Effect of methylphenidate on motivation in children with attention-deficit/hyperactivity disorder

The effects of methylphenidate (MPH) on motivation were examined using a progressive ratio (PR) task in children who were prescribed MPH for the treatment of ADHD. Twenty-one children, 7 to 12 years of age, completed two test sessions, one under the effects of medication and one not. During each session, children pressed a lever to earn nickel reinforcers, where the first press resulted in a reinforcer and 10 additional presses were required for each subsequent reinforcer. Children on MPH had a significantly higher breakpoint than when off medication. This MPH-associated increase in the breakpoint manifested as a significant decrease in the interresponse times (IRT). Further, MPH administration resulted in a significant decrease in IRT variability. In contrast, MPH administration had no significant effects on the means and variability of postreinforcement pause duration. These results suggest that MPH increased motivation in children being treated for ADHD. Further, the inability of MPH to significantly reduce postreinforcement pause duration while simultaneously decreasing IRTs suggests that while MPH may increase motivation to perform an ongoing task, it may have little effect on the initiation of that task.     

Acute tryptophan depletion and self-injurious behavior in aggressive patients and healthy volunteers

Rationale  An association between serotonin (5-HT) activity and self-injurious (i.e., self-aggressive) behavior across the spectrum of lethality (from self-mutilation through completed suicide) is a well-replicated finding. Studies to date, however, have relied on nonexperimental designs to examine this relationship, limiting the causal inferences that can be drawn about the role of 5-HT in self-aggressive behavior. Objective  Examine the effect of experimentally altered 5-HT activity (via dietary tryptophan depletion) on self-aggressive behavior among adults with and without intermittent explosive disorder (IED). Individuals with a marked history of aggression, such as those with IED, are characterized by compromised 5-HT and heightened risk for self-aggression, making this a population of interest for examining the proposed relations. Materials and methods  IED patients (n = 16) and healthy controls (n = 16) received a tryptophan depletion and a placebo drink on separate days at least 1 week apart. Self-aggressive behavior was assessed on both study days using a well-validated laboratory-based behavioral assessment with self-aggression defined as the intensity of shock self-administered. Results  Tryptophan depletion facilitated selection of more intense shocks, on average, in both groups. Patients with IED were also more self-aggressive overall than healthy volunteers. No IED by drink condition interactions were found. Conclusion  Experimentally lowered 5-HT bioavailability enhances overall self-injurious behavior irrespective of aggression history.

Identification of Novel Specific and General Inhibitors of the Three Major Human ATP-Binding Cassette Transporters P-gp,BCRP and MRP2 Among Registered Drugs

Purpose  To study the inhibition patterns of the three major human ABC transporters P-gp (ABCB1), BCRP (ABCG2) and MRP2 (ABCC2), using a dataset of 122 structurally diverse drugs. Methods  Inhibition was investigated in cellular and vesicular systems over-expressing single transporters. Computational models discriminating either single or general inhibitors from non-inhibitors were developed using multivariate statistics. Results  Specific (n = 23) and overlapping (n = 19) inhibitors of the three ABC transporters were identified. GF120918 and Ko143 were verified to specifically inhibit P-gp/BCRP and BCRP in defined concentration intervals, whereas the MRP inhibitor MK571 was revealed to inhibit all three transporters within one log unit of concentration. Virtual docking experiments showed that MK571 binds to the ATP catalytic site, which could contribute to its multi-specific inhibition profile. A computational model predicting general ABC inhibition correctly classified 80% of both ABC transporter inhibitors and non-inhibitors in an external test set. Conclusions  The inhibitor specificities of P-gp, BCRP and MRP2 were shown to be highly overlapping. General ABC inhibitors were more lipophilic and aromatic than specific inhibitors and non-inhibitors. The identified specific inhibitors can be used to delineate transport processes in complex experimental systems, whereas the multi-specific inhibitors are useful in primary ABC transporter screening in drug discovery settings. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Efficacy and safety of bifeprunox in patients with an acute exacerbation of schizophrenia: results from a randomized, double-blind, placebo-controlled, multicenter, dose-finding study

Rationale  Bifeprunox is a partial dopamine agonist with a unique receptor-binding profile and potential antipsychotic properties. Objectives  The current study evaluated the efficacy and safety of bifeprunox in patients with an acute exacerbation of schizophrenia. Materials and methods  In this 6-week, double-blind, placebo-controlled study, 589 patients were randomly assigned to once-daily treatment with bifeprunox 5, 10, or 20 mg, placebo, or risperidone 6 mg. Efficacy was assessed by changes in symptom rating scales [Positive and Negative Syndrome Scale (PANSS) total and subscale scores; PANSS-derived BPRS scores; Clinical Global Impression—Severity (CGI—S) and Clinical Global Impression—Improvement (CGI—I) scores]. Safety and tolerability were assessed by monitoring adverse events, extrapyramidal symptoms (EPS), laboratory values, electrocardiograms, prolactin levels, and weight. Results  Compared with placebo, bifeprunox 20 mg produced a statistically significantly greater reduction from baseline to last assessment in the primary efficacy variable (PANSS total score; effect size = −0.339), as well as most secondary efficacy measures. No statistically significant differences in efficacy were seen with lower doses of bifeprunox. The most common treatment-emergent adverse events (TEAEs) noted with bifeprunox were gastrointestinal; no clear dose-related trend in the incidence of any TEAE was observed in the bifeprunox groups. Compared to placebo, treatment with bifeprunox led to small but statistically significant decreases in weight and prolactin levels. EPS were comparable between bifeprunox and placebo. The active reference in this study, risperidone 6 mg, showed statistically significant differences from placebo for the primary efficacy parameter (effect size = −0.628) and all secondary efficacy parameters. Conclusions  These data suggest that 20 mg of bifeprunox may be efficacious in improving symptoms in patients with an acute exacerbation of schizophrenia. Bifeprunox appeared to be safe and well tolerated by patients in this 6-week study.

Assessing methylphenidate preference in ADHD patients using a choice procedure

Rationale Methylphenidate (MPH) is widely used in the treatment of attention deficit hyperactivity disorder (ADHD) and is associated with positive clinical effects across a wide range of domains. Despite the clinical effectiveness of MPH, concern has arisen with respect to its abuse potential.Objectives To assess MPH preference in adults diagnosed with ADHD using a choice procedure and to evaluate the relationship among drug preference, therapeutic efficacy, and abuse potential in a clinical sample.Methods Participants were ten volunteers (ages 18–22 years) with ADHD who were receiving MPH treatment. Preference was assessed using a double-blind choice procedure with four sampling sessions wherein subjects received either placebo or MPH and eight choice sessions when they chose either capsule or no capsules.Results Overall, MPH was chosen significantly more often than placebo ( ²=52.5; P<0.001) and participants were equally separated into groups of those who chose MPH reliably (MPH choosers) and those who did not (MPH non-choosers). MPH decreased ADHD symptoms and resulted in lower ratings of stimulant effects among MPH choosers. MPH choosers also reported higher levels of baseline ADHD symptoms.Conclusions Despite higher preference of MPH than placebo in this clinical sample, other measures of abuse potential were not elevated, and MPH choosers were more symptomatic than non-choosers. As such, MPH preference in ADHD populations likely reflects therapeutic efficacy rather than abuse potential. Future work should examine MPH choice in diagnosed and non-diagnosed populations to further explore the role of clinical efficacy in the preference of this stimulant drug.     

Response to cocaine, alone and in combination with methylphenidate, in cocaine abusers with ADHD

Attention deficit hyperactivity disorder (ADHD) is prevalent in adult cocaine abusers. Yet, it remains to be determined how the response to cocaine differs in cocaine abusers with ADHD compared to cocaine abusers without ADHD. Further, since ADHD is commonly treated with stimulants, such as methylphenidate (MPH), it is important to examine whether MPH maintenance alters the response to cocaine in cocaine abusers with ADHD. Thus, the first phase of this study compared the response to cocaine in adult cocaine abusers with ADHD to those without ADHD. The second phase assessed the effects of oral sustained-release methylphenidate (MPH-SR) maintenance (40 and 60 mg) on the response to cocaine only in those with ADHD. Cocaine abusers with ADHD (N=7) and without ADHD (N=7) who were not seeking treatment remained inpatient initially for 1 week, when the effects of cocaine alone were tested (Phase 1). Cocaine abusers with ADHD remained inpatient for an additional 3 weeks, during which the effects of cocaine during oral MPH-SR maintenance were tested (Phase 2). During cocaine fixed dosing sessions, participants received four injections of i.v. cocaine (0, 16 or 48 mg/70 kg), spaced 14 min apart. During cocaine choice sessions, participants had a choice between receiving i.v. cocaine (16 or 48 mg/70 kg) or two tokens, each exchangeable for 2 US dollars. Subjective effects related to ADHD symptoms (e.g. ratings of "Able to Concentrate") were significantly lower in cocaine abusers with ADHD compared to those without ADHD when placebo cocaine was administered. Active cocaine produced similar increases in cardiovascular and positive subjective effects in both groups and there was no difference in cocaine choice between the two groups. These data suggest that the response to cocaine is not different between cocaine abusers with ADHD compared to those without ADHD. When the cocaine abusers with ADHD were maintained on MPH-SR, cardiovascular effects were increased, however, this did not warrant termination of any test session. Maintenance on MPH-SR decreased some of the positive subjective effects of cocaine. Further, maintenance on a high dose of MPH-SR decreased cocaine choice. Thus, oral MPH-SR is safe in combination with repeated cocaine doses and decreases some of the positive and reinforcing effects of cocaine in cocaine abusers with ADHD.     

Effects of methylphenidate hydrochloride on the cardiovascular system in vivo and in vitro: A safety pharmacology study

Introduction:We examined the effects of methylphenidate hydrochloride (MPH) on the cardiovascular system using in vivo and in vitro study methods in accordance with the ICH-S7B guideline.MethodsMPH was orally administered at doses of 3, 10 and 30 mg/kg to unrestrained conscious dogs implanted with a telemetry transmitter and attached with body surface electrodes, and electrocardiogram (ECG) leads. The QTcF interval was determined while heart rate (HR), and blood pressure (BP) were measured. Action potentials in isolated guinea-pig papillary muscle and the rapid component of the delayed rectifier potassium current (I_Kr) in HEK-293 cells stably transfected with hERG were also investigated at concentrations of 0.1, 0.3 and 1 µg/mL (0.37, 1.1 and 3.7 µmol/L) of MPH.ResultsNo ECG changes were observed except for a shortening of the QT interval due to a shortening of the RR interval at the maximum dose tested, 30 mg/kg. The only observed change was an elevation of BP in dogs at the dose of 30 mg/kg, which is approximately 10 times higher than the maximum therapeutic dose for use in children with attention deficit hyperactivity disorder (ADHD). Neither APD prolongation nor I_Kr inhibition was observed by MPH in the in vitro studies up to the maximum concentration tested, 1 µg/mL (3.7 µmol/L), which is approximately 34 times higher than the clinically attainable unbound plasma MPH concentrations in children with ADHD.DiscussionThese results suggest that it is unlikely that MPH affects ventricular repolarization processes at the therapeutically recommended dose levels in patients with ADHD.     

A new progressive ratio schedule for support of morphine self-administration in opiate dependent rats

Rationale and objectives In preliminary studies, we observed that opiate dependent rats self-administered only a small number of morphine injections under a PR (progressive ratio) schedule developed to study psychostimulant self-administration. Therefore, a new schedule was developed to support morphine self-administration by incrementing response requirements in a relatively gradual manner. The present study compared morphine self-administration under a commonly used PR schedule to self-administration maintained by our modified PR schedule. Methods After pretreatment with non-contingent morphine, rats acquired self-administration under fixed-ratio (FR) schedules of intravenous morphine delivery. Morphine-maintained behavior was evaluated under a standard PR schedule (termed "PR3–4", because the third response requirement was four lever presses), and our modified PR schedule (termed "PR9–4", because the ninth response requirement was four lever presses). The PR9–4 schedule was also evaluated for self-administration of morphine doses of 0.001–3.2 mg/kg per injection. Results The number of ratios completed for morphine self-administration on the PR9–4 schedule, but not the PR3–4 schedule, exceeded values obtained during extinction. Dose-related increases in completed ratios occurred for morphine self-administration on the PR9–4 schedule, with stable patterns emerging after three sessions. A relatively flat dose-response relationship was observed, which did not increase monotonically with morphine dose. Morphine self-administration on the PR9–4 schedule decreased mean inter-injection interval and prolonged the duration of responding during 6-h sessions. Conclusions In the present study, a schedule that incremented response requirement gradually (PR9–4) supported reliable self-administration across a range of morphine doses.     

Attenuation of the effects of <Emphasis Type="Italic">d</Emphasis>-amphetamine on interval timing behavior by central 5-hydroxytryptamine depletion

Rationale  Interval timing in the free-operant psychophysical procedure is sensitive to the monoamine-releasing agent d-amphetamine, the D₂-like dopamine receptor agonist quinpirole, and the D₁-like agonist 6-chloro-2,3,4,5-tetrahydro-1-phenyl-1H-3-benzepine (SKF-81297). The effect of d-amphetamine can be antagonized by selective D₁-like and 5-HT_2A receptor antagonists. It is not known whether d-amphetamine’s effect requires an intact 5-hydroxytryptamine (5-HT) pathway. Objective  The objective of this study was to examine the effects of d-amphetamine, quinpirole, and SKF-81297 on timing in intact rats and rats whose 5-hydroxytryptaminergic (5-HTergic) pathways had been ablated. Materials and methods  Rats were trained under the free-operant psychophysical procedure to press levers A and B in 50-s trials in which reinforcement was provided intermittently for responding on A in the first half, and B in the second half of the trial. Percent responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic functions were fitted to the data for derivation of timing indices (T ₅₀, time corresponding to %B = 50%; Weber fraction). The effects of d-amphetamine (0.4 mg kg⁻¹ i.p.), quinpirole (0.08 mg kg⁻¹ i.p.), and SKF-81297 (0.4 mg kg⁻¹ s.c.) were compared between intact rats and rats whose 5-HTergic pathways had been destroyed by intra-raphe injection of 5,7-dihydroxytryptamine. Results  Quinpirole and SKF-81297 reduced T ₅₀ in both groups; d-amphetamine reduced T ₅₀ only in the sham-lesioned group. The lesion reduced 5-HT levels by 80%; catecholamine levels were not affected. Conclusions   d-Amphetamine’s effect on performance in the free-operant psychophysical procedure requires an intact 5-HTergic system. 5-HT, possibly acting at 5-HT_2A receptors, may play a ‘permissive’ role in dopamine release.

Glutamatergic and GABAergic modulations of ultrasonic vocalizations during maternal separation distress in mouse pups

Rationale  Deficits in amygdala-related stimulus-reward learning are produced following 18 drug-free days of cocaine self-administration or its passive delivery in rats exposed during adulthood. No deficits in stimulus-reward learning are produced by cocaine exposure initiated during adolescence. Objectives  To determine if age of initiating cocaine exposure differentially affects behavioral functioning of an additional memory system linked to cocaine addiction, the orbitofrontal cortex. Materials and methods  A yoked-triad design (n = 8) was used. One rat controlled cocaine delivery and the other two passively received cocaine or saline. Rats controlling drug delivery (1.0 mg/kg) self-administered cocaine from either P37–P59 or P77–P99, and then underwent 18 drug-free days (P60–P77 vs. P100–P117). Rats next were tested for acquisition of odor-delayed win-shift behavior conducted over 15 sessions (P78–P96 vs. P118–P136). Results  Cocaine self-administration did not differ between adults and adolescents. During the test phase of the odor-delayed win-shift task (relatively difficult task demands), rats from both drug-onset ages showed learning deficits. Rats with cocaine self-administration experience committed more errors and had longer session latencies compared to rats passively receiving saline or cocaine. Rats with adolescent-onset cocaine self-administration experience showed an additional learning deficit by requiring more sessions to reach criterion levels for task acquisition compared to same-aged passive saline controls or rats with adult-onset cocaine self-administration experience. Rats passively receiving cocaine did not differ from the passive saline control from either age group. Conclusions  Rats with adolescent-onset cocaine self-administration experience were more impaired in an orbitofrontal cortex-related learning task than rats with adult-onset cocaine self-administration experience. This research was supported in part by CELEST, a National Science Foundation Science of Learning Center (SBE-0354378; S. Grossberg, PI), and by the National Institute on Drug Abuse (DA11716; K.M. Kantak, PI).     

Attention-deficit/hyperactivity disorder and the explore/exploit trade-off

The ability to maximize rewards and minimize the costs of obtaining them is vital to making advantageous explore/exploit decisions. Exploratory decisions are theorized to be greater among individuals with attention-deficit/hyperactivity disorder (ADHD), potentially due to deficient catecholamine transmission. Here, we examined the effects of ADHD status and methylphenidate, a common ADHD medication, on explore/exploit decisions using a 6-armed bandit task. We hypothesized that ADHD participants would make more exploratory decisions than controls, and that MPH would reduce group differences. On separate study days, adults with (n = 26) and without (n = 23) ADHD completed the bandit task at baseline, and after methylphenidate or placebo in counter-balanced order. Explore/exploit decisions were modeled using reinforcement learning algorithms. ADHD participants made more exploratory decisions (i.e., chose options without the highest expected reward value) and earned fewer points than controls in all three study days, and methylphenidate did not affect these outcomes. Baseline exploratory choices were positively associated with hyperactive ADHD symptoms across all participants. These results support several theoretical models of increased exploratory choices in ADHD and suggest the unexplained variance in ADHD decisions may be due to less value tracking. The inability to suppress actions with little to no reward value may be a key feature of hyperactive ADHD symptoms.Subject terms: ADHD, Cognitive control     

Nicotinic receptors differentially modulate the induction and expression of behavioral sensitization to methylphenidate in rats

Rationale  Nicotinic acetylcholine receptors (nAChRs) regulate sensitization to stimulant drugs such as d-amphetamine and cocaine. Objectives  The current study determined if nAChRs modulate the induction and/or expression of behavioral sensitization to high methylphenidate doses. Methods  In experiment 1, rats received saline or mecamylamine (3 mg/kg, sc), followed by saline or methylphenidate (5.6 or 10 mg/kg, sc) during 10 daily sessions; the effect of methylphenidate (1–17 mg/kg, sc) alone was determined 14 days later. In experiment 2, rats received saline or dihydro-β-erythroidine (DHβE; 3 mg/kg, sc), followed by saline or 5.6 mg/kg of methylphenidate. In experiment 3, rats received saline or methylphenidate (5.6 or 10 mg/kg, sc) alone for 10 days; the effect of acute mecamylamine (3 mg/kg, sc) on the response to methylphenidate (1–17 mg/kg, sc) was determined 14 days later. Locomotor activity, sniffing, rearing, grooming, and stereotypy ratings were dependent measures. Results  Methylphenidate produced dose-dependent increases in locomotor activity, sniffing, and stereotypy on day 1 and these effects were enhanced on day 10, indicative of sensitization. Mecamylamine attenuated methylphenidate-induced stereotypy only on day 1, but reduced locomotor activity, sniffing, rearing, and stereotypy on day 10 and during the methylphenidate challenge phase; similar results were obtained with DHβE. However, acute mecamylamine did not alter the effects of the methylphenidate challenge following the induction of sensitization to methylphenidate alone. Conclusions  Although nAChRs do not appear to regulate the expression of methylphenidate-induced behavioral sensitization, inhibition of high-affinity β2 subunit nAChRs attenuates the induction of behavioral sensitization to high doses of methylphenidate. The asterisk (*) found in the body denotes possible inclusion of additional nAChR subunits.     

Non-specific effects of methylphenidate (Ritalin) on cognitive ability and decision-making of ADHD and healthy adults

Introduction  

The effect of a single dose of methylphenidate (MPH) on cognitive measures and decision-making processes was assessed in a sample of adults with ADHD and in a control sample.     

Strain differences in self-administration of methylphenidate and sucrose pellets in a rat model of attention-deficit hyperactivity disorder

Despite its abuse potential, methylphenidate (MPH) is widely prescribed for treatment of attention-deficit hyperactivity disorder (ADHD). The purpose of the present study was to examine MPH self-administration in a rat model of ADHD. Experiment 1 examined the acquisition of MPH self-administration and assessed the MPH dose-effect curve in spontaneously hypertensive rats (SHR), an inbred rat model of ADHD, Wistar Kyotos (WKY), the progenitor strain for SHR, and Sprague-Dawley (SD), an outbred control strain. Experiment 2 replicated Experiment 1, but replaced MPH infusions with sucrose pellets. Initial acquisition of MPH self-administration was greater in SHR and SD than WKY. However, with extended training using an incrementing fixed ratio schedule SHR and WKY did not differ in responding for MPH using the training dose (0.3 mg/kg/infusion) or other unit doses, except that SHR showed greater responding than WKY at 0.1 mg/kg/infusion. SHR also showed greater acquisition and maintenance of sucrose-reinforced responding compared with both WKY and SD. Greater initial acquisition of MPH self-administration in SHR than WKY may not be due to a strain-specific difference in sensitivity to the reinforcing effect of MPH.     

Reward processing in male adults with childhood ADHD—a comparison between drug-naïve and methylphenidate-treated subjects

Rationale  

Dysfunctional reward processing has been proposed as a main deficit in attention-deficit/hyperactivity disorder (ADHD), which could be modulated by treatment with methylphenidate (MPH).     

Lack of sedative effects after vespertine intake of oxazepam as hypnotic in healthy volunteers

Aims  An objective physiological test was used to investigate the hangover effect, its time course and dose relationship compared to placebo and an herbal relaxant. Methods  Pupillographic Sleepiness Test as an objective measurement, Stanford Sleepiness Scale (SSS) and visual analogue scales (VAS) were used. Study design included: (a) randomised, double-blind, double-dummy, placebo-controlled crossover trial; (b) double-blind, placebo-controlled, randomised study. Primary end point was the Pupillary Unrest Index (lnPUI). Results  Oxazepam 10 mg did not increase PUI. In the VAS and SSS, there was no increase in sleepiness after the three treatment periods. Neither 10 nor 30 mg oxazepam caused sedation in healthy volunteers. Subjective and objective sleepiness measures correlated significantly. Discussion  The lack of sedative effects after vespertine intake of oxazepam (10/30 mg) seems to be relevant with respect to product safety. With regard to the subjective perception at 30 mg, fatigue rather than sleepiness may be the underlying reason.

Cocaine-induced reinstatement during limited and extended drug access conditions in rhesus monkeys

Rationale  The progression of addiction from controlled to compulsive drug use leads to serious adverse consequences, including a greater propensity to relapse to drug use after sustained periods of abstinence. Objective  The present study assessed the potential effects of cocaine self-administration history on the magnitude and persistence of cocaine-induced reinstatement in rhesus monkeys (n = 6). Methods  During a 3-month period of limited access to cocaine self-administration under a second-order schedule, subjects could take a maximum of 0.5 mg/kg per session 5 days per week. During a subsequent 3-month period of extended access to cocaine self-administration, subjects could take an additional 3.0 mg/kg under a fixed-ratio 20 schedule 3 days per week. Reinstatement effects were evaluated on six separate occasions that included limited and extended access conditions. Saline was substituted for cocaine, and once extinction criteria were met (response rates <20% of cocaine-maintained rates), response-independent cocaine (0.1 mg/kg) was administered i.v. prior to extinction sessions. Reinstatement was defined as a restoration of drug-appropriate responding above extinction criteria. Reinstatement experiments were conducted repeatedly on a daily basis until response rates returned to extinction levels. Peak response rates provided a measure of reinstatement magnitude whereas number of sessions required to meet extinction levels provided a measure of reinstatement persistence. Results  Both the magnitude and persistence of reinstatement were consistent across all determinations regardless of drug history. Conclusions  The results indicate that reinstatement under the second-order schedule is remarkably stable even when supplemental drug intake is provided over several months.     

Binge cocaine self-administration in humans: intravenous cocaine

Cocaine is frequently used in intermittent cycles of repeated dosing, or “binges.” This pattern of cocaine use has been difficult to study in humans because currently available laboratory models use only one daily session during which a single dose or multiple doses are administered. In the present study, seven adult male IV cocaine users completed a protocol investigating changes in cardiovascular and subjective responses during the repeated self-administration of cocaine. Volunteers participated in a 2-day and a 3-day access condition. On each day of access, they participated in two 2.5-h sessions, one at 1200 and another at 1600 hours. In the 2- and 3-day conditions, participants had access to cocaine on 2 or 3 consecutive days, respectively. During sessions, participants could self-administer up to six doses of IV cocaine (32 mg/70 kg) every 14 min. Participants chose not to self-administer cocaine on only 10% of the 420 trials. Acute tolerance developed to the cardiovascular and several subjective effects of cocaine. Heart rate was the only measure that tended to decrease across days of repeated cocaine self-administration. Ratings of “I want cocaine” decreased at the end of the last self-administration session during both 2- and 3-day conditions. There was no difference between the 2- and 3-day conditions for any measure. The laboratory model of “binge” cocaine use established in this study can be used to describe changes in cardiovascular and subjective effects of cocaine within and between bouts of repeated cocaine use. Received: 14 November 1996/Final version: 8 March 1997     

Assessing the abuse potential of methylphenidate in nonhuman and human subjects: a review

Methylphenidate (MPH) is widely used for the treatment of Attention Deficit Hyperactivity Disorder (ADHD) in children, adolescents, and adults. Methylphenidate is clearly effective for the treatment of ADHD, but there is controversy as to whether it has significant abuse potential like other psychostimulants (e.g., D-amphetamine and cocaine). In general, the drug is believed to be abused at rates much lower than those for other stimulants. The present review examines studies that investigated the behavioral pharmacological profile of methylphenidate and discusses how results from these studies address its abuse liability. Using MEDLINE search terms methylphenidate, drug discrimination, reinforcement, self-administration, subjective effects, subject-rated effects, abuse potential, and abuse liability, along with a review of the references from identified articles, 60 studies were located in which the reinforcing, discriminative-stimulus, or subjective effects of methylphenidate were directly assessed in nonhumans or humans. Forty-eight (80.0%) of the studies reviewed indicate that methylphenidate either functions in a manner similar to D-amphetamine or cocaine (e.g., functions as a reinforcer, substitutes fully in drug discrimination experiments), or produces a pattern of subjective effects suggestive of abuse potential. The results are discussed as they pertain to factors that may account for the apparent discrepancy in abuse rates between methylphenidate and other stimulants, including characterization of actual abuse rates, defining abuse and misuse, pharmacokinetic factors, and validity of abuse liability assays.     

Normalized gait parameters in NDT-Bobath post-stroke gait rehabilitation

The aim of the research was to evaluate the results of NDT-Bobath method in gait re-education of adult patients after ischemic stroke using normalized parameters of gait. The investigation group consisted of 60 patients, all sufferers of an ischemic stroke, and participated in a rehabilitation program: 10 sessions of NDT-Bobath therapy through 2 weeks (ten days of the therapy). Normalized parameters of gait were calculated based on anthropometric measures of patients and their gait parameters (gait velocity, cadence and stride length) measured in every patient on admission (before the therapy) and after the last session of the therapy to assess rehabilitation effects. Results among patients involved in the research were as follows: