Sex Differences in Nicotine-Conditioned Hyperactivity in a Model of Dopamine D2 Receptor Priming: Roles of Dopamine D2 and D3 Receptor Subtypes
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East Tennessee State University Digital Commons @ East Tennessee State University Electronic Theses and Dissertations Student Works 8-2008 Sex Differences in Nicotine-Conditioned Hyperactivity in a Model of Dopamine D2 Receptor Priming: Roles of Dopamine D2 and D3 Receptor Subtypes. Ashley Brianna Sheppard East Tennessee State University Follow this and additional works at: https://dc.etsu.edu/etd Part of the Hormones, Hormone Substitutes, and Hormone Antagonists Commons Recommended Citation Sheppard, Ashley Brianna, "Sex Differences in Nicotine-Conditioned Hyperactivity in a Model of Dopamine D2 Receptor Priming: Roles of Dopamine D2 and D3 Receptor Subtypes." (2008). Electronic Theses and Dissertations. Paper 1978. https://dc.etsu.edu/etd/ 1978 This Thesis - Open Access is brought to you for free and open access by the Student Works at Digital Commons @ East Tennessee State University. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of Digital Commons @ East Tennessee State University. For more information, please contact [email protected]. Sex Differences in Nicotine-conditioned Hyperactivity in a Model of Dopamine D2 Receptor Priming: Roles of Dopamine D2 and D3 Receptor Subtypes A thesis presented to the faculty of the Department of Psychology East Tennessee State University In partial fulfillment of the requirements for the degree of Master of Arts in Psychology by Ashley Brianna Sheppard August 2008 Russell Brown, PhD., Chair Michael Woodruff, PhD., Committee member Otto Zinser, PhD., Committee member Keywords: Conditioned Hyperactivity, Contextual Associations, D2 Priming, Antagonists, Nicotine, Schizophrenia, Sensitization, Sex Differences, Smoking ABSTRACT Sex Differences in Nicotine-conditioned Hyperactivity in a Model of Dopamine D2 Receptor Priming: Roles of Dopamine D2 and D3 Receptor Subtypes by Ashley Brianna Sheppard The aim of this investigation was to determine the effect of a nicotine-conditioned context on locomotor hyperactivity in an animal model of D2-priming, and whether conditioned hyperactivity could be blocked by the D2 antagonist eticlopride or the D3 antagonist nafadotride. D2-primed male rats showed enhanced nicotine sensitization as evidenced by statistically significant differences in horizontal activity. D2-primed female rats administered nicotine demonstrated an increased hypoactive response after initial sensitization and increased stereotypy. Eticlopride and nafadotride blocked sensitization to nicotine in both D2-primed and non D2-primed males and females. Eticlopride blocked conditioned hyperactivity in females but not in males. D2-primed female rats administered nicotine demonstrated significantly higher conditioned-hyperactivity as compared to non D2-primed females and controls, and this increase was more effectively blocked by nafadotride as compared to eticlopride. These results suggest differential roles of the dopamine D2 and D3 receptors in both adolescent nicotine sensitization and conditioned activating effects of nicotine. 2 DEDICATION This work is dedicated to Ben, Mom, Dad, and Tiff for being so supportive; Dr. Russ Brown for being a great advisor and also a great friend; and finally, the “weekend crew” who has been my family in our home away from home for the past two years: Zack, Daniel, Kim, and of course, Ben. “Go confidently in the direction of your dreams. Live the life you have imagined.” -Henry David Thoreau 3 ACKNOWLEDGEMENTS This work was supported by a grant from the East Tennessee State University School of Graduate Studies. I would also like to acknowledge my thesis committee, Dr. Russ Brown, Dr. Mike Woodruff, and Dr. Otto Zinser, for their insightful and helpful suggestions in the preparation of this manuscript. 4 CONTENTS Page ABSTRACT ….……………………………………………………………………………… 2 DEDICATION………………………………………………………………………………… 3 ACKNOWLEDGEMENTS…………………………………………………………………….. 4 LIST OF FIGURES …………………………………………………………………………. 8 Chapter 1. INTRODUCTION ………………………………………………………………… 9 The Dopamine System ………………………………………………… 10 Rodent Models of Schizophrenia ………………………………………. 11 Rationale for Use of Animal Models ……………………………….. 11 Past Models of Schizophrenia: Dopamine Hyperactivity…………. 12 Neonatal Quinpirole Model: A New Model of Schizophrenia……. 14 Behavioral Sensitization ………………………………………………. 17 Anatomy of the Nucleus Accumbens ………………………………. 18 Role of the Nucleus Accumbens in Behavioral Sensitization …….. 18 Involvement of Dopamine Receptors in Nicotine Sensitization … 20 Involvement of Non-dopaminergic Systems in Sensitization …… 22 Nicotine Conditioned Hyperactivity ……………………………………… 23 Age Differences in the Effects of Nicotine on Behavior………….. 24 Sex Differences in the Effects of Nicotine on Behavior ………….. 26 Research Questions Addressed in this Thesis …………………………… 29 2. METHODS……………………………………………………………………… 31 5 Subjects ……………………………………………………………………… 31 Drug Dosage….……………………………………………………………… 31 Drug Treatment………………………………………………………………. 32 Neonatal……………………………………………………………... 32 Adolescent…………………………………………………………… 32 Apparatus……………………………………………………………………… 32 Behavioral Testing Procedure ………………………………………………… 33 Research Design and Data Analysis ………………………………………….. 34 3. RESULTS…………………………………………………………………………… 35 Sex Differences in Nicotine Sensitization for Rats Administered Eticlopride…………………………………………………………………….. 35 Initial Analyses………………………………….....………………….. 35 Horizontal Activity for Male Rats Administered Eticlopride ………. 36 Horizontal Activity for Female Rats Administered Eticlopride…….. 37 Sex Differences in Nicotine-Conditioned Hyperactivity for Rats Administered Eticlopride……………………………………………………………………. 39 Conditioned Hyperactivity for Male Rats Administered Eticlopride…. 39 Conditioned Hyperactivity for Female Rats Administered Eticlopride.. 40 Sex Differences in Nicotine Sensitization for Rats Administered Nafadotride…………………………………………………………………… 41 Initial Analyses ………………………………………………………... 41 Horizontal Activity for Male Rats Administered Nafadotride……….. 42 Horizontal Activity for Female Rats Administered Nafadotride……… 43 6 Sex Differences in Nicotine-Conditioned Hyperactivity for Rats Administered Nafadotride……………………………………………………………………. 45 Conditioned Hyperactivity for Male Rats Administered Nafadotride.. 45 Conditioned Hyperactivity for Female Rats Administered Nafadotride 45 4. DISCUSSION………………………………………………………………………. 47 Nicotine Sensitization…………………………………………………………. 47 Antagonism of Dopamine Receptor Subtypes………………………………… 49 D2 Receptor…………………………………………………………… 49 D3 Receptor……………………………………………………………. 49 Dopamine Receptor Density in Adolescence ………………………… 50 Alternative Mechanisms……………………………………………….. 51 Nicotine-Conditioned Hyperactivity…………………………………………… 51 Clinical Relevance……………………………………………………………… 54 Conclusion……………………………………………………………………… 55 REFERENCES ……………………………………………………………………………… 56 VITA ………………………………………………………………………………………… 79 7 LIST OF FIGURES Figure Page 1. Horizontal Activity for Males Administered Eticlopride……………………………. 37 2. Horizontal Activity for Females Administered Eticlopride………………………… 38 3. Conditioned Hyperactivity for Males Administered Eticlopride…………………….. 40 4. Conditioned Hyperactivity for Females Administered Eticlopride………………… 41 5. Horizontal Activity for Males Administered Nafadotride……………………….…… 43 6. Horizontal Activity for Females Administered Nafadotride…………………………. 44 7. Conditioned Hyperactivity for Males Administered Nafadotride……………………. 45 8. Conditioned Hyperactivity for Females Administered Nafadotride…………………. 46 8 CHAPTER 1 INTRODUCTION Smoking is a convenient and legal form of drug self-administration that often begins in adolescence. Addiction to nicotine, the psychomotor stimulant drug found in cigarettes, often results (Benowitz, 1988; Faraday, Elliott, Phillips, & Grunberg, 2003; Jarvis, 2004). Nicotine has positive reinforcing effects that typically become associated with environmental and contextual cues (Bevins & Palmatier, 2003; Bevins, Eurek, & Besheer, 2004; Jarvis; Lazev, Herzog, & Brandon, 1999). After many pairings of smoking with a particular environment or within a specific context, the context in which the individual smokes appears to elicit strong cigarette cravings followed by smoking behavior (Bevins & Palmatier; Brandon, Piasecki, Quinn, & Baker as cited in Lazev et al., 1999; Jarvis). A rise in smoking-related health problems, evidenced by lung cancer surpassing breast cancer as the leading type of cancer in women in the United States, suggests that women in general are more sensitive to the effects of nicotine, have greater difficulty quitting, and use tobacco more frequently than men (Grunberg, Winders, & Wewers, 1991; Kandel, Warner, & Kessler as cited in Harrod et al., 2004; Waldron, 1991). The schizophrenic population in particular exhibits especially high rates of smoking which is nearly three times that of the general population (Kelly & McCreadle, 1999). According to the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 2000), schizophrenia is a psychotic disorder in which patients experience symptoms such as delusions, hallucinations, disorganized speech, catatonic motor behavior, and negative affect. The disorder usually has an age of onset between the late teens and mid-30s (American Psychiatric Association). Individuals suffering from schizophrenia exhibit impairments in many cognitive functions such as memory, attention, and 9 psychomotor abilities (American Psychiatric Association). The