Influence of chronic dopamine transporter inhibition by RTI-336 on motor behavior, sleep, and hormone levels in rhesus monkeys

Potential use of actigraphy to measure sleep in monkeys: comparison with behavioral analysis from videography

Sleep is indispensable for human health, with sleep disorders initiating a cascade of negative consequences. As our closest phylogenetic relatives, non-human primates (NHPs) are invaluable for comparative sleep studies and exhibit tremendous potential for improving our understanding of human sleep and related disorders. Previous work on measuring sleep in NHPs has mostly used electroencephalography or videography. In this study, simultaneous videography and actigraphy were applied to observe sleep patterns in 10 cynomolgus monkeys ( Macaca fascicularis) over seven nights (12 h per night). The durations of wake, transitional sleep, and relaxed sleep were scored by analysis of animal behaviors from videography and actigraphy data, using the same behavioral criteria for each state, with findings then compared. Here, results indicated that actigraphy constituted a reliable approach for scoring the state of sleep in monkeys and showed a significant correlation with that scored by videography. Epoch-by-epoch analysis further indicated that actigraphy was more suitable for scoring the state of relaxed sleep, correctly identifying 97.57% of relaxed sleep in comparison with video analysis. Only 34 epochs (0.13%) and 611 epochs (2.30%) were differently interpreted as wake and transitional sleep compared with videography analysis. The present study validated the behavioral criteria and actigraphy methodology for scoring sleep, which can be considered as a useful and a complementary technique to electroencephalography and/or videography analysis for sleep studies in NHPs.

Effects of a Serotonin 2C Agonist and a 2A Antagonist on Actigraphy-Based Sleep Parameters Disrupted by Methamphetamine Self-Administration in Rhesus Monkeys

Sleep disorders and substance abuse are highly comorbid and we have previously shown that methamphetamine self-administration significantly disrupts activity-based sleep parameters in rhesus monkeys. To the best of our knowledge, no study has evaluated the effectiveness of any pharmacological intervention to attenuate the effects of methamphetamine on nighttime activity under well-controlled conditions in laboratory animals. Thus, we examined the effects of a 5-HT_2C receptor agonist, WAY163909, and a 5-HT_2A receptor antagonist, M100907, given alone and in combination, on actigraphy-based sleep parameters disrupted by methamphetamine self-administration in non-human primates. Adult male/female rhesus monkeys self-administered methamphetamine (0.03 mg/kg/injection, i.v.) under a fixed-ratio 20 schedule of reinforcement (60-min sessions once a day, 5 days per week). Nighttime activity was evaluated using Actiwatch monitors. WAY163909 (0.1, 0.3, and 1.0 mg/kg), M100907 (0.03, 0.1, and 0.3 mg/kg), and a combination (0.1 mg/kg M100+0.3 mg/kg WAY) were administered i.m. before lights-out. Each dose was given for five consecutive days during which self-administration took place in the morning. Both drugs improved activity-based sleep measures disrupted by methamphetamine by decreasing sleep latency and increasing sleep efficiency compared with vehicle. By combining these drugs, their individual effects were significantly enhanced. Agonists at the 5-HT_2C receptor and antagonists at the 5-HT_2A receptor show promise as potential treatments for the sleep-disrupting effects of stimulants when used alone and in combination. Combining subthreshold doses of WAY and M100 produced significant improvements in nighttime activity measures while avoiding the general motor-decreasing effects of the high dose of WAY.

Dopamine transporters govern diurnal variation in extracellular dopamine tone

The majority of neurotransmitter systems shows variations in state-dependent cell firing rates that are mechanistically linked to variations in extracellular levels, or tone, of their respective neurotransmitter. Diurnal variation in dopamine tone has also been demonstrated within the striatum, but this neurotransmitter is unique, in that variation in dopamine tone is likely not related to dopamine cell firing; this is largely because of the observation that midbrain dopamine neurons do not display diurnal fluctuations in firing rates. Therefore, we conducted a systematic investigation of possible mechanisms for the variation in extracellular dopamine tone. Using microdialysis and fast-scan cyclic voltammetry in rats, as well as wild-type and dopamine transporter (DAT) knock-out mice, we demonstrate that dopamine uptake through the DAT and the magnitude of subsecond dopamine release is inversely related to the magnitude of extracellular dopamine tone. We investigated dopamine metabolism, uptake, release, D2 autoreceptor sensitivity, and tyrosine hydroxylase expression and activity as mechanisms for this variation. Using this approach, we have pinpointed the DAT as a critical governor of diurnal variation in extracellular dopamine tone and, as a consequence, influencing the magnitude of electrically stimulated dopamine release. Understanding diurnal variation in dopamine tone is critical for understanding and treating the multitude of psychiatric disorders that originate from perturbations of the dopamine system.

The relationship between cocaine self-administration and actigraphy-based measures of sleep in adult rhesus monkeys

RATIONALE

Clinical trials show that chronic cocaine users suffer from sleep disturbances and preclinical research has shown that acute sleep deprivation increases the rate of cocaine self-administration in rats.

OBJECTIVE

This study examined the effect of cocaine self-administration on behavioral indices of sleep and alternatively the effect of sleep disruption on cocaine-maintained responding by rhesus monkeys.

METHODS

Seven adult rhesus monkeys, fitted with Actical® activity monitors, were trained to respond under a concurrent choice paradigm with food (three 1.0-g pellets) and cocaine (0.003-0.3 mg/kg) or saline presentation. For each monkey, the lowest preferred dose of cocaine (>80% cocaine choice) was determined. Activity data were analyzed during lights out (2000-0600) to determine sleep efficiency, sleep latency, and total activity counts. Subsequently, the monkeys' sleep was disrupted (every hour during lights-out period) the night prior to food-cocaine choice sessions.

RESULTS

Self-administration of the preferred dose of cocaine resulted in a significant decrease in sleep efficiency, with a significant increase in total lights-out activity. Sleep disruption significantly altered behavioral indices of sleep, similar to those seen following cocaine self-administration. However, sleep disruption did not affect cocaine self-administration under concurrent choice conditions.

CONCLUSIONS

Based on these findings, cocaine self-administration does appear to disrupt behavioral indices of sleep, although it remains to be determined if treatments that improve sleep measures can affect future cocaine taking.

Effects of methamphetamine self-administration on actigraphy-based sleep parameters in rhesus monkeys

RATIONALE

Sleep disorders and substance abuse are highly comorbid. Although methamphetamine is a very commonly abused drug, to the best of our knowledge, no study has evaluated its effects on sleep during drug use and abstinence under well-controlled conditions in laboratory animals.

OBJECTIVES

The objective of this study was to examine the effects of methamphetamine self-administration on sleep-like measures in nonhuman primates.

METHODS

Adult male rhesus monkeys (Macaca mulatta; n = 4) self-administered methamphetamine (0.01 and 0.03 mg/kg/injection, i.v.) under a fixed-ratio 20 schedule of reinforcement (60-min sessions once a day, 5 days per week) for 5 weeks. Sleep-like measures were evaluated with Actiwatch monitors before, during, and after each period of drug self-administration.

RESULTS

Both doses of methamphetamine reliably maintained self-administration. Methamphetamine (0.03 mg/kg) increased derived measures of latency to sleep onset and sleep fragmentation, and decreased sleep efficiency compared to abstinence, and higher methamphetamine intake predicted worse sleep quality. However, sleep normalized immediately after the discontinuation of methamphetamine self-administration.

CONCLUSIONS

Methamphetamine markedly disrupted sleep-like measures; however, methamphetamine self-administration did not disrupt sleep quality during subsequent periods of drug abstinence.