NMDA receptor antagonist disrupts acute and chronic effects of methylphenidate

What are the consequences of Methylphenidate exposure for maternally separated rats?

Methylphenidate (MPH) abuse is prevalent among youth. Drug abuse results in pain perception. We sought to investigate whether Maternal separation (MS) prone to MPH addiction. The next question was whether MPH abusers with MS differ in pain perception. We investigated the impact of MS on addiction and drug reward as well as pain perception following 5 days of MPH injection in males and females rats. Initially, rats underwent MS protocol of 3 hr daily for 21 days. Conditioned place preference (CPP) test was an attempt to investigate whether MS rats experience more reward with MPH. The protocol consisted of 10 min habituation on Day 1, conditioning on Day 2-Day 6 (5 mg per kg MPH injection in drug compartment and saline in saline compartment with 4 hr gap between injections) and 10 min test on Day 7. Furthermore, using another group, differences in pain perception were investigated after 5 days of daily MPH injection with 5 mg per kg. Sensory pain sensitivity was tested on PND 39 using tail flick and hotplate in MS and control groups with and without MPH exposure. Results indicated that female rats are equally prone to addiction in CPP. On the other hand, MS males experience a higher reward in CPP. In tail flick test, female MS rats exposed to MPH show a lower sensory pain threshold with similar MPH exposure. Experiencing MPH similarly declined hotplate pain perception in MS and controls in the females. Males, on the other hand, did not show any difference in sensory pain tests. According to results one can argue MS is detrimental. MS males experience more reward with MPH, females are equally addiction prone and MS females experience more pain in tail flick. On the other hand pain threshold can decline in hotplate test for both control and MS females that received MPH.

Association of the GRIN2B rs2284411 polymorphism with methylphenidate response in attention-deficit/hyperactivity disorder

OBJECTIVE

We investigated the possible association between two NMDA subunit gene polymorphisms (GRIN2B rs2284411 and GRIN2A rs2229193) and treatment response to methylphenidate (MPH) in attention-deficit/hyperactivity disorder (ADHD).

METHODS

A total of 75 ADHD patients aged 6-17 years underwent 6 months of MPH administration. Treatment response was defined by changes in scores of the ADHD-IV Rating Scale (ADHD-RS), clinician-rated Clinical Global Impression-Improvement (CGI-I), and Continuous Performance Test (CPT). The association of the GRIN2B and GRIN2A polymorphisms with treatment response was analyzed using logistic regression analyses.

RESULTS

The GRIN2B rs2284411 C/C genotype showed significantly better treatment response as assessed by ADHD-RS inattention ( p=0.009) and CGI-I scores ( p=0.009), and there was a nominally significant association in regard to ADHD-RS hyperactivity-impulsivity ( p=0.028) and total ( p=0.023) scores, after adjusting for age, sex, IQ, baseline Clinical Global Impression-Severity (CGI-S) score, baseline ADHD-RS total score, and final MPH dose. The GRIN2B C/C genotype also showed greater improvement at the CPT response time variability ( p<0.001). The GRIN2A G/G genotype was associated with a greater improvement in commission errors of the CPT compared to the G/A genotype ( p=0.001).

CONCLUSIONS

The results suggest that the GRIN2B rs2284411 genotype may be an important predictor of MPH response in ADHD.

Psychostimulants and atomoxetine alter the electrophysiological activity of prefrontal cortex neurons, interaction with catecholamine and glutamate NMDA receptors

RATIONALE

Attention-deficit hyperactivity disorder (ADHD) is the most frequently diagnosed neuropsychiatric disorder in childhood. Currently available ADHD drugs include the psychostimulants methylphenidate (MPH) and D-amphetamine (D-AMP), acting on norepinephrine and dopamine transporters/release, and atomoxetine (ATX), a selective norepinephrine uptake inhibitor. Recent evidence suggests an involvement of glutamate neurotransmission in the pathology and treatment of ADHD, via mechanisms to be clarified.

OBJECTIVE

We have investigated how ADHD drugs could modulate, through interaction with catecholamine receptors, basal and glutamate-induced excitability of pyramidal neurons in the prefrontal cortex (PFC), a region which plays a major role in control of attention and impulsivity.

METHODS

We have used the technique of extracellular single-unit recording in anaesthetised rats coupled with microiontophoresis.

RESULTS

Both MPH (1-3 mg/kg) and D-AMP (1-9 mg/kg) increased the firing activity of PFC neurons in a dopamine D1 receptor-dependent manner. ATX administration (1-6 mg/kg) also increased the firing of neurons, but this effect is not significantly reversed by D1 (SCH 23390) or alpha1 (prazosin) receptor antagonists but potentiated by alpha2 antagonist (yohimbine). All drugs induced a clear potentiation of the excitatory response of PFC neurons to the microiontophoretic application of the glutamate agonist N-methyl-D-aspartate (NMDA), but not to the glutamate agonist α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). The potentiating effect of D-AMP on NMDA-induced activation of PFC neurons was partially reversed or prevented by dopamine D1 receptor blockade.

CONCLUSION

Our data shows that increase in excitability of PFC neurons in basal conditions and via NMDA receptor activation may be involved in the therapeutic response to ADHD drugs.

Single exposure of dopamine D1 antagonist prevents and D2 antagonist attenuates methylphenidate effect

Methylphenidate (MPD) is a readily prescribed drug for the treatment of attention deficit hyperactivity disorder (ADHD) and moreover is used illicitly by youths for its cognitive-enhancing effects and recreation. MPD exposure in rodents elicits increased locomotor activity. Repetitive MPD exposure leads to further augmentation of their locomotor activity. This behavioral response is referred to as behavioral sensitization. Behavioral sensitization is used as an experimental marker for a drug’s ability to elicit dependence. There is evidence that dopamine (DA) is a key player in the acute and chronic MPD effect; however, the role of DA in the effects elicited by MPD is still debated. The objective of this study was to investigate the role of D1 and/or D2 DA receptors in the acute and chronic effect of MPD on locomotor activity. The study lasted for 12 consecutive days. Seven groups of male Sprague Dawley^® rats were used. A single D1 or D2 antagonist was given before and after acute and chronic MPD administration. Single injection of D1 DA antagonist was able to significantly attenuate the locomotor activity when given prior to the initial MPD exposure and after repetitive MPD exposure, while the D2 DA antagonist partially attenuated the locomotor activity only when given before the second MPD exposure. The results show the role, at least in part, of the D1 DA receptor in the mechanism of behavioral sensitization, whereas the D2 DA receptor only partially modulates the response to acute and chronic MPD.

Behavioral and dorsal raphe neuronal activity following acute and chronic methylphenidate in freely behaving rats

Concomitant behavioral and dorsal raphe (DR) neuronal activity were recorded following acute and chronic dose response of methylphenidate (MPD) in freely moving rats previously implanted with permanent semi-microelectrodes using telemetric (wireless) technology. On experimental day (ED) 1, the neuronal and locomotor activity were recorded after saline (baseline) and MPD (0.6, 2.5 or 10.0mg/kg) injection (i.p.). Animals were injected daily with a single dose of MPD for five consecutive days (ED 2-6) to elicit behavioral sensitization or tolerance. After three washout days, the neuronal and locomotor activity recording was resumed on ED 10 followed by saline and MPD rechallenge injection. The main findings were: (1) the same dose of chronic MPD administration elicited behavioral sensitization in some animals and behavioral tolerance in others. (2) 46%, 56% and 73% of DR units responded to acute 0.6, 2.5 and 10.0mg/kg MPD respectively. (3) 89%, 70% and 86% of DR units changed their baseline activity on ED 10 compared to that on ED 1 in the 0.6, 2.5 and 10.0mg/kg MPD groups respectively. (4) A significant difference in ED 10 baseline activity was observed in the DR neuronal population recording from animals expressing behavioral sensitization compared to that of animals expressing behavioral tolerance. (5) 89%, 78% and 88% of DR units responded to chronic 0.6, 2.5 and 10.0mg/kg MPD respectively. (6) The DR neuronal population recording following acute MPD on ED 1 and rechallenge MPD on ED 10 from animals expressing behavioral sensitization was significantly different from the neuronal population recorded from animals exhibited behavioral tolerance. The correlation between the DR neuronal activity and animal's behavior following chronic MPD exposure suggested that the DR neuronal activity may play an important role in the expression of behavioral sensitization and tolerance induced by chronic MPD administration.

Adult female rats' altered diurnal locomotor activity pattern following chronic methylphenidate treatment

Methylphenidate (MPD) is one of the most prescribed pharmacological agents, which is also used for cognitive enhancement and recreational purposes. The objective of this study was to investigate the repetitive dose-response effects of MPD on circadian rhythm of locomotor activity pattern of female WKY rats. The hypothesis is that a change in the circadian activity pattern indicates a long-lasting effect of the drug. Four animal groups (saline control, 0.6, 2.5, and 10.0 mg/kg MPD dose groups) were housed in a sound-controlled room at 12:12 light/dark cycle. All received saline injections on experimental day 1 (ED 1). On EDs 2-7, the control group received saline injection; the other groups received 0.6, 2.5, or 10.0 mg/kg MPD, respectively. On ED 8-10, injections were withheld. On ED 11, each group received the same dose as EDs 2-7. Hourly histograms and cosine statistical analyses calculating the acrophase (ϕ), amplitude (A), and MESOR (M) were applied to assess the 24-h circadian activity pattern. The 0.6 and 2.5 mg/kg MPD groups exhibited significant (p < 0.05) change in their circadian activity pattern on ED 11. The 10.0 mg/kg MPD group exhibited tolerance on ED 11 and also a significant change in activity pattern on ED 8 compared to ED 1, consistent with withdrawal behavior (p < 0.007). In conclusion, chronic MPD administration alters circadian locomotor activity of adult female WKY rats and confirms that chronic MPD use elicits long-lasting effects.

Dorsal raphe neuronal activities are modulated by methylphenidate

This study investigated the electrophysiological properties of the dorsal raphe nucleus (DR) neurons in response to the acute and repetitive administration of methylphenidate (MPH). Activities of DR neurons were recorded from non-anesthetized, freely behaving rats previously implanted bilaterally with permanent semi microelectrodes. The main findings were: (1) after initial (acute) administration of MPH (2.5 mg/kg i.p.) on experimental day one (ED1), 56 % of DR units significantly changed their firing rates. The majority of the responsive units (88 %) exhibited increased firing rate; (2) daily MPH injections were given on ED2 through ED6 followed by 3 washout days. On ED10, 83 % of the DR units significantly changed their baseline activity compared to the baseline activity on ED1; (3) after rechallenge MPH administration on ED10, 63 % of DR units exhibited significant change in their firing rate; the majority of the responsive units (76 %) exhibited a significant increase in their firing rate; (4) The effect of rechallenge MPH administration on ED10 was compared to the effect of initial MPH on ED1, 47 % DR units exhibited a further significant increase in their firing rate while 53 % DR units exhibited decrease or non-change in their firing rate which can be interpreted as electrophysiological sensitization or tolerance. In conclusion, this study demonstrated that acute MPH administration modulated the DR neuronal activities. Repetitive MPH administration modulated the baseline activities of DR units and elicited neurophysiological sensitization or tolerance. The results indicated that MPH affects DR neuronal activity.

Methylphenidate enhances NMDA-receptor response in medial prefrontal cortex via sigma-1 receptor: a novel mechanism for methylphenidate action

Methylphenidate (MPH), commercially called Ritalin or Concerta, has been widely used as a drug for Attention Deficit Hyperactivity Disorder (ADHD). Noteworthily, growing numbers of young people using prescribed MPH improperly for pleasurable enhancement, take high risk of addiction. Thus, understanding the mechanism underlying high level of MPH action in the brain becomes an important goal nowadays. As a blocker of catecholamine transporters, its therapeutic effect is explained as being due to proper modulation of D1 and α2A receptor. Here we showed that higher dose of MPH facilitates NMDA-receptor mediated synaptic transmission via a catecholamine-independent mechanism, in layer V∼VI pyramidal cells of the rat medial prefrontal cortex (PFC). To indicate its postsynaptic action, we next found that MPH facilitates NMDA-induced current and such facilitation could be blocked by σ1 but not D1/5 and α2 receptor antagonists. And this MPH eliciting enhancement of NMDA-receptor activity involves PLC, PKC and IP3 receptor mediated intracellular Ca(2+) increase, but does not require PKA and extracellular Ca(2+) influx. Our additional pharmacological studies confirmed that higher dose of MPH increases locomotor activity via interacting with σ1 receptor. Together, the present study demonstrates for the first time that MPH facilitates NMDA-receptor mediated synaptic transmission via σ1 receptor, and such facilitation requires PLC/IP3/PKC signaling pathway. This novel mechanism possibly explains the underlying mechanism for MPH induced addictive potential and other psychiatric side effects.

Methylphenidate modulates the locus ceruleus neuronal activity in freely behaving rat

The electrophysiological properties of the locus coeruleus (LC) neurons in response to acute and chronic administration of methylphenidate (MPD) were investigated. The extracellular LC neuronal activities were recorded from non-anesthetized, freely behaving rats previously implanted bilaterally with permanent semi microelectrodes. The main findings were: (1) On experimental day 1 (ED1), 87% (94/108) of LC units significantly changed their firing rate after initial (acute) MPD (2.5mg/kg, i.p.) administration. The majority of the responsive units (80%, 75/94) increased their firing rate; (2) Daily MPD (2.5mg/kg) injection was given on ED2 through ED6 followed by 3 washout days (ED7 to 9). On ED10, all LC units exhibited a significant change of their baseline activity compared to their baseline activity on ED1; (3) MPD rechallenge on ED10 elicits 94% (101/108) of LC units significantly changed their firing rate; the majority of them (78%, 79/101) increased their firing rate; (4) The effect of rechallenge MPD administration on ED10 were compared to the effect of initial MPD on ED1, 98% of the LC units exhibited a significant change in their firing rate. 41% (43/106) of them exhibited a significant increase in their firing rate while 59% (63/106) units significantly decreased their firing rate which can be interpreted as electrophysiological sensitization or tolerance respectively. In conclusion, the majority of LC neurons significantly increased their firing rate after acute and chronic MPD administration. This data demonstrated that enhanced LC neuronal activities play important role in the effect of MPD.

Acute and chronic methylphenidate alters prefrontal cortex neuronal activity recorded from freely behaving rats

Today's students around the world are striking deals to buy and sell the drug methylphenidate (MPD) for cognitive enhancement. Our knowledge on the effects of MPD on the brain is very limited. The present study was designed to investigate the acute and chronic effect of MPD on the prefrontal cortex (PFC) neurons. On experimental day 1 (ED1) recordings were obtained following saline injections and after 2.5 mg/kg MPD. On ED2 through ED6, daily single 2.5 mg/kg MPD was given followed by 3 washout days (ED7 to 9). On ED10, neuronal recordings were resumed from the same animal after saline and MPD injection similar to that obtained at ED1. Ninety PFC units were recorded, all responded to the initial MPD injection, 66 units (73%) increased their activity at ED10. Recordings were resumed for the 66 units that increased their firing rate at ED1, and following MPD injection 54 units (82%) exhibited significant increases in their baseline firing rates compared to ED1 baseline. When these 54 units were rechallenged (chronic effect) with MPD, 39/54 (72%) exhibited reduction in their firing rate which can be interpreted as tolerance. From the 24 (27%) units that responded to MPD at ED1 by decreasing their activity, 14 units (58%) exhibited a decrease in their baseline firing rates at ED10 compared to ED1 baseline. However, following MPD rechallenge of these 14 units, 11 units (79%) exhibited an increase in their firing rate which is interpreted as sensitization. In conclusion, all PFC units modified their neural baseline activity.

Nucleus accumbens lesions modulate the effects of methylphenidate

The psychostimulant methylphenidate (MPD, Ritalin) is the prescribed drug of choice for treatment of ADHD. In recent years, the diagnosis rate of ADHD has increased dramatically, as have the number of MPD prescriptions. Repeated exposure to psychostimulants produces behavioral sensitization in rats, an experimental indicator of a drug's potential liability. In studies on cocaine and amphetamine, this effect has been reported to involve the nucleus accumbens (NAc), one of the nuclei belonging to the motive circuit. The aim of this study was to investigate the role of the NAc on the expression of behavioral sensitization as a response to MPD exposure. In the present study, 20 male Sprague-Dawley rats were divided randomly into three groups: an intact control group, a sham-operated group, and a NAc bilateral electrical lesion group. Locomotor activity was assessed for the first 2h following 2.5mg/kg MPD injection, using open field monitoring systems. Recordings were made during 6 days of continuous MPD administration, and then upon re-challenge with the same dose following 3 days of washout. Acute MPD exposure elicited an increase in locomotor activity in all three groups. However, the NAc lesion group exhibited significantly increased locomotor activity in comparison to sham and control groups. Chronic MPD did not elicit sensitization in the NAc lesion group, while both sham and control groups did exhibit behavioral sensitization to repetitive MPD administration. These findings suggest that the NAc plays a significant role in eliciting locomotor activity as an acute effect of MPD, and in the expression of sensitization due to chronic MPD exposure.

MDMA (ecstasy) modulates locomotor and prefrontal cortex sensory evoked activity

Ingestion of 3, 4-methylenedioxymethamphetamine (MDMA) leads to heightened response to sensory stimulation; thus, MDMA is referred to as "ecstasy" because it produces pleasurable enhancement of such sensation. There have been no electrophysiological studies that report the consequences of MDMA on sensory input. The present study was initiated to study the effects of acute and chronic MDMA on locomotor activity and sensory evoked field potential from freely behaving rats previously implanted with permanent electrodes in the prefrontal cortex (PFC). The main findings of this study are that: (1) acute MDMA augments locomotor behavior and attenuates the incoming sensory input, (2) chronic treatment of MDMA elicits behavioral sensitization, (3) chronic administration of MDMA results in attenuation of the baseline activity of the sensory evoked field potential, and (4) administration of rechallenge MDMA result in enhancement of the PFC sensory evoked field potential.

METHYLPHENIDATE (RITALIN): BEHAVIORAL STUDIES IN THE RAT

Attention Deficit Hyperactivity Disorder (ADHD) is a neuropsychiatric syndrome with an onset in childhood characterized by an inability to remain focused or to concentrate for prolonged periods of time. Children suffering from this disease are many times described as either inattentive or as hyperactive-impulsive depending on what form of the disease they manifest. Methylphenidate is the preferred treatment for this behavioral disorder and is used for long term disease management. Much still remains unknown concerning this stimulant and its effects on behavior and future abuse potential are pertinent questions. Since animal models are used to study the mechanism of drug action and rats are used often in drug studies, the objective of this review is to summarize the research reports that mainly have used rats as the model to investigate the action of methylphenidate. Topics discussed in this review include: (1) What effect does a single dose of methylphenidate have on locomotion activity; (2) Does repeated administration of methylphenidate result in tolerance or sensitization; and (3) Does methylphenidate have rewarding properties as measured by the self-administration and condition placed preference paradigms.

Methylphenidate improves cue navigation in the Morris water maze in rats

Despite its still rapidly increasing use in the treatment of the attention deficit/hyperactivity disorder, the effects of methylphenidate on behavior and learning are not yet fully understood. We have used the Morris water maze to study effects of methylphenidate (1 mg/kg) on target-oriented behavior and visuospatial learning in young rats. Although the relatively low dose of 1 mg/kg methylphenidate changed the behavior in the Morris water maze when the goal was visible, reducing times to reach the visible platform, learning of the position of the hidden platform, was not influenced, nor was 'relearning' after shifting the position of the platform. These results indicate that methylphenidate can influence goal-oriented behavior at doses that do not change visuospatial learning.

Acute and chronic methylphenidate dose-response assessment on three adolescent male rat strains

Methylphenidate (MPD), commonly known as Ritalin, is the most frequently prescribed drug to treat children and adults with attention deficit hyperactivity disorder (ADHD). Adolescence is a period of development involving numerous neuroplasticities throughout the central nervous system (CNS). Exposure to a psychostimulant such as MPD during this crucial period of neurodevelopment may cause transient or permanent changes in the CNS. Genetic variability may also influence these differences. Thus, the objective of the present study was to determine whether acute and chronic administration of MPD (0.6, 2.5, or 10.0mg/kg, i.p.) elicit effects among adolescent WKY, SHR, and SD rats and to compare whether there were strain differences. An automated, computerized, open-field activity monitoring system was used to study the dose-response characteristics of acute and repeated MPD administration throughout the 11-day experimental protocol. Results showed that all three adolescent rat groups exhibited dose-response characteristics following acute and chronic MPD administration, as well as strain differences. These strain differences depended on the MPD dose and locomotor index. Chronic treatment of MPD in these animals did not elicit behavioral sensitization, a phenomenon described in adult rats that is characterized by the progressive augmentation of the locomotor response to repeated administration of the drug. These results suggest that the animal's age at time of drug treatment and strain/genetic variability play a crucial role in the acute and chronic effect of MPD and in the development of behavioral sensitization.