Controlled cooling-rate experiments on olivine-hosted melt inclusions: chemical diffusion and quantification of eruptive cooling‐rates on Hawaii and Mars

Controlled cooling‐rate experiments were conducted on olivine‐hosted melt inclusions to characterize the development of compositional zoning observed in natural inclusions. All of the experimentally cooled inclusions are zoned due to olivine crystallization on the inclusion wall and diffusive exchange between the boundary layer adjacent to the growing olivine and the inclusion centers. Experimentally cooled inclusions are characterized by lower MgO and FeO and higher SiO₂, Al₂O₃, and Na₂O (and other incompatible oxides) near the inclusion wall relative to the inclusion center. The compositions at the centers of inclusions are susceptible to modification by diffusion, particularly for small inclusions and those subjected to low cooling rates. Uphill diffusion is evident in every oxide and is recognized by local extrema along a diffusion profile. CaO exhibits the most extreme manifestation of uphill diffusion, and a model attributes the diffusion behavior in CaO to solution nonideality in the boundary layer liquid. MgO profiles from experimentally cooled inclusions were fit with a diffusion model by varying the cooling rate. The cooling rates that resulted in the best fit models were always within a factor of 2 and typically within ±10% of the experimental cooling rates, which ranged from 70 to 50,000 °C/hr. The model was applied to MgO profiles across natural glassy olivine‐hosted melt inclusions from Hawaii and the shergottite Yamato 980459. Cooling rates from zoned melt inclusions in Yamato 980459 range from 85 to 1,047 °C/hr (mean = 383±43 °C/hr, 1σ, n=8) and support the hypothesis that the sample erupted at or near the Martian surface

Experimental Studies on the Thermodynamics and Kinetics of Coexisting Olivine, Silicate Melt, and Vapor

This thesis focuses on experiments run in 1 atm gas-mixing furnaces exploring the thermodynamics and kinetics of coexisting olivine, silicate melt, and vapor. Chapter 1 provides a high-level introduction and summary of the results for each of the following chapters. Chapter 2 and Chapter 3 both involve experiments run on natural olivines containing melt inclusions. Chapter 2 describes a set of homogenization and cooling rate experiments designed to characterize chemical zonation that develops across melt inclusions during cooling. A diffusion model for MgO in the inclusion liquid was calibrated based on these experiments and then used to calculate the syneruptive cooling rates of lavas on Earth and on Mars based on comparison of the model to experimental and natural diffusion profiles in melt inclusions. Chapter 3 presents the first co-determined measurements of S and Fe oxidation state in experimental silicate melts that were equilibrated with the oxygen fugacity of a gas-mixing furnace. The use of melt inclusions as sulfur-bearing experimental vessels is explored, as are implications for interpreting room temperature measurements of the oxidation state of multivalent elements. A set of natural melt inclusions are used as a case study to demonstrate that the temperature-dependence of sulfur-iron electron exchange in basaltic liquids is either weak or leads to the conversion of ferric iron to ferrous iron during cooling. Chapter 4 presents a new parameterization of the composition-dependence of the olivine-liquid Fe-Mg exchange coefficient, Kᴅol/liq,Fe2+-Mg, based on experiments at low oxygen fugacity where corrections for Fe3+ are minor. A quantitative thermodynamic model is fit to the data, showing that the Kᴅ is a function of the Si, Al, Ti, Na+K contents of the liquid as well as olivine composition. Models of Kᴅol/liq,Fe2+-Mg that do not incorporate liquid compositional variables cannot account for the variability of Kᴅ (~0.22-0.38) observed at low oxygen fugacity in a compilation of high-quality literature experiments. Lastly, in Appendix 1, the published version of Richter, Saper, et al. (2021), GCA 295 is included. For this chapter, I contributed MELTS calculations (Ghiorso and Sack 1995; Smith and Asimow 2005) which were used to model crystallization processes and to set boundary conditions for models elemental and isotopic diffusion of Mg and Li in lunar olivines and martian olivines and augites. The combined elemental and isotopic diffusion profiles were used to discriminate between zoning formed due to crystallization from that due to diffusion.</p

Thalamic reticular nucleus induces fast and local modulation of arousal state

During low arousal states such as drowsiness and sleep, cortical neurons exhibit rhythmic slow wave activity associated with periods of neuronal silence. Slow waves are locally regulated, and local slow wave dynamics are important for memory, cognition, and behaviour. While several brainstem structures for controlling global sleep states have now been well characterized, a mechanism underlying fast and local modulation of cortical slow waves has not been identified. Here, using optogenetics and whole cortex electrophysiology, we show that local tonic activation of thalamic reticular nucleus (TRN) rapidly induces slow wave activity in a spatially restricted region of cortex. These slow waves resemble those seen in sleep, as cortical units undergo periods of silence phase-locked to the slow wave. Furthermore, animals exhibit behavioural changes consistent with a decrease in arousal state during TRN stimulation. We conclude that TRN can induce rapid modulation of local cortical state.National Institutes of Health (U.S.) (TR01 GM104948)Canadian Institutes of Health Research (Fellowship)Harvard University. Society of Fellows (Fellowship

Identification of octopaminergic neurons that modulate sleep suppression by male sex drive

Molecular and circuit mechanisms for balancing competing drives are not well understood. While circadian and homeostatic mechanisms generally ensure sufficient sleep at night, other pressing needs can overcome sleep drive. Here, we demonstrate that the balance between sleep and sex drives determines whether male flies sleep or court, and identify a subset of octopaminergic neurons (MS1) that regulate sleep specifically in males. When MS1 neurons are activated, isolated males sleep less, and when MS1 neurons are silenced, the normal male sleep suppression in female presence is attenuated and mating behavior is impaired. MS1 neurons do not express the sexually dimorphic FRUITLESS (FRU) transcription factor, but form male-specific contacts with FRU-expressing neurons; calcium imaging experiments reveal bidirectional functional connectivity between MS1 and FRU neurons. We propose octopaminergic MS1 neurons interact with the FRU network to mediate sleep suppression by male sex drive.National Institute of Neurological Disorders and Stroke R21NS094782 Kyunghee KohNational Institute of Neurological Disorders and Stroke R01NS086887 Kyunghee KohNational Heart, Lung, and Blood Institute T32HL07713 Emilia H MoscatoBurroughs Wellcome Fund Career Award for Medical Scientists Matthew KayserPortuguese Foundation for Science and Technology SFRH-BD-52321-2013 Daniel R MachadoPortuguese Foundation for Science and Technology SFRH-BD-51726-2011 Dinis JS Afons

Cafeteria Diet Is a Robust Model of Human Metabolic Syndrome With Liver and Adipose Inflammation: Comparison to High-Fat Diet

Obesity has reached epidemic proportions worldwide and reports estimate that American children consume up to 25% of calories from snacks. Several animal models of obesity exist, but studies are lacking that compare high-fat diets (HFD) traditionally used in rodent models of diet-induced obesity (DIO) to diets consisting of food regularly consumed by humans, including high-salt, high-fat, low-fiber, energy dense foods such as cookies, chips, and processed meats. To investigate the obesogenic and inflammatory consequences of a cafeteria diet (CAF) compared to a lard-based 45% HFD in rodent models, male Wistar rats were fed HFD, CAF or chow control diets for 15 weeks. Body weight increased dramatically and remained significantly elevated in CAF-fed rats compared to all other diets. Glucose- and insulin-tolerance tests revealed that hyperinsulinemia, hyperglycemia, and glucose intolerance were exaggerated in the CAF-fed rats compared to controls and HFD-fed rats. It is well-established that macrophages infiltrate metabolic tissues at the onset of weight gain and directly contribute to inflammation, insulin resistance, and obesity. Although both high fat diets resulted in increased adiposity and hepatosteatosis, CAF-fed rats displayed remarkable inflammation in white fat, brown fat and liver compared to HFD and controls. In sum, the CAF provided a robust model of human metabolic syndrome compared to traditional lard-based HFD, creating a phenotype of exaggerated obesity with glucose intolerance and inflammation. This model provides a unique platform to study the biochemical, genomic and physiological mechanisms of obesity and obesity-related disease states that are pandemic in western civilization today

The thalamic mGluR1-PLC??4 pathway is critical in sleep architecture

The transition from wakefulness to a nonrapid eye movement (NREM) sleep state at the onset of sleep involves a transition from low-voltage, high-frequency irregular electroencephalography (EEG) waveforms to large-amplitude, low-frequency EEG waveforms accompanying synchronized oscillatory activity in the thalamocortical circuit. The thalamocortical circuit consists of reciprocal connections between the thalamus and cortex. The cortex sends strong excitatory feedback to the thalamus, however the function of which is unclear. In this study, we investigated the role of the thalamic metabotropic glutamate receptor 1 (mGluR1)-phospholipase C ??4 (PLC??4) pathway in sleep control in PLC??4-deficient (PLC??4-/-) mice. The thalamic mGluR1-PLC??4 pathway contains synapses that receive corticothalamic inputs. In PLC??4-/- mice, the transition from wakefulness to the NREM sleep state was stimulated, and the NREM sleep state was stabilized, which resulted in increased NREM sleep. The power density of delta (??) waves increased in parallel with the increased NREM sleep. These sleep phenotypes in PLC??4-/- mice were consistent in TC-restricted PLC??4 knockdown mice. Moreover, in vitro intrathalamic oscillations were greatly enhanced in the PLC??4-/- slices. The results of our study showed that thalamic mGluR1-PLC??4 pathway was critical in controlling sleep architecture.ope

The Neuronal Transition Probability (NTP) Model for the Dynamic Progression of Non-REM Sleep EEG: The Role of the Suprachiasmatic Nucleus

Little attention has gone into linking to its neuronal substrates the dynamic structure of non-rapid-eye-movement (NREM) sleep, defined as the pattern of time-course power in all frequency bands across an entire episode. Using the spectral power time-courses in the sleep electroencephalogram (EEG), we showed in the typical first episode, several moves towards-and-away from deep sleep, each having an identical pattern linking the major frequency bands beta, sigma and delta. The neuronal transition probability model (NTP) – in fitting the data well – successfully explained the pattern as resulting from stochastic transitions of the firing-rates of the thalamically-projecting brainstem-activating neurons, alternating between two steady dynamic-states (towards-and-away from deep sleep) each initiated by a so-far unidentified flip-flop. The aims here are to identify this flip-flop and to demonstrate that the model fits well all NREM episodes, not just the first. Using published data on suprachiasmatic nucleus (SCN) activity we show that the SCN has the information required to provide a threshold-triggered flip-flop for timing the towards-and-away alternations, information provided by sleep-relevant feedback to the SCN. NTP then determines the pattern of spectral power within each dynamic-state. NTP was fitted to individual NREM episodes 1–4, using data from 30 healthy subjects aged 20–30 years, and the quality of fit for each NREM measured. We show that the model fits well all NREM episodes and the best-fit probability-set is found to be effectively the same in fitting all subject data. The significant model-data agreement, the constant probability parameter and the proposed role of the SCN add considerable strength to the model. With it we link for the first time findings at cellular level and detailed time-course data at EEG level, to give a coherent picture of NREM dynamics over the entire night and over hierarchic brain levels all the way from the SCN to the EEG