Chronic Ritalin administration during adulthood increases serotonin pool in rat medial frontal cortex

Effects of Methylphenidate on the Dopamine Transporter and Beyond

The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.

Integrative proteomics and pharmacogenomics analysis of methylphenidate treatment response

Transcriptomics and candidate gene/protein expression studies have indicated several biological processes modulated by methylphenidate (MPH), widely used in attention-deficit/hyperactivity disorder (ADHD) treatment. However, the lack of a differential proteomic profiling of MPH treatment limits the understanding of the most relevant mechanisms by which MPH exerts its pharmacological effects at the molecular level. Therefore, our aim is to investigate the MPH-induced proteomic alterations using an experimental design integrated with a pharmacogenomic analysis in a translational perspective. Proteomic analysis was performed using the cortices of Wistar-Kyoto rats, which were treated by gavage with MPH (2 mg/kg) or saline for two weeks (n = 6/group). After functional enrichment analysis of the differentially expressed proteins (DEP) in rats, the significant biological pathways were tested for association with MPH response in adults with ADHD (n = 189) using genome-wide data. Following MPH treatment in rats, 98 DEPs were found (P < 0.05 and FC < -1.0 or > 1.0). The functional enrichment analysis of the DEPs revealed 18 significant biological pathways (gene-sets) modulated by MPH, including some with recognized biological plausibility, such as those related to synaptic transmission. The pharmacogenomic analysis in the clinical sample evaluating these pathways revealed nominal associations for gene-sets related to neurotransmitter release and GABA transmission. Our results, which integrate proteomics and pharmacogenomics, revealed putative molecular effects of MPH on several biological processes, including oxidative stress, cellular respiration, and metabolism, and extended the results involving synaptic transmission pathways to a clinical sample. These findings shed light on the molecular signatures of MPH effects and possible biological sources of treatment response variability.

Effect of Methylphenidate on Orthodontic Tooth Movement and Histological Features of Bone Tissue in Rats: An Experimental Study

INTRODUCTION

Methylphenidate is a psychostimulant drug, which is commonly used by children and teenagers. This age group receives most orthodontic treatment. Effect of this drug on tooth movement is unknown.

AIM

The aim of this study was to evaluate the effect of methylphenidate on orthodontic tooth movement and histological features of bone tissue in rats.

MATERIALS AND METHODS

Forty-two Wistar rats (male) were selected and divided to three groups, randomly (n=14). The control group (Group 1) received no drug, the experimental Group 2 received a constant dose of methylphenidate daily for 14 days while the experimental Group 3 received increasing doses of methylphenidate daily. To exert force, a NiTi coil spring was placed between the maxillary right first molar and the maxillary right central incisor. At the end of the study period, the amount of tooth movement was measured and then the rats were sacrificed for histological analysis of bone tissue. Differences between the experimental groups were analysed using Kruskal-wallis and Mann-Whitney U tests.

RESULTS

No significant differences were found in the amount of orthodontic tooth movement or osteoclasts and lacunae, between the experimental groups (p>0.05). Mann-Whitney U analysis showed significant differences in the depth of resorption lacuna between Group 2 and 3 (p=0.037).

CONCLUSION

Methylphenidate has no significant effect on orthodontic tooth movement or histological features of bone tissue in rats.