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.

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.

Experimental protocols for behavioral imaging: seeing animal models of drug abuse in a new light.

Behavioral neuroimaging is a rapidly evolving discipline that represents a marriage between the fields of behavioral neuroscience and preclinical molecular imaging. This union highlights the changing role of imaging in translational research. Techniques developed for humans are now widely applied in the study of animal models of brain disorders such as drug addiction. Small animal or preclinical imaging allows us to interrogate core features of addiction from both behavioral and biological endpoints. Snapshots of brain activity allow us to better understand changes in brain function and behavior associated with initial drug exposure, the emergence of drug escalation, and repeated bouts of drug withdrawal and relapse. Here we review the development and validation of new behavioral imaging paradigms and several clinically relevant radiotracers used to capture dynamic molecular events in behaving animals. We will discuss ways in which behavioral imaging protocols can be optimized to increase throughput and quantitative methods. Finally, we discuss our experience with the practical aspects of behavioral neuroimaging, so investigators can utilize effective animal models to better understand the addicted brain and behavior.

Overexpression of extracellular superoxide dismutase has a protective role against hyperoxia-induced brain injury in neonatal mice.

There is increasing evidence that hyperoxia, particularly at the time of birth, may result in neurological injury, in particular to the susceptible vasculature of these tissues. This study was aimed at determining whether overexpression of extracellular superoxide dismutase (EC-SOD) is protective against brain injury induced by hyperoxia. Transgenic (TG) mice (with an extra copy of the human extracellular superoxide dismutase gene) and wild-type (WT) neonate mice were exposed to hyperoxia (95% of F(i) o(2) ) for 7 days after birth versus the control group in room air. Brain positron emission tomography (PET) scanning with fludeoxyglucose (FDG) isotope uptake was performed after exposure. To assess apoptosis induced by hyperoxia exposure, caspase 3 ELISA and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were performed. Quantitative western blot for the following inflammatory markers was performed: glial fibrillary acidic protein, ionized calcium-binding adaptor molecule 1, macrophage-inhibiting factor, and phospho-AMP-activated protein kinase. PET scanning with FDG isotope uptake showed significantly higher uptake in the WT hyperoxia neonate brain group (0.14 ± 0.03) than in both the TG group (0.09 ± 0.01) and the control group (0.08 ± 0.02) (P< 0.05). Histopathological investigation showed more apoptosis and dead neurons in hippocampus and cerebellum brain sections of WT neonate mice after exposure to hyperoxia than in TG mice; this finding was also confirmed by TUNEL staining. The caspase 3 assay confirmed the finding of more apoptosis in WT hyperoxia neonates (0.814 ± 0.112) than in the TG hyperoxic group (0.579 ± 0.144) (P < 0.05); this finding was also confirmed by TUNEL staining. Quantitative western blotting for the inflammatory and metabolic markers showed significantly higher expression in the WT group than in the TG and control groups. Thus, overexpression of EC-SOD in the neonate brain offers significant protection against hyperoxia-induced brain damage.

A linear model for estimation of neurotransmitter response profiles from dynamic PET data.

The parametric ntPET model (p-ntPET) estimates the kinetics of neurotransmitter release from dynamic PET data with receptor-ligand radiotracers. Here we introduce a linearization (lp-ntPET) that is computationally efficient and can be applied to single scan data. lp-ntPET employs a non-invasive reference region input function and extends the LSRRM of Alpert et al. (2003) using basis functions to characterize the time course of neurotransmitter activation. In simulation studies, the temporal precision of neurotransmitter profiles estimated by lp-ntPET was similar to that of p-ntPET (standard deviation ~3 min for responses early in the scan) while computation time was reduced by several orders of magnitude. Violations of model assumptions such as activation-induced changes in regional blood flow or specific binding in the reference tissue have negligible effects on lp-ntPET performance. Application of the lp-ntPET method is demonstrated on [11C]raclopride data acquired in rats receiving methamphetamine, which yielded estimated response functions that were in good agreement with simultaneous microdialysis measurements of extracellular dopamine concentration. These results demonstrate that lp-ntPET is a computationally efficient, linear variant of ntPET that can be applied to PET data from single or multiple scan designs to estimate the time course of neurotransmitter activation.

(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.

Cerebellothalamocortical pathway abnormalities in torsinA DYT1 knock-in mice.

The factors that determine symptom penetrance in inherited disease are poorly understood. Increasingly, magnetic resonance diffusion tensor imaging (DTI) and PET are used to separate alterations in brain structure and function that are linked to disease symptomatology from those linked to gene carrier status. One example is DYT1 dystonia, a dominantly inherited movement disorder characterized by sustained muscle contractions, postures, and/or involuntary movements. This form of dystonia is caused by a 3-bp deletion (i.e., ΔE) in the TOR1A gene that encodes torsinA. Carriers of the DYT1 dystonia mutation, even if clinically nonpenetrant, exhibit abnormalities in cerebellothalamocortical (CbTC) motor pathways. However, observations in human gene carriers may be confounded by variability in genetic background and age. To address this problem, we implemented a unique multimodal imaging strategy in a congenic line of DYT1 mutant mice that contain the ΔE mutation in the endogenous mouse torsinA allele (i.e., DYT1 knock-in). Heterozygous knock-in mice and littermate controls underwent microPET followed by ex vivo high-field DTI and tractographic analysis. Mutant mice, which do not display abnormal movements, exhibited significant CbTC tract changes as well as abnormalities in brainstem regions linking cerebellar and basal ganglia motor circuits highly similar to those identified in human nonmanifesting gene carriers. Moreover, metabolic activity in the sensorimotor cortex of these animals was closely correlated with individual measures of CbTC pathway integrity. These findings further link a selective brain circuit abnormality to gene carrier status and demonstrate that DYT1 mutant torsinA has similar effects in mice and humans.

Differential effects of anesthetics on cocaine's pharmacokinetic and pharmacodynamic effects in brain.

Most studies of the effect of cocaine on brain activity in laboratory animals are preformed under anesthesia, which could potentially affect the physiological responses to cocaine. Here we assessed the effects of two commonly used anesthetics [alpha-chloralose (alpha-CHLOR) and isofluorane (ISO)] on the effects of acute cocaine (1 mg/kg i.v.) on cerebral blood flow (CBF), cerebral blood volume (CBV), and tissue hemoglobin oxygenation (S(t)O(2)) using optical techniques and cocaine's pharmacokinetics (PK) and binding in the rat brain using (PET) and [(11)C]cocaine. We showed that acute cocaine at a dose abused by cocaine abusers decreased CBF, CBV and S(t)O(2) in rats anesthetized with ISO, whereas it increased these parameters in rats anesthetized with alpha-CHLOR. Importantly, in ISO-anesthetized animals cocaine-induced changes in CBF and S(t)O(2) were coupled, whereas for alpha-CHLOR these measures were uncoupled. Moreover, the clearance of [(11)C]cocaine from the brain was faster for ISO (peak half-clearance 15.8 +/- 2.8 min) than for alpha-CHLOR (27.5 +/- 0.6 min), and the ratio of specific to non-specific binding of [(11)C]cocaine in the brain was higher for ISO- (3.37 +/- 0.32) than for alpha-CHLOR-anesthetized rats (2.24 +/- 0.4). For both anesthetics, cocaine-induced changes in CBF followed the fast uptake of [(11)C]cocaine in the brain (peaking at approximately 2.5-4 min), but only for ISO did the duration of the CBV and S(t)O(2) changes correspond to the rate of [(11)C]cocaine's clearance from the brain. These results demonstrate that anesthetics influence cocaine's hemodynamic and metabolic changes in the brain, and its binding and PK, which highlights the need to better understand the interactions between anesthetics and pharmacological challenges in brain functional imaging studies.

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.

Metabolic changes in the rodent brain after acute administration of salvinorin A.

PURPOSE: Salvinorin A (SA) is a potent and highly selective kappa-opioid receptor (KOR) agonist with rapid kinetics and commensurate behavioral effects; however, brain regions associated with these effects have not been determined. PROCEDURES: Freely moving adult male rats were given SA intraperitoneally during uptake and trapping of the brain metabolic radiotracer, 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG), followed by image acquisition in a dedicated animal positron emission tomography (PET) system. Age-matched control animals received vehicle treatment. Animal behavior during FDG uptake was recorded digitally and later analyzed for locomotion. Group differences in regional FDG uptake normalized to whole brain were determined using Statistical Parametric Mapping (SPM) and verified by region of interest (ROI) analysis. RESULTS: SA-treated animals demonstrated significant increases in FDG uptake compared to controls in several brain regions associated with the distribution of KOR such as the periaqueductal grey, bed nucleus of the stria terminalis and the cerebellar vermis, as well as in the hypothalamus. Significant bilateral activations were also observed in the auditory, sensory, and frontal cortices. Regional decreases in metabolic demand were observed bilaterally in the dorsolateral striatum and hippocampus. Locomotor activity did not differ between SA and vehicle during FDG uptake. CONCLUSIONS: We have provided the first extensive maps of cerebral metabolic activation due to the potent kappa-opioid agonist, salvinorin A. A major finding from our small animal PET studies using FDG was that neural circuits affected by SA may not be limited to direct activation or inhibition of kappa-receptor-expressing cells. Instead, salvinorin A may trigger brain circuits that mediate the effects of the drug on cognition, mood, fear and anxiety, and motor output.

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.

Initial comparison of ntPET with microdialysis measurements of methamphetamine-induced dopamine release in rats: support for estimation of dopamine curves from PET data.

A recently introduced mathematical method for extracting temporal characteristics of neurotransmitter release from dynamic positron emission tomography (PET) data was tested. The method was developed with the hope that by uncovering temporal information about neurotransmitter (nt) dynamics in PET data, researchers could shed new light on mechanisms of psychiatric diseases such as drug abuse and its treatment. In this study, we apply our model-based method, "ntPET", to (11)C-raclopride PET scans of rats in which the dopaminergic response to a microinfusion of methamphetamine in one striatum was assayed simultaneously by microdialysis and PET. Uptake of (11)C-raclopride into the untreated contralateral striatum was used as an input to the ntPET model. Direct comparisons of the model-based ntPET analysis and the microdialysis measurements confirmed that ntPET produced dopamine curves that were very similar in timing (takeoff and peak times) to the microdialysis curves. Variances in takeoff and peak times were comparable for the two methods. Neither method detected a false dopamine response to drug in a control animal. The high degree of correspondence between ntPET estimates and microdialysis measurements lends strong support to the idea that temporal information regarding dopamine release exists in dynamic (11)C-raclopride PET data and that it can be estimated reliably via ntPET. The method is entirely translatable to human PET imaging.

Targeting the treatment of drug abuse with molecular imaging.

Although imaging studies in and of themselves have significant contributions to the study of human behavior, imaging in drug abuse has a much broader agenda. Drugs of abuse bind to molecules in specific parts of the brain in order to produce their effects. Positron emission tomography (PET) provides a unique opportunity to track this process, capturing the kinetics with which an abused compound is transported to its site of action. The specific examples discussed here were chosen to illustrate how PET can be used to map the regional distribution and kinetics of compounds that may or may not have abuse liability. We also discussed some morphological and functional changes associated with drug abuse and different stages of recovery following abstinence. PET measurements of functional changes in the brain have also led to the development of several treatment strategies, one of which is discussed in detail here. Information such as this becomes more than a matter of academic interest. Such knowledge can provide the bases for anticipating which compounds may be abused and which may not. It can also be used to identify biological markers or changes in brain function that are associated with progression from drug use to drug abuse and also to stage the recovery process. This new knowledge can guide legislative initiatives on the optimal duration of mandatory treatment stays, promoting long-lasting abstinence and greatly reducing the societal burden of drug abuse. Imaging can also give some insights into potential pharmacotherapeutic targets to manage the reinforcing effects of addictive compounds, as well as into protective strategies to minimize their toxic consequences.

A novel approach for imaging brain-behavior relationships in mice reveals unexpected metabolic patterns during seizures in the absence of tissue plasminogen activator.

Medically refractory seizures cause inflammation and neurodegeneration. Seizure initiation thresholds have been linked in mice to the serine protease tissue plasminogen activator (tPA); mice lacking tPA exhibit resistance to seizure induction, and the ensuing inflammation and neurodegeneration are similarly suppressed. Seizure foci in humans can be examined using PET employing 2-deoxy-2[(18)F]fluoro-d-glucose ((18)FDG) as a tracer to visualize metabolic dysfunction. However, there currently exist no such methods in mice to correlate measures of brain activation with behavior. Using a novel method for small animal PET data analysis, we examine patterns of (18)FDG uptake in wild-type and tPA(-/-) mice and find that they correlate with the severity of drug-induced seizure initiation. Furthermore, we report unexpected activations that may underlie the tPA modulation of seizure susceptibility. The methods described here should be applicable to other mouse models of human neurological disease.

Metabolic and behavioral deficits following a routine surgical procedure in rats.

To test the hypothesis that functional metabolic deficits observed following surgical brain injury are associated with changes in cognitive performance in rodents, we performed serial imaging studies in parallel with behavioral measures in control animals and in animals with surgical implants. Memory function was assessed using the novel object recognition (NOR) test, administered 3 days prior to and 3, 7, 14 and 56 days after surgery. At each time point, general locomotion was also measured. Metabolic imaging with 18F-fluorodeoxyglucose ([18F]FDG) occurred 28 and 58 days after surgery. Animals with surgical implants performed significantly worse on tests of object recognition, while general locomotion was unaffected by the implant. There was a significant decrease in glucose uptake after surgery in most of the hemisphere ipsilateral to the implant relative to the contralateral hemisphere. At both time points, the most significant metabolic deficits occurred in the primary motor cortex (-25%; p<0.001), sensory cortex (-15%, p<0.001) and frontal cortex (-12%; p<0.001). Ipsilateral areas further from the site of insertion became progressively worse, including the sensory cortex, dorsal striatum and thalamus. These data was supported by a voxel-based analysis of the PET data, which revealed again a unilateral decrease in [18F]FDG uptake that extended throughout the ipsilateral cortex and persisted for the duration of the 58-day study. Probe implantation in the striatum results in a widespread and long-lasting decline in cortical glucose metabolism together with a persistent, injury-related deficit in the performance of a cognitive (object recognition) task in rats.

Optimizing experimental protocols for quantitative behavioral imaging with 18F-FDG in rodents.

UNLABELLED: Small-animal PET provides the opportunity to image brain activation during behavioral tasks in animal models of human conditions. The present studies aimed to simplify behavioral imaging procedures without a loss of quantitation by using an intraperitoneal route of administration (no cannulation, no anesthesia) and using a standardized uptake value (SUV) to reduce scan duration. METHODS: Sixteen animals with carotid artery cannulations were studied with 18F-FDG small-animal PET accompanied by serial arterial blood sampling. Ten of these animals were anesthetized and were inside the tomograph during 18F-FDG uptake, whereas 6 animals were awake in their home cages and scanned after 60 min of uptake. Of the 10 anesthetized animals, 6 received intraperitoneal 18F-FDG, whereas 4 received intravenous 18F-FDG, and all 6 awake animals received intraperitoneal 18F-FDG. Intravenously injected animals were positioned far enough inside the tomograph to obtain region-of-interest-based measures from the heart and the brain. In all animals, a full arterial input function and plasma glucose levels were obtained. To establish the optimal time during 18F-FDG uptake for blood sampling when using an SUV, a Patlak kinetic model was used to derive absolute rates of glucose metabolism and compared with SUVs calculated using different plasma points from the arterial input function. RESULTS: A single plasma point taken at 60 min after injection for intraperitoneal injections or 45 min after injection for intravenous injections provides a sensitive index of glucose metabolic rate with the highest correlation with data obtained from a fully quantitative input function. CONCLUSION: These studies support an experimental protocol in which animals can receive the 18F-FDG tracer injection intraperitoneally, away from the small-animal tomograph and with minimal impact on behavior. Further, animals can occupy the tomograph bed for a 10- to 30-min scan with a consequent increase in animal throughput.

Metabolic correlates of toluene abuse: decline and recovery of function in adolescent animals.

RATIONALE: Children and adolescents will readily abuse household products that contain solvents such as toluene. It is likely that reinforcing exposures to toluene alter brain glucose metabolism. OBJECTIVE: Using an animal model of drug reinforcement, we sought to identify a metabolic signature of toluene abuse in the adolescent rodent brain. Small animal PET (microPET), in combination with the glucose analog radiotracer, (18)FDG, were used to evaluate the metabolic consequences of inhaled toluene. METHODS: The exposure protocol paralleled our previously established method for assessing the conditioned reinforcing effects of toluene (5,000 ppm) using the conditioned place preference (CPP) paradigm. Animals were scanned at baseline and 2 h after the last exposure. Follow-up (18)FDG scans occurred 1 day, 3 weeks, and 2 months later. RESULTS: After six pairings, 38% of the animals preferred the toluene paired chamber and 25% were averse. The immediate metabolic effect in toluene-exposed animals was a 20% decline in whole brain (18)FDG uptake. Twenty-four hours following the last exposure, the whole brain decline was 40%, and 2 months later, the decline was 30% of pretoluene levels. A region-by-region analysis demonstrated significant additional decreases in the pons, cerebellum, striatum, midbrain, temporal cortex, and hippocampus. Two months after toluene cessation, regions of complete metabolic recovery were the thalamus and cerebellum; however, the temporal cortex did not recover. CONCLUSIONS: Brain uptake of (18)FDG appears to be a useful tool for examining the metabolic impact of toluene abuse, which include a profound decline followed by region-specific recovery after cessation.