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. ? The following summarizes our findings measuring the effects of acute administration of methylphenidate (MP) and amphetamine in D4 mice on locomotor activity and on conditioned place preference (CPP). This work was recently submitted to the journal psychopharmacology. Results indicated that D4KO and WT mice displayed CPP and increased locomotor activity in response to each of the 3 psychostimulants tested. However, significant differences were observed with respect to each genotypes overall behavioral responses. D4KO mice displayed significantly enhanced CPP only at the highest dose of MP (3 mg/kg, i.p.) and cocaine (4 mg/kg, i.p.) and the lowest dose of AMPH (1 mg/kg, ip). In the locomotor test D4 KO mice only displayed significantly increased locomotor activity when exposed to the highest dose of each drug. Locomotor responses of WT and KO mice to cocaine and MP were not significantly different. These results suggest distinct mechanisms for D4 modulation of the rewarding (perhaps via attenuating dopamine signaling) and locomotor (perhaps by serotonin) properties of these drugs. Thus individuals with D4 polymorphisms might show enhanced reinforcing responses to stimulant medications and attenuated sensitivity to the locomotor stimulatory effects of AMPH. ? We utilized DATKO mice to study the brain metabolic effects of cocaine and, in particular, examine the contribution to DAT in brain metabolic response to cocaine by measuring the effects of cocaine on brain glucose metabolism (BGM) in DATWT and DATKO mice using PET and FDG. At baseline DATKO mice had significantly greater metabolism in thalamus and cerebellum than DATWT. Acute cocaine decreased BGM and this effect was greater in DATWT (15%) than in DATKO mice (5%). WT mice showed regional decreases in the olfactory bulb, motor cortex, striatum, hippocampus, thalamus and cerebellum whereas KO showed decreases only in thalamus. The differential pattern of regional responses to cocaine in KO and WT suggests that most of the BGM changes from acute cocaine are due to DAT blockade. Cocaine-induced decreases in metabolism in thalamus (dense NE innervation) in DATKO suggest that these were mediated by cocaines blockade of NET. The greater baseline metabolism in DATKO than DATWT mice in cerebellum (brain region mostly devoid of DAT) suggests that DA indirectly regulates activity of these brain regions. This paper was just accepted by Synapse.? 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. Adolescent SHR and Wistar rats were tested on a food VDAT using shaping with variable cue-light intervals and after baseline was established, were exposed to ip: vehicle, 1 or 2 mg/kg MP. This project has been completed and manuscript is in preparation. ? III. NEUROBIOLOGY OF ADDICTIVE BEHAVIORS: The phenomenology of obesity has many similarities to the compulsive behaviors observed in addiction. We used adolescent male Zucker obese and lean rats, divided into unrestricted (U) and restricted (R) diet groups. We examined the age and diet effects on D2 in these rats by both autoradiography (ARG) and PET at 1 and 4 months of age. Results showed lower D2 in Ob U than Le U rats observed with ARG most likely reflects decreases in striatal D2 receptors levels whereas the increased availability observed with PET is likely to reflect reduced DA release (resulting in decreased competition with endogenous DA). The ARG finding of an attenuation of the age-related loss of D2 binding corroborates previous studies of the salutary effects of food restriction in the aging process. Because 11C raclopride is sensitive to competition with endogenous DA, the higher D2 binding in obese rats with raclopride despite the lower D2 levels shown with spiperone could reflect lower extracellular DA in the Ob rats and merits further investigation. This work was completed and on line published in Synapse. ? In a separate experiment we have done FDG PET assessment of BGM of the above groups of animals in a) baseline and b) food challenge state. This experiment was recently completed and we have submitted it for review to the International J of Obesity. These results showed that conditioned food stimuli generate robust activation responses in the rodent brain that are influenced by access to food and leptin receptor function. The differences were most prominent in the hippocampus, which is a brain region that is increasingly being recognized as playing a central role in food behaviors and the superior colliculus which appears to modulate the saliency value of reinforcers and is therefore likely to mediate the enhanced value of food reinforcers as a function of deprivation. These findings have therapeutic implications since they suggest that interventions to restrict food access are likely to have different responses as a functions of genetic diversity and that a better understanding of this interaction is likely to lead to tailored interventions that maximize success in weight gain regimes.? IV. MECHANISMS UNDERLYING VULNERABILITY TO DRUG ABUSE & ADDICTION. The present study utilized a rodent chronic oral methylphenidate (MP) paradigm. Adolescent rats were divided into three treatment groups: vehicle, 2 mg/kg or 1mg/kg MP for 8 months. Rats were implanted with a jugular catheter and placed in operant test chambers for daily 1h cocaine (1mg/kg) sessions. Results showed that eight month treatment with oral MP decreased cocaine SA during adulthood which could reflect the increases in D2 availability observed (D2 increases are associated with reduced propensity for cocaine self administration). Two month MP treatment decreased D2 availability, which could raise concern that at this life stage short treatments could possibly increase vulnerability to drug abuse during adulthood. These findings indicate that MP effects in D2 expression in striatum are sensitive not only to length of treatment but also to the developmental stage at which treatment is given. Future studies will evaluating the effects of different lengths of MP treatment on drug self-administration are required to assess optimal duration of treatment regimes to minimize adverse effects on the propensity for drug use. This study submitted and accepted for publication in PBB.? -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 the SFN meeting. ? -The brains of the rats above were perfused and scanned with 17T MRI microscopy to assess structural and volumetric regional brain size between the MP treated and vehicle groups. The brain scans were completed analysis are in progress. ? -In a further study we are looking at the effects of D2 genotype on chronic ethanol drinking induced effects on cerebral and CSF volume using 9.4T MRI; as well as cb1, D3, D4 and DAT levels using ARG. The scans are completed and analysis in progress.
Showing the most recent 10 out of 21 publications
