In utero exposure to maternal anti-aquaporin-4 antibodies alters brain vasculature and neural dynamics in male mouse offspring.

The fetal brain is constantly exposed to maternal IgG before the formation of an effective blood-brain barrier (BBB). Here, we studied the consequences of fetal brain exposure to an antibody to the astrocytic protein aquaporin-4 (AQP4-IgG) in mice. AQP4-IgG was cloned from a patient with neuromyelitis optica spectrum disorder (NMOSD), an autoimmune disease that can affect women of childbearing age. We found that embryonic radial glia cells in neocortex express AQP4. These cells are critical for blood vessel and BBB formation through modulation of the WNT signaling pathway. Male fetuses exposed to AQP4-IgG had abnormal cortical vasculature and lower expression of WNT signaling molecules Wnt5a and Wnt7a. Positron emission tomography of adult male mice exposed in utero to AQP4-IgG revealed increased blood flow and BBB leakiness in the entorhinal cortex. Adult male mice exposed in utero to AQP4-IgG had abnormal cortical vessels, fewer dendritic spines in pyramidal and stellate neurons, and more S100ß+ astrocytes in the entorhinal cortex. Behaviorally, they showed impairments in the object-place memory task. Neural recordings indicated that their grid cell system, within the medial entorhinal cortex, did not map the local environment appropriately. Collectively, these data implicate in utero binding of AQP4-IgG to radial glia cells as a mechanism for alterations of the developing male brain and adds NMOSD to the conditions in which maternal IgG may cause persistent brain dysfunction in offspring.

Design and Mechanism of (S)-3-Amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic Acid, a Highly Potent γ-Aminobutyric Acid Aminotransferase Inactivator for the Treatment of Addiction.

γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system. Inhibition of GABA aminotransferase (GABA-AT), a pyridoxal 5'-phosphate (PLP)-dependent enzyme that degrades GABA, has been established as a possible strategy for the treatment of substance abuse. The raised GABA levels that occur as a consequence of this inhibition have been found to antagonize the rapid release of dopamine in the ventral striatum (nucleus accumbens) that follows an acute challenge by an addictive substance. In addition, increased GABA levels are also known to elicit an anticonvulsant effect in patients with epilepsy. We previously designed the mechanism-based inactivator (1S,3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (2), now called CPP-115, that is 186 times more efficient in inactivating GABA-AT than vigabatrin, the only FDA-approved drug that is an inactivator of GABA-AT. CPP-115 was found to have high therapeutic potential for the treatment of cocaine addiction and for a variety of epilepsies, has successfully completed a Phase I safety clinical trial, and was found to be effective in the treatment of infantile spasms (West syndrome). Herein we report the design, using molecular dynamics simulations, synthesis, and biological evaluation of a new mechanism-based inactivator, (S)-3-amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic acid (5), which was found to be almost 10 times more efficient as an inactivator of GABA-AT than CPP-115. We also present the unexpected crystal structure of 5 bound to GABA-AT, as well as computational analyses used to assist the structure elucidation process. Furthermore, 5 was found to have favorable pharmacokinetic properties and low off-target activities. In vivo studies in freely moving rats showed that 5 was dramatically superior to CPP-115 in suppressing the release of dopamine in the corpus striatum, which occurs subsequent to either an acute cocaine or nicotine challenge. Compound 5 also attenuated increased metabolic demands (neuronal glucose metabolism) in the hippocampus, a brain region that encodes spatial information concerning the environment in which an animal receives a reinforcing or aversive drug. This multidisciplinary computational design to preclinical efficacy approach should be applicable to the design and improvement of mechanism-based inhibitors of other enzymes whose crystal structures and inactivation mechanisms are known.

Levodopa-induced abnormal involuntary movements correlate with altered permeability of the blood-brain-barrier in the basal ganglia.

Chronic levodopa treatment leads to the appearance of dyskinesia in the majority of Parkinson's disease patients. Neurovascular dysregulation in putaminal and pallidal regions is thought to be an underlying feature of this complication of treatment. We used microPET to study unilaterally lesioned 6-hydroxydopamine rats that developed levodopa-induced abnormal involuntary movements (AIMs) after three weeks of drug treatment. Animals were scanned with [15O]-labeled water and [18F]-fluorodeoxyglucose, to map regional cerebral blood flow and glucose metabolism, and with [11C]-isoaminobutyric acid (AIB), to assess blood-brain-barrier (BBB) permeability, following separate injections of levodopa or saline. Multitracer scan data were acquired in each animal before initiating levodopa treatment, and again following the period of daily drug administration. Significant dissociation of vasomotor and metabolic levodopa responses was seen in the striatum/globus pallidus (GP) of the lesioned hemisphere. These changes were accompanied by nearby increases in [11C]-AIB uptake in the ipsilateral GP, which correlated with AIMs scores. Histopathological analysis revealed high levels of microvascular nestin immunoreactivity in the same region. The findings demonstrate that regional flow-metabolism dissociation and increased BBB permeability are simultaneously induced by levodopa within areas of active microvascular remodeling, and that such changes correlate with the severity of dyskinesia.

Imaging Sex Differences in Regional Brain Metabolism during Acute Opioid Withdrawal.

The rate of opioid overdose continues to rise, necessitating improved treatment options. Current therapeutic approaches rely on administration of either a blocking agent, such as naloxone, or chronic treatment with replacement drugs, including methadone and/or buprenorphine. Recent findings suggest that males and females respond to these treatments uniquely. In an effort to better understand this sex-specific variation in treatment efficacy, we investigated the effects of acute opioid withdrawal in male and female rats using 18FDG and microPET. These data demonstrate that acute opioid withdrawal produces metabolic alterations in brain regions associated with reward and drug dependence, namely corpus striatum, thalamic nuclei, septum, and frontal cortex. Furthermore, certain changes are unique to males. Specifically, males demonstrated increased metabolism in the anterior cingulate cortex and the ventral hippocampus (CA3) following acute opioid withdrawal. If males and females exhibit sex-specific changes in regional brain metabolism following acute opioid withdrawal, then perhaps it is not surprising that they respond to treatment differently.

Sex Differences in Regional Brain Glucose Metabolism Following Opioid Withdrawal and Replacement.

Methadone and buprenorphine are currently the most common pharmacological treatments for opioid dependence. Interestingly, the clinical response to these drugs appears to be sex specific. That is, females exhibit superior therapeutic efficacy, defined as extended periods of abstinence and longer time to relapse, compared with males. However, the underlying metabolic effects of opioid withdrawal and replacement have not been examined. Therefore, using 18FDG and microPET, we measured differences in regional brain glucose metabolism in males and females following morphine withdrawal and subsequent methadone or buprenorphine replacement. In both males and females, spontaneous opioid withdrawal altered glucose metabolism in regions associated with reward and drug dependence. Specifically, metabolic increases in the thalamus, as well as metabolic decreases in insular cortex and the periaqueductal gray, were noted. However, compared with males, females exhibited increased metabolism in the preoptic area, primary motor cortex, and the amygdala, and decreased metabolism in the caudate/putamen and medial geniculate nucleus. Methadone and buprenorphine initially abolished these changes uniformly, but subsequently produced their own regional metabolic alterations that varied by treatment and sex. Compared with sex-matched control animals undergoing spontaneous opioid withdrawal, male animals treated with methadone exhibited increased caudate/putamen metabolism, whereas buprenorphine produced increased ventral striatum and motor cortex metabolism in females, and increased ventral striatum and somatosensory cortex metabolism in males. Notably, when treatment effects were compared between sexes, methadone-treated females showed increased cingulate cortex metabolism, whereas buprenorphine-treated females showed decreased metabolism in cingulate cortex and increased metabolism in the globus pallidus. Perhaps the initial similarities in males and females underlie early therapeutic efficacy, whereas these posttreatment sex differences contribute to clinical treatment failure more commonly experienced by the former.

In vivo evaluation of IGF1R/IR PET ligand [18F]BMS-754807 in rodents.

In vivo evaluation of [18F]BMS-754807 binding in mice and rats using microPET and biodistribution methods is described herein. The radioligand shows consistent binding characteristics, in vivo, in both species. Early time frames of the microPET images and time activity curves of brain indicate poor penetration of the tracer across the blood brain barrier (BBB) in both species. However, microPET experiments in mice and rats show high binding of the radioligand outside the brain to heart, pancreas and muscle, the organs known for higher expression of IGF1R/1R. Biodistribution analysis 2h after injection of [18F]BMS-754807 in rats show negligible [18F]defluorination as reflected by the low bone uptake and clearance from blood. Overall, the data indicate that [18F]BMS-754807 can potentially be a radiotracer for the quantification of IGF1R/IR outside the brain using PET.

Dissociation of metabolic and hemodynamic levodopa responses in the 6-hydroxydopamine rat model.

Dissociation of vasomotor and metabolic responses to levodopa has been observed in human subjects with Parkinson's disease (PD) studied with PET and in autoradiograms from 6-hydroxydopamine (6-OHDA) rat. In both species, acute levodopa administration was associated with increases in basal ganglia cerebral blood flow (CBF) with concurrent reductions in cerebral metabolic rate (CMR) for glucose in the same brain regions. In this study, we used a novel dual-tracer microPET technique to measure CBF and CMR levodopa responses in the same animal. Rats with unilateral 6-OHDA or sham lesion underwent sequential 15O-water (H215O) and 18F-fluorodeoxyglucose (FDG) microPET to map CBF and CMR following the injection of levodopa or saline. A subset of animals was separately scanned under ketamine/xylazine and isoflurane to compare the effects of these anesthetics. Regardless of anesthetic agent, 6-OHDA animals exhibited significant dissociation of vasomotor (ΔCBF) and metabolic (ΔCMR) responses to levodopa, with stereotyped increases in CBF and reductions in CMR in the basal ganglia ipsilateral to the dopamine lesion. No significant changes were seen in sham-lesioned animals. These data faithfully recapitulate analogous dissociation effects observed previously in human PD subjects scanned sequentially during levodopa infusion. This approach may have utility in the assessment of new drugs targeting the exaggerated regional vasomotor responses seen in human PD and in experimental models of levodopa-induced dyskinesia.

A Novel Strategy for Attenuating Opioid Withdrawal in Neonates.

The rate of Neonatal Abstinence Syndrome (NAS) has drastically increased over the past decade. The average hospital expense per NAS patient has tripled, while the number of babies born to opioid-dependent mothers has increased to 5 in 1000 births. Current treatment options are limited to opioid replacement and tapering. Consequently, we examined the efficacy of prenatal, low-dose and short-term vigabatrin (γ-vinyl GABA, GVG) exposure for attenuating these symptoms as well as the metabolic changes observed in the brains of these animals upon reaching adolescence. Pregnant Sprague-Dawley rats were treated in one of four ways: 1) saline; 2) morphine alone; 3) morphine+GVG at 25 mg/kg; 4) morphine+GVG at 50 mg/kg. Morphine was administered throughout gestation, while GVG administration occurred only during the last 5 days of gestation. On post-natal day 1, naloxone-induced withdrawal behaviours were recorded in order to obtain a gross behaviour score. Approximately 28 days following birth, 18FDG microPET scans were obtained on these same animals (Groups 1, 2, and 4). Morphine-treated neonates demonstrated significantly higher withdrawal scores than saline controls. However, GVG at 50 but not 25 mg/kg/day significantly attenuated them. Upon reaching adolescence, morphine treated animals showed regionally specific changes in 18FDG uptake. Again, prenatal GVG exposure blocked them. These data demonstrate that low-dose, short-term prenatal GVG administration blocks naloxone-induced withdrawal in neonates. Taken together, these preliminary findings suggest that GVG may provide an alternative and long-lasting pharmacologic approach for the management of neonatal and adolescent symptoms associated with NAS.

18FDG-microPET and MR DTI findings in Tor1a+/- heterozygous knock-out mice.

TorsinA is an important protein in brain development, and plays a role in the regulation of neurite outgrowth and synaptic function. Patients with the most common form of genetic dystonia carry a mutation (DYT1) in one copy of the Tor1a gene, a 3-bp deletion, causing removal of a single glutamic acid from torsinA. Previous imaging studies have shown that abnormal cerebellar metabolism and damaged cerebello-thalamo-cortical pathway contribute to the pathophysiology of DYT1 dystonia. However, how a mutation in one copy of the Tor1a gene causes these abnormalities is not known. We studied Tor1a heterozygous knock-out mice in vivo with FDG-PET and ex vivo with diffusion tensor imaging. We found metabolic abnormalities in cerebellum, caudate-putamen, globus pallidus, sensorimotor cortex and subthalamic nucleus. We also found that FA was increased in caudate-putamen, sensorimotor cortex and brainstem. We compared our findings with a previous imaging study of the Tor1a knock-in mice. Our study suggested that having only one normal copy of Tor1a gene may be responsible for the metabolic abnormalities observed; having a copy of mutant Tor1a, on the other hand, may be responsible for white matter pathway damages seen in DYT1 dystonia subjects.

Regional brain metabolism in a murine systemic lupus erythematosus model.

Systemic lupus erythematosus (SLE) is characterized by multiorgan inflammation, neuropsychiatric disorders (NPSLE), and anti-nuclear antibodies. We previously identified a subset of anti-DNA antibodies (DNRAb) cross-reactive with the N-methyl-D-aspartate receptor, present in 30% to 40% of patients, able to enhance excitatory post-synaptic potentials and trigger neuronal apoptosis. DNRAb+ mice exhibit memory impairment or altered fear response, depending on whether the antibody penetrates the hippocampus or amygdala. Here, we used 18F-fluorodeoxyglucose (FDG) microPET to plot changes in brain metabolism after regional blood-brain barrier (BBB) breach. In DNRAb+ mice, metabolism declined at the site of BBB breach in the first 2 weeks and increased over the next 2 weeks. In contrast, DNRAb- mice exhibited metabolic increases in these regions over the 4 weeks after the insult. Memory impairment was present in DNRAb+ animals with hippocampal BBB breach and altered fear conditioning in DNRAb+ mice with amygdala BBB breach. In DNRAb+ mice, we observed an inverse relationship between neuron number and regional metabolism, while a positive correlation was observed in DNRAb- mice. These findings suggest that local metabolic alterations in this model take place through different mechanisms with distinct time courses, with important implications for the interpretation of imaging data in SLE subjects.

(1S, 3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (CPP-115), a potent γ-aminobutyric acid aminotransferase inactivator for the treatment of cocaine addiction.

Vigabatrin, a GABA aminotransferase (GABA-AT) inactivator, is used to treat infantile spasms and refractory complex partial seizures and is in clinical trials to treat addiction. We evaluated a novel GABA-AT inactivator (1S, 3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (CPP-115, compound 1) and observed that it does not exhibit other GABAergic or off-target activities and is rapidly and completely orally absorbed and eliminated. By use of in vivo microdialysis techniques in freely moving rats and microPET imaging techniques, 1 produced similar inhibition of cocaine-induced increases in extracellular dopamine and in synaptic dopamine in the nucleus accumbens at (1)/(300) to (1)/(600) the dose of vigabatrin. It also blocks expression of cocaine-induced conditioned place preference at a dose (1)/(300) that of vigabatrin. Electroretinographic (ERG) responses in rats treated with 1, at doses 20-40 times higher than those needed to treat addiction in rats, exhibited reductions in ERG responses, which were less than the reductions observed in rats treated with vigabatrin at the same dose needed to treat addiction in rats. In conclusion, 1 can be administered at significantly lower doses than vigabatrin, which suggests a potential new treatment for addiction with a significantly reduced risk of visual field defects.

PET imaging of thin objects: measuring the effects of positron range and partial-volume averaging in the leaf of Nicotiana tabacum.

INTRODUCTION: PET imaging in plants is receiving increased interest as a new strategy to measure plant responses to environmental stimuli and as a tool for phenotyping genetically engineered plants. PET imaging in plants, however, poses new challenges. In particular, the leaves of most plants are so thin that a large fraction of positrons emitted from PET isotopes ((18)F, (11)C, (13)N) escape while even state-of-the-art PET cameras have significant partial-volume errors for such thin objects. Although these limitations are acknowledged by researchers, little data have been published on them. METHODS: Here we measured the magnitude and distribution of escaping positrons from the leaf of Nicotiana tabacum for the radionuclides (18)F, (11)C and (13)N using a commercial small-animal PET scanner. Imaging results were compared to radionuclide concentrations measured from dissection and counting and to a Monte Carlo simulation using GATE (Geant4 Application for Tomographic Emission). RESULTS: Simulated and experimentally determined escape fractions were consistent. The fractions of positrons (mean±S.D.) escaping the leaf parenchyma were measured to be 59±1.1%, 64±4.4% and 67±1.9% for (18)F, (11)C and (13)N, respectively. Escape fractions were lower in thicker leaf areas like the midrib. Partial-volume averaging underestimated activity concentrations in the leaf blade by a factor of 10 to 15. CONCLUSIONS: The foregoing effects combine to yield PET images whose contrast does not reflect the actual activity concentrations. These errors can be largely corrected by integrating activity along the PET axis perpendicular to the leaf surface, including detection of escaped positrons, and calculating concentration using a measured leaf thickness.

Microglial ablation and lipopolysaccharide preconditioning affects pilocarpine-induced seizures in mice.

Activated microglia have been associated with neurodegeneration in patients and in animal models of Temporal Lobe Epilepsy (TLE), however their precise functions as neurotoxic or neuroprotective is a topic of significant investigation. To explore this, we examined the effects of pilocarpine-induced seizures in transgenic mice where microglia/macrophages were conditionally ablated. We found that unilateral ablation of microglia from the dorsal hippocampus did not alter acute seizure sensitivity. However, when this procedure was coupled with lipopolysaccharide (LPS) preconditioning (1 mg/kg given 24 h prior to acute seizure), we observed a significant pro-convulsant phenomenon. This effect was associated with lower metabolic activation in the ipsilateral hippocampus during acute seizures, and could be attributed to activity in the mossy fiber pathway. These findings reveal that preconditioning with LPS 24 h prior to seizure induction may have a protective effect which is abolished by unilateral hippocampal microglia/macrophage ablation.

Decreased serotonin levels associated with behavioral disinhibition in tissue plasminogen activator deficient (tPA-/-) mice.

Tissue Plasminogen Activator (tPA) is a serine protease expressed in different areas of the mammalian brain. It has been used clinically to dissolve clots and shown to have a role in neurodegeneration. Early studies suggested that tPA plays an important role in the processes of learning and memory, demonstrated at the level of behavior and synaptic plasticity. Herein, we extend the behavioral characterization of these mice to the related dimension of exploratory-related behavior using an extensive battery of behavioral tests as well as the neurotransmitter metabolism associated with the behavioral measures. Our results indicate a behavior tendency in these mice consistent with "impulsivity" or reduced exploratory inhibition. These patterns are accompanied by decreased levels of serotonin in several brain regions important in behavioral regulation in the tPA(-/-) mice compared to control animals. Systemic administration of fluoxetine reversed the behavioral disinhibition of tPA(-/-) mice, further supporting an important alteration in behavior regulation mediated by serotonin systems as underappreciated but important element of the behavioral phenotype of these animals.

Randomized, double-blind, placebo-controlled trial of vigabatrin for the treatment of cocaine dependence in Mexican parolees.

OBJECTIVE: Cocaine dependence is associated with severe medical, psychiatric, and social morbidity, but no pharmacotherapy is approved for its treatment in the United States. The atypical antiepileptic vigabatrin (gamma-vinyl gamma-aminobutyric acid [GABA]) has shown promise in animal studies and open-label trials. The purpose of the present study was to assess the efficacy of vigabatrin for short-term cocaine abstinence in cocaine-dependent individuals. METHOD: Participants were treatment seeking parolees who were actively using cocaine and had a history of cocaine dependence. Subjects were randomly assigned to a fixed titration of vigabatrin (N=50) or placebo (N=53) in a 9-week double-blind trial and 4-week follow-up assessment. Cocaine use was determined by directly observed urine toxicology testing twice weekly. The primary endpoint was full abstinence for the last 3 weeks of the trial. RESULTS: Full end-of-trial abstinence was achieved in 14 vigabatrin-treated subjects (28.0%) versus four subjects in the placebo arm (7.5%). Twelve subjects in the vigabatrin group and two subjects in the placebo group maintained abstinence through the follow-up period. The retention rate was 62.0% in the vigabatrin arm versus 41.5% in the placebo arm. Among subjects who reported prestudy alcohol use, vigabatrin, relative to placebo, was associated with superior self-reported full end-of-trial abstinence from alcohol (43.5% versus 6.3%). There were no differences between the two groups in drug craving, depressed mood, anxiety, or Clinical Global Impression scores, and no group differences in adverse effects emerged. CONCLUSIONS: This first randomized, double-blind, placebo-controlled trial supports the safety and efficacy of short-term vigabatrin treatment of cocaine dependence.

Cue-induced dopamine release predicts cocaine preference: positron emission tomography studies in freely moving rodents.

Positron emission tomography studies in drug-addicted patients have shown that exposure to drug-related cues increases striatal dopamine, which displaces binding of the D(2) ligand, [(11)C]-raclopride. However, it is not known if animals will also show cue-induced displacement of [(11)C]-raclopride binding. In this study, we use [(11)C]-raclopride imaging in awake rodents to capture cue-induced changes in dopamine release associated with the conditioned place preference model of drug craving. Ten animals were conditioned to receive cocaine in a contextually distinct environment from where they received saline. Following conditioning, each animal was tested for preference and then received two separate [(11)C]-raclopride scans. For each scan, animals were confined to the cocaine and/or the saline-paired environment for the first 25 min of uptake, after which they were anesthetized and scanned. [(11)C]-raclopride uptake in the saline-paired environment served as a within-animal control for uptake in the cocaine-paired environment. Cocaine produced a significant place preference (p = 0.004) and exposure to the cocaine-paired environment decreased [(11)C]-raclopride binding relative to the saline-paired environment in both the dorsal (20%; p < 0.002) and ventral striatum (22%; p < 0.05). The change in [(11)C]-raclopride binding correlated with preference in the ventral striatum (R(2) = -0.87; p = 0.003). In this region, animals who showed little or no preference exhibited little or no change in [(11)C]-raclopride binding in the cocaine-paired environment. This noninvasive procedure of monitoring neurochemical events in freely moving, behaving animals advances preclinical molecular imaging by interrogating the degree to which animal models reflect the human condition on multiple dimensions, both biological and behavioral.

Racemic gamma vinyl-GABA (R,S-GVG) blocks methamphetamine-triggered reinstatement of conditioned place preference.

Preventing relapse poses a significant challenge to the successful management of methamphetamine (METH) dependence. Although no effective medication currently exists for its treatment, racemic gamma vinyl-GABA (R,S-GVG, vigabatrin) shows enormous potential as it blocks both the neurochemical and behavioral effects of a variety of drugs, including METH, heroin, morphine, ethanol, nicotine, and cocaine. Using the reinstatement of a conditioned place preference (CPP) as an animal model of relapse, the present study specifically investigated the ability of an acute dose of R,S-GVG to block METH-triggered reinstatement of a METH-induced CPP. Animals acquired a METH CPP following a 20-day-period of conditioning, in which they received 10 pairings of alternating METH and saline injections. During conditioning, rats were assigned to one of four METH dosage groups: 1.0, 2.5, 5.0, or 10.0 mg/kg (i.p., n = 8/group). Animals in all dosage groups demonstrated a robust and consistent CPP. This CPP was subsequently extinguished in each dosage group with repeated saline administration. Upon extinction, all groups reinstated following an acute METH challenge. On the following day, an acute dose of R,S-GVG (300 mg/kg, i.p.) was administered 2.5 h prior to an identical METH challenge. R,S-GVG blocked METH-triggered reinstatement in all four groups. Given that drug re-exposure may potentiate relapse to drug-seeking behavior, the ability of R,S-GVG to block METH-triggered reinstatement offers further support for its use in the successful management of METH dependence.

Subchronic racemic gamma vinyl-GABA produces weight loss in Sprague Dawley and Zucker fatty rats.

Given the growing obesity epidemic, pressure to develop an effective pharmacologic treatment is mounting. Following the completion of a randomized, double-blind, placebo controlled trial as well as two small open label trials, gamma vinyl-GABA (GVG) has been shown to be safe and effective for treating cocaine and/or methamphetamine dependence. In an extension of these findings, the present study examined whether GVG could produce weight loss in adolescent as well as genetically obese animals. Specifically, adolescent Sprague Dawley and adolescent and adult Zucker fatty rats received GVG at various doses (75-300 mg/kg, i.p., racemic) for treatment periods lasting no longer than 14 consecutive days. GVG produced significant weight loss in a dose dependent fashion in all groups. These effects were marked, as average decreases of 12-20% of original body weight were observed. These findings suggest that GVG may be useful as a treatment for obesity. Further, that these results occurred in genetically obese animals offers the possibility that GVG may even help manage severe obesity resulting from binge-eating, a disorder involving food consumption in a pattern similar to the compulsive drug-seeking behavior observed in cocaine and methamphetamine dependent subjects.

Imaging dopamine release with Positron Emission Tomography (PET) and (11)C-raclopride in freely moving animals.

We investigated an imaging strategy that provides simultaneous measurements of radiotracer binding and behavior in awake, freely moving animals. In this strategy, animals are injected intravenously (i.v.) through a catheterized line and permitted to move freely for 30 min during uptake of the imaging agent, in this case 11C-raclopride. After this Awake Uptake period, animals are anesthetized and scanned for 25 min. We tested the utility of this strategy for measuring changes in striatal 11C-raclopride binding under control conditions (awake and freely moving in the home cage) and with several drug challenges: a loading dose of unlabeled raclopride, pretreatment with methamphetamine (METH) or pretreatment with gamma-vinyl-GABA [S+-GVG] followed by METH. An additional group of animals underwent a stress paradigm that we have previously shown increases brain dopamine. For drug challenge experiments, the change in 11C-raclopride binding was compared to data from animals that were anesthetized for the uptake period ("Anesthetized Uptake") and full time activity curves were used to calculate 11C-raclopride binding. Regardless of the drug treatment protocol, there was no difference in 11C-raclopride striatum to cerebellum ratio between the Awake versus the Anesthetized Uptake conditions. Awake and Anesthetized groups demonstrated over 90% occupancy of dopamine receptors with a loading dose of cold raclopride, both groups demonstrated approximately 30% reduction in 11C-raclopride binding from METH pretreatment and this effect was modulated to the same degree by GVG under both uptake conditions. Restraint during Awake Uptake decreased 11C-raclopride binding by 29%. These studies support a unique molecular imaging strategy in which radiotracer uptake occurs in freely moving animals, after which they are anesthetized and scanned. This imaging strategy extends the applicability of small animal PET to include functional neurotransmitter imaging and the neurochemical correlates of behavioral tasks.