Mutations in the circadian gene period alter behavioral and biochemical responses to ethanol in Drosophila

A Brief Overview of Ethanol Tolerance and Its Potential Association with Circadian Rhythm in Drosophila

Alcohol consumption and addiction remain global health concerns, with significant loss of productivity, morbidity, and mortality. Drosophila melanogaster, a widely used model organism, offers valuable insights into the genetic and neuronal mechanisms underlying ethanol-induced behaviors (EIBs) such as sedation, recovery, and tolerance. This narrative review focuses on studies in the Drosophila model system suggesting an association between circadian rhythm genes as modulators of ethanol tolerance. Mutations in these genes disrupt both the circadian cycle and tolerance, underscoring the interplay between circadian rhythm and ethanol processing although the exact mechanisms remain largely unknown. Additionally, genes involved in stress response, gene expression regulation, neurotransmission, and synaptic activity were implicated in ethanol tolerance modulation. At the neuronal level, recent studies have highlighted the involvement of corazonin (CRZ) and neuropeptide F (NPF) neurons in modulating EIBs. Understanding the temporal dynamics of tolerance development is crucial for describing the molecular basis of ethanol tolerance. Ultimately, insights gained from Drosophila studies hold promise for elucidating the neurobiological underpinnings of alcohol use disorders and addiction, contributing to more effective interventions and treatments.

Caffeine Delays Ethanol-Induced Sedation in Drosophila

Caffeine and ethanol are among the most widely available and commonly consumed psychoactive substances. Both interact with adenosine receptor-mediated signaling which regulates numerous neurological processes including sleep and waking behaviors. In mammals, caffeine is an adenosine receptor antagonist and thus acts as a stimulant. Conversely, ethanol is a sedative because it promotes GABAergic neurotransmission, inhibits glutamatergic neurotransmission, and increases the amount of adenosine in the brain. Despite seemingly overlapping interactions, not much is known about the effect of caffeine on ethanol-induced sedation in Drosophila. In this study, using Drosophila melanogaster as a model, we show that caffeine supplementation in food delays the onset of ethanol-induced sedation in males and females of different strains. The resistance to sedation reverses upon caffeine withdrawal. Heterozygous adenosine receptor mutant flies are resistant to sedation. These findings suggest that caffeine and adenosine receptors modulate the sedative effects of ethanol in Drosophila.

Drinking in the morning versus evening: Time-dependent differential effects of acute alcohol administration on the behavior of zebrafish

Alcohol (ethanol) abuse remains to be a leading cause of medical, including mental, problems throughout the world. Whether alcohol consumption leads to chronic use, and subsequent alcohol dependency and abuse is known to be influenced by the acute effects of this drug. Numerous factors may influence how alcohol administered acutely affects the individual. For example, the mechanisms engaged by drugs of abuse, e.g. cocaine as well as alcohol, have been shown to overlap with those underlying circadian rhythm, and conversely, the effects of these drugs may be dependent upon the time of day of their consumption. To investigate the interaction between circadian rhythm and alcohol, here we employ a simple vertebrate model organism that was previously successfully utilized in other aspects of alcohol research, the zebrafish. We expose zebrafish to alcohol for 20 min in the morning or in the evening, and analyze the effects of this treatment by comparing 1% (vol/vol) alcohol-treated and control (alcohol naive) zebrafish. We record numerous swim path parameters, and report, for the first time, that the time of day of alcohol administration differentially affects certain behavioral parameters, enhancing some while blunting others. Our results suggest a complex interaction between circadian dependent and alcohol engaged mechanisms, findings that represent both practical complications as well as opportunities for understanding how alcohol affects brain function and behavior of vertebrates.

A Fly's Eye View of Natural and Drug Reward

Animals encounter multiple stimuli each day. Some of these stimuli are innately appetitive or aversive, while others are assigned valence based on experience. Drugs like ethanol can elicit aversion in the short term and attraction in the long term. The reward system encodes the predictive value for different stimuli, mediating anticipation for attractive or punishing stimuli and driving animal behavior to approach or avoid conditioned stimuli. The neurochemistry and neurocircuitry of the reward system is partly evolutionarily conserved. In both vertebrates and invertebrates, including Drosophila melanogaster, dopamine is at the center of a network of neurotransmitters and neuromodulators acting in concert to encode rewards. Behavioral assays in D. melanogaster have become increasingly sophisticated, allowing more direct comparison with mammalian research. Moreover, recent evidence has established the functional modularity of the reward neural circuits in Drosophila. This functional modularity resembles the organization of reward circuits in mammals. The powerful genetic and molecular tools for D. melanogaster allow characterization and manipulation at the single-cell level. These tools are being used to construct a detailed map of the neural circuits mediating specific rewarding stimuli and have allowed for the identification of multiple genes and molecular pathways that mediate the effects of reinforcing stimuli, including their rewarding effects. This report provides an overview of the research on natural and drug reward in D. melanogaster, including natural rewards such as sugar and other food nutrients, and drug rewards including ethanol, cocaine, amphetamine, methamphetamine, and nicotine. We focused mainly on the known genetic and neural mechanisms underlying appetitive reward for sugar and reward for ethanol. We also include genes, molecular pathways, and neural circuits that have been identified using assays that test the palatability of the rewarding stimulus, the preference for the rewarding stimulus, or other effects of the stimulus that indicate how it can modify behavior. Commonalities between mechanisms of natural and drug reward are highlighted and future directions are presented, putting forward questions best suited for research using D. melanogaster as a model organism.

Inhibition of expression of the circadian clock gene Period causes metabolic abnormalities including repression of glycometabolism in Bombyx mori cells

Abnormalities in the circadian clock system are known to affect the body’s metabolic functions, though the molecular mechanisms responsible remain uncertain. In this study, we achieved continuous knockdown of B. mori Period (BmPer) gene expression in the B. mori ovary cell line (BmN), and generated a Per-KD B. mori model with developmental disorders including small individual cells and slow growth. We conducted cell metabolomics assays by gas chromatography/liquid chromatography-mass spectrometry and showed that knockdown of BmPer gene expression resulted in significant inhibition of glycometabolism. Amino acids that used glucose metabolites as a source were also down-regulated, while lipid metabolism and nucleotide metabolism were significantly up-regulated. Metabolite correlation analysis showed that pyruvate and lactate were closely related to glycometabolism, as well as to metabolites such as aspartate, alanine, and xanthine in other pathways. Further validation experiments showed that the activities of the key enzymes of glucose metabolism, hexokinase, phosphofructokinase, and citrate synthase, were significantly decreased and transcription of their encoding genes, as well as that of pyruvate kinase, were also significantly down-regulated. We concluded that inhibition of the circadian clock gene BmPer repressed glycometabolism, and may be associated with changes in cellular amino acid metabolism, and in cell growth and development.

Genetic architecture of natural variation in visual senescence in Drosophila

Senescence, i.e., functional decline with age, is a major determinant of health span in a rapidly aging population, but the genetic basis of interindividual variation in senescence remains largely unknown. Visual decline and age-related eye disorders are common manifestations of senescence, but disentangling age-dependent visual decline in human populations is challenging due to inability to control genetic background and variation in histories of environmental exposures. We assessed the genetic basis of natural variation in visual senescence by measuring age-dependent decline in phototaxis using Drosophila melanogaster as a genetic model system. We quantified phototaxis at 1, 2, and 4 wk of age in the sequenced, inbred lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) and found an average decline in phototaxis with age. We observed significant genetic variation for phototaxis at each age and significant genetic variation in senescence of phototaxis that is only partly correlated with phototaxis. Genome-wide association analyses in the DGRP and a DGRP-derived outbred, advanced intercross population identified candidate genes and genetic networks associated with eye and nervous system development and function, including seven genes with human orthologs previously associated with eye diseases. Ninety percent of candidate genes were functionally validated with targeted RNAi-mediated suppression of gene expression. Absence of candidate genes previously implicated with longevity indicates physiological systems may undergo senescence independent of organismal life span. Furthermore, we show that genes that shape early developmental processes also contribute to senescence, demonstrating that senescence is part of a genetic continuum that acts throughout the life span.