Metabolic Changes in the Rodent Brain after Acute Administration of Salvinorin AAbstractIntroductionMaterials and MethodsAnimalsMaterialsProtocolLocomotionImage AcquisitionPost Acquisition ProcessingSpatial PreprocessingStatistical Design and Analysis in SPMResults and DiscussionConclusionAcknowledgmentsReferencesB Academy of Molecular Imaging, 2009Published Online: 9 January 2009 DOI: 10.1007/s11307-008-0192-xMol Imaging Biol (2009) 11:137Y143BRIEF ARTICLEMetabolic Changes in the Rodent Brainafter Acute Administration of Salvinorin AJacob M. Hooker,1Vinal Patel,1Shiva Kothari,1Wynne K. Schiffer1Medical Department, Brookhaven National Laboratory, Upton, NY, 11973, USAAbstractPurpose: Salvinorin A (SA) is a potent and highly selective kappa-opioid receptor (KOR) agonistwith rapid kinetics and commensurate behavioral effects; however, brain regions associated withthese effects have not been determined.Procedures: Freely moving adult male rats were given SA intraperitoneally during uptake andtrapping of the brain metabolic radiotracer, 2-deoxy-2-[F-18]fluoro-D-glucose (FDG), followed byimage acquisition in a dedicated animal positron emission tomography (PET) system. Age-matchedcontrol animals received vehicle treatment. Animal behavior during FDG uptake was recordeddigitally and later analyzed for locomotion. Group differences in regional FDG uptake normalized towhole brain were determined using Statistical Parametric Mapping (SPM) and verified by region ofinterest (ROI) analysis.Results: SA-treated animals demonstrated significant increases in FDG uptake compared tocontrols in several brain regions associated with the distribution of KOR such as the periaqueductalgrey, 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 andhippocampus. 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 tothe potent κ-opioid agonist, salvinorin A. A major finding from our small animal PET studiesusing FDG was that neural circuits affected by SA may not be limited to direct activation orinhibition of kappa-receptor-expressing cells. Instead, salvinorin A may trigger brain circuits thatmediate the effects of the drug on cognition, mood, fear and anxiety, and motor output.Key words: Salvia, Salvinorin A, Kappa opioid, Hallucinogen, Positron emission tomographyIntroductionOpioid receptor ligands have a rich pharmacology, bothbeneficial and adverse, often controlling human per-ceptions of nociception, stress, and danger. Agonists actingat any of the three main classes of opioid receptors (μ, κ,orδ) throughout the c entral nervous system can cause analgesiaand are thus used clinically in pain management [1, 2]. Inaddition, due to their ability to modulate neurotransmitterrelease, causing euphoria or dysphoria, opioid ligands havegained attention in the management of mood d isordersincluding depression [ 3 , 4]. Of the three main classes, κ-opioid receptor (KOR) agonists appear to exhibit robustElectronic supplementary material The online version of this article(doi:10.1007/s11307-008-0192-x) contains supplementary material, whichis available to authorized users.Significance: Salvinorin A is the major psychoactive compound from Salviadivinorum and is a potent kappa-opioid receptor agonist. Owing to itshallucinogenic properties, abuse liability, and medicinal potential as akappa-agonist there has been a growing effort to characterize itsphysiological effects in rodents. Our manuscript describes our efforts tofurther inform how salvinorin A leads to behavioral (and physiological)changes in rodents. We have determined the regional differences (relative tocontrols) in glucose utilization in the brains of freely behaving rats afteracute administration of salvinorin A. Using FDG, we have mapped brainregions that are activated or deactivated as a result of the kappa agonist. Wefeel there will be an increasing need to systematically understand howaffinity, pharmacokinetics, and distribution influence behavior throughregional changes in brain activation. Our studies highlight the potential ofFDG with small animal PET to accomplish this.Correspondence to: Jacob M. Hooker; e-mail: [email protected]; Wynne K.Schiffer; e-mail: [email protected] with lower abuse potential [5, 8]. Consequently,there have been many research efforts focused on develop-ing selective KOR agonists not only for medicinal uses, butalso to study the KOR itself.One of the most selective KOR agonists known to datecomes from nature. Salvinorin A (SA), isolated from Salviadivinorum, and many of its semi-synthetic derivatives haveproved to be valuable tools to study the KOR system.Several reports have shown the in vivo study of SA, a potentand highly selective κ-opioid agonist [9], may provideinsight into the role of KORs in mediating both pain andmood [10 ]. These studies have interrogated the physiologicaland behavioral effects of SA, which has been increasinglyused as a legal hallucinogen [11]. While extremely lowdoses of SA may be rewarding [12, 13], doses above 0.1 mg/kg (i.p.) caused conditioned place aversion in rodents anddecreased extracellular dopamine in the striatum, consistentwith the effects of other κ-agonists [14, 15]. In addition,acute administration of SA increased the occurrence ofimmobility in the forced swim test and the threshold forintracranial self-stimulation [16, 17 ]. The antinociceptiveand sedative effects of SA were demonstrated in mice byobserving latency in the radiant heat tail flick assay [18, 19],decreased locomotion [14], impaired climbing behavior [20],and abdominal constriction test [21].The pharmacological effects of SA appear to be highlyspecific to the κ-opioid receptor as proposed by in vitrostudies [9]. This has been supported by successful blockadeof physiological and behavioral effects in vivo with KORantagonists, the use of KOR knockout mice [19], and KORdiscriminatory tests [22]. Of course, binding at the initial siteof action (i.e., the KOR) leads to many physiologicalchanges in the brain, notabl e for example in decreases instriatal dopamine. The downstream effects of SA on brainfunction (i.e., changes secondary to neuron firing) arelargely