Circadian modulation of dopamine receptor responsiveness in Drosophila melanogaster

Rhythms in insect olfactory systems: underlying mechanisms and outstanding questions

Olfaction is a critical sensory modality for invertebrates, and it mediates a wide range of behaviors and physiological processes. Like most living organisms, insects live in rhythmic environments: the succession of nights and days is accompanied by cyclic variations in light intensity and temperature, as well as in the availability of resources and the activity of predators. Responding to olfactory cues in the proper temporal context is thus highly adaptive and allows for the efficient allocation of energy resources. Given the agricultural or epidemiological importance of some insect species, understanding olfactory rhythms is critical for the development of effective control strategies. Although the vinegar fly Drosophila melanogaster has been a classical model for the study of olfaction and circadian rhythms, recent studies focusing on non-model species have expanded our understanding of insect olfactory rhythms. Additionally, recent evidence revealing receptor co-expression by sensory neurons has brought about an ongoing paradigm shift in our understanding of insect olfaction, making it timely to review the state of our knowledge on olfactory rhythms and identify critical future directions for the field. In this Review, we discuss the multiple biological scales at which insect olfactory rhythms are being analyzed, and identify outstanding questions.

In vivo Effects of Salicornia herbacea and Calystegia soldanella Extracts for Memory Improvement

The global elderly population, aged 65 and over, reached approximately 10% in 2020, and this proportion is expected to continue rising. Therefore, the prevalence of neurodegenerative diseases such as Parkinson's disease (PD), which are characterized by declining memory capabilities, is anticipated to increase. In a previous study, we successfully restored the diminished memory capabilities in a fruit fly model of PD by administering an omija extract. To identify functional ingredients that can enhance memory akin to the effects of the omija extract, we conducted screenings by administering halophyte extracts to the PD model. Halophytes are plants that thrive in high-salt environments, and given Korea's geographic proximity to the sea on three sides, it serves as an optimal hub for the utilization of these plants. Upon examining the effects of the oral administration of 12 halophyte extracts, Salicornia herbacea and Calystegia soldanella emerged as potential candidates for ameliorating memory loss in PD model flies. Moreover, our findings suggested that C. soldanella, but not S. herbacea, can mitigate oxidative stress in DJ-1β mutants.

The Use of Drosophila to Understand Psychostimulant Responses

The addictive properties of psychostimulants such as cocaine, amphetamine, methamphetamine, and methylphenidate are based on their ability to increase dopaminergic neurotransmission in the reward system. While cocaine and methamphetamine are predominately used recreationally, amphetamine and methylphenidate also work as effective therapeutics to treat symptoms of disorders including attention deficit and hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Although both the addictive properties of psychostimulant drugs and their therapeutic efficacy are influenced by genetic variation, very few genes that regulate these processes in humans have been identified. This is largely due to population heterogeneity which entails a requirement for large samples. Drosophila melanogaster exhibits similar psychostimulant responses to humans, a high degree of gene conservation, and allow performance of behavioral assays in a large population. Additionally, amphetamine and methylphenidate reduce impairments in fly models of ADHD-like behavior. Therefore, Drosophila represents an ideal translational model organism to tackle the genetic components underlying the effects of psychostimulants. Here, we break down the many assays that reliably quantify the effects of cocaine, amphetamine, methamphetamine, and methylphenidate in Drosophila. We also discuss how Drosophila is an efficient and cost-effective model organism for identifying novel candidate genes and molecular mechanisms involved in the behavioral responses to psychostimulant drugs.

Delegating Sex: Differential Gene Expression in Stolonizing Syllids Uncovers the Hormonal Control of Reproduction

Stolonization in syllid annelids is a unique mode of reproduction among animals. During the breeding season, a structure resembling the adult but containing only gametes, called stolon, is formed generally at the posterior end of the animal. When stolons mature, they detach from the adult and gametes are released into the water column. The process is synchronized within each species, and it has been reported to be under environmental and endogenous control, probably via endocrine regulation. To further understand reproduction in syllids and to elucidate the molecular toolkit underlying stolonization, we generated Illumina RNA-seq data from different tissues of reproductive and nonreproductive individuals of Syllis magdalena and characterized gene expression during the stolonization process. Several genes involved in gametogenesis (ovochymase, vitellogenin, testis-specific serine/threonine-kinase), immune response (complement receptor 2), neuronal development (tyrosine-protein kinase Src42A), cell proliferation (alpha-1D adrenergic receptor), and steroid metabolism (hydroxysteroid dehydrogenase 2) were found differentially expressed in the different tissues and conditions analyzed. In addition, our findings suggest that several neurohormones, such as methyl farnesoate, dopamine, and serotonin, might trigger stolon formation, the correct maturation of gametes and the detachment of stolons when gametogenesis ends. The process seems to be under circadian control, as indicated by the expression patterns of r-opsins. Overall, our results shed light into the genes that orchestrate the onset of gamete formation and improve our understanding of how some hormones, previously reported to be involved in reproduction and metamorphosis processes in other invertebrates, seem to also regulate reproduction via stolonization.

Impaired Taste Associative Memory and Memory Enhancement by Feeding Omija in Parkinson's Disease Fly Model

Neurodegeneration can result in memory loss in the central nervous system (CNS) and impairment of taste and smell in the peripheral nervous system (PNS). The neurodegeneration seen in Parkinson's disease (PD) is characterized by functional loss of dopaminergic neurons. Recent studies have also found a role for dopaminergic neurons in regulating taste memory rewards in insects. To investigate how taste memories and sugar sensitivity can be affected in PD, we utilized the DJ-1β mutant fruit fly, DJ-1βex54 , as a PD model. We performed binary choice feeding assays, electrophysiology and taste-mediated memory tests to explore the function of the DJ-1β gene in terms of sugar sensitivity as well as associative taste memory. We found that PD flies exhibited an impaired ability to discriminate sucrose across a range of sugar concentrations, with normal responses at only very high concentrations of sugar. They also showed an impairment in associative taste memory. We highlight that the taste impairment and memory defect in DJ-1βex54 can be recovered by the expression of wild-type DJ-1β gene in the dopaminergic neurons. We also emphasized the role of dopaminergic neurons in restoring taste memory function. This impaired memory property of DJ-1βex54 flies also allows them to be used as a model system for finding supplementary dietary foods that can improve memory function. Here we provide evidence that the associative taste memory of both control and DJ-1βex54 flies can be enhanced with dietary supplementation of the medicinal plant, omija.

Neurobiological Functions of the Period Circadian Clock 2 Gene, Per2

Most organisms have adapted to a circadian rhythm that follows a roughly 24-hour cycle, which is modulated by both internal (clock-related genes) and external (environment) factors. In such organisms, the central nervous system (CNS) is influenced by the circadian rhythm of individual cells. Furthermore, the period circadian clock 2 (Per2) gene is an important component of the circadian clock, which modulates the circadian rhythm. Per2 is mainly expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus as well as other brain areas, including the midbrain and forebrain. This indicates that Per2 may affect various neurobiological activities such as sleeping, depression, and addiction. In this review, we focus on the neurobiological functions of Per2, which could help to better understand its roles in the CNS.

Drosophila: An Emergent Model for Delineating Interactions between the Circadian Clock and Drugs of Abuse

Endogenous circadian oscillators orchestrate rhythms at the cellular, physiological, and behavioral levels across species to coordinate activity, for example, sleep/wake cycles, metabolism, and learning and memory, with predictable environmental cycles. The 21st century has seen a dramatic rise in the incidence of circadian and sleep disorders with globalization, technological advances, and the use of personal electronics. The circadian clock modulates alcohol- and drug-induced behaviors with circadian misalignment contributing to increased substance use and abuse. Invertebrate models, such as Drosophila melanogaster, have proven invaluable for the identification of genetic and molecular mechanisms underlying highly conserved processes including the circadian clock, drug tolerance, and reward systems. In this review, we highlight the contributions of Drosophila as a model system for understanding the bidirectional interactions between the circadian system and the drugs of abuse, alcohol and cocaine, and illustrate the highly conserved nature of these interactions between Drosophila and mammalian systems. Research in Drosophila provides mechanistic insights into the corresponding behaviors in higher organisms and can be used as a guide for targeted inquiries in mammals.

The Sensitivity of the Crayfish Reward System to Mammalian Drugs of Abuse

The idea that addiction occurs when the brain is not able to differentiate whether specific reward circuits were triggered by adaptive natural rewards or falsely activated by addictive drugs exist in several models of drug addiction. The suitability of crayfish (Orconectes rusticus) for drug addiction research arises from developmental variation of growth, life span, reproduction, behavior and some quantitative traits, especially among isogenic mates reared in the same environment. This broad spectrum of traits makes it easier to analyze the effect of mammalian drugs of abuse in shaping behavioral phenotype. Moreover, the broad behavioral repertoire allows the investigation of self-reinforcing circuitries involving appetitive and exploratory motor behavior, while the step-wise alteration of the phenotype by metamorphosis allows accurate longitudinal analysis of different behavioral states. This paper reviews a series of recent experimental findings that evidence the suitability of crayfish as an invertebrate model system for the study of drug addiction. Results from these studies reveal that unconditioned exposure to mammalian drugs of abuse produces a variety of stereotyped behaviors. Moreover, if presented in the context of novelty, drugs directly stimulate exploration and appetitive motor patterns along with molecular processes for drug conditioned reward. Findings from these studies indicate the existence of drug sensitive circuitry in crayfish that facilitates exploratory behavior and appetitive motor patterns via increased incentive salience of environmental stimuli or by increasing exploratory motor patterns. This work demonstrates the potential of crayfish as a model system for research into the neural mechanisms of addiction, by contributing an evolutionary, comparative context to our understanding of natural reward as an important life-sustaining process.

Restless Legs Syndrome: From Pathophysiology to Clinical Diagnosis and Management

Restless legs syndrome (RLS), a common neurological sensorimotor disorder in western countries, has gained more and more attention in Asian countries. The prevalence of RLS is higher in older people and females. RLS is most commonly related to iron deficiency, pregnancy and uremia. The RLS symptoms show a significant circadian rhythm and a close relationship to periodic limb movements (PLMs) in clinical observations, while the pathophysiological pathways are still unknown. The diagnostic criteria have been revised in 2012 to improve the validity of RLS diagnosis. Recent studies have suggested an important role of iron decrease of brain in RLS pathophysiology. Dopaminergic (DA) system dysfunction in A11 cell groups has been recognized long ago from clinical treatment and autopsy. Nowadays, it is believed that iron dysfunction can affect DA system from different pathways and opioids have a protective effect on DA system. Several susceptible single nucleotide polymorphisms such as BTBD9 and MEIS1, which are thought to be involved in embryonic neuronal development, have been reported to be associated with RLS. Several pharmacological and non-pharmacological treatment are discussed in this review. First-line treatments of RLS include DA agents and α2δ agonists. Augmentation is very common in long-term treatment of RLS which makes prevention and management of augmentation very important for RLS patients. A combination of different types of medication is effective in preventing and treating augmentation. The knowledge on RLS is still limited, the pathophysiology and better management of RLS remain to be discovered.

Circadian Rhythm Neuropeptides in Drosophila: Signals for Normal Circadian Function and Circadian Neurodegenerative Disease

Circadian rhythm is a ubiquitous phenomenon in many organisms ranging from prokaryotes to eukaryotes. During more than four decades, the intrinsic and exogenous regulations of circadian rhythm have been studied. This review summarizes the core endogenous oscillation in Drosophila and then focuses on the neuropeptides, neurotransmitters and hormones that mediate its outputs and integration in Drosophila and the links between several of these (pigment dispersing factor (PDF) and insulin-like peptides) and neurodegenerative disease. These signaling molecules convey important network connectivity and signaling information for normal circadian function, but PDF and insulin-like peptides can also convey signals that lead to apoptosis, enhanced neurodegeneration and cognitive decline in flies carrying circadian mutations or in a senescent state.

A Genetic Screen To Assess Dopamine Receptor (DopR1) Dependent Sleep Regulation in Drosophila

Sleep is an essential behavioral state of rest that is regulated by homeostatic drives to ensure a balance of sleep and activity, as well as independent arousal mechanisms in the central brain. Dopamine has been identified as a critical regulator of both sleep behavior and arousal. Here, we present results of a genetic screen that selectively restored the Dopamine Receptor (DopR/DopR1/dumb) to specific neuroanatomical regions of the adult Drosophila brain to assess requirements for DopR in sleep behavior. We have identified subsets of the mushroom body that utilizes DopR in daytime sleep regulation. These data are supported by multiple examples of spatially restricted genetic rescue data in discrete circuits of the mushroom body, as well as immunohistochemistry that corroborates the localization of DopR protein within mushroom body circuits. Independent loss of function data using an inducible RNAi construct in the same specific circuits also supports a requirement for DopR in daytime sleep. Additional circuit activation of discrete DopR⁺ mushroom body neurons also suggests roles for these subpopulations in sleep behavior. These conclusions support a new separable function for DopR in daytime sleep regulation within the mushroom body. This daytime regulation is independent of the known role of DopR in nighttime sleep, which is regulated within the Fan-Shaped Body (FSB). This study provides new neuroanatomical loci for exploration of dopaminergic sleep functions in Drosophila, and expands our understanding of sleep regulation during the day vs. night.

Schizophrenia: the role of sleep and circadian rhythms in regulating dopamine and psychosis

Schizophrenia has long been associated with abnormalities in circadian rhythms and sleep. Up until now, there have been no thorough reviews of the potential mechanisms behind the myriad of circadian and sleep abnormalities observed in schizophrenia and psychosis. We present evidence of sleep playing an important role in psychosis predominantly mediated by dopaminergic pathways. A synthesis of both human and animal experimental work suggests that the interplay between sleep and dopamine is important in the generation and maintenance of psychosis. In particular, both animal and human data point to sleep disruption increasing dopamine release and sensitivity. Furthermore, elevated dopamine levels disrupt sleep and circadian rhythms. The synthesis of knowledge suggests that circadian rhythms, dopamine dysregulation, and psychosis are intricately linked. This suggests that treatment of circadian disturbance may be a useful target in improving the lives and symptoms of patients with schizophrenia.

A Review of Sleep and Its Disorders in Patients with Parkinson's Disease in Relation to Various Brain Structures

Sleep is an indispensable normal physiology of the human body fundamental for healthy functioning. It has been observed that Parkinson's disease (PD) not only exhibits motor symptoms, but also non-motor symptoms such as metabolic irregularities, altered olfaction, cardiovascular dysfunction, gastrointestinal complications and especially sleep disorders which is the focus of this review. A good understanding and knowledge of the different brain structures involved and how they function in the development of sleep disorders should be well comprehended in order to treat and alleviate these symptoms and enhance quality of life for PD patients. Therefore it is vital that the normal functioning of the body in relation to sleep is well understood before proceeding on to the pathophysiology of PD correlating to its symptoms. Suitable treatment can then be administered toward enhancing the quality of life of these patients, perhaps even discovering the cause for this disease.

Functional PDF Signaling in the Drosophila Circadian Neural Circuit Is Gated by Ral A-Dependent Modulation

The neuropeptide PDF promotes the normal sequencing of circadian behavioral rhythms in Drosophila, but its signaling mechanisms are not well understood. We report daily rhythmicity in responsiveness to PDF in critical pacemakers called small LNvs. There is a daily change in potency, as great as 10-fold higher, around dawn. The rhythm persists in constant darkness and does not require endogenous ligand (PDF) signaling or rhythmic receptor gene transcription. Furthermore, rhythmic responsiveness reflects the properties of the pacemaker cell type, not the receptor. Dopamine responsiveness also cycles, in phase with that of PDF, in the same pacemakers, but does not cycle in large LNv. The activity of RalA GTPase in s-LNv regulates PDF responsiveness and behavioral locomotor rhythms. Additionally, cell-autonomous PDF signaling reversed the circadian behavioral effects of lowered RalA activity. Thus, RalA activity confers high PDF responsiveness, providing a daily gate around the dawn hours to promote functional PDF signaling.

Circadian and ultradian glucocorticoid rhythmicity: Implications for the effects of glucocorticoids on neural stem cells and adult hippocampal neurogenesis

Psychosocial stress, and within the neuroendocrine reaction to stress specifically the glucocorticoid hormones, are well-characterized inhibitors of neural stem/progenitor cell proliferation in the adult hippocampus, resulting in a marked reduction in the production of new neurons in this brain area relevant for learning and memory. However, the mechanisms by which stress, and particularly glucocorticoids, inhibit neural stem/progenitor cell proliferation remain unclear and under debate. Here we review the literature on the topic and discuss the evidence for direct and indirect effects of glucocorticoids on neural stem/progenitor cell proliferation and adult neurogenesis. Further, we discuss the hypothesis that glucocorticoid rhythmicity and oscillations originating from the activity of the hypothalamus-pituitary-adrenal axis, may be crucial for the regulation of neural stem/progenitor cells in the hippocampus, as well as the implications of this hypothesis for pathophysiological conditions in which glucocorticoid oscillations are affected.

Clock genes × stress × reward interactions in alcohol and substance use disorders

Adverse life events and highly stressful environments have deleterious consequences for mental health. Those environmental factors can potentiate alcohol and drug abuse in vulnerable individuals carrying specific genetic risk factors, hence producing the final risk for alcohol- and substance-use disorders development. The nature of these genes remains to be fully determined, but studies indicate their direct or indirect relation to the stress hypothalamo-pituitary-adrenal (HPA) axis and/or reward systems. Over the past decade, clock genes have been revealed to be key-players in influencing acute and chronic alcohol/drug effects. In parallel, the influence of chronic stress and stressful life events in promoting alcohol and substance use and abuse has been demonstrated. Furthermore, the reciprocal interaction of clock genes with various HPA-axis components, as well as the evidence for an implication of clock genes in stress-induced alcohol abuse, have led to the idea that clock genes, and Period genes in particular, may represent key genetic factors to consider when examining gene × environment interaction in the etiology of addiction. The aim of the present review is to summarize findings linking clock genes, stress, and alcohol and substance abuse, and to propose potential underlying neurobiological mechanisms.

A dopamine receptor contributes to paraquat-induced neurotoxicity in Drosophila

Long-term exposure to environmental oxidative stressors, like the herbicide paraquat (PQ), has been linked to the development of Parkinson's disease (PD), the most frequent neurodegenerative movement disorder. Paraquat is thus frequently used in the fruit fly Drosophila melanogaster and other animal models to study PD and the degeneration of dopaminergic neurons (DNs) that characterizes this disease. Here, we show that a D1-like dopamine (DA) receptor, DAMB, actively contributes to the fast central nervous system (CNS) failure induced by PQ in the fly. First, we found that a long-term increase in neuronal DA synthesis reduced DAMB expression and protected against PQ neurotoxicity. Secondly, a striking age-related decrease in PQ resistance in young adult flies correlated with an augmentation of DAMB expression. This aging-associated increase in oxidative stress vulnerability was not observed in a DAMB-deficient mutant. Thirdly, targeted inactivation of this receptor in glutamatergic neurons (GNs) markedly enhanced the survival of Drosophila exposed to either PQ or neurotoxic levels of DA, whereas, conversely, DAMB overexpression in these cells made the flies more vulnerable to both compounds. Fourthly, a mutation in the Drosophila ryanodine receptor (RyR), which inhibits activity-induced increase in cytosolic Ca(2+), also strongly enhanced PQ resistance. Finally, we found that DAMB overexpression in specific neuronal populations arrested development of the fly and that in vivo stimulation of either DNs or GNs increased PQ susceptibility. This suggests a model for DA receptor-mediated potentiation of PQ-induced neurotoxicity. Further studies of DAMB signaling in Drosophila could have implications for better understanding DA-related neurodegenerative disorders in humans.

Dopamine transporters govern diurnal variation in extracellular dopamine tone

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

Rhythmic egg-laying behaviour in virgin females of fruit flies Drosophila melanogaster

Fruit fly Drosophila melanogaster females display rhythmic egg-laying under 12:12 h light/dark (LD) cycles which persists with near 24 h periodicity under constant darkness (DD). We have shown previously that persistence of this rhythm does not require the neurons expressing pigment dispersing factor (PDF), thought to be the canonical circadian pacemakers, and proposed that it could be controlled by peripheral clocks or regulated/triggered by the act of mating. We assayed egg-laying behaviour of wild-type Canton S (CS) females under LD, DD and constant light (LL) conditions in three different physiological states; as virgins, as females allowed to mate with males for 1 day and as females allowed to mate for the entire duration of the assay. Here, we report the presence of a circadian rhythm in egg-laying in virgin D. melanogaster females. We also found that egg-laying behaviour of 70 and 90% females from all the three male presence/absence protocols follows circadian rhythmicity under DD and LL, with periods ranging between 18 and 30 h. The egg-laying rhythm of all virgin females synchronized to LD cycles with a peak occurring soon after lights-off. The rhythm in virgins was remarkably robust with maximum number of eggs deposited immediately after lights-off in contrast to mated females which show higher egg-laying during the day. These results suggest that the egg-laying rhythm of D. melanogaster is endogenously driven and is neither regulated nor triggered by the act of mating; instead, the presence of males results in reduction in entrainment to LD cycles.

Selective degeneration of dopaminergic neurons by MPP(+) and its rescue by D2 autoreceptors in Drosophila primary culture

Drosophila melanogaster is widely used to study genetic factors causing Parkinson's disease (PD) largely because of the use of sophisticated genetic approaches and the presence of a high conservation of gene sequence/function between Drosophila and mammals. However, in Drosophila, little has been done to study the environmental factors which cause over 90% of PD cases. We used Drosophila primary neuronal culture to study degenerative effects of a well-known PD toxin MPP(+) . Dopaminergic (DA) neurons were selectively degenerated by MPP(+) , whereas cholinergic and GABAergic neurons were not affected. This DA neuronal loss was because of post-mitotic degeneration, not by inhibition of DA neuronal differentiation. We also found that MPP(+) -mediated neurodegeneration was rescued by D2 agonists quinpirole and bromocriptine. This rescue was through activation of Drosophila D2 receptor DD2R, as D2 agonists failed to rescue MPP(+) -toxicity in neuronal cultures prepared from both a DD2R deficiency line and a transgenic line pan-neuronally expressing DD2R RNAi. Furthermore, DD2R autoreceptors in DA neurons played a critical role in the rescue. When DD2R RNAi was expressed only in DA neurons, MPP(+) toxicity was not rescued by D2 agonists. Our study also showed that rescue of DA neurodegeneration by Drosophila DD2R activation was mediated through suppression of action potentials in DA neurons.

Ih current is necessary to maintain normal dopamine fluctuations and sleep consolidation in Drosophila

HCN channels are becoming pharmacological targets mainly in cardiac diseases. But apart from their well-known role in heart pacemaking, these channels are widely expressed in the nervous system where they contribute to the neuron firing pattern. Consequently, abolishing Ih current might have detrimental consequences in a big repertoire of behavioral traits. Several studies in mammals have identified the Ih current as an important determinant of the firing activity of dopaminergic neurons, and recent evidences link alterations in this current to various dopamine-related disorders. We used the model organism Drosophila melanogaster to investigate how lack of Ih current affects dopamine levels and the behavioral consequences in the sleep∶activity pattern. Unlike mammals, in Drosophila there is only one gene encoding HCN channels. We generated a deficiency of the DmIh core gene region and measured, by HPLC, levels of dopamine. Our data demonstrate daily variations of dopamine in wild-type fly heads. Lack of Ih current dramatically alters dopamine pattern, but different mechanisms seem to operate during light and dark conditions. Behaviorally, DmIh mutant flies display alterations in the rest∶activity pattern, and altered circadian rhythms. Our data strongly suggest that Ih current is necessary to prevent dopamine overproduction at dark, while light input allows cycling of dopamine in an Ih current dependent manner. Moreover, lack of Ih current results in behavioral defects that are consistent with altered dopamine levels.

Cocaine modulates pathways for photic and nonphotic entrainment of the mammalian SCN circadian clock

Cocaine abuse is highly disruptive to circadian physiological and behavioral rhythms. The present study was undertaken to determine whether such effects are manifest through actions on critical photic and nonphotic regulatory pathways in the master circadian clock of the mouse suprachiasmatic nucleus (SCN). Impairment of SCN photic signaling by systemic (intraperitoneal) cocaine injection was evidenced by strong (60%) attenuation of light-induced phase-delay shifts of circadian locomotor activity during the early night. A nonphotic action of cocaine was apparent from its induction of 1-h circadian phase-advance shifts at midday. The serotonin receptor antagonist, metergoline, blocked shifting by 80%, implicating a serotonergic mechanism. Reverse microdialysis perfusion of the SCN with cocaine at midday induced 3.7 h phase-advance shifts. Control perfusions with lidocaine and artificial cerebrospinal fluid had little shifting effect. In complementary in vitro experiments, photic-like phase-delay shifts of the SCN circadian neuronal activity rhythm induced by glutamate application to the SCN were completely blocked by cocaine. Cocaine treatment of SCN slices alone at subjective midday, but not the subjective night, induced 3-h phase-advance shifts. Lidocaine had no shifting effect. Cocaine-induced phase shifts were completely blocked by metergoline, but not by the dopamine receptor antagonist, fluphenazine. Finally, pretreatment of SCN slices for 2 h with a low concentration of serotonin agonist (to block subsequent serotonergic phase resetting) abolished cocaine-induced phase shifts at subjective midday. These results reveal multiple effects of cocaine on adult circadian clock regulation that are registered within the SCN and involve enhanced serotonergic transmission.

Pre-fibrillar α-synuclein mutants cause Parkinson's disease-like non-motor symptoms in Drosophila

Parkinson's disease (PD) is linked to the formation of insoluble fibrillar aggregates of the presynaptic protein α-Synuclein (αS) in neurons. The appearance of such aggregates coincides with severe motor deficits in human patients. These deficits are often preceded by non-motor symptoms such as sleep-related problems in the patients. PD-like motor deficits can be recapitulated in model organisms such as Drosophila melanogaster when αS is pan-neurally expressed. Interestingly, both these deficits are more severe when αS mutants with reduced aggregation properties are expressed in flies. This indicates that that αS aggregation is not the primary cause of the PD-like motor symptoms. Here we describe a model for PD in Drosophila which utilizes the targeted expression of αS mutants in a subset of dopadecarboxylase expressing serotonergic and dopaminergic (DA) neurons. Our results show that targeted expression of pre-fibrillar αS mutants not only recapitulates PD-like motor symptoms but also the preceding non-motor symptoms such as an abnormal sleep-like behavior, altered locomotor activity and abnormal circadian periodicity. Further, the results suggest that the observed non-motor symptoms in flies are caused by an early impairment of neuronal functions rather than by the loss of neurons due to cell death.

Drug-sensitive reward in crayfish: an invertebrate model system for the study of SEEKING, reward, addiction, and withdrawal

In mammals, rewarding properties of drugs depend on their capacity to activate appetitive motivational states. With the underlying mechanisms strongly conserved in evolution, invertebrates have recently emerged as a powerful new model in addiction research. In crayfish natural reward has proven surprisingly sensitive to human drugs of abuse, opening an unlikely avenue of research into the basic biological mechanisms of drug addiction. In a series of studies we first examined the presence of natural reward systems in crayfish, then characterized its sensitivity to a wide range of human drugs of abuse. A conditioned place preference (CPP) paradigm was used to demonstrate that crayfish seek out those environments that had previously been paired with the psychostimulants cocaine and amphetamine, and the opioid morphine. The administration of amphetamine exerted its effects at a number of sites, including the stimulation of circuits for active exploratory behaviors (i.e., SEEKING). A further study examined morphine-induced reward, extinction and reinstatement in crayfish. Repeated intra-circulatory infusions of morphine served as a reward when paired with distinct visual or tactile cues. Morphine-induced CPP was extinguished after repeated saline injections. Following this extinction phase, morphine-experienced crayfish were once again challenged with the drug. The priming injections of morphine reinstated CPP at all tested doses, suggesting that morphine-induced CPP is unrelenting. In an exploration of drug-associated behavioral sensitization in crayfish we concurrently mapped measures of locomotion and rewarding properties of morphine. Single and repeated intra-circulatory infusions of morphine resulted in persistent locomotory sensitization, even 5 days following the infusion. Moreover, a single dose of morphine was sufficient to induce long-term behavioral sensitization. CPP for morphine and context-dependent cues could not be disrupted over a drug free period of 5 days. This work demonstrates that crayfish offer a comparative and complementary approach in addiction research. Serving as an invertebrate animal model for the exposure to mammalian drugs of abuse, modularly organized and experimentally accessible nervous systems render crayfish uniquely suited for studying (1) the basic biological mechanisms of drug effects, (2) to explore how the appetitive/seeking disposition is implemented in a simple neural system, and (3) how such a disposition is related to the rewarding action of drugs of abuse. This work aimed to contribute an evolutionary, comparative context to our understanding of a key component in learning, and of natural reward as an important life-sustaining process.

Glucocorticoid ultradian rhythmicity directs cyclical gene pulsing of the clock gene period 1 in rat hippocampus

In vivo glucocorticoid (GC) secretion exhibits a distinctive ultradian rhythmicity. The lipophilic hormone can rapidly diffuse into cells, although only the pulse peak is of sufficient amplitude to activate the low affinity glucocorticoid receptor (GR). Discrete pulses readily access brain regions such as the hippocampus where GR expression is enriched and known to regulate neuronal function, including memory and learning processes. In the present study, we have tested the hypothesis that GR brain targets are responsive to ultradian GC rhythmicity. We have used adrenalectomised rats replaced with pulses of corticosterone to determine the transcriptional effects of ultradian pulses in the hippocampus. Confocal microscopy confirmed that each GC pulse results in transient GR nuclear localisation in hippocampal CA1 neurones. Concomitant GR activation and DNA binding was demonstrated by synthetic glucocorticoid response element oligonucleotide binding, and verified for the Clock gene Period 1 promoter region by chromatin immunoprecipitation assays. Strikingly each GC pulse induced a 'burst' of transcription of Period 1 measured by heterogeneous nuclear RNA quantitative polymerase chain reaction. The net effect of pulsatile GC exposure on accumulation of the mature transcript was also assessed, revealing a plateau of mRNA levels throughout the time course of pulsatile exposure, indicating the pulse timing works optimally for steady state Per1 expression. The plateau dropped to baseline within 120 min of the final pulse, indicating a relatively short half-life for hippocampal Per1. The significance of this strict temporal control is that any perturbation to the pulse frequency or duration would have rapid quantitative effects on the levels of Per1. This in turn could affect hippocampal function, especially circadian related memory and learning processes.

Dopamine enhances locomotor activity for mating in male honeybees (Apis mellifera L.)

Dopamine plays multiple roles in the regulation of reproduction in female honeybees where it appears to act independently of juvenile hormone (JH). In males the role of dopamine and its relationship to JH control have not been elucidated. In the present study we determined hemolymph levels of dopamine and its metabolite (N-acetyldopamine) in males at post-emergence days 0-16. The development of locomotor and flight activities were recorded over the same period. Hemolymph levels of dopamine and N-acetyldopamine were found to increase at the time of onset of mating flight activity and those of dopamine decreased thereafter. Both locomotor and flight activities increased in parallel with hemolymph dopamine levels but the increased activity levels were maintained following decline of dopamine levels. Brain and meso-metathoracic ganglia levels of dopamine showed a similar developmental profile to hemolymph dopamine levels. Locomotor activities were temporarily inhibited by injection of a dopamine-receptor antagonist (cis(Z)-flupenthixol) into the thorax, and were enhanced by injection of a dopamine-receptor agonist (6,7-ADTN). These results suggest that dopamine regulates locomotor activities for mating and plays a role downstream of JH in premature males in honeybees.

Biogenic amines, caffeine and tonic immobility in Tribolium castaneum

Biogenic amines are physiologically neuroactive substances that affect behavioural and physiological traits in invertebrates. In the present study, the effects of dopamine, octopamine, tyramine and serotonin on tonic immobility, or death-feigning, were investigated in Tribolium castaneum. These amines were injected into the abdomens of beetles artificially selected for long or short duration of tonic immobility. In beetles of the long strains, the durations of tonic immobility were shortened by injection of dopamine, octopamine and tyramine, and the effects of these amines were dose-dependent. On the other hand, serotonin injection did not affect the duration of tonic immobility. In the short-strain beetles that rarely feign death, no significant effects of the amines were found on the duration of tonic immobility. Brain expression levels of octopamine, tyramine and serotonin did not differ between long- and short-strain beetles, in contrast to the higher dopamine levels in short strains previously reported. Caffeine decreased the duration of death-feigning in both oral absorption and injection experiments. It is known that caffeine activates dopamine. Therefore, the present results suggest that the duration of tonic immobility is affected by dopamine via the dopamine receptor in T. castaneum.

The functional organisation of glia in the adult brain of Drosophila and other insects

This review annotates and categorises the glia of adult Drosophila and other model insects and analyses the developmental origins of these in the Drosophila optic lobe. The functions of glia in the adult vary depending upon their sub-type and location in the brain. The task of annotating glia is essentially complete only for the glia of the fly's lamina, which comprise: two types of surface glia-the pseudocartridge and fenestrated glia; two types of cortex glia-the distal and proximal satellite glia; and two types of neuropile glia-the epithelial and marginal glia. We advocate that the term subretinal glia, as used to refer to both pseudocartridge and fenestrated glia, be abandoned. Other neuropiles contain similar glial subtypes, but other than the antennal lobes these have not been described in detail. Surface glia form the blood brain barrier, regulating the flow of substances into and out of the nervous system, both for the brain as a whole and the optic neuropiles in particular. Cortex glia provide a second level of barrier, wrapping axon fascicles and isolating neuronal cell bodies both from neighbouring brain regions and from their underlying neuropiles. Neuropile glia can be generated in the adult and a subtype, ensheathing glia, are responsible for cleaning up cellular debris during Wallerian degeneration. Both the neuropile ensheathing and astrocyte-like glia may be involved in clearing neurotransmitters from the extracellular space, thus modifying the levels of histamine, glutamate and possibly dopamine at the synapse to ultimately affect behaviour.

Roles of dopamine in circadian rhythmicity and extreme light sensitivity of circadian entrainment

Light has profound behavioral effects on almost all animals, and nocturnal animals show sensitivity to extremely low light levels [1-4]. Crepuscular, i.e., dawn/dusk-active animals such as Drosophila melanogaster are thought to show far less sensitivity to light [5-8]. Here we report that Drosophila respond to extremely low levels of monochromatic blue light. Light levels three to four orders of magnitude lower than previously believed impact circadian entrainment and the light-induced stimulation of locomotion known as positive behavioral masking. We use GAL4;UAS-mediated rescue of tyrosine hydroxylase (DTH) mutant (ple) flies to study the roles of dopamine in these processes. We present evidence for two roles of dopamine in circadian behaviors. First, rescue with either a wild-type DTH or a DTH mutant lacking neural expression leads to weak circadian rhythmicity, indicating a role for strictly regulated DTH and dopamine in robust circadian rhythmicity. Second, the DTH rescue strain deficient in neural dopamine selectively shows a defect in circadian entrainment to low light, whereas another response to light, positive masking, has normal light sensitivity. These findings imply separable pathways from light input to the behavioral outputs of masking versus circadian entrainment, with only the latter dependent on dopamine.

Selective boosting of transcriptional and behavioral responses to drugs of abuse by histone deacetylase inhibition

Histone acetylation and other modifications of the chromatin are important regulators of gene expression and, consequently, may contribute to drug-induced behaviors and neuroplasticity. Earlier studies have shown that a reduction in histone deacetylase (HDAC) activity results in the enhancement of some psychostimulant-induced behaviors. In this study, we extend those seminal findings by showing that the administration of the HDAC inhibitor sodium butyrate enhances morphine-induced locomotor sensitization and conditioned place preference. In contrast, this compound has no effects on the development of morphine tolerance and dependence. Similar effects were observed for cocaine and ethanol-induced behaviors. These behavioral changes were accompanied by a selective boosting of a component of the transcriptional program activated by chronic morphine administration that included circadian clock genes and other genes relevant to addictive behavior. Our results support a specific function for histone acetylation and the epigenetic modulation of transcription at a reduced number of biologically relevant loci on non-homeostatic, long-lasting, drug-induced behavioral plasticity.

Dosing time-dependent actions of psychostimulants

The concept of the dosing time-dependent (DTD) actions of drugs has been used to describe the effects of diurnal rhythms on pharmacological responsiveness. Notwithstanding the importance of diurnal variability in drug pharmacokinetics and bioavailability, it appears that in the central nervous system (CNS), the DTD actions of psychotropic drugs involve diurnal changes in the CNS-specific expression of genes encoding for psychotropic drug targets and transcription factors known as clock genes. In this review, we focused our discussion on the DTD effects of the psychostimulants cocaine and amphetamines. Both cocaine and amphetamines produce differential lasting behavioral alterations, that is, locomotor sensitization, depending on the time of the day they are administered. This exemplifies a DTD action of these drugs. The DTD effects of these psychostimulants correlate with diurnal changes in the system of transcription factors termed clock genes, for example, Period 1, and with changes in the availability of certain subtypes of dopamine receptors, for example, D2 and D3. Diurnal synthesis and release of the pineal hormone melatonin influence the DTD behavioral actions of cocaine and amphetamines. The molecular mechanism of melatonin's effects on the responsiveness of CNS to psychostimulants appears to involve melatonin receptors and clock genes. It is proposed that the DTD characteristics of psychostimulant action and the contributions of the melatonergic system may have clinical implications that include treatments for the attention deficit hyperactivity disorder and possibly neurotoxicity/neuroprotection.

A "bottom-counting" video system for measuring cocaine-induced behaviors in Drosophila

Cocaine exposure elicits a set of stereotypic behaviors in Drosophila that are strikingly similar to the cocaine-induced behaviors observed in vertebrates. This provides a valuable model for the study of cocaine abuse and has led to the discovery of a connection between the cocaine response pathway and the circadian system. This article describes a simplified assessment of cocaine-induced behavior combined with an image acquisition system, which allows the assay to be semiautomated. With this new system, cocaine response can be evaluated in a fraction of the time required by the previous assay, and subjectivity in scoring is reduced dramatically.

Dopamine receptor-mediated regulation of neuronal "clock" gene expression

Using a transgenic mice model (i.e. "clock" knockouts), clock transcription factors have been suggested as critical regulators of dopaminergic behaviors induced by drugs of abuse. Moreover, it has been shown that systemic administration of psychostimulants, such as cocaine and methamphetamine regulates the striatal expression of clock genes. However, it is not known whether dopamine receptors mediate these regulatory effects of psychostimulants at the cellular level. Primary striatal neurons in culture express dopamine receptors as well as clock genes and have been successfully used in studying dopamine receptor functioning. Therefore, we investigated the role of dopamine receptors on neuronal clock gene expression in this model using specific receptor agonists. We found an inhibitory effect on the expression of mClock and mPer1 genes with the D2-class (i.e. D2/D3) receptor agonist quinpirole. We also found a generalized stimulatory effect on the expression of clock genes mPer1, mClock, mNPAS2 (neuronal PAS domain protein 2), and mBmal1 with the D1-class (i.e. D1) receptor agonist SKF38393. Further, we tested whether systemic administration of dopamine receptor agonists causes similar changes in striatal clock gene expression in vivo. We found quinpirole-induced alterations in mPER1 protein levels in the mouse striatum (i.e. rhythm shift). Collectively, our results indicate that the dopamine receptor system may mediate psychostimulant-induced changes in clock gene expression. Using striatal neurons in culture as a model, further research is needed to better understand how dopamine signaling modulates the expression dynamics of clock genes (i.e. intracellular signaling pathways) and thereby influences neuronal gene expression, neuronal transmission, and brain functioning.

Differential entrainment of a social rhythm in adolescent mice

Daily routines in animal activities range from sleep-wake cycles, to foraging bouts, to social interactions. Among animals living within groups, it is unclear whether the motivations that underlie social interactions respond to daily light-dark (LD) cycles or endogenous circadian rhythms. Employing two mouse strains (BALB/cJ [BALB] and C57BL/6J [B6]) with genetically based differences in social affect and circadian rhythms, we examined how social investigation (SI) is modulated by social deprivation and circadian factors. We found a genetic influence on SI that was moderated by the preceding duration of social deprivation, requiring 3-6 h of social isolation prior to testing. Following 6h of social deprivation, the SI responses of adolescent B6 mice were greater than those of BALB mice only when the isolation period was imposed during the dark phase of the LD cycle. When B6 mice were weaned into conditions of constant darkness, a novel, endogenous social rhythm emerged, which was characterized by two pronounced peaks of social responsiveness (relative to one peak under LD entrainment) that were separated by 12-h intervals. Irrespective of the lighting conditions during social isolation, the SI responses of adolescent BALB mice did not oscillate across the day. Similar strain-dependent patterns of sociability were evident within groups of mice that were left undisturbed in their home cage under LD entrainment or constant darkness. Overall, genetic influences on the social phenotypes of adolescent mice are thus moderated by an interaction between social deprivation and oscillations of an endogenous social rhythm that entrains to the LD cycle.

A role for the circadian genes in drug addiction

Diurnal and circadian rhythms are prominent in nearly all bodily functions. Chronic disruptions in normal sleep wake and social schedules can lead to serious health problems such as those seen in shift worker's syndrome. Moreover, genetic disruptions in normal circadian gene functions have recently been linked to a variety of psychiatric conditions including depression, bipolar disorder, seasonal affective disorder and alcoholism. Recent studies are beginning to determine how these circadian genes and rhythms are involved in the development of drug addiction. Several of these studies suggest an important role for these genes in limbic regions of the brain, outside of the central circadian pacemaker in the suprachiasmatic nucleus (SCN). This review summarizes some of the basic research into the importance of circadian genes in drug addiction.

Circadian modulation of light-induced locomotion responses in Drosophila melanogaster

The relationship between light and the circadian system has long been a matter of discussion. Many studies have focused on entrainment of light with the internal biological clock. Light also functions as an environmental stimulus that affects the physiology and behaviour of animals directly. In this study, we used light as an unexpected stimulus for flies at different circadian times. We found that wildtype flies showed circadian changes in light-induced locomotion responses. Elevation of locomotor activity by light occurred during the subjective night, and performance in response to light pulses declined to trough during the subjective day. Moreover, arrhythmic mutants lost the rhythm of locomotion responses to light, with promotion of activity by light in timeless(01)mutants and inhibition of activity by light in Clock(ar)mutants. However, neither ablation of central oscillators nor disturbance of the functional clock inside compound eyes was sufficient to disrupt the rhythm of light responses. We show that, compound eyes, which have been identified as the control point for normal masking (promotion of activity by light), are sufficient but not necessary for paradoxical masking (suppression of activity by light) under high light intensity. This, taken together with the clear difference of light responses in wildtype flies, suggests that two different masking mechanisms may underlie the circadian modulation of light-induced locomotion responses.

Regulation of monoamine oxidase A by circadian-clock components implies clock influence on mood

The circadian clock has been implicated in addiction and several forms of depression [1, 2], indicating interactions between the circadian and the reward systems in the brain [3-5]. Rewards such as food, sex, and drugs influence this system in part by modulating dopamine neurotransmission in the mesolimbic dopamine reward circuit, including the ventral tegmental area (VTA) and the ventral striatum (NAc). Hence, changes in dopamine levels in these brain areas are proposed to influence mood in humans and mice [6-10]. To establish a molecular link between the circadian-clock mechanism and dopamine metabolism, we analyzed the murine promoters of genes encoding key enzymes important in dopamine metabolism. We find that transcription of the monoamine oxidase A (Maoa) promoter is regulated by the clock components BMAL1, NPAS2, and PER2. A mutation in the clock gene Per2 in mice leads to reduced expression and activity of MAOA in the mesolimbic dopaminergic system. Furthermore, we observe increased levels of dopamine and altered neuronal activity in the striatum, and these results probably lead to behavioral alterations observed in Per2 mutant mice in despair-based tests. These findings suggest a role of circadian-clock components in dopamine metabolism highlighting a role of the clock in regulating mood-related behaviors.

Molecular cloning and characterization of cDNAs encoding dopamine receptor-1 and -2 from brain-suboesophageal ganglion of the silkworm, Bombyx mori

In order to better understand the relationship between dopamine and the release of diapause hormone into the blood, we cloned and characterized cDNAs encoding Bombyx mori dopamine receptor-1 and -2 (BmDopR1 and 2) from the pupal brain-suboesophageal ganglion. BmDopR1 and 2 had high similarities to group 1 (Drosophila melanogaster DOP1 and Apis mellifera DOP1) and group 2 (D. melanogaster DopR99B, A. mellifera DOP2 and Papilio xuthus DOP1), respectively. When BmDopR1 and 2 were expressed in human embryonic kidney (HEK) cells, they responded to dopamine by increasing intracellular cAMP levels, thus indicating the presence of D1-like receptors. There were no clear differences in BmDopR1 and 2 mRNA levels between brain-suboesophageal ganglion complexes of diapause and nondiapause egg producers during pupal-adult development. BmDopR1 and 2 mRNAs were concentrated in the mushroom body calyx rather than in the suboesophageal ganglion. Taking into account the results of earlier experiments on excised regions corresponding to mushroom bodies, BmDopR1 and 2 in the mushroom body apparently play a role in the release of diapause hormone.

The extracellular signal-regulated kinase signaling pathway is involved in the modulation of morphine-induced reward by mPer1

Although there are clear interactions between circadian rhythms and drug addiction, mechanisms for such interactions remain unknown. Studies have shown that the circadian clock gene Period in Drosophila melanogaster could influence behavioral responses to cocaine, and the mouse homologues, mPer1 and mPer2, modulate cocaine sensitization and reward. In the present study, we applied DNAzyme targeting mPer1 to interfere the expression of mPer1 in CNS in mice, and studied its effects on morphine-induced reward and its molecular mechanism. The results demonstrated that the DNAzyme could attenuate the expression of mPer1 in CNS in mice and downregulate the increased extracellular signal-regulated kinase (ERK) activity induced by morphine in whole brain and the nucleus accumbens, the key region of drug addiction. Mice treated with morphine and injected intracerebroventricularly with DNAzyme did not show preference to the morphine-trained side. These results indicate that drug dependence seems to be influenced at least partially by mPer1 and its mechanism may involve the ERK signal pathway.

Manipulating the light/dark cycle: effects on dopamine levels in optic lobes of the honey bee (Apis mellifera) brain

This study examines the relationship between cyclical variations in optic-lobe dopamine levels and the circadian behavioural rhythmicity exhibited by forager bees. Our results show that changing the light-dark regimen to which bees are exposed has a significant impact not only on forager behaviour, but also on the levels of dopamine that can be detected in the optic lobes of the brain. Consistent with earlier reports, we show that foraging behaviour exhibits properties characteristic of a circadian rhythm. Foraging activity is entrained by daily light cycles to periods close to 24 h, it changes predictably in response to phase shifts in light, and it is able to free-run under constant conditions. Dopamine levels in the optic lobes also undergo cyclical variations, and fluctuations in endogenous dopamine levels are influenced significantly by alterations to the light/dark cycle. However, the time course of these changes is markedly different from changes observed at a behavioural level. No direct correlation could be identified between levels of dopamine in the optic lobes and circadian rhythmic activity of the honey bee.

Mapping of serotonin, dopamine, and histamine in relation to different clock neurons in the brain of Drosophila

Several sets of clock neurons cooperate to generate circadian activity rhythms in Drosophila melanogaster. To extend the knowledge on neurotransmitters in the clock circuitry, we analyzed the distribution of some biogenic amines in relation to identified clock neurons. This was accomplished by employing clock neuron-specific GAL4 lines driving green fluorescent protein (GFP) expression, combined with immunocytochemistry with antisera against serotonin, histamine, and tyrosine hydroxylase (for dopamine). In the larval and adult brain, serotonin-immunoreactive (-IR) neuron processes are in close proximity of both the dendrites and the dorsal terminals of the major clock neurons, the s-LN(v)s. Additionally, the terminals of the l-LN(v) clock neurons and serotonergic processes converge in the distal medulla. No histamine (HA)-IR processes contact the s-LN(v)s in the larval brain, but possibly impinge on the dorsal clock neurons, DN2. In the adult brain, HA-IR axons of the extraocular eyelet photoreceptors terminate on the dendritic branches of the LN(v)s. A few tyrosine hydroxylase (TH)-IR processes were seen close to the dorsal terminals of the s-LN(v)s, but not their dendrites, in the larval and adult brain. TH-IR processes also converge with the distal medulla branches of the l-LN(v)s in adults. None of the monoamines was detectable in the different clock neurons. By using an imaging system to monitor intracellular Ca(2+) levels in dissociated GFP-labeled larval s-LN(v)s, loaded with Fura-2, we demonstrated that application of serotonin induced dose-dependent decreases in Ca(2+). Thus, serotonergic neurons form functional inputs on the s-LN(v)s in the larval brain and possibly also in adults.

The restless legs syndrome

The restless legs syndrome (RLS) is one of the commonest neurological sensorimotor disorders at least in the Western countries and is often associated with periodic limb movements (PLM) during sleep leading to severe insomnia. However, it remains largely underdiagnosed and its underlying pathogenesis is presently unknown. Women are more affected than men and early-onset disease is associated with familial cases. A genetic origin has been suggested but the mode of inheritance is unknown. Secondary causes of RLS may share a common underlying pathophysiology implicating iron deficiency or misuse. The excellent response to dopaminegic drugs points to a central role of dopamine in the pathophysiology of RLS. Iron may also represent a primary factor in the development of RLS, as suggested by recent pathological and brain imaging studies. However, the way dopamine and iron, and probably other compounds, interact to generate the circadian pattern in the occurrence of RLS and PLM symptoms remains unknown. The same is also the case for the level of interaction of the two compounds within the central nervous system (CNS). Recent electrophysiological and animals studies suggest that complex spinal mechanisms are involved in the generation of RLS and PLM symptomatology. Dopamine modulation of spinal reflexes through dopamine D3 receptors was recently highlighted in animal models. The present review suggests that RLS is a complex disorder that may result from a complex dysfunction of interacting neuronal networks at one or several levels of the CNS and involving numerous neurotransmitter systems.

Deoxyribozymes inhibit the expression of period1 gene in vitro

To investigate the effect of two deoxyribozymes targeting period1 (per1) mRNA in vitro for exploring a novel gene therapy approach about circadian rhythm diseases, the specific deoxyribozymes targeting per1 were designed and synthesized chemically following MFold analysis according to its mRNA secondary structure. per1 RNA fragments were prepared by in vitro transcription of pcDNA3.1(+)-per1(164:256). The cleavage reactions containing deoxyribozymes and per1 RNA fragments were performed under certain conditions. With the transfection technique mediated by LipofectAMINE, pcDNA3-per1 and DRz164 or DRz256 were introduced into NIH3T3 cells. The effects of deoxyribozymes on per1 were studied by reverse transcript-polymerase chain reaction (RT-PCR) and flow cytometry (FCM). When deoxyribozymes and RNA transcripts were incubated under the adopted conditions at 37 degrees C for 2 h, about 63% of per1(164:256) RNA transcripts were cleaved by DRz164 and about 50.5% by DRz256. After cotransfecting pcDNA3-per1 with DRz164 or DRz256, the expression of per1 mRNA was decreased, as indicated by RT-PCR semi-quantity analysis. FCM analysis showed that Per1 protein was inhibited. Both DRz164 and DRz256 targeting per1 have the specific cleavage activity toward per1 mRNA in vitro and can highly block the expression of per1 gene in cellular milieu.

Amines and motivated behaviors: a simpler systems approach to complex behavioral phenomena

Recent investigations in invertebrate neurobiology have opened up new lines of research into the basic roles of behavioral, neurochemical, and physiological effects in complex behavioral phenomena, such as aggression and drug-sensitive reward. This review summarizes a body of quantitative work, which identifies biogenic amines as a pharmacological substrate for motivated behaviors in the crayfish, Orconectes rusticus. Specifically, this paper details progress that has (1) explored links between serotonin and an individual's aggressive state, and (2) demonstrated the existence of crayfish reward systems that are sensitive to human drugs of abuse, such as psychostimulants. First, we summarize a set of experimental approaches that explore aggression in crayfish and the significance of aminergic systems in its control. Agonistic behavior in crustaceans can be characterized within a quantitative framework; different types of behavioral plasticity in aggressive behavior are in need of physiological explanation, and pharmacological intervention involving serotonergic systems bring about characteristic changes in behavior. A second set of experiments demonstrates that psychostimulants (cocaine and D: -amphetamine) serve as rewards when an intra-circulatory infusion is coupled to a distinct visual environment. Work in novel model systems such as crayfish constitutes a useful comparative approach to the study of aggression and drug addiction.

Diurnal rhythms in quinpirole-induced locomotor behaviors and striatal D2/D3 receptor levels in mice

Dopaminergic drugs, including the D2/D3 agonist quinpirole, produce lasting changes in the brain that lead to altered behavioral responses. The action of these drugs is dosing time-dependent; in fruit flies, behavioral response to quinpirole shows a marked circadian variability. Here we demonstrate diurnal rhythm-dependent variations both in quinpirole-induced locomotor behaviors and in striatal D2 and D3 protein levels in mice. We found opposing diurnal rhythms in striatal D2 and D3 protein levels, resulting in a high D2/D3 ratio during the day and a low D2/D3 ratio at night. Protracted quinpirole treatment differentially altered striatal D2/D3 rhythms depending on the time of injection (i.e., day or night). When quinpirole-induced locomotor activity was analyzed for 90 min, we found hypomotility after the first day or nighttime drug injection. By the seventh injection, daytime quinpirole treatment produced clear hyperactivity while nighttime quinpirole treatment continued to induce a significant initial hypoactivity followed by a hyperactivity period. Our data indicate that quinpirole-induced long-term alterations in the brain include dosing time-dependent changes in dopamine receptor rhythms. Therefore, we propose that diurnal mechanisms, which participate in drug-induced long-term changes in the dopamine system, are important for the development of dopaminergic behaviors.

Systems approaches to biological rhythms in Drosophila

The chronobiological system of Drosophila is considered from the perspective of rhythm-regulated genes. These factors are enumerated and discussed not so much in terms of how the gene products are thought to act on behalf of circadian-clock mechanisms, but with special emphasis on where these molecules are manufactured within the organism. Therefore, with respect to several such cell and tissue types in the fly head, what is the "systems meaning" of a given structure's function insofar as regulation of rest-activity cycles is concerned? (Systematic oscillation of daily behavior is the principal overt phenotype analyzed in studies of Drosophila chronobiology). In turn, how do the several separate sets of clock-gene-expressing cells interact--or in some cases act in parallel--such that intricacies of the fly's sleep-wake cycles are mediated? Studying Drosophila chrono-genetics as a system-based endeavor also encompasses the fact that rhythm-related genes generate their products in many tissues beyond neural ones and during all stages of the life cycle. What, then, is the meaning of these widespread gene-expression patterns? This question is addressed with regard to circadian rhythms outside the behavioral arena, by considering other kinds of temporally based behaviors, and by contemplating how broadly systemic expression of rhythm-related genes connects with even more pleiotropic features of Drosophila biology. Thus, chronobiologically connected factors functioning within this insect comprise an increasingly salient example of gene versatility--multi-faceted usages of, and complex interactions among, entities that set up an organism's overall wherewithal to form and function. A corollary is that studying Drosophila development and adult-fly actions, even when limited to analysis of rhythm-systems phenomena, involves many of the animal's tissues and phenotypic capacities. It follows that such chronobiological experiments are technically demanding, including the necessity for investigators to possess wide-ranging expertise. Therefore, this chapter includes several different kinds of Methods set-asides. These techniques primers necessarily lack comprehensiveness, but they include certain discursive passages about why a given method can or should be applied and concerning real-world applicability of the pertinent rhythm-related technologies.