Fluoxetine potentiation of methylphenidate-induced neuropeptide expression in the striatum occurs selectively in direct pathway (striatonigral) neurons

Vilazodone, a Selective Serotonin Reuptake Inhibitor with Diminished Impact on Methylphenidate-Induced Gene Regulation in the Striatum: Role of 5-HT1A Receptor

Selective serotonin reuptake inhibitors (SSRIs), including fluoxetine, are frequently combined with medical psychostimulants such as methylphenidate (Ritalin), for example, in the treatment of attention-deficit hyperactivity disorder/depression comorbidity. Co-exposure to these medications also occurs with misuse of methylphenidate as a recreational drug by patients on SSRIs. Methylphenidate, a dopamine reuptake blocker, produces moderate addiction-related gene regulation. Findings show that SSRIs such as fluoxetine given in conjunction with methylphenidate potentiate methylphenidate-induced gene regulation in the striatum in rats, consistent with a facilitatory action of serotonin on addiction-related processes. These SSRIs may thus increase methylphenidate's addiction liability. Here, we investigated the effects of a novel SSRI, vilazodone, on methylphenidate-induced gene regulation. Vilazodone differs from prototypical SSRIs in that, in addition to blocking serotonin reuptake, it acts as a partial agonist at the 5-HT1A serotonin receptor subtype. Studies showed that stimulation of the 5-HT1A receptor tempers serotonin input to the striatum. We compared the effects of acute treatment with vilazodone (10-20 mg/kg) with those of fluoxetine (5 mg/kg) on striatal gene regulation (zif268, substance P, enkephalin) induced by methylphenidate (5 mg/kg), by in situ hybridization histochemistry combined with autoradiography. We also assessed the impact of blocking 5-HT1A receptors by the selective antagonist WAY-100635 (0.5 mg/kg) on these responses. Behavioral effects of these drug treatments were examined in parallel in an open-field test. Our results show that, in contrast to fluoxetine, vilazodone did not potentiate gene regulation induced by methylphenidate in the striatum, while vilazodone enhanced methylphenidate-induced locomotor activity. However, blocking 5-HT1A receptors by WAY-100635 unmasked a potentiating effect of vilazodone on methylphenidate-induced gene regulation, thus confirming an inhibitory role for 5-HT1A receptors. Our findings suggest that vilazodone may serve as an adjunct SSRI with diminished addiction facilitating properties and identify the 5-HT1A receptor as a potential therapeutic target to treat addiction.

Combined methylphenidate and fluoxetine treatment in adolescent rats significantly impairs weight gain with minimal effects on skeletal development

Methylphenidate (MP) is frequently prescribed to treat Attention-Deficit/Hyperactivity Disorder (ADHD); however, many patients with ADHD experience depression and anxiety. As such, concomitant administration of selective serotonin reuptake inhibitors such as fluoxetine (FLX) is common. Our laboratory and others have shown that MP impairs skeletal development in preclinical and clinical settings, and FLX has also been linked to skeletal deficits. Unfortunately, little is known about the effects of combined MP and FLX treatment on skeletal development. The objective of this study was to investigate the effects of MP and FLX on bone morphology and biomechanical properties in adolescent rats. Four-week-old male Sprague-Dawley rats were randomly divided into the following 4 groups: Water, MP, FLX, and MP + FLX. As body weights in the MP, FLX, and MP + FLX groups were all lower than Water, the data were compared directly and after adjusting to body weight via linear regression. The direct comparison revealed that MP + FLX rats had significantly shorter (~12 %) and narrower femora and tibiae (~10 %) compared to most other groups, along with shorter (26-35 %), disorganized tibial growth plates. MicroCT analyses of the trabecular compartment of the proximal tibia identified reductions of 47 % for TV, 86 % for BV, 74 % for BV/TV, 68 % for Tb.N, 25 % in Tb.Th, and 74 % in vBMD concomitant with increases of 44 % for Tb.Sp for MP + FLX compared to Water. Similar analyses of femoral midshaft cortical bone identified reductions of 29 % for Ct.V, 30 % for Ps.V, 30 % for Ec. V, and 51 % for pMOI, as well as increases of 17 % for Ct.Th and 2 % for TMD for MP + FLX compared to Water. Biomechanically, MP + FLX femora were weaker, as indicated by a reduction in ultimate force (14 %) in MP + FLX compared to Water. The microstructural and biomechanical effects of MP + FLX were eliminated after adjustment for body weight, though the detrimental effects on growth plate morphology remained. We conclude that while the adverse microstructural and biomechanical effects of MP + FLX seen via direct comparison are predominantly attributable to reductions in body weight rather than direct effects on bone, MP and FLX, particularly in combination show detrimental effects on growth plate structure and chondrocyte morphology. These findings warrant further research into the effect of these drugs on weight gain, skeletal development and growth plate morphology, as well as consideration by physicians treating children and adolescents with ADHD.

Fluoxetine Potentiates Oral Methylphenidate-Induced Gene Regulation in the Rat Striatum

Methylphenidate (MP) is combined with selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (FLX) to treat various disorders. MP, a dopamine reuptake inhibitor, helps manage attention-deficit hyperactivity disorder (ADHD) and is abused as a cognitive enhancer; it has a reduced addiction liability. We showed that combining FLX (serotonin) with MP potentiates MP-induced gene regulation in the striatum. These studies used intraperitoneal drug administration, which is relevant for MP abuse. Clinically, MP and FLX are taken orally (slower bioavailability). Here, we investigated whether chronic oral administration of MP and FLX also altered striatal gene regulation. MP (30/60 mg/kg/day), FLX (20 mg/kg/day), and MP + FLX were administered in rats' drinking water for 8 h/day over 4 weeks. We assessed the expression of dynorphin and substance P (both markers for striatal direct pathway neurons) and enkephalin (indirect pathway) by in situ hybridization histochemistry. Chronic oral MP alone produced a tendency for increased dynorphin and substance P expression and no changes in enkephalin expression. Oral FLX alone did not increase gene expression. In contrast, when given together, FLX greatly enhanced MP-induced expression of dynorphin and substance P and to a lesser degree enkephalin. Thus, FLX potentiated oral MP-induced gene regulation predominantly in direct pathway neurons, mimicking cocaine effects. The three functional domains of the striatum were differentially affected. MP + SSRI concomitant therapies are indicated in ADHD/depression comorbidity and co-exposure occurs with MP misuse as a cognitive enhancer by patients on SSRIs. Our findings indicate that MP + SSRI combinations, even given orally, may enhance addiction-related gene regulation.

Exploring the Effects of Pharmacological, Psychosocial, and Alternative/Complementary Interventions in Children and Adolescents With Attention-Deficit/Hyperactivity Disorder: Meta-Regression Approach

BACKGROUND

There have been various therapies for attention-deficit/hyperactivity disorder (ADHD), but the previous meta-analysis of ADHD efficacy remains unclear. This study aims to systemically meta-regress the effect sizes (ES) of psychostimulant pharmacotherapy (methylphenidate and lisdexamfetamine), non-stimulant pharmacotherapy (atomoxetine and alpha-2 agonists), psychosocial therapy (parental behavioral therapy [PBT]), combination therapy (psychostimulant plus PBT), and alternative/complementary interventions to determine the right treatment for ADHD.

METHODS

We searched various ADHD interventions from the MEDLINE and PubMed databases (National Center for Biotechnology Information) between January 1, 1980, and July 30, 2018. Following the meta-analysis of random effects, the meta-regression analyses were used to explore factors potentially influencing treatment efficacy. The confounding variables included type of treatment, type of study, age, type of symptom scale used, and year of publication.

RESULTS

A total of 107 trials (n = 9883 participants) were included. After adjustment, compared with the psychostimulant therapy (28 trial, 2134 participants), non-stimulant pharmacotherapy (28 trials, 4991 participants) and alternative/complement intervention (25 trials, 1195 participants) were less effective by the ES of -0.384 (P = .004) and -0.419 (P = .028), respectively. However, compared with psychostimulant, PBT (19 trials, 1122 participants; ES = -0.308, P = .095) and the combination of psychostimulant and PBT (7 trials, 441participants; ES = -0.196, P = .209) did not differ significantly.

CONCLUSIONS

Psychostimulant therapy surpassed non-stimulant pharmacotherapy and alternative/complement intervention. Psychostimulant therapy, PBT, and the combination of psychostimulant therapy and PBT appear to be similar in efficacy according to this meta-regression.

Fluoxetine potentiation of methylphenidate-induced gene regulation in striatal output pathways: potential role for 5-HT1B receptor

Drug combinations that include the psychostimulant methylphenidate plus a selective serotonin reuptake inhibitor (SSRI) such as fluoxetine are increasingly used in children and adolescents. For example, this combination is indicated in the treatment of attention-deficit/hyperactivity disorder and depression comorbidity and other mental disorders. Such co-exposure also occurs in patients on SSRIs who use methylphenidate as a cognitive enhancer. The neurobiological consequences of these drug combinations are poorly understood. Methylphenidate alone can produce gene regulation effects that mimic addiction-related gene regulation by cocaine, consistent with its moderate addiction liability. We have previously shown that combining SSRIs with methylphenidate potentiates methylphenidate-induced gene regulation in the striatum. The present study investigated which striatal output pathways are affected by the methylphenidate + fluoxetine combination, by assessing effects on pathway-specific neuropeptide markers, and which serotonin receptor subtypes may mediate these effects. Our results demonstrate that a 5-day repeated treatment with fluoxetine (5 mg/kg) potentiates methylphenidate (5 mg/kg)-induced expression of both dynorphin (direct pathway marker) and enkephalin (indirect pathway). These changes were accompanied by correlated increases in the expression of the 5-HT1B, but not 5-HT2C, serotonin receptor in the same striatal regions. A further study showed that the 5-HT1B receptor agonist CP94253 (3-10 mg/kg) mimics the fluoxetine potentiation of methylphenidate-induced gene regulation. These findings suggest a role for the 5-HT1B receptor in the fluoxetine effects on striatal gene regulation. Given that 5-HT1B receptors are known to facilitate addiction-related gene regulation and behavior, our results suggest that SSRIs may enhance the addiction liability of methylphenidate by increasing 5-HT1B receptor signaling.

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

Use of psychostimulants such as methylphenidate (Ritalin) in medical treatments and as cognitive enhancers in the healthy is increasing. Methylphenidate produces some addiction-related gene regulation in animal models. Recent findings show that combining selective serotonin reuptake inhibitor (SSRI) antidepressants such as fluoxetine with methylphenidate potentiates methylphenidate-induced gene regulation. We investigated the endurance of such abnormal gene regulation by assessing an established marker for altered gene regulation after drug treatments - blunting (repression) of immediate-early gene (IEG) inducibility - 14 days after repeated methylphenidate+fluoxetine treatment in adolescent rats. Thus, we measured the effects of a 6-day repeated treatment with methylphenidate (5 mg/kg), fluoxetine (5 mg/kg) or their combination on the inducibility (by cocaine) of neuroplasticity-related IEGs (Zif268, Homer1a) in the striatum, by in situ hybridization histochemistry. Repeated methylphenidate treatment alone produced modest gene blunting, while fluoxetine alone had no effect. In contrast, fluoxetine given in conjunction with methylphenidate produced pronounced potentiation of methylphenidate-induced blunting for both genes. This potentiation was seen in many functional domains of the striatum, but was most robust in the lateral, sensorimotor striatum. These enduring molecular changes were associated with potentiated induction of behavioral stereotypies in an open-field test. For illicit psychostimulants, blunting of gene expression is considered part of the molecular basis of addiction. Our results thus suggest that SSRIs such as fluoxetine may increase the addiction liability of methylphenidate. Key words: cognitive enhancer, dopamine, serotonin, gene expression, psychostimulant, SSRI antidepressant, striatum.

Selective serotonin re-uptake inhibitors potentiate gene blunting induced by repeated methylphenidate treatment: Zif268 versus Homer1a

There is a growing use of psychostimulants, such as methylphenidate (Ritalin; dopamine re-uptake inhibitor), for medical treatments and as cognitive enhancers in the healthy. Methylphenidate is known to produce some addiction-related gene regulation. Recent findings in animal models show that selective serotonin re-uptake inhibitors (SSRIs), including fluoxetine, can potentiate acute induction of gene expression by methylphenidate, thus indicating an acute facilitatory role for serotonin in dopamine-induced gene regulation. We investigated whether repeated exposure to fluoxetine, in conjunction with methylphenidate, in adolescent rats facilitated a gene regulation effect well established for repeated exposure to illicit psychostimulants such as cocaine-blunting (repression) of gene inducibility. We measured, by in situ hybridization histochemistry, the effects of a 5-day repeated treatment with methylphenidate (5 mg/kg), fluoxetine (5 mg/kg) or a combination on the inducibility (by cocaine) of neuroplasticity-related genes (Zif268, Homer1a) in the striatum. Repeated methylphenidate treatment alone produced minimal gene blunting, while fluoxetine alone had no effect. In contrast, fluoxetine added to methylphenidate robustly potentiated methylphenidate-induced blunting for both genes. This potentiation was widespread throughout the striatum, but was most robust in the lateral, sensorimotor striatum, thus mimicking cocaine effects. For illicit psychostimulants, blunting of gene expression is considered part of the molecular basis of addiction. Our results thus suggest that SSRIs, such as fluoxetine, may increase the addiction liability of methylphenidate.

Life-long consequences of juvenile exposure to psychotropic drugs on brain and behavior

Psychostimulants such as methylphenidate (MPH) and antidepressants such as fluoxetine (FLX) are widely used in the treatment of various mental disorders or as cognitive enhancers. These medications are often combined, for example, to treat comorbid disorders. There is a considerable body of evidence from animal models indicating that individually these psychotropic medications can have detrimental effects on the brain and behavior, especially when given during sensitive periods of brain development. However, almost no studies investigate possible interactions between these drugs. This is surprising given that their combined neurochemical effects (enhanced dopamine and serotonin neurotransmission) mimic some effects of illicit drugs such as cocaine and amphetamine. Here, we summarize recent studies in juvenile rats on the molecular effects in the mid- and forebrain and associated behavioral changes, after such combination treatments. Our findings indicate that these combined MPH+FLX treatments can produce similar molecular changes as seen after cocaine exposure while inducing behavioral changes indicative of dysregulated mood and motivation, effects that often endure into adulthood.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Addiction-related gene regulation: risks of exposure to cognitive enhancers vs. other psychostimulants

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.