Effects of the selective dopamine D-2 receptor agonist, quinpirole on sleep and wakefulness in the rat

Neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epilepsy in rats and its underlying mechanisms

INTRODUCTION

Epilepsy is a common neurological disorder that presents with challenging mechanisms and treatment strategies. This study investigated the neuroprotective effects of quinpirole on lithium chloride pilocarpine-induced epileptic rats and explored its potential mechanisms.

METHODS

Lithium chloride pilocarpine was used to induce an epileptic model in rats, and the effects of quinpirole on seizure symptoms and cognitive function were evaluated. The Racine scoring method, electroencephalography, and Morris water maze test were used to assess seizure severity and learning and memory functions in rats in the epileptic group. Additionally, immunohistochemistry and Western blot techniques were used to analyze the protein expression levels and morphological changes in glutamate receptor 2 (GluR2; GRIA2), BAX, and BCL2 in the hippocampi of rats in the epileptic group.

RESULTS

First, it was confirmed that the symptoms in rats in the epileptic group were consistent with features of epilepsy. Furthermore, these rats demonstrated decreased learning and memory function in the Morris water maze test. Additionally, gene and protein levels of GluR2 in the hippocampi of rats in the epileptic group were significantly reduced. Quinpirole treatment significantly delayed seizure onset and decreased the mortality rate after the induction of a seizure. Furthermore, electroencephalography showed a significant decrease in the frequency of the spike waves. In the Morris water maze test, rats from the quinpirole treatment group demonstrated a shorter latency period to reach the platform and an increased number of crossings through the target quadrant. Network pharmacology analysis revealed a close association between quinpirole and GluR2 as well as its involvement in the cAMP signaling pathway, cocaine addiction, and dopaminergic synapses. Furthermore, immunohistochemistry and Western blot analysis showed that quinpirole treatment resulted in a denser arrangement and a more regular morphology of the granule cells in the hippocampi of rats in the epileptic group. Additionally, quinpirole treatment decreased the protein expression of BAX and increased the protein expression of BCL2.

CONCLUSION

The current study demonstrated that quinpirole exerted neuroprotective effects in the epileptic rat model induced by lithium chloride pilocarpine. Additionally, it was found that the treatment not only alleviated the rats' seizure symptoms, but also improved their learning and memory abilities. This improvement was linked to the modulation of protein expression levels of GLUR2, BAX, and BCL2. These findings provided clues that would be important for further investigation of the therapeutic potential of quinpirole and its underlying mechanisms for epilepsy treatment.

An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease

Sleep disorders are among the most common nonmotor symptoms in Parkinson's disease and are associated with reduced cognition and health-related quality of life. Disturbed sleep can often present in the prodromal or early stages of this neurodegenerative disease, rendering it crucial to manage and treat these symptoms. Levodopa and dopaminergic agonists are frequently prescribed to treat motor symptoms in Parkinson's disease, and there is increasing interest in how these pharmacological agents affect sleep and their effect on concomitant sleep disturbances and disorders. In this review, we discuss the role of dopamine in regulating the sleep-wake state and the impact of neurodegeneration on sleep. We provide an overview of the effects of levodopa and dopaminergic agonists on sleep architecture, insomnia, excessive daytime sleepiness, sleep-disordered breathing, rapid eye movement sleep behavior disorder, and restless legs syndrome in Parkinson's disease. Levodopa and dopaminergic drugs may have different effects, beneficial or adverse, depending on dosing, method of administration, and differential effects on the different dopamine receptors. Future research in this area should focus on elucidating the specific mechanisms by which these drugs affect sleep in order to better understand the pathophysiology of sleep disorders in Parkinson's disease and aid in developing suitable therapies and treatment regimens.

CITATION

Scanga A, Lafontaine A-L, Kaminska M. An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease. J Clin Sleep Med. 2023;19(6):1133-1144.

The dopamine D2 agonist quinpirole impairs frontal mismatch responses to sound frequency deviations in freely moving rats

Aim

A reduced mismatch negativity (MMN) response is a promising electrophysiological endophenotype of schizophrenia that reflects neurocognitive impairment. Dopamine dysfunction is associated with symptoms of schizophrenia. However, whether the dopamine system is involved in MMN impairment remains controversial. In this study, we investigated the effects of the dopamine D2‐like receptor agonist quinpirole on mismatch responses to sound frequency changes in an animal model.

Methods

Event‐related potentials were recorded from electrocorticogram electrodes placed on the auditory and frontal cortices of freely moving rats using a frequency oddball paradigm consisting of ascending and equiprobable (ie, many standards) control sequences before and after the subcutaneous administration of quinpirole. To detect mismatch responses, difference waveforms were obtained by subtracting nondeviant control waveforms from deviant waveforms.

Results

Here, we show the significant effects of quinpirole on frontal mismatch responses to sound frequency deviations in rats. Quinpirole delayed the frontal N18 and P30 mismatch responses and reduced the frontal N55 MMN‐like response, which resulted from the reduction in the N55 amplitude to deviant stimuli. Importantly, the magnitude of the N55 amplitude was negatively correlated with the time of the P30 latency in the difference waveforms. In contrast, quinpirole administration did not clearly affect the temporal mismatch responses recorded from the auditory cortex.

Conclusion

These results suggest that the disruption of dopamine D2‐like receptor signaling by quinpirole reduces frontal MMN to sound frequency deviations and that delays in early mismatch responses are involved in this MMN impairment.

The subcutaneous administration of quinpirole delayed early mismatch response latencies and reduced a late MMN‐like response amplitude recorded from the frontal cortex but had no effect on those recorded from the auditory cortex. These observations suggest that increased dopamine D2‐like receptor signaling impairs MMN generation to sound frequency changes in the frontal cortex and that the neurochemical mechanisms of MMN vary according to the cortical area. As MMN is associated with cognitive function, these new findings may help develop treatment modalities for cognitive dysfunctions in schizophrenia.

Disrupted Sleep and Circadian Rhythms in Schizophrenia and Their Interaction With Dopamine Signaling

Sleep and circadian rhythm disruption (SCRD) is a common feature of schizophrenia, and is associated with symptom severity and patient quality of life. It is commonly manifested as disturbances to the sleep/wake cycle, with sleep abnormalities occurring in up to 80% of patients, making it one of the most common symptoms of this disorder. Severe circadian misalignment has also been reported, including non-24 h periods and phase advances and delays. In parallel, there are alterations to physiological circadian parameters such as body temperature and rhythmic hormone production. At the molecular level, alterations in the rhythmic expression of core clock genes indicate a dysfunctional circadian clock. Furthermore, genetic association studies have demonstrated that mutations in several clock genes are associated with a higher risk of schizophrenia. Collectively, the evidence strongly suggests that sleep and circadian disruption is not only a symptom of schizophrenia but also plays an important causal role in this disorder. The alterations in dopamine signaling that occur in schizophrenia are likely to be central to this role. Dopamine is well-documented to be involved in the regulation of the sleep/wake cycle, in which it acts to promote wakefulness, such that elevated dopamine levels can disturb sleep. There is also evidence for the influence of dopamine on the circadian clock, such as through entrainment of the master clock in the suprachiasmatic nuclei (SCN), and dopamine signaling itself is under circadian control. Therefore dopamine is closely linked with sleep and the circadian system; it appears that they have a complex, bidirectional relationship in the pathogenesis of schizophrenia, such that disturbances to one exacerbate abnormalities in the other. This review will provide an overview of the evidence for a role of SCRD in schizophrenia, and examine the interplay of this with altered dopamine signaling. We will assess the evidence to suggest common underlying mechanisms in the regulation of sleep/circadian rhythms and the pathophysiology of schizophrenia. Improvements in sleep are associated with improvements in symptoms, along with quality of life measures such as cognitive ability and employability. Therefore the circadian system holds valuable potential as a new therapeutic target for this disorder.

Escape From Oblivion: Neural Mechanisms of Emergence From General Anesthesia

The question of how general anesthetics suppress consciousness has persisted since the mid-19th century, but it is only relatively recently that the field has turned its focus to a systematic understanding of emergence. Once assumed to be a purely passive process, spontaneously occurring as residual levels of anesthetics dwindle below a critical value, emergence from general anesthesia has been reconsidered as an active and controllable process. Emergence is driven by mechanisms that can be distinct from entry to the anesthetized state. In this narrative review, we focus on the burgeoning scientific understanding of anesthetic emergence, summarizing current knowledge of the neurotransmitter, neuromodulators, and neuronal groups that prime the brain as it prepares for its journey back from oblivion. We also review evidence for possible strategies that may actively bias the brain back toward the wakeful state.

Dorsal Striatum Dopamine Levels Fluctuate Across the Sleep-Wake Cycle and Respond to Salient Stimuli in Mice

Dopamine is involved in numerous neurological processes, and its deficiency has been implicated in Parkinson’s disease, whose patients suffer from severe sleep disorders. Destruction of nigrostriatal dopaminergic neurons or dorsal striatum disrupts the sleep–wake cycle. However, whether striatal dopamine levels correlate with vigilance states still remains to be elucidated. Here, we employed an intensity-based genetically encoded dopamine indicator, dLight1.1, to track striatal dopamine levels across the spontaneous sleep–wake cycle and the dopaminergic response to external stimuli. We found that the striatal dLight1.1 signal was at its highest during wakefulness, lower during non-rapid eye movement (non-REM or NREM) sleep, and lowest during REM sleep. Moreover, the striatal dLight1.1 signal increased significantly during NREM sleep-to-wake transitions, while it decreased during wake-to-NREM sleep transitions. Furthermore, different external stimuli, such as sudden door-opening of the home cage or cage-change to a new environment, caused striatal dopamine release, whereas an unexpected auditory tone did not. Finally, despite both modafinil and caffeine being wake-promoting agents that increased wakefulness, modafinil increased striatal dopamine levels while caffeine did not. Taken together, our findings demonstrated that striatal dopamine levels correlated with the spontaneous sleep–wake cycle and responded to specific external stimuli as well as the stimulant modafinil.

Sleep and Wakefulness Are Controlled by Ventral Medial Midbrain/Pons GABAergic Neurons in Mice

Sleep-wake behavior is controlled by a wide range of neuronal populations in the mammalian brain. Although the ventral midbrain/pons (VMP) area is suggested to participate in sleep-wake regulation, the neuronal mechanisms have remained unclear. Here, we found that nonspecific cell ablation or selective ablation of GABAergic neurons by expressing diphtheria toxin fragment A in the VMP in male mice induced a large increase in wakefulness that lasted at least 4 weeks. In contrast, selective ablation of dopaminergic neurons in the VMP had little effect on wakefulness. Chemogenetic inhibition of VMP GABAergic neurons also markedly increased wakefulness. The wake-promoting effect of the VMP GABAergic neuron ablation or inhibition was attenuated to varying degrees by the administration of dopamine D1 or D2/3 receptor antagonists and abolished by the administration of both antagonists together. In contrast, chemogenetic activation of VMP GABAergic neurons very strongly increased slow-wave sleep and reduced wakefulness. These findings suggest that VMP GABAergic neurons regulate dopaminergic actions in the sleep-wake behavior of mice.SIGNIFICANCE STATEMENT Current understanding of the neuronal mechanisms and populations that regulate sleep-wake behavior is incomplete. Here, we identified a GABAergic ventral midbrain/pons area that is necessary for controlling the daily amount of sleep and wakefulness in mice. We also found that these inhibitory neurons control wakefulness by suppressing dopaminergic systems. Surprisingly, activation of these neurons strongly induced slow-wave sleep while suppressing wakefulness. Our study reveals a new brain mechanism critical for sleep-wake regulation.

Multifactorial sleep disturbance in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, ranking only behind Alzheimer's disease and affecting 2% of the population over the age of 65. Pathophysiologically, PD is characterized by selective degeneration of the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and striatal dopamine depletion. Patients may also exhibit mild-to-severe degeneration of other central and peripheral nervous tissues. The most dramatic symptoms of the disease are profound dopamine-responsive motor disturbances, including bradykinesia, akinesia, rigidity, resting tremor, and postural instability. PD patients commonly present with debilitating non-motor symptoms, including cognitive impairment, autonomic nervous system dysfunction, and sleep disturbance. Of these, sleep disturbance is the most consistently reported, and likely represents a disorder integrative of PD-related motor impairment, autonomic nervous system dysfunction, iatrogenic insult, and central neurodegeneration. The pathophysiology of PD may also indirectly disrupt sleep by increasing susceptibility to sleep disorders, including sleep disordered breathing, periodic limb movements, and REM behavior disorder. In this review, we will discuss these systems representing a multifactorial etiology in PD sleep disturbance.

Rotigotine may improve sleep architecture in Parkinson's disease: a double-blind, randomized, placebo-controlled polysomnographic study

BACKGROUND/OBJECTIVES

Growing evidence demonstrates that in Parkinson's Disease (PD) sleep disturbances are frequent and difficult to treat. Since the efficacy of rotigotine on sleep is corroborated by studies lacking polysomnography (PSG), this study explores the possible rotigotine-mediated impact on PSG parameters in PD patients.

METHODS

This is a randomized, double-blind, placebo-controlled, parallel-group study to determine the efficacy of rotigotine vs placebo on PSG parameters in moderately advanced PD patients. An unusual protocol was utilized, since patches were maintained from 18:00 h to awakening, minimizing the possible diurnal impact on motor symptoms. All participants underwent sleep PSG recordings, subjective sleep questionnaires (Parkinson Disease Sleep Scale [PDSS], Pittsburgh Sleep Quality Index [PSQI]), and the assessment of early-morning motor disability.

RESULTS

We evaluated 42 PD patients (Hoehn & Yahr stages 2 and 3) with sleep impairment randomly assigned to active branch (N =21) or placebo (N = 21). Rotigotine significantly increased sleep efficiency and reduced both wakefulness after sleep onset and sleep latency compared to placebo. Moreover, the mean change in REM sleep quantity was significantly higher in the rotigotine than placebo group. The improvement of PSG parameters corresponded to the amelioration of PDSS and PSQI scores together with the improvement of patient morning motor symptoms.

CONCLUSIONS

This study demonstrated the significant effect of rotigotine on sleep quality and continuity in PD patients by promoting sleep stability and increasing REM. The effectiveness of rotigotine on sleep may be ascribed to its pharmacokinetic/pharmacodynamic profile directly on both D1 and D2 receptors.

Effect of dopamine D4 receptor agonists on sleep architecture in rats

Dopamine plays a key role in the regulation of sleep-wake states, as revealed by the observation that dopamine-releasing agents such as methylphenidate have wake-promoting effects. However, the precise mechanisms for the wake-promoting effect produced by the enhancement of dopamine transmission are not fully understood. Although dopamine D1, D2, and D3 receptors are known to have differential effects on sleep architecture, the role of D4 receptors (D4Rs), and particularly the influence of D4R activation on the sleep-wake state, has not been studied so far. In this study, we investigated for the first time the effects of two structurally different D4R agonists, Ro 10-5824 and A-412997, on the sleep-wake states in rats. We found that both D4R agonists generally increased waking duration, and conversely, reduced non-rapid eye movement (NREM) sleep duration in rats. The onset of NREM sleep was also generally delayed. However, only the A-412997 agonist (but not the Ro 10-5824) influenced rapid eye movement sleep onset and duration. Furthermore, these effects were accompanied with an enhancement of EEG spectral power in the theta and the gamma bands. Our results suggest the involvement of dopamine D4R in the regulation of sleep-wake states. The activation of the D4R could enhance the arousal states as revealed by the behavioral and electrophysiological patterns in this study. Dopamine D4R may contribute to the arousal effects of dopamine-releasing agents such as methylphenidate.

Sleep Disturbances in Schizophrenia

Sleep disturbances are prevalent in patients with schizophrenia and play a critical role in the morbidity and mortality associated with the illness. Subjective and objective assessments of sleep in patients with schizophrenia have identified certain consistent findings. Findings related to the sleep structure abnormalities have shown correlations with important clinical aspects of the illness. Disruption of specific neurotransmitter systems and dysregulation of clock genes may play a role in the pathophysiology of schizophrenia-related sleep disturbances. Antipsychotic medications play an important role in the treatment of sleep disturbances in these patients and have an impact on their sleep structure.

D1 receptor agonist improves sleep-wake parameters in experimental parkinsonism

Both excessive daytime sleepiness (EDS) and rapid eye movement (REM) sleep deregulation are part of Parkinson's disease (PD) non-motor symptoms and may complicate dopamine replacement therapy. We report here that dopamine agonists act differentially on sleep architecture in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine macaque monkey. Continuous sleep and wake electroencephalographic monitoring revealed no effect of the selective dopamine D2 receptor agonist quinpirole on EDS, whereas the selective dopamine D1 receptor agonist SKF38393 efficiently alleviated EDS and restored REM sleep to baseline values. The present results question the relevance of abandoning D1 receptor agonist treatment in PD as it might actually improve sleep-related disorders.

Association between dopaminergic medications and nocturnal sleep in early-stage Parkinson's disease

BACKGROUND

Poor nocturnal sleep is common in Parkinson's disease (PD) and negatively impacts quality of life. There is little data on how dopaminergic drugs influence nocturnal sleep in PD, particularly in relation to medication timing. We examined the association between dopaminergic medications and subjective and objective nocturnal sleep in PD.

METHODS

Individuals with PD were recruited from the outpatient clinic. Demographics and disease information were collected. Patients underwent one-night polysomnography and responded to SCOPA-SLEEP, a self-administered questionnaire which includes a section on nighttime sleep and an overall measure of sleep quality; higher scores indicate worse sleep. Medication intake, including medication timing in relation to bedtime, was obtained and converted to levodopa equivalents.

RESULTS

41 Males and 21 females, median age 63.9 years, participated. Median disease duration was 5 years. After adjusting for age, sex, disease severity, and disease duration, greater total levodopa equivalent intake within 4 h of sleep was associated with higher total SCOPA-nighttime score (p = 0.009) and greater wake time after sleep onset (p = 0.049). Greater dopaminergic medication intake prior to sleep was also associated with less rapid eye movement (REM) sleep as a percent of total sleep time (p = 0.004).

CONCLUSIONS

Higher amounts of dopaminergic medications taken prior to sleep were associated with poor sleep quality and less REM sleep. Although poor nocturnal sleep in PD is likely multi-factorial in etiology, our findings suggest that timing and dose of medications prior to sleep need to be considered in its management.

Sleep and circadian rhythm dysregulation in schizophrenia

Sleep-onset and maintenance insomnia is a common symptom in schizophrenic patients regardless of either their medication status (drug-naive or previously treated) or the phase of the clinical course (acute or chronic). Regarding sleep architecture, the majority of studies indicate that non-rapid eye movement (NREM), N3 sleep and REM sleep onset latency are reduced in schizophrenia, whereas REM sleep duration tends to remain unchanged. Many of these sleep disturbances in schizophrenia appear to be caused by abnormalities of the circadian system as indicated by misalignments of the endogenous circadian cycle and the sleep-wake cycle. Circadian disruption, sleep onset insomnia and difficulties in maintaining sleep in schizophrenic patients could be partly related to a presumed hyperactivity of the dopaminergic system and dysfunction of the GABAergic system, both associated with core features of schizophrenia and with signaling in sleep and wake promoting brain regions. Since multiple neurotransmitter systems within the CNS can be implicated in sleep disturbances in schizophrenia, the characterization of the neurotransmitter systems involved remains a challenging dilemma.

Activation of D1 dopamine receptors induces emergence from isoflurane general anesthesia

BACKGROUND

A recent study showed that methylphenidate induces emergence from isoflurane anesthesia. Methylphenidate inhibits dopamine and norepinephrine reuptake transporters. The objective of this study was to test the hypothesis that selective dopamine receptor activation induces emergence from isoflurane anesthesia.

METHODS

In adult rats, we tested the effects of chloro-APB (D1 agonist) and quinpirole (D2 agonist) on time to emergence from isoflurane general anesthesia. We then performed a dose-response study to test for chloro-APB-induced restoration of righting during continuous isoflurane anesthesia. SCH-23390 (D1 antagonist) was used to confirm that the effects induced by chloro-APB are specifically mediated by D1 receptors. In a separate group of animals, spectral analysis was performed on surface electroencephalogram recordings to assess neurophysiologic changes induced by chloro-APB and quinpirole during isoflurane general anesthesia.

RESULTS

Chloro-APB decreased median time to emergence from 330 to 50 s. The median difference in time to emergence between the saline control group (n = 6) and the chloro-APB group (n = 6) was 222 s (95% CI: 77-534 s, Mann-Whitney test). This difference was statistically significant (P = 0.0082). During continuous isoflurane anesthesia, chloro-APB dose-dependently restored righting (n = 6) and decreased electroencephalogram δ power (n = 4). These effects were inhibited by pretreatment with SCH-23390. Quinpirole did not restore righting (n = 6) and had no significant effect on the electroencephalogram (n = 4) during continuous isoflurane anesthesia.

CONCLUSIONS

Activation of D1 receptors by chloro-APB decreases time to emergence from isoflurane anesthesia and produces behavioral and neurophysiologic evidence of arousal during continuous isoflurane anesthesia. These findings suggest that selective activation of a D1 receptor-mediated arousal mechanism is sufficient to induce emergence from isoflurane general anesthesia.

Neuropharmacology of Sleep and Wakefulness: 2012 Update

The development of sedative/hypnotic molecules has been empiric rather than rational. The empiric approach has produced clinically useful drugs but for no drug is the mechanism of action completely understood. All available sedative/hypnotic medications have unwanted side effects and none of these medications creates a sleep architecture that is identical to the architecture of naturally occurring sleep. This chapter reviews recent advances in research aiming to elucidate the neurochemical mechanisms regulating sleep and wakefulness. One promise of rational drug design is that understanding the mechanisms of sedative/hypnotic action will significantly enhance drug safety and efficacy.

The roles of the reward system in sleep and dreaming

The mesolimbic dopaminergic system (ML-DA) allows adapted interactions with the environment and is therefore of critical significance for the individual's survival. The ML-DA system is implicated in reward and emotional functions, and it is perturbed in schizophrenia, addiction, and depression. The ML-DA reward system is not only recruited during wakeful behaviors, it is also active during sleep. Here, we introduce the Reward Activation Model (RAM) for sleep and dreaming, according to which activation of the ML-DA reward system during sleep contributes to memory processes, to the regulation of rapid-eye movement (REM) sleep, and to the generation and motivational content of dreams. In particular, the engagement of ML-DA and associated limbic structures prioritizes information with high emotional or motivational relevance for (re)processing during sleep and dreaming. The RAM provides testable predictions and has clinical implications for our understanding of the pathogenesis of major depression and addiction.

To what extent do neurobiological sleep-waking processes support psychoanalysis?

Sigmund Freud's thesis was that there is a censorship during waking that prevents memory of events, drives, wishes, and feelings from entering the consciousness because they would induce anxiety due to their emotional or ethical unacceptability. During dreaming, because the efficiency of censorship is decreased, latent thought contents can, after dream-work involving condensation and displacement, enter the dreamer's consciousness under the figurative form of manifest content. The quasi-closed dogma of psychoanalytic theory as related to unconscious processes is beginning to find neurobiological confirmation during waking. Indeed, there are active processes that suppress (repress) unwanted memories from entering consciousness. In contrast, it is more difficult to find neurobiological evidence supporting an organized dream-work that would induce meaningful symbolic content, since dream mentation most often only shows psychotic-like activities.

Neuropharmacology of Sleep and Wakefulness

The development of sedative/hypnotic molecules has been empiric rather than rational. The empiric approach has produced clinically useful drugs but for no drug is the mechanism of action completely understood. All available sedative/hypnotic medications have unwanted side effects and none of these medications creates a sleep architecture that is identical to the architecture of naturally occurring sleep. This chapter reviews recent advances in research aiming to elucidate the neurochemical mechanisms regulating sleep and wakefulness. One promise of rational drug design is that understanding the mechanisms of sedative/hypnotic action will significantly enhance drug safety and efficacy.

Dopaminergic regulation of sleep and cataplexy in a murine model of narcolepsy

STUDY OBJECTIVES

To determine if the dopaminergic system modulates cataplexy, sleep attacks and sleep-wake behavior in narcoleptic mice.

DESIGN

Hypocretin/orexin knockout (i.e., narcoleptic) and wild-type mice were administered amphetamine and specific dopamine receptor modulators to determine their effects on sleep, cataplexy and sleep attacks.

PATIENTS OR PARTICIPANTS

Hypocretin knockout (n = 17) and wild-type mice (n = 21).

INTERVENTIONS

Cataplexy, sleep attacks and sleep-wake behavior were identified using electroencephalogram, electromyogram and videography. These behaviors were monitored for 4 hours after an i.p. injection of saline, amphetamine and specific dopamine receptor modulators (D1- and D2-like receptor modulators).

MEASUREMENTS AND RESULTS

Amphetamine (2 mg/kg), which increases brain dopamine levels, decreased sleep attacks and cataplexy by 61% and 67%, suggesting that dopamine transmission modulates such behaviors. Dopamine receptor modulation also had powerful effects on sleep attacks and cataplexy. Activation (SKF 38393; 20 mg/kg) and blockade (SCH 23390; 1 mg/kg) of D1-like receptors decreased and increased sleep attacks by 77% and 88%, without affecting cataplexy. Pharmacological activation of D2-like receptors (quinpirole; 0.5 mg/kg) increased cataplectic attacks by 172% and blockade of these receptors (eticlopride; 1 mg/kg) potently suppressed them by 97%. Manipulation of D2-like receptors did not affect sleep attacks.

CONCLUSIONS

We show that the dopaminergic system plays a role in regulating both cataplexy and sleep attacks in narcoleptic mice. We found that cataplexy is modulated by a D2-like receptor mechanism, whereas dopamine modulates sleep attacks by a D1-like receptor mechanism. These results support a role for the dopamine system in regulating sleep attacks and cataplexy in a murine model of narcolepsy.

Effect of dopaminergic substances on sleep/wakefulness in saline- and MPTP-treated mice

Sleep/wakefulness (S/W) disorders are frequent in Parkinson's disease (PD). The underlying causes have yet to be elucidated but dopaminergic neurodegenerative lesions seem to contribute to appearance of the disorders and anti-Parkinsonian medication is known to accentuate S/W problems. Hence, we reasoned that studying the acute effect of dopaminergic compounds on S/W in an animal model of PD might improve our knowledge of S/W regulation in the context of partial dopaminergic depletion. To this end, we tested the effect of levodopa (l-dopa), pergolide (a mixed D(2)/D(1) agonist) and lisuride (a D(2) agonist) on S/W recordings in MPTP-treated mice, in comparison with controls. Our results showed that dopaminergic compounds modify S/W amounts in both control and MPTP mice. Wakefulness amounts are greater in MPTP mice after l-dopa (50 mg kg(-1)) and lisuride (1 mg kg(-1)) injections compared with control mice. Moreover, the paradoxical sleep latency was significantly longer in MPTP mice after high-dose l-dopa administration. Our observations suggest that the actions of both l-dopa and lisuride on S/W differ slightly in MPTP mice relative to controls. Hence, MPTP-induced partial DA depletion may modulate the effect of dopaminergic compounds on S/W regulation.

The involvement of dopamine in the modulation of sleep and waking

Dopamine (DA)-containing neurons involved in the regulation of sleep and waking (W) arise in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). The VTA and SNc cells have efferent and afferent connections with the dorsal raphe nucleus (DRN), the pedunculopontine and laterodorsal tegmental nuclei (PPT/LDT), the locus coeruleus (LC), the lateral and posterior hypothalamus (LH), the basal forebrain (BFB), and the thalamus. Molecular cloning techniques have enabled the characterization of two distinct groups of DA receptors, D(1)-like and D(2)-like receptors. The D(1) subfamily includes the D(1) and D(5) receptors, whereas the D(2) subfamily comprises the D(2), D(3), and D(4) receptors. Systemic administration of a selective D(1) receptor agonist induces behavioral arousal, together with an increase of W and a reduction of slow wave sleep (SWS) and REM sleep (REMS). Systemic injection of a DA D(2) receptor agonist induces biphasic effects, such that low doses reduce W and increase SWS and REMS (predominant activation of the D(2) autoreceptor), whereas large doses induce the opposite effect (predominant facilitation of the D(2) postsynaptic receptor). Compounds with DA D(1) or D(2) receptor blocking properties augment non-REMS and reduce W. Preliminary findings tend to indicate that the administration of a DA D(3)-preferring agonist induces somnolence and sleep in laboratory animals and man. DA neurons in the VTA and the SNc do not change their mean firing rate across the sleep-wake cycle. It has been proposed that DA cells in the midbrain show a change in temporal pattern rather than firing rate during the sleep-wake cycle. The available evidence tends to indicate that during W there occurs an increase of burst firing activity of DA neurons, and an enhanced release of DA in the VTA, the nucleus accumbens (NAc), and a number of forebrain structures. A series of structures relevant for the regulation of the behavioral state, including the DRN, LDT/PPT, LC, and LH, could be partly responsible for the changes in the temporal pattern of activity of DA neurons.

Neural substrates of psychostimulant-induced arousal

Extensive research has provided substantial insight into the neurobiological mechanisms underlying the reinforcing, locomotor-activating and stereotypy-inducing actions of psychostimulants. The diverse behavioral effects of these drugs are superimposed on potent arousal-enhancing actions. Psychostimulant-induced arousal is a prominent contributing factor to the widespread use and abuse of these drugs. Moreover, enhanced arousal may be a critical component of the reinforcing and other behavioral actions of these drugs. Although long overlooked, recent work begins to identify the neural mechanisms involved in psychostimulant-induced arousal. For example, microdialysis studies demonstrate a close relationship between amphetamine-induced waking/arousal and amphetamine-induced increases in norepinephrine and dopamine efflux. Additionally, it is now clear that both norepinephrine and dopamine exert robust wake-promoting actions. The wake-promoting effects of norepinephrine involve synergistic actions of alpha1- and beta-receptors, whereas dopamine-induced waking involves both D1 and D2 receptors. Finally, additional studies have identified subcortical regions involved in the wake-promoting actions of both norepinephrine and amphetamine. These regions include, but may not be limited to, the medial septal area, the medial preoptic area, and the lateral hypothalamus. Combined, these and other observations indicate a prominent involvement of both norepinephrine and dopamine in stimulant-induced arousal via actions within a network of subcortical regions. Although it is clear that both norepinephrine and dopamine contribute to psychostimulant-induced arousal, the degree to which each transmitter system is necessary for the expression of stimulant-induced arousal remains to be fully elucidated.

Effects of selective dopamine D4 receptor antagonist, L-741,741, on sleep and wakefulness in the rat

The influence of the dopamine system upon sleep/wake states is not fully understood. To date, the role of dopamine D4 receptor has not been studied. The aim of this work is to study the influence of dopamine D4 receptor upon sleep/wake states in male rats. Male Wistar rats were implanted with electroencephalography and electromyography electrodes for sleep recording. Sleep/wake times were compared in rats first treated with control solution (vehicle) and the day after treated with a potent and highly selective D4 dopamine receptor antagonist. L-741,741 (1.5, 3, 6 mg/kg) or vehicle solution (10% DMSO in saline) was administered intraperitoneally at the beginning of the light period. Subsequently, 3 h of polysomnography were recorded and sleep-wake parameters evaluated. For statistical comparisons, Wilcoxon ranges test was performed. L-741,741 (1.5 mg/kg) only increased Light Slow Wave Sleep (SWS). 3 mg/kg enhanced Quiet Waking (QW) increasing number of episodes, whereas Active Waking (AW) was reduced decreasing mean episode duration. 6 mg/kg reduced number of episodes of Deep SWS and increased its latency. Light SWS was decreased reducing number of episodes and their duration. Total time spent asleep was reduced and time spent in AW was increased. REM latency was increased. These results suggest a role for D4 receptors in the regulation of wake and sleep.

Dopaminergic-adrenergic interactions in the wake promoting mechanism of modafinil

Adrenergic signaling regulates the timing of sleep states and sleep state-dependent changes in muscle tone. Recent studies indicate a possible role for noradrenergic transmission in the wake-promoting action of modafinil, a widely used agent for the treatment of excessive sleepiness. We now report that noradrenergic projections from the locus coeruleus to the forebrain are not necessary for the wake-promoting action of modafinil. The efficacy of modafinil was maintained after treatment of C57BL/6 mice with N-(2-chloroethyl)-N-ethyl 2-bromobenzylamine (DSP-4), which eliminates all noradrenaline transporter-bearing forebrain noradrenergic projections. However, the necessity for adrenergic receptors in the wake-promoting action of modafinil was demonstrated by the observation that the adrenergic antagonist terazosin suppressed the response to modafinil in DSP-4 treated mice. The wake-promoting efficacy of modafinil was also blunted by the dopamine autoreceptor agonist quinpirole. These findings implicate non-noradrenergic, dopamine-dependent adrenergic signaling in the wake-promoting mechanism of modafinil. The anatomical specificity of these dopaminergic-adrenergic interactions, which are present in forebrain areas that regulate sleep timing but not in brain stem areas that regulate sleep state-dependent changes in muscle tone, may explain why modafinil effectively treats excessive daytime sleepiness in narcolepsy but fails to prevent the loss of muscle tone that occurs in narcoleptic patients during cataplexy.

Sleep in schizophrenia patients and the effects of antipsychotic drugs

Insomnia is a common feature in schizophrenia. However, it seldom is the predominant complaint. Nevertheless, severe insomnia is often seen during exacerbations of schizophrenia, and may actually precede the appearance of other symptoms of relapse. The sleep disturbances of either never-medicated or previously treated schizophrenia patients are characterized by a sleep-onset and maintenance insomnia. In addition, stage 4 sleep, slow wave sleep (stages 3 and 4), non-REM (NREM) sleep in minutes and REM latency are decreased. The atypical antipsychotics olanzapine, risperidone, and clozapine significantly increase total sleep time and stage 2 sleep. Moreover, olanzapine and risperidone enhance slow wave sleep. On the other hand, the typical antipsychotics haloperidol, thiothixene, and flupentixol significantly reduce stage 2 sleep latency and increase sleep efficiency. Future research should address: (1) the sleep patterns in subtypes of schizophrenia patients; (2) the role of neurotransmitters other than dopamine in the disruption of sleep in schizophrenia; (3) the functional alterations in CNS areas related to the pathophysiology of schizophrenia during NREM sleep and REM sleep (brain imaging studies); (4) the short-term, intermediate-term, and long-term effects of atypical antisychotics on sleep variables.

Brain inhibitory mechanisms involved in basic and higher integrated sleep processes

Brain function is supported by central activating processes that are significant during waking, decrease during slow wave sleep following waking and increase again during paradoxical sleep during which brain activation is as high as, or higher than, during waking in nearly all structures. However, inhibitory mechanisms are crucial for sleep onset. They were first identified by behavioral, neuroanatomical and electrophysiological criteria, then by pharmacological and neurochemical ones. During slow wave sleep, they are supported by GABAergic mechanisms located at midbrain, mesopontine and pontine levels but are induced and sustained by forebrain and hindbrain influences. GABAergic processes are also responsible for paradoxical sleep occurrence, particularly by suppression of noradrenaline and serotonin (5-HT) inhibition of paradoxical sleep-generating structures. Hindbrain and forebrain modulate these structures situated at the mesopontine level. For sleep mentation, the noradrenergic and serotonergic silence is thought, today, to be directly, or indirectly, responsible for dopamine predominance and glutamate decrease in the nucleus accumbens, which could be the background of the well-known psychotic-like mental activity of dreaming.

AMPA receptor stimulation within the central nucleus of the amygdala elicits a differential activation of central dopaminergic systems

Appetitive and aversive arousing stimuli increase rates of dopamine (DA) release, particularly within the prefrontal cortex (PFC). Evidence suggests an activating influence of both the central (CeA) and basolateral (BlA) nuclei of the amygdala on DA neurotransmission. For example, lesions of CeA block stressor-induced increases in DA release. Additionally, electrical stimulation of BlA increases DA release in select terminal fields. Previous studies indicate that glutamatergic AMPA receptors modulate CeA and BlA output. However, the extent to which AMPA receptors participate in amygdala-dependent activation of DA neurotransmission is unknown. The current studies examined the effects of bilateral AMPA infusions within CeA or BlA on post-mortem and in vivo microdialysis indices of DA release. Additionally, stress is associated with moderate increases in serotonin (5-HT) neurotransmission that are also blocked by CeA lesions. Thus, the current studies also examined the impact of AMPA infusions on post-mortem indices of 5-HT utilization. AMPA infusion into CeA, but not BlA, increased post-mortem indices of DA and 5-HT release in a pattern comparable to that observed under appetitive/aversive conditions. In vivo microdialysis studies confirmed that AMPA infusions into CeA, but not BlA, increase extracellular PFC DA levels. When infused into sleeping animals, CeA-AMPA infusion also elicited a rapid-onset transition into waking. Thus, CeA-AMPA receptors exert an excitatory influence on DA and 5-HT neurotransmission and on behavioral state. Combined, these results suggest that CeA-AMPA receptors may participate in the coordination of neural systems involved in the regulation of behavioral state under high-arousal conditions.

Wake-promoting actions of dopamine D1 and D2 receptor stimulation

Multiple ascending neurotransmitter systems participate in the regulation of behavioral state. For example, noradrenergic, cholinergic, and serotonergic systems increase EEG and, in some cases, behavioral indices of arousal. The extent to which dopaminergic systems exert a similar activating influence on behavioral state remains unclear. The current studies examined the wake-promoting actions of centrally administered D1 and D2 receptor agonists. In these studies, intracerebroventricular infusions of a D1 (SKF-82958; 2.5 and 25 nmol) or D2 (quinpirole; 40 and 140 nmol)-agonist were made into sleeping animals. The effects of these infusions on electroencephalogram/electromyographic indices of sleep-wake state and behavior were examined. D1 agonist administration dose dependently increased time spent awake and suppressed rapid eye movement and slow-wave sleep in the 2 h immediately after infusion. D1 agonist administration also elicited modest increases in measures of locomotion and time spent grooming and eating. D2 agonist administration had similar wake-promoting actions, accompanied by modest effects on drinking and locomotion. Interestingly, D2 agonist administration also significantly increased time spent chewing on inedible material, an arousal/stress-related behavior. Overall, these results demonstrate that dopamine contributes to the alert waking state via actions of D1 and D2 receptors. Additionally or alternatively, these results further suggest a potential involvement of dopamine receptors in the induction of high-arousal states, including stress.

Relationship between low-dose amphetamine-induced arousal and extracellular norepinephrine and dopamine levels within prefrontal cortex

Despite the well-known and potent arousal-enhancing effects of amphetamine (AMPH)-like stimulants, the neurobiological substrates of AMPH-induced arousal have rarely been examined explicitly. Available evidence suggests the possible participation of noradrenergic and/or dopaminergic systems in the arousal-enhancing actions of AMPH-like stimulants. The current studies examined the extent to which low-dose AMPH-induced increases in waking are related to AMPH-induced increases in extracellular norepinephrine (NE) and dopamine (DA) levels within the prefrontal cortex (PFC), as measured by in vivo microdialysis. Vehicle injections elicited brief epochs of waking. Vehicle-induced waking was closely associated with a brief and moderate (50% above baseline) increase in NE levels. DA levels were less sensitive to the arousing actions of vehicle injections, with maximal increases of approximately 25% above baseline observed. 0.15 mg/kg and 0.25 mg/kg AMPH increased time spent awake, which resulted primarily from increases in quiet waking. Although the magnitude of the waking response did not differ substantially between the two doses across time, a trend for a more rapid recovery to baseline waking levels was observed at the higher dose, possibly suggesting the development of a relatively rapid-onset tolerance to the wake-promoting actions of AMPH at this dose. At the 0.15 mg/kg dose, AMPH elicited maximum increases of approximately 175% and 125% above baseline levels for NE and DA, respectively. The time course of AMPH-induced increases in waking closely paralleled the time course of AMPH-induced increases in both NE and DA efflux. These observations are consistent with the hypothesis that both increased DA and NE efflux contribute to the low-dose behavioral effects of AMPH-like stimulants, including the arousal-enhancing actions of these drugs. Additionally, these observations also suggest a possibly greater sensitivity of NE efflux, relative to DA, to moderately arousing conditions including low-dose AMPH-like stimulant administration.

Differential distribution and regulation of OX1 and OX2 orexin/hypocretin receptor messenger RNA in the brain upon fasting

To further understand the functions of the orexin/hypocretin system, we examined the expression and regulation of the orexin/hypocretin receptor (OX1R and OX2R) mRNA in the brain by using quantitative in situ hybridization. Expression of OX1R and OX2R mRNA exhibited distinct distribution patterns. Within the hypothalamus, expression for the OX1R mRNA was largely restricted in the ventromedial (VMH) and dorsomedial hypothalamic nuclei, while high levels of OX2R mRNA were contained in the paraventricular nucleus, VMH, and arcuate nucleus as well as in mammilary nuclei. In the amygdala, OX1R mRNA was expressed throughout the amygdaloid complex with robust labeling in the medial nucleus, while OX2R mRNA was only present in the posterior cortical nucleus of amygdala. High levels of OX2R mRNA were also observed in the ventral tegmental area. Moreover, both OX1R and OX2R mRNA were observed in the hippocampus, some thalamic nuclei, and subthalamic nuclei. Furthermore, we analyzed the effect of fasting on levels of OX1R and OX2R mRNA in the hypothalamic and amygdaloid subregions. After 20 h of fasting, levels of OX1R mRNA were significantly increased in the VMH and the medial division of amygdala. An initial decrease (14 h) and a subsequent increase (20 h) in OX1R mRNA levels after fasting were observed in the dorsomedial hypothalamic nucleus and lateral division of amygdala. Levels of OX2R mRNA were augmented in the arcuate nucleus, but remained unchanged in the dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, and amygdala following fasting. The time-dependent and region-specific regulatory patterns of OX1R and OX2R suggest that they may participate in distinct neural circuits under the condition of food deprivation.

Changes in EEG spectral power in the prefrontal cortex of conscious rats elicited by drugs interacting with dopaminergic and noradrenergic transmission

1. The electroencephalographic (EEG) effects of drugs interacting with dopaminergic and noradrenergic systems were studied in conscious rats. Power spectra (0 - 30 Hz) were recorded from electrodes implanted bilaterally in the prefrontal cortex. Drug effects on EEG power were calculated as the spectral power following drug administration divided by the spectral power after vehicle administration. 2. Dopaminergic agonists at low doses, (apomorphine 0. 01 mg kg-1 s.c., quinpirole 0.01 mg kg-1 i.p.) and dopaminergic antagonists (haloperidol 1 mg kg-1 i.p., raclopride 2.5 mg kg-1 s.c. ), which decrease dopaminergic transmission, induced an increase of EEG power. Conversely, dopaminergic agonists at higher doses (apomorphine 0.5 mg kg-1 s.c., quinpirole 0.5 mg kg-1 i.p.) which increase activation of postsynaptic D2 and D3 receptors, induced a decrease of EEG power. 3. The alpha1-adrenoceptor antagonists (phenoxybenzamine 0.64 mg kg-1 s.c., prazosin 0.32 mg kg-1 s.c.) and the alpha2-adrenoceptor agonists (UK 14304 0.05 mg kg-1 s.c., clonidine 0.025 mg kg-1 i.p.), which decrease noradrenergic transmission, induced an increase of EEG power. Conversely, the alpha1-adrenoceptor agonist, cirazoline (0.05 mg kg-1 s.c.), the adrenergic agent modafinil (250, 350 mg kg-1 i.p.) and alpha2-adrenoceptor antagonists (RX 821002 0.01 mg kg-1 s.c., yohimbine 0.5 mg kg-1 i.p.), which increase noradrenergic transmission, induced a decrease of EEG power. The effects of prazosin (0.64 mg kg-1 s.c.) were dose-dependently antagonized by co-administration with modafinil and cirazoline, but not by apomorphine. 4. In conclusion, pharmacological modulation of dopaminergic and noradrenergic transmission may result in consistent EEG changes: decreased dopaminergic or noradrenergic activity induces an increase of EEG spectral power; while increased dopaminergic or noradrenergic activity decreases EEG spectral power.

Effects of prolactin on sleep in cyclic rats

We previously demonstrated that pregnancy-associated sleep enhancement is correlated with the daily surges of prolactin (PRL). However, in spite of a surge of PRL in the proestrous night, a reduction of nocturnal sleep occurs in phase with proestrus. Therefore, to clarify the physiological role of PRL in sleep regulation during the estrous cycle, time-course changes in sleep were analyzed in bromocriptine (CB-154)-treated and/or PRL-supplemented female rats. Sleep patterns characteristic of proestrus-to-estrus were not affected by the CB-154 treatment. In contrast, nocturnal rapid eye movement sleep (REMS) was significantly increased after the PRL supplementation. The CB-154 treatment diminished the REMS-enhancing effect of PRL. Thus, the results suggest that the endogenous PRL is not crucial for the regulation of sleep during the estrous cycle, while exogenous PRL can enhance REMS.

Reaction of sleep-wakefulness cycle to stress is related to differences in hypothalamo-pituitary-adrenal axis reactivity in rat

Acute stress is known to modify sleep-wakefulness cycle, although with considerable interindividual differences. The origin of these individual differences remains unknown. One possibility is an involvement of the hypothalamo-pituitary-adrenal axis (HPA), as its reactivity is correlated with an individual's behavioral reactivity to stress, and it is known to influence the sleep-wakefulness cycle. The present study was designed to analyze relationships between natural differences in behavioral reactivity to stress associated with differential HPA reactivity and stress-induced changes in sleep-wakefulness. Adult rats were classified into two sub-groups according to their locomotor reactivity to a mild stress (novel environment): the 'low responders (LR)' and the 'high responders (HR)' animals exhibited different glucocorticoid secretion in response to stress. We show that immobilization stress induced an increase in wakefulness in LR animals and a decrease in wakefulness in HR animals. On the other hand, paradoxical sleep was increased in both LR and HR animals. Moreover, we observed that LR animals slept more than the HR animals, whereas the two groups had similar levels of paradoxical sleep. These results indicate that the response of the sleep-wakefulness cycle to stress is related to the behavioral reactivity to stress, in turn governed by the individual's reactivity of the HPA axis. The involvement of dopaminergic mechanisms is discussed.

Effects of the D3 preferring dopamine agonist pramipexole on sleep and waking, locomotor activity and striatal dopamine release in rats

Quantitation of 2 h sessions after administration of the D3 preferring dopamine (DA) agonist pramipexole (10-500 microg/kg) showed dose-related effects on wakefulness (W), slow wave sleep (SWS) and REM sleep in rats. The 30 microg/kg dose of the DA agonist increased SWS and REM sleep and reduced W during the first recording hour, while the 500 microg/kg dose augmented W. On the other hand, W was increased while SWS and REMS were decreased after the 500 microg/kg dose during the second recording hour. The mixed D2- and D3 receptor antagonist YM-09151-2 (30-500 microg/kg), which per se affected sleep variables prevented the increase of REMS induced by pramipexole. Furthermore, the highest doses (500-1000 microg/kg) of the DA antagonist effectively antagonized the increase of W and reduction of SWS induced by the 500 microg/kg dose of the DA agonist. Pramipexole (30-100 microg/kg) induced a decrease of locomotor activity during the 2 h recording period. In addition, the 500 microg/kg dose gave rise to an initial reduction of motor behavior which was reverted 2 h later. Pramipexole (30 and 500 microg/kg) did not significantly affect striatal DA release during the first two hours following drug administration, as measured by microdialysis. It is tentatively suggested that D3 receptor could be involved in the pramipexole-induced increase of sleep and reduction of locomotor activity. On the other hand, the increase of W and of motor behavior after relatively high doses could be related to activation of postsynaptic D2 receptor.

Interactions between D1 and D2 dopamine receptor family agonists and antagonists: the effects of chronic exposure on behavior and receptor binding in rats and their clinical implications

Functional interactions between dopamine receptor subtypes may affect behavioral and biochemical responses which serve as models for neuropsychiatric illnesses and the clinical effects of drug therapy. We evaluated the effects of chronic exposure to the selective D1 receptor antagonist SCH 23390, and the selective D2 receptor antagonist metoclopramide, on spontaneous and drug-induced behavior and receptor density in rats, and then determined how these effects would be modified by concurrent administration of antagonists or agonists [SKF 38393, LY 171555 (quinpirole)] selective for the complementary receptor subtype. Administered alone, both the D1 and D2 antagonists had acute cataleptic effects to which animals became tolerant following chronic treatment, but the selective antagonists had opposing effects on spontaneous locomotor activity. Both antagonists produced equivalent, supersensitive behavioral responses to apomorphine, and resulted in an increase in D2 receptor density. Coadministration of the D1 and D2 antagonists had a synergistic effect on catalepsy, attenuated the effects on spontaneous locomotor activity observed with either drug alone, and had an additive effect on both apomorphine-induced stereotypic behavior and D2 receptor proliferation. On the other hand, when either selective antagonist was combined with the agonist selective for the complementary receptor subtype, both D2 receptor proliferation and behavioral supersensitivity were completely blocked. Combined antagonist-agonist treatments had opposing effects on the development of tolerance to antagonist-induced catalepsy. D2 - but not D1 - receptor densities were correlated with animals' behavioral responses to apomorphine. There results support and extend the notion that complex functional interactions between D1 and D2 receptor families occur within the central nervous system, and suggest that novel effects might be derived from combined administration of receptor selective agonists and antagonists.

Evidence for the occurrence of depressant EEG effects after stimulation of dopamine D3 receptors: a computerized study in rabbits

The putative dopamine D3 receptor agonist, (+/-) 7-OH-di-n-propylaminotetralin (+/- 7-OH-DPAT), induced depressant effects on rabbit EEG at the dose of 1 mg/kg i.v. Bromocriptine, a preferential dopamine D2 receptor agonist, induced EEG activation at the dose of 0.5 mg/kg i.v. Although the lack of very selective ligands makes it difficult to discriminate between D2- and D3- dependent effects, these findings suggest that -unlike D2 receptors-dopamine D3 receptors may mediate depressant effects on the electrocorticogram.

Local administration of dopaminergic drugs into the ventral tegmental area modulates cataplexy in the narcoleptic canine

Cataplexy in the narcoleptic canine may be modulated by systemic administration of monoaminergic compounds. In the present study, we have investigated the effects of monoaminergic drugs on cataplexy in narcoleptic canines when perfused locally via microdialysis probes in the amygdala, globus pallidus/putamen, basal forebrain, pontine reticular formation and ventral tegmental area of narcoleptic and control Doberman pinchers. Cataplexy was quantified using the Food-Elicited Cataplexy Test and analyzed by electroencephalogram, electroculogram and electromyogram. Local perfusion with the monoaminergic agonist quinpirole, 7-OH-DPAT and BHT-920, into the ventral tegmental area produced a dose-dependent increase in cataplexy without significantly reducing basal muscle tone. Perfusion with the antagonist raclopride in the same structure produced a moderate reduction in cataplexy. Local perfusion with quinpirole, 7-OH-DPAT and BHT-920 into the globus pallidus/putamen also produced an increase, while raclopride produced a decrease, in cataplexy in narcoleptic canines. In control animals, none of the above drugs produced cataplexy or muscle atonia when perfused into either the ventral tegmental area or the globus pallidus/putamen. Other monoaminergic drugs tested in these two brain areas; prazosin, yohimbine, amphetamine, SKF 38393 and SCH 23390 had no effects on cataplexy. Local perfusion with each of the above listed drugs had no effect on cataplexy in any of the other brain regions examined. These findings show that cataplexy may be regulated by D2/D3 dopaminergic receptors in the ventral tegmental area and perhaps the globus pallidus/ putamen. It is suggested that neurons in the mesolimbic dopamine system of narcoleptics are hypersensitive to dopaminergic autoreceptor agonists.

Effects of a D2 receptor agonist RO 41-9067 alone and with clonidine on sleep parameters in the rat

The effects of RO 41-9067, a D2 dopamine receptors agonist, on different sleep parameters were studied in the rat. RO 41-9067 dose dependently decreased paradoxical sleep, and only at the higher dose increased waking during the light period. In contrast, the higher dose of RO 41-9067 increased paradoxical sleep and decreased waking during the dark period. Finally, the combination of RO 41-9067 and clonidine significantly prevent the decrease of total sleep time and paradoxical sleep found after clonidine alone. These results, compared with those of classical D2 dopamine receptors agonists, suggest an action for RO 41-9067 on D2 dopamine receptors depending on the cerebral structure, a different action particularly on the striatum and/or on the structures responsible for paradoxical sleep. An active role for D2 dopamine receptors and an interaction between noradrenergic and dopaminergic systems in the regulation of sleep is proposed.

Increased waking after intra-accumbens injection of m-chlorophenylbiguanide: prevention with serotonin or dopamine receptor antagonists

Bilateral injection of the selective 5-HT3 receptor agonist m-chlorophenylbiguanide (5.0-40.0 micrograms) into the nucleus accumbens of the rat significantly increased waking and decreased slow wave sleep. Rapid eye movement (REM) sleep remained unchanged. Pretreatment with the 5-HT3 receptor antagonist MDL 72222 (1aH,3a,5a, H-tropan-3-yl-3,5-dichloro-benzoate) (0.5 mg/kg s.c.) reversed the effects of m-chlorophenylbiguanide (10.0-20.0 micrograms) on sleep and waking. Blockade of the dopamine D1 or D2 receptor with (+)-SCH 23390 (0.25 mg/kg s.c.) or YM-09151-2 (cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4- methylaminobenzamide) (0.5 mg/kg s.c.), respectively antagonized the increase of waking and reduction of slow wave sleep induced by m-chloro-phenylbiguanide (10.0 micrograms). Our results tend to indicate that the increase of wakefulness after injection of the selective 5-HT3 receptor agonist m-chlorophenylbiguanide into the nucleus accumbens is partly related to the release of endogenous dopamine. In addition, they suggest that concomitant stimulation of both accumbens dopamine D1 and D2 receptor-related mechanisms is a necessary prerequisite to increase wakefulness.

Autoradiographic analysis of D1 and D2 dopaminergic receptors in rat brain after paradoxical sleep deprivation

Previous work had shown that paradoxical sleep deprivation (PSD) results in potentiation of several apomorphine-induced behaviors, leading to the suggestion that PSD induces an upregulation of brain dopamine receptors. In this study, quantitative receptor autoradiography was used to verify whether PSD does, in fact, induce alterations in D1 or D2 receptor binding, and to investigate the regional brain specificity of such effects. After 96 h of PSD, [3H]SCH-23390 binding to D1 receptors was examined in 30 different brain areas of 10 experimental and 10 cage control rats. [3H]Spiperone was used to label D2 sites in adjacent tissue sections. Results revealed a 39% increase in [3H]SCH-23390 binding in the entorhinal cortex of PSD rats (p < 0.05), but no other changes in any of the remaining 29 brain areas examined. In contrast, [3H]spiperone binding was significantly elevated in the n. accumbens (+45%) and in all subregions of the caudate-putamen (range: +13% to +23%). These results, thus, provide evidence that PSD increases D2 but not D1 receptor binding in brain. The present results also suggest that upregulated D2 receptors can account for the previously reported changes in apomorphine-induced behaviors after PSD.

Effects of dopamine on type I chemoreceptor cells of the rat carotid body

The effects of dopamine (DA) were studied on type I cells of the rat carotid body. DA (0.35 to 8.4 x 10(-4) M) elicited a long-lasting depolarization and decreased input resistance (Ro) in 75% of the cells, in a dose-dependent manner. Hyperpolarization and increased Ro were observed in 8% of cells. Membrane potential (Em) and Ro changes were highly correlated (-0.62, P < 0.001). The reversal potential (Erev) of the DA effect was +2.16 +/- 4.75 (mV +/- S.E.M.).

Biphasic effects of dopamine agonist N-0434 on locomotor behaviors in rats

The effects of a dopamine agonist, (+/-)-2-(N-penylethyl-N-propyl)amino-5- hydroxytetralin (N-0434) (SC doses of 0.00, 0.01, 0.1, and 1.0 mg/kg) were tested in rats for 120 min in an activity monitor. The durations in seconds of horizontal locomotor time, rearing time, stereotypy time, and margin time (thigmotaxis) were measured during 12 10-min time blocks. N-0434 (0.1 and 1.0 mg/kg) resulted in biphasic effects (initial inhibition followed by potentiation) of linear locomotor time and an attenuation of thigmotaxis. The 0.1- and 1.0-mg/kg doses initially suppressed rearing time but had mixed potentiation effects. The 0.01- to 1.0-mg/kg doses suppressed stereotypy time. The differential behavioral profiles were discussed in reference to the functions of dopamine receptors.

Electroencephalographic correlates of the sedative effects of dopamine agonists presumably acting on autoreceptors

Alterations both in the activity of the cortical EEG and behaviour were studied after administration of dopamine receptor agonists. In addition to apomorphine, which provided contrasting effects, both on the EEG and behaviour, when small and large doses were compared, alterations elicited by the D2 agonist, quinpirole and another agonist, with preference for dopamine D2 autoreceptors, talipexole (B-HT 920), were evaluated by using telemetric EEG recordings in rats. Similarly to apomorphine, quinpirole produced opposite effects after small and large doses: a small dose (0.05 mg/kg) led to sedation and an increase of EEG power spectra in all of the bands, except beta 2, whereas a larger dose (0.5 mg/kg) elicited stereotypy and desynchronization of the EEG, with a characteristic increase of power in the alpha 1 band. The effects on the EEG and on behaviour, obtained with the small dose of quinpirole were very similar to those of a small dose of apomorphine (0.05 mg/kg) and a small dose of talipexole (0.02 mg/kg) but even the large dose of talipexole (0.5 mg/kg) produced similar effects: all of these treatments produced behavioural sedation and an increase of power in the EEG in all of the bands, except beta 2; such increases appeared most pronounced in the delta band. The present study provides further evidence that drugs, which are assumed to activate dopamine autoreceptors, are effective in inducing sedation. This sedation was accompanied by a characteristic pattern, observed in EEG power spectra analysis.

D-1 agonist, SKF 38393, but not a D-2 agonist, produces a cholinergically mediated analeptic effect in rabbits

SKF 38393 (2-15 mg/kg, IV), but not quinpirole, shortened the duration of loss of righting reflex produced in pentobarbital-narcotized rabbits. This effect was blocked by atropine (2-5 mg/kg, IV), but not by atropine methylbromide, suggesting that a central cholinergic mechanism was involved. The analeptic effect was also blocked by SCH 23390 (0.1 mg/kg, IV) or raclopride (5 mg/kg, IV). These results indicate that SKF 38393 activates central cholinergic neurons, which in turn initiate the analeptic effect. However, the fact that raclopride also blocked the SKF 38393 analeptic effect, but quinpirole did not exert any analeptic effect, suggests that a D-1/D-2 modulation of cholinergic systems may be involved in the SKF 38393-induced analeptic effect. These results also support our earlier findings and view that cocaine-induced analeptic activity is mediated by a dopaminergic-cholinergic mechanism.

The dopamine D1 receptor is involved in the regulation of REM sleep in the rat

The dopamine D1 receptor agonist, SKF 38393, and the D1 antagonist, SCH 23390, were studied for their effects on sleep in the rat. Over 6 h, SKF 38393 (0.1-10 mg/kg s.c.) dose dependently reduced the amount of rapid eye movement (REM) sleep and enhanced the duration of wakefulness. The drug affected REM at low doses (ED50 = 0.4 mg/kg) at which wakefulness was unchanged and the characteristic grooming behavior was not apparent. REM changes were characterized by a decrease in the number of episodes with no alteration of latency to the first episode. Over a very low dose range (0.003-0.3 mg/kg s.c.), SCH 23390 enhanced the amount of REM by increasing both number and average duration of episodes. There was also a moderate increase of non-REM sleep but the percent change was less marked than that occurring for REM. Given at 0.003 mg/kg, SCH 23390 prevented the REM changes induced by SKF 38393 (0.3-3 mg/kg). It is suggested that D1 receptors are involved in the regulation of the REM sleep process.