administration alters the subcellular distribution of vesicular monoamine transporter-2 (VMAT-2)-containing vesicles in rat striatum. This report reveals previously undescribed pharmacological features of MPD by elucidating its receptor-mediated effects on VMAT-2-containing vesicles that cofractionate with synaptosomal membranes after osmotic lysis (referred to herein as membrane-associated vesicles) and on striatal dopamine (DA) release. MPD administration increased DA transport into, and decreased the VMAT-2 immunoreactivity of, the membrane-associated vesicle subcellular fraction. These effects were mimicked by the D2 receptor agonist quinpirole and blocked by the D2 receptor antagonist eticlopride. Both MPD and quinpirole increased vesicular DA content. However, MPD increased, whereas quinpirole decreased, K ϩ -stimulated DA release from striatal suspensions. Like MPD, the muscarinic receptor agonist, oxotremorine, increased K ϩ -stimulated DA release. Both eticlopride and the muscarinic receptor antagonist scopolamine blocked MPD-induced increases in K ϩ -stimulated DA release, whereas the N-methyl-D-aspartate receptor antagonist (Ϫ)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) was without effect. This suggests that D2 receptors mediate both the MPD-induced redistribution of vesicles away from synaptosomal membranes and the MPD-induced up-regulation of vesicles remaining at the membrane. This results in a redistribution of DA within the striatum from the cytoplasm into vesicles, leading to increased DA release. However, D2 receptor activation alone is not sufficient to mediate the MPD-induced increases in striatal DA release because muscarinic receptor activation is also required. These novel findings provide insight into the mechanism of action of MPD, regulation of DA sequestration/release, and treatment of disorders affecting DA disposition, including attention-deficit hyperactivity disorder, substance abuse, and Parkinson's disease.The ritalinic acid psychostimulant methylphenidate (MPD) is frequently used to treat attention-deficit hyperactivity disorder. It is well established that MPD prevents the clearance of dopamine (DA) from the synaptic cleft by binding to the neuronal DA transporter (DAT) (Wayment et al., 1999;. In addition, MPD also indirectly affects the vesicular monoamine transporter (VMAT)-2, a protein that sequesters cytoplasmic DA inside the synaptic vesicles of nerve terminals. A single MPD treatment increases DA transport, VMAT-2 immunoreactivity, and binding of the VMAT-2 ligand [ 3 H]dihydrotetrabenazine in cytoplasmic vesicles purified from osmotic lysates of rat striatal synaptosomes (Sandoval et al., 2002(Sandoval et al., , 2003Volz et al., 2007a). These effects on cytoplasmic vesicles are D2 receptor-mediated, because the D2 receptor antagonist eticlopride (ETIC) attenuates or blocks these effects, and the D2 receptor agonist quinpirole (QUIN) mimics the effects of MPD (Sandoval et al., 2002;Truong et al., 2004).In co...

Age-dependent and age-independent human memory persistence is enhanced by delayed posttraining methylphenidate administration

“…Methylphenidate stimulates dopamine release in the forebrain by influences on the dopamine vesicular transporter (24)(25)(26)(27), and it was reported long ago to enhance learned behaviors in rats (28,29) and, more recently, in humans (30). The hippocampus detects novelty (31,32) and plays a key role in memory consolidation (2), which relies on novelty (33).…”

Illicit dopamine transients: Reconciling actions of abused drugs

“…Cocaine and methylphenidate may mobilize the reserve dopamine pool through actions on synaptic proteins [ 54,57,59 ] and enhance both vesicular dopamine uptake and trafficking [ 63-67 ]. AMPH may similarly promote mobilization of the reserve pool [ 60 ] and vesicular trafficking [ 66 ] but also up-regulate vesicular dopamine release by distinct mechanisms.…”

Method development and validation of an in vitro model of the effects of methylphenidate on membrane-associated synaptic vesicles

“…After in vitro incubation and resuspension in 2 ml of fresh sucrose buffer (see section 2.3.), samples for use in synaptic vesicle experiments were subjected to a centrifugation protocol in order to isolate the cytoplasmic and membrane-associated vesicles as described previously (Volz et al, 2007; Volz et al, 2008). Each sample was centrifuged (800 × g for 12 min at 4 °C) to remove nuclear debris.…”

“…Several in vivo studies have revealed that D2 receptor activation mediates the MPD-induced vesicle trafficking, kinetic upregulation, and increase in vesicular DA content, while both D2 and muscarinic receptor activation mediate the MPD-induced increase in exocytotic DA release (Sandoval et al, 2002; Truong et al, 2004; Volz et al, 2008). However, additional studies have been hampered by lack of an in vitro model system that would allow further study while avoiding generalized (e.g., systemic) toxicity.…”