circadian clock

Mismatching clocks: the effect of circadian misalignment on peripheral 24-h rhythms in humans

Night shift work is associated with adverse health effects and leads to misalignment between timing cues from the environment and the endogenous circadian clock. In this presentation, I will discuss the effect of circadian misalignment induced by night shift work on peripheral 24-h rhythms on the transcriptome and metabolome in humans, presenting findings from both controlled laboratory studies and field studies. Furthermore, I will highlight the importance of taking into account interindividual differences in the response to circadian misalignment.

What does time of day mean for vision?

Profound changes in the visual environment occur over the course of the day-night cycle. There is therefore a profound pressure for cells and circuits within the visual system to adjust their function over time, to match the prevailing visual environment. Here, I will discuss electrophysiological data collected from nocturnal and diurnal rodents that reveal how the visual code is ‘temporally optimised’ by 1) the retina’s circadian clock, and 2) a change in behavioural temporal niche.

Why is the suprachiasmatic nucleus such a brilliant circadian time-keeper?

Circadian clocks dominate our lives. By creating and distributing an internal representation of 24-hour solar time, they prepare us, and thereby adapt us, to the daily and seasonal world. Jet-lag is an obvious indicator of what can go wrong when such adaptation is disrupted acutely. More seriously, the growing prevalence of rotational shift-work which runs counter to our circadian life, is a significant chronic challenge to health, presenting as increased incidence of systemic conditions such as metabolic and cardiovascular disease. Added to this, circadian and sleep disturbances are a recognised feature of various neurological and psychiatric conditions, and in some cases may contribute to disease progression. The “head ganglion” of the circadian system is the suprachiasmatic nucleus (SCN) of the hypothalamus. It synchronises the, literally, innumerable cellular clocks across the body, to each other and to solar time. Isolated in organotypic slice culture, it can maintain precise, high-amplitude circadian cycles of neural activity, effectively, indefinitely, just as it does in vivo. How is this achieved: how does this clock in a dish work? This presentation will consider SCN time-keeping at the level of molecular feedback loops, neuropeptidergic networks and neuron-astrocyte interactions.

The circadian clock and neural circuits maintaining body fluid homeostasis

Neurons in the suprachiasmatic nucleus (SCN, the brain’s master circadian clock) display a 24 hour cycle in the their rate of action potential discharge whereby firing rates are high during the light phase and lower during the dark phase. Although it is generally agreed that this cycle of activity is a key mediator of the clock’s neural and humoral output, surprisingly little is known about how changes in clock electrical activity can mediate scheduled physiological changes at different times of day. Using opto- and chemogenetic approaches in mice we have shown that the onset of electrical activity in vasopressin releasing SCN neurons near Zeitgeber time 22 (ZT22) activates glutamatergic thirst-promoting neurons in the OVLT (organum vasculosum lamina terminalis) to promote water intake prior to sleep. This effect is mediated by activity-dependent release of vasopressin from the axon terminals of SCN neurons which acts as a neurotransmitter on OVLT neurons. More recently we found that the clock receives excitatory input from a different subset of sodium sensing neurons in the OVLT. Activation of these neurons by a systemic salt load delivered at ZT19 stimulated the electrical activity of SCN neurons which are normally silent at this time. Remarkably, this effect induced an acute reduction in non-shivering thermogenesis and body temperature, which is an adaptive response to the salt load. These findings provide information regarding the mechanisms by which the SCN promotes scheduled physiological rhythms and indicates that the clock’s output circuitry can also be recruited to mediate an unscheduled homeostatic response.

Why we all need a good night’s sleep

We seek to determine how circadian rhythms and sleep are integrated with physiological processes to provide optimal fitness and health. Using initially a Drosophila model, and more recently also mammalian models, we have found that aspects of the blood brain barrier (BBB) are controlled by the circadian clock. BBB properties are also influenced by sleep:wake state in Drosophila, and, in fact, appear to be contribute to functions of sleep. This and other work, which implicates sleep in the regulation of metabolic processes, is providing insights into sleep function

The suprachiasmatic nucleus: the brain's circadian clock

Sleep and all of the other circadian rhythms that adapt us to the 24 hour world are controlled by the suprachiasmatic nucleus (SCN), the brain's central circadian clock. And yet, the SCN consists of only 20,000 neurons and astrocytes, so what makes it such a powerful clock, able to set the tempo to our lives? Professor Hastings will consider the cell-autonomus and neural circuit-level mechanisms that sustain the SCN clock and how it regulates rest, activity and sleep.

Sleep and the gut

Sleep is generally associated with the brain but poor sleep impacts the entire body - many diseases are caused or exacerbated by sleep loss. Our work is uncovering ways in which sleep and the body interact. We found a special, two-way relationship between sleep and the gut: the gut is uniquely impacted by sleep loss, and it actively controls sleep quality. These findings could help us understand the origins of sleep as well as develop strategies to offset the negative consequences of inadequate sleep.

Sensing Light for Sight and Physiological Control

Organisms sense light for purposes that range from recognizing objects to synchronizing activity with environmental cycles. What mechanisms serve these diverse tasks? This seminar will examine the specializations of two cell types. First are the foveal cone photoreceptors. These neurons are used by primates to see far greater detail than other mammals, which lack them. How do the biophysical properties of foveal cones support high-acuity vision? Second are the melanopsin retinal ganglion cells, which are conserved among mammals and essential for processes that include regulation of the circadian clock, sleep, and hormone levels. How do these neurons encode light, and is encoding customized for animals of different niches? In pursuing these questions, a broad goal is to learn how various levels of biological organization are shaped to behavioural needs.

Altered circadian clock gene expression in the mPFC of mouse model of depression and its modulation by rapid antidepressant treatments

The role of Rev-ERBα circadian clock gene in stress resilience and development of depression-like behaviour

Sleep disturbance and changes in oscillatory activity in a mouse model of depression: effects of sleep deprivation, ketamine and circadian clock modulation

Circadian clock in choroid plexus is resistant to immune challenge

FENS Forum 2024

Decoding transcriptional regulation in response to sunlight in vertebrates: Circadian clocks and beyond

FENS Forum 2024