Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (39 results)

  • Thesis
  • Peer Reviewed
UC Santa Barbara Electronic Theses and Dissertations (2022)

Our understanding of the brain’s beautiful and complex machinery is largely driven by our ability to measure the chemical and electrical signals that govern its convoluted circuitry. As such, our knowledge is only as good as the tools we have at our disposal. The study of neurochemistry and neuropharmacology research has largely been driven by the use of microdialysis and electrochemical methods to measure targets of interest in the brain. While these techniques are powerful and have contributed immensely to our conceptualization of brain activity, they are not without their limitations. Briefly, microdialysis suffers from poor temporal resolution and lacks the potential for real-time data delivery, while previous electrochemical methods suffer from debatable specificity and limited generalizability for the detection of many critical targets. In response to these limitations, I have applied electrochemical aptamer-based (E-AB) sensors to the field of in-brain molecular sensing. The modular E-AB platform does not rely on the reactivity of its intended target, is generalizable to the detection of a wide range of analytes and has been shown to support real-time detection of small molecules directly in the living body. By modifying the existing E-AB platform, which has demonstrated success for peripheral measurements in blood, I have developed a novel E-AB sensor platform for making in-brain measurements of small molecules. In-brain E-AB sensing opens a path towards measuring a wide range of targets in the brain. To showcase this, I have applied this platform to model drug transport (using simultaneous measurements in blood and CSF), as well as study neuropsychopharmacology (using simultaneous measurements of a psychoactive drug and on-going behavior). Together these studies lay the foundation for a powerful new tool with which to study neurochemistry and neuropharmacology.

    Cover page: Building biosensors for neuropsychopharmacology
    • Thesis
    • Peer Reviewed
    UC Santa Barbara Electronic Theses and Dissertations (2017)

    Gene by environment interactions may be important etiological factors that confer risk of numerous psychiatric disorders. Psychiatric disorders are found to be heritable, indicating genetic variants contribute to risk and resilience. In addition to genetics, early life stress confers significant risk. Prenatal stress (PNS) is associated with numerous disorders and alterations to affect and cognition that suggest profound and enduring consequences. Preclinical studies causally indicate the deleterious effects of PNS on models of psychiatric disorders, including effects on prepulse inhibition (PPI) and cocaine reward and locomotion. The intersection of genetics and PNS has been explored and PNS was found to interact with genetic background. PNS differentially alters PPI and cocaine reward and locomotion in the C57/6J (B6) and DBA/2J (D2) inbred mouse strains. These strains may serve as progenitors for populations that can be utilized in forward genetic studies for discovery of quantitative trait loci (QTLs) that will facilitate discovery of PNS interacting variants. The following will present studies that utilized the BXD recombinant inbred mouse panel, derived from the B6 and D2 strains, to discover QTLs that interact with PNS to alter sensorimotor and cocaine-induced behaviors. A QTL by PNS interaction was discovered for PPI and acute cocaine locomotion. The BXD panel is a genetic reference population that allows for extensive accumulation and sharing of data across studies. Following discovery of these QTLs, publicly available BXD mRNA expression data was utilized to prioritize positional candidate genes. These efforts prioritized several positional candidate genes. In addition to offspring phenotypes, the maternal stress corticosterone response and effects of stress on dam-pup contact were assessed, as heritable maternal stress responses may contribute to strain differences in offspring phenotype, with implications for the interpretation of QTLs. Strain differences in the maternal corticosterone response and the maternal behavior response to stress associated with strain differences in PNS effects on male offspring cocaine phenotypes, suggesting a potential role for genetic variants that moderate the maternal stress response. The results obtained are a preliminary step in identifying genes that interact with PNS to confer risk of psychiatric disease.

      Cover page: Discovery of quantitative trait loci that mediate the effects of prenatal stress on cocaine and sensorimotor behaviors: Implications for gene by environment interactions that contribute to psychiatric disorders
      • Thesis
      • Peer Reviewed
      UC Santa Barbara Electronic Theses and Dissertations (2017)

      Similar to the pattern observed in people with substance abuse disorders, laboratory animals will exhibit escalation of cocaine intake when the drug is readily available and will exhibit increased drug-seeking behaviors after long periods of abstinence. Additionally, there are long term changes in neuron structure, receptor function, and neurotransmission associated with abstinence from cocaine in humans and animals. DNA methylation is an epigenetic modification to the DNA structure that mediates mRNA expression to confer different cell types, but has recently been implicated in learning and memory mechanisms. The long-term control that DNA methylation has over gene expression in animals makes it a prime candidate for controlling gene expression over the course of abstinence in animals with previous drug experience. Therefore, here, I investigated the contribution of behavioral contingency of cocaine administration on escalation of cocaine intake and re-exposure to cocaine cues as well as DNA methylation and gene expression within the dorsal medial prefrontal cortex (dmPFC) in adult male Sprague-Dawley rats. I exposed rats to daily training for saline (1 h/ day) or cocaine (0.25 mg/kg/inf) in limited- (1 h access per day), prolonged- (6 h access per day), or limited + yoked-access (1 h contingent + 5 h non-contingent access per day) for 15 days. Rats were then put through forced abstinence for 1, 14, or 60 days, and then the dmPFC was dissected out. Saline- and prolonged-access rats were additionally separated into cue- and no cue- conditions after 60 days of abstinence, where cue rats were re-exposed to the operant chamber without cocaine delivery for 2 h. These studies led to 4 main findings. 1) cocaine contingency affects mRNA expression for glutamatergic genes, 2) DNA methylation changes dynamically throughout abstinence, 3) re-exposure to cocaine cues rapidly alters DNA methylation and mRNA expression, and 4) DNA methylation, hydroxymethylation, and transcription factor binding all contribute to altered mRNA expression.

      • 1 supplemental file
      Cover page: Self-Administration Results in Dynamic Changes in DNA Methylation of the Dorsal Medial Prefrontal Cortex Throughout Forced Abstinence, and After Re-exposure to Cues
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2019)

      Background and purpose

      Addiction vulnerability involves complex gene X environment interactions leading to a pathological response to drugs. Identification of the genes involved in these interactions is an important step in understanding the underlying neurobiology and rarely have such analyses examined sex-specific influences. To dissect this interaction, we examined the impact of prenatal stress (PNS) on cocaine responsiveness in male and female mice of the BXD recombinant inbred panel.

      Experimental approach

      BXD strains were subjected to timed mating and assigned to PNS or control groups. PNS dams were subjected to restraint stress (1-hr restraint, three times daily) starting between embryonic day (E) 11 and 14 and continued until parturition. Adult male and female, control and PNS offspring were tested for locomotor response to initial and repeated cocaine injections (sensitization) as well as cocaine-induced conditioned place preference (CPP).

      Key results

      Strain, PNS, and sex interacted to modulate initial and sensitized cocaine-induced locomotion, as well as CPP. Moreover, a quantitative trait locus (QTL) interacting with PNS regulating initial locomotor response to cocaine (chromosome X, 37.91 to 50.95 Mb) was identified. Also PNS-independent, female-specific QTLs regulating CPP (chromosome 11, 65.50 to 81.31 Mb) and sensitized cocaine-induced locomotion (chromosome 16, 95.79 to 98.32 Mb) were identified. Publicly available mRNA expression data were utilized to identify cis-eQTL and transcript covariation with the behavioural phenotype to prioritize candidate genes; including Aifm1.

      Conclusions and implications

      These QTL encompass genes that may moderate genetic susceptibility to PNS and interact with sex to determine adult responsiveness to cocaine and addiction vulnerability.

      Linked articles

      This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.
        Cover page: Discovery of early life stress interacting and sex-specific quantitative trait loci impacting cocaine responsiveness.
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2021)
        Current knowledge of the disposition kinetics of endogenous metabolites is founded almost entirely on poorly time-resolved experiments in which samples are removed from the body for later, benchtop analysis. Here, in contrast, we describe real-time, seconds-resolved measurements of plasma phenylalanine collected in situ in the body via electrochemical aptamer-based (EAB) sensors, a platform technology that is independent of the reactivity of its targets and thus is generalizable to many. Specifically, using indwelling EAB sensors, we have monitored plasma phenylalanine in live rats with a few micromolar precision and a 12 s temporal resolution, identifying a large-amplitude, few-seconds phase in the animals' metabolic response that had not previously been reported. Using the hundreds of individual measurements that the approach provides from each animal, we also identify inter-subject variability, including statistically significant differences associated with the feeding status. These results highlight the power of in vivo EAB measurements, an advancement that could dramatically impact our understanding of physiology and provide a valuable new tool for the monitoring and treatment of metabolic disorders.
          Cover page: Seconds-Resolved, In Situ Measurements of Plasma Phenylalanine Disposition Kinetics in Living Rats
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2023)
          AIM: Pharmacokinetics have historically been assessed using drug concentration data obtained via blood draws and bench-top analysis. The cumbersome nature of these typically constrains studies to at most a dozen concentration measurements per dosing event. This, in turn, limits our statistical power in the detection of hours-scale, time-varying physiological processes. Given the recent advent of in vivo electrochemical aptamer-based (EAB) sensors, however, we can now obtain hundreds of concentration measurements per administration. Our aim in this paper was to assess the ability of these time-dense datasets to describe time-varying pharmacokinetic models with good statistical significance. METHODS: We used seconds-resolved measurements of plasma tobramycin concentrations in rats to statistically compare traditional one- and two-compartmental pharmacokinetic models to new models in which the proportional relationship between a drugs plasma concentration and its elimination rate varies in response to changing kidney function. RESULTS: We found that a modified one-compartment model in which the proportionality between the plasma concentration of tobramycin and its elimination rate falls reciprocally with time either meets or is preferred over the standard two-compartment pharmacokinetic model for half of the datasets characterized. When we reduced the impact of the drugs rapid distribution phase on the model, this one-compartment, time-varying model was statistically preferred over the standard one-compartment model for 80% of our datasets. CONCLUSIONS: Our results highlight both the impact that simple physiological changes (such as varying kidney function) can have on drug pharmacokinetics and the ability of high-time resolution EAB sensor measurements to identify such impacts.
            Cover page: Using seconds-resolved pharmacokinetic datasets to assess pharmacokinetic models encompassing time-varying physiology.
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2022)
            Electrochemical aptamer-based (EAB) sensors support the real-time, high frequency measurement of pharmaceuticals and metabolites in-situ in the living body, rendering them a potentially powerful technology for both research and clinical applications. Here we explore quantification using EAB sensors, examining the impact of media selection and temperature on measurement performance. Using freshly-collected, undiluted whole blood at body temperature as both our calibration and measurement conditions, we demonstrate accuracy of better than ± 10% for the measurement of our test bed drug, vancomycin. Comparing titrations collected at room and body temperature, we find that matching the temperature of calibration curve collection to the temperature used during measurements improves quantification by reducing differences in sensor gain and binding curve midpoint. We likewise find that, because blood age impacts the sensor response, calibrating in freshly collected blood can improve quantification. Finally, we demonstrate the use of non-blood proxy media to achieve calibration without the need to collect fresh whole blood.
              Cover page: Improved calibration of electrochemical aptamer-based sensors.
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2017)

              Background

              A high degree of co-morbidity exists between methamphetamine (MA) addiction and alcohol use disorders and both sequential and simultaneous MA-alcohol mixing increases risk for co-abuse. As little preclinical work has focused on the biobehavioral interactions between MA and alcohol within the context of drug-taking behavior, we employed simple murine models of voluntary oral drug consumption to examine how prior histories of either MA- or alcohol-taking influence the intake of the other drug.

              Methods

              In one study, mice with a 10-day history of binge alcohol-drinking [5,10, 20 and 40% (v/v); 2h/day] were trained to self-administer oral MA in an operant-conditioning paradigm (10-40mg/L). In a second study, mice with a 10-day history of limited-access oral MA-drinking (5, 10, 20 and 40mg/L; 2h/day) were presented with alcohol (5-40% v/v; 2h/day) and then a choice between solutions of 20% alcohol, 10mg/L MA or their mix.

              Results

              Under operant-conditioning procedures, alcohol-drinking mice exhibited less MA reinforcement overall, than water controls. However, when drug availability was not behaviorally-contingent, alcohol-drinking mice consumed more MA and exhibited greater preference for the 10mg/L MA solution than drug-naïve and combination drug-experienced mice. Conversely, prior MA-drinking history increased alcohol intake across a range of alcohol concentrations.

              Discussion

              These exploratory studies indicate the feasibility of employing procedurally simple murine models of sequential and simultaneous oral MA-alcohol mixing of relevance to advancing our biobehavioral understanding of MA-alcohol co-abuse.
                Cover page: Methamphetamine-alcohol interactions in murine models of sequential and simultaneous oral drug-taking
                • Article
                • Peer Reviewed
                UC Santa Barbara Previously Published Works (2017)
                The development of a technology capable of tracking the levels of drugs, metabolites, and biomarkers in the body continuously and in real time would advance our understanding of health and our ability to detect and treat disease. It would, for example, enable therapies guided by high-resolution, patient-specific pharmacokinetics (including feedback-controlled drug delivery), opening new dimensions in personalized medicine. In response, we demonstrate here the ability of electrochemical aptamer-based (E-AB) sensors to support continuous, real-time, multihour measurements when emplaced directly in the circulatory systems of living animals. Specifically, we have used E-AB sensors to perform the multihour, real-time measurement of four drugs in the bloodstream of even awake, ambulatory rats, achieving precise molecular measurements at clinically relevant detection limits and high (3 s) temporal resolution, attributes suggesting that the approach could provide an important window into the study of physiology and pharmacokinetics.
                  Cover page: Real-time measurement of small molecules directly in awake, ambulatory animals
                  • Article
                  • Peer Reviewed
                  UC Santa Barbara Previously Published Works (2019)
                  The field of precision medicine-the possibility to accurately tailor pharmacological treatments to each specific patient-would be significantly advanced by the ability to rapidly, conveniently, and cost-effectively measure biomarkers directly at the point of care. Electrochemical aptamer-based (E-AB) sensors appear a promising approach to this end due to their low cost, ease of use, and good analytical performance in complex clinical samples. Thus motivated, we present here the development of an E-AB sensor for the measurement of the amino acid L-tryptophan, a diagnostic marker indicative of a number of metabolic and mental health disorders, in urine. The sensor employs a previously reported DNA aptamer able to recognize the complex formed between tryptophan and a rhodium-based receptor. We adopted the aptamer to the E-AB sensing platform by truncating it, causing it to undergo a binding-induced conformational change, modifying it with a redox-reporting methylene blue, and attaching it to an interrogating electrode. The resulting sensor is able to measure tryptophan concentrations in the micromolar range in minutes and readily discriminates between its target and other aromatic and non-aromatic amino acids. Using it, we demonstrate the measurement of clinically relevant tryptophan levels in synthetic urine in a process requiring only a single dilution step. The speed and convenience with which this is achieved suggest that the E-AB platform could significantly improve the ease and frequency with which metabolic diseases are monitored. Graphical Abstract.
                    Cover page: An electrochemical aptamer-based sensor for the rapid and convenient measurement of l-tryptophan
                    Top