I. INVESTIGATE MECHANISMS UNDERLYING REINFORCING AND THERAPEUTIC EFFECTS OF ALCOHOL & STIMULANT DRUGS Several studies have focused on the role of several genes in the mechanism(s) of stimulant drugs and alcohol. Some of these studies were published this year, some were presented or will be presented and others have been submitted for publication. Briefly the receptors / genes examined in studies this year were: D2R, D3R, D4R, DAT and CB1. A transgenic breeding facility for D2 and D4 mice has facilitated this research. Finally we were able to set up and successful in doing mouse cocaine self-administration (SA) studies. We are interested in this so to further examine the role of these receptors / genes using transgenic mice. Results from the mouse SA will be presented next month at the SFN meeting. The following summarizes our findings measuring the effects of acute administration of methylphenidate (MP) and amphetamine in D4R transgenic mice on locomotor activity and on conditioned place preference (CPP). The D4R mice work was recently completed and will be presented very soon at the annual conference of the Society for Neuroscience (SFN). In addition this manuscript is in preparation and we plan on submitting it by the time of the meeting. Results indicated significant differences in behavioral response to MP among the three mice strains. Specifically, the D4R-/- and D4R -/+ mice showed no preference for the MP-paired environment, compared to the D4R+/+ mice at 1mg/kg. However, at higher doses (3mg/kg), CPP was seen in all mice, indicating that the D4R plays a critical role in the behavioral profile of MP. We utilized D4R-/- mice to study the brain metabolic effects of MP and, in particular, examine the contribution to D4R in brain metabolic response to MP by measuring the effects of MP on brain glucose metabolism in male D4R+/+, D4R+/- and D4R-/- mice using mPET and FDG. Results indicated differences in baseline activity between strains in several cortical areas. The most profound difference was noted in the cerebellum baseline vs MP challenge. We are presently reanalyzing the data now that we have added this year mMRI data of the same animals. This will allow us a high resolution coregistration and quantitative analysis of brain changes in metabolic activity (mPET + mMRI). Our findings support the notion that D4R plays a critical role in the brain metabolic response to MP and may further be used to predict individual response to drug treatment. This data will be completed in late fall this year. In addition we examined drug induced metabolic brain activity in dopamine transport (DAT) mice with mPET. DAT +/+ and DAT -/- mice were scanned twice with mPET and FDG (a: saline and b: cocaine pretreatment). Results demonstrated a difference in brain metabolic activity between DAT +/+ and -/- mice at baseline and that cocaine resulted in significant decline in brain metabolic activity. Detailed findings will be presented next month at the SFN conference and the paper is presently being written up for journal submission.II. VISUAL DISCRIMINATION ATTENTION TASK (VDAT) TO ASSESS BEHAVIORAL EFFECTS OF MP The VDAT is a sustained attention task that signals the formation of a habit by taking into account hits, misses, false alarms, and correct rejections in a food operant conditioning paradigm. SHR are an excellent rodent model for ADHD because they have behavioral and neurochemical characteristics similar to ADHD. Four-week old preadolescent SHR and Wistar rats were tested on a food VDAT using shaping cue-light intervals (1-s, 500 ms, 50 ms, and 25 ms) and after baseline was established, were exposed to ip injections of: 2 mg/kg MP; 1 mg/kg MP; or vehicle for 2 weeks. This project has progressed and the IP MP results will be completed in time to be presented at next months SFN meeting. We plan on completing this first paper this fall for journal submission. Also in parallel we did a study looking at the kinetics of various oral drinking procedures with MP blood plasma levels so that we can begin the oral MP treatment segment of the experiment with clinically comparable plasma levels. This experiment was completed this summer and we are analyzing the data for this paper at this time. III. NEUROBIOLOGY OF ADDICTIVE BEHAVIORS: The phenomenology of obesity has many similarities to the compulsive behaviors observed in addiction. DA is involved in reinforcing the effects of drugs of abuse and food. The involvement of DA in pathological eating and obesity is poorly understood and has not been directly assessed. DA is involved in the regulation of food intake and Wang et al (2004) found that obese persons have decreased D2R availability in the striatum. 4-week old male Zucker obese (leptin deficiency that makes them more prone to obesity) and lean rats, divided into unrestricted and restricted (70% of unrestricted food intake/day) diet groups. We examined the developmental and diet effects on D2R levels in obese and lean Zucker rats. D2R levels were examined by both ARG and mPET at 1 and 4 months. The ARG data has been submitted for publication and the mPET data for the same time period is being presented at the SFN conference and will be submitted for publication very soon. In addition this study is continuing as part of a longitudinal study that will last for the lifespan of the animals. We are thus assessing in the 4 groups above as well as animals that have been switched from restricted to unrestricted and vice versa at 4 months of age the following: 1) weight; 2) food intake; 3) locomotor activity; 4) D2R miPET; 5) D2R ARG; 6) neuropeptide ELISA assessment of blood plasma samples over time. In a separate experiment we have done FDG microPET assessment of brain metabolic activity of the above groups of animals in a) baseline and b) food challenge state. We will compare brain regional activity in each group. This experiment is complete and we are in the process of analyzing the data.IV. MECHANISMS UNDERLYING VULNERABILITY TO DRUG ABUSE & ADDICTION The present study utilized a rodent chronic oral MP paradigm. Four-week old male Sprague Dawley rats were divided into three treatment groups: 2 mg/kg MP; 1mg/kg MP; and Vehicle (water). At this point, all animals were microsurgically implanted with a jugular vein catheter and placed in operant test chambers for daily 1h sessions. In each session, rats had the opportunity to press an active lever that would result in an intravenous infusion of cocaine (1 mg/kg). Behavioral analysis revealed Significant differences in the number of cocaine infusions, lever presses and in the pattern of administration between the three groups. This study also examined the D2 receptor profile in these same rats before MP exposure and after 28 weeks of MP exposure using mPET. This study has been completed and the paper will soon be submitted for journal publication. Also the brains of the rats above were perfused and scanned with 17T MRI microscopy to assess structural brain differences between the groups. The brain scans were completed analysis remains. In a new study we are looking at the effects of D2R genotype on chronic ethanol drinking induced effects on cerebral & CSF volume (9.4T MRI); as well as d2, cdk5, ChAT, FosB NOS immunohistochemistry.
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