Adolescent rat circadian activity is modulated by psychostimulants

Sleep and Circadian Rhythmicity in Adult ADHD and the Effect of Stimulants

OBJECTIVE

This review updates information on sleep and circadian rhythmicity in adult ADHD, especially circadian rhythmicity and the influence of stimulants.

METHOD

Investigations into sleep, chronotype, and circadian rhythm in adult ADHD were searched in the Cochrane Library, Embase, Medline, and PsycInfo databases.

RESULTS

ADHD in adults is associated with longer objective sleep latency, irrespective of insomnia complaints. Sleep maintenance is disturbed and waking up time is delayed. Adult ADHD is associated with increased eveningness, delayed dim light melatonin onset (DLMO), and later waking up time. Stimulant treatment induces delay of nonparametric circadian parameters, whereas light therapy (LT) induces shifts toward morningness, which is associated with a reduction of ADHD symptoms.

CONCLUSION

Adult ADHD is associated with delayed circadian rhythmicity and analogous sleep characteristics, which are typical of a delayed sleep phase disorder. Stimulants induce delay of circadian rhythmicity.

Chronic cocaine administration induces long-term impairment in the drive to obtain natural reinforcers in high- but not low-demanding tasks

Repeated drug exposure induces short- and long-term neuroadaptations in brain reward circuitries that are normally involved in the regulation of motivation. Hence, repeated drug exposure has been suggested to also affect the drive to acquire natural reinforcers. Here, we tested how chronic exposure of rats to cocaine, as well as a subsequent withdrawal period, affects acquisition of natural reinforcers in high- and low-demanding tasks (HD and LD tasks, respectively). We chronically administered cocaine (i.p., 15 mg/kg once daily, or saline in control) for 30 days, followed by a 30-day withdrawal period. We tested the effect of this treatment on the acquisition of two natural appetitive reinforcers, namely self-administering a 10% sucrose solution and mounting a receptive female, under LD and HD conditions. During the cocaine exposure period, behavioral testing took place 18 hours after cocaine injection, namely after the acute pharmacologic effect of the drug dissipated. We show that chronic i.p. cocaine exposure decreased procurement of both reinforcers in HD but not in LD tasks. The effect was observed throughout the administration period with partial recovery after withdrawal. Taken together, we present empirical evidence that chronic exposure to a constant dose of cocaine is sufficient to reduce natural reinforcement, and that this decrease can outlast drug exposure. Importantly, such effects are observed only when high demands are opposing the consumption of the natural reinforcer.

Caudate neuronal recording in freely behaving animals following acute and chronic dose response methylphenidate exposure

The misuse and abuse of the psychostimulant, methylphenidate (MPD) the drug of choice in the treatment of attention deficit hyperactivity disorder (ADHD) has seen a sharp uprising in recent years among both youth and adults for its cognitive enhancing effects and for recreational purposes. This uprise in illicit use has lead to many questions concerning the long-term consequences of MPD exposure. The objective of this study was to record animal behavior concomitantly with the caudate nucleus (CN) neuronal activity following acute and repetitive (chronic) dose response exposure to methylphenidate (MPD). A saline control and three MPD dose (0.6, 2.5, and 10.0mg/kg) groups were used. Behaviorally, the same MPD dose in some animals following chronic MPD exposure elicited behavioral sensitization and other animals elicited behavioral tolerance. Based on this finding, the CN neuronal population recorded from animals expressing behavioral sensitization was also evaluated separately from CN neurons recorded from animals expressing behavioral tolerance to chronic MPD exposure, respectively. Significant differences in CN neuronal population responses between the behaviorally sensitized and the behaviorally tolerant animals were observed for the 2.5 and 10.0mg/kg MPD exposed groups. For 2.5mg/kg MPD, behaviorally sensitized animals responded by decreasing their firing rates while behaviorally tolerant animals showed mainly an increase in their firing rates. The CN neuronal responses recorded from the behaviorally sensitized animals following 10.0mg/kg MPD responded by increasing their firing rates whereas the CN neuronal recordings from the behaviorally tolerant animals showed that approximately half decreased their firing rates in response to 10.0mg/kg MPD exposure. The comparison of percentage change in neuronal firing rates showed that the behaviorally tolerant animals trended to exhibit increases in their neuronal firing rates at ED1 following initial MPD exposure and oppositely at ED10 MPD rechallenge. While the behaviorally sensitized animals in general increased in their percentage change of firing rats were observed following acute 10.0mg/kg MPD and the behaviorally sensitized 10.0mg/kg MPD animals and a robust increase in neuronal firing rates at ED1 and ED10 rechallenge. These results suggest the need to first individually analyze animal behavioral activity, and then to evaluate the neuronal responses to the drug based on the animals behavioral response to chronic MPD exposure.

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.

Acute and chronic psychostimulant treatment modulates the diurnal rhythm activity pattern of WKY female adolescent rats

The psychostimulants considered the gold standard in the treatment of attention deficit hyperactivity disorder, one of the most common childhood disorders, are also finding their way into the hands of healthy young adults as brain augmentation to improve cognitive performance. The possible long-term effects of psychostimulant exposure in adolescence are considered controversial, and thus, the objective of this study was to investigate whether the chronic exposure to the psychostimulant amphetamine affects the behavioral diurnal rhythm activity patterns of female adolescent Wistar-Kyoto (WKY) rat. The hypothesis of this study is that change in diurnal rhythm activity pattern is an indicator for the long-term effect of the treatment. Twenty-four rats were divided into two groups, control (N = 12) and experimental (N = 12), and kept in a 12:12-h light/dark cycle in an open-field cage. After 5-7 days of acclimation, 11 days of consecutive non-stop behavioral recordings began. On experimental day 1 (ED1), all groups were given an injection of saline. On ED2 to ED7, the experimental group was injected with 0.6 mg/kg amphetamine followed by 3 days of washout from ED8 to ED10, and amphetamine re-challenge on ED11 similar to ED2. The locomotor movements were counted by the computerized animal activity monitoring system, and the cosinor statistical test analysis was used to fit a 24-h curve of the control recording to the activity pattern after treatment. The horizontal activity, total distance, number of stereotypy, vertical activity, and stereotypical movements were analyzed to find out whether the diurnal rhythm activity patterns were altered. Data obtained using these locomotor indices of diurnal rhythm activity pattern suggest that amphetamine treatment significantly modulates the locomotor diurnal rhythm activity pattern of female WKY adolescent rats.

Acute and chronic dose-response effect of methylphenidate on ventral tegmental area neurons correlated with animal behavior

Methylphenidate (MPD) is used to treat ADHD and as a cognitive enhancement and recreationally. MPD's effects are not fully understood. One of the sites of psychostimulant action is the ventral tegmental area (VTA). The VTA neuronal activity was recorded from freely behaving rats using a wireless system. 51 animals were divided into groups: saline, 0.6, 2.5, and 10.0 mg/kg MPD. The same repetitive MPD dose can elicit either behavioral sensitization or tolerance; thus the evaluation of the VTA neuronal activity was based on the animals' behavioral response to chronic MPD exposure: animals exhibiting behavioral tolerance or sensitization. Acute MPD elicits dose-related increases in behavioral activity. About half of the animals exhibited behavioral sensitization or tolerance to each of the MPD doses. 361 units were recorded from the VTA and exhibited similar spike shape on experimental day 1 (ED1) and on ED10. 71, 84, and 79 % of VTA units responded to acute 0.6, 2.5, and 10.0 mg/kg MPD, respectively. The neuronal baseline activity at ED10 was significantly modified in 94, 95, and 100 % of VTA units following 0.6, 2.5 and 10.0 mg/kg MPD, respectively. Following chronic MPD exposure, 91, 98, and 100 % exhibit either electrophysiological tolerance or sensitization of 0.6, 2.6, or 10.0 mg/kg MPD, respectively. In conclusion, the chronic administration of the same dose of MPD caused some animals to exhibit behavioral sensitization and other animals to exhibit tolerance. The VTA units recorded from animals exhibiting behavioral sensitization responded significantly differently to MPD from animals that exhibited behavioral tolerance.

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.

Behavioral daily rhythmic activity pattern of adolescent female rat is modulated by acute and chronic cocaine

Cocaine is one of well-known drugs of abuse, and many children experience early exposure to cocaine. Because of an immature neuronal system in adolescents, they may react differently to repeated cocaine administration compared to adults. Most of the published papers report the effect of cocaine on adult male rats and this paper focused on the effects of cocaine on the 24 h locomotor activity rhythm patterns activity of adolescent Sprague Dawley (SD) female rats. Changes in the locomotor activity rhythm patterns could indicate that cocaine elicits long-term changes in the clock genes of the body that regulate different physiological processes. The objective of this study was to investigate whether cocaine in adolescent female rats modulated their daily activity pattern. Animals were divided into control (saline), 3.0, 7.5, 15.0 mg/kg cocaine groups. On experimental day 1 (ED 1), all groups were given saline injection. From ED 2 to ED 7, either saline or cocaine (3.0, 7.5, or 15.0 mg/kg) was given daily. ED 8 to ED 10 were the washout days, where no injection was given. On ED 11, the animals were injected with saline or with the same dose of cocaine as they were treated on ED 2 to ED 7. Each animal's locomotor activities was recorded nonstop following saline or cocaine injection for 11 consecutive days using the open field assay. In conclusion, it was observed that all three groups receiving repeated cocaine administration (3.0, 7.5, and 15.0 mg/kg) displayed significantly altered locomotor activity rhythm patterns.