Role of 5-HT1A Receptor in Vilazodone-Mediated Suppression of L-DOPA-Induced Dyskinesia and Increased Responsiveness to Cortical Input in Striatal Medium Spiny Neurons in an Animal Model of Parkinson's Disease.

L-DOPA therapy in Parkinson's disease (PD) is limited due to emerging L-DOPA-induced dyskinesia. Research has identified abnormal dopamine release from serotonergic (5-HT) terminals contributing to this dyskinesia. Selective serotonin reuptake inhibitors (SSRIs) or 5-HT receptor (5-HTr) agonists can regulate 5-HT activity and attenuate dyskinesia, but they often also produce a loss of the antiparkinsonian efficacy of L-DOPA. We investigated vilazodone, a novel multimodal 5-HT agent with SSRI and 5-HTr1A partial agonist properties, for its potential to reduce dyskinesia without interfering with the prokinetic effects of L-DOPA, and underlying mechanisms. We assessed vilazodone effects on L-DOPA-induced dyskinesia (abnormal involuntary movements, AIMs) and aberrant responsiveness to corticostriatal drive in striatal medium spiny neurons (MSNs) measured with in vivo single-unit extracellular recordings, in the 6-OHDA rat model of PD. Vilazodone (10 mg/kg) suppressed all subtypes (axial, limb, orolingual) of AIMs induced by L-DOPA (5 mg/kg) and the increase in MSN responsiveness to cortical stimulation (shorter spike onset latency). Both the antidyskinetic effects and reversal in MSN excitability by vilazodone were inhibited by the 5-HTr1A antagonist WAY-100635, demonstrating a critical role for 5-HTr1A in these vilazodone actions. Our results indicate that vilazodone may serve as an adjunct therapeutic for reducing dyskinesia in patients with PD.

Transcranial direct current stimulation produces long-lasting attenuation of cocaine-induced behavioral responses and gene regulation in corticostriatal circuits.

Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability. This technique is a promising emerging tool to treat several neuropathologies, including addiction. We have previously shown in mice that repeated tDCS normalizes pathological behaviors associated with chronic nicotine exposure. Here, we evaluated, in adult female mice, the impact of tDCS on cocaine-induced behavior and gene regulation in corticostriatal circuits implicated in psychostimulant addiction. Anodal tDCS was applied transcranially over the frontal cortex. Three weeks after repeated tDCS, we investigated the induction of a gene expression marker (Zif268) by cocaine (25 mg/kg) in 26 cortical and 23 striatal regions using in situ hybridization histochemistry. We also assessed place preference conditioning by cocaine (5, 10 and 25 mg/kg). tDCS pretreatment increased basal expression and attenuated cocaine (25 mg/kg)-induced expression of Zif268 in specific corticostriatal circuits. Cocaine-induced locomotor activation (25 mg/kg) and place preference conditioning (5 and 25 mg/kg) were also reduced. These results demonstrate that tDCS can attenuate molecular and behavioral responses to cocaine for several weeks. Together, our findings provide pre-clinical evidence that such electrical brain stimulation may be useful to modify the psychostimulant addiction risk.

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.

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.

Mother's little helper turned a foe: Alprazolam use, misuse, and abuse.

Benzodiazepines are effective in managing anxiety and related disorders when used properly (short-term). Their inappropriate use, however, carries significant risks, involving amnesia, rebound insomnia, rebound anxiety, depression, dependence, abuse, addiction, and an intense and exceedingly prolonged withdrawal, among other complications. Benzodiazepines also amplify the effects of opioids and, consequently, have been implicated in approximately 30 % of opioid overdose deaths. Despite their unfavorable profile, sharp increases in medical and non-medical use of benzodiazepines have been steadily reported worldwide. Alprazolam (Xanax®), a potent, short-acting benzodiazepine, is among the most prescribed and abused anxiolytics in the United States. This medication is commonly co-abused with opioids, increasing the likelihood for oversedation, overdose, and death. Notwithstanding these risks, it is surprising that research investigating how benzodiazepines, such as alprazolam, interact with opioids is severely lacking in clinical and preclinical settings. This review therefore aims to present our current knowledge of benzodiazepine use and misuse, with an emphasis on alprazolam when data is available, and particularly in populations at higher risk for developing substance use disorders. Additionally, the potential mechanism(s) surrounding tolerance, dependence and abuse liability are discussed. Despite their popularity, our understanding of how benzodiazepines and opioids interact is less than adequate. Therefore, it is now more important than ever to understand the short- and long-term consequences of benzodiazepine/alprazolam use.

Methylphenidate with or without fluoxetine triggers reinstatement of cocaine seeking behavior in rats.

Methylphenidate (MP) is commonly prescribed to treat attention-deficit hyperactivity disorder (ADHD). MP is also taken for non-medical purposes as a recreational drug or "cognitive enhancer". Combined exposure to MP and selective serotonin reuptake inhibitors such as fluoxetine (FLX) can also occur, such as in the treatment of ADHD with depression comorbidity or when patients taking FLX use MP for non-medical purposes. It is unclear if such exposure could subsequently increase the risk for relapse in former cocaine users. We investigated if an acute challenge with MP, FLX, or the combination of MP + FLX could trigger reinstatement of cocaine seeking behavior in a model for relapse in rats. Juvenile rats self-administered cocaine (600 µg/kg/infusion, 1-2 h/day, 7-8 days) and then underwent extinction and withdrawal during late adolescence-early adulthood. Reinstatement was tested at a low dose of MP (2 mg/kg, I.P., comparable to doses used therapeutically) or a high dose of MP (5 mg/kg, comparable to doses used recreationally or as a cognitive enhancer), with or without FLX (2.5-5 mg/kg, I.P.). An acute challenge with the high dose of MP (5 mg/kg), with or without FLX, reinstated cocaine seeking behavior to levels comparable to those seen after an acute challenge with cocaine (15 mg/kg, I.P.). The low dose of MP (2 mg/kg) with or without FLX did not reinstate cocaine seeking behavior. Our results suggest that acute exposure to a high dose of MP, with or without FLX, may increase the risk for relapse in individuals who used cocaine during the juvenile period.

Fluoxetine potentiates methylphenidate-induced behavioral responses: Enhanced locomotion or stereotypies and facilitated acquisition of cocaine self-administration.

The medical psychostimulant methylphenidate (MP) is used to treat attention-deficit hyperactivity disorder and recreationally as a "cognitive enhancer". MP is a dopamine reuptake inhibitor, but does not affect serotonin. Serotonin contributes to addiction-related gene regulation and behavior. Previously, we showed that enhancing serotonin action by adding a selective serotonin reuptake inhibitor, fluoxetine (FLX), to MP potentiates MP-induced gene regulation in striatum and nucleus accumbens, mimicking cocaine effects. Here, we investigated the behavioral consequences of MP+FLX treatment. Young adult male rats received MP (5 mg/kg, i.p.) or MP+FLX (5 mg/kg each) daily for 6-8 days. Behavioral effects were assessed in an open-field test during the repeated treatment. Two weeks later the motor response to a cocaine challenge (25 mg/kg) and the rate of acquisition of cocaine self-administration behavior were determined. Our results demonstrate that FLX potentiates effects of MP on open-field behavior. However, we found differential behavioral responses to MP+FLX treatment, as approximately half of the rats developed high rates of focal stereotypies (termed "MP+FLX/high reactivity" group), whereas the other half did not, and only showed increased locomotion ("MP+FLX/low reactivity" group). Two weeks later, cocaine-induced locomotion and stereotypies were positively correlated with MP+FLX-induced behavior seen at the end of the repeated MP+FLX treatment. Moreover, the MP+FLX/high reactivity group, but not the low reactivity group, showed facilitated acquisition of cocaine self-administration. These results demonstrate that repeated MP+FLX treatment can facilitate subsequent cocaine taking behavior in a subpopulation of rats. These findings suggest that MP+FLX exposure in some individuals may increase the risk for psychostimulant use later in life.

Combined Chronic Oral Methylphenidate and Fluoxetine Treatment During Adolescence: Effects on Behavior.

BACKGROUND: Attention Deficit Hyperactivity Disorder (ADHD) can be comorbid with depression, often leading to the prescription of both methylphenidate (MP) and selective serotonin reuptake inhibitor (SSRI) antidepressants, such as fluoxetine (FLX). Moreover, these drugs are often misused as cognitive enhancers. This study examined the effects of chronic oral co-administration of MP and FLX on depressive- and anxiety-like behaviors. METHODS: Adolescent rats received daily either water (control), MP, FLX, or the combination of MP plus FLX in their drinking water over the course of 4 weeks. RESULTS: Data analysis shows a decrease in food consumption and body weight for rats exposed to FLX or the combination of MP and FLX. Sucrose consumption was significantly greater in FLX or MP+FLX groups compared to controls. FLX-treated rats showed no effect in the elevated plus maze (EPM; open arm time) and forced swim test (FST; latency to immobility). However, rats treated with the combination (MP+FLX) showed significant anxiolytic-like and anti-depressive-like behaviors (as measured by EPM and FST), as well as significant increases in overall activity (distance traveled in open field test). Finally, the combined MP+FLX treatment induced a decrease in anxiety and depressive- like behaviors significantly greater than the response from either of these drugs alone. CONCLUSION: These behavioral results characterize the long-term effects of these drugs (orally administered) that are widely co-administered and co-misused and provide important insight into the potential neurobiological and neurochemical effects. Future research will determine the potential risks of the long-term use of MP and FLX together.

Chronic oral methylphenidate plus fluoxetine treatment in adolescent rats increases cocaine self-administration.

Background: Depression and attention deficit hyperactivity disorder are known to be comorbid. Treatment of these commonly coexisting diseases typically involves the combined prescription of methylphenidate (MP), a psychostimulant, and fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI). MP and cocaine have similar mechanisms of action and this study examined the effects of chronic treatment of MP combined with FLX on cocaine consumption in rats. Methods: Four groups of rats received access to drinking solutions of water (control), MP (30/60 mg/kg/day), FLX (20 mg/kg/day), or the combination of MP (30/60 mg/kg/day) plus FLX (20 mg/kg/day), during 8 h per day for one month. Following these drug treatments, rats were allowed to self-administer cocaine for 14 days. Results: Our results showed that, during the first week of cocaine self-administration, the MP-treated rats had significantly greater numbers of active lever presses (plus 127%) and increased consumption of cocaine compared to the control rats. In contrast, during week two of cocaine self-administration, the rats treated with the MP + FLX combination showed significantly more lever presses (plus 198%) and significantly greater cocaine consumption (plus 84%) compared to the water controls. Conclusion: Chronic oral treatment during adolescence with the combination of MP plus FLX resulted in increased cocaine use after 2 weeks of cocaine self-administration in rats. These novel findings suggest that the combined exposure to these two drugs chronically, during adolescence, may produce increased vulnerability towards cocaine abuse during young adulthood.

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

Concomitant therapies combining psychostimulants such as methylphenidate and selective serotonin reuptake inhibitors (SSRIs) are used to treat several mental disorders, including attention-deficit hyperactivity disorder/depression comorbidity. The neurobiological consequences of these drug combinations are poorly understood. Methylphenidate alone induces gene regulation that mimics partly effects of cocaine, consistent with some addiction liability. We previously showed that the SSRI fluoxetine 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. Results demonstrate that fluoxetine (5 mg/kg) potentiates methylphenidate (5 mg/kg)-induced expression of substance P and dynorphin, markers for direct pathway neurons. In contrast, no drug effects on the indirect pathway marker enkephalin were found. Because methylphenidate alone has minimal effects on dynorphin, the potentiation of dynorphin induction represents a more cocaine-like effect for the drug combination. On the other hand, the lack of an effect on enkephalin suggests a greater selectivity for the direct pathway compared with psychostimulants such as cocaine. Overall, the fluoxetine potentiation of gene regulation by methylphenidate occurs preferentially in sensorimotor striatal circuits, similar to other addictive psychostimulants. These results suggest that SSRIs may enhance the addiction liability of methylphenidate.

Phosphodiesterase 10A (PDE10A): Regulator of Dopamine Agonist-Induced Gene Expression in the Striatum.

Dopamine and other neurotransmitters have the potential to induce neuroplasticity in the striatum via gene regulation. Dopamine receptor-mediated gene regulation relies on second messenger cascades that involve cyclic nucleotides to relay signaling from the synapse to the nucleus. Phosphodiesterases (PDEs) catalyze cyclic nucleotides and thus potently control cyclic nucleotide signaling. We investigated the role of the most abundant striatal PDE, PDE10A, in striatal gene regulation by assessing the effects of PDE10A inhibition (by a selective PDE10A inhibitor, TP-10) on gene regulation and by comparing the basal expression of PDE10A mRNA throughout the striatum with gene induction by dopamine agonists in the intact or dopamine-depleted striatum. Our findings show that PDE10A expression is most abundant in the sensorimotor striatum, intermediate in the associative striatum and lower in the limbic striatum. The inhibition of PDE10A produced pronounced increases in gene expression that were directly related to levels of local PDE10A expression. Moreover, the gene expression induced by L-DOPA after dopamine depletion (by 6-OHDA), or by psychostimulants (cocaine, methylphenidate) in the intact striatum, was also positively correlated with the levels of local PDE10A expression. This relationship was found for gene markers of both D1 receptor- and D2 receptor-expressing striatal projection neurons. Collectively, these results indicate that PDE10A, a vital part of the dopamine receptor-associated second messenger machinery, is tightly linked to drug-induced gene regulation in the striatum. PDE10A may thus serve as a potential target for modifying drug-induced gene regulation and related neuroplasticity.

Differential developmental trajectories for CB1 cannabinoid receptor expression in limbic/associative and sensorimotor cortical areas.

Cannabis use during adolescence is associated with an increased risk for schizophrenia and other disorders. The neuronal basis is unclear, but prefrontal cortical mechanisms have been implicated. Here, we investigated developmental changes in the endocannabinoid system by assessing expression and function of the CB1 cannabinoid receptor in prefrontal and other cortical areas in juvenile (postnatal day 25, P25), adolescent (P40), and adult (P70) rats. Overall, the expression of CB1 receptors in the cortex is highest in juveniles and drops thereafter toward adult levels. However, CB1 receptor expression follows distinct developmental trajectories in different cortical areas. The most pronounced and progressive decrease in CB1 expression was observed in medial prefrontal and other limbic/associative regions. In contrast, major changes in sensorimotor cortices occurred only after P40. We also assessed electrophysiological measures of CB1 receptor function and found that CB1-dependent inhibition of synaptic transmission in the prefrontal cortex follows the same developmental trajectory as observed for receptor expression. Together, these findings indicate that CB1 receptor-mediated signaling decreases during development but is differentially regulated in limbic/associative vs. sensorimotor systems. Therefore, cannabis use during adolescence likely differentially affects limbic/associative and sensorimotor cortical circuits.

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.

Selective serotonin reuptake inhibitor antidepressants potentiate methylphenidate (Ritalin)-induced gene regulation in the adolescent striatum.

The psychostimulant methylphenidate (Ritalin) is used in conjunction with selective serotonin reuptake inhibitors (SSRIs) in the treatment of medical conditions such as attention-deficit hyperactivity disorder with anxiety/depression comorbidity and major depression. Co-exposure also occurs in patients on SSRIs who use psychostimulant 'cognitive enhancers'. Methylphenidate is a dopamine/norepinephrine reuptake inhibitor that produces altered gene expression in the forebrain; these effects partly mimic gene regulation by cocaine (dopamine/norepinephrine/serotonin reuptake inhibitor). We investigated whether the addition of SSRIs (fluoxetine or citalopram; 5 mg/kg) modified gene regulation by methylphenidate (2-5 mg/kg) in the striatum and cortex of adolescent rats. Our results show that SSRIs potentiate methylphenidate-induced expression of the transcription factor genes zif268 and c-fos in the striatum, rendering these molecular changes more cocaine-like. Present throughout most of the striatum, this potentiation was most robust in its sensorimotor parts. The methylphenidate + SSRI combination also enhanced behavioral stereotypies, consistent with dysfunction in sensorimotor striatal circuits. In so far as such gene regulation is implicated in psychostimulant addiction, our findings suggest that SSRIs may enhance the addiction potential of methylphenidate.

The Multimodal Serotonergic Agent Vilazodone Inhibits L-DOPA-Induced Gene Regulation in Striatal Projection Neurons and Associated Dyskinesia in an Animal Model of Parkinson's Disease.

Levodopa (L-DOPA) treatment in Parkinson's disease is limited by the emergence of L-DOPA-induced dyskinesia. Such dyskinesia is associated with aberrant gene regulation in neurons of the striatum, which is caused by abnormal dopamine release from serotonin terminals. Previous work showed that modulating the striatal serotonin innervation with selective serotonin reuptake inhibitors (SSRIs) or 5-HT1A receptor agonists could attenuate L-DOPA-induced dyskinesia. We investigated the effects of a novel serotonergic agent, vilazodone, which combines SSRI and 5-HT1A partial agonist properties, on L-DOPA-induced behavior and gene regulation in the striatum in an animal model of Parkinson's disease. After unilateral dopamine depletion by 6-hydroxydopamine (6-OHDA), rats received repeated L-DOPA treatment (5 mg/kg) alone or in combination with vilazodone (10 mg/kg) for 3 weeks. Gene regulation was then mapped throughout the striatum using in situ hybridization histochemistry. Vilazodone suppressed the development of L-DOPA-induced dyskinesia and turning behavior but did not interfere with the prokinetic effects of L-DOPA (forelimb stepping). L-DOPA treatment drastically increased the expression of dynorphin (direct pathway), 5-HT1B, and zif268 mRNA in the striatum ipsilateral to the lesion. These effects were inhibited by vilazodone. In contrast, vilazodone had no effect on enkephalin expression (indirect pathway) or on gene expression in the intact striatum. Thus, vilazodone inhibited L-DOPA-induced gene regulation selectively in the direct pathway of the dopamine-depleted striatum, molecular changes that are considered critical for L-DOPA-induced dyskinesia. These findings position vilazodone, an approved antidepressant, as a potential adjunct medication for the treatment of L-DOPA-induced motor side effects.

Selective Regulation of 5-HT1B Serotonin Receptor Expression in the Striatum by Dopamine Depletion and Repeated L-DOPA Treatment: Relationship to L-DOPA-Induced Dyskinesias.

Dopamine and serotonin in the basal ganglia interact in a bidirectional manner. On the one hand, serotonin (5-HT) receptors regulate the effects of dopamine agonists on several levels, ranging from molecular signaling to behavior. These interactions include 5-HT receptor-mediated facilitation of dopamine receptor-induced gene regulation in striatal output pathways, which involves the 5-HT1B receptor and others. Conversely, there is evidence that dopamine action by psychostimulants regulates 5-HT1B receptor expression in the striatum. To further investigate the effects of dopamine and agonists on 5-HT receptors, we assessed the expression of 5-HT1B and other serotonin receptor subtypes in the striatum after unilateral dopamine depletion by 6-OHDA and subsequent treatment with L-DOPA (5 mg/kg; 4 weeks). Neither dopamine depletion nor L-DOPA treatment produced significant changes in 5-HT2C, 5-HT4, or 5-HT6 receptor expression in the striatum. In contrast, the 6-OHDA lesion caused a (modest) increase in 5-HT1B mRNA levels throughout the striatum. Moreover, repeated L-DOPA treatment markedly further elevated 5-HT1B expression in the dopamine-depleted striatum, an effect that was most robust in the sensorimotor striatum. A minor L-DOPA-induced increase in 5-HT1B expression was also seen in the intact striatum. These changes in 5-HT1B expression mimicked changes in the expression of neuropeptide markers (dynorphin, enkephalin mRNA) in striatal projection neurons. After repeated L-DOPA treatment, the severity of L-DOPA-induced dyskinesias and turning behavior was positively correlated with the increase in 5-HT1B expression in the associative, but not sensorimotor, striatum ipsilateral to the lesion, suggesting that associative striatal 5-HT1B receptors may play a role in L-DOPA-induced behavioral abnormalities.

Long-lasting dysregulation of gene expression in corticostriatal circuits after repeated cocaine treatment in adult rats: effects on zif 268 and homer 1a.

Human imaging studies show that psychostimulants such as cocaine produce functional changes in several areas of cortex and striatum. These may reflect neuronal changes related to addiction. We employed gene markers (zif 268 and homer 1a) that offer a high anatomical resolution to map cocaine-induced changes in 22 cortical areas and 23 functionally related striatal sectors, in order to determine the corticostriatal circuits altered by repeated cocaine exposure (25 mg/kg, 5 days). Effects were investigated 1 day and 21 days after repeated treatment to assess their longevity. Repeated cocaine treatment increased basal expression of zif 268 predominantly in sensorimotor areas of the cortex. This effect endured for 3 weeks in some areas. These changes were accompanied by attenuated gene induction by a cocaine challenge. In the insular cortex, the cocaine challenge produced a decrease in zif 268 expression after the 21-day, but not 1-day, withdrawal period. In the striatum, cocaine also affected mostly sensorimotor sectors. Repeated cocaine resulted in blunted inducibility of both zif 268 and homer 1a, changes that were still very robust 3 weeks later. Thus, our findings demonstrate that cocaine produces robust and long-lasting changes in gene regulation predominantly in sensorimotor corticostriatal circuits. These neuronal changes were associated with behavioral stereotypies, which are thought to reflect dysfunction in sensorimotor corticostriatal circuits. Future studies will have to elucidate the role of such neuronal changes in psychostimulant addiction.

Methylphenidate and cocaine: the same effects on gene regulation?

Methylphenidate (Ritalin), a psychostimulant used in the treatment of Attention-Deficit Hyperactivity Disorder, has pharmacological effects similar to cocaine and amphetamine. Clinical use of methylphenidate, as well as diversion and abuse, have significantly increased during the past 10-15 years, heightening concerns regarding the long-term effects of methylphenidate on the developing brain. Here we review the effects of acute and repeated methylphenidate treatment on molecules of neuronal signaling and neuroplasticity (including transcription factors, neuropeptides, and components of second messenger cascades) and compare these molecular effects with those produced by cocaine and amphetamine. Some molecular changes, such as altered transcription factor gene regulation, are similar to those of cocaine and amphetamine. Other effects, notably those on the expression of opioid peptides and postsynaptic density molecules (Homer 1a), differ between methylphenidate and cocaine or amphetamine treatment. These differences support the notion that methylphenidate produces less neuroadaptations than cocaine and amphetamine, and might provide a molecular basis for reduced addiction liability of methylphenidate compared with these other psychostimulants.

The 5-HT1B serotonin receptor regulates methylphenidate-induced gene expression in the striatum: Differential effects on immediate-early genes.

Drug combinations that include a psychostimulant such as methylphenidate (Ritalin) and a selective serotonin reuptake inhibitor such as fluoxetine are indicated in several medical conditions. Co-exposure to these drugs also occurs with "cognitive enhancer" use by individuals treated with selective serotonin reuptake inhibitors. Methylphenidate, a dopamine reuptake inhibitor, by itself produces some addiction-related gene regulation in the striatum. We have demonstrated that co-administration of selective serotonin reuptake inhibitors potentiates these methylphenidate-induced molecular effects, thus producing a more "cocaine-like" profile. There is evidence that the 5-HT1B serotonin receptor subtype mediates some of the cocaine-induced gene regulation. We thus investigated whether the 5-HT1B receptor also modifies methylphenidate-induced gene regulation, by assessing effects of a selective 5-HT1B receptor agonist (CP94253) on immediate-early gene markers ( Zif268, c- Fos, Homer1a) in adolescent male rats. Gene expression was measured by in situ hybridization histochemistry. Our results show that CP94253 (3, 10 mg/kg) produced a dose-dependent potentiation of methylphenidate (5 mg/kg)-induced expression of Zif268 and c- Fos. This potentiation was widespread in the striatum and was maximal in lateral (sensorimotor) sectors, thus mimicking the effects seen after cocaine alone, or co-administration of fluoxetine. However, in contrast to fluoxetine, this 5-HT1B agonist did not influence methylphenidate-induced expression of Homer1a. CP94253 also potentiated methylphenidate-induced locomotor activity. These findings indicate that stimulation of the 5-HT1B receptor can enhance methylphenidate (dopamine)-induced gene regulation. This receptor may thus participate in the potentiation induced by fluoxetine (serotonin) and may serve as a pharmacological target to attenuate methylphenidate + selective serotonin reuptake inhibitor-induced "cocaine-like" effects.

Motor-skill learning-associated gene regulation in the striatum: effects of cocaine.

Psychostimulant-induced molecular changes in cortico-basal ganglia-cortical circuits play a critical role in addiction and dependence. These changes include alterations in gene regulation particularly in projection neurons of the sensorimotor striatum. We previously showed that cocaine-induced gene regulation in such neurons is dependent on the behavior performed during drug action. Rats trained on a running wheel under the influence of cocaine for 4 days subsequently displayed greater c-fos induction by cocaine than untrained controls. This effect was selective for the sensorimotor striatum, which is known to mediate forms of motor learning. In the present study, we investigated whether this enhanced cellular responsiveness was associated with learning of wheel running or with prolonged running (exercising), by assessing c-fos inducibility after 1, 2, or 8 days of training. Wheel training was performed after injection of cocaine (25 mg/kg) or vehicle, and c-fos induction by a cocaine challenge was measured 24 h later. Rats that trained under cocaine (but not vehicle) showed a greater c-fos response in the striatum compared to locked-wheel controls. This effect was present after the 1-day training, peaked after 2 days, and dissipated by 8 days of training. Similar effects were found for substance P, but not enkephalin, expression. These changes in striatal gene regulation paralleled improvement in wheel running, which was facilitated by cocaine. Thus, these training-induced molecular changes do not appear to represent exercising effects, but may reflect motor learning-associated neuronal changes altered by cocaine. Such cocaine effects may contribute to aberrant motor learning implicated in psychostimulant addiction.