Signals In Brain Regions Research Articles

Widespread, perception-related information in the human brain scales with levels of consciousness

Abstract How does the human brain generate coherent, subjective perceptions—transforming yellow and oblong visual sensory information into the perception of an edible banana? This is a hard problem. According to the standard viewpoint, processing in groups of dedicated regions—identified as active “blobs” when using functional magnetic resonance imaging (fMRI)—gives rise to perception. Here, our research reveals a new organizational concept by discovering stimulus-specific information distributed throughout the whole brain. Using fMRI, we found stimulus-specific information across the neocortex, even in voxels previously considered “noise,” challenging traditional analytical approaches. Surprisingly, these stimulus-specific signals were also present in the subcortex and cerebellum and could be detected from across-subject variances. Additionally, we observed that the widespread signal in brain regions beyond the primary and secondary sensory cortices is influenced by sedation levels, suggesting a connection to perception rather than sensory encoding. We hypothesize that these widespread, stimulus-specific, and consciousness level-dependent signals may underlie coherent and subjective perceptions.

Effects of ulotaront on brain circuits of reward, working memory, and emotion processing in healthy volunteers with high or low schizotypy

Ulotaront, a trace amine-associated receptor 1 (TAAR1) and serotonin 5-HT1A receptor agonist without antagonist activity at dopamine D2 or the serotonin 5-HT2A receptors, has demonstrated efficacy in the treatment of schizophrenia. Here we report the phase 1 translational studies that profiled the effect of ulotaront on brain responses to reward, working memory, and resting state connectivity (RSC) in individuals with low or high schizotypy (LS or HS). Participants were randomized to placebo (n = 32), ulotaront (50 mg; n = 30), or the D2 receptor antagonist amisulpride (400 mg; n = 34) 2 h prior to functional magnetic resonance imaging (fMRI) of blood oxygen level-dependent (BOLD) responses to task performance. Ulotaront increased subjective drowsiness, but reaction times were impaired by less than 10% and did not correlate with BOLD responses. In the Monetary Incentive Delay task (reward processing), ulotaront significantly modulated striatal responses to incentive cues, induced medial orbitofrontal responses, and prevented insula activation seen in HS subjects. In the N-Back working memory task, ulotaront modulated BOLD signals in brain regions associated with cognitive impairment in schizophrenia. Ulotaront did not show antidepressant-like biases in an emotion processing task. HS had significantly reduced connectivity in default, salience, and executive networks compared to LS participants and both drugs reduced this difference. Although performance impairment may have weakened or contributed to the fMRI findings, the profile of ulotaront on BOLD activations elicited by reward, memory, and resting state is compatible with an indirect modulation of dopaminergic function as indicated by preclinical studies. This phase 1 study supported the subsequent clinical proof of concept trial in people with schizophrenia.Clinical trial registration: Registry# and URL: ClinicalTrials.gov NCT01972711, https://clinicaltrials.gov/ct2/show/NCT01972711

A high-performance genetically encoded fluorescent indicator for in vivo cAMP imaging

cAMP is a key second messenger that regulates diverse cellular functions including neural plasticity. However, the spatiotemporal dynamics of intracellular cAMP in intact organisms are largely unknown due to low sensitivity and/or brightness of current genetically encoded fluorescent cAMP indicators. Here, we report the development of the new circularly permuted GFP (cpGFP)-based cAMP indicator G-Flamp1, which exhibits a large fluorescence increase (a maximum ΔF/F0 of 1100% in HEK293T cells), decent brightness, appropriate affinity (a Kd of 2.17 μM) and fast response kinetics (an association and dissociation half-time of 0.20 and 0.087 s, respectively). Furthermore, the crystal structure of the cAMP-bound G-Flamp1 reveals one linker connecting the cAMP-binding domain to cpGFP adopts a distorted β-strand conformation that may serve as a fluorescence modulation switch. We demonstrate that G-Flamp1 enables sensitive monitoring of endogenous cAMP signals in brain regions that are implicated in learning and motor control in living organisms such as fruit flies and mice.

Conflict- and error-related theta activities are coupled to BOLD signals in different brain regions

Both conflict and error processing have been linked to the midfrontal theta power (4–8 Hz) increase as indicated by EEG studies and greater hemodynamic activity in the anterior midcingulate cortex (aMCC) as indicated by fMRI studies. Conveniently, the source of the midfrontal theta power was estimated in or nearby aMCC. However, previous studies using concurrent EEG and fMRI recordings in resting-state or other cognitive tasks observed only a negative relationship between theta power and BOLD signal in the brain regions typically showing task-related deactivations. In this study, we used a simultaneous EEG-fMRI technique to investigate a trial-by-trial coupling between theta power and hemodynamic activity during the performance of two conflict tasks. Independent component analysis (ICA) was applied to denoise the EEG signal and select individual midfrontal EEG components, whereas group ICA was applied to fMRI data to obtain a functional parcellation of the frontal cortex. Using a linear mixed-effect model, theta power was coupled with the peak of hemodynamic responses from various frontal, cingulate, and insular cortical sites to unravel the potential brain sources that contribute to conflict- and error-related theta variability. Although several brain regions exhibited conflict-related increases in hemodynamic activity, the conflict pre-response theta showed only a negative correlation to BOLD signal in the midline area 9 (MA9), a region exhibiting conflict-sensitive deactivation. Conversely, and more expectedly, error-related theta showed a positive relationship to activity in the aMCC. Our results provide novel evidence suggesting that the amplitude of pre-response theta reflects the process of active inhibition that suppresses the MA9 activity. This process is affected independently by the stimulus congruency, reaction times variance, and is susceptible to the time-on-task effect. Finally, it predicts the commitment of an omission error. Together, our findings highlight that conflict- and error-related theta oscillations represent fundamentally different processes.

Fentanyl-induced changes in brain activity in awake nonhuman primates at 9.4 Tesla.

Functional magnetic resonance imaging (fMRI) has been used to study the influence of opioids on neural circuitry implicated in opioid use disorder, such as the cortico-striatal-thalamo-cortical (CSTC) circuit. Given the increase in fentanyl-related deaths, this study was conducted to characterize the effects of fentanyl on patterns of brain activation in awake nonhuman primates. Four squirrel monkeys were acclimated to awake scanning procedures conducted at 9.4 Tesla. Subsequently, test sessions were conducted in which a dose of fentanyl that reliably maintains intravenous (IV) self-administration behavior in monkeys, 1μg/kg, was administered and the effects on patterns of brain activity were assessed using: (1) a pharmacological regressor to elucidate fentanyl-induced patterns of neural activity, and (2) seed-based approaches targeting bilateral anterior cingulate, thalamus, or nucleus accumbens (NAc) to determine alterations in CSTC functional connectivity. Results showed a functional inhibition of BOLD signal in brain regions that mediate behavioral effects of opioid agonists, such as cingulate cortex, striatum and midbrain. Functional connectivity between each of the seed regions and areas involved in motoric, sensory and cognition-related behavior generally decreased. In contrast, NAc functional connectivity with other striatal regions increased. These results indicate that fentanyl produces changes within CSTC circuitry that may reflect key features of opioid use disorder (e.g. persistent drug-taking/seeking) and thereby contribute to long-term disruptions in behavior and addiction. They also indicate that fMRI in alert nonhuman primates can detect drug-induced changes in neural circuits and, in turn, may be useful for investigating the effectiveness of medications to reverse drug-induced dysregulation.

Fractional amplitude of low-frequency fluctuation in patients with neovascular glaucoma: a resting-state functional magnetic resonance imaging study.

Neovascular glaucoma (NVG) is a secondary refractory disease with a poor prognosis, and there are few advanced studies on its pathogenesis and treatment. In this research, the fractional amplitude of low-frequency fluctuation (fALFF) technology was used in resting-state functional magnetic resonance imaging (rsfMRI) to investigate intrinsic neuron activity in the patient's brain with NVG. Sixteen patients with NVG (eight males and eight females) and 16 healthy controls (HCs) of similar age and sex were included. All patients and controls received rsfMRI scans, and the differences between the two groups in fALFF values were compared by independent sample t-test. Receiver operating characteristic (ROC) curves were used to compare fALFF values in the brain regions of NVG patients and HCs and assess accuracy. Finally, Pearson linear correlation analysis assessed the correlation between fALFF signals in brain regions and the clinical evaluation indicators of patients with NVG. In patients with NVG, fALFF signal values in the right Rolandic operculum, left anterior cingulate and paracingulate gyri, and right caudate were significantly decreased. In contrast, fALFF signal values in the left precuneus were significantly higher than those recorded in the HCs. Analysis of the ROC curve for each brain region showed that the area under the ROC curve of NVG patients was large (close to 1), and the accuracy was good. In the NVG group, the hospital anxiety and depression scale (r=-0.952, P<0.001) and left best-corrected visual acuity (r=-0.802, P<0.001) had a negative linear correlation with the fALFF signal value of the right Rolandic operculum. The hospital anxiety and depression scale had a negative linear correlation with the fALFF signal value of the right caudate (r=-0.948, P<0.001). NVG patients showed dysfunction in several brain regions. These findings may assist in revealing the underlying neural mechanism of brain activity associated with NVG.

Whole brain dynamics during optogenetic self-stimulation of the medial prefrontal cortex in mice

Intracranial self-stimulation, in which an animal performs an operant response to receive regional brain electrical stimulation, is a widely used procedure to study motivated behavior. While local neuronal activity has long been measured immediately before or after the operant, imaging the whole brain in real-time remains a challenge. Herein we report a method that permits functional MRI (fMRI) of brain dynamics while mice are cued to perform an operant task: licking a spout to receive optogenetic stimulation to the medial prefrontal cortex (MPFC) during a cue ON, but not cue OFF. Licking during cue ON results in activation of a widely distributed network consistent with underlying MPFC projections, while licking during cue OFF (without optogenetic stimulation) leads to negative fMRI signal in brain regions involved in acute extinction. Noninvasive whole brain readout combined with circuit-specific neuromodulation opens an avenue for investigating adaptive behavior in both healthy and disease models.

Astrocyte glutamate uptake impacts [18F]FDG‐PET signal

AbstractBackgroundThe role of astrocytes on brain functioning has become an important topic of debate. In this regard, an issue that still remains controversial is the astrocytes contribution to glucose brain metabolism and, therefore, to the uptake of 2‐Deoxy‐2‐[18F]Fluoroglucose([18F]FDG) detected by positron emission tomography(PET). For many years, it was widely assumed that the brain [18F]FDG‐PET signal directly reflects the neuronal use of glucose, overlooking the possible participation of other brain cells. Recently, rodent and human studies have demonstrated that astrocytes may contribute to [18F]FDG‐PET signal. To further explore these early findings, here, we used a pharmacological challenge on rodents. Clozapine was selected because it is known to decrease, on astrocytes, glutamate transport and the glutamate transporter 1 (GLT‐1) levels, an important trigger for glucose uptake in astrocytes.MethodsClozapine was administered for six weeks (25‐35mg/kg) to adult Wistar rats. Glucose brain metabolism was assessed using [18F]FDG‐microPET before and after the treatment. [3H]D‐Aspartate uptake was evaluated on brain slices. [3H]Glutamate release was analyzed on synaptosomal preparations. [3H]D‐Aspartate and [3H]2‐Deoxyglucose uptake were analyzed on primary cortical astrocytic and neuronal cultures treated with clozapine (50uM) for 48h. Immunocontent and expression of GLT‐1 and Glutamate‐Aspartate Transporter(GLAST) were assessed on the cortical tissue and cell cultures.ResultsClozapine treatment significantly reduced [18F]FDG metabolism in the cerebral cortex, hippocampus, and striatum of adult rats. In addition, clozapine decreased cortical glutamate transport in brain slices – indexed by [3H]D‐Aspartate uptake – and reduced the cortical immunocontent and expression of GLT‐1. Astrocytic cultures treated with clozapine presented a decline on GLT‐1 density, [3H]D‐Aspartate uptake and [3H]2‐Deoxyglucose uptake, while the neuronal cultures presented no changes.ConclusionHere, we present microPET data showing that a challenge with clozapine causes a reduction on [18F]FDG signal in brain regions presenting high GLT‐1 density. Our cell culture findings indicate that astrocytes are, at least partially, the cells underlying the brain glucose metabolism response to clozapine. These results corroborate previous studies that highlight the need for a reevaluation in the way that brain [18F]FDG‐PET data is interpreted. Additionally, clozapine is a drug approved for clinical use, therefore, these findings could have high translational implications.

Modified Xiaoyaosan (MXYS) Exerts Anti-depressive Effects by Rectifying the Brain Blood Oxygen Level-Dependent fMRI Signals and Improving Hippocampal Neurogenesis in Mice.

As the traditional Chinese herbal formula, Xiaoyaosan and its modified formula have been described in many previous studies with definite anti-depressive effects, but its underlying mechanism remains mystery. Previous work in our lab has demonstrated that depression induced by chronic stress could generate brain blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals disorder, accompanied by the impairment of hippocampal neuronal plasticity, decrease of brain-derived neurotrophic factor, and reduction of the number and complexity of adult neurons in the dentate gyrus. We hypothesized that herbal formula based on Xiaoyaosan could exert anti-depressive effects through restoring these neurobiological dysfunctions and rectifying BOLD-fMRI signals. To test this hypothesis, we examined the effect of modified Xiaoyaosan (MXYS) on depressive-like behaviors, as well as hippocampal neurogenesis and BOLD signals in a mice model of chronic unpredictable mild stress (CUMS)-induced depression. MXYS exerted anti-depressant effects on CUMS-induced depression that were similar to the effects of classical antidepressants drug (fluoxetine hydrochloride), with a significant alleviation of depressive-like behaviors, an improvement of hippocampal neurogenesis, and a reversal of activation of BOLD in the limbic system, particularly in the hippocampus. These results suggested that MXYS attenuated CUMS-induced depressive behaviors by rectifying the BOLD signals in the mice hippocampus. These novel results demonstrated that MXYS had anti-depressive effects accompanied by improving BOLD signals and hippocampal neurogenesis, which suggested that BOLD-fMRI signals in brain regions could be a key component for the evaluation of novel antidepressant drugs.

Brain response to food cues varying in portion size is associated with individual differences in the portion size effect in children

Large portions promote intake of energy dense foods (i.e., the portion size effect--PSE), but the neurobiological drivers of this effect are not known. We tested the association between blood oxygen level dependent (BOLD) brain response to food images varied by portion size (PS) and energy density (ED) and children's intake at test-meals of high- and low-ED foods served at varying portions. Children (N = 47; age 7–10 years) participated in a within-subjects, crossover study consisting of 4 meals of increasing PS of high- and low-ED foods and 1 fMRI to evaluate food images at 2 levels of PS (Large, Small) and 2 levels of ED (High, Low). Contrast values between PS conditions (e.g., Large PS - Small PS) were calculated from BOLD signal in brain regions implicated in cognitive control and reward and input as covariates in mixed models to determine if they moderated the PSE curve. Results showed a significant effect of PS on intake. Responses to Large relative to Small PS in brain regions implicated in salience (e.g., ventromedial prefrontal cortex and orbitofrontal cortex) were positively associated with the linear slope (i.e., increase in intake from baseline) of the PSE curve, but negatively associated with the quadratic coefficient for the total meal. Responses to Large PS High ED relative to Small PS High ED cues in regions associated with cognitive control (e.g., dorsolateral prefrontal cortex) were negatively associated with the linear slope of the PSE curve for high-ED foods. Brain responses to PS cues were associated with individual differences in children's susceptibility to overeating from large portions. Responses in food salience regions positively associated with PSE susceptibility while activation in control regions negatively associated with PSE susceptibility.

Imaging B Cells in a Mouse Model of Multiple Sclerosis Using 64Cu-Rituximab PET.

B lymphocytes are a key pathologic feature of multiple sclerosis (MS) and are becoming an important therapeutic target for this condition. Currently, there is no approved technique to noninvasively visualize B cells in the central nervous system (CNS) to monitor MS disease progression and response to therapies. Here, we evaluated 64Cu-rituximab, a radiolabeled antibody specifically targeting the human B cell marker CD20, for its ability to image B cells in a mouse model of MS using PET. Methods: To model CNS infiltration by B cells, experimental autoimmune encephalomyelitis (EAE) was induced in transgenic mice that express human CD20 on B cells. EAE mice were given subcutaneous injections of myelin oligodendrocyte glycoprotein fragment1-125 emulsified in complete Freund adjuvant. Control mice received complete Freund adjuvant alone. PET imaging of EAE and control mice was performed 1, 4, and 19 h after 64Cu-rituximab administration. Mice were perfused and sacrificed after the final PET scan, and radioactivity in dissected tissues was measured with a γ-counter. CNS tissues from these mice were immunostained to quantify B cells or were further analyzed via digital autoradiography. Results: Lumbar spinal cord PET signal was significantly higher in EAE mice than in controls at all evaluated time points (e.g., 1 h after injection: 5.44 ± 0.37 vs. 3.33 ± 0.20 percentage injected dose [%ID]/g, P < 0.05). 64Cu-rituximab PET signal in brain regions ranged between 1.74 ± 0.11 and 2.93 ± 0.15 %ID/g for EAE mice, compared with 1.25 ± 0.08 and 2.24 ± 0.11 %ID/g for controls (P < 0.05 for all regions except striatum and thalamus at 1 h after injection). Similarly, ex vivo biodistribution results revealed notably higher 64Cu-rituximab uptake in the brain and spinal cord of huCD20tg EAE, and B220 immunostaining verified that increased 64Cu-rituximab uptake in CNS tissues corresponded with elevated B cells. Conclusion: B cells can be detected in the CNS of EAE mice using 64Cu-rituximab PET. Results from these studies warrant further investigation of 64Cu-rituximab in EAE models and consideration of use in MS patients to evaluate its potential for detecting and monitoring B cells in the progression and treatment of this disease. These results represent an initial step toward generating a platform to evaluate B cell-targeted therapeutics en route to the clinic.

Acute nicotine administration increases BOLD fMRI signal in brain regions involved in reward signaling and compulsive drug intake in rats.

Background:Acute nicotine administration potentiates brain reward function and enhances motor and cognitive function. These studies investigated which brain areas are being activated by a wide range of doses of nicotine, and if this is diminished by pretreatment with the nonselective nicotinic receptor antagonist mecamylamine.Methods:Drug-induced changes in brain activity were assessed by measuring changes in the blood oxygen level dependent (BOLD) signal using an 11.1-Tesla magnetic resonance scanner. In the first experiment, nicotine naïve rats were mildly anesthetized and the effect of nicotine (0.03–0.6mg/kg) on the BOLD signal was investigated for 10min. In the second experiment, the effect of mecamylamine on nicotine-induced brain activity was investigated.Results:A high dose of nicotine increased the BOLD signal in brain areas implicated in reward signaling, such as the nucleus accumbens shell and the prelimbic area. Nicotine also induced a dose-dependent increase in the BOLD signal in the striato-thalamo-orbitofrontal circuit, which plays a role in compulsive drug intake, and in the insular cortex, which contributes to nicotine craving and relapse. In addition, nicotine induced a large increase in the BOLD signal in motor and somatosensory cortices. Mecamylamine alone did not affect the BOLD signal in most brain areas, but induced a negative BOLD response in cortical areas, including insular, motor, and somatosensory cortices. Pretreatment with mecamylamine completely blocked the nicotine-induced increase in the BOLD signal.Conclusions:These studies demonstrate that acute nicotine administration activates brain areas that play a role in reward signaling, compulsive behavior, and motor and cognitive function.

Neural correlates of inhibitory control and functional genetic variation in the dopamine D4 receptor gene

BackgroundThe dopamine D4 receptor gene (DRD4) has been implicated in psychiatric disorders in which deficits of self-regulation are a prominent feature (e.g., attention-deficit hyperactivity disorder and substance use disorders) and in dopamine D4 receptor insensitivity within prefrontal regions of the brain. Our hypothesis was that carriers of 7-repeats in the Variable Number of Tandem Repeats (VNTR) of DRD4 (7R+) would recruit prefrontal brain regions involved in successful inhibitory control to a lesser degree than non-carriers (7R−) and demonstrate less inhibitory control as confirmed by observation of locally reduced blood oxygenation level dependent (BOLD) % signal change and lower accuracy while performing “No-Go” trials of a Go/No-Go task. MethodsParticipants (age=18, n=62, 33 females) were recruited from the general population of the St. Louis, Missouri region. Participants provided a blood or saliva sample for genotyping, completed drug and alcohol-related questionnaires and IQ testing, and performed a Go/No-Go task inside of a 3T fMRI scanner. ResultsGo/No-Go task performance did not significantly differ between 7R+ and 7R− groups. Contrast of brain activity during correct “No-Go” trials with a non-target letter baseline revealed significant BOLD activation in a network of brain regions previously implicated in inhibitory control including bilateral dorsolateral prefrontal, inferior frontal, middle frontal, medial prefrontal, subcortical, parietal/temporal, and occipital/cerebellar brain regions. Mean BOLD % signal change during “No-Go” trials was significantly modulated by DRD4 genotype, with 7R+ showing a lower hemodynamic response than 7R− in right anterior prefrontal cortex/inferior frontal gyrus, left premotor cortex, and right occipital/cerebellar areas. Follow-up analyses suggested that 7-repeat status accounted for approximately 5–6% of the variance in the BOLD response during “No-Go” trials. DiscussionThe DRD4 7-repeat allele may alter dopaminergic function in brain regions involved in inhibitory control. When individuals must inhibit a prepotent motor response, presence of this allele may account for 5–6% of the variance in BOLD signal in brain regions critically associated with inhibitory control, but its influence may be associated with a greater effect on brain than on behavior in 18-year-olds from the general population.

Influence of Cognitive Status, Age, and APOE-4 Genetic Risk on Brain FDDNP Positron-Emission Tomography Imaging in Persons Without Dementia

Amyloid senile plaques and tau neurofibrillary tangles are neuropathological hallmarks of Alzheimer disease that accumulate in the brains of people without dementia years before they develop dementia. Positron emission tomography (PET) scans after intravenous injections of 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP), which binds to plaques and tangles in vitro, demonstrate increased cerebral binding in patients with Alzheimer disease compared with cognitively intact controls. Here we investigated whether known risk factors for Alzheimer disease and dementia are associated with FDDNP-PET binding. To determine if impaired cognitive status, older age, apolipoprotein E-4 (APOE-4) genetic risk for Alzheimer disease, family history of dementia, and less education are associated with increased regional cerebral FDDNP-PET binding. Cross-sectional clinical study. A university research institute. Volunteer sample of 76 middle-aged and older persons without dementia (mean age, 67 years) including 36 with mild cognitive impairment. Of the 72 subjects with genetic data, 34 were APOE-4 carriers. The FDDNP-PET signal in brain regions of interest, including medial and lateral temporal, posterior cingulate, parietal, and frontal. For all regions studied, cognitive status was associated with increased FDDNP binding (P < .02 to .005). Older age was associated with increased lateral temporal FDDNP binding. Carriers of APOE-4 demonstrated higher frontal FDDNP binding than noncarriers. In the mild cognitive impairment group, age was associated with increased medial and lateral temporal FDDNP binding, and APOE-4 carriers had higher medial temporal binding than noncarriers. Impaired cognitive status, older age, and APOE-4 carrier status are associated with increased brain FDDNP-PET binding in persons without dementia, consistent with previous clinical and postmortem studies associating these risk factors with amyloid plaque and tau tangle accumulation. Stratifying subject groups according to APOE-4 carrier status, age, and cognitive status may therefore be an informative strategy in future clinical trials using FDDNP-PET.

5-Hydroxytryptamine2C Receptor Contribution to m-Chlorophenylpiperazine and N-Methyl-β-carboline-3-carboxamide-Induced Anxiety-Like Behavior and Limbic Brain Activation

Activation of 5-hydroxytryptamine2C (5-HT(2C)) receptors by the 5-HT(2) receptor agonist m-chlorophenylpiperazine (m-CPP) elicits anxiety in humans and anxiety-like behavior in animals. We compared the effects of m-CPP with the anxiogenic GABA(A) receptor inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142) on both anxiety-like behavior and regional brain activation using functional magnetic resonance imaging (fMRI) in the rat. We also determined whether the selective 5-HT(2C) receptor antagonist SB 242084 [6-chloro-2,3-dihydro-5-methyl-N-[6-[(2-methyl-3-pyridinyl)oxy]-3-pyridinyl]-1H-indole-1-carboxyamide dihydrochloride] would blunt m-CPP or FG-7142-induced neuronal activation. Both m-CPP (3 mg/kg i.p.) and FG-7142 (10 mg/kg i.p.) elicited anxiety-like behavior when measured in the social interaction test, and pretreatment with SB 242084 (1 mg/kg i.p.) completely blocked the behavioral effects of both anxiogenic drugs. Regional brain activation in vivo in response to anxiogenic drug challenge was determined by blood oxygen level-dependent (BOLD) fMRI using a powerful 9.4T magnet. Region of interest analyses revealed that m-CPP and FG-7142 significantly increased BOLD signals in brain regions that have been linked to anxiety, including the amygdala, dorsal hippocampus, and medial hypothalamus. These BOLD signal increases were blocked by pretreatment with SB 242084. In contrast, injection of m-CPP and FG-7142 resulted in BOLD signal decreases in the medial prefrontal cortex that were not blocked by SB 242084. In conclusion, the brain activation signals produced by anxiogenic doses of both m-CPP and FG-7142 are mediated at least partially by the 5-HT(2C) receptor, indicating that this receptor is a key component in anxiogenic neural circuitry.