A systematic review of psychostimulant treatment of negative symptoms of schizophrenia: Challenges and therapeutic opportunities
ABSTRACT BACKGROUND: Primary negative symptoms of schizophrenia (NSS) contribute heavily to functional disability and treatment of these symptoms continues to be a major unmet need even when the positive (psychotic) symptoms are controlled. The modified dopamine (DA) hypothesis posits that positive symptoms are associated with increased DA activity in the mesolimbic tract whereas NSS and cognitive symptoms are associated with decreased DA activity in the mesocortical (frontal) region. Several studies have reported improvement in NSS with DA agonist use, but with varying degrees of risk for triggering psychotic symptoms, especially in the absence of concurrent antipsychotic drug treatment. This article aims to examine older and newer evidence suggesting that psychostimulants may have a potential therapeutic role in the treatment of NSS together with a thorough review of the potential risks and benefits of psychostimulant administration in individuals with schizophrenia. METHODS: A systematic search of relevant literature using electronic databases, reference lists, and data presented at recent meetings was conducted. RESULTS: Improvement of NSS after psychostimulant administration is reviewed both in challenge and treatment paradigms with various agents such as methylphenidate, amphetamine, and modafinil or armodafinil. The literature points to evidence that, used adjunctively, DA agonists may improve NSS without worsening of positive symptoms in selected patients who are stable and treated with effective antipsychotic medications. Several areas of inadequate study and limitations are identified including small study samples, single-site trials, varying rigor of bias control, the dose and the duration of adjunctive psychostimulant administration, and the potential for development of tolerance. CONCLUSION: Large, controlled clinical trials to further characterize effects of psychostimulants on NSS in carefully selected patients are warranted.
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ABSTRACT: Schizophrenia is thought to be caused, at least in part, by dysfunction in striatal dopamine neurotransmission. Both clinical studies and animal research have implicated the dopamine neuromodulator neurotensin (NT) in the pathophysiology of schizophrenia. Utilizing male mice lacking the NT gene (NT(-/-)), these studies examined the consequences of NT deficiency on dopaminergic tone and function, investigating (1) dopamine concentrations and dopamine receptor and transporter expression and binding in dopaminergic terminal regions, and (2) the behavioral effects of selective dopamine receptor agonists on locomotion and sensorimotor gating in adult NT(-/-) mice compared to wildtype (NT(+/+)) mice. NT(-/-) mice did not differ from NT(+/+) mice in concentrations of dopamine or its metabolite DOPAC in any brain region examined. However, NT(-/-) mice showed significantly increased D1 receptor, D2 receptor, and dopamine transporter (DAT) mRNA in the caudate putamen compared to NT(+/+) controls. NT(-/-) mice also showed elevated D2 receptor binding densities in both the caudate putamen and nucleus accumbens shell compared to NT(+/+) mice. In addition, some of the behavioral effects of the D1-type receptor agonist SKF-82958 and the D2-type receptor agonist quinpirole on locomotion, startle amplitude, and prepulse inhibition were dose-dependently altered in NT(-/-) mice, showing altered D1-type and D2-type receptor sensitivity to stimulation by agonists in the absence of NT. The results indicate that NT deficiency alters striatal dopamine receptor expression, binding, and function. This suggests a critical role for the NT system in the maintenance of striatal DA system homeostasis and implicates NT deficiency in the etiology of dopamine-associated disorders such as schizophrenia. Copyright © 2014. Published by Elsevier B.V.Behavioural Brain Research 11/2014; 280. DOI:10.1016/j.bbr.2014.11.014 · 3.39 Impact Factor
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ABSTRACT: We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) of modafinil or armodafinil (ar/mod) augmentation in schizophrenia. We searched PubMed, clinical trial registries, reference lists, and other sources for parallel group, placebo-controlled RCTs. Our primary outcome variable was the effect of ar/mod on negative symptom outcomes. Eight RCTs (pooled N = 372; median duration, 8 weeks) met our selection criteria. Ar/mod (200 mg/day) significantly attenuated negative symptom ratings (6 RCTs; N = 322; standardized mean difference [SMD], -0.26; 95% CI, -0.48 to -0.04). This finding remained similar in all but one sensitivity analysis - when the only RCT in acutely ill patients was excluded, the outcome was no longer statistically significant (SMD, -0.17; 95% CI, -0.51 to 0.06). The absolute advantage for ar/mod was small: just 0.27 points on the PANSS-N (6 RCTs). Ar/mod attenuated total psychopathology ratings (7 RCTs; N = 342; SMD, -0.23; 95% CI, -0.45 to -0.02) but did not influence positive symptom ratings (5 RCTs; N = 302; mean difference, -0.58; 95% CI, -1.71 to 0.55). Although data were limited, cognition, fatigue, daytime drowsiness, adverse events, and drop out rates did not differ significantly between ar/mod and placebo groups. Fixed and random effects models yielded similar results. There was no heterogeneity in all but one analysis. Publication bias could not be tested. We conclude that ar/mod (200 mg/day) is safe and well tolerated in the short-term treatment of schizophrenia. Ar/mod reduces negative symptoms with a small effect size; the absolute advantage is also small, and the advantage disappears when chronically ill patients or those with high negative symptom burden are treated. Ar/mod does not benefit or worsen other symptom dimensions in schizophrenia.Journal of Psychiatric Research 09/2014; 60. DOI:10.1016/j.jpsychires.2014.09.013 · 4.09 Impact Factor
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ABSTRACT: The primary mechanism by which amphetamine exerts its neurobehavioral effects is through an enhancement of synaptic monoamine levels, which is mediated by interactions with monoamine transporters, storage, and metabolism. However, preclinical data are now emerging that support more widespread neurobiologic effects for amphetamine. This review describes preclinical evidence suggesting that direct interactions of amphetamine with monoamine systems, which results in increased synaptic monoamine availability, has downstream effects on nonmonoaminergic systems, including glutamate, endogenous opioid, endocannabinoid, and acetylcholine systems. Furthermore, evidence suggests that amphetamine can modulate synaptic plasticity through modulation of glutamatergic systems, intracellular signaling cascades, and neurotrophic factor activity. Functional activity of these systems is implicated in the regulation of neurobehavioral processes that include cognition, mood, motivated behavior/hedonic processes/addiction, and arousal. As such, the ability of amphetamine to influence the function of systems that mediate these processes suggests amphetamine-based agents may have utility in the treatment of psychiatric disorders in which these systems and processes are dysfunctional. Amphetamine-based agents are currently approved by the US Food and Drug Administration only for the treatment of attention-deficit/hyperactivity disorder and narcolepsy. Preclinical and clinical research for amphetamine-based pharmacotherapy for other psychiatric disease states is examined. This should encourage further research on the preclinical pharmacology of amphetamine and its implications for the treatment of neuropsychiatric disorders.Pharmacology [?] Therapeutics 03/2014; 143(3). DOI:10.1016/j.pharmthera.2014.03.005 · 7.75 Impact Factor