Imperial College London

Professor Nick Franks, FRS

Faculty of Natural SciencesDepartment of Life Sciences

Professor of Biophysics and Anaesthetics
 
 
 
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Contact

 

+44 (0)20 7594 7629n.franks Website

 
 
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Location

 

401ASir Ernst Chain BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

204 results found

Harding EC, Ba W, Zahir R, Yu X, Yustos R, Hsieh B, Lignos L, Vyssotski AL, Constandinou T, Franks NP, Wisden Wet al., 2021, Nitric oxide synthase neurons in the preoptic hypothalamus are sleep-active and contribute to regulating NREM and REM sleep and lowering body temperature, Publisher: Cold Spring Harbor Laboratory

When mice are exposed to external warmth, nitric oxide synthase (NOS1) neurons in the median and medial preoptic (MnPO/MPO) hypothalamus induce sleep and concomitant body cooling. However, how these neurons regulate baseline sleep and body temperature is unknown. Using calcium photometry, we show that NOS1 neurons in MnPO/MPO are predominantly NREM active. This is the first instance of a predominantly NREM-active population in the PO area, or to our knowledge, elsewhere in the brain. In addition to releasing nitric oxide, NOS1 neurons in MnPO/MPO can release GABA, glutamate and peptides. We expressed tetanus-toxin light-chain in MnPO/MPO NOS1 cells to reduce vesicular release of transmitters. This induced changes in sleep structure: over 24 hours, mice had less NREM sleep in their dark (active) phase, and more NREM sleep in their light (sleep) phase. REM sleep episodes in the dark phase were longer, and there were fewer REM transitions between other vigilance states. REM sleep had less theta power. Mice with synaptically blocked MnPO/MPO NOS1 neurons were also warmer. In particular, mice were warmer than control mice at the dark-light transition (ZT0), as well as during the dark phase siesta (ZT16-20), where there is usually a body temperature dip. Also, at this siesta point of cooled body temperature, mice usually have more NREM, but mice with synaptically blocked MnPO/MPO NOS1 cells showed reduced NREM sleep at this time. Overall, MnPO/MPO NOS1 neurons promote both NREM and REM sleep and contribute to chronically lowering body temperature, particularly at transitions where the mice normally enter NREM sleep.

Working paper

Campos-Pires R, Onggradito H, Ujvari E, Karimi S, Aldhoun J, Edge C, Franks N, Dickinson Ret al., 2021, Xenon is neuroprotective and promotes beneficial early neuroinflammation in a rat model of severe traumatic brain injury, Society for Neuroscience

Conference paper

Campos-Pires R, Onggradito H, Ujvari E, Karimi S, Valeo F, Edge C, Franks N, Dickinson Ret al., 2021, Xenon is neuroprotective and promotes beneficial early neuroinflammation in a rat model of severe traumatic brain injury, Society for Neuroscience

Conference paper

Campos-Pires R, Onggradito H, Ujvari E, Karimi S, Valeo F, Aldhoun J, Edge C, Franks N, Dickinson Ret al., 2020, Xenon treatment after severe traumatic brain injury improves locomotor outcome, reduces acute neuronal loss and enhances early beneficial neuroinflammation: a randomized, blinded, controlled animal study, Critical Care (UK), Vol: 24, Pages: 1-18, ISSN: 1364-8535

BackgroundTraumatic brain injury (TBI) is a major cause of morbidity and mortality, but there are no clinically proven treatments that specifically target neuronal loss and secondary injury development following TBI. In this study, we evaluate the effect of xenon treatment on functional outcome, lesion volume, neuronal loss and neuroinflammation after severe TBI in rats.MethodsYoung adult male Sprague Dawley rats were subjected to controlled cortical impact (CCI) brain trauma or sham surgery followed by treatment with either 50% xenon:25% oxygen balance nitrogen, or control gas 75% nitrogen:25% oxygen. Locomotor function was assessed using Catwalk-XT automated gait analysis at baseline and 24 h after injury. Histological outcomes were assessed following perfusion fixation at 15 min or 24 h after injury or sham procedure.ResultsXenon treatment reduced lesion volume, reduced early locomotor deficits, and attenuated neuronal loss in clinically relevant cortical and subcortical areas. Xenon treatment resulted in significant increases in Iba1-positive microglia and GFAP-positive reactive astrocytes that was associated with neuronal preservation.ConclusionsOur findings demonstrate that xenon improves functional outcome and reduces neuronal loss after brain trauma in rats. Neuronal preservation was associated with a xenon-induced enhancement of microglial cell numbers and astrocyte activation, consistent with a role for early beneficial neuroinflammation in xenon’s neuroprotective effect. These findings suggest that xenon may be a first-line clinical treatment for brain trauma.

Journal article

Miracca G, Soto BA, Tossell K, Yustos R, Vyssotski AL, Franks NP, Wisden Wet al., 2020, Hypothalamic NMDA receptors stabilize NREM sleep and are essential for REM sleep

<jats:title>SUMMARY</jats:title><jats:p>The preoptic hypothalamus regulates both NREM and REM sleep. We found that calcium levels in mouse lateral preoptic (LPO) neurons were highest during REM. Deleting the core GluN1 subunit of NMDA receptors from LPO neurons abolished calcium signals during all vigilance states, and the excitatory drive onto LPO neurons was reduced. Mice had less NREM sleep and were incapable of generating conventionally classified REM sleep episodes: cortical theta oscillations were greatly reduced but muscle atonia was maintained. Additionally, mice lacking NMDA receptors in LPO neurons had highly fragmented sleep-wake patterns. The fragmentation persisted even under high sleep pressure produced by sleep deprivation. Nevertheless, the sleep homeostasis process remained intact, with an increase in EEG delta power. The sedative dexmedetomidine and sleeping medication zolpidem could transiently restore consolidated sleep. High sleep-wake fragmentation, but not sleep loss, was also produced by selective GluN1 knock-down in GABAergic LPO neurons. We suggest that NMDA glutamate receptor signalling stabilizes the firing of “GABAergic NREM sleep-on” neurons and is also essential for the theta rhythm in REM sleep.</jats:p>

Journal article

Lignos L, Nollet M, Wisden W, Franks NPet al., 2020, Does sleep deprivation cause stress in mice? A comparison of gentle handling versus novel object presentation sleep deprivation methods, 25th Congress of the European-Sleep-Research-Society (ESRS), Publisher: WILEY, Pages: 195-196, ISSN: 0962-1105

Conference paper

Tossell K, Yu X, Soto BA, Vicente M, Miracca G, Giannos P, Miao A, Hsieh B, Ma Y, Yustos R, Vyssotski A, Constandinou T, Franks N, Wisden Wet al., 2020, Sleep deprivation triggers somatostatin neurons in prefrontal cortex to initiate nesting and sleep via the preoptic and lateral hypothalamus, Publisher: bioRxiv

Animals undertake specific behaviors before sleep. Little is known about whether these innate behaviors, such as nest building, are actually an intrinsic part of the sleep-inducing circuitry. We found, using activity-tagging genetics, that mouse prefrontal cortex (PFC) somatostatin/GABAergic (SOM/GABA) neurons, which become activated during sleep deprivation, induce nest building when opto-activated. These tagged neurons induce sustained global NREM sleep if their activation is prolonged metabotropically. Sleep-deprivation-tagged PFC SOM/GABA neurons have long-range projections to the lateral preoptic (LPO) and lateral hypothalamus (LH). Local activation of tagged PFC SOM/GABA terminals in LPO and the LH induced nesting and NREM sleep respectively. Our findings provide a circuit link for how the PFC responds to sleep deprivation by coordinating sleep preparatory behavior and subsequent sleep.

Working paper

Yu X, Ba W, Zhao G, Ma Y, Harding EC, Yin L, Wang D, Li H, Zhang P, Shi Y, Yustos R, Vyssotski AL, Wisden W, Franks NP, Dong Het al., 2020, Dysfunction of ventral tegmental area GABA neurons causes mania-like behavior., Molecular Psychiatry, ISSN: 1359-4184

Journal article

Campos-Pires R, Mohamed-Ali N, Franks N, Aldhoun J, Dickinson Ret al., 2020, Hypothermia combined with xenon reduces secondary injury development and enhances neuroprotection by preventing neuronal cell loss in a rat model of traumatic brain injury, European Journal of Anaesthesia vol e37, Pages: 300-300

Conference paper

Harding EC, Franks NP, Wisden W, 2020, Sleep and thermoregulation, Current Opinion in Physiology, Vol: 15, Pages: 7-13, ISSN: 2468-8673

Journal article

Nollet M, Wisden W, Franks N, 2020, Sleep deprivation and stress - a reciprocal relationship, Interface Focus, Vol: 10, Pages: 1-11, ISSN: 2042-8901

Sleep is highly conserved across evolution, suggesting vital biological functions that are yet to be fully understood. Animals and humans experiencing partial sleep restriction usually exhibit detrimental physiological responses, while total and prolonged sleep loss could lead to death. The perturbation of sleep homeostasis is usually accompanied by an increase of the hypothalamic-pituitary-adrenal (HPA) axis, leading to a rise of circulating level of stress hormones (e.g., cortisol in humans, corticosterone in rodents). Such hormones follow a circadian release pattern under undisturbed conditions and participate in the regulation of sleep. The investigation of the consequences of sleep deprivation, from molecular changes to behavioural alterations, has been used to study the fundamental functions of sleep. However, the reciprocal relationship between sleep and the activity of the HPA axis is problematic when investigating sleep using traditional sleep-deprivation protocols that can induce stress per se. This is especially true in studies using rodents in which sleep deprivation is achieved by exogenous, and potentially stressful, sensory-motor stimulations that can undoubtedly confuse their conclusions. While more research is needed to explore the mechanisms underlying sleep loss and health, avoiding stress as a confounding factor in sleep-deprivation studies is therefore crucial. This review examines the evidence of the intricate links between sleep and stress in the context of experimental sleep deprivation, and proposes a more sophisticated research framework for sleep-deprivation procedures that could benefit from recent progress in biotechnological tools for precise neuromodulation, such as chemogenetics and optogenetics, as well as improved automated real-time sleep scoring algorithms.

Journal article

Wisden W, Franks NP, 2020, The stillness of sleep., Scienc, Vol: 367, Pages: 366-367, ISSN: 1095-9203

Journal article

Hsieh B, Harding E, Wisden W, Franks N, Constandinou Tet al., 2019, A miniature neural recording device to investigate sleep and temperature regulation in mice, IEEE Biomedical Circuits and Systems (BioCAS) Conference, Publisher: IEEE, Pages: 1-4

Sleep is an important and ubiquitous process that,despite decades of research, a large part of its underlyingbiological circuity still remain elusive. To conduct research inthis field, many devices capable of recording neural signalssuch as LFP and EEG have been developed. However, most ofthese devices are unsuitable for sleep studies in mice, the mostcommonly used animals, due to their size and weight. Thus, thispaper presents a novel 4 channel, compact ( 2.1cm by 1.7cm )and lightweight ( 3.6g ) neural-logging device that can recordfor 3 days on just two 0.6g zinc air 312 batteries. Instead ofthe typical solution of using multiple platforms, the presenteddevice integrates high resolution EEG, EMG and temperaturerecordings into one platform. The onboard BLE module allowsthe device to be controlled wirelessly as well as stream data in realtime, enabling researchers to check the progress of the recordingwith minimal animal disturbance. The device demonstrates itsability to accurately record EEG and temperature data throughthe long 24 hour in-vivo recordings conducted. The obtainedEEG data could be easily sleep scored and the temperaturesvalues were all within expected physiological range.

Conference paper

Koziakova M, Harris K, Edge C, Franks N, White I, Dickinson Ret al., 2019, Noble gas neuroprotection: Xenon and argon protect against hypoxic-ischaemic injury in rat hippocampus in vitro via distinct mechanisms, British Journal of Anaesthesia, Vol: 123, Pages: 601-609, ISSN: 1471-6771

BackgroundNoble gases may provide novel treatments for neurological injuries such as ischaemic and traumatic brain injury. Few studies have evaluated the complete series of noble gases under identical conditions in the same model.MethodsWe used an in vitro model of hypoxia–ischaemia to evaluate the neuroprotective properties of the series of noble gases, helium, neon, argon, krypton, and xenon. Organotypic hippocampal brain slices from mice were subjected to oxygen-glucose deprivation, and injury was quantified using propidium iodide fluorescence.ResultsBoth xenon and argon were equally effective neuroprotectants, with 0.5 atm of xenon or argon reducing injury by 96% (P<0.0001), whereas helium, neon, and krypton were devoid of any protective effect. Neuroprotection by xenon, but not argon, was reversed by elevated glycine.ConclusionsXenon and argon are equally effective as neuroprotectants against hypoxia–ischaemia in vitro, with both gases preventing injury development. Although xenon's neuroprotective effect may be mediated by inhibition of the N-methyl-d-aspartate receptor at the glycine site, argon acts via a different mechanism. These findings may have important implications for their clinical use as neuroprotectants.

Journal article

Ma Y, Miracca G, Yu X, Harding EC, Miao A, Yustos R, Vyssotski AL, Franks NP, Wisden Wet al., 2019, Galanin Neurons Unite Sleep Homeostasis and α2-Adrenergic Sedation., Current biology : CB, Vol: 29, Pages: 3315-3322.e3, ISSN: 0960-9822

Our urge to sleep increases with time spent awake, until sleep becomes inescapable. The sleep following sleep deprivation is longer and deeper, with an increased power of delta (0.5-4 Hz) oscillations, a phenomenon termed sleep homeostasis [1-4]. Although widely expressed genes regulate sleep homeostasis [1, 4-10] and the process is tracked by somnogens and phosphorylation [1, 3, 7, 11-14], at the circuit level sleep homeostasis has remained mysterious. Previously, we found that sedation induced with α2-adrenergic agonists (e.g., dexmedetomidine) and sleep homeostasis both depend on the preoptic (PO) hypothalamus [15, 16]. Dexmedetomidine, increasingly used for long-term sedation in intensive care units [17], induces a non-rapid-eye-movement (NREM)-like sleep but with undesirable hypothermia [18, 19]. Within the PO, various neuronal subtypes (e.g., GABA/galanin and glutamate/NOS1) induce NREM sleep [20-22] and concomitant body cooling [21, 22]. This could be because NREM sleep's restorative effects depend on lower body temperature [23, 24]. Here, we show that mice with lesioned PO galanin neurons have reduced sleep homeostasis: in the recovery sleep following sleep deprivation there is a diminished increase in delta power, and the mice catch up little on lost sleep. Furthermore, dexmedetomidine cannot induce high-power delta oscillations or sustained hypothermia. Some hours after dexmedetomidine administration to wild-type mice there is a rebound in delta power when they enter normal NREM sleep, reminiscent of emergence from torpor. This delta rebound is reduced in mice lacking PO galanin neurons. Thus, sleep homeostasis and dexmedetomidine-induced sedation require PO galanin neurons and likely share common mechanisms.

Journal article

Campos-Pires R, Mohamed-Ali N, Balaet M, Aldhoun J, Abelleira-Hervas L, Aitken P, Edge C, Franks N, Dickinson Ret al., 2019, Xenon prevents early neuronal loss and neuroinflammation in a rat model of traumatic brain injury, BJA Research Forum / Anaesthetic Research Society, Publisher: Elsevier, Pages: e508-e509, ISSN: 0007-0912

Conference paper

Campos-Pires R, Hirnet T, Valeo F, Ong BE, Radyushkin K, Aldhoun J, Saville J, Edge CJ, Franks NP, Thal SC, Dickinson Ret al., 2019, XENON PREVENTS NEURODEGENERATION AND LATE-ONSET COGNITIVE IMPAIRMENT, AND IMPROVES SURVIVAL AFTER TRAUMATIC BRAIN INJURY IN MICE, 37th Annual National Neurotrauma Symposium, Publisher: MARY ANN LIEBERT, INC, Pages: A47-A47, ISSN: 0897-7151

Conference paper

Campos-Pires R, Yonis A, Pau A, Macdonald W, Harris K, Franks N, Edge C, Dickinson Ret al., 2019, Delayed xenon treatment prevents injury development following blast-neurotrauma in vitro, 37th Annual National Neurotrauma Symposium, Publisher: Mary Ann Liebert, Pages: A40-A41, ISSN: 0897-7151

Conference paper

Campos-Pires R, Mohamed-Ali N, Balaet M, Aldhoun J, Abelleira-Hervas L, Aitken P, Edge CJ, Franks NP, Dickinson Ret al., 2019, XENON REDUCES SECONDARY INJURY, PREVENTS NEURONAL LOSS AND NEUROINFLAMMATION IN A RAT MODEL OF TRAUMATIC BRAIN INJURY, 37th Annual National Neurotrauma Symposium, Publisher: MARY ANN LIEBERT, INC, Pages: A116-A116, ISSN: 0897-7151

Conference paper

Campos-Pires R, Hirnet T, Valeo F, Ong BE, Radyushkin K, Aldhoun J, Saville J, Edge C, Franks N, Thal S, Dickinson Ret al., 2019, Xenon improves long-term cognitive function, reduces neuronal loss and chronic neuroinflammation, and improves survival after traumatic brain injury in mice, British Journal of Anaesthesia, Vol: 123, Pages: 60-73, ISSN: 1471-6771

Background.Xenon is a noble gas with neuroprotective properties. We previously showed that xenon improves short and long-term outcomes in young adult mice after controlled cortical impact (CCI). This is a follow-up study investigating xenon’s effect on very long-term outcome and survival. Methods.C57BL/6N (n=72) young adult male mice received single CCI or sham surgery and were treated with either xenon (75%Xe:25%O2) or control gas (75% N2:25%O2). The outcomes used were: 1) 24-hour lesion volume and neurological outcome score; 2)contextual fear-conditioning at 2 weeks and 20 months; 3) corpus callosum white matter quantification; 4) immunohistological assessment of neuroinflammation and neuronal loss; 5) long-term survival. Results.Xenon treatment significantly reduced secondary injury development (p<0.05), improved short-term vestibulomotor function (p<0.01),and prevented development of very late-onset traumatic brain injury (TBI)-related memory deficits. Xenon treatment reducedwhite matter loss in the contralateral corpus callosum and neuronal loss in the contralateral hippocampal CA1 andDG areas at 20 months. Xenon’s long-term neuroprotective effects were associated with a significant (p<0.05) reduction in neuroinflammation in multiple brain areas involved in associative memory, including reduction in reactive astrogliosis and microglial cell proliferation. Survival was improved significantly (p<0.05) in xenon-treated animals, compared to untreated animals up to 12 months after injury.Conclusions.These results show that xenon treatment after TBI results in very long-term improvements in clinically relevant outcomes and survival. Our findings support the idea that xenon treatment shortly after TBI may have long-term benefits in the treatment of brain trauma patients.

Journal article

Yu X, Ba W, Zhao G, Ma Y, Harding E, Yin L, Wang D, Shi Y, Vyssotski A, Dong H, Franks N, Wisden Wet al., 2019, Dysfunction of ventral tegmental area GABA neurons causes mania-like behavior, bioRxiv.org

Abstract The ventral tegmental area (VTA), an important source of dopamine, regulates goal- and reward-directed and social behaviors, wakefulness and sleep. Hyperactivation of dopamine neurons generates behavioral pathologies. But any roles of non-dopamine VTA neurons in psychiatric illness have been little explored. Lesioning or chemogenetically inhibiting VTA GABAergic (VTA Vgat ) neurons generated persistent wakefulness with mania-like qualities: locomotor activity was increased; sensitivity to D-amphetamine was heightened; immobility times decreased on the tail suspension and forced swim tests; and sucrose preference increased. Furthermore, after sleep deprivation, mice with lesioned VTA Vgat neurons did not catch up on the lost NREM sleep, even though they were starting from an already highly sleep-deprived baseline, suggesting that the sleep homeostasis process was bypassed. The mania-like behaviors, including the sleep loss, were reversed by the mood-stabilizing drug valproate, and re-emerged when valproate treatment was stopped. Lithium salts, however, had no effect. The mania like-behaviors partially depended on dopamine, because giving D1/D2/D3 receptor antagonists partially restored the behaviors, but also on VTA Vgat projections to the lateral hypothalamus (LH). Optically or chemogenetically inhibiting VTA Vgat terminals in the LH elevated locomotion and decreased immobility time during the tail suspension and forced swimming tests. VTA Vgat neurons are centrally positioned to help set an animal’s (and human’s) level of mental and physical activity. Inputs that inhibit VTA Vgat neurons intensify wakefulness (increased activity, enhanced alertness and motivation), qualities useful for acute survival. Taken to the extreme, however, decreased or failed inhibition from VTA Vgat neurons produces mania-like qualities (hyperactivity, hedonia, decreased sleep).

Journal article

Harding E, Franks N, Wisden W, 2019, The temperature dependence of sleep, Frontiers in Neuroscience, Vol: 13, ISSN: 1662-4548

Mammals have evolved a range of behavioural and neurological mechanisms that coordinate cycles of thermoregulation and sleep. Whether diurnal or nocturnal, sleep onset and a reduction in core temperature occur together. Non-rapid eye movement (NREM) sleep episodes are also accompanied by core and brain cooling. Thermoregulatory behaviours, like nest building and curling up, accompany this circadian temperature decline in preparation for sleeping. This could be a matter of simply comfort as animals seek warmth to compensate for lower temperatures. However, in both humans and other mammals, direct skin warming can shorten sleep-latency and promote NREM sleep. We discuss the evidence that body cooling and sleep are more fundamentally connected and that thermoregulatory behaviours, prior to sleep, form warm microclimates that accelerate NREM directly through neuronal circuits. Paradoxically, this warmth might also induce vasodilation and body cooling. In this way, warmth seeking and nesting behaviour might enhance the circadian cycle by activating specific circuits that link NREM initiation to body cooling. We suggest that these circuits explain why NREM onset is most likely when core temperature is at its steepest rate of decline and why transitions to NREM are accompanied by a decrease in brain temperature. This connection may have implications for energy homeostasis and the function of sleep.

Journal article

Ma Y, Miracca G, Yu X, Harding EC, Miao A, Yustos R, Vyssotski AL, Franks NP, Wisden Wet al., 2019, Galanin neurons in the hypothalamus link sleep homeostasis, body temperature and actions of the α2 adrenergic agonist dexmedetomidine

<jats:title>Abstract</jats:title><jats:p>Sleep deprivation induces a characteristic rebound in NREM sleep accompanied by an immediate increase in the power of delta (0.5 - 4 Hz) oscillations, proportional to the prior time awake. To test the idea that galanin neurons in the mouse lateral preoptic hypothalamus (LPO) regulate this sleep homeostasis, they were selectively genetically ablated. The baseline sleep architecture of <jats:italic>LPO</jats:italic>-Δ<jats:italic>Gal</jats:italic> mice became heavily fragmented, their average core body temperature permanently increased (by about 2°C) and the diurnal variations in body temperature across the sleep-wake cycle also markedly increased. Additionally, <jats:italic>LPO</jats:italic>-Δ<jats:italic>Gal</jats:italic> mice showed a striking spike in body temperature and increase in wakefulness at a time (ZT24) when control mice were experiencing the opposite - a decrease in body temperature and becoming maximally sleepy (start of “lights on”). After sleep deprivation sleep homeostasis was largely abolished in <jats:italic>LPO</jats:italic>-Δ<jats:italic>Gal</jats:italic> mice: the characteristic increase in the delta power of NREM sleep following sleep deprivation was absent, suggesting that LPO galanin neurons track the time spent awake. Moreover, the amount of recovery sleep was substantially reduced over the following hours. We also found that the α2 adrenergic agonist dexmedetomidine, used for long-term sedation during intensive care, requires LPO galanin neurons to induce both the NREM-like state with increased delta power and the reduction in body temperature, characteristic features of this drug. This suggests that dexmedetomidine over-activates the natural sleep homeostasis pathway via galanin neurons. Collectively, the results emphasize that NREM sleep and the concurrent reduction in b

Journal article

Yu X, Ma Y, Harding E, Yustos R, Vyssotski A, Franks N, Wisden Wet al., 2019, Genetic lesioning of histamine neurons increases sleep-wake fragmentation and reveals their contribution to modafinil-induced wakefulness, Sleep, Vol: 42, Pages: 1-13, ISSN: 0161-8105

Acute chemogenetic inhibition of histamine (HA) neurons in adult mice induced nonrapid eye movement (NREM) sleep with an increased delta power. By contrast, selective genetic lesioning of HA neurons with caspase in adult mice exhibited a normal sleep–wake cycle overall, except at the diurnal start of the lights-off period, when they remained sleepier. The amount of time spent in NREM sleep and in the wake state in mice with lesioned HA neurons was unchanged over 24 hr, but the sleep–wake cycle was more fragmented. Both the delayed increase in wakefulness at the start of the night and the sleep–wake fragmentation are similar phenotypes to histidine decarboxylase knockout mice, which cannot synthesize HA. Chronic loss of HA neurons did not affect sleep homeostasis after sleep deprivation. However, the chronic loss of HA neurons or chemogenetic inhibition of HA neurons did notably reduce the ability of the wake-promoting compound modafinil to sustain wakefulness. Thus, part of modafinil’s wake-promoting actions arise through the HA system.

Journal article

Scammell TE, Jackson AC, Franks NP, Wisden W, Dauvilliers Yet al., 2019, Histamine: neural circuits and new medications, Sleep, Vol: 42, ISSN: 0161-8105

Histamine was first identified in the brain about 50 years ago, but only in the last few years have researchers gained an understanding of how it regulates sleep/wake behavior. We provide a translational overview of the histamine system, from basic research to new clinical trials demonstrating the usefulness of drugs that enhance histamine signaling. The tuberomammillary nucleus is the sole neuronal source of histamine in the brain, and like many of the arousal systems, histamine neurons diffusely innervate the cortex, thalamus, and other wake-promoting brain regions. Histamine has generally excitatory effects on target neurons, but paradoxically, histamine neurons may also release the inhibitory neurotransmitter GABA. New research demonstrates that activity in histamine neurons is essential for normal wakefulness, especially at specific circadian phases, and reducing activity in these neurons can produce sedation. The number of histamine neurons is increased in narcolepsy, but whether this affects brain levels of histamine is controversial. Of clinical importance, new compounds are becoming available that enhance histamine signaling, and clinical trials show that these medications reduce sleepiness and cataplexy in narcolepsy.

Journal article

Yu X, Li W, Ma Y, Tossell K, Harris J, Harding E, Ba W, Miracca G, Wang D, Li L, Guo J, Chen M, Li Y, Yustos R, Vyssotski A, Burdakov D, Yang Q, Dong H, Franks N, Wisden Wet al., 2019, GABA and glutamate neurons in the VTA regulate sleep and wakefulness, Nature Neuroscience, Vol: 22, Pages: 106-119, ISSN: 1097-6256

We screened for novel circuits in the mouse brain that promote wakefulness. Chemogenetic activation experiments and electroencephalogram recordings pointed to glutamatergic/nitrergic (NOS1) and GABAergic neurons in the ventral tegmental area (VTA). Activating glutamatergic/NOS1 neurons, which were wake- and rapid eye movement (REM) sleep-active, produced wakefulness through projections to the nucleus accumbens and the lateral hypothalamus. Lesioning the glutamate cells impaired the consolidation of wakefulness. By contrast, activation of GABAergic VTA neurons elicited long-lasting non-rapid-eye-movement-like sleep resembling sedation. Lesioning these neurons produced an increase in wakefulness that persisted for at least 4 months. Surprisingly, these VTA GABAergic neurons were wake- and REM sleep-active. We suggest that GABAergic VTA neurons may limit wakefulness by inhibiting the arousal-promoting VTA glutamatergic and/or dopaminergic neurons and through projections to the lateral hypothalamus. Thus, in addition to its contribution to goal- and reward-directed behaviors, the VTA has a role in regulating sleep and wakefulness.

Journal article

Paul EJ, Kalk E, Tossell K, Irvine E, Franks NP, Wisden W, Withers DJ, Leiper JM, Ungless MAet al., 2018, nNOS-expressing neurons in the ventral tegmental area and substantia nigra pars compacta, eNeuro, Vol: 5, ISSN: 2373-2822

GABA neurons in the VTA and SNc play key roles in reward and aversion through their local inhibitory control of dopamine neuron activity and through long-range projections to several target regions including the nucleus accumbens. It is not clear whether some of these GABA neurons are dedicated local interneurons or if they all collateralize and send projections externally as well as making local synaptic connections. Testing between these possibilities has been challenging in the absence of interneuron-specific molecular markers. We hypothesized that one potential candidate might be neuronal nitric oxide synthase (nNOS), a common interneuronal marker in other brain regions. To test this, we used a combination of immunolabelling (including antibodies for nNOS that we validated in tissue from nNOS-deficient mice) and cell type-specific virus-based anterograde tracing in mice. We found that nNOS-expressing neurons, in the parabrachial pigmented (PBP) part of the VTA and the SNc were GABAergic and did not make detectable projections, suggesting they may be interneurons. In contrast, nNOS-expressing neurons in the rostral linear nucleus (RLi) were mostly glutamatergic and projected to a number of regions, including the lateral hypothalamus (LH), the ventral pallidum (VP), and the median raphe (MnR) nucleus. Taken together, these findings indicate that nNOS is expressed by neurochemically- and anatomically-distinct neuronal sub-groups in a sub-region-specific manner in the VTA and SNc.

Journal article

Harding E, Yu X, Miao A, Andrews N, Ma Y, Ye Z, Lignos L, Miracca G, Ba W, Yustos R, Vyssotski A, Wisden W, Franks Net al., 2018, A neuronal hub binding sleep initiation and body cooling in response to a warm external stimulus, Current Biology, Vol: 28, Pages: 2263-2273.e4, ISSN: 1879-0445

Mammals, including humans, prepare for sleep by nesting and curling up, creating microclimates of skin warmth. To address if external warmth induces sleep through defined circuitry, we used c-Fos-dependent activity-tagging, which captures populations of activated cells, and allows them to be reactivated to test their physiological role. External warming tagged two principal groups of neurons in the MnPO/MPO hypothalamic area. GABA neurons located mainly in MPO produced NREM sleep but no body temperature decrease. Nitrergic/glutamatergic neurons in MnPO/MPO induced both body cooling and NREM sleep. This circuitry explains how skin warming induces sleep, and why the maximal rate of core body cooling positively correlates with sleep onset. Thus, the pathways that promote NREM-sleep, reduced energy expenditure, and body cooling are inextricably linked, commanded by the same neurons. This implies that one function of NREM sleep is to lower brain temperature and/or conserve energy.

Journal article

Campos Pires R, Koziakova M, Yonis A, Pau A, Macdonald W, Harris K, Edge C, Franks N, Mahoney P, Dickinson Ret al., 2018, Xenon protects against blast-induced traumatic brain injury in an in vitro model, Journal of Neurotrauma, Vol: 35, Pages: 1037-1044, ISSN: 0897-7151

The aim of this study was to evaluate the neuroprotective efficacy of the inert gas xenon as a treatment for patients with blast-induced traumatic brain injury in an in vitro laboratory model. We developed a novel blast traumatic brain injury model using C57BL/6N mouse organotypic hippocampal brain-slice cultures exposed to a single shockwave, with the resulting injury quantified using propidium iodide fluorescence. A shock tube blast generator was used to simulate open field explosive blast shockwaves, modeled by the Friedlander waveform. Exposure to blast shockwave resulted in significant (p < 0.01) injury that increased with peak-overpressure and impulse of the shockwave, and which exhibited a secondary injury development up to 72 h after trauma. Blast-induced propidium iodide fluorescence overlapped with cleaved caspase-3 immunofluorescence, indicating that shock-wave–induced cell death involves apoptosis. Xenon (50% atm) applied 1 h after blast exposure reduced injury 24 h (p < 0.01), 48 h (p < 0.05), and 72 h (p < 0.001) later, compared with untreated control injury. Xenon-treated injured slices were not significantly different from uninjured sham slices at 24 h and 72 h. We demonstrate for the first time that xenon treatment after blast traumatic brain injury reduces initial injury and prevents subsequent injury development in vitro. Our findings support the idea that xenon may be a potential first-line treatment for those with blast-induced traumatic brain injury.

Journal article

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