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Previous research has suggested that schizotypal personality disorder (SPD), a condition that shares clinical and cognitive features with schizophrenia, may be associated with elevated striatal dopamine functioning; however, there are no published studies of dopamine release within subregions of the striatum in SPD. To characterize dopamine release capacity in striatal subregions and its relation to clinical and cognitive features in SPD. We used positron emission tomography with [11C]raclopride and an amphetamine challenge to measure dopamine D2-receptor availability (binding potential, BPND), and its percent change post-amphetamine (∆BPND) to index amphetamine-induced dopamine release, in subregions of the striatum in 16 SPD and 16 healthy control participants. SPD participants were evaluated with measures of schizotypal symptom severity and working memory. There were no significant group differences in BPND or ∆BPND in any striatal subregion or whole striatum. Among SPD participants, cognitive-perceptual symptoms were associated at trend level with ∆BPND in the ventral striatum, and disorganized symptoms were significantly negatively related to ∆BPND in several striatal subregions. In contrast to previous findings, SPD was not associated with elevated striatal dopamine release. However, in SPD, there was a moderate positive association between ventral striatal dopamine release and severity of cognitive-perceptual symptoms, and negative associations between striatal dopamine release and severity of disorganized symptoms. Future larger scale investigations that allow for the separate examination of subgroups of participants based on clinical presentation will be valuable in further elucidating striatal DA functioning in SPD.

Neuromelanin-sensitive MRI (NM-MRI) purports to detect the content of neuromelanin (NM), a product of dopamine metabolism that accumulates with age in dopamine neurons of the substantia nigra (SN). Interindividual variability in dopamine function may result in varying levels of NM accumulation in the SN; however, the ability of NM-MRI to measure dopamine function in nonneurodegenerative conditions has not been established. Here, we validated that NM-MRI signal intensity in postmortem midbrain specimens correlated with regional NM concentration even in the absence of neurodegeneration, a prerequisite for its use as a proxy for dopamine function. We then validated a voxelwise NM-MRI approach with sufficient anatomical sensitivity to resolve SN subregions. Using this approach and a multimodal dataset of molecular PET and fMRI data, we further showed the NM-MRI signal was related to both dopamine release in the dorsal striatum and resting blood flow within the SN. These results suggest that NM-MRI signal in the SN is a proxy for function of dopamine neurons in the nigrostriatal pathway. As a proof of concept for its clinical utility, we show that the NM-MRI signal correlated to severity of psychosis in schizophrenia and individuals at risk for schizophrenia, consistent with the well-established dysfunction of the nigrostriatal pathway in psychosis. Our results indicate that noninvasive NM-MRI is a promising tool that could have diverse research and clinical applications to investigate in vivo the role of dopamine in neuropsychiatric illness.

Working memory deficits in schizophrenia may be associated with impairments in the integration of neural activity across a distributed network of cortical areas. However, evaluation of the contribution of this integration to working memory impairments in patients is severely confounded by behavioral performance. In the present multidimensional-neuroimaging study, measures of neural oscillations at baseline and during a working memory task, baseline gamma-aminobutyric acid (GABA) level in the left dorsolateral prefrontal cortex (DLPFC), and behavioral performance were obtained. Controlling behavioral performance by recruiting only "high-performing" patients with schizophrenia, we investigated whether the strength of cross-area communications differs between patients with schizophrenia and healthy participants under accurate and equivalent behavioral performance. Results of phase-locking value indicated that these high-performing patients recruited significantly more between frontal and occipital regions in the left hemisphere, t(13) = -2.16, p = .05, Cohen's d = -1.20, and between frontal and temporal regions in the right hemisphere, t(13) = -2.63, p = .02, Cohen's d = -1.46. These cross-area communication patterns may be associated with visuoverbal and visuospatial working memory networks of the left and right hemispheres, respectively. Moreover, correlations of patient's cross-area communication with in vivo GABA levels of the left DLPFC revealed a significant positive relationship (r = .77, p = .04), demonstrating that the critical role of GABA functions in gamma band oscillations may go beyond local neuronal assemblies in the left DLPFC. Altogether, these exploratory findings point to the heterogeneity among schizophrenia patients and highlight the notion that high-performing patients may engage in potential compensatory mechanisms and may represent a subgroup of patients that may be categorically or dimensionally divergent in psychopathology.

We previously reported the rapid and robust clinical effects of ketamine versus saline infusions in a proof-of-concept crossover trial in unmedicated adults with obsessive-compulsive disorder (OCD). This study examined the concurrent neurochemical effects of ketamine versus saline infusions using proton magnetic resonance spectroscopy ((1)H MRS) during the clinical proof-of-concept crossover trial. Levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and the excitatory neurochemicals glutamate+glutamine (Glx) were acquired in the medial prefrontal cortex (MPFC), a region implicated in OCD pathology. Seventeen unmedicated OCD adults received two intravenous infusions at least 1 week apart, one of saline and one of ketamine, while lying supine in a 3.0 T GE MR scanner. The order of each infusion pair was randomized. Levels of GABA and Glx were measured in the MPFC before, during, and after each infusion and normalized to water (W). A mixed effects model found that MPFC GABA/W significantly increased over time in the ketamine compared with the saline infusion. In contrast, there were no significant differences in Glx/W between the ketamine and saline infusions. Together with earlier evidence of low cortical GABA in OCD, our findings suggest that models of OCD pathology should consider the role of GABAergic abnormalities in OCD symptomatology.

Glutamatergic signaling abnormalities in cortico-striatal circuits are hypothesized to lead to the repetitive thoughts and behaviors of obsessive-compulsive disorder (OCD). To test this hypothesis, studies have used proton magnetic resonance spectroscopy (1H MRS) to measure glutamatergic compounds in the striatum of individuals with OCD. However, no studies have used methods that could measure glutamate minimally contaminated by glutamine and γ-aminobutyric acid (GABA) in striatal subregions. Therefore, in this study, a proton MRS imaging (1H MRSI) technique with relatively high spatial resolution at 3.0 T was used to measure minimally contaminated glutamate levels in three striatal subregions (i.e., dorsal caudate, dorsal putamen, and ventral striatum) in 15 unmedicated adults with OCD and 16 matched healthy control subjects. No significant group differences in glutamate levels were found in any of the three striatal subregions. In contrast, a study in unmedicated pediatric OCD patients that measured glutamatergic compounds in the dorsal caudate by MRS at 1.5 T found significant elevations. Further studies are warranted to assess whether these discrepant MRS findings are due to differences in subject age or MRS methodology, or potentially are associated with glutamatergic gene variants implicated in OCD.

The last fifteen years have seen a great increase in our understanding of the role of glutamate in schizophrenia (SCZ). The glutamate hypothesis focuses on disturbances in brain glutamatergic pathways and impairment in signaling at glutamate receptors. Proton Magnetic Resonance Spectroscopy ((1)H-MRS) is an MR-based technique that affords investigators the ability to study glutamate function by measuring in vivo glutamatergic indices in the brains of individuals with SCZ. (1)H-MRS studies have been performed comparing glutamatergic levels of individuals with SCZ and healthy control subjects or studying the effect of antipsychotic medications on glutamatergic levels. In this article we summarize the results of these studies by brain region. We will review the contribution of (1)H-MRS studies to our knowledge about glutamatergic abnormalities in the brains of individuals with SCZ and discuss the implications for future research and clinical care.

Schizophrenia is associated with extensive neurocognitive and behavioral impairments. Studies indicate that N-acetylaspartate (NAA), a marker of neuronal integrity, and choline, a marker of cell membrane turnover and white matter integrity, may be altered in schizophrenia. Davunetide is a neurotrophic peptide that can enhance cognitive function in animal models of neurodegeneration. Davunetide has recently demonstrated modest functional improvement in a study of people with schizophrenia. In a subset of these subjects, proton magnetic resonance spectroscopy ((1)H-MRS) was conducted to explore the effects of davunetide on change in NAA/creatine (NAA/Cr) and choline/creatine (choline/Cr) over 12 weeks of treatment. Of 63 outpatients with schizophrenia who received randomized davunetide (5 and 30 mg/day) or placebo in the parent clinical trial, 18 successfully completed (1)H-MRS in dorsolateral prefrontal cortex (DLPFC) at baseline and at 12 weeks. Cognition was assessed using the MATRICS Consensus Cognitive Battery (MCCB). NAA/Cr was unchanged for combined high- and low-dose davunetide groups (N=11). NAA/Cr in the high-dose davunetide group (N=8) suggested a trend increase of 8.0% (P=0.072) over placebo (N=7). Choline/Cr for combined high- and low-dose davunetide groups suggested a 6.4% increase (P=0.069), while the high-dose group showed a 7.9% increase (P=0.040) over placebo. Baseline NAA/Cr correlated with the composite MCCB score (R=0.52, P=0.033), as did individual cognitive domains of attention/vigilance, verbal learning, and social cognition; however, neither metabolite correlated with functional capacity. In this exploratory study, 12 weeks of adjunctive davunetide appeared to produce modest increases in NAA/Cr and choline/Cr in DLPFC in people with schizophrenia. This is consistent with a potential neuroprotective mechanism for davunetide. The data also support use of MRS as a useful biomarker of baseline cognitive function in schizophrenia. Future clinical and preclinical studies are needed to fully define the mechanism of action and cognitive effects of davunetide in schizophrenia.

Endogenous dopamine (DA) levels at dopamine D2/3 receptors (D2/3 R) have been quantified in the living human brain using the agonist radiotracer [(11) C]-(+)-PHNO. As an agonist radiotracer, [(11) C]-(+)-PHNO is more sensitive to endogenous DA levels than antagonist radiotracers. We sought to determine the proportion of the variance in baseline [(11) C]-(+)-PHNO binding to D2/3 Rs which can be accounted for by variation in endogenous DA levels. This was done by computing the Pearson's coefficient for the correlation between baseline binding potential (BPND ) and the change in BPND after acute DA depletion, using previously published data. All correlations were inverse, and the proportion of the variance in baseline [(11) C]-(+)-PHNO BPND that can be accounted for by variation in endogenous DA levels across the striatal subregions ranged from 42-59%. These results indicate that lower baseline values of [(11) C]-(+)-PHNO BPND reflect greater stimulation by endogenous DA. To further validate this interpretation, we sought to examine whether these data could be used to estimate the dissociation constant (Kd) of DA at D2/3 R. In line with previous in vitro work, we estimated the in vivo Kd of DA to be around 20 nM. In summary, the agonist radiotracer [(11) C]-(+)-PHNO can detect the impact of endogenous DA levels at D2/3 R in the living human brain from a single baseline scan, and may be more sensitive to this impact than other commonly employed radiotracers.

Glutamatergic abnormalities in corticostriatal brain circuits are thought to underlie obsessive-compulsive disorder (OCD). Whether these abnormalities exist in adults with OCD is not clear. We used proton magnetic resonance spectroscopy (¹H MRS) to test our hypothesis that unmedicated adults with OCD have reduced glutamate plus glutamine (Glx) levels in the medial prefrontal cortex (MPFC) compared with healthy controls. Levels of γ-aminobutyric acid (GABA) were also explored. Twenty-four unmedicated adults with OCD and 22 matched healthy control subjects underwent ¹H MRS scans at 3.0 T. Resonances of both Glx and GABA were obtained using the standard J-editing technique and assessed as ratios relative to voxel tissue water (W) in the MPFC (the region of interest) and the dorsolateral prefrontal cortex (DLPFC) to explore the regional specificity of any finding. In the MPFC, Glx/W did not differ by diagnostic group (p=0.98) or sex (p=0.57). However, GABA/W was decreased in OCD (2.16±0.46 × 10⁻³) compared with healthy controls (2.43±0.45 × 10⁻³, p=0.045); moreover, age of OCD onset was inversely correlated with MPFC GABA/W (r=-0.50, p=0.015). MPFC GABA/W was higher in females than in males. In the DLPFC, there were no main effects of diagnosis or gender on Glx/W or GABA/W. These data indicate that unmedicated adults with OCD do not have Glx abnormalities in a MPFC voxel that includes the pregenual anterior cingulate cortex. However, they may have decreased MPFC GABA levels. How GABA abnormalities might contribute to corticostriatal dysfunction in OCD deserves further study.

3,4-Methylenedioxymethamphetamine (MDMA), the main psychoactive component of the recreational drug ecstasy, is a potent serotonin (5-HT) releaser. In animals, MDMA induces 5-HT depletion and toxicity in 5-HT neurons. The aim of this study was to investigate both presynaptic (5-HT transporter, SERT) and postsynaptic (5-HT(2A) receptor) markers of 5-HT transmission in recently abstinent chronic MDMA users compared with matched healthy controls. We hypothesized that MDMA use is associated with lower SERT density and concomitant upregulation of 5-HT(2A) receptors. Positron emission tomography studies using the SERT ligand [¹¹C]DASB and the 5-HT(2A) receptor ligand [¹¹C]MDL 100907 were evaluated in 13 current and recently detoxified MDMA users and 13 matched healthy controls. MDMA users reported a mean duration of ecstasy use of 8 years, regular exposure, and at least 2 weeks of abstinence before the scans. SERT and 5-HT(2A) receptor availability (binding potential, BP(ND)) were analyzed with a two-tissue compartment model with arterial input function. Current recreational MDMA use was significantly associated with lower SERT BP(ND) and higher 5-HT(2A) receptor BP(ND) in cortical, but not subcortical regions. Decreased SERT BP(ND) was regionally associated with upregulated 5-HT(2A) receptor BP(ND). In light of the animal literature, the most parsimonious interpretation is that repeated exposure to MDMA in humans, even in moderate amounts, leads to damage in 5-HT neuron terminals innervating the cortex. Alterations in mood, cognition, and impulse control associated with these changes might contribute to sustain MDMA use. The reversibility of these changes upon abstinence remains to be firmly established.

Background A decrease in dopamine type 2 receptors (D 2 ) and mesolimbic dopamine transmission predisposes animals to consume alcohol. This study measured D 2 receptors and dopamine transmission in human alcohol-dependent (AD) subjects using positron emission tomography (PET) and [ 11 C]raclopride. Methods Fifteen AD and 15 healthy control (HC) subjects were scanned before and after a psychostimulant challenge (amphetamine .3 mg/kg intravenous). The outcome measures for baseline D 2 receptor availability were binding potential (BP) and the equilibrium partition coefficient (V 3 ″). Amphetamine-induced [ 11 C]raclopride displacement was measured as the difference in V 3 ″ between the two scans. Results [ 11 C]raclopride BP was significantly reduced by 16.6% in the limbic striatum, 19.2% in the associative striatum, and 21.3% in the sensorimotor striatum in AD subjects compared with HC. The alcohol-dependent subjects showed a blunting of amphetamine-induced dopamine release in the limbic striatum: [ 11 C]raclopride displacement was −5.2% ± 3.6% in AD subjects compared with −13.0% ± 8.8% in HC. However, no significant difference in [ 11 C]raclopride displacement was seen in the associative (−4.6% ± 5.8% in AD subjects vs. −6.7 ± 5.4% in HC) and sensorimotor (−12.3% ± 7.3% in AD subjects vs. −13.7 ± 7.5% in HC) subdivisions of the striatum between the two groups. Conclusions Alcohol dependence was associated with a decrease in D 2 receptors in each striatal subdivision, whereas amphetamine-induced dopamine release was reduced in the limbic striatum only.

Background: The fundamental pathologic processes associated with schizophrenia remain uncertain. Objective: The goal of this article was to review imaging evidence suggesting that schizophrenia is associated with excessive stimulation of D 2 receptors, as well as imaging experiments supporting the hypothesis that this dysregulation might be secondary to N - methyl-d-aspartate (NMDA) dysfunction. Conclusions: Recent imaging data support the association of schizophrenia with a dopamine endophenotype involving excessive subcortical dopamine function. Animal and imaging data are consistent with the idea that this abnormality might be secondary to a synaptic disconnectivity involving the prefrontal cortex, which is well modeled by NMDA antagonist administration. In turn, this dopamine dysregulation might worsen synaptic connectivity and NMDA function. Thus, both glutamate/dopamine and dopamine/glutamate interactions may be relevant to schizophrenia pathophysiology and treatment. A deficit in glutamate transmission may lead to the dopamine endophenotype associated with this illness, and dopamine alterations in turn might exacerbate glutamate transmission deficits. The view that NMDA alterations are primary and dopamine alterations are secondary is probably oversimplistic, as both sets of abnormalities reinforce each other. A consequence of this general model is that direct intervention to support NMDA function might be beneficial as an augmentation strategy for the treatment of schizophrenia. Thus, it is proposed that schizophrenia is associated with strongly interconnected abnormalities of glutamate and dopamine transmission: NMDA hypofunction in the prefrontal cortex and its connections might generate a pattern of dysregulation of dopamine systems that, in turn, further weakens NMDA-mediated connectivity and plasticity.

Background Previous imaging studies demonstrated that schizophrenia is associated with increased amphetamine-induced dopamine (DA) release in the striatum, most pronounced during episodes of illness exacerbation. Schizotypal personality disorder (SPD) is a schizophrenia spectrum disorder, genetically related to schizophrenia. The goal of this study was to investigate striatal DA function in patients with SPD. Methods In our study, 13 SPD patients and 13 matched healthy control subjects underwent single photon emission computed tomography (SPECT) scan during bolus plus constant infusion of the D2/3 radiotracer [123I]iodobenzamide (IBZM). Striatal specific to nonspecific equilibrium partition coefficient (V3′′) was measured at baseline and following amphetamine administration (.3 mg/kg). Results No significant differences were observed in baseline V3′′ between groups. Amphetamine induced a larger decrease in [123I]IBZM V3′′ in SPD patients (−12 ± 5%) compared with control subjects (−7 ± 5%, p = .03). Conclusions The reduction in [123I]IBZM V3′′ induced by amphetamine in SPD was similar to that observed in remitted schizophrenia patients (−10 ± 9%, n = 17), but significantly lower than that observed during illness exacerbation (−24 ± 13%, n = 17). This suggests that DA dysregulation in schizophrenia spectrum disorders might have a trait component, present in remitted patients with schizophrenia and in SPD, and a state component, associated with psychotic exacerbations but not SPD.

Background Long-term behavioral, immunologic, and neurochemical alterations have been found in primates exposed to adverse early rearing. Methods Bonnet macaque ( Macaca radiata ) mother–infant dyads were exposed to uncertain requirements for food procurement (variable foraging demand, VFD) for a few months. Ten years later, these offspring and age- and gender-matched control subjects were studied using proton magnetic resonance spectroscopic imaging (MRSI). Results In anterior cingulate, VFD-reared subjects displayed significantly decreased N -acetylaspartate (NAA) resonance and significantly increased glutamate–glutamine–γ-aminobutyric acid (Glx) resonance relative to the stable neurometabolite creatine (Cr). Across all subjects, NAA/Cr and Glx/Cr ratios in the anterior cingulate were negatively correlated ( r = −.638, p = .014). In the medial temporal lobe, the ratio of choline-containing compounds to Cr was significantly increased in VFD subjects. Conclusions These findings indicate that adverse early rearing in primates has an enduring impact on adult MRSI measures considered reflective of neuronal integrity and metabolism, membrane structure and glial function, and cerebral glutamate content, and that these alterations occur in the same brain regions implicated in trauma-related psychiatric disorders.

In subjects with mood disorders, positron emission tomography (PET) with [(18)F]fluorodeoxyglucose has shown prefrontal cortical metabolism deficits, including in a subgenual region in subjects with familial illness. The authors applied a dl-fenfluramine challenge method to study metabolic response in this region to serotonergic challenge in familial major depression.The study group consisted of 19 depressed subjects with major depressive disorder or bipolar disorder, all of whom had at least one first-degree relative with history of major depression, and 10 healthy volunteers with similar age and gender distributions. PET images were acquired under placebo and challenge conditions, and volumetric MRI scans were also obtained. Group comparisons of metabolic and volumetric data were performed. Ratings of acute mood change during serotonergic challenge were compared with the imaging data.Within Brodmann's area 32, a glucose metabolism deficit in the depressed subjects on placebo day was observed by voxel-level analysis, but no volumetric deficit was found in the subgenual regions examined. Under challenge, both groups suppressed metabolism similarly. Within the patient group, the correlation between acute mood improvement during challenge and greater metabolic suppression approached significance.In familial mood disorders, a ventromedial prefrontal cortical deficit in baseline metabolism is not due to altered structural volume, and the response to serotonergic challenge appears predictive of acute mood response. The potential to predict treatment response can be tested by a combined challenge and treatment study.

BACKGROUND: Previous studies demonstrated increased striatal dopamine (DA) release after amphetamine challenge and increased striatal baseline occupancy of D2 receptors in patients with schizophrenia compared with control subjects. We report here on the relationship between these two aspects of DA release in drug-naïve patients with schizophrenia (SCZ) and matched healthy control subjects (HC). METHODS: Six drug-naïve SCZ and eight HC underwent single-photon emission computed tomography (SPECT) scans after bolus followed by constant infusion of (S)-(-)-3-[123I]iodo-2-hydroxy-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl]benzamide ([123I]IBZM) under three conditions to determine the equilibrium specific to non-displaceable binding potential (BP(ND)) for striatal D2 at baseline, after amphetamine administration and after DA depletion. RESULTS: Amphetamine induced decrease in BP(ND) was positively correlated with BP(ND) increase after DA depletion in SCZ (p = .02) but not in HC (p = .44). Additionally, both were significantly increased. CONCLUSIONS: In drug-naïve patients with schizophrenia but not in control subjects, stimulated and baseline DA release are both increased and positively correlated. At the neuronal level this association suggests that capacity for storage in presynaptic terminals, measured with the amphetamine paradigm, and baseline intrasynaptic DA release, measured with the alpha-methyl-para-tyrosine (alpha MPT) paradigm, are associated in schizophrenia, both consistent with increased midbrain DA cells activity

Binding competition between endogenous dopamine (DA) and the D2 receptor radiotracer [123I]IBZM allows measurement of the change in synaptic DA following amphetamine challenge with SPECT in the living human brain. Previous investigations using this technique in healthy subjects have shown that the magnitude of amphetamine effect on [123I]IBZM binding potential (BP) is small (range between 5 to 15% decrease), and that a large between-subject variability in this effect is observed. Therefore, it was unclear how much of the apparent between-subject variability was due to a low signal-to-noise ratio in the measurement, vs. true between-subject differences in the magnitude of the response. The goals of this investigation were to test the within-subject reproducibility and reliability of amphetamine-induced decrease in [123I]IBZM BP with a test/retest paradigm, and to establish the presence or absence of tolerance or sensitization to single administration ofi.v. amphetamine. Six healthy male subjects, never previously exposed to psychostimulants, twice underwent measurement of striatal amphetamine-induced DA release (between-measurement interval 16 +/- 10 days) using SPECT and the [123I]IBZM constant infusion technique. Results demonstrated an excellent within-subject reproducibility of amphetamine-induced DA release: amphetamine-induced decreases in [123I]IBZM BP were significant on each day, and had an intraclass correlation coefficient (ICC) of 0.89. Moreover, values from the second experiment were not significantly different from first experiment, suggesting the absence of either sensitization or tolerance to the effect of amphetamine on DA release in these experimental conditions. The subjective activation, as rated by the subjects on analog scales, was also highly reproducible. In conclusion, this scanning technique provides a reliable measurement of amphetamine-induced reduction of [123I]IBZM BP and enables detection of between-subject differences that appear stable over time.

(-)-N-(11)C-propyl-norapomorphine ((11)C-NPA) is a new dopamine agonist PET radiotracer that holds potential for imaging the high-affinity states of dopamine D(2)-like receptors in the living brain. The goal of this study was to develop and evaluate analytic strategies to derive in vivo (11)C-NPA binding parameters.Two baboons were scanned 4 times after (11)C-NPA injections. The metabolite-corrected arterial input functions were measured. Regional brain time-activity curves were analyzed with kinetic and graphical analyses, using the arterial time-activity curve as the input function. Data were also analyzed with the simplified reference-tissue model (SRTM) and graphical analysis with reference-region input.(11)C-NPA exhibited moderately fast metabolism, with 31% +/- 5% of arterial plasma concentration corresponding to the parent compound at 40 min after injection. Plasma clearance was 29 +/- 1 L/h, and plasma free fraction (f(1)) was 5% +/- 1%. For kinetic analysis, a 1-tissue compartment model (1TCM) provided a good fit to the data and more robust derivations of the tissue distribution volumes (V(T), in mL/g) than a 2-tissue compartment model (2TCM). Using 1TCM, V(T)s in the cerebellum and striatum were 3.4 +/- 0.4 and 7.5 +/- 2 mL/g, respectively, which led to estimates of striatal binding potential (BP) of 4.0 +/- 1.1 mL/g and striatal equilibrium specific-to-nonspecific partition coefficient (V(3)") of 1.2 +/- 0.2. V(T) values derived with graphical analysis were well correlated with but slightly lower than V(T) values derived with kinetic analysis. V(3)" values derived with SRTM were well correlated with but slightly higher than V(3)" values derived with kinetic analysis. Using any method, a significant difference was detected in BP and V(3)" values between the 2 animals. It was determined that 30 min of scanning data were sufficient to derive V(3)" values using kinetic, graphical (arterial input and reference-region input), and SRTM analyses.This study indicates that (11)C-NPA is a suitable PET tracer to quantify the agonist high-affinity sites of D(2)-like receptors.

A positive experience during a first encounter with a drug of abuse is predictive of subsequent use and might represent a vulnerability factor to develop addiction. This paper presents a meta-analysis of data acquired in 60 healthy volunteers who underwent a low-dose amphetamine challenge (0.3 mg/kg, i.v.) during imaging of dopamine D2 receptor availability with SPECT and the D2/D3 radiotracer [123I]IBZM. Amphetamine-stimulated DA release induced a small, significant and highly variable decrease in striatal D2 receptor availability (-8.3 +/- 6.7%). The magnitude of the decrease in D2 receptor availability was significantly associated with the positive reinforcing effects of the drug reported by the subject (r2 = 0.14, p = 0.003). Age was associated with decreased potency of dopamine to elicit positive reinforcing effects. This study indicates that both a large dopaminergic response and young age during a first encounter with a drug of abuse potential contribute to higher positive reinforcing effects.

D. Martinez1 °, M. Slifstein1, N. Nabulsi2, A. Grassetti1, N. Urban1, A. Perez1, F. Liu1, S. Lin2, J. Ropchan2, X. Mao3, L.S. Kegeles1, D. Shungu3, R.E. Carson4, Y. Huang2 1Columbia University, Department of Psychiatry, New York, USA; 2Yale University, Yale PET Center, New Haven, USA; 3Weill Medical College of Cornell University, Department of Radiology, New York, USA; 4Yale University, Yale PET Center, New York, USA

Postmortem studies have found evidence of γ-aminobutyric acid (GABA) deficits in fast-spiking, parvalbumin-positive interneurons in the prefrontal cortex in schizophrenia. Magnetic resonance spectroscopy studies in unmedicated patients have reported glutamine or glutamate-glutamine (Glx) elevations in this region. Abnormalities in these transmitters are thought to play a role in cognitive impairments in the illness.To measure GABA and Glx levels in vivo in 2 prefrontal brain regions in unmedicated and medicated patients with schizophrenia and healthy controls.Case-control study.Inpatient psychiatric research unit and associated outpatient clinic.Sixteen unmedicated patients with schizophrenia, 16 medicated patients, and 22 healthy controls matched for age, sex, ethnicity, parental socioeconomic status, and cigarette smoking.Proton magnetic resonance spectroscopy with a 3-T system and the J-edited spin-echo difference method. The GABA and Glx levels were measured in the dorsolateral and medial prefrontal cortex and normalized to the simultaneously acquired water signal. Working memory performance was assessed in all subjects.The GABA and Glx concentrations determined by proton magnetic resonance spectroscopy.In the medial prefrontal cortex region, 30% elevations were found in GABA (P = .02) and Glx (P = .03) levels in unmedicated patients compared with controls. There were no alterations in the medicated patients or in either group in the dorsolateral prefrontal cortex. Both regions showed correlations between GABA and Glx levels in patients and controls. No correlations with working memory performance were found.To our knowledge, this study presents the first GABA concentration measurements in unmedicated patients with schizophrenia, who showed elevations in both GABA and Glx levels in the medial prefrontal cortex but not the dorsolateral prefrontal cortex. Medicated patients did not show these elevations, suggesting possible normalization of levels with antipsychotic medication. The Glx elevations agree with prior magnetic resonance spectroscopy literature, but GABA elevations were unexpected and suggest possible involvement of classes of interneurons not found to show impairments in postmortem studies.

Analytic solutions to Maxwell’s equations in the Schwarzschild geometry are given. These are obtained by differentiating a single superpotential, which is valid (and bounded) at and everywhere outside the gravitational radius. The results have application to black‐hole and neutron‐star electrodynamics.