Attention Deficit Hyperactivity Disorder

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.

Long-term efficacy of methylphenidate in enhancing attention regulation, social skills, and academic abilities of childhood cancer survivors

PURPOSE

Methylphenidate (MPH) ameliorates attention problems experienced by some cancer survivors in the short term, but its long-term efficacy is unproven.

PATIENTS AND METHODS

This study investigates the long-term effectiveness of maintenance doses of MPH in survivors of childhood brain tumors (n = 35) and acute lymphoblastic leukemia (n = 33) participating in a 12-month MPH trial. Measures of attention (Conners' Continuous Performance Test [CPT], Conners' Rating Scales [CRS]), academic abilities (Wechsler Individual Achievement Test [WIAT]), social skills (Social Skills Rating System [SSRS]), and behavioral problems (Child Behavior Checklist [CBCL]) were administered at premedication baseline and at the end of the MPH trial while on medication. A cancer control group composed of patients who were not administered MPH (brain tumor = 31 and acute lymphoblastic leukemia = 23) was assessed on the same measures 12 [corrected] months apart.

RESULTS

For the MPH group, repeated measures analysis of variance revealed significant improvement in performance on a measure of sustained attention (CPT indices, P < .05); parent, teacher, and self-report ratings of attention (CRS indices, P < .05), and parent ratings of social skills or behavioral problems (SSRS and CBCL indices; P < .05). In contrast, the cancer control group only showed improvement on parent ratings of attention (Conners' Parent Rating Scale indices; P < .05) and social skills (SSRS and CBCL indices; P < .05). There was no significant improvement on the academic measure (WIAT) in either group.

CONCLUSION

Attention and behavioral benefits of MPH for childhood cancer survivors are maintained across settings over the course of a year. Although academic gains were not identified, MPH may offer benefits in academic areas not assessed.

Attention-deficit hyperactivity disorder in girls: epidemiology and management

Attention-deficit hyperactivity disorder (ADHD) in girls is a topic of growing research and clinical interest. For many years, girls with ADHD have been ignored and overshadowed by hyperkinetic and impulsive boys, but they are now attracting interest in an effort to understand the similarities and differences in the prevalence, symptoms, familial risk, comorbidities and treatment of ADHD in the two sexes. A review of past and current literature finds that the symptoms of ADHD are not sex specific, but that identification of girls with ADHD is hampered by parental and teacher bias, and confusion. Girls are more likely to be inattentive without being hyperactive or impulsive, compared with boys. Girls and boys share the same familial risk patterns, as well as similar, although not identical, comorbidity or impairment patterns. The risk of non-treatment is as great in girls as it is in boys; up to 70-80% of identified children will have persistent symptoms and impairment that extends into adolescence and adulthood. Treatment modalities are equally effective in girls and boys. Stimulants, non-stimulants and behavioural modalities are the mainstays of effective treatment.

Dose-response characteristics of methylphenidate on locomotor behavior and on sensory evoked potentials recorded from the VTA, NAc, and PFC in freely behaving rats

BACKGROUND

Methylphenidate (MPD) is a psychostimulant commonly prescribed for attention deficit/hyperactivity disorder. The mode of action of the brain circuitry responsible for initiating the animals' behavior in response to psychostimulants is not well understood. There is some evidence that psychostimulants activate the ventral tegmental area (VTA), nucleus accumbens (NAc), and prefrontal cortex (PFC).

METHODS

The present study was designed to investigate the acute dose-response of MPD (0.6, 2.5, and 10.0 mg/kg) on locomotor behavior and sensory evoked potentials recorded from the VTA, NAc, and PFC in freely behaving rats previously implanted with permanent electrodes. For locomotor behavior, adult male Wistar-Kyoto (WKY; n = 39) rats were given saline on experimental day 1 and either saline or an acute injection of MPD (0.6, 2.5, or 10.0 mg/kg, i.p.) on experimental day 2. Locomotor activity was recorded for 2-h post injection on both days using an automated, computerized activity monitoring system. Electrophysiological recordings were also performed in the adult male WKY rats (n = 10). Five to seven days after the rats had recovered from the implantation of electrodes, each rat was placed in a sound-insulated, electrophysiological test chamber where its sensory evoked field potentials were recorded before and after saline and 0.6, 2.5, and 10.0 mg/kg MPD injection. Time interval between injections was 90 min.

RESULTS

Results showed an increase in locomotion with dose-response characteristics, while a dose-response decrease in amplitude of the components of sensory evoked field responses of the VTA, NAc, and PFC neurons. For example, the P3 component of the sensory evoked field response of the VTA decreased by 19.8% +/- 7.4% from baseline after treatment of 0.6 mg/kg MPD, 37.8% +/- 5.9% after 2.5 mg/kg MPD, and 56.5% +/- 3.9% after 10 mg/kg MPD. Greater attenuation from baseline was observed in the NAc and PFC. Differences in the intensity of MPD-induced attenuation were also found among these brain areas.

CONCLUSION

These results suggest that an acute treatment of MPD produces electrophysiologically detectable alterations at the neuronal level, as well as observable, behavioral responses. The present study is the first to investigate the acute dose-response effects of MPD on behavior in terms of locomotor activity and in the brain involving the sensory inputs of VTA, NAc, and PFC neurons in intact, non-anesthetized, freely behaving rats previously implanted with permanent electrodes.

Cytokines as mediators of depression: what can we learn from animal studies?

It has recently been postulated that cytokines may cause depressive illness in man. This hypothesis is based on the following observations: 1. Treatment of patients with cytokines can produce symptoms of depression; 2. Activation of the immune system is observed in many depressed patients; 3. Depression occurs more frequently in those with medical disorders associated with immune dysfunction; 4. Activation of the immune system, and administration of endotoxin (LPS) or interleukin-1 (IL-1) to animals induces sickness behavior, which resembles depression, and chronic treatment with antidepressants has been shown to inhibit sickness behavior induced by LPS; 5. Several cytokines can activate the hypothalamo-pituitary-adrenocortical axis (HPAA), which is commonly activated in depressed patients; 6. Some cytokines activates cerebral noradrenergic systems, also commonly observed in depressed patients; 7. Some cytokines activate brain serotonergic systems, which have been implicated in major depressive illness and its treatment. The evidence for each of these tenets is reviewed and evaluated along with the effects of cytokines in classical animal tests of depression. Although certain sickness behaviors resemble the symptoms of depression, they are not identical and each has distinct features. Thus the value of sickness behavior as an animal model of major depressive disorder is limited, so that care should be taken in extrapolating results from the model to the human disorder. Nevertheless, the model may provide insight into the etiology and the mechanisms underlying some symptoms of major depressive disorder. It is concluded that immune activation and cytokines may be involved in depressive symptoms in some patients. However, cytokines do not appear to be essential mediators of depressive illness.

Effects of transcutaneous electrical nerve stimulation (TENS) on cognition, behavior, and the rest-activity rhythm in children with attention deficit hyperactivity disorder, combined type

OBJECTIVE

The aim of this study was to examine the effects of transcutaneous electrical nerve stimulation (TENS) on cognition, behavior, and the rest-activity rhythm in children with attention deficit hyperactivity disorder, combined type (ADHD-CT).

METHODS

Twenty-two children diagnosed with ADHD-CT received TENS treatment during 6 weeks, 2 times 30 min a day. Neuropsychological tests were administered to assess cognition, parent/teacher behavioral rating scales were used to measure behavior, and actigraphy was used to assess the rest-activity rhythm.

RESULTS

TENS appeared to have a moderate beneficial influence on cognitive functions that load particularly on executive function. There was also improvement in behavior as measured by parent/teacher behavioral rating scales. Moreover, motor restlessness during sleep and motor activity during the day decreased by TENS.

CONCLUSIONS

The effects of TENS in children with ADHD are modest but encouraging and warrant further research.

Treatment modalities among US children diagnosed with attention-deficit hyperactivity disorder: 1995-99

The objective of this study was to determine the prevalence of single and combination treatment modalities among US children aged 5-18 years who were diagnosed with attention-deficit hyperactivity disorder (ADHD). Treatments included: (i) stimulant pharmacotherapy alone; (ii) psychotherapy and/or mental health counselling alone; (ii) a combination; or (iv) no treatment. Data from the US National Ambulatory Medical Care Survey (NAMCS) for the years 1995-99, were used for this analysis. Office-based physician-patient visits documenting a recorded diagnosis of ADHD (ICD-9-CM codes 314.00 or 314.01) were extracted from the NAMCS. Findings are presented for children diagnosed with ADHD with or without comorbid mental illness, for children diagnosed with ADHD without comorbid mental illness, by gender, and by age groups. Over the timeframe 1995-99, an estimated 14 402 090 office-based visits documented a diagnosis of ADHD, with (24%) or without (76%) comorbid mental illness, among children aged 5-18 years. Overall, the most frequent treatment was stimulant medication alone (42.0%). This was followed by the combination treatment of stimulant medication plus psychotherapy and/or mental health counselling (32.1%). Only 10.8% of the children received psychotherapy and/or mental health counselling alone; 15.1% received no treatment beyond the office-based visit. This pattern was consistent for boys and girls; however, a larger proportion of boys (11.7%) were receiving psychotherapy and/or mental health counselling alone than girls (8.2%). More girls (18.7%) were receiving no treatment option compared to boys (13.9%). The percentage of children receiving psychotherapy and/or mental health counselling alone increased with each age group (6.7%, 5-8 years; 11.3%, 9-12 years; 13.6%, 13-18 years), as did the combination treatment of stimulant medication plus psychotherapy and/or mental health counselling (28.2%, 31%, 37.3%, respectively). Only 8.2% of children age 13-18 years were receiving no treatment option compared to 16.9% of children age 9-12 years, and 19.5% of those aged 5-8 years. The reasons for the gender and age group differences discerned in this study require further investigation, as does the reason why 15.1% of children were receiving no treatment beyond the office-based visit.

Adolescent exposure to methylphenidate alters the activity of rat midbrain dopamine neurons

BACKGROUND

Methylphenidate is commonly used to treat children and adolescents with attention-deficit/hyperactivity disorder. A health concern is its long-term effects with respect to later stimulant exposure. We reported that repeated exposure to a low dose of methylphenidate during adolescence increases self-administration of a low, typically nonreinforcing dose of cocaine in adult rats. We also showed that enhanced vulnerability to cocaine is associated with elevated impulse and bursting activity of midbrain dopamine neurons in drug-naïve adult rats and might constitute a substrate critically associated with abuse liability. Thus we sought to determine whether repeated exposure to low-dose methylphenidate in adolescence alters dopamine neuronal excitability in adulthood.

METHODS

After 3-day and 2-week withdrawal from repeated low-dose adolescent exposure to methylphenidate, we used extracellular single-unit recording in chloral hydrate-anesthetized rats to determine basal firing and bursting activity of midbrain dopamine neurons and dopamine autoreceptor sensitivity to the D2-class direct receptor agonist quinpirole.

RESULTS

Dopamine neuronal impulse activity was increased after 3 days and decreased after 2 weeks' withdrawal from methylphenidate given in adolescence. No difference between groups was evident with respect to autoreceptor sensitivity to quinpirole.

CONCLUSIONS

Adolescent exposure to methylphenidate induces neuronal changes associated with increased addiction liability in rats.