The organization of biological activities into daily cycles is universal in organisms as diverse as cyanobacteria, fungi, algae, plants, flies, birds and man. Comparisons of circadian clocks in unicellular and multicellular organisms using molecular genetics and genomics have provided new insights into the mechanisms and complexity of clock systems. Whereas unicellular organisms require stand-alone clocks that can generate 24-hour rhythms for diverse processes, organisms with differentiated tissues can partition clock function to generate and coordinate different rhythms. In both cases, the temporal coordination of a multi-oscillator system is essential for producing robust circadian rhythms of gene expression and biological activity.

http://www.ifc.unam.mx/curso_ritmos/capitulo8/Bell-Pedersen05.pdf

Circadian rhythms from multiple oscillators: lessons from diverse organisms

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

/pdf/control-of-sleep-and-wakefulness-51vkuya5ho.pdf

Control of Sleep and Wakefulness

The suprachiasmatic nucleus (SCN) is the primary circadian pacemaker in mammals. Individual SCN neurons in dispersed culture can generate independent circadian oscillations of clock gene expression and neuronal firing. However, SCN rhythmicity depends on sufficient membrane depolarization and levels of intracellular calcium and cAMP. In the intact SCN, cellular oscillations are synchronized and reinforced by rhythmic synaptic input from other cells, resulting in a reproducible topographic pattern of distinct phases and amplitudes specified by SCN circuit organization. The SCN network synchronizes its component cellular oscillators, reinforces their oscillations, responds to light input by altering their phase distribution, increases their robustness to genetic perturbations, and enhances their precision. Thus, even though individual SCN neurons can be cell-autonomous circadian oscillators, neuronal network properties are integral to normal function of the SCN.

/pdf/suprachiasmatic-nucleus-cell-autonomy-and-network-properties-p52lbkseja.pdf

Suprachiasmatic Nucleus: Cell Autonomy and Network Properties

A wide variety of biological experiments rely on the ability to express an exogenous gene in a transgenic animal at a defined level and in a spatially and temporally controlled pattern. We describe major improvements of the methods available for achieving this objective in Drosophila melanogaster. We have systematically varied core promoters, UTRs, operator sequences, and transcriptional activating domains used to direct gene expression with the GAL4, LexA, and Split GAL4 transcription factors and the GAL80 transcriptional repressor. The use of site-specific integration allowed us to make quantitative comparisons between different constructs inserted at the same genomic location. We also characterized a set of PhiC31 integration sites for their ability to support transgene expression of both drivers and responders in the nervous system. The increased strength and reliability of these optimized reagents overcome many of the previous limitations of these methods and will facilitate genetic manipulations of greater complexity and sophistication.

https://www.genetics.org/content/genetics/186/2/735.full.pdf

Refinement of Tools for Targeted Gene Expression in Drosophila

Endogenous rhythms of locomotion in the American horseshoe crab, Limulus polyphemus

Daily rhythms of physiology and behaviour are precisely timed by an endogenous circadian clock1,2. These include separate bouts of morning and evening activity, characteristic of Drosophila melanogaster and many other taxa, including mammals3,4,5. Whereas multiple oscillators have long been proposed to orchestrate such complex behavioural programmes6, their nature and interplay have remained elusive. By using cell-specific ablation, we show that the timing of morning and evening activity in Drosophila derives from two distinct groups of circadian neurons: morning activity from the ventral lateral neurons that express the neuropeptide PDF, and evening activity from another group of cells, including the dorsal lateral neurons. Although the two oscillators can function autonomously, cell-specific rescue experiments with circadian clock mutants indicate that they are functionally coupled.

Coupled oscillators control morning and evening locomotor behaviour of Drosophila

https://www.cell.com/neuron/pdf/S0896-6273(08)01088-X.pdf

PDF Cells Are a GABA-Responsive Wake-Promoting Component of the Drosophila Sleep Circuit

Many lines of evidence indicate that GABA and GABA(A) receptors make important contributions to human sleep regulation. Pharmacological manipulation of these receptors has differential effects on sleep onset and sleep maintenance insomnia. Here we show that sleep is regulated by GABA in Drosophila and that a mutant GABA(A) receptor, Rdl(A302S), specifically decreases sleep latency. The drug carbamazepine (CBZ) has the opposite effect on sleep; it increases sleep latency as well as decreasing sleep. Behavioral and physiological experiments indicated that Rdl(A302S) mutant flies are resistant to the effects of CBZ on sleep latency and that mutant RDL(A302S) channels are resistant to the effects of CBZ on desensitization, respectively. These results suggest that this biophysical property of the channel, specifically channel desensitization, underlies the regulation of sleep latency in flies. These experiments uncouple the regulation of sleep latency from that of sleep duration and suggest that the kinetics of GABA(A) receptor signaling dictate sleep latency.

/pdf/modulation-of-gabaa-receptor-desensitization-uncouples-sleep-w69xoib656.pdf

Modulation of GABAA receptor desensitization uncouples sleep onset and maintenance in Drosophila

The miticide effect of lithium on the honey bee (Apis mellifera) parasite Varroa has been discovered. Varroa mite is considered the principal threat to bee health and, as a result, to pollination and food security. In this study, we investigated the behavioral effects of lithium on honey bees, specifically locomotor activity (LMA) level and circadian patterns of LMA, such as rhythmicity, and periodicity. Any effects of lithium on activity may be important for bee health since timing and daylight are critical for bee foraging and bee’s use of the sun compass for navigation and communication. Both acute and chronic lithium treatments affected the LMA of honey bees. The effect varies depending on light and dark conditions. Chronic treatment with lithium disrupted the rhythmicity and altered the period of the circadian rhythm. While the circadian period was not affected by the light condition in the control group, lithium treatment lengthened the period in constant light condition. Lithium decreased total LMA in a constant light condition where typically activity is increased and not under the dark condition, both in acute and chronic treatments. However, mortality in the high-dose lithium treatment group is higher in the dark environment in the acute experiment. Lithium is also the first-line therapy for bipolar disorder. This disorder causes excessively elevated activity called mania and circadian rhythm abnormalities. The effects of lithium on reducing light-induced activity and the circadian rhythm of bees are reminiscent of its stabilizing effect on activity and circadian rhythms in bipolar disorder treatment.

/pdf/effects-of-lithium-on-locomotor-activity-and-circadian-2yn6j5rn.pdf

Jose Agosto

Papers

Coupled oscillators control morning and evening locomotor behaviour of Drosophila

PDF Cells Are a GABA-Responsive Wake-Promoting Component of the Drosophila Sleep Circuit

Modulation of GABAA receptor desensitization uncouples sleep onset and maintenance in Drosophila

Effects of lithium on locomotor activity and circadian rhythm of honey bees