Marine aerosols play a large role in the Earth’s climate by cooling via interaction with energy from the sun and altering the chemical and physical properties of clouds. The dissolved organic matter at the ocean surface, where sea spray aerosols and marine gases can be generated, is formed by the microbial loop by circulating nutrients and the ingestion of organisms like phytoplankton or bacteria – with additional inputs from terrestrial sources. The colored fraction of this organic matter, known as marine chromophoric dissolved organic matter, is a subject of considerable interest due to its ability to photosensitize nearby molecules. This indirect photochemical mechanism in the marine environment is not well understood. This dissertation first investigates the composition and properties of this fraction by conducting both simple model experiments in the laboratory and larger experiments such as the use of an indoor ocean-atmosphere facility. The ability to bridge the gap between these two types of study provides this thesis an excellent opportunity to answer various questions regarding the importance of understanding the role of heterogeneous chemistry and photochemistry in our surrounding environment. Lastly, this dissertation applies a similar perspective on photochemistry to explore the multiphase chemistry relevant to indoor environments. Humans spend 20 hours a day on average inside buildings, and while atmospheric pollution has been thoroughly studied, the pollution indoors is widely unknown and unregulated. Inspired by experiments conducted in a real home, various experimental model systems were investigated regarding indoor surfaces. The ultimate goal of the thesis being, to provide insight into the many vital heterogeneous and multiphase processes currently undiscovered in environmental chemistry community.
The thalamus is usually regarded as the gateway sensory information must cross to reach the cortex, the higher cognitive processing plant of the brain. This gateway is guarded by the nucleus Reticularis Thalami (nRT). The nRT is a group of inhibitory neurons that through synaptic connections to the thalamic relay nuclei, temper and control the information stream from thalamus to cortex. The nRT is known to play important roles in sickness and in health. In Chapter 2, we deconstruct the nRT to its various cell types and study their role in health. Traditionally, the nRT was described as a relatively homogenous structure: containing mostly Parvalbumin (PV) expressing neurons that have Transient-type (T-type) Calcium currents that confer onto them a burst firing mode. Recent work has suggested that not all nRT neurons are created equal. There have been studies suggesting that nRT cells have different molecular, electrophysiological, and circuit properties. In other areas of the brain, many of these differences between inhibitory neurons can be correlated with expression of markers such as PV and Somatostatin (SOM). We found this to hold true in the nRT as well. PV-expressing neurons are the bursting cells that are preferentially connected to somatosensory circuits and primed to be involved in generating the physiological sleep-spindle and pathological seizure activities. SOM-expressing neurons are non-bursting cells preferentially connected to limbic circuits, and seem to be less involved in sleep-spindles and seizures. In Chapter 3, we explore the role of the nRT neurons in an animal model of a human chronic neuropsychiatric disorder. Dravet syndrome (DS) is an incurable form of childhood epilepsy associated with severe seizures, autism, sleep disorders, and sudden death. DS is brought about by a loss-of-function mutation in the sodium channel gene SCN1A. SCN1A is highly expressed in nRT neurons. We found that the bursting nRT neurons had prolonged post-hyperpolarization rebound bursting activity, caused by a decrease in the small conductance calcium-activated potassium (SK) current. This increased bursting in nRT neurons caused intra-thalamic circuit hyperexcitability, which may cause the epileptic events observed in these mice. Increasing SK current through the SK agonist EBIO allowed us to normalize the bursting activity in nRT cells, reduce the intra-thalamic circuit hyperexcitability, and consequentially, reduce the seizure activity. Understanding the guardians of the gateway in sickness and in health ultimately help us understand how the brain transfers and processes information.
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