Juvenile Administration of Concomitant Methylphenidate and Fluoxetine Alters Behavioral Reactivity to Reward- and Mood-Related Stimuli and Disrupts Ventral Tegmental Area Gene Expression in Adulthood

Abstract

There is a rise in the concurrent use of methylphenidate (MPH) and fluoxetine (FLX) in pediatric populations. However, the long-term neurobiological consequences of combined MPH and FLX treatment (MPH+FLX) during juvenile periods are unknown. We administered saline (VEH), MPH, FLX, or MPH+FLX to juvenile Sprague-Dawley male rats from postnatal day 20–35, and assessed their reactivity to reward- and mood-related stimuli 24-h or 2-months after drug exposure. We also assessed mRNA and protein levels within the ventral tegmental area (VTA) to determine the effect of MPH, FLX, or MPH+FLX on the extracellular signal-regulated protein kinase-1/2 (ERK) pathway – a signaling cascade implicated in motivation and mood regulation. MPH+FLX enhanced sensitivity to drug (i.e., cocaine) and sucrose rewards, as well as anxiety- (i.e., elevated plus-maze) and stress- (i.e., forced swimming) eliciting situations when compared to VEH-treated rats. MPH+FLX exposure also increased mRNA of ERK2 and its downstream targets cAMP response element-binding protein (CREB), brain-derived neurotrophic factor (BDNF), cFos, early growth response protein-1 (zif268), and mammalian target of rapamycin (mTOR), and also increased protein phosphorylation of ERK2, CREB, and mTOR 2-months after drug exposure when compared to VEH-treated rats. Using herpes simplex virus-mediated gene transfer to block ERK2 activity within the VTA, we rescued the MPH+FLX-induced behavioral deficits seen in the forced swimming task 2-months after drug treatment. These results indicate that concurrent MPH+FLX exposure during preadolescence increases sensitivity to reward-related stimuli while simultaneously enhancing susceptibility to stressful situations, at least in part, due to long-lasting disruptions in ERK signaling within the VTA.

Potentiated gene regulation by methylphenidate plus fluoxetine treatment: Long-term gene blunting (Zif268, Homer1a) and behavioral correlates

“…The present rats were treated during adolescence (postnatal days 35–40); these molecular changes thus endured towards young adulthood of the animals. Our findings complement other recent findings showing that methylphenidate+fluoxetine pretreatment in juvenile rats produced molecular changes in midbrain dopamine neurons and behavioral alterations that in part were still present (or even more robust) in adult animals [33] (see below).…”

“…However, a recent study showed that methylphenidate+fluoxetine pretreatment in juvenile rats modifies place preference conditioning by cocaine in adulthood [33]. Thus, adding fluoxetine to repeated methylphenidate pretreatment produced enhanced preference for the cocaine-paired environment, in contrast to the cocaine avoidance expressed by the methylphenidate only-pretreated controls [33]. This finding of an enhanced cocaine preference (sensitivity) later in life does suggest an increased abuse/addiction risk for the drug combination (for review, see [10]).…”

“…Oligonucleotide probes (48-mers; Invitrogen, Rockville, MD, USA) were labeled with [33P]-dATP as described earlier [30]. The probes had the following sequence: Zif268 ( Egr1 ), complementary to bases 352–399, GenBank accession number M18416; Homer1a , bases 1493–1540, AB003726.…”

Methylphenidate Exerts Dose-Dependent Effects on Glutamate Receptors and Behaviors

“…However, overdose of MPH produce agitation, restlessness and hallucinations in human beings (5) as well as hyper-locomotion and impaired cognition in animals (6). Subchronic administration of methylphenidate in juvenile rodents has been found to induce long-lasting behavioral adaptations (7,8). To achieve therapeutic benefit and minimal side-effects, it is suggested that the doses of MPH should be titrated to an optimal level.…”

Association of Anxiety Symptoms in Offspring of Bipolar Parents with Serotonin Transporter-Linked Polymorphic Region (5-HTTLPR) Genotype

“…However, a study with children and adolescents with depression and/or anxiety (Kronenberg et al 2007) found that the s/s genotype was associated with poor antidepressant treatment response only to depressive symptoms but not anxiety symptoms. Further, animal studies have shown that, unlike the anxiolytic effects of antidepressants in adults (Holick et al 2008), antidepressant exposure during adolescence appears to have anxiogenic rather than anxiolytic effects (Oh et al 2009;Warren et al 2011). Moreover, studies with children and adolescents with depression or anxiety disorders have reported high rates of agitation or anxiety-like symptoms during antidepressant treatment (ReySánchez and Gutiérrez-Casares 1997;March et al 1998;Ambrosini et al 1999;Cook et al 2001;Emslie et al 2002;Braconnier et al 2003;Wagner et al 2003).…”