IMPACTS OF ACUTE AND NEUROTOXIC MDMA EXPOSURE ON OLFACTORY MEMORY PERFORMANCE IN RATS Andrew B. Hawkey A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Arts Department of Psychology University of North Carolina at Wilmington 2012 Approved by Advisory Committee Julian Keith Katherine Bruce Mark Galizio Chair Accepted by Dean, Graduate School TABLE OF CONTENTS ABSTRACT .................................................................................................................................. iv ACKNOWLEDGMENTS ...............................................................................................................v INTRODUCTION ...........................................................................................................................1 Drug History and Classification ..........................................................................................1 Ecstasy Use in Humans ........................................................................................................2 PHARMACOLOGY OF MDMA ....................................................................................................4 Acute Effects of MDMA .....................................................................................................5 Persistent Effects ..................................................................................................................9 COGNITIVE IMPACTS OF MDMA USE IN HUMANS ...........................................................16 LIMITATIONS OF HUMAN TESTING AND NEED FOR ANIMAL MODELS .....................18 MDMA EFFECTS ON MEMORY ...............................................................................................19 MDMA and Working Memory Tasks in Rats ...............................................................................20 An Alternative Approach to Working Memory Testing ....................................................40 Span....................................................................................................................................41 EXPERIMENT 1: ACUTE EFFECTS OF MDMA ......................................................................45 Method ...............................................................................................................................48 Span Training .....................................................................................................................53 Drug Administration ..........................................................................................................59 Results and Discussion ......................................................................................................59 EXPERIMENT 2: EFFECTS OF BINGE MDMA ADMINISTRATION ...................................67 Methods..............................................................................................................................72 Drug Administration ..........................................................................................................73 ii Results and Discussion ......................................................................................................74 GENERAL DISCUSSION ............................................................................................................87 REFERENCES ..............................................................................................................................92 iii LIST OF TABLES Table Page 1. Acute MDMA Studies of Memory in Rats ........................................................................46 2. Pool of scents for Odor Span and SD Tasks ......................................................................51 3. Training timeline ................................................................................................................56 4. Binge MDMA Studies of Memory Tasks in Rats ..............................................................68 iv LIST OF FIGURES Figure Page 1. Basic Rodent Incrementing Non-Match-to-Sample or Span procedure ............................43 2. Ex.1 Key Dependent Measures ..........................................................................................61 3. Ex.1 Within-Session Analysis ...........................................................................................63 4. Ex.2 Key Dependent Measures ..........................................................................................77 5. Ex.2 Session-by-Session Data ...........................................................................................78 6. Individual Subject Graphs..................................................................................................79 7. Ex.2 Within Session Analysis ............................................................................................81 8. Reversal Data .....................................................................................................................83 v ABSTRACT MDMA is an amphetamine derivative which is taken recreationally in social contexts and has been linked to disruptions in neurologic and cognitive functioning. In rodents, the effects of MDMA have been tested on a variety of working memory tasks, but none have measured the effects of the drug on working memory capacity. The current study used the rodent Odor Span Task (OST) to assess the impact of two drug administration schedules on load-dependent learning. Experiment 1 tested the impact of acute doses of MDMA (Saline, 0.3, 1.0, 1.8, 3.0 mg/kg) on the OST. Results from Experiment 1 showed a dose dependent decrease in performance on the OST and a control task (SD). This is interpreted as a general impairment which is unrelated to memory. Experiment 2 tested the impact of a binge dosing regimen of MDMA (10mg/kg, 2 per day x 4 days) or saline on the OST for 4 weeks post-binge. Rats in the MDMA group scored similarly to controls on all OST measures except omissions, where they failed to respond more often than controls. This effect was task-independent and appeared to recover over time. This is interpreted as a general impairment which is unrelated to memory. MDMA-treated rats did show impaired acquisition on early trials of a simple discrimination reversal, replicating a previous finding that binge MDMA produces cognitive inflexibility. In conclusion, the current study suggests that acute MDMA exposure does not produce impairments on accuracy in the OST or an SD control at any dose. Acute MDMA disrupts olfactory memory task performance primarily by reducing responding. Furthermore, the current study suggests that binge or neurotoxic MDMA administration does not produce deficits on olfactory memory, as accuracies were unaffected in both the OST and SD tasks. Measurable performance disruptions were related to non-responding (omissions) and reversal learning. iv ACKNOWLEDGEMENTS The author would like to thank his Advisor and Thesis Committee Chair, Dr. Mark Galizio for his support and direction in the design and completion of this project, as well as Dr. Kate Bruce and Dr. Julian Keith for their support and input. Special thanks are also due to the members of the Galizio lab at UNC-Wilmington: Brooke April, graduate researchers Melissa Deal and Christine Hausmann, and undergraduate researcher Kevin Jacobs; for assistance in data collection. This study was funded by DA029252 through NIDA. v IMPACTS OF ACUTE AND NEUROTOXIC MDMA EXPOSURE ON OLFACTORY MEMORY PERFORMANCE IN RATS Drug History and Classification Methylenedioxymethamphetamine (MDMA) is a ring-substituted amphetamine, commonly referred to as ecstasy. Merck Corporation first synthesized MDMA in the early 1900s as a parent compound (McDowell & Kleber, 1994), and it was patented with related compounds in an effort to develop a new blood clotting drug (Freudenmann, Oxler & Bernschneider-Reif, 2006). Very little is known about the drug for the next several decades beyond development, but it became publicly available in the United States in the early 1970’s (Freudenmann et al., 2006). From the mid-1970’s until the drug was given the Schedule 1 designation in 1985, the drug was sometimes used in psychotherapy, as it was thought to increase openness and aid insight-oriented therapy (McDowell & Kleber, 1994). Since restrictions were put in place, the licit uses of the drug have been few, so much of the research on the drug focuses on risks associated with recreational use. MDMA is related to a group of compounds with a similar chemical structure (Green, Mechan, Elliott, O’Shea, & Colado, 2003). In addition to MDMA, this class of compounds includes amphetamine (AMPH), methamphetamine (MA), 3,4-methylenedioxyamphetamine (MDA), and 3,4 methylenedioxyethamphetamine (MDEA), among others. MDA, MDEA, and MDMA have been shown to reduce serotonin reuptake (Green et al., 2003), as well as producing effects on other neurotransmitter systems. Despite structural similarities, they produce different effects on an array of cognitive/behavioral tests and tend to produce distinct behavioral profiles, at least in rodents (Quinteros-Munoz et al., 2010). The MDMA compound has two isoforms, S+ and R-, both of which are pharmacologically active (Karlsen, Spigset & Slordal, 2007). The drug tends to exhibit stimulant-like effects, as well as a number of socially relevant effects on mood and behavior. These effects complicate the classification of the drug and have led some to refer to it as an entactogen (e.g. Gouzoulis-Mayfrank and Daumann, 2006; Quinteros-Munos et al., 2010), rather than a psychostimulant. An entactogen increases social behavior such as communication or physical contact, and increases subjective feelings of emotional connection or closeness to others. In its pure form, MDMA is a white, tasteless powder, but human users typically take the drug in pill form (Karlsen et al, 2007). It can also be found in other forms, allowing it to be injected, inhaled, or smoked. Street drugs bearing the name ecstasy may include MDMA or a number of other drugs with similar properties (Karlsen et al., 2007), but research on the drug has generally focused on these compounds separately. Within the drug literature, it is often assumed that the effects of ecstasy are due to the actions of MDMA, but given that a variety of chemicals may be in ecstasy tablets, there are limits to the validity of this assumption. Within this discussion, only the illicit use of specific forms of ecstasy, ones which contain solely or primarily MDMA, can be adequately modeled by studies of MDMA-induced effects. Ecstasy Use in Humans Ecstasy users tend to report a wide variety of euphoric and dysphoric symptoms (Karlsen et al., 2007). Reported physiological effects generally include increased heart rate and body temperature, dry mouth, nausea, reduced hunger, and insomia. Ecstasy users also tend to report bruxism (or teeth grinding) and trismus, an involuntary muscular tightening in the jaw. Sensory symptoms tend to include vestibular abnormalities and altered perception. Subjective emotional symptoms often include feelings of euphoria, closeness to others, well-being, extroversion and 2 heightened social communication. In some cases, anxiety or panic can also occur. At high doses, hallucinations or acute psychoses have been reported. Ecstasy use has been largely associated with adolescents and young adults, particularly within “rave culture” (McDowell & Kleber, 1994). Raves are parties with loud electronic or techno music that encourages extended periods of dancing in crowded dance halls. It has been noted that these conditions encourage the use of stimulants, to assist in sustaining high energy activities like dancing, and hallucinogens, which alter sensory perception. While raves certainly contribute to the popularity of the drug, findings from a recent study suggest that ecstasy is often used in private settings as well (Ramtekkar, Striley & Cottler, 2010). In addition, this study found that ecstasy is commonly consumed with other substances, most often marijuana or alcohol. Overall, ecstasy is perceived as being a relatively safe drug and patterns of use appear to be mediated by a number of different factors (Ramtekkar et al., 2010). One important factor in the patterns of ecstasy use appears to be based on the rewarding nature of the context in relation to the drug. Klein, Elifsen and Sterk (2009) investigated behaviors which occur based on their amplification of the effects of ecstasy. Such behaviors often include seeking environments with opportunities for intense stimulation. Other behaviors are exhibited within these environments to provide further stimulation, such as the tendency to use soft objects to provide tactile stimulation or using certain beverages or lotions to intensify gustatory and olfactory stimulation. The occurrence of these stimulation-promoting behaviors was associated with binge consumption of the drug and more adverse effects related to ecstasy use. Historically, ecstasy has been considered to be a relatively non-addictive drug, as compared to other club drugs. Cases of dependence on ecstasy were considered to be relatively 3