Dopamine transporter silencing in the rat: systems-level alterations in striato-cerebellar and prefrontal-midbrain circuits.

Silencing of dopamine transporter (DAT), a main controlling factor of dopaminergic signaling, results in biochemical and behavioral features characteristic for neuropsychiatric diseases with presumed hyperdopaminergia including schizophrenia, attention deficit hyperactivity disorder (ADHD), bipolar disorder, and obsessive-compulsive disorder (OCD). Investigation of DAT silencing thus provides a transdiagnostic approach towards a systems-level understanding of common underlying pathways. Using a high-field multimodal imaging approach and a highly sensitive cryogenic coil, we integrated structural, functional and metabolic investigations in tandem with behavioral assessments on a newly developed preclinical rat model, comparing DAT homozygous knockout (DAT-KO, N = 14), heterozygous knockout (N = 8) and wild-type male rats (N = 14). We identified spatially distributed structural and functional brain alterations encompassing motor, limbic and associative loops that demonstrated strong behavioral relevance and were highly consistent across imaging modalities. DAT-KO rats manifested pronounced volume loss in the dorsal striatum, negatively correlating with cerebellar volume increase. These alterations were associated with hyperlocomotion, repetitive behavior and loss of efficient functional small-world organization. Further, prefrontal and midbrain regions manifested opposite changes in functional connectivity and local network topology. These prefrontal disturbances were corroborated by elevated myo-inositol levels and increased volume. To conclude, our imaging genetics approach provides multimodal evidence for prefrontal-midbrain decoupling and striato-cerebellar neuroplastic compensation as two key features of constitutive DAT blockade, proposing them as transdiagnostic mechanisms of hyperdopaminergia. Thus, our study connects developmental DAT blockade to systems-level brain changes, underlying impaired action inhibition control and resulting in motor hyperactivity and compulsive-like features relevant for ADHD, schizophrenia and OCD.

TRIAC Treatment Improves Impaired Brain Network Function and White Matter Loss in Thyroid Hormone Transporter Mct8/Oatp1c1 Deficient Mice.

Dysfunctions of the thyroid hormone (TH) transporting monocarboxylate transporter MCT8 lead to a complex X-linked syndrome with abnormal serum TH concentrations and prominent neuropsychiatric symptoms (Allan-Herndon-Dudley syndrome, AHDS). The key features of AHDS are replicated in double knockout mice lacking MCT8 and organic anion transporting protein OATP1C1 (Mct8/Oatp1c1 DKO). In this study, we characterize impairments of brain structure and function in Mct8/Oatp1c1 DKO mice using multimodal magnetic resonance imaging (MRI) and assess the potential of the TH analogue 3,3',5-triiodothyroacetic acid (TRIAC) to rescue this phenotype. Structural and functional MRI were performed in 11-weeks-old male Mct8/Oatp1c1 DKO mice (N = 10), wild type controls (N = 7) and Mct8/Oatp1c1 DKO mice (N = 13) that were injected with TRIAC (400 ng/g bw s.c.) daily during the first three postnatal weeks. Grey and white matter volume were broadly reduced in Mct8/Oatp1c1 DKO mice. TRIAC treatment could significantly improve white matter thinning but did not affect grey matter loss. Network-based statistic showed a wide-spread increase of functional connectivity, while graph analysis revealed an impairment of small-worldness and whole-brain segregation in Mct8/Oatp1c1 DKO mice. Both functional deficits could be substantially ameliorated by TRIAC treatment. Our study demonstrates prominent structural and functional brain alterations in Mct8/Oatp1c1 DKO mice that may underlie the psychomotor deficiencies in AHDS. Additionally, we provide preclinical evidence that early-life TRIAC treatment improves white matter loss and brain network dysfunctions associated with TH transporter deficiency.

Differential resting-state patterns across networks are spatially associated with Comt and Trmt2a gene expression patterns in a mouse model of 22q11.2 deletion.

Copy number variations (CNV) involving multiple genes are ideal models to study polygenic neuropsychiatric disorders. Since 22q11.2 deletion is regarded as the most important single genetic risk factor for developing schizophrenia, characterizing the effects of this CNV on neural networks offers a unique avenue towards delineating polygenic interactions conferring risk for the disorder. We used a Df(h22q11)/+ mouse model of human 22q11.2 deletion to dissect gene expression patterns that would spatially overlap with differential resting-state functional connectivity (FC) patterns in this model (N = 12 Df(h22q11)/+ mice, N = 10 littermate controls). To confirm the translational relevance of our findings, we analyzed tissue samples from schizophrenia patients and healthy controls using machine learning to explore whether identified genes were co-expressed in humans. Additionally, we employed the STRING protein-protein interaction database to identify potential interactions between genes spatially associated with hypo- or hyper-FC. We found significant associations between differential resting-state connectivity and spatial gene expression patterns for both hypo- and hyper-FC. Two genes, Comt and Trmt2a, were consistently over-expressed across all networks. An analysis of human datasets pointed to a disrupted co-expression of these two genes in the brain in schizophrenia patients, but not in healthy controls. Our findings suggest that COMT and TRMT2A form a core genetic component implicated in differential resting-state connectivity patterns in the 22q11.2 deletion. A disruption of their co-expression in schizophrenia patients points out a prospective cause for the aberrance of brain networks communication in 22q11.2 deletion syndrome on a molecular level.

Interactive tool to create adjustable anatomical atlases for mouse brain imaging.

OBJECTIVE: Brain atlases are important research tools enabling researchers to focus their investigations on specific anatomically defined brain regions and are used in many MRI applications, e.g. in fMRI, morphometry, whole brain spectroscopy, et cetera. Despite their extensive use and numerous versions they usually consist of predefined rigid brain regions with a given level of detail often degrading them to a non-ideal tool in special research topics. RESULT: To overcome this intrinsic weakness we present a graphical user interface application which allows researchers to easily create mouse brain atlases with an adjustable user-defined level of detail and coverage to match specific research questions.

Common functional networks in the mouse brain revealed by multi-centre resting-state fMRI analysis.

Preclinical applications of resting-state functional magnetic resonance imaging (rsfMRI) offer the possibility to non-invasively probe whole-brain network dynamics and to investigate the determinants of altered network signatures observed in human studies. Mouse rsfMRI has been increasingly adopted by numerous laboratories worldwide. Here we describe a multi-centre comparison of 17 mouse rsfMRI datasets via a common image processing and analysis pipeline. Despite prominent cross-laboratory differences in equipment and imaging procedures, we report the reproducible identification of several large-scale resting-state networks (RSN), including a mouse default-mode network, in the majority of datasets. A combination of factors was associated with enhanced reproducibility in functional connectivity parameter estimation, including animal handling procedures and equipment performance. RSN spatial specificity was enhanced in datasets acquired at higher field strength, with cryoprobes, in ventilated animals, and under medetomidine-isoflurane combination sedation. Our work describes a set of representative RSNs in the mouse brain and highlights key experimental parameters that can critically guide the design and analysis of future rodent rsfMRI investigations.

In vivo structural imaging in rats reveals neuroanatomical correlates of behavioral sub-dimensions of cocaine addiction.

Cocaine addiction is a multi-dimensional behavioral disorder characterized by a loss of control over cocaine taking despite of detrimental consequences. Structural MRI studies have revealed association between cocaine consumption and gray matter volume (GMV) in cocaine-addicted patients. However, the behavioral correlates of GMV in cocaine addiction are poorly understood. Here, we used a DSM-IV-based rat model of cocaine addiction with high face validity for structural imaging. According to three behavioral sub-dimensions of addiction, rats were separated into two groups showing either addict-like or non-addict-like behavior. These behavioral sub-dimensions were (1) the inability to refrain from drug-seeking and taking, (2) high motivation for the drug, and (3) maintained drug use despite negative consequences. In these rats, we performed structural MRI with voxel-based morphometry and analyzed the interaction of GMV with behavioral sub-dimensions in cocaine-addicted rats. Our major findings are that GMV differentially correlate with the inability to refrain from drug-seeking and taking in addict-like and non-addict-like rats within the somatosensory cortices and the amygdala. High motivation for the drug differentially correlates with GMV in addict-like and non-addict-like rats within the medial prefrontal cortex, and maintained drug use despite negative consequences differentially correlates with GMV in these two groups of rats within the periaqueductal gray. Our results demonstrate that the behavioral differences characterizing addict-like and non-addict-like rats in each behavioral sub-dimension of addiction are reflected by divergent covariance with GMV. We conclude that structural imaging provides specific neuroanatomical correlates of behavioral sub-dimensions of addiction.

Negative Association Between MR-Spectroscopic Glutamate Markers and Gray Matter Volume After Alcohol Withdrawal in the Hippocampus: A Translational Study in Humans and Rats.

BACKGROUND: Both chronic alcohol consumption and alcohol withdrawal lead to neural tissue damage which partly recovers during abstinence. This study investigated withdrawal-associated changes in glutamatergic compounds, markers of neuronal integrity, and gray matter volumes during acute alcohol withdrawal in the hippocampus, a key region in development and maintenance of alcohol dependence in humans and rats. METHODS: Alcohol-dependent patients (N = 39) underwent magnetic resonance imaging (MRI) and MR spectroscopy (MRS) measurements within 24 hours after the last drink and after 2 weeks of abstinence. MRI and MRS data of healthy controls (N = 34) were acquired once. Our thorough quality criteria resulted in N = 15 available spectra from the first and of N = 21 from the second measurement in patients, and of N = 19 from healthy controls. In a translational approach, chronic intermittent ethanol-exposed rats and respective controls (8/group) underwent 5 MRS measurements covering baseline, intoxication, 12 and 60 hours of withdrawal, and 3 weeks of abstinence. RESULTS: In both species, higher levels of markers of glutamatergic metabolism were associated with lower gray matter volumes in the hippocampus in early abstinence. Trends of reduced N-acetylaspartate levels during intoxication persisted in patients with severe alcohol withdrawal symptoms over 2 weeks of abstinence. We observed a higher ratio of glutamate to glutamine during alcohol withdrawal in our animal model. CONCLUSIONS: Due to limited statistical power, we regard the results as preliminary and discuss them in the framework of the hypothesis of withdrawal-induced hyperglutamatergic neurotoxicity, alcohol-induced neural changes, and training-associated effects of abstinence on hippocampal tissue integrity.

Influence of regional cerebral blood volume on voxel-based morphometry.

The investigation of structural brain alterations is one focus in research of brain diseases like depression. Voxel-based morphometry (VBM) based on high-resolution 3D MRI images is a widely used non-invasive tool for such investigations. However, the result of VBM might be sensitive to local physiological parameters such as regional cerebral blood volume (rCBV) changes. In order to investigate whether rCBV changes may contribute to variation in VBM, we performed analyses in a study with the congenital learned helplessness (cLH) model for long-term findings. The 3D structural and rCBV data were acquired with T2 -weighted rapid acquisition with relaxation enhancement (RARE) pulse sequences. The group effects were determined by standard statistical parametric mapping (SPM) and biological parametric mapping (BPM) and examined further using atlas-based regions. In our genetic animal model of depression, we found co-occurrence of differences in gray matter volume and rCBV, while there was no evidence of significant interaction between both. However, the multimodal analysis showed similar gray matter differences compared with the standard VBM approach. Our data corroborate the idea that two group VBM differences might not be influenced by rCBV differences in genetically different strains. Copyright © 2016 John Wiley & Sons, Ltd.

Restricted vs. unrestricted wheel running in mice: Effects on brain, behavior and endocannabinoids.

Beneficial effects of voluntary wheel running on hippocampal neurogenesis, morphology and hippocampal-dependent behavior have widely been studied in rodents, but also serious side effects and similarities to stereotypy have been reported. Some mouse strains run excessively when equipped with running wheels, complicating the comparability to human exercise regimes. Here, we investigated how exercise restriction to 6h/day affects hippocampal morphology and metabolism, stereotypic and basal behaviors, as well as the endocannabinoid system in wheel running C57BL/6 mice; the strain most commonly used for behavioral analyses and psychiatric disease models. Restricted and unrestricted wheel running had similar effects on immature hippocampal neuron numbers, thermoregulatory nest building and basal home-cage behaviors. Surprisingly, hippocampal gray matter volume, assessed with magnetic resonance (MR) imaging at 9.4 Tesla, was only increased in unrestricted but not in restricted runners. Moreover, unrestricted runners showed less stereotypic behavior than restricted runners did. However, after blockage of running wheels for 24h stereotypic behavior also increased in unrestricted runners, arguing against a long-term effect of wheel running on stereotypic behavior. Stereotypic behaviors correlated with frontal glutamate and glucose levels assessed by 1H-MR spectroscopy. While acute running increased plasma levels of the endocannabinoid anandamide in former studies in mice and humans, we found an inverse correlation of anandamide with the daily running distance after long-term running. In conclusion, although there are some diverging effects of restricted and unrestricted running on brain and behavior, restricted running does not per se seem to be a better animal model for aerobic exercise in mice.

31P RINEPT MRSI and VBM reveal alterations in brain aging associated with major depression.

PURPOSE: Phosphomono- and diesters, the major components of the choline peak in (1) H magnetic resonance spectroscopy, are associated with membrane anabolic and catabolic mechanisms. With the refocused insensitive nuclei-enhanced polarization transfer technique, these phospholipids are edited and enhanced in the (31) P MR spectrum. In depressed patients, alterations of the choline peak and cerebral volume have been found, indicating a possible relation. Thus, combining MR phosphorous spectroscopy and volumetry in depressed patients seems to be a promising approach to detect underlying pathomechanisms. METHODS: Depressed in-patients were either treated with antidepressive medication or with electroconvulsive therapy and compared to matched healthy controls. (31) P magnetic resonance spectroscopy imaging was conducted before and after the treatment phases. A 3D MRI dataset for volumetry was acquired in a dedicated (1) H head coil. RESULTS: Phosphocholine and phosphoethanolamine were increased in depressed patients. Though patients responded to the treatments, phospholipids were not significantly altered. An increased age-related gray matter loss in fronto-limbic regions along with an altered relation of phosphomonoesters/phosphodiesters with age were found in depressed patients. DISCUSSION: The findings of increased phosphomonoesthers and an age*group interaction for gray matter volumes need further research to define the role of phospholipids in major depression and possible associations to gray matter loss.

Recreational alcohol use induces changes in the concentrations of choline-containing compounds and total creatine in the brain: a (1)H MRS study of healthy subjects.

OBJECTIVE: It has previously been reported that even social alcohol consumption affects the magnetic resonance spectroscopy (MRS) signals of choline-containing compounds (tCho). The purpose of this study was to investigate whether the consumption of alcohol affects the concentrations of the metabolites tCho, N-acetylaspartate, creatine, or myo-inositol and/or their T 2 relaxation times. MATERIALS AND METHODS: (1)H MR spectra were obtained at 3 T from a frontal white matter voxel of 25 healthy subjects with social alcohol consumption (between 0 and 25.9 g/day). Absolute brain metabolite concentrations and T 2 relaxation times of metabolites were examined via MRS measurements at different echo times. Metabolite concentrations and their T 2 relaxation times were correlated with subjects' alcohol consumption, controlling for age. RESULTS: We observed positive correlations of absolute tCho and phosphocreatine and creatine (tCr) concentrations with alcohol consumption but no correlation between any metabolite T 2 relaxation time and alcohol consumption. CONCLUSIONS: This study shows that even social alcohol consumption affects the concentrations of tCho and tCr in cerebral white matter. Future studies assessing brain tCho and tCr levels should control for the confounding factor alcohol consumption.

Exercise boosts hippocampal volume by preventing early age-related gray matter loss.

Recently, a larger hippocampus was found in exercising mice and men. Here we studied the morphological underpinnings in wheel running mice by longitudinal magnetic resonance imaging. Voxel-based morphometry revealed that running increases hippocampal volume by inhibiting an early age-related gray matter loss. Disruption of neurogenesis-related neuroplasticity by focalized irradiation is sufficient to block positive effects of exercise on macroscopic brain morphology.

Effects of normal aging and SCN1A risk-gene expression on brain metabolites: evidence for an association between SCN1A and myo-inositol.

Previously reported MRS findings in the aging brain include lower N-acetylaspartate (NAA) and higher myo-inositol (mI), total creatine (Cr) and choline-containing compound (Cho) concentrations. Alterations in the sodium channel voltage gated type I, alpha subunit SCN1A variant rs10930201 have been reported to be associated with several neurological disorders with cognitive deficits. MRS studies in SCN1A-related diseases have reported striking differences in the mI concentrations between patients and controls. In a study on 'healthy aging', we investigated metabolite spectra in a sample of 83 healthy volunteers and determined their age dependence. We also investigated a potential link between SCN1A and mI. We observed a significantly negative association of NAA (p = 0.004) and significantly positive associations of mI (p ≤ 0.001), Cr (p ≤ 0.001) and Cho (p = 0.034) with age in frontal white matter. The linear association of Cho ends at the age of about 50 years and is followed by an inverted 'U'-shaped curve. Further, mI was higher in C allele carriers of the SCN1A variant rs10930201. Our results corroborated the age-related changes in metabolite concentrations, and found evidence for a link between SCN1A and frontal white matter mI in healthy subjects.

Advantages and challenges of small animal magnetic resonance imaging as a translational tool.

The utilization of magnetic resonance imaging (MRI) methods in rodent models of psychiatric disorders provides considerable benefits for the identification of disease-associated brain circuits and metabolic changes. In this review, we discuss advantages and challenges of animal MRI and provide an overview of the major structural (voxel-based morphometry and diffusion tensor imaging) and functional approaches [resting-state functional MRI (rs-fMRI), MR spectroscopy (MRS), regional cerebral blood volume measurement and arterial spin labelling] that are applied in animal MRI research. The review mainly focuses on rs-fMRI and MRS. Finally, we take a look at some recent developments and refinements in the field.

Loss of control of alcohol use and severity of alcohol dependence in non-treatment-seeking heavy drinkers are related to lower glutamate in frontal white matter.

BACKGROUND: The development and maintenance of alcohol use disorders (AUD) have been hypothesized to be associated with an imbalance of glutamate (GLU) homeostasis. White matter (WM) loss, especially in anterior brain regions, has been reported in alcohol dependence, which may involve disturbances in both myelin and axonal integrity. Frontal lobe dysfunction plays an important role in addiction, because it is suggested to be associated with the loss of control over substance use. This study investigated magnetic resonance spectroscopy (MRS)-detectable Glu levels in frontal WM of non-treatment-seeking heavy drinkers and its associations with AUD symptoms. METHODS: Single-voxel MR spectra optimized for Glu assessment (TE 80 ms) were acquired at 3T from a frontal WM voxel in a group of heavy drinking, non-treatment-seeking subjects in comparison with a group of subjects with only light alcohol consumption. RESULTS: The results corroborate previous findings of increased total choline in heavy drinking subjects. A negative association of Glu levels with severity of alcohol dependence and especially loss of control over time and amount of alcohol intake was observed. CONCLUSIONS: In contrast to the rather unspecific rise in choline-containing compounds, low Glu in frontal WM may be specific for the shift from nondependent heavy drinking to dependence and does not reflect a simple effect of the amount of alcohol consumption alone.

Experience of social discrimination correlates with neurometabolism: a pilot study in heroin addicts.

Experimental social neuroscience has shown that being socially excluded is processed in the anterior cingulate cortex (ACC). We hypothesize that a chronic form of social exclusion resembling one aspect of social stigmatization is associated with altered neural plasticity reflected by neurometabolic alterations in the ACC. To test this hypothesis, a highly stigmatized patient group of heroin addicts (N = 15) during opiate maintenance therapy rated a questionnaire about being stigmatized, and neurometabolic markers in the ACC were determined using (1)H MR spectroscopy. We found a negative correlation between discrimination experience and N-acetylaspartate (NAA), indicating attenuated neuron functioning in the anterior cingulate cortex in those patients reporting high discrimination experience. Furthermore, perceived stigmatization showed an association with anxiety that was mediated by NAA. Although the correlative analysis cannot give evidence for a causal relationship, the relation of NAA in the ACC and discrimination experience indicates a malfunction of the neural system involved in cognitive control over emotionally relevant social stimuli in discrimination reporting heroin addicts. Further research is needed to elucidate factors associated with chronic stigmatization.

Psilocybin-induced default mode network hypoconnectivity is blunted in alcohol-dependent rats.

Alcohol Use Disorder (AUD) adversely affects the lives of millions of people, but still lacks effective treatment options. Recent advancements in psychedelic research suggest psilocybin to be potentially efficacious for AUD. However, major knowledge gaps remain regarding (1) psilocybin's general mode of action and (2) AUD-specific alterations of responsivity to psilocybin treatment in the brain that are crucial for treatment development. Here, we conducted a randomized, placebo-controlled crossover pharmaco-fMRI study on psilocybin effects using a translational approach with healthy rats and a rat model of alcohol relapse. Psilocybin effects were quantified with resting-state functional connectivity using data-driven whole-brain global brain connectivity, network-based statistics, graph theory, hypothesis-driven Default Mode Network (DMN)-specific connectivity, and entropy analyses. Results demonstrate that psilocybin induced an acute wide-spread decrease in different functional connectivity domains together with a distinct increase of connectivity between serotonergic core regions and cortical areas. We could further provide translational evidence for psilocybin-induced DMN hypoconnectivity reported in humans. Psilocybin showed an AUD-specific blunting of DMN hypoconnectivity, which strongly correlated to the alcohol relapse intensity and was mainly driven by medial prefrontal regions. In conclusion, our results provide translational validity for acute psilocybin-induced neural effects in the rodent brain. Furthermore, alcohol relapse severity was negatively correlated with neural responsivity to psilocybin treatment. Our data suggest that a clinical standard dose of psilocybin may not be sufficient to treat severe AUD cases; a finding that should be considered for future clinical trials.

In vivo voxel based morphometry: detection of increased hippocampal volume and decreased glutamate levels in exercising mice.

Voluntary exercise has tremendous effects on adult hippocampal plasticity and metabolism and thus sculpts the hippocampal structure of mammals. High-field (1)H magnetic resonance (MR) investigations at 9.4 T of metabolic and structural changes can be performed non-invasively in the living rodent brain. Numerous molecular and cellular mechanisms mediating the effects of exercise on brain plasticity and behavior have been detected in vitro. However, in vivo attempts have been rare. In this work a method for voxel based morphometry (VBM) was developed with automatic tissue segmentation in mice using a 9.4 T animal scanner equipped with a (1)H-cryogenic coil. The thus increased signal to noise ratio enabled the acquisition of high resolution T2-weighted images of the mouse brain in vivo and the creation of group specific tissue class maps for the segmentation and normalization with SPM. The method was used together with hippocampal single voxel (1)H MR spectroscopy to assess the structural and metabolic differences in the mouse brain due to voluntary wheel running. A specific increase of hippocampal volume with a concomitant decrease of hippocampal glutamate levels in voluntary running mice was observed. An inverse correlation of hippocampal gray matter volume and glutamate concentration indicates a possible implication of the glutamatergic system for hippocampal volume.

Central metabolite changes and activation of microglia after peripheral interleukin-2 challenge.

Interleukin (IL)-2 regulates the immune response through the proliferation of activated T-cells and also exerts effects on the central nervous system (CNS). Alongside having marked neurobehavioral effects, IL-2 has been suggested to impact on various psychiatric disorders. The immune-CNS communication of IL-2 remains unclear, although, it is suggested that microglia are the source and target of IL-2. Here, we analyzed changes in brain metabolites following a peripheral IL-2 challenge and examined the contribution of microglia in mediating these effects. Rats were assessed by magnetic resonance spectroscopy (MRS) in a 9.4 T scanner for baseline metabolite levels in the prefrontal cortex (PFC) and the hippocampus. After 7 days animals were scanned again following a single injection of IL-2 (2.5 µg/kg) and then tested on the elevated plus-maze for the correlation of IL-2-induced brain metabolites and measures of anxiety. In another experiment CD25(+) microglia cells were determined. A separate group of rats was injected either with IL-2 or vehicle, and afterward the PFC and hippocampus were dissected and fluorescence activated cell sorting (FACS) analysis was performed. The MRS scans in the intra-individual study design showed a significant increase in myo-inositol in the analyzed regions. A significant correlation of anxiety-like measures and myo-inositol, a marker for microglia activity, was found in the hippocampus. The FACS analysis showed a significant increase in CD25(+) microglia in the hippocampus compared to controls. The results support the role of microglia as a mediator in the immune-CNS communication and the effects of peripheral IL-2.

Relevance of orbitofrontal neurochemistry for the outcome of cognitive-behavioural therapy in patients with obsessive-compulsive disorder.

Since the advent of non-invasive methods such as proton magnetic resonance spectroscopy ((1)H-MRS), obsessive-compulsive disorder (OCD) has been increasingly associated with an altered composition of neurometabolites and neurotransmitters in several brain areas. Particularly, Inositol has not only been implicated in OCD pathophysiology, but also shown effective in pilot studies in therapy-refractory OCD patients. However, the relevance of regional brain neurochemistry for therapy outcome has not yet been investigated. Whereas numerous neuroimaging findings support a dysfunction of the orbitofrontal cortex (OFC) in OCD, MR-spectroscopic investigations of this region are missing. (1)H-MRS and psychometric measurements were obtained from twenty unmedicated patients with OCD, subsequently enrolled in a 3-month structured inpatient cognitive-behavioural therapy programme, and from eleven matched control subjects. Multiple regression of symptom score changes (Y-BOCS) on (myo-)inositol concentrations in three areas (right orbitofrontal cortex (OFC), right striatum and anterior cingulate cortex) was performed. The concentration of (myo-)inositol in the OFC only predicted the outcome of subsequent CBT regarding Y-BOCS score reduction (Spearman's r(s) = .81, P < 0.003, corrected). The (myo-)inositol concentration did not differ between OCD patients and healthy controls and did not change during therapy. We provide preliminary evidence for a neurochemical marker that may prove informative about a patient's future benefit from behaviour therapy. Inositol, a metabolite involved in cellular signal transduction and a spectroscopic marker of glial activity, predicted the response to CBT selectively in the OFC, adding to the evidence for OFC involvement in OCD and highlighting neurobiological underpinnings of psychotherapy.