The increasing use of Methylphenidate (MPD) among adolescents and adults raises important concerns regarding its developmental and long-term neurophysiological effects. This study examined behavioral and neuronal responses in the Locus Coeruleus (LC)—a critical hub for Norepinephrine (NE) signaling—following administration of various MPD doses in adolescent and adult rats. Four experimental groups were used for each age cohort: saline, 0.6, 2.5, and 10.0 mg/kg MPD. Animals received six consecutive daily MPD injections from Experimental Days (ED) 1 to 6, followed by a threeday washout period and a single rechallenge dose on ED10. A total of 174 adolescent and 157 adult rats were used for concurrent behavioral assessments, while LC neuronal activity was recorded from 409 and 461 neurons, respectively. Significant age-dependent differences emerged in both acute and chronic responses to MPD. As the MPD dose increased, a greater number of rats and LC neurons exhibited altered activity. Notably, some animals displayed behavioral and neuronal sensitization at all MPD doses, whereas others exhibited tolerance. These effects varied significantly between age and MPD groups in both magnitude and incidence. Furthermore, Baseline (BL) LC activity following the six-day MPD regimen and after the washout period (ED10) was markedly altered, particularly in adolescents, indicating withdrawal-related changes. These shifts in BL activity from ED1 to ED10 indicate the presence of withdrawal behavior. This study highlights clear age-dependent differences in response to chronic MPD exposure. The observed patterns of sensitization, tolerance, and withdrawal serve as potential experimental biomarkers for drug dependence, emphasizing the clinical relevance of these findings. Importantly, the results underscore the value of combining electrophysiological and behavioral analyses and reaffirm the central role of the LC and NE signaling in mediating MPD’s effects, with distinct implications for adolescent and adult populations

Effects of methylphenidate on mitochondrial dynamics and bioenergetics in the prefrontal cortex of juvenile rats are sex-dependent

A total of 3102 neurons were recorded before and following acute and chronic methylphenidate (MPD) administration. Acute MPD exposure elicits mainly increases in neuronal and behavioral activity in dose-response characteristics. The response to chronic MPD exposure, as compared to acute 0.6, 2.5, or 10.0 mg/kg MPD administration, elicits electrophysiological and behavioral sensitization in some animals and electrophysiological and behavioral tolerance in others when the neuronal recording evaluations were performed based on the animals' behavioral responses, or amount of locomotor activity, to chronic MPD exposure. The majority of neurons recorded from those expressing behavioral sensitization responded to chronic MPD with further increases in firing rate as compared to the initial MPD responses. The majority of neurons recorded from animals expressing behavioral tolerance responded to chronic MPD with decreases in their firing rate as compared to the initial MPD exposures. Each of the six brain areas studied-the ventral tegmental area, locus coeruleus, dorsal raphe, nucleus accumbens, prefrontal cortex, and caudate nucleus (VTA, LC, DR, NAc, PFC, and CN)-responds significantly (p < 0.001) differently to MPD, suggesting that each one of the above brain areas exhibits different roles in the response to MPD. Moreover, this study demonstrates that it is essential to evaluate neuronal activity responses to psychostimulants based on the animals' behavioral responses to acute and chronic effects of the drug from several brain areas simultaneously to obtain accurate information on each area's role in response to the drug.

Currently, methylphenidate (MPD) is one of the most commonly prescribed psychostimulants for management and treatment of attention deficit hyperactivity disorder (ADHD). A rise in the consumption of MPD by “ordinary” youth and adults prompted concern regarding the ontogeny effects of acute and chronic MPD exposure. The objective of this study is to concomitantly record behavioral and neuronal activity from the dorsal raphe (DR) nucleus, a major source of serotonergic innervation in the mammalian brain before and following different doses of acute and chronic administration of MPD in freely behaving adolescent (young) and adult rats previously implanted with electrodes in the DR. A wireless recording system over 10 consecutive experimental days was used. Four experimental groups were used: saline, 0.6, 2.5, and 10.0 mg/kg MPD for young and similar groups for adult rats. Animals received one daily MPD injection on experimental days 1-6, followed by three washout days, and then drug rechallenge on experimental day 10 (ED10). 860 DR units were recorded, 356 from adult rats and 504 from young rats. The study provides experimental evidence that the responses to acute and chronic MPD were significantly different between the two age groups. Moreover, the study implies that it is essential to evaluate the electrophysiological responses to a drug based on the animal’s behavioral response to chronic drug exposure and that the DR and serotonin signaling has a significant role in the response to MPD as well as a different role in young as compared to adult rats.

Effects of methylphenidate on femoral bone growth in male rats.

Methylphenidate (MPH) is among the main drugs prescribed to treat patients with attention-deficit and hyperactivity disease (ADHD). MPH blocks both the norepinephrine and dopamine reuptake transporters (NET and DAT, respectively). Our study was aimed at further understanding the mechanisms by which MPH could modulate neurotransmitter efflux, using ex vivo radiolabelled neurotransmitter assays isolated from rats. Here, we observed significant dopamine and norepinephrine efflux from the prefrontal cortex (PFC) after MPH (100 µM) exposure. Efflux was mediated by both dopamine and norepinephrine terminals. In the striatum, MPH (100 µM) triggered dopamine efflux through both sodium- and vesicular-dependent mechanisms. Chronic MPH exposure (4 mg/kg/day/animal, voluntary oral intake) for 15 days, followed by a 28-day washout period, increased the firing rate of PFC pyramidal neurons, assessed by in vivo extracellular single-cell electrophysiological recordings, without altering the responses to locally applied NMDA, via micro-iontophoresis. Furthermore, chronic MPH treatment resulted in decreased efficiency of extracellular dopamine to modulate NMDA-induced firing activities of medium spiny neurons in the striatum, together with lower MPH-induced (100 µM) dopamine outflow, suggesting desensitization to both dopamine and MPH in striatal regions. These results indicate that MPH can modulate neurotransmitter efflux in brain regions enriched with dopamine and/or norepinephrine terminals. Further, long-lasting alterations of striatal and prefrontal neurotransmission were observed, even after extensive washout periods. Further studies will be needed to understand the clinical implications of these findings.

Adolescent rats respond differently to methylphenidate as compared to adult rats- concomitant VTA neuronal and behavioral Recordings

Methylphenidate (MPH) is the most commonly prescribed drug for the treatment of ADHD in males and females. However, a majority of previous studies investigated the effect of MPH in only males, and little is known regarding consequences of female exposure to MPH. This is unfortunate because the few studies that have been conducted indicate that females have a greater sensitivity to MPH. Previous research in male mice has shown that chronic exposure to MPH causes dopaminergic neurons within the nigrostriatal pathway to be more sensitive to the Parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). However, estrogen has been shown to protect dopaminergic neurons from MPTP neurotoxicity. Therefore, in this study, we test the hypothesis that chronic MPH exposure in female mice will render dopaminergic neurons in the nigrostriatal pathway more sensitive to MPTP, and that estrogen may play a protective role. Interestingly, proestrus females exhibited greater sensitivity to MPTP, with significantly reduced dopaminergic neurons in the SN and significant increases in DA quinone production. Chronic MPH exposure contributed to GSH depletion, but surprisingly, it did not increase dopamine quinone levels or dopaminergic cell loss. There were no significant differences in anestrus animals, with the exception of a depletion in GSH seen when animals received chronic high-dose (10mg/kg) MPH followed by MPTP. Thus, estrogen may actually sensitize neurons to MPTP in this model, and chronic MPH may contribute to GSH depletion within the striatum. This study provides insight into how chronic psychostimulant use may affect males and females differently.

The prefrontal cortex and the caudate nucleus respond conjointly to methylphenidate (Ritalin). Concomitant behavioral and neuronal recording study

Chronic methylphenidate induces increased quinone production and subsequent depletion of the antioxidant glutathione in the striatum.

Glutamate and dopamine in the VTA participate differently in the acute and chronic effect of methylphenidate

Glutaminergic signaling in the caudate nucleus is required for behavioral sensitization to methylphenidate

The psychostimulant methylphenidate (MPD) is the most common medication used in treating ADHD in children. Studies have shown an increasing prevalence among adolescents without ADHD to take MPD as a cognitive booster and recreational drug, even though it is a Schedule II drug and has a high potential for abuse. The objective of this study is to explore if there is an association between the animals' behavioral and neurophysiological responses to acute and/or chronic methylphenidate exposure within the ventral tegmental area and the nucleus accumbens, and to compare how these two brain structures fire in response to methylphenidate. Freely moving adolescent rats implanted with semimicroelectrodes within the VTA and NAc were divided into three MPD dosing groups: 0.6, 2.5, and 10mg/kg i.p., as well as a saline control group. The animals were divided into two groups based on their behavioral responses to chronic MPD, behavioral sensitization and tolerance, and the neuronal responses of the two groups were compared for each MPD dosing. Significant differences in the proportion of neuronal units in the VTA and NAc responding to MPD were observed at the 0.6 and 10.0mg/kg MPD dosing groups. Moreover, the same doses of 0.6, 2.5, and 10.0mg/kg MPD elicited behavioral sensitization in some animals and behavioral tolerance in others. This specific study shows that the VTA and NAc neurons respond differently to the same doses of MPD. MPD has different neuronal and behavioral effects depending on the individual, the dosage of MPD, and the brain structure studied.

Background:Whether long-term methylphenidate (MPH) results in any changes in cardiovascular function or structure can only be properly addressed through a randomized trial using an animal model which permits elevated dosing over an extended period of time.Methods:We studied 28 male rhesus monkeys (M. mulatta) approximately seven years of age who had been randomly assigned to one of three MPH dosages: vehicle control (0 mg/kg, bid, n = 9), low-dose (2.5 mg/kg, bid, n = 9), or high-dose (12.5 mg/kg, bid, n = 10). Dosage groups were compared on serum cardiovascular and inflammatory biomarkers, electrocardiograms (ECG), echocardiograms, myocardial biopsies, and clinical pathology parameters following five years of uninterrupted dosing.Results:With the exception of serum myoglobin, there were no statistical differences or apparent dose response trends in clinical pathology, cardiac inflammatory biomarkers, ECG’s echocardiograms, or myocardial biopsies. The high-dose MPH group had a lower serum myoglobin concentration (979 ng/ml) than either the low dose (1882 ng/ml) or control group (2182 ng/ml). The dose response was inversely proportional to dosage (P = .0006).Conclusions:Although the findings cannot be directly generalized to humans, chronic MPH exposure is unlikely to be associated with increased cardiovascular risk in healthy children.

Exposure to methylphenidate in adolescence and adulthood modulates cross-sensitization to amphetamine in adulthood in three genetically variant female rat strains

Concomitant behavioral and prefrontal cortex neuronal responses following acute and chronic methylphenidate exposure in adolescent and adult rats

Methylphenidate is a psychostimulant used to treat attention deficit hyperactivity disorder. Neurogenesis occurs throughout adulthood within the dentate gyrus of the hippocampus and can be altered by psychoactive medications; however, the impact of methylphenidate on neurogenesis is not fully understood. We investigated the effects of chronic low (1mg/kg) and high (10mg/kg) intraperitoneal doses of methylphenidate on neurogenesis in mouse hippocampus following 28 days and 56 days of treatment. Interestingly, methylphenidate, at both doses, increased neurogenesis. However, if methylphenidate treatment was not continued, the newly generated cells did not survive after 28 days. If treatment was continued, the newly generated neurons survived only in the mice receiving low-dose methylphenidate. To investigate the mechanism for this effect, we examined levels of proteins linked to cell proliferation in the hippocampus, including brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF), tropomyosin receptor kinase B (TrkB), and beta-catenin. BDNF or GDNF levels were not significantly different between groups. However, hippocampal VEGF, TrkB, and beta-catenin were significantly increased in mice receiving low-dose methylphenidate for 28 days compared to controls. Interestingly, high-dose methylphenidate significantly decreased beta-catenin after 28 days and decreased VEGF, beta-catenin, and TrkB after 56 days compared to controls. Thus, low-dose methylphenidate appears to increase cell proliferation and cell survival in the hippocampus, and these effects may be mediated by increase in VEGF, TrkB, and beta-catenin. While high dose methylphenidate may initially increase neuronal proliferation, newly generated neurons are unable to survive long-term, possibly due to decrease in VEGF, TrkB and beta-catenin.

Caudate nucleus neurons participate in methylphenidate function: Behavioral and neuronal recordings from freely behaving adolescent rats

The objective of this study is to gain insight into the behavioral and neuronal changes induced by acute and chronic methylphenidate (MPD) administration. Specifically, there is limited knowledge of the effects of MPD on the locus coeruleus (LC), the main site of norepinephrine synthesis in the brain. In this study, LC neuronal firing rate was recorded simultaneously with locomotor activity in freely moving adolescent rats. Adolescent rats were chosen to mimic the age group in humans most affected by MPD exposure. Following acute dose of 0.6, 2.5 or 10mg/kg MPD, all rats showed an increase in locomotor activity. However, in response to chronic MPD doses, individual rats showed either a further increase or decrease in their locomotor activity as compared to the effect initiated by the acute dose-expressing either behavioral sensitization or tolerance, respectively. The LC neuronal recordings from animals expressing behavioral sensitization showed that the majority of units responded to chronic MPD exposure by further increasing firing rates as compared to the initial response to the acute MPD exposure. For the LC neuronal units recorded from animals expressing behavioral tolerance, however, the majority of the units responded to chronic exposure by attenuating or no significant effect on their firing rate as compared to the acute MPD exposure. This observation indicates a correlation between the LC neuronal responses and behavioral activity to chronic MPD exposure. The study shows that LC participates in the effect of MPD and the behavioral expression of sensitization and tolerance to chronic exposure of MPD.

Methylphenidate (MPD), also known as Ritalin, is a psychostimulant used to treat attention deficit hyperactivity disorder. However, it is increasingly being misused by normal adolescents for recreation and academic advantage. Therefore, it is important to elucidate the behavioral and neurophysiological effects of MPD in normal subjects. MPD inhibits the reuptake of catecholamines, mainly found in the ventral tegmental area (VTA) and locus coeruleus (LC). The VTA and LC normally mediate attention, motivation, and drug reward behaviors. Selective neuronal connections between the VTA and LC have been identified implicating regular interaction between the structures. The objective of this study was to compare the neuronal responses of the VTA and LC to MPD in normal adolescent rats. Animals were implanted with permanent electrodes in the VTA and LC, and neuronal units were recorded following acute and repetitive (chronic) saline or 0.6, 2.5, or 10.0 mg/kg MPD exposure. Animals displayed either behavioral sensitization or tolerance to all three doses of MPD. Acute MPD exposure elicited excitation in the majority of all VTA and LC units. Chronic MPD exposure elicited a further increase in VTA and LC neuronal activity in animals exhibiting behavioral sensitization and an attenuation in VTA and LC neuronal activity in animals exhibiting behavioral tolerance, demonstrating neurophysiological sensitization and tolerance, respectively. The similar pattern in VTA and LC unit activity suggests that the two structures are linked in their response to MPD. These results may help determine the exact mechanism of action of MPD, resulting in optimized treatment of patients.NEW & NOTEWORTHY The same dose of 0.6, 2.5, and 10 mg/kg methylphenidate (MPD) elicits either behavioral sensitization or tolerance in adolescent rats. There is a direct correlation between the ventral tegmental area (VTA) and locus coeruleus (LC) neuronal response to chronic MPD exposure. Both the VTA and LC are involved in the behavioral and neurophysiological effects of chronic MPD.