Relative importance of intensity and spectrum of artificial light at night in disrupting behavior of a nocturnal rodent.

The influence of light spectral properties on circadian rhythms is of substantial interest to laboratory-based investigation of the circadian system and to field-based understanding of the effects of artificial light at night. The trade-offs between intensity and spectrum regarding masking behaviors are largely unknown, even for well-studied organisms. We used a custom LED illumination system to document the response of wild-type house mice (Mus musculus) to 1-h nocturnal exposure of all combinations of four intensity levels (0.01, 0.5, 5 and 50 lx) and three correlated color temperatures (CCT; 1750, 1950 and 3000 K). Higher intensities of light (50 lx) suppressed cage activity substantially, and consistently more for the higher CCT light (91% for 3000 K, 53% for 1750 K). At the lowest intensity (0.01 lx), mean activity was increased, with the greatest increases for the lowest CCT (12.3% increase at 1750 K, 3% increase at 3000 K). Multiple linear regression confirmed the influence of both CCT and intensity on changes in activity, with the scaled effect size of intensity 3.6 times greater than that of CCT. Activity suppression was significantly lower for male than for female mice. Assessment of light-evoked cFos expression in the suprachiasmatic nucleus at 50 lx showed no significant difference between high and low CCT exposure. The significant differences by spectral composition illustrate a need to account for light spectrum in circadian studies of behavior, and confirm that spectral controls can mitigate some, but certainly not all, of the effects of light pollution on species in the wild.

Transcranial focused ultrasound modulates cortical and thalamic motor activity in awake sheep.

Transcranial application of pulsed low-intensity focused ultrasound (FUS) modulates the excitability of region-specific brain areas, and anesthetic confounders on brain activity warrant the evaluation of the technique in awake animals. We examined the neuromodulatory effects of FUS in unanesthetized sheep by developing a custom-fit headgear capable of reproducibly placing an acoustic focus on the unilateral motor cortex (M1) and corresponding thalamic area. The efferent responses to sonication, based on the acoustic parameters previously identified in anesthetized sheep, were measured using electromyography (EMG) from both hind limbs across three experimental conditions: on-target sonication, off-target sonication, and without sonication. Excitatory sonication yielded greater amplitude of EMG signals obtained from the hind limb contralateral to sonication than that from the ipsilateral limb. Spurious appearance of motion-related EMG signals limited the amount of analyzed data (~ 10% selection of acquired data) during excitatory sonication, and the averaged EMG response rates elicited by the M1 and thalamic stimulations were 7.5 ± 1.4% and 6.7 ± 1.5%, respectively. Suppressive sonication, while sheep walked on the treadmill, temporarily reduced the EMG amplitude from the limb contralateral to sonication. No significant change was found in the EMG amplitudes during the off-target sonication. Behavioral observation throughout the study and histological analysis showed no sign of brain tissue damage caused by the acoustic stimulation. Marginal response rates observed during excitatory sonication call for technical refinement to reduce motion artifacts during EMG acquisitions as well as acoustic aberration correction schemes to improve spatial accuracy of sonication. Yet, our results indicate that low-intensity FUS modulated the excitability of regional brain tissues reversibly and safely in awake sheep, supporting its potential in theragnostic applications.

In vivo local transcranial static magnetic field stimulation alters motor behavior in normal rats.

Transcranial static magnetic field stimulation (tSMS) has inhibitory neuromodulatory effects on the human brain. Most of the studies on static magnetic fields have been performed in vitro. To further understand the biological mechanisms of tSMS, we investigated the effects of in vivo tSMS on motor behavior in normal awake rats. The skull of a male Wistar rat was exposed and a polyethylene tube was attached to the skull using dental cement at the center of the motor cortex (n = 7) or the other cortex (n = 6). By attaching a cylindrical NdFeB neodymium magnet into the tube, in vivo tSMS (REAL) was performed. For SHAM, we applied a similar size non-magnetic stainless-steel cylinder. All rats received twice each SHAM and REAL stimulation every two days using a crossover design, and motor function was measured during the stimulation. Activity level and asymmetry of forelimb use were not affected, but less accurate movements in the horizontal ladder test were found in REAL stimulation of the motor cortex. This study shows that in vivo tSMS has inhibitory neuromodulatory effects on motor behavior depending on the stimulated region on the rat cortex.

Effects of photobiomodulation combined with MSCs transplantation on the repair of spinal cord injury in rat.

Stem cell transplantation has shown promising regenerative effects against neural injury, and photobiomodulation (PBM) can aid tissue recovery. This study aims to evaluate the therapeutic effect of human umbilical cord mesenchymal stem cells (hUCMSCs) and laser alone or combined on spinal cord injury (SCI). The animals were divided into SCI, hUCMSCs, laser treatment (LASER) and combination treatment (hUCMSCs + LASER) groups. Cell-enriched grafts of hUCMSCs (1 × 106 cells/ml) were injected at the site of antecedent trauma in SCI model rats. A 2 cm2 damaged area was irradiated with 630 nm laser at 100 mW/cm2 power for 20 min. Locomotion was evaluated using Basso-Beattie-Bresnahan (BBB) scores, and neurofilament repair were monitored by histological staining and diffusion tensor imaging (DTI). First, after SCI, the motor function of each group was restored with different degrees, the combination treatment significantly increased the BBB scores compared to either monotherapy. In addition, Nissl bodies were more numerous, and the nerve fibers were longer and thicker in the combination treatment group. Consistent with this, the in situ expression of NF-200 and glial fibrillary acidic protein in the damaged area was the highest in the combination treatment group. Finally, DTI showed that the combination therapy optimally improved neurofilament structure and arrangement. These results may show that the combination of PBM and hUCMSCs transplantation is a feasible strategy for reducing secondary damage and promoting functional recovery following SCI.

Dose-dependent long-term effects of a single radiation event on behaviour and glial cells.

PURPOSE: The increasing use of low-dose ionizing radiation in medicine requires a systematic study of its long-term effects on the brain, behaviour and its possible association with neurodegenerative disease vulnerability. Therefore, we analysed the long-term effects of a single low-dose irradiation exposure at 10 weeks of age compared to medium and higher doses on locomotor, emotion-related and sensorimotor behaviour in mice as well as on hippocampal glial cell populations. MATERIALS AND METHODS: We determined the influence of radiation dose (0, 0.063, 0.125 or 0.5 Gy), time post-irradiation (4, 12 and 18 months p.i.), sex and genotype (wild type versus mice with Ercc2 DNA repair gene point mutation) on behaviour. RESULTS: The high dose (0.5 Gy) had early-onset adverse effects at 4 months p.i. on sensorimotor recruitment and late-onset negative locomotor effects at 12 and 18 months p.i. Notably, the low dose (0.063 Gy) produced no early effects but subtle late-onset (18 months) protective effects on sensorimotor recruitment and exploratory behaviour. Quantification and morphological characterization of the microglial and the astrocytic cells of the dentate gyrus 24 months p.i. indicated heightened immune activity after high dose irradiation (0.125 and 0.5 Gy) while conversely, low dose (0.063 Gy) induced more neuroprotective features. CONCLUSION: This is one of the first studies demonstrating such long-term and late-onset effects on brain and behaviour after a single radiation event in adulthood.

Whole brain proton irradiation in adult Sprague Dawley rats produces dose dependent and non-dependent cognitive, behavioral, and dopaminergic effects.

Proton radiotherapy causes less off-target effects than X-rays but is not without effect. To reduce adverse effects of proton radiotherapy, a model of cognitive deficits from conventional proton exposure is needed. We developed a model emphasizing multiple cognitive outcomes. Adult male rats (10/group) received a single dose of 0, 11, 14, 17, or 20 Gy irradiation (the 20 Gy group was not used because 50% died). Rats were tested once/week for 5 weeks post-irradiation for activity, coordination, and startle. Cognitive assessment began 6-weeks post-irradiation with novel object recognition (NOR), egocentric learning, allocentric learning, reference memory, and proximal cue learning. Proton exposure had the largest effect on activity and prepulse inhibition of startle 1-week post-irradiation that dissipated each week. 6-weeks post-irradiation, there were no effects on NOR, however proton exposure impaired egocentric (Cincinnati water maze) and allocentric learning and caused reference memory deficits (Morris water maze), but did not affect proximal cue learning or swimming performance. Proton groups also had reduced striatal levels of the dopamine transporter, tyrosine hydroxylase, and the dopamine receptor D1, effects consistent with egocentric learning deficits. This new model will facilitate investigations of different proton dose rates and drugs to ameliorate the cognitive sequelae of proton radiotherapy.

Short and long-term evaluation of the impact of proton minibeam radiation therapy on motor, emotional and cognitive functions.

Radiotherapy (RT) is one of the most frequently used methods for cancer treatment. Despite remarkable advancements in RT techniquesthe treatment of radioresistant tumours (i.e. high-grade gliomas) is not yet satisfactory. Finding novel approaches less damaging for normal tissues is of utmost importance. This would make it possible to increase the dose applied to tumours, resulting in an improvement in the cure rate. Along this line, proton minibeam radiation therapy (pMBRT) is a novel strategy that allows the spatial modulation of the dose, leading to minimal damage to brain structures compared to a high dose (25 Gy in one fraction) of standard proton therapy (PT). The aim of the present study was to evaluate whether pMBRT also preserves important cerebral functions. Comprehensive longitudinal behavioural studies were performed in irradiated (peak dose of 57 Gy in one fraction) and control rats to evaluate the impact of pMBRT on motor function (motor coordination, muscular tonus, and locomotor activity), emotional function (anxiety, fear, motivation, and impulsivity), and cognitive function (learning, memory, temporal processing, and decision making). The evaluations, which were conducted over a period of 10 months, showed no significant motor or emotional dysfunction in pMBRT-irradiated rats compared with control animals. Concerning cognitive functions, similar performance was observed between the groups, although some slight learning delays might be present in some of the tests in the long term after irradiation. This study shows the minimal impact of pMBRT on the normal brain at the functional level.

Distinct Components of Photoperiodic Light Are Differentially Encoded by the Mammalian Circadian Clock.

Seasonal light cycles influence multiple physiological functions and are mediated through photoperiodic encoding by the circadian system. Despite our knowledge of the strong connection between seasonal light input and downstream circadian changes, less is known about the specific components of seasonal light cycles that are encoded and induce persistent changes in the circadian system. Using combinations of 3 T cycles (23, 24, 26 h) and 2 photoperiods per T cycle (long and short, with duty cycles scaled to each T cycle), we investigate the after-effects of entrainment to these 6 light cycles. We measure locomotor behavior duration (α), period (τ), and entrained phase angle (ψ) in vivo and SCN phase distribution (σφ), τ, and ψ ex vivo to refine our understanding of critical light components for influencing particular circadian properties. We find that both photoperiod and T-cycle length drive determination of in vivo ψ but differentially influence after-effects in α and τ, with photoperiod driving changes in α and photoperiod length and T-cycle length combining to influence τ. Using skeleton photoperiods, we demonstrate that in vivo ψ is determined by both parametric and nonparametric components, while changes in α are driven nonparametrically. Within the ex vivo SCN, we find that ψ and σφ of the PER2∷LUCIFERASE rhythm follow closely with their likely behavioral counterparts (ψ and α of the locomotor activity rhythm) while also confirming previous reports of τ after-effects of gene expression rhythms showing negative correlations with behavioral τ after-effects in response to T cycles. We demonstrate that within-SCN σφ changes, thought to underlie α changes in vivo, are induced primarily nonparametrically. Taken together, our results demonstrate that distinct components of seasonal light input differentially influence ψ, α, and τ and suggest the possibility of separate mechanisms driving the persistent changes in circadian behaviors mediated by seasonal light.

Low dose γ radiation enhances antidepressant effect of resveratrol: Behavioral and neurochemical studies.

The low dose of radiation (LDR) has received growing attention for its beneficial neuroprotective effect. This study was designed to investigate the enhancing effect of LDR on the antidepressant potential of resveratrol against diazepam-induced depression in mice. Female mice divided into five groups; control, diazepam (2 mg/kg), LDR (0.5Gy) + diazepam, resveratrol (20 mg/kg) + diazepam, LDR + resveratrol+diazepam. Mice received diazepam showed depressive symptoms as evidenced by decreased locomotor activity in the open field and increased immobility time in the forced swimming and tail suspension tests integrated with a marked decline in biogenic amines (serotonin, norepinephrine, and dopamine) in brain tissues. These effects were ameliorated by LDR or resveratrol administration demonstrating an antidepressant activity. Interestingly, LDR triggered the antidepressant effect of resveratrol as it restored the changes in behavioral tests, neurotransmitters, and neuro-histoarchitecture. In conclusion, these findings suggested that LDR could be considered as a novel adjuvant that augmented the resveratrol antidepressant effect and might serve as a potential therapeutic approach for depression.

Sensory and motor responses after photobiomodulation associated with physiotherapy in patients with incomplete spinal cord injury: clinical, randomized trial.

Complete or incomplete spinal cord injury (SCI) results in permanent neurological deficits due to the interruption of nerve impulses, causing the loss of motor and sensory function, which leads to a reduction in quality of life. The focus of rehabilitation for such individuals is to improve quality of life and promote functional recovery. Photobiomodulation (PBM) has proved to be promising complementary treatment in cases of SCI. The aim of the present study was to investigate the effects of PBM combined with physiotherapy on sensory-motor responses below the level of the injury and quality of life in individuals with SCI. Thirty participants were randomized for allocation to the PBM group (active PBM + physiotherapy) or sham group (sham PBM + physiotherapy). Physiotherapy was administered three times a week. Sensitivity and motor skills were evaluated using the ASIA impairment scale. Quality of life was assessed using the WHOQOL-BREF questionnaire. The data were analyzed with the level of significance set to 5%. Improvements in sensitivity and an increase in the perception of muscle contraction were found in the active PBM group 30 days after treatment compared with the sham group. The results of the WHOQOL-BREF questionnaire revealed a significant difference in general quality of life favoring the active PBM group over the sham group after treatment. Physiotherapy combined with PBM leads to better sensory-motor recovery in patients with SCI as well as a better perception of health and quality of life. Trial registration identifier: NCT03031223.

Application of Focal Photoinduced Thrombosis for Modeling Spinal Cord Ischemia.

Typical ischemic damage to neurons were detected in the focus of experimental photothrombosis and in the transition zone. They were associated with symptoms of impaired motor functions and dysfunction of pelvic organs. The applied method of focal photothrombosis can be used for simulation of spinal cord ischemia for the development of methods for pharmacological correction and restoration of impaired sensorimotor functions.

Existence of a Dose-Length Effect in Spinal Nerves Receiving Single-Session Stereotactic Ablative Radiation Therapy.

PURPOSE: The spinal nerves have been observed to have a similar single-session dose tolerance to that of the spinal cord in pigs. Small-animal studies have shown that spinal cord dose tolerance depends on the length irradiated. This work aims to determine whether a dose-length effect exists for spinal nerves. METHODS AND MATERIALS: Twenty-seven Yucatan minipigs underwent computed tomography and magnetic resonance imaging for treatment planning, followed by single-session stereotactic ablative radiation therapy. A 0.5 cm length of the left-sided C6, C7, and C8 spinal nerves was targeted. The pigs were distributed into 6 groups with prescription doses of 16 Gy (n = 5), 18 Gy (n = 5), 20 Gy (n = 5), 22 Gy (n = 5), 24 Gy (n = 5), or 36 Gy (n = 2) and corresponding maximum doses of 16.7, 19.1, 21.3, 23.1, 25.5, and 38.6 Gy, respectively. Neurologic status was assessed with a serial electrodiagnostic examination and daily observation of gait for approximately 52 weeks. A histopathologic examination of paraffin-embedded sections with Luxol fast blue/periodic acid-Schiff's staining was also performed. RESULTS: Marked gait change was observed in 8 of 27 irradiated pigs. The latency for responding pigs was 11 to 16 weeks after irradiation. The affected animals presented with a limp in the left front limb, and 62.5% of these pigs had electrodiagnostic evidence of denervation in the C6 and C7 innervated muscles. A probit analysis showed the dose associated with a 50% incidence of gait change is 23.9 Gy (95% confidence interval, 22.5-25.8 Gy), which is 20% higher than that reported in a companion study where a 1.5 cm length was irradiated. All symptomatic pigs had demyelination and fibrosis in the irradiated nerves, but the contralateral nerves and spinal cord were normal. CONCLUSIONS: A dose-length effect was observed for single-session irradiation of the spinal nerves in a Yucatan minipig model.

Photobiomodulation Therapy Inhibit the Activation and Secretory of Astrocytes by Altering Macrophage Polarization.

Spinal cord injury (SCI) stimulates reactive astrogliosis and the infiltration of macrophages, which interact with each other at the injured area. We previously found Photobiomodulation (PBM) significantly decreases the number of M1 macrophages at the injured area of SCI. But the exact nature of the astrocyte response following PBM and relationship with the macrophage have not been explored in detail. In this study, a BALB/c mice model with standardized bilateral spinal cord compression and a macrophage-astrocyte co-culture model were applied to study effects of PBM on astrocytes. Results showed that PBM inhibit the expression of the astrocyte markers glial fibrillary acidic protein (GFAP) and the secretion of chondroitin sulfate proteoglycans (CSPG) in the para-epicenter area, decrease the number of M1 macrophage in vivo. The in vitro experiments indicated M1 macrophages promote the cell viability of astrocytes and the expression of CSPG. However, PBM significantly inhibited the expression of GFAP, decreased activation of astrocyte, and downregulated the expression of CSPG by regulating M1 macrophages. These results demonstrate that PBM may regulate the interaction between macrophages and astrocytes after spinal cord injury, which inhibited the formation of glial scar.

Effects of chronic exposure to a mixed field of neutrons and photons on behavioral and cognitive performance in mice.

To simulate the space radiation environment astronauts are exposed to, most studies involve acute exposures but during a space mission there will be chronic (long-lasting) exposures. To address this knowledge gap, a neutron irradiator using a 252Cf (252Californium) source was used to generate a mixed field of neutrons and photons to simulate chronic, low dose rate exposures to high LET radiation. In the present study, we assessed the effects chronic neutron exposure starting at 60 days of age on behavioral and cognitive performance of BALB/c female and C3H male mice at 600 and 700 days of age as part of an opportunistic study that took advantage of the availability of neutron and sham-irradiated mice from a radiation carcinogenesis experiment. There were profound dose- and time point-dependent effects of chronic neutron exposure. At the 600-day time point, irradiated BALB/c female mice showed improved nest building at all three doses. At the 700-day, but not 600-day, time point slightly but significantly increased body weights were seen in C3H male mice exposed to 0.118 Gy. At the 600-day time point BALB/c female mice irradiated with 0.2 Gy did, like sham-irradiated, not show preferential exploration of the novel object that was seen in mice irradiated with 0.118 or 0.4 Gy. In C3H male mice exposed to 0.4 Gy and at the 600-day time point, increased measures of anxiety were observed on days 1 and 2 in the open field. Thus, different outcome measures show distinct dose-response relationships, with some anticipated to worsen performance during space missions, like increased measures of anxiety, while other anticipated to enhance performance, such as increased nest building and object recognition.

Wearable Electronics Assess the Effectiveness of Transcranial Direct Current Stimulation on Balance and Gait in Parkinson's Disease Patients.

Currently, clinical evaluation represents the primary outcome measure in Parkinson's disease (PD). However, clinical evaluation may underscore some subtle motor impairments, hidden from the visual inspection of examiners. Technology-based objective measures are more frequently utilized to assess motor performance and objectively measure motor dysfunction. Gait and balance impairments, frequent complications in later disease stages, are poorly responsive to classic dopamine-replacement therapy. Although recent findings suggest that transcranial direct current stimulation (tDCS) can have a role in improving motor skills, there is scarce evidence for this, especially considering the difficulty to objectively assess motor function. Therefore, we used wearable electronics to measure motor abilities, and further evaluated the gait and balance features of 10 PD patients, before and (three days and one month) after the tDCS. To assess patients' abilities, we adopted six motor tasks, obtaining 72 meaningful motor features. According to the obtained results, wearable electronics demonstrated to be a valuable tool to measure the treatment response. Meanwhile the improvements from tDCS on gait and balance abilities of PD patients demonstrated to be generally partial and selective.

Photoresponsivity and motility in the planarian Schmidtea mediterranea vary diurnally.

The planarian flatworm has become one of the leading animal model systems for studying stem cell behavior and tissue regeneration. Recent studies have shown that components of the circadian clockwork have important roles in tissue homeostasis and repair. However, it remains unknown whether planarians exhibit circadian or diurnal rhythms in physiology or behavior. Here, we developed a behavioral assay to evaluate diurnal activity in planarians based upon their well-established propensity to swim away from light (negative phototaxis). We show evidence that the planarian Schmidtea mediterranea has diurnal variability in negative phototaxis as a function of daily variation in motility. We also demonstrate that variation in planarian motility over 48 h occurs with 24-h periodicity. Our data suggest that S. mediterranea may be a useful model for studying the interplay between the circadian system and tissue regeneration.

Space-like 56Fe irradiation manifests mild, early sex-specific behavioral and neuropathological changes in wildtype and Alzheimer's-like transgenic mice.

Space travel will expose people to high-energy, heavy particle radiation, and the cognitive deficits induced by this exposure are not well understood. To investigate the short-term effects of space radiation, we irradiated 4-month-old Alzheimer's disease (AD)-like transgenic (Tg) mice and wildtype (WT) littermates with a single, whole-body dose of 10 or 50 cGy 56Fe ions (1 GeV/u) at Brookhaven National Laboratory. At ~1.5 months post irradiation, behavioural testing showed sex-, genotype-, and dose-dependent changes in locomotor activity, contextual fear conditioning, grip strength, and motor learning, mainly in Tg but not WT mice. There was little change in general health, depression, or anxiety. Two months post irradiation, microPET imaging of the stable binding of a translocator protein ligand suggested no radiation-specific change in neuroinflammation, although initial uptake was reduced in female mice independently of cerebral blood flow. Biochemical and immunohistochemical analyses revealed that radiation reduced cerebral amyloid-ß levels and microglia activation in female Tg mice, modestly increased microhemorrhages in 50 cGy irradiated male WT mice, and did not affect synaptic marker levels compared to sham controls. Taken together, we show specific short-term changes in neuropathology and behaviour induced by 56Fe irradiation, possibly having implications for long-term space travel.

White LED Light Exposure Inhibits the Development and Xanthophore Pigmentation of Zebrafish Embryo.

Circadian rhythm in all living organisms is disturbed continuously by artificial light sources and artificial lighting has become a hazard for public health. Circadian rhythm of melatonin maintains high levels of melatonin during the night and low levels during the day. N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT) is one of the four enzymes required for melatonin synthesis and mtnr1ba is a melatonin receptor-encoding mRNA that is expressed widely in the embryonic brain. Pax7 has important roles during neural crest development and especially xanthophore pigmentation. Due to its diurnal nature, zebrafish provide a special opportunity for research on circadian rhythms that are regulated by melatonin. Here in this study, we showed that when compared with the white light control group, white LED light exposure resulted in loss of yellow pigmentation, decreased body length and locomotor activity, oxidant-antioxidant imbalance and decreased expressions of aanat2, mtnr1ba, and pax7 in zebrafish embryos. Histological analysis of this group revealed disorganization of the spaces among photoreceptor cells, decreased total retinal thickness and photoreceptor cell layer thickness compared with the control group. Artificial lighting pollution has the potential to become an important risk factor for different diseases including cancer especially for industrialized countries, therefore, more studies should be performed and necessary regulations should be made regarding this risk factor.

Exceptional Entrainment of Circadian Activity Rhythms With Manipulations of Rhythm Waveform in Male Syrian Hamsters.

The activity/rest rhythm of mammals reflects the output of an endogenous circadian oscillator entrained to the solar day by light. Despite detailed understanding of the neural and molecular bases of mammalian rhythms, we still lack practical tools for achieving rapid and flexible adjustment of clocks to accommodate shift-work, trans-meridian jet travel, or space exploration. Efforts to adapt clocks have focused on resetting the phase of an otherwise unaltered circadian clock. Departing from this tradition, recent work has demonstrated that bifurcation of circadian waveform in mice facilitates entrainment to extremely long and short zeitgeber periods. Here we evaluate the formal nature of entrainment to extreme non-24 h days in male Syrian hamsters. Wheel-running rhythms were first bifurcated into a 24 h rest/activity/rest/activity cycle according to established methods. Thereafter the 24 h lighting cycle was incrementally adjusted over several weeks to 30 h or to 18 h. Almost without exception, wheel-running rhythms of hamsters in gradually lengthened or shortened zeitgebers remained synchronized with the lighting cycle, with greater temporal precision observed in the former condition. Data from animals transferred abruptly from 24 h days to long or short cycles suggested that gradual adaptation facilitates but is not necessary for successful behavioral entrainment. The unprecedented behavioral adaptation following waveform bifurcation reveals a latent plasticity in mammalian circadian systems that can be realized in the absence of pharmacological or genetic manipulations. Oscillator interactions underlying circadian waveform manipulation, thus, represent a tractable target for understanding and enhancing circadian rhythm resetting.

Thermal constraints on in vivo optogenetic manipulations.

A key assumption of optogenetics is that light only affects opsin-expressing neurons. However, illumination invariably heats tissue, and many physiological processes are temperature-sensitive. Commonly used illumination protocols increased the temperature by 0.2-2 °C and suppressed spiking in multiple brain regions. In the striatum, light delivery activated an inwardly rectifying potassium conductance and biased rotational behavior. Thus, careful consideration of light-delivery parameters is required, as even modest intracranial heating can confound interpretation of optogenetic experiments.