A theoretical and empirical study of addiction

Consumption of addictive substances poses a challenge to economic models of rational, forward-looking agents. This dissertation presents a theoretical and empirical examination of consumption of addictive goods.

The theoretical model draws on evidence from psychology and neurobiology to improve on the standard assumptions used in intertemporal consumption studies. I model agents who may misperceive the severity of the future consequences from consuming addictive substances and allow for an agent's environment to shape her preferences in a systematic way suggested by numerous studies that have found craving to be induced by the presence of environmental cues associated with past substance use. The behavior of agents in this behavioral model of addiction can mimic the pattern of quitting and relapsing that is prevalent among addictive substance users.

Chapter 3 presents an empirical analysis of the Becker and Murphy (1988) model of rational addiction using data on grocery store sales of cigarettes. This essay empirically tests the model's predictions concerning consumption responses to future and past price changes as well as the prediction that the response to an anticipated price change differs from the response to an unanticipated price change. In addition, I consider the consumption effects of three institutional changes that occur during the time period 1996 through 1999.

Fluorescence microscopy of nicotinic acetylcholine receptors

Neuronal nicotinic acetylcholine receptors (nAChRs) are pentameric ligand gated ion channels abundantly expressed in the central nervous system. Changes in the assembly and trafficking of nAChRs are pertinent to disease states including nicotine dependence, autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), and Parkinson’s disease (PD). Here we investigate the application of high resolution fluorescence techniques for the study of nAChR assembly and trafficking. We also describe the construction and validation of a fluorescent α5 subunit and subsequent experiments to elucidate the cellular mechanisms through which α5 subunits are expressed, assembled into mature receptors, and trafficked to the cell surface. The effects of a known single nucleotide polymorphism (D398N) in the intracellular loop of α5 are also examined.

Additionally, this report describes the development of a combined total internal reflection fluorescence (TIRF) and lifetime imaging (FLIM) technique and the first application of this methodology for elucidation of stochiometric composition of nAChRs. Many distinct subunit combinations can form functional receptors. Receptor composition and stoichiometry confers unique biophysical and pharmacological properties to each receptor sub-type. Understanding the nature of assembly and expression of each receptor subtype yields important information about the molecular processes that may underlie the mechanisms through which nAChR contribute to disease and addiction states.

Binding Studies of Neuronal Nicotinic Acetylcholine Receptors Expressing Unnatural Amino Acids

Nicotinic acetylcholine receptors are pentameric ligand-gated ion channels mediating fast synaptic transmission throughout the peripheral and central nervous systems. They have been implicated in various processes related to cognitive functions, learning and memory, arousal, reward, motor control and analgesia. Therefore, these receptors present alluring potential therapeutic targets for the treatment of pain, epilepsy, Alzheimer’s disease, Parkinson’s disease, Tourette’s syndrome, schizophrenia, anxiety, depression and nicotine addiction. The work detailed in this thesis focuses on binding studies of neuronal nicotinic receptors and aims to further our knowledge of subtype specific functional and structural information.

Chapter 1 is an introductory chapter describing the structure and function of nicotinic acetylcholine receptors as well as the methodologies used for the dissertation work described herein. There are several different subtypes of nicotinic acetylcholine receptors known to date and the subtle variations in their structure and function present a challenging area of study. The work presented in this thesis deals specifically with the α4β2 subtype of nicotinic acetylcholine receptor. This subtype assembles into 2 closely related stoichiometries, termed throughout this thesis as A3B2 and A2B3 after their respective subunit composition. Chapter 2 describes binding studies of select nicotinic agonists on A3B2 and A2B3 receptors determined by whole-cell recording. Three key binding interactions, a cation-π and two hydrogen bonds, were probed for four nicotinic agonists, acetylcholine, nicotine, smoking cessation drug varenicline (Chantix®) and the related natural product cytisine.

Results from the binding studies presented in Chapter 2 show that the major difference in binding of these four agonists to A3B2 and A2B3 receptors lies in one of the two hydrogen bond interactions where the agonist acts as the hydrogen bond acceptor and the backbone NH of a conserved leucine residue in the receptor acts as the hydrogen bond donor. Chapter 3 focuses on studying the effect of modulating the hydrogen bond acceptor ability of nicotine and epibatidine on A3B2 receptor function determined by whole-cell recording. Finally, Chapter 4 describes single-channel recording studies of varenicline binding to A2B3 and A3B2 receptors.