Test-retest reliability of the Epworth Sleepiness Scale in clinical trial settings.

The present analysis examined the test-retest reliability of the Epworth Sleepiness Scale in participants with excessive daytime sleepiness associated with narcolepsy or obstructive sleep apnea in three clinical trials. Intraclass correlation coefficient estimates for Epworth Sleepiness Scale scores from two solriamfetol 12-week placebo-controlled trials (one narcolepsy, one obstructive sleep apnea) and one long-term open-label extension trial (narcolepsy or obstructive sleep apnea) were calculated using postbaseline time-point pairs for the overall population in each trial, by treatment, and by primary obstructive sleep apnea therapy adherence. In the 12-week narcolepsy trial, intraclass correlation coefficients (95% confidence intervals) were 0.83 (0.79, 0.87) for weeks 4 and 8 (n = 199), 0.87 (0.83, 0.90) for weeks 8 and 12 (n = 196), and 0.81 (0.76, 0.85) for weeks 4 and 12 (n = 196). In the 12-week obstructive sleep apnea trial, intraclass correlation coefficients (95% confidence intervals) were 0.74 (0.69, 0.78) (n = 416), 0.80 (0.76, 0.83) (n = 405), and 0.74 (0.69, 0.78) (n = 405), respectively. In the open-label extension trial, intraclass correlation coefficients (95% confidence intervals) were 0.82 (0.79, 0.85) for weeks 14 and 26/27 (n = 495), 0.85 (0.82, 0.87) for weeks 26/27 and 39/40 (n = 463), and 0.78 (0.74, 0.81) for weeks 14 and 39/40 (n = 463). Placebo/solriamfetol treatment or adherence to primary obstructive sleep apnea therapy did not affect reliability. In conclusion, across three large clinical trials of participants with narcolepsy or obstructive sleep apnea, Epworth Sleepiness Scale scores demonstrated a robust acceptable level of test-retest reliability in evaluating treatment response over time.

Long-term effects of solriamfetol on quality of life and work productivity in participants with excessive daytime sleepiness associated with narcolepsy or obstructive sleep apnea.

STUDY OBJECTIVES: Solriamfetol, a dopamine/norepinephrine reuptake inhibitor, is approved in the United States and European Union for excessive daytime sleepiness in adults with narcolepsy (75-150 mg/day) or obstructive sleep apnea (OSA; 37.5-150 mg/day). In 12-week studies, solriamfetol was associated with improvements in quality of life in participants with narcolepsy or OSA. These analyses evaluated the long-term effects of solriamfetol on quality of life. METHODS: Participants with narcolepsy or OSA who completed previous solriamfetol studies were eligible. A 2-week titration was followed by a maintenance phase ≤ 50 weeks (stable doses: 75, 150, or 300 mg/day). Quality of life assessments included Functional Outcomes of Sleep Questionnaire short version, Work Productivity and Activity Impairment Questionnaire: Specific Health Problem, and 36-Item Short Form Health Survey version 2. Mean (standard deviation) changes from baseline to end of study were evaluated. Data were summarized descriptively. Adverse events were assessed. RESULTS: Safety population comprised 643 participants (417 OSA, 226 narcolepsy). Solriamfetol improved Functional Outcomes of Sleep Questionnaire short version Total scores (mean change [standard deviation], 3.7 [3.0]) and 36-Item Short Form Health Survey version 2 Physical and Mental Component Summary scores (3.1 [6.9] and 4.3 [8.4], respectively); improvements were sustained throughout treatment. On Work Productivity and Activity Impairment Questionnaire: Specific Health Problem, solriamfetol reduced (improved) % presenteeism, % overall work impairment, and % activity impairment by a minimum of 25%. Common adverse events (≥ 5%): headache, nausea, nasopharyngitis, insomnia, dry mouth, anxiety, decreased appetite, and upper respiratory tract infection. CONCLUSIONS: Long-term solriamfetol treatment was associated with clinically meaningful, sustained improvements in functional status, work productivity, and quality of life for up to 52 weeks. Adverse events were similar between narcolepsy and OSA. CLINICAL TRIAL REGISTRATION: Registry: ClinicalTrials.gov; Name: A Long-Term Safety Study of JZP-110 in the Treatment of Excessive Sleepiness in Subjects with Narcolepsy or OSA; Identifier: NCT02348632; URL: https://clinicaltrials.gov/ct2/show/NCT02348632. CITATION: Weaver TE, Pepin J-L, Schwab R, et al. Long-term effects of solriamfetol on quality of life and work productivity in participants with excessive daytime sleepiness associated with narcolepsy or obstructive sleep apnea. J Clin Sleep Med. 2021;17(10):1995-2007.

Randomized Controlled Trial of Solriamfetol for Excessive Daytime Sleepiness in OSA: An Analysis of Subgroups Adherent or Nonadherent to OSA Treatment.

BACKGROUND: Solriamfetol, a dopamine-norepinephrine reuptake inhibitor, is approved in the United States to improve wakefulness in adults with excessive daytime sleepiness (EDS) associated with OSA (37.5-150 mg/d). RESEARCH QUESTION: Does solriamfetol have differential effects on EDS based on adherence to primary OSA therapy and does solriamfetol affect primary OSA therapy use? STUDY DESIGN AND METHODS: Participants were randomized to 12 weeks of placebo or solriamfetol 37.5, 75, 150, or 300 mg/d (stratified by primary OSA therapy adherence). Coprimary end points were week 12 change from baseline in 40-min Maintenance of Wakefulness Test (MWT) and Epworth Sleepiness Scale (ESS) in the modified intention-to-treat population. Primary OSA therapy use (hours per night, % nights) and safety were evaluated. RESULTS: At baseline, 324 participants (70.6%) adhered to OSA therapy (positive airway pressure use ≥ 4 h/night on ≥ 70% nights, surgical intervention, or oral appliance use on ≥ 70% nights) and 135 participants (29.4%) did not adhere. Least squares (LS) mean differences from placebo in MWT sleep latency (minutes) in the 37.5-, 75-, 150-, and 300-mg/d groups among adherent participants were 4.8 (95% CI, 0.6-9.0), 8.4 (95% CI, 4.3-12.5), 10.2 (95% CI, 6.8-13.6), and 12.5 (95% CI, 9.0-15.9) and among nonadherent participants were 3.7 (95% CI, -2.0 to 9.4), 9.9 (95% CI, 4.4-15.4), 11.9 (95% CI, 7.5-16.3), and 13.5 (95% CI, 8.8-18.3). On ESS, LS mean differences from placebo in the 37.5-, 75-, 150-, and 300-mg/d groups among adherent participants were -2.4 (95% CI, -4.2 to -0.5), -1.3 (95% CI, -3.1 to 0.5), -4.2 (95% CI, -5.7 to -2.7), and -4.7 (95% CI, -6.1 to -3.2) and among nonadherent participants were -0.7 (95% CI, -3.5 to 2.1), -2.6 (95% CI, -5.4 to 0.1), -5.0 (95% CI, -7.2 to -2.9), and -4.6 (95% CI, -7.0 to -2.3). Common adverse events included headache, nausea, anxiety, decreased appetite, nasopharyngitis, and diarrhea. No clinically meaningful changes were seen in primary OSA therapy use with solriamfetol. INTERPRETATION: Solriamfetol improved EDS in OSA regardless of primary OSA therapy adherence. Primary OSA therapy use was unaffected with solriamfetol. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT02348606; URL: www.clinicaltrials.gov; EU Clinical Trials Register; No.: EudraCT2014-005514-31; URL: www.clinicaltrialsregister.eu.

Effects of solriamfetol in a long-term trial of participants with obstructive sleep apnea who are adherent or nonadherent to airway therapy.

STUDY OBJECTIVES: Solriamfetol, a dopamine/norepinephrine reuptake inhibitor, is approved in the United States and European Union to treat excessive daytime sleepiness in patients with obstructive sleep apnea (OSA) (37.5-150 mg/day) and narcolepsy (75-150 mg/day). This analysis evaluated solriamfetol's efficacy in subgroups of participants with OSA who were adherent or nonadherent to primary OSA therapy at baseline and examined whether solriamfetol affected the use of primary therapy in an open-label extension trial. METHODS: Participants with OSA who completed prior solriamfetol studies received solriamfetol 75, 150, or 300 mg/day for ≤ 52 weeks. The main efficacy outcome was the Epworth Sleepiness Scale score. Primary therapy use was summarized as the percentage of nights, the number of hours/night, and the percentage of nights with use ≥ 50%/night (%). Efficacy and primary therapy use are reported for participants who directly enrolled from a previous 12-week study and had ≤ 40 weeks of open-label treatment (n = 333). Safety data are reported for all participants (n = 417). RESULTS: Mean ESS scores in adherent (n = 255) and nonadherent (n = 78) subgroups, respectively, were 15.0 and 15.8 at baseline (of 12-week study) and 6.5 and 6.8 at week 40. For participants using an airway therapy, mean use at baseline was 90% of nights, 6.6 hours/night, and use ≥ 50%/night on 90% of nights; changes from baseline to week 40 were minimal (0.9%, -0.8 hours, and 6.5%, respectively). Common adverse events (both subgroups) included headache, nasopharyngitis, insomnia, dry mouth, nausea, anxiety, and upper respiratory tract infection. CONCLUSIONS: Long-term efficacy and safety of solriamfetol were similar regardless of adherence to primary OSA therapy. Solriamfetol did not affect primary therapy use. CLINICAL TRIAL REGISTRATION: Registry: ClinicalTrials.gov; Name: A Long-Term Safety Study of JZP-110 in the Treatment of Excessive Sleepiness in Subjects with Narcolepsy or OSA; URL: https://clinicaltrials.gov/ct2/show/NCT02348632; Identifier: NCT02348632 and Registry: EU Clinical Trials Register; Identifier: 2014-005489-31; URL: https://www.clinicaltrialsregister.eu/ctr-search/search?query=2014-005489-31..

Clinically relevant effects of solriamfetol on excessive daytime sleepiness: a posthoc analysis of the magnitude of change in clinical trials in adults with narcolepsy or obstructive sleep apnea.

STUDY OBJECTIVES: To evaluate the clinical relevance of solriamfetol in treating excessive daytime sleepiness in participants with narcolepsy or obstructive sleep apnea (OSA). METHODS: This posthoc analysis includes data from two 12-week, randomized phase 3 studies in participants with narcolepsy or OSA treated with once-daily placebo or solriamfetol 37.5 mg (OSA only), 75 mg, 150 mg, or 300 mg. Excessive daytime sleepiness was assessed with the Epworth Sleepiness Scale (ESS) at baseline and at week 12. Cumulative distribution function plots were generated using a last-observation-carried-forward approach to determine the percentage of participants who achieved ESS scores ≤ 10, within the normal range, and the percentage who achieved a reduction (improvement) in ESS ≥ 25% relative to baseline. Safety was also assessed. RESULTS: In narcolepsy (n = 231), 30.5%-49.2% of participants treated with solriamfetol (across doses) reported ESS scores ≤ 10 and 44.1%-62.7% achieved a ≥ 25% decrease from baseline in ESS scores at week 12, compared with 15.5% and 27.6%, respectively, of placebo recipients. In OSA (n = 459), 51.8%-73.0% of participants treated with solriamfetol (across doses) reported ESS scores ≤ 10 and 50.0%-81.9% achieved a ≥ 25% decrease from baseline in ESS scores at week 12, compared with 37.7% and 36.8%, respectively, of placebo recipients. Results were generally dose-dependent, with more responders at higher solriamfetol doses. Common treatment-emergent adverse events (≥ 5% of solriamfetol recipients in either study) were headache, nausea, decreased appetite, nasopharyngitis, dry mouth, and anxiety. CONCLUSIONS: A greater percentage of participants treated with solriamfetol achieved normal ESS scores (≤ 10) or clinically meaningful improvements on the ESS compared with those receiving placebo. The safety profile was similar between participants with narcolepsy and those with OSA. CLINICAL TRIAL REGISTRATIONS: Registry: ClinicalTrials.gov. Names: TONES 2 and TONES 3. URLs: https://www.clinicaltrials.gov/ct2/show/NCT02348593 and https://www.clinicaltrials.gov/ct2/show/NCT02348606. Identifiers: NCT02348593, NCT02348606. Registry: European Union Drug Regulating Authorities Clinical Trials. Names: TONES 2 and TONES 3. URL: https://www.eudract.ema.europa.eu. Identifiers: EudraCT 2014-005487-15, EudraCT 2014-005514-31.

Long-term study of the safety and maintenance of efficacy of solriamfetol (JZP-110) in the treatment of excessive sleepiness in participants with narcolepsy or obstructive sleep apnea.

STUDY OBJECTIVES: To evaluate long-term safety and maintenance of efficacy of solriamfetol treatment for excessive daytime sleepiness in narcolepsy and obstructive sleep apnea (OSA). METHODS: Participants with narcolepsy or OSA who completed a prior solriamfetol study were eligible. A 2-week titration period was followed by a maintenance phase (up to 50 weeks). Efficacy was assessed by Epworth Sleepiness Scale (ESS) and Patient and Clinical Global Impression of Change (PGI-C and CGI-C, respectively). After approximately 6 months of treatment, a subgroup entered a 2-week placebo-controlled randomized withdrawal (RW) phase. Change in ESS from beginning to end of the RW phase was the primary endpoint; PGI-C and CGI-C were secondary endpoints. Safety was assessed throughout the study. RESULTS: In the maintenance phase, solriamfetol-treated participants demonstrated clinically meaningful improvements on ESS, PGI-C, and CGI-C. In the RW phase, least squares mean change on ESS was 1.6 in participants continuing solriamfetol versus 5.3 in participants switched to placebo (p < .0001). For both secondary endpoints, higher percentages of participants receiving placebo were reported as worse at the end of the RW phase versus solriamfetol (p < .0001). Common treatment-emergent adverse events (TEAEs) with solriamfetol were headache, nausea, nasopharyngitis, insomnia, dry mouth, anxiety, decreased appetite, and upper respiratory tract infection; 27 (4.2%) participants experienced at least one serious TEAE, and 61 (9.5%) withdrew because of TEAEs. CONCLUSIONS: This study demonstrated long-term maintenance of efficacy of solriamfetol under open-label and double-blind, placebo-controlled conditions. Safety profile of solriamfetol was consistent with previous 12-week studies; no new safety concerns were identified. TRIAL REGISTRATION: NCT02348632.

Characterization of the Neurochemical and Behavioral Effects of Solriamfetol (JZP-110), a Selective Dopamine and Norepinephrine Reuptake Inhibitor.

Excessive sleepiness (ES) is associated with several sleep disorders, including narcolepsy and obstructive sleep apnea (OSA). A role for monoaminergic systems in treating these conditions is highlighted by the clinical use of US Food and Drug Administration-approved drugs that act on these systems, such as dextroamphetamine, methylphenidate, modafinil, and armodafinil. Solriamfetol (JZP-110) is a wake-promoting agent that is currently being evaluated to treat ES in patients with narcolepsy or OSA. Clinical and preclinical data suggest that the wake-promoting effects of solriamfetol differ from medications such as modafinil and amphetamine. The goal of the current studies was to characterize the mechanism of action of solriamfetol at monoamine transporters using in vitro and in vivo assays. Results indicate that solriamfetol has dual reuptake inhibition activity at dopamine (DA; IC50 = 2.9 µM) and norepinephrine (NE; IC50 = 4.4 µM) transporters, and this activity is associated in vivo with increased extracellular concentration of DA and NE as measured by microdialysis. Solriamfetol has negligible functional activity at the serotonin transporter (IC50 > 100 µM). Moreover, the wake-promoting effects of solriamfetol are probably owing to activity at DA and NE transporters rather than other neurotransmitter systems, such as histamine or orexin. The dual activity of solriamfetol at DA and NE transporters and the lack of significant monoamine-releasing properties of solriamfetol might explain the differences in the in vivo effects of solriamfetol compared with modafinil or amphetamine. Taken together, these data suggest that solriamfetol may offer an important advancement in the treatment of ES in patients with narcolepsy or OSA.

Prior nicotine self-administration attenuates subsequent dopaminergic deficits of methamphetamine in rats: role of nicotinic acetylcholine receptors.

Preclinical studies have demonstrated that oral nicotine exposure attenuates long-term dopaminergic damage induced by toxins, including repeated, high doses of methamphetamine. It is suggested that alterations in nicotinic acetylcholine receptor (nAChR) expression, including α4ß2* and α6ß2* subtypes, likely contribute to this protection. The current study extended these findings by investigating whether nicotine self-administration in male, Sprague-Dawley rats (a) attenuates short-term dopaminergic damage induced by methamphetamine and (b) causes alterations in levels of α4ß2* and α6ß2* nAChR subtypes. The findings indicate that nicotine self-administration (0.032 mg/kg/infusion for 14 days) per se did not alter α4ß2* and α6ß2* nAChR expression or dopamine transporter (DAT) expression and function. Interestingly, prior nicotine self-administration attenuated methamphetamine-induced decreases in DAT function when assessed 24 h, but not 1 h, after methamphetamine treatment (4×7.5 mg/kg/injection). The ability of nicotine to attenuate the effects of methamphetamine on DAT function corresponded with increases in α4ß2*, but not α6ß2*, nAChR binding density. Understanding the role of nAChRs in methamphetamine-induced damage has the potential to elucidate mechanisms underlying the etiology of disorders involving dopaminergic dysfunction, as well as to highlight potential new therapeutic strategies for prevention or reduction of dopaminergic neurodegeneration.

Regulation of the Dopamine and Vesicular Monoamine Transporters: Pharmacological Targets and Implications for Disease.

Dopamine (DA) plays a well recognized role in a variety of physiologic functions such as movement, cognition, mood, and reward. Consequently, many human disorders are due, in part, to dysfunctional dopaminergic systems, including Parkinson's disease, attention deficit hyperactivity disorder, and substance abuse. Drugs that modify the DA system are clinically effective in treating symptoms of these diseases or are involved in their manifestation, implicating DA in their etiology. DA signaling and distribution are primarily modulated by the DA transporter (DAT) and by vesicular monoamine transporter (VMAT)-2, which transport DA into presynaptic terminals and synaptic vesicles, respectively. These transporters are regulated by complex processes such as phosphorylation, protein-protein interactions, and changes in intracellular localization. This review provides an overview of 1) the current understanding of DAT and VMAT2 neurobiology, including discussion of studies ranging from those conducted in vitro to those involving human subjects; 2) the role of these transporters in disease and how these transporters are affected by disease; and 3) and how selected drugs alter the function and expression of these transporters. Understanding the regulatory processes and the pathologic consequences of DAT and VMAT2 dysfunction underlies the evolution of therapeutic development for the treatment of DA-related disorders.

Eating high fat chow decreases dopamine clearance in adolescent and adult male rats but selectively enhances the locomotor stimulating effects of cocaine in adolescents.

BACKGROUND: Feeding conditions can influence dopamine neurotransmission and impact behavioral and neurochemical effects of drugs acting on dopamine systems. This study examined whether eating high fat chow alters the locomotor effects of cocaine and dopamine transporter activity in adolescent (postnatal day 25) and adult (postnatal day 75) male Sprague-Dawley rats. METHODS: Dose-response curves for cocaine-induced locomotor activity were generated in rats with free access to either standard or high fat chow or restricted access to high fat chow (body weight matched to rats eating standard chow). RESULTS: Compared with eating standard chow, eating high fat chow increased the sensitivity of adolescent, but not adult, rats to the acute effects of cocaine. When tested once per week, sensitization to the locomotor effects of cocaine was enhanced in adolescent rats eating high fat chow compared with adolescent rats eating standard chow. Sensitization to cocaine was not different among feeding conditions in adults. When adolescent rats that previously ate high fat chow ate standard chow, sensitivity to cocaine returned to normal. As measured by chronoamperometry, dopamine clearance rate in striatum was decreased in both adolescent and adult rats eating high fat chow compared with age-matched rats eating standard chow. CONCLUSIONS: These results suggest that high fat diet-induced reductions in dopamine clearance rate do not always correspond to increased sensitivity to the locomotor effects of cocaine, suggesting that mechanisms other than dopamine transporter might play a role. Moreover, in adolescent but not adult rats, eating high fat chow increases sensitivity to cocaine and enhances the sensitization that develops to cocaine.

Prior methylphenidate self-administration alters the subsequent reinforcing effects of methamphetamine in rats.

Methylphenidate (MPD) is clinically effective in treating the symptoms of attention-deficit hyperactivity disorder; however, its relatively widespread availability has raised public health concerns on nonmedical use of MPD among certain adult populations. Most preclinical studies investigate whether presumed therapeutically relevant doses of MPD alter sensitivity to the reinforcing effects of other drugs, but it remains unclear whether doses of MPD likely exceeding therapeutic relevance impact the subsequent reinforcing effects of drugs. To begin to address this question, the effect of prior MPD self-administration (0.56 mg/kg/infusion) on the subsequent reinforcing effects of methamphetamine (METH, 0.032 or 0.1 mg/kg/infusion) was investigated in male Sprague-Dawley rats. For comparison, it was also determined whether prior experimenter-administered MPD, injected daily at a presumed therapeutically relevant dose (2 mg/kg), altered the subsequent reinforcing effects of METH. Results indicated that, under the current conditions, only a history of MPD self-administration increased sensitivity to the subsequent reinforcing effects of METH. Furthermore, MPD did not impact food-maintained responding, suggesting that the effect of MPD might be specific to drug reinforcers. These data suggest that short-term, nonmedical use of MPD might alter the positive reinforcing effects of METH in a manner relevant to vulnerability to drug use in humans.

Dopamine D(3) receptors contribute to methamphetamine-induced alterations in dopaminergic neuronal function: role of hyperthermia.

Methamphetamine administration causes long-term deficits to dopaminergic systems that, in humans, are thought to be associated with motor slowing and memory impairment. Methamphetamine interacts with the dopamine transporter (DAT) and increases extracellular concentrations of dopamine that, in turn, binds to a number of dopamine receptor subtypes. Although the relative contribution of each receptor subtype to the effects of methamphetamine is not fully known, non-selective dopamine D2/D3 receptor antagonists can attenuate methamphetamine-induced changes to dopamine systems. The present study extended these findings by testing the role of the dopamine D3 receptor subtype in mediating the long-term dopaminergic, and for comparison serotonergic, deficits caused by methamphetamine. Results indicate that the dopamine D3 receptor selective antagonist, PG01037, attenuated methamphetamine-induced decreases in striatal DAT, but not hippocampal serotonin (5HT) transporter (SERT), function, as assessed 7 days after treatment. However, PG01037 also attenuated methamphetamine-induced hyperthermia. When methamphetamine-induced hyperthermia was maintained by treating rats in a warm ambient environment, PG01037 failed to attenuate the effects of methamphetamine on DAT uptake. Furthermore, PG01037 did not attenuate methamphetamine-induced decreases in dopamine and 5HT content. Taken together, the present study demonstrates that dopamine D3 receptors mediate, in part, the long-term deficits in DAT function caused by methamphetamine, and that this effect likely involves an attenuation of methamphetamine-induced hyperthermia.

Feeding condition and the relative contribution of different dopamine receptor subtypes to the discriminative stimulus effects of cocaine in rats.

RATIONALE: The contribution of dopamine receptor subtypes in mediating the discriminative stimulus effects of cocaine is not fully established. Many drug discrimination studies use food to maintain responding, necessitating food restriction, which can alter drug effects. OBJECTIVE: This study established stimulus control with cocaine (10 mg/kg) in free-feeding and food-restricted rats responding under a schedule of stimulus shock termination (SST) and in food-restricted rats responding under a schedule of food presentation to examine whether feeding condition or the reinforcer used to maintain responding impacts the effects of cocaine. METHOD: Dopamine receptor agonists and antagonists were examined for their ability to mimic or attenuate, respectively, the effects of cocaine. RESULTS: Apomorphine, quinpirole, and lisuride occasioned >90 % responding on the cocaine-associated lever in free-feeding rats responding under a schedule of SST; apomorphine, but not quinpirole or lisuride, occasioned >90 % responding on the cocaine lever in food-restricted rats responding under a schedule of SST. In food-restricted rats responding for food these drugs occasioned little cocaine lever responding and were comparatively more potent in decreasing responding. In free-feeding rats, the effects of cocaine were attenuated by the D2/D3 receptor antagonist raclopride and the D3 receptor-selective antagonist PG01037. In food-restricted rats, raclopride and the D2 receptor-selective antagonist L-741,626 attenuated the effects of cocaine. Raclopride antagonized quinpirole in all groups while PG01037 antagonized quinpirole only in free-feeding rats. CONCLUSION: These results demonstrate significant differences in the discriminative stimulus of cocaine that are due to feeding conditions and not to the use of different reinforcers across procedures.

You are what you eat: influence of type and amount of food consumed on central dopamine systems and the behavioral effects of direct- and indirect-acting dopamine receptor agonists.

The important role of dopamine (DA) in mediating feeding behavior and the positive reinforcing effects of some drugs is well recognized. Less widely studied is how feeding conditions might impact the sensitivity of drugs acting on DA systems. Food restriction, for example, has often been the focus of aging and longevity studies; however, other studies have demonstrated that mild food restriction markedly increases sensitivity to direct- and indirect-acting DA receptor agonists. Moreover, it is becoming clear that not only the amount of food, but the type of food, is an important factor in modifying the effects of drugs. Given the increased consumption of high fat and sugary foods, studies are exploring how consumption of highly palatable food impacts DA neurochemistry and the effects of drugs acting on these systems. For example, eating high fat chow increases sensitivity to some behavioral effects of direct- as well as indirect-acting DA receptor agonists. A compelling mechanistic possibility is that central DA pathways that mediate the effects of some drugs are regulated by one or more of the endocrine hormones (e.g. insulin) that undergo marked changes during food restriction or after consuming high fat or sugary foods. Although traditionally recognized as an important signaling molecule in regulating energy homeostasis, insulin can also regulate DA neurochemistry. Because direct- and indirect-acting DA receptor drugs are used therapeutically and some are abused, a better understanding of how food intake impacts response to these drugs would likely facilitate improved treatment of clinical disorders and provide information that would be relevant to the causes of vulnerability to abuse drugs. This article is part of a Special Issue entitled 'Central Control of Food Intake'.

Eating high fat chow enhances the locomotor-stimulating effects of cocaine in adolescent and adult female rats.

RATIONALE: Dopamine systems vary through development in a manner that can impact drugs acting on those systems. Dietary factors can also impact the effects of drugs acting on dopamine systems. OBJECTIVES: This study examined whether eating high fat chow alters locomotor effects of cocaine (1-56 mg/kg) in adolescent and adult female rats. METHODS: Cocaine was studied in rats (n = 6/group) with free access to standard (5.7% fat) or high fat (34.3%) chow or restricted access to high fat chow (body weight matched to rats eating standard chow). RESULTS: After 1 week of eating high fat chow (free or restricted access), sensitivity to cocaine was significantly increased in adolescent and adult rats, compared with rats eating standard chow. Sensitivity to cocaine was also increased in adolescent rats with restricted, but not free, access to high fat chow for 4 weeks. When adolescent and adult rats that previously ate high fat chow ate standard chow, sensitivity to cocaine returned to normal. In adolescent and adult female rats eating high fat chow, but not those eating standard chow, sensitivity to cocaine increased progressively over once weekly tests with cocaine (i.e., sensitization) in a manner that was not statistically different between adolescents and adults. CONCLUSIONS: These results show that eating high fat chow alters sensitivity of female rats to acutely administered cocaine and also facilitates the development of sensitization to cocaine. That the type of food consumed can increase drug effects might have relevance to vulnerability to abuse cocaine in the female population.

Sensitivity to apomorphine-induced yawning and hypothermia in rats eating standard or high-fat chow.

RATIONALE: Feeding conditions modify sensitivity to indirect- and direct-acting dopamine receptor agonists as well as the development of sensitization to these drugs. OBJECTIVES: This study examined whether feeding condition affects acute sensitivity to apomorphine-induced yawning or changes in sensitivity that occur over repeated drug administration. Quinpirole-induced yawning was also evaluated to see whether sensitization to apomorphine confers cross-sensitization to quinpirole. METHODS: Drug-induced yawning was measured in different groups of male Sprague Dawley rats (n = 6/group) eating high (34.3%) fat or standard (5.7% fat) chow. RESULTS: Five weeks of eating high-fat chow rendered otherwise drug-naïve rats more sensitive to apomorphine- (0.01-1.0 mg/kg, i.p.) and quinpirole- (0.0032-0.32 mg/kg, i.p.) induced yawning, compared with rats eating standard chow. In other rats, tested weekly with apomorphine, sensitivity to apomorphine-induced yawning increased (sensitization) similarly in rats with free access to standard or high-fat chow; conditioning to the testing environment appeared to contribute to increased yawning in both groups of rats. Food restriction decreased sensitivity to apomorphine-induced yawning across five weekly tests. Rats with free access to standard or high-fat chow and sensitized to apomorphine were cross-sensitized to quinpirole-induced yawning. The hypothermic effects of apomorphine and quinpirole were not different regardless of drug history or feeding condition. CONCLUSIONS: Eating high-fat chow or restricting access to food alters sensitivity to direct-acting dopamine receptor agonists (apomorphine, quinpirole), although the relative contribution of drug history and dietary conditions to sensitivity changes appears to vary among agonists.

Eating high fat chow increases the sensitivity of rats to 8-OH-DPAT-induced lower lip retraction.

Eating high fat food can alter sensitivity to drugs acting on dopamine systems; this study examined whether eating high fat food alters sensitivity to a drug acting on serotonin (5-HT) systems. Sensitivity to (+)-8-hydroxy-2-(dipropylamino) tetralin hydrobromide (8-OH-DPAT; 5-HT1A receptor agonist)-induced lower lip retraction was examined in separate groups (n=8-9) of rats with free access to standard (5.7% fat) or high fat (34.3% fat) chow; sensitivity to quinpirole (dopamine D3/D2 receptor agonist)-induced yawning was also examined. Rats eating high fat chow gained more body weight than rats eating standard chow and, after 6 weeks of eating high fat chow, they were more sensitive to 8-OH-DPAT (0.01-0.1 mg/kg)-induced lower lip retraction and quinpirole (0.0032-0.32 mg/kg)-induced yawning. These changes were not reversed when rats that previously ate high fat chow were switched to eating standard chow and sensitivity to 8-OH-DPAT and quinpirole increased when rats that previously ate standard chow ate high fat chow. These data extend previous results showing changes in sensitivity to drugs acting on dopamine systems in animals eating high fat chow to a drug acting at 5-HT1A receptors and they provide support for the notion that eating certain foods impacts sensitivity to drugs acting on monoamine systems.

Drinking sucrose enhances quinpirole-induced yawning in rats.

Food and drugs can activate brain dopamine systems and sensitivity to the effects of drugs acting on those systems is influenced by amount and content of food consumed. This study examined the effects of drinking sucrose on behavioral effects of the direct-acting dopamine receptor agonist quinpirole. Male Sprague-Dawley rats (n=6/group) had free access to water or 10% sucrose and quinpirole dose-response curves (yawning and hypothermia) were generated weekly for 8 weeks. Subsequently, all rats drank water for 8 weeks with quinpirole dose-response curves determined on weeks 9, 10, and 16. In rats drinking sucrose, the ascending (D3 receptor-mediated), but not descending (D2 receptor-mediated), limb of the yawning dose-response curve shifted leftward. The D3 receptor-selective antagonist PG01037 shifted the ascending limb of the dose-response curve to the right in all rats. When rats that previously drank sucrose drank water, their sensitivity to quinpirole did not return to normal. Quinpirole-induced hypothermia was not different between groups. These data show that drinking sucrose increases sensitivity to a dopamine D3, but not D2, receptor-mediated effect and that this change is long lasting. Dopamine receptors mediate the effects of many drugs and the actions of those drugs are likely impacted by dietary factors.

Influence of body weight and type of chow on the sensitivity of rats to the behavioral effects of the direct-acting dopamine-receptor agonist quinpirole.

RATIONALE: Amount and type of food can alter dopamine systems and sensitivity to drugs acting on those systems. OBJECTIVES: This study examined whether changes in body weight, food type, or both body weight and food type contribute to these effects. METHODS: Rats had free or restricted access (increasing, decreasing, or maintaining body weight) to standard (5.7% fat) or high-fat (34.3%) chow. RESULTS: In rats gaining weight with restricted or free access to high-fat chow, both limbs of the quinpirole yawning dose-response curve (0.0032-0.32 mg/kg) shifted leftward compared with rats eating standard chow. Restricting access to standard or high-fat chow (maintaining or decreasing body weight) decreased or eliminated quinpirole-induced yawning; within 1 week of resuming free feeding, sensitivity to quinpirole was restored, although the descending limb of the dose-response curve was shifted leftward in rats eating high-fat chow. These are not likely pharmacokinetic differences because quinpirole-induced hypothermia was not different among groups. PG01037 and L-741,626 antagonized the ascending and descending limbs of the quinpirole dose-response curve in rats eating high-fat chow, indicating D3 and D2 receptor mediation, respectively. Rats eating high-fat chow also developed insulin resistance. CONCLUSIONS: These results show that amount and type of chow alter sensitivity to a direct-acting dopamine-receptor agonist with the impact of each factor depending on whether body weight increases, decreases, or is maintained. These data demonstrate that feeding conditions, perhaps related to insulin and insulin sensitivity, profoundly impact the actions of drugs acting on dopamine systems.

Eating high-fat chow enhances sensitization to the effects of methamphetamine on locomotion in rats.

Eating high-fat chow can modify the effects of drugs acting directly or indirectly on dopamine systems and repeated intermittent drug administration can markedly increase sensitivity (i.e., sensitization) to the behavioral effects of indirect-acting dopamine receptor agonists (e.g., methamphetamine). This study examined whether eating high-fat chow alters the sensitivity of male Sprague Dawley rats to the locomotor stimulating effects of acute or repeated administration of methamphetamine. The acute effects of methamphetamine on locomotion were not different between rats (n=6/group) eating high-fat or standard chow for 1 or 4 weeks. Sensitivity to the effects of methamphetamine (0.1-10mg/kg, i.p.) increased progressively across 4 once per week tests; this sensitization developed more rapidly and to a greater extent in rats eating high-fat chow as compared with rats eating standard chow. Thus, while eating high-fat chow does not appear to alter sensitivity of rats to acutely-administered methamphetamine, it significantly increases the sensitization that develops to repeated intermittent administration of methamphetamine. These data suggest that eating certain foods influences the development of sensitization to drugs acting on dopamine systems.