Dopamine and noradrenaline efflux in the prefrontal cortex in the light and dark period: effects of novelty and handling and comparison to the nucleus accumbens

Neurological Insights into Sleep Disorders in Parkinson's Disease

Parkinson's disease (PD) is a common multidimensional neurological disorder characterized by motor and non-motor features and is more prevalent in the elderly. Sleep disorders and cognitive disturbances are also significant characteristics of PD. Sleep is an important physiological process for normal human cognition and physical functioning. Sleep deprivation negatively impacts human physical, mental, and behavioral functions. Sleep disturbances include problems falling asleep, disturbances occurring during sleep, abnormal movements during sleep, insufficient sleep, and excessive sleep. The most recognizable and known sleep disorders, such as rapid-eye-movement behavior disorder (RBD), insomnia, excessive daytime sleepiness (EDS), restless legs syndrome (RLS), sleep-related breathing disorders (SRBDs), and circadian-rhythm-related sleep-wake disorders (CRSWDs), have been associated with PD. RBD and associated emotional disorders are common non-motor symptoms of PD. In individuals, sleep disorders and cognitive impairment are important prognostic factors for predicting progressing neurodegeneration and developing dementia conditions in PD. Studies have focused on RBD and its associated neurological changes and functional deficits in PD patients. Other risks, such as cognitive decline, anxiety, and depression, are related to RBD. Sleep-disorder diagnosis is challenging, especially in identifying the essential factors that disturb the sleep-wake cycle and the co-existence of other concomitant sleep issues, motor symptoms, and breathing disorders. Focusing on sleep patterns and their disturbances, including genetic and other neurochemical changes, helps us to better understand the central causes of sleep alterations and cognitive functions in PD patients. Relations between α-synuclein aggregation in the brain and gender differences in sleep disorders have been reported. The existing correlation between sleep disorders and levels of α-synuclein in the cerebrospinal fluid indicates the risk of progression of synucleinopathies. Multidirectional approaches are required to correlate sleep disorders and neuropsychiatric symptoms and diagnose sensitive biomarkers for neurodegeneration. The evaluation of sleep pattern disturbances and cognitive impairment may aid in the development of novel and effective treatments for PD.

Dopamine activity on the perceptual salience for recognition memory

To survive, animals must recognize relevant stimuli and distinguish them from inconspicuous information. Usually, the properties of the stimuli, such as intensity, duration, frequency, and novelty, among others, determine the salience of the stimulus. However, previously learned experiences also facilitate the perception and processing of information to establish their salience. Here, we propose “perceptual salience” to define how memory mediates the integration of inconspicuous stimuli into a relevant memory trace without apparently altering the recognition of the physical attributes or valence, enabling the detection of stimuli changes in future encounters. The sense of familiarity is essential for successful recognition memory; in general, familiarization allows the transition of labeling a stimulus from the novel (salient) to the familiar (non-salient). The novel object recognition (NOR) and object location recognition (OLRM) memory paradigms represent experimental models of recognition memory that allow us to study the neurobiological mechanisms involved in episodic memory. The catecholaminergic system has been of vital interest due to its role in several aspects of recognition memory. This review will discuss the evidence that indicates changes in dopaminergic activity during exposure to novel objects or places, promoting the consolidation and persistence of memory. We will discuss the relationship between dopaminergic activity and perceptual salience of stimuli enabling learning and consolidation processes necessary for the novel-familiar transition. Finally, we will describe the effect of dopaminergic deregulation observed in some pathologies and its impact on recognition memory.

HIV-Associated Apathy/Depression and Neurocognitive Impairments Reflect Persistent Dopamine Deficits

Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.

Synergistic Effect of Several Neurotransmitters in PFC-NAc-VTA Neural Circuit for the Anti-Depression Effect of Shuganheweitang in a Chronic Unpredictable Mild Stress Model

Depression, a major worldwide mental disorder, leads to massive disability and can result in death. The PFC-NAc-VTA neuro circuit is related to emotional, neurovegetative, and cognitive functions, which emerge as a circuit-level framework for understanding reward deficits in depression. Neurotransmitters, which are widely distributed in different brain regions, are important detected targets for the evaluation of depression. Shuganheweitang (SGHWT) is a popular prescription in clinical therapy for depression. In order to investigate its possible pharmacodynamics and anti-depressive mechanism, the complex plant material was separated into different fractions. These in low and high doses, along with low and high doses of SGHWT were tested in animal behavior tests. The low and high doses of SGHWT were more effective than the various fractions, which indicate the importance of synergistic function in traditional Chinese medicine. Furthermore, amino acid (GABA, Glu) and monoamine neurotransmitters (DA, 5-HT, NA, 5-HIAA) in the PFC-NAc-VTA neuro circuit were investigated by UPLC-MS/MS. The level trend of DA and 5-HT were consistent in the PFC-NAc-VTA neuro circuit, whereas 5-HIAA was decreased in the PFC, Glu was decreased in the PFC and VTA, and NA and GABA were decreased in the NAc. The results indicate that the pathogenesis of depression is associated with dysfunction of the PFC-NAc-VTA neural circuit, mainly through the neural projection effects of neurotransmitters associated with various brain regions in the neural circuit. PCA and OPLS-DA score plots demonstrated the similarities of individuals within each group and the differences among the groups. In this study, SGHWT could regulate the concentration level of different neurotransmitters in the PFC-NAc-VTA neuro circuit to improve the depression, which benefitted from the recognition of the brain reward circuitry in mood disorders.

Altered dopaminergic firing pattern and novelty response underlie ADHD-like behavior of SorCS2-deficient mice

Attention deficit hyperactivity disorder (ADHD) is the most frequently diagnosed neurodevelopmental disorder worldwide. Affected individuals present with hyperactivity, inattention, and cognitive deficits and display a characteristic paradoxical response to drugs affecting the dopaminergic system. However, the underlying pathophysiology of ADHD and how this relates to dopaminergic transmission remains to be fully understood. Sorcs2^-/- mice uniquely recapitulate symptoms reminiscent of ADHD in humans. Here, we show that lack of SorCS2 in mice results in lower sucrose intake, indicating general reward deficits. Using in-vivo recordings, we further find that dopaminergic transmission in the ventral tegmental area (VTA) is shifted towards a more regular firing pattern with marked reductions in the relative occurrence of irregular firing in Sorcs2^-/- mice. This was paralleled by abnormal acute behavioral responses to dopamine receptor agonists, suggesting fundamental differences in dopaminergic circuits and indicating a perturbation in the balance between the activities of the postsynaptic dopamine receptor DRD1 and the presynaptic inhibitory autoreceptor DRD2. Interestingly, the hyperactivity and drug response of Sorcs2^-/- mice were markedly affected by novelty. Taken together, our findings show how loss of a candidate ADHD-risk gene has marked effects on dopaminergic circuit function and the behavioral response to the environment.

Autophagy status as a gateway for stress-induced catecholamine interplay in neurodegeneration

The catecholamine-containing brainstem nuclei locus coeruleus (LC) and ventral tegmental area (VTA) are critically involved in stress responses. Alterations of catecholamine systems during chronic stress may contribute to neurodegeneration, including cognitive decline. Stress-related catecholamine alterations, while contributing to anxiety and depression, might accelerate neuronal degeneration by increasing the formation of toxic dopamine and norepinephrine by-products. These, in turn, may impair proteostasis within a variety of cortical and subcortical areas. In particular, the molecular events governing neurotransmission, neuroplasticity, and proteostasis within LC and VTA affect a variety of brain areas. Therefore, we focus on alterations of autophagy machinery in these nuclei as a relevant trigger in this chain of events. In fact, these catecholamine-containing areas are mostly prone to autophagy-dependent neurodegeneration. Thus, we propose a dynamic hypothesis according to which stress-induced autophagy alterations within the LC-VTA network foster a cascade towards early neurodegeneration within these nuclei.

Autophagy-Based Hypothesis on the Role of Brain Catecholamine Response During Stress

Stressful events, similar to abused drugs, significantly affect the homeostatic balance of the catecholamine brain systems while activating compensation mechanisms to restore balance. In detail, norepinephrine (NE)- and dopamine (DA)-containing neurons within the locus coeruleus (LC) and ventral tegmental area (VTA), are readily and similarly activated by psychostimulants and stressful events involving neural processes related to perception, reward, cognitive evaluation, appraisal, and stress-dependent hormonal factors. Brain catecholamine response to stress results in time-dependent regulatory processes involving mesocorticolimbic circuits and networks, where LC-NE neurons respond more readily than VTA-DA neurons. LC-NE projections are dominant in controlling the forebrain DA-targeted areas, such as the nucleus accumbens (NAc) and medial pre-frontal cortex (mPFC). Heavy and persistent coping demand could lead to sustained LC-NE and VTA-DA neuronal activity, that, when persisting chronically, is supposed to alter LC-VTA synaptic connections. Increasing evidence has been provided indicating a role of autophagy in modulating DA neurotransmission and synaptic plasticity. This alters behavior, and emotional/cognitive experience in response to drug abuse and occasionally, to psychological stress. Thus, relevant information to address the role of stress and autophagy can be drawn from psychostimulants research. In the present mini-review we discuss the role of autophagy in brain catecholamine response to stress and its dysregulation. The findings here discussed suggest a crucial role of regulated autophagy in the response and adaptation of LC-NE and VTA-DA systems to stress.

Nigrostriatal and mesolimbic control of sleep-wake behavior in rat

The midbrain dopamine system via the dorsal and ventral striatum regulates a wide range of behaviors. To dissect the role of dopaminergic projections to the dorsal striatum (nigrostriatal projection) and ventral striatum (mesolimbic projection) in sleep-wake behavior, we selectively chemogenetically stimulated nigrostriatal or mesolimbic projections and examined the resulting effects on sleep in rats. Stimulation of nigrostriatal pathways increased sleep and EEG delta power, while stimulation of mesolimbic pathways decreased sleep and reduced cortical EEG power. These results indicate that midbrain dopamine signaling in the dorsal or ventral striatum promotes sleep or wake, respectively.

Shank3 modulates sleep and expression of circadian transcription factors

Autism Spectrum Disorder (ASD) is the most prevalent neurodevelopmental disorder in the United States and often co-presents with sleep problems. Sleep problems in ASD predict the severity of ASD core diagnostic symptoms and have a considerable impact on the quality of life of caregivers. Little is known, however, about the underlying molecular mechanisms of sleep problems in ASD. We investigated the role of Shank3, a high confidence ASD gene candidate, in sleep architecture and regulation. We show that mice lacking exon 21 of Shank3 have problems falling asleep even when sleepy. Using RNA-seq we show that sleep deprivation increases the differences in prefrontal cortex gene expression between mutants and wild types, downregulating circadian transcription factors Per3, Bhlhe41, Hlf, Tef, and Nr1d1. Shank3 mutants also have trouble regulating wheel-running activity in constant darkness. Overall, our study shows that Shank3 is an important modulator of sleep and clock gene expression.

Monitoring deep brain stimulation by measuring regional brain oxygen responses in freely moving mice

BACKGROUND

Translational studies investigating the effects of deep brain stimulation (DBS) on brain function up to now mainly relied on BOLD responses measured with fMRI. However, fMRI studies in rodents face technical and practical limitations (e.g., immobilization, sedation or anesthesia, spatial and temporal resolution of data). Direct measurement of oxygen concentration in the brain using electrochemical sensors is a promising alternative to the use of fMRI. Here, we tested for the first time if such measurements can be combined with DBS.

NEW METHOD

We combined bilateral DBS in the internal capsule (IC-DBS) with simultaneous amperometric measurements of oxygen in the medial prefrontal cortex (prelimbic area) and striatum of freely moving mice. Using a two-day within-animal experimental design, we tested the effects of DBS on baseline oxygen concentrations, and on novelty- and restraint-induced increases in oxygen concentration.

RESULTS

Basal oxygen levels were stable across the daily sampling periods. Exposure to novelty and immobilization reproducibly increased oxygen concentrations in both areas. IC-DBS did not significantly alter basal oxygen, but reduced the novelty-induced increase in the striatum.

COMPARISON WITH EXISTING METHOD(S)

Amperometric detection of brain oxygen concentration with high temporal and spatial resolution can be performed in a number of key brain areas to study the effects of DBS in animal models of disease. The method is easily implemented and does not require expensive equipment or complicated data analysis processes.

CONCLUSIONS

Direct and simultaneous measurement of brain oxygen concentration in multiple brain areas can be used to study the effects of bilateral DBS neuromodulation on brain activity in freely moving mice.

Intracerebral Adenosine During Sleep Deprivation: A Meta-Analysis and New Experimental Data

The neuroregulator adenosine is involved in sleep-wake control. Basal forebrain (BF) adenosine levels increase during sleep deprivation. Only a few studies have addressed the effect of sleep deprivation on extracellular adenosine concentrations in other brain regions. In this paper, we describe a microdialysis experiment as well as a meta-analysis of published data. The 64 h microdialysis experiment determined the extracellular adenosine and adenosine monophosphate (AMP) concentrations in the medial prefrontal cortex of rats before, during and after 12 h of sleep deprivation by forced locomotion. The meta-analysis comprised published sleep deprivation animal experiments measuring adenosine by means of microdialysis. In the animal experiment, the overall median adenosine concentration was 0.36 nM and ranged from 0.004 nM to 27 nM. No significant differences were observed between the five conditions: 12 h of wash-out, baseline light phase, baseline dark phase, 12 h of sleep deprivation and 12 h of subsequent recovery. The overall median AMP concentration was 0.10 nM and ranged from 0.001 nM to 7.56 nM. Median AMP concentration increased during sleep deprivation (T = 47; p = 0.047) but normalised during subsequent recovery. The meta-analysis indicates that BF dialysate adenosine concentrations increase with 74.7% (95% CI: 54.1-95.3%) over baseline during sleep deprivation. Cortex dialysate adenosine concentrations during sleep deprivation were so far only reported by 2 publications. The increase in adenosine during sleep deprivation might be specific to the BF. At this stage, the evidence for adenosine levels in other brain regions is based on single experiments and insufficient for generalised conclusions. Further experiments are currently still warranted.

Metabolomic analysis of mouse prefrontal cortex reveals upregulated analytes during wakefulness compared to sleep

By identifying endogenous molecules in brain extracellular fluid metabolomics can provide insight into the regulatory mechanisms and functions of sleep. Here we studied how the cortical metabolome changes during sleep, sleep deprivation and spontaneous wakefulness. Mice were implanted with electrodes for chronic sleep/wake recording and with microdialysis probes targeting prefrontal and primary motor cortex. Metabolites were measured using ultra performance liquid chromatography-high resolution mass spectrometry. Sleep/wake changes in metabolites were evaluated using partial least squares discriminant analysis, linear mixed effects model analysis of variance, and machine-learning algorithms. More than 30 known metabolites were reliably detected in most samples. When used by a logistic regression classifier, the profile of these metabolites across sleep, spontaneous wake, and enforced wake was sufficient to assign mice to their correct experimental group (pair-wise) in 80-100% of cases. Eleven of these metabolites showed significantly higher levels in awake than in sleeping mice. Some changes extend previous findings (glutamate, homovanillic acid, lactate, pyruvate, tryptophan, uridine), while others are novel (D-gluconate, N-acetyl-beta-alanine, N-acetylglutamine, orotate, succinate/methylmalonate). The upregulation of the de novo pyrimidine pathway, gluconate shunt and aerobic glycolysis may reflect a wake-dependent need to promote the synthesis of many essential components, from nucleic acids to synaptic membranes.

Environmental novelty modulates the induction and expression of single injection-induced behavioral sensitization to morphine

Opioid addiction is a growing public health problem, being currently considered an epidemic in the United States. Investigating the behavioral effects of opioids and the factors influencing their development becomes of major importance. In animals, the effects of drugs of abuse can be assessed using the behavioral sensitization model, which shares similar neuronal substrates with drug craving in humans. Importantly, novelty plays a critical role on the development of behavioral sensitization. The aim of the present study was to investigate the influence of a new environment on both the induction and expression phases of morphine (Mor)-induced behavioral sensitization in the two-injection protocol. Mice were initially treated with saline, 15 or 30 mg/kg Mor (induction phase), and subsequently challenged 7 days later with 15 mg/Kg Mor (expression phase). Locomotor frequency was evaluated during behavioral sessions, performed as follow: induction session on a novel environment and expression on a familiar open-filed apparatus; induction session on animals' home-cage (familiar environment) and expression session on an unknown open-filed apparatus; both sessions on novel environments; and both sessions on familiar contexts. Mor-induced behavioral sensitization was only observed when animals were exclusively exposed to novelty during the induction phase, not being observed when both the induction and expression sessions were performed on similar (novel or familiar) environments. Our results suggest that the development of behavioral sensitization to Mor depends on the exposure to novelty during the induction phase and absence of novelty during the expression phase, indicating a complex relationship between novelty and Mor-induced behavioral effects.

Unstable Maternal Environment Affects Stress Response in Adult Mice in a Genotype-Dependent Manner

Early postnatal events exert powerful effects on development, inducing persistent functional alterations in different brain network, such as the catecholamine prefrontal-accumbal system, and increasing the risk of developing psychiatric disorders later in life. However, a vast body of literature shows that the interaction between genetic factors and early environmental conditions is crucial for expression of psychopathologies in adulthood. We evaluated the long-lasting effects of a repeated cross-fostering (RCF) procedure in 2 inbred strains of mice (C57BL/6J, DBA/2), known to show a different susceptibility to the development and expression of stress-induced psychopathologies. Coping behavior (forced swimming test) and preference for a natural reinforcing stimulus (saccharine preference test) were assessed in adult female mice of both genotypes. Moreover, c-Fos stress-induced activity was assessed in different brain regions involved in stress response. In addition, we evaluated the enduring effects of RCF on catecholamine prefrontal-accumbal response to acute stress (restraint) using, for the first time, a new "dual probes" in vivo microdialysis procedure in mouse. RCF experience affects behavioral and neurochemical responses to acute stress in adulthood in opposite direction in the 2 genotypes, leading DBA mice toward an "anhedonic-like" phenotype and C57 mice toward an increased sensitivity for a natural reinforcing stimulus.

Monoaminergic Modulation of Motor Cortex Function

Elaboration of appropriate responses to behavioral situations rests on the ability of selecting appropriate motor outcomes in accordance to specific environmental inputs. To this end, the primary motor cortex (M1) is a key structure for the control of voluntary movements and motor skills learning. Subcortical loops regulate the activity of the motor cortex and thus contribute to the selection of appropriate motor plans. Monoamines are key mediators of arousal, attention and motivation. Their firing pattern enables a direct encoding of different states thus promoting or repressing the selection of actions adapted to the behavioral context. Monoaminergic modulation of motor systems has been extensively studied in subcortical circuits. Despite evidence of converging projections of multiple neurotransmitters systems in the motor cortex pointing to a direct modulation of local circuits, their contribution to the execution and learning of motor skills is still poorly understood. Monoaminergic dysregulation leads to impaired plasticity and motor function in several neurological and psychiatric conditions, thus it is critical to better understand how monoamines modulate neural activity in the motor cortex. This review aims to provide an update of our current understanding on the monoaminergic modulation of the motor cortex with an emphasis on motor skill learning and execution under physiological conditions.

Medial Prefrontal Cortical Dopamine Responses During Operant Self-Administration of Sweetened Ethanol

BACKGROUND

Medial prefrontal cortex (mPFC) dysfunction is present in heavy alcohol consumers. Dopamine signaling in mPFC is associated with executive functioning and affects drinking behavior; however, direct measurement of extracellular mPFC dopamine during appetitive and consummatory ethanol (EtOH) self-administration behavior has not been reported.

METHODS

We used in vivo microdialysis in freely behaving, adult, male, Long Evans rats to determine extracellular dopamine concentration in the mPFC during operant self-administration of an EtOH-plus-sucrose or sucrose solution. The model separated appetitive/seeking from consummatory phases of the operant session. Dopamine was also monitored in an untrained handling control group, and dialysate EtOH was measured in the EtOH-drinking group.

RESULTS

Home cage baseline dopamine was lower in rats that experienced a week of drinking sweetened EtOH compared with sucrose-drinking and handling controls. Transfer into the operant chamber and the initiation of consumption stimulated a relatively higher change in dopamine over baseline in the sweetened EtOH group compared with sucrose and handling controls. However, all groups show a dopamine response during transfer into the operant chamber, and the sucrose group had a relatively higher change in dopamine over baseline during initiation of consumption compared with handling controls. The time courses of dopamine and EtOH in the mPFC differ in the EtOH-consuming rats.

CONCLUSIONS

Differences in extracellular mPFC dopamine between EtOH drinkers compared with control groups suggest that mPFC dopamine is involved in the mechanism of operant self-administration of sweetened EtOH and sucrose. Furthermore, the increase in dopamine during consumption is consistent with a role of mPFC dopamine in reward prediction.

Long-Term Citalopram Treatment Alters the Stress Responses of the Cortical Dopamine and Noradrenaline Systems: the Role of Cortical 5-HT1A Receptors

BACKGROUND

Cortical dopamine and noradrenaline are involved in the stress response. Citalopram, a selective serotonin reuptake inhibitor, has direct and indirect effects on the serotonergic system. Furthermore, long-term treatment with citalopram affects the dopamine and noradrenaline systems, which could contribute to the therapeutic action of antidepressants.

METHODS

The effects of long-term treatment with citalopram on the responses of the dopamine and noradrenaline systems in the rat prefrontal cortex to acute handling stress were evaluated using in vivo microdialysis.

RESULTS

Acute handling stress increased dopamine and noradrenaline levels in the prefrontal cortex. The dopamine and noradrenaline responses were suppressed by local infusion of a 5-HT1A receptor agonist, 7-(Dipropylamino)-5,6,7,8-tetrahydronaphthalen-1-ol;hydrobromide, into the prefrontal cortex. The dopamine response was abolished by long-term treatment with citalopram, and the abolished dopamine response was reversed by local infusion of a 5-HT1A receptor antagonist, (Z)-but-2-enedioic acid;N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexanecarboxamide into the prefrontal cortex. On the other hand, long-term treatment with citalopram reduced the basal noradrenaline levels (approximately 40% of the controls), but not the basal dopamine levels. The noradrenaline response was maintained despite the low basal noradrenaline levels. Signaling from the 5-HT1A receptors and α2-adrenoceptors was not involved in the decrease in the basal noradrenaline levels but partially affected the noradrenaline response.

CONCLUSIONS

Chronic citalopram treatment differentially suppresses the dopamine and noradrenaline systems in the prefrontal cortex, and the dopamine stress response was preferentially controlled by upregulating 5-HT1A receptor signaling. Our findings provide insight into how antidepressants modulate the dopamine and noradrenaline systems to overcome acute stress.

Modulating the map: dopaminergic tuning of hippocampal spatial coding and interactions

Salient events activate the midbrain dopaminergic system and have important impacts on various aspects of mnemonic function, including the stability of hippocampus-dependent memories. Dopamine is also central to modulation of neocortical memory processing, particularly during prefrontal cortex-dependent working memory. Here, we review the current state of the circuitry and physiology underlying dopamine's actions, suggesting that--alongside local effects within hippocampus and prefrontal cortex--dopamine released from the midbrain ventral tegmental area is well positioned to dynamically tune interactions between limbic-cortical circuits through modulation of rhythmic network activity.

Transcranial light affects plasma monoamine levels and expression of brain encephalopsin in the mouse

Encephalopsin (OPN3) belongs to the light-sensitive transmembrane receptor family mainly expressed in the brain and retina. It is believed that light affects mammalian circadian rhythmicity only through the retinohypothalamic tract, which transmits light information to the suprachiasmatic nucleus in the hypothalamus. However, it has been shown that light penetrates the skull. Here, we present the effect of transcranial light treatment on OPN3 expression and monoamine concentrations in mouse brain and other tissues. Mice were randomly assigned to control group, morning-light group and evening-light group, and animals were illuminated transcranially five times a week for 8 min for a total of 4 weeks. The concentrations of OPN3 and monoamines were analysed using western blotting and HPLC, respectively. We report that transcranial light treatment affects OPN3 expression in different brain areas and plasma/adrenal gland monoamine concentrations. In addition, when light was administered at a different time of the day, the response varied in different tissues. These results provide new information on the effects of light on transmitters mediating mammalian rhythmicity.

Diurnal and circadian regulation of reward-related neurophysiology and behavior

Here, we review work over the past two decades that has indicated drug reward is modulated by the circadian system that generates daily (i.e., 24h) rhythms in physiology and behavior. Specifically, drug-self administration, psychomotor stimulant-induced conditioned place preference, and locomotor sensitization vary widely across the day in various species. These drug-related behavioral rhythms are associated with rhythmic neural activity and dopaminergic signaling in the mesocorticolimbic pathways, with a tendency toward increased activity during the species typical wake period. While the mechanisms responsible for such cellular rhythmicity remain to be fully identified, circadian clock genes are expressed in these brain areas and can function locally to modulate both dopaminergic neurotransmission and drug-associated behavior. In addition, neural and endocrine inputs to these brain areas contribute to cellular and reward-related behavioral rhythms, with the medial prefrontal cortex playing a pivotal role. Acute or chronic administration of drugs of abuse can also alter clock gene expression in reward-related brain regions. Emerging evidence suggests that drug craving in humans is under a diurnal regulation and that drug reward may be influenced by clock gene polymorphisms. These latter findings, in particular, indicate that the development of therapeutic strategies to modulate the circadian influence on drug reward may prove beneficial in the treatment of substance abuse disorders.

Animal models of compulsive eating behavior

Eating disorders are multifactorial conditions that can involve a combination of genetic, metabolic, environmental, and behavioral factors. Studies in humans and laboratory animals show that eating can also be regulated by factors unrelated to metabolic control. Several studies suggest a link between stress, access to highly palatable food, and eating disorders. Eating "comfort foods" in response to a negative emotional state, for example, suggests that some individuals overeat to self-medicate. Clinical data suggest that some individuals may develop addiction-like behaviors from consuming palatable foods. Based on this observation, "food addiction" has emerged as an area of intense scientific research. A growing body of evidence suggests that some aspects of food addiction, such as compulsive eating behavior, can be modeled in animals. Moreover, several areas of the brain, including various neurotransmitter systems, are involved in the reinforcement effects of both food and drugs, suggesting that natural and pharmacological stimuli activate similar neural systems. In addition, several recent studies have identified a putative connection between neural circuits activated in the seeking and intake of both palatable food and drugs. The development of well-characterized animal models will increase our understanding of the etiological factors of food addiction and will help identify the neural substrates involved in eating disorders such as compulsive overeating. Such models will facilitate the development and validation of targeted pharmacological therapies.

Baclofen and gamma-hydroxybutyrate differentially altered behavior, EEG activity and sleep in rats

OBJECTIVES

Animal and human studies have shown that sleep may have an impact on functional recovery after brain damage. Baclofen (Bac) and gamma-hydroxybutyrate (GHB) have been shown to induce physiological sleep in humans, however, their effects in rodents are unclear. The aim of this study is to characterize sleep and electroencelphalogram (EEG) after Bac and GHB administration in rats. We hypothesized that both drugs would induce physiological sleep.

METHODS

Adult male Sprague-Dawley rats were implanted with EEG/electromyogram (EMG) electrodes for sleep recordings. Bac (10 or 20 mg/kg), GHB (150 or 300 mg/kg) or saline were injected 1 h after light and dark onset to evaluate time of day effect of the drugs. Vigilance states and EEG spectra were quantified.

RESULTS

Bac and GHB induced a non-physiological state characterized by atypical behavior and an abnormal EEG pattern. After termination of this state, Bac was found to increase the duration of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep (∼90 and 10 min, respectively), reduce sleep fragmentation and affect NREM sleep episode frequency and duration (p<0.05). GHB had no major effect on vigilance states. Bac drastically increased EEG power density in NREM sleep in the frequencies 1.5-6.5 and 9.5-21.5 Hz compared to saline (p<0.05), while GHB enhanced power in the 1-5-Hz frequency band and reduced it in the 7-9-Hz band. Slow-wave activity in NREM sleep was enhanced 1.5-3-fold during the first 1-2 h following termination of the non-physiological state. The magnitude of drug effects was stronger during the dark phase.

CONCLUSION

While both Bac and GHB induced a non-physiological resting state, only Bac facilitated and consolidated sleep, and promoted EEG delta oscillations thereafter. Hence, Bac can be considered a sleep-promoting drug and its effects on functional recovery after stroke can be evaluated both in humans and rats.

The Modulating Role of Stress in the Onset and Course of Tourette’s Syndrome

Accumulating data indicate a common occurrence of tic exacerbations and periods of psychosocial stress. Patients with Tourette’s syndrome (TS) also exhibit aberrant markers of hypothalamic-pituitary-adrenal (HPA) axis activation. Based on these findings, a functional relationship between stress and tic disorders has been suggested, but the underlying mechanism of how stress may affect tic pathology remains to be elucidated. We suggest that dopaminergic and noradrenergic neurotransmission as well as immunology play a crucial role in mediating this relationship. Two possibilities of causal direction might be assumed: (a) psychosocial stress might lead to an exacerbation of tics via activation of HPA axis and subsequent changes in neurotransmission or immunology and (b) TS-related abnormalities in neurotransmission or immunology result in a higher vulnerability of affected patients to respond to psychosocial stress with a strong activation of the HPA axis. It may also be the case that both assumptions hold true and interact with each other.

Sleep disturbances in Parkinson's disease: the contribution of dopamine in REM sleep regulation

Nearly all patients with Parkinson's disease (PD) have sleep disturbances. While it has been suggested that these disturbances involve a dopaminergic component, the specific mechanisms that contribute to this behavior are far from being fully understood. In this article, we have reviewed the current understanding of the linkage between sleep and PD, focusing on the participation of the dopaminergic system in the regulation of rapid eye movement (REM) sleep. The presence of an REM sleep behavior disorder in patients with PD might reflect the early involvement of dopaminergic neurotransmission in REM sleep-related structures. Therefore, it has been suggested that these structures are affected by an imbalance of dopamine levels. Several studies have demonstrated that neurons in the substantia nigra pars compacta (SNpc) and in the ventral tegmental area (VTA) are active during REM sleep and that sleep-related disturbances may result when these neurons are targeted by neurotoxins. We discuss current evidence suggesting the presence of a putative reciprocal connectivity between the SNpc, VTA, the pedunculopontine tegmental nucleus and reticular formation, which may exert an important influence on the REM sleep mechanism. This review provides a comprehensive overview of the literature that addresses this challenging and unrecognized component of PD.

Novelty-induced emotional arousal modulates cannabinoid effects on recognition memory and adrenocortical activity

Although it is well established that cannabinoid drugs can influence cognitive performance, the findings-describing both enhancing and impairing effects-have been ambiguous. Here, we investigated the effects of posttraining systemic administration of the synthetic cannabinoid agonist WIN55,212-2 (0.1, 0.3, or 1.0 mg/kg) on short- and long-term retention of object recognition memory under two conditions that differed in their training-associated arousal level. In male Sprague-Dawley rats that were not previously habituated to the experimental context, WIN55,212-2 administered immediately after a 3-min training trial, biphasically impaired retention performance at a 1-h interval. In contrast, WIN55,212-2 enhanced 1-h retention of rats that had received extensive prior habituation to the experimental context. Interestingly, immediate posttraining administration of WIN55,212-2 to non-habituated rats, in doses that impaired 1-h retention, enhanced object recognition performance at a 24-h interval. Posttraining WIN55,212-2 administration to habituated rats did not significantly affect 24-h retention. In light of intimate interactions between cannabinoids and the hypothalamic-pituitary-adrenal axis, we further investigated whether cannabinoid administration might differently influence training-induced glucocorticoid activity in rats in these two habituation conditions. WIN55,212-2 administered after object recognition training elevated plasma corticosterone levels in non-habituated rats whereas it decreased corticosterone levels in habituated rats. Most importantly, following pretreatment with the corticosterone-synthesis inhibitor metyrapone, WIN55,212-2 effects on 1- and 24-h retention of non-habituated rats became similar to those seen in the low-aroused habituated animals, indicating that cannabinoid-induced regulation of adrenocortical activity contributes to the environmentally sensitive effects of systemically administered cannabinoids on short- and long-term retention of object recognition memory.

Intravenous ethanol increases extracellular dopamine in the medial prefrontal cortex of the Long-Evans rat

BACKGROUND

Ethanol (EtOH) affects prefrontal cortex functional roles such as decision making, working memory, and behavioral control. Yet, the pharmacological effect of EtOH on dopamine, a neuromodulator in the medial prefrontal cortex (mPFC), is unclear. Past studies exploring this topic produced conflicting outcomes; however, a handful of factors (temporal resolution, method of drug administration, estrous cycle) possibly contributed to these discrepancies. We sought to mitigate these factors in order to elucidate EtOH's pharmacological effects on mPFC dopamine in Long-Evans rats.

METHODS

We administered experimental solutions via an intravenous (iv), handling-free route, monitored dopamine in the mPFC via microdialysis (10-minute samples), and used male rats to avoid estrous cycle/EtOH interactions. First, we rapidly (approximately 2.7 ml/min) or slowly (approximately 0.6 ml/min) administered 1.0 g/kg EtOH and saline infusions, showing that the experimental methods did not contribute to dopamine changes. Then, a cumulative dosing protocol was used to administer 0.25, 0.75, 1.50, and 2.25 g/kg iv EtOH doses to evaluate dose-response. Finally, we monitored dialysate EtOH levels during an oral EtOH self-administration session to compare the dialysate EtOH levels achieved during the pharmacological experiments to those seen during self-administration.

RESULTS

IV administration of a rapid or slow 1.0 g/kg EtOH infusion resulted in similar significant 55 ± 9 and 63 ± 15% peak dialysate dopamine increases, respectively. The 0.25, 0.75, 1.50, and 2.25 g/kg EtOH doses produced a nonsignificant 17 ± 5% and significant 36 ± 15, 68 ± 19, and 86 ± 20% peak dialysate dopamine increases, respectively. Self-administration dialysate EtOH concentrations fell within the range of concentrations noted during the EtOH dose-response curve.

CONCLUSIONS

These experiments show that, using experimental methods that minimize possibly confounding factors, acute iv EtOH increases extracellular dopamine in the mPFC in a dose-dependent manner, thereby clarifying EtOH's pharmacological effects on the mesocortical dopamine system.

Individual differences and social influences on the neurobehavioral pharmacology of abused drugs

The interaction of drugs with biologic targets is a critical area of research, particularly for the development of medications to treat substance use disorders. In addition to understanding these drug-target interactions, however, there is a need to understand more fully the psychosocial influences that moderate these interactions. The first section of this review introduces some examples from human behavioral pharmacology that illustrate the clinical importance of this research. The second section covers preclinical evidence to characterize some of the key individual differences that alter drug sensitivity and abuse vulnerability, related primarily to differences in response to novelty and impulsivity. Evidence is presented to indicate that critical neuropharmacological mechanisms associated with these individual differences involve integrated neurocircuits underlying stress, reward, and behavioral inhibitory processes. The third section covers social influences on drug abuse vulnerability, including effects experienced during infancy, adolescence, and young adulthood, such as maternal separation, housing conditions, and social interactions (defeat, play, and social rank). Some of the same neurocircuits involved in individual differences also are altered by social influences, although the precise neurochemical and cellular mechanisms involved remain to be elucidated fully. Finally, some speculation is offered about the implications of this research for the prevention and treatment of substance abuse.

Baseline prepulse inhibition expression predicts the propensity of developing sensitization to the motor stimulant effects of amphetamine in C57BL/6 mice

RATIONALE

The startle reflex to a sudden intense acoustic pulse stimulus is attenuated if the pulse is shortly preceded by a weak prepulse stimulus. This represents a form of sensory gating, known as prepulse inhibition (PPI), observable across species. PPI is modulated by dopamine and readily disrupted by acute amphetamine. Prior repeated exposures to amphetamine also disrupt PPI even when the drug is not present during test, suggesting that a sensitized mesolimbic dopamine system-inducible even by a single exposure to amphetamine-might be responsible. However, this causative link has been challenged by inconsistent efficacy between different amphetamine pre-treatment regimes, which all robustly sensitize the behavioral response to amphetamine.

METHODS

Here, the presence of such a link in reverse was tested by comparing the propensity to develop amphetamine sensitization between high- and low-PPI expressing individuals identified within a homogeneous cohort of C57BL/6 mice. Comparison of dopamine content including its metabolites was performed separately in drug naïve mice by post-mortem HPLC.

RESULTS

Behavioral sensitization was substantially stronger in the low-PPI group compared with the high-PPI group, while the magnitude of their response to the first amphetamine challenge was similar. Dopamine content within the nucleus accumbens and medial prefrontal cortex was significantly higher in low-PPI relative to high-PPI mice.

CONCLUSION

Individuals with weak sensory gating characterized by low basal PPI expression may be more susceptible to the development of dopamine sensitization and therefore at greater risk of developing schizophrenia. Conversely, high baseline expression might predict a resistance to dopaminergic sensitization.

Deep brain stimulation of the accumbens increases dopamine, serotonin, and noradrenaline in the prefrontal cortex

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) is effective in treatment-refractory obsessive-compulsive disorder and major depressive disorder. However, little is known about the neurobiological mechanisms underlying the rapid and effective changes of DBS. One of the hypotheses is that DBS modulates activity of monoamine neurotransmitters. In this study, we evaluated the effects of DBS in the NAc core on the extracellular concentration of monoaminergic neurotransmitters in the medial (mPFC) and orbital prefrontal cortex (OFC). Freely moving rats were bilaterally stimulated in the NAc core for 2 h while dopamine, serotonin, and noradrenaline were measured using in vivo microdialysis in the mPFC and the OFC. We report rapid increases in the release of dopamine and serotonin to a maximum of 177% and 127% in the mPFC and an increase up to 171% and 166% for dopamine and noradrenaline in the OFC after onset of stimulation in the NAc core. These results provide further evidence for the distal effects of DBS and corroborate previous clinical and pre-clinical findings of altered neuronal activity in prefrontal areas.

Stress modulates reinforcement learning in younger and older adults

Animal research and human neuroimaging studies indicate that stress increases dopamine levels in brain regions involved in reward processing, and stress also appears to increase the attractiveness of addictive drugs. The current study tested the hypothesis that stress increases reward salience, leading to more effective learning about positive than negative outcomes in a probabilistic selection task. Changes to dopamine pathways with age raise the question of whether stress effects on incentive-based learning differ by age. Thus, the present study also examined whether effects of stress on reinforcement learning differed for younger (age 18-34) and older participants (age 65-85). Cold pressor stress was administered to half of the participants in each age group, and salivary cortisol levels were used to confirm biophysiological response to cold stress. After the manipulation, participants completed a probabilistic learning task involving positive and negative feedback. In both younger and older adults, stress enhanced learning about cues that predicted positive outcomes. In addition, during the initial learning phase, stress diminished sensitivity to recent feedback across age groups. These results indicate that stress affects reinforcement learning in both younger and older adults and suggests that stress exerts different effects on specific components of reinforcement learning depending on their neural underpinnings.

Prefrontal/accumbal catecholamine system processes high motivational salience

Motivational salience regulates the strength of goal seeking, the amount of risk taken, and the energy invested from mild to extreme. Highly motivational experiences promote highly persistent memories. Although this phenomenon is adaptive in normal conditions, experiences with extremely high levels of motivational salience can promote development of memories that can be re-experienced intrusively for long time resulting in maladaptive outcomes. Neural mechanisms mediating motivational salience attribution are, therefore, very important for individual and species survival and for well-being. However, these neural mechanisms could be implicated in attribution of abnormal motivational salience to different stimuli leading to maladaptive compulsive seeking or avoidance. We have offered the first evidence that prefrontal cortical norepinephrine (NE) transmission is a necessary condition for motivational salience attribution to highly salient stimuli, through modulation of dopamine (DA) in the nucleus accumbens (NAc), a brain area involved in all motivated behaviors. Moreover, we have shown that prefrontal-accumbal catecholamine (CA) system determines approach or avoidance responses to both reward- and aversion-related stimuli only when the salience of the unconditioned stimulus (UCS) is high enough to induce sustained CA activation, thus affirming that this system processes motivational salience attribution selectively to highly salient events.

Postnatal aversive experience impairs sensitivity to natural rewards and increases susceptibility to negative events in adult life

Evidence shows that maternal care and postnatal traumatic events can exert powerful effects on brain circuitry development but little is known about the impact of early postnatal experiences on processing of rewarding and aversive stimuli related to the medial prefrontal cortex (mpFC) function in adult life. In this study, the unstable maternal environment induced by repeated cross-fostering (RCF) impaired palatable food conditioned place preference and disrupted the natural preference for sweetened fluids in the saccharin preference test. By contrast, RCF increased sensitivity to conditioned place aversion (CPA) and enhanced immobility in the forced swimming test. Intracerebral microdialysis data showed that the RCF prevents mpFC dopamine (DA) outflow regardless of exposure to rewarding or aversive stimuli, whereas it induces a strong and sustained prefrontal norepinephrine (NE) release in response to different aversive experiences. Moreover, the selective mpFC NE depletion abolished CPA, thus indicating that prefrontal NE is required for motivational salience attribution to aversion-related stimuli. These findings demonstrate that an unstable maternal environment impairs the natural propensity to seek pleasurable sources of reward, enhances sensitivity to negative events in adult life, blunts prefrontal DA outflow, and modulates NE release in the reverse manner depending on the exposure to rewarding or aversive stimuli.

Genetics of dopamine receptors and drug addiction

Dopamine plays a key role in reward behavior, yet the association of drug dependence as a chronic, relapsing disorder with the genes encoding the various dopaminergic receptor subtypes remains difficult to delineate. In the context of subsequent genome-wide association (GWAS) research and post-GWAS investigations, we summarize the novel data that link genes encoding molecules involved in the dopaminergic system (dopamine receptors, transporter and enzymes in charge of its metabolism) to drug addiction. Recent reports indicate that the heritability of drug addiction should be high enough to allow a significant role for a specific set of genes, and the available genetic studies, which might not be already conclusive because of the heterogeneity of designs, methods and recruited samples, should support the idea of a significant role of at least one gene related to dopaminergic system. Evolutionary changes in primates and non-primate animals of genes coding for molecules involved in dopaminergic system highlight why addictive disorders are mainly limited to humans. Restricting the analyses to more specific intermediate phenotypes (or endophenotypes) such as attention allocation, stress reactivity, novelty seeking, behavioral disinhibition and impulsivity, instead of the broad addictive disorder concept can be instrumental to identify novel genes associated with these traits in the context of genome-wide studies.

Stress, neurotransmitters, corticosterone and body-brain integration

Stress can be defined as a brain-body reaction towards stimuli arising from the environment or from internal cues that are interpreted as a disruption of homeostasis. The organization of the response to a stressful situation involves not only the activity of different types of neurotransmitter systems in several areas of the limbic system, but also the response of neurons in these areas to several other chemicals and hormones, chiefly glucocorticoids, released from peripheral organs and glands. Thus, stress is probably the process through which body-brain integration plays a major role. Here we review first the responses to an acute stress in terms of neurotransmitters such as dopamine, acetylcholine, glutamate and GABA in areas of the brain involved in the regulation of stress responses. These areas include the prefrontal cortex, amygdala, hippocampus and nucleus accumbens and the interaction among those areas. Then, we consider the role of glucocorticoids and review some recent data about the interaction of these steroids with several neurotransmitters in those same areas of the brain. Also the actions of other substances (neuromodulators) released from peripheral organs such as the pancreas, liver or gonads (insulin, IGF-1, estrogens) are reviewed. The role of an environmental enrichment on these same responses is also discussed. Finally a section is devoted to put into perspective all these environmental-brain-body-brain interactions during stress and their consequences on aging. It is concluded that the integrative perspective framed in this review is relevant for better understanding of how the organism responds to stressful challenges and how this can be modified through different environmental conditions during the process of aging. This article is part of a Special Issue entitled: Brain Integration.

Post-learning molecular reactivation underlies taste memory consolidation

It is considered that memory consolidation is a progressive process that requires post-trial stabilization of the information. In this regard, it has been speculated that waves of receptors activation, expression of immediate early genes, and replenishment of receptor subunit pools occur to induce functional or morphological changes to maintain the information for longer periods. In this paper, we will review data related to neuronal changes in the post-acquisition stage of taste aversion learning that could be involved in further stabilization of the memory trace. In order to achieve such stabilization, evidence suggests that the functional integrity of the insular cortex (IC) and the amygdala (AMY) is required. Particularly the increase of extracellular levels of glutamate and activation of N-methyl-d-aspartate (NMDA) receptors within the IC shows a main role in the consolidation process. Additionally the modulatory actions of the dopaminergic system in the IC appear to be involved in the mechanisms that lead to taste aversion memory consolidation through the activation of pathways related to enhancement of protein synthesis such as the Protein Kinase A pathway. In summary, we suggest that post-acquisition molecular and neuronal changes underlying memory consolidation are dependent on the interactions between the AMY and the IC.

Unilateral deep brain stimulation in the nucleus accumbens core does not affect local monoamine release

Recent publications have shown promising results of deep brain stimulation (DBS) in the nucleus accumbens for patients with obsessive compulsive disorder and major depressive disorder. Despite its increasing application in the clinical setting, the neurobiological mechanism of action of DBS is still uncertain. One of the possible effects of DBS might be phasic or tonic changes in monoamine release either locally in the target area or in a distant, connected region. In the present study we investigate whether unilateral DBS of the Nucleus Accumbens Core (NAc core) has a local effect on in vivo monoamine release. Freely moving animals were unilaterally stimulated with 300 μA or 400 μA (120 Hz, pulse width 80 μs) in the NAc core for 5 h. 1h before and during stimulation we measured dopamine, serotonin, their metabolites and noradrenaline using in vivo microdialysis. We found no significant effect of stimulation on extracellular concentrations of monoaminergic neurotransmitters or their metabolites in the NAc core during stimulation. Our results suggest that the rapid effects of DBS in the NAc are not a result of changes in local monoamine release in the NAc core. For future directions it is interesting to note that several microdialysis and electrophysiology studies have shown effects of DBS in areas distant from the stimulation target.

Photoperiodic suppression of drug reinstatement

The rewarding influence of drugs of abuse varies with time of day and appears to involve interactions between the circadian and the mesocorticolimbic dopamine systems. The circadian system is also intimately involved in measuring daylength. Thus, the present study examined the impact of changing daylength (photoperiod) on cocaine-seeking behaviors. Male Sprague-Dawley rats were trained and tested on a 12L:12D light:dark schedule for cocaine-induced reinstatement of conditioned place preference (CPP) at three times of day (Zeitgeber time (ZT): 4, 12, and 20) to determine a preference score. Rats were then shifted to either shorter (6L:18D) or longer (18L:6D) photoperiods and then to constant conditions, re-tested for cocaine-induced reinstatement under each different condition, and then returned to their original photoperiod (12L:12D) and tested once more. Rats exhibited a circadian profile of preference score in constant darkness with a peak at 12 h after lights-off. At both ZT4 and ZT20, but not at ZT12, shorter photoperiods profoundly suppressed cocaine reinstatement, which did not recover even after switching back to 12L:12D. In contrast, longer photoperiods did not alter reinstatement. Separate studies showed that the suppression of cocaine reinstatement was not due to repeated testing. In an additional experiment, we examined the photoperiodic regulation of tyrosine hydroxylase (TH) and dopamine transporter (DAT) proteins in drug-naive rats. These results revealed photoperiodic modulation of proteins in the prefrontal cortex and dorsal striatum, but not in the nucleus accumbens or ventral tegmental area. Together, these findings add further support to the circadian genesis of cocaine-seeking behaviors and demonstrate that drug-induced reinstatement is modulated by photoperiod. Furthermore, the results suggest that photoperiod partly contributes to the seasonal expression of certain drug-related behaviors in humans living at different latitudes and thus our findings may have implications for novel targeting of circadian rhythms in the treatment of addiction.

Effects of orexin-A on propofol anesthesia in rats

PURPOSE

An active sleep homeostatic process is present during propofol anesthesia. Activation of the orexin system induces wakefulness, and inhibition of the orexin system causes narcolepsy. We hypothesized that orexin would affect propofol anesthesia.

METHODS

The effects of an intracerebroventricular (i.c.v.) injection of orexin-A (OXA) or an orexin-1 (OX-1) receptor antagonist, SB-334867, on the times to the loss and return of the righting reflex induced by propofol were examined in Wistar rats. The effects of propofol or OXA on norepinephrine (NE) and dopamine (DA) release from the prefrontal cortex (PFC) were examined using in vivo microdialysis.

RESULTS

An i.c.v. injection of OXA (1 nmol) decreased the time to emergence from propofol anesthesia mediated by the OX-1 receptor without changing anesthetic induction (n = 8). An i.c.v. injection of SB-334867 (5 and 50 nmol) increased the time to emergence from propofol anesthesia without changing anesthetic induction (n = 8). Intravenous infusion of propofol decreased NE (48 ± 8%; n = 8) and DA (61.2 ± 11%; n = 8) release from PFC mediated by the GABA(A) receptor. An i.c.v. injection of OXA reversed the decreases in NE and DA release induced by propofol mediated by the OX-1 receptor (n = 8).

CONCLUSION

These results indicate that the orexin system may accelerate the emergence from propofol anesthesia associated with increases in the central noradrenergic and dopaminergic activity.