The Role of the Hippocampus in Predicting Future Posttraumatic Stress Disorder Symptoms in Recently Traumatized Civilians

BACKGROUND

Understanding the neurobiological mechanisms that predict posttraumatic stress disorder (PTSD) in recent trauma survivors is important for early interventions. Impaired inhibition of fear or behavioral responses is thought to be central to PTSD symptomatology, but its role in predicting PTSD is unknown. Here we examine whether brain function during response inhibition early after a civilian trauma can predict future PTSD symptoms.

METHODS

Participants (original sample, n = 27; replication sample, n = 31) were recruited in the emergency department within 24 hours of trauma exposure. PTSD symptoms were assessed in the emergency department and 1, 3, and 6 months posttrauma. A Go/NoGo procedure in a 3T magnetic resonance imaging scanner was used to measure neural correlates of response inhibition 1 to 2 months posttrauma. Elastic net regression was used to define the most optimal model to predict PTSD symptoms at 3 and 6 months among demographic, clinical, and imaging measures.

RESULTS

Less hippocampal activation was a significant predictor in the model predicting PTSD symptoms at 3 months (F_11,22 = 4.33, p = .01) and 6 months (F_9,19 = 4.96, p = .01). Other significant predictors in the model were race and pain level in the emergency department (3 months), and race and baseline depression symptoms (6 months). Using these predictors in a linear regression in the replication sample again resulted in significant models (3 months [F_3,23 = 3.03, p = .05], 6 months [F_3,20 = 5.74, p = .007]) with hippocampal activation predicting PTSD symptoms at 3 and 6 months.

CONCLUSIONS

Decreased inhibition-related hippocampal activation soon after trauma predicted future PTSD symptom severity. This finding may contribute to early identification of at-risk individuals and reveals potential targets for intervention or symptom prevention in the aftermath of trauma.

Neural correlates and structural markers of emotion dysregulation in traumatized civilians

Emotion dysregulation (ED) reflects deficits in understanding and managing negative emotions and may serve as a transdiagnostic mechanism of risk for trauma-related psychiatric disorders. Therefore, understanding neurobiological substrates of ED in traumatized individuals is critical. The present study examined associations between ED and baseline structural differences and patterns of functional activity during an emotional task in a sample of African American women (n = 136) recruited from an urban hospital. Participants engaged in a structural magnetic resonance imaging (MRI) session. A subsample (n = 92) also viewed emotional face stimuli during functional MRI. ED was related to greater dorsal anterior cingulate cortex (dACC) surface area (P_corr < 0.05) and increased dorsomedial prefrontal cortex (dmPFC) and ventromedial PFC activation to fearful stimuli (P_corr < 0.05), independent of the trauma and psychiatric symptoms. DMPFC activation was also associated with posttraumatic stress disorder and depression symptoms. Mediation analyses showed a significant mediation effect of ED on the relation between dmPFC activation and psychiatric symptoms. These findings are important since dACC and dmPFC play central roles in fear expression and attention to emotional stimuli. Future longitudinal research is needed to help solidify a model of risk for how such neural substrates may be impacted by traumatic experiences to create ED.

Episodic memory after trauma exposure: Medial temporal lobe function is positively related to re-experiencing and inversely related to negative affect symptoms

Hippocampal structure is particularly sensitive to trauma and other stressors. However, previous findings linking hippocampal function with trauma-related psychopathology have been mixed. Heterogeneity in psychological responses to trauma has not been considered with respect to hippocampal function and may contribute to mixed findings. To address these issues, we examined associations between data-driven symptom dimensions and episodic memory formation, a key function of the hippocampus, in a trauma-exposed sample. Symptom dimensions were defined using principal components analysis (PCA) in 3881 trauma-exposed African-American women recruited from primary care waiting rooms of a large urban hospital. Hippocampal and amygdala function were subsequently investigated in an fMRI study of episodic memory formation in a subset of 54 women. Participants viewed scenes with neutral, negative, and positive content during fMRI, and completed a delayed cued recall task. PCA analysis produced five symptom dimensions interpreted as reflecting negative affect, somatic symptoms, re-experiencing, hyper-arousal, and numbing. Re-experiencing was the only symptom type associated with hippocampal function, predicting increased memory encoding-related activation in the hippocampus as well as the amygdala. In contrast, the negative affect component predicted lower amygdala activation for subsequently recalled scenes, and lower functional coupling with other important memory-related regions including the precuneus, inferior frontal gyrus, and occipital cortex. Symptom dimensions were not related to hippocampal volume. The fMRI findings for re-experiencing versus negative affect parallel differences in behavioral memory phenomena in PTSD versus MDD, and highlight a need for more complex models of trauma-related pathology.

Amygdala Reactivity and Anterior Cingulate Habituation Predict Posttraumatic Stress Disorder Symptom Maintenance After Acute Civilian Trauma

BACKGROUND

Studies suggest that exaggerated amygdala reactivity is a vulnerability factor for posttraumatic stress disorder (PTSD); however, our understanding is limited by a paucity of prospective, longitudinal studies. Recent studies in healthy samples indicate that, relative to reactivity, habituation is a more reliable biomarker of individual differences in amygdala function. We investigated reactivity of the amygdala and cortical areas to repeated threat presentations in a prospective study of PTSD.

METHODS

Participants were recruited from the emergency department of a large level I trauma center within 24 hours of trauma. PTSD symptoms were assessed at baseline and approximately 1, 3, 6, and 12 months after trauma. Growth curve modeling was used to estimate symptom recovery trajectories. Thirty-one individuals participated in functional magnetic resonance imaging around the 1-month assessment, passively viewing fearful and neutral face stimuli. Reactivity (fearful > neutral) and habituation to fearful faces was examined.

RESULTS

Amygdala reactivity, but not habituation, 5 to 12 weeks after trauma was positively associated with the PTSD symptom intercept and predicted symptoms at 12 months after trauma. Habituation in the ventral anterior cingulate cortex was positively associated with the slope of PTSD symptoms, such that decreases in ventral anterior cingulate cortex activation over repeated presentations of fearful stimuli predicted increasing symptoms.

CONCLUSIONS

Findings point to neural signatures of risk for maintaining PTSD symptoms after trauma exposure. Specifically, chronic symptoms were predicted by amygdala hyperreactivity, and poor recovery was predicted by a failure to maintain ventral anterior cingulate cortex activation in response to fearful stimuli. The importance of identifying patients at risk after trauma exposure is discussed.

CHILDHOOD MALTREATMENT PREDICTS REDUCED INHIBITION-RELATED ACTIVITY IN THE ROSTRAL ANTERIOR CINGULATE IN PTSD, BUT NOT TRAUMA-EXPOSED CONTROLS

BACKGROUND

A deficit in the ability to inhibit fear has been proposed as a biomarker of posttraumatic stress disorder (PTSD). Previous research indicates that individuals with PTSD show reduced inhibition-related activation in rostral anterior cingulate cortex (rACC). The goal of the current study was to investigate differential influences of an early environmental risk factor for PTSD-childhood maltreatment-on inhibition-related brain function in individuals with PTSD versus trauma-exposed controls.

METHODS

Individuals with PTSD (n = 37) and trauma-exposed controls (n = 53) were recruited from the primary care waiting rooms of an urban public hospital in Atlanta, GA. Participants completed an inhibition task during fMRI, and reported childhood and adult traumatic experiences. The groups were matched for adult and child trauma load.

RESULTS

We observed an interaction between childhood maltreatment severity and PTSD status in the rACC (P < .05, corrected), such that maltreatment was negatively associated with inhibition-related rACC activation in the PTSD group, but did not influence rACC activation in the TC group. Rostral ACC activation was associated with inhibition-related task performance in the TC group but not the PTSD group, suggesting a possible contribution to stress resilience.

CONCLUSIONS

Findings highlight individual differences in neural function following childhood trauma, and point to inhibition-related activation in rostral ACC as a risk factor for PTSD.

Childhood Trauma and COMT Genotype Interact to Increase Hippocampal Activation in Resilient Individuals

Both childhood trauma and a functional catechol-O-methyltransferase (COMT) genetic polymorphism have been associated with posttraumatic stress disorder (PTSD) and depression; however, it is still unclear whether the two interact and how this interaction relates to long-term risk or resilience. Imaging and genotype data were collected on 73 highly traumatized women. DNA extracted from saliva was used to determine COMT genotype (Val/Val, n = 38, Met carriers, n = 35). Functional MRI data were collected during a Go/NoGo task to investigate the neurocircuitry underlying response inhibition. Self-report measures of adult and childhood trauma exposure, PTSD and depression symptom severity, and resilience were collected. Childhood trauma was found to interact with COMT genotype to impact inhibition-related hippocampal activation. In Met carriers, more childhood trauma was associated with decreased hippocampal activation, whereas in the Val/Val group childhood trauma was related to increased hippocampal activation. Second, hippocampal activation correlated negatively with PTSD and depression symptoms and positively with trait resilience. Moreover, hippocampal activation mediated the relationship between childhood trauma and psychiatric risk or resilience in the Val/Val, but not in the Met carrier group. These data reveal a potential mechanism by which childhood trauma and COMT genotype interact to increase risk for trauma-related psychopathology or resilience. Hippocampal recruitment during inhibition may improve the ability to use contextual information to guide behavior, thereby enhancing resilience in trauma-exposed individuals. This finding may contribute to early identification of individuals at risk and suggests a mechanism that can be targeted in future studies aiming to prevent or limit negative outcomes.

Disrupted amygdala-prefrontal functional connectivity in civilian women with posttraumatic stress disorder

Many features of posttraumatic stress disorder (PTSD) can be linked to exaggerated and dysregulated emotional responses. Central to the neurocircuitry regulating emotion are functional interactions between the amygdala and the ventromedial prefrontal cortex (vmPFC). Findings from human and animal studies suggest that disruption of this circuit predicts individual differences in emotion regulation. However, only a few studies have examined amygdala-vmPFC connectivity in the context of emotional processing in PTSD. The aim of the present research was to investigate the hypothesis that PTSD is associated with disrupted functional connectivity of the amygdala and vmPFC in response to emotional stimuli, extending previous findings by demonstrating such links in an understudied, highly traumatized, civilian population. 40 African-American women with civilian trauma (20 with PTSD and 20 non-PTSD controls) were recruited from a large urban hospital. Participants viewed fearful and neutral face stimuli during functional magnetic resonance imaging (fMRI). Relative to controls, participants with PTSD showed an increased right amygdala response to fearful stimuli (p(corr) < .05). Right amygdala activation correlated positively with the severity of hyperarousal symptoms in the PTSD group. Participants with PTSD showed decreased functional connectivity between the right amygdala and left vmPFC (p(corr) < .05). The findings are consistent with previous findings showing PTSD is associated with an exaggerated response of amygdala-mediated emotional arousal systems. This is the first study to show that the amygdala response may be accompanied by disruption of an amygdala-vmPFC functional circuit that is hypothesized to be involved in prefrontal cortical regulation of amygdala responsivity.

Neural correlates of attention bias to threat in post-traumatic stress disorder

Attentional biases have been proposed to contribute to symptom maintenance in posttraumatic stress disorder (PTSD), although the neural correlates of these processes have not been well defined; this was the goal of the present study. We administered an attention bias task, the dot probe, to a sample of 37 (19 control, 18 PTSD+) traumatized African-American adults during fMRI. Compared to controls, PTSD+ participants demonstrated increased activation in the dorsolateral prefrontal cortex (dlPFC) in response to threat cue trials. In addition, attentional avoidance of threat corresponded with increased ventrolateral prefrontal cortex (vlPFC) and dorsal anterior cingulate cortex (dACC) activation in the PTSD group, a pattern that was not observed in controls. These data provide evidence to suggest that relative increases in dlPFC, dACC and vlPFC activation represent neural markers of attentional bias for threat in individuals with PTSD, reflecting selective disruptions in attentional control and emotion processing networks in this disorder.

Mode of effective connectivity within a putative neural network differentiates moral cognitions related to care and justice ethics

Background

Moral sensitivity refers to the interpretive awareness of moral conflict and can be justice or care oriented. Justice ethics is associated primarily with human rights and the application of moral rules, whereas care ethics is related to human needs and a situational approach involving social emotions. Among the core brain regions involved in moral issue processing are: medial prefrontal cortex, anterior (ACC) and posterior (PCC) cingulate cortex, posterior superior temporal sulcus (pSTS), insula and amygdala. This study sought to inform the long standing debate of whether care and justice moral ethics represent one or two different forms of cognition.

Methodology/Principal Findings

Model-free and model-based connectivity analysis were used to identify functional neural networks underlying care and justice ethics for a moral sensitivity task. In addition to modest differences in patterns of associated neural activity, distinct modes of functional and effective connectivity were observed for moral sensitivity for care and justice issues that were modulated by individual variation in moral ability.

Conclusions/Significance

These results support a neurobiological differentiation between care and justice ethics and suggest that human moral behavior reflects the outcome of integrating opposing rule-based, self-other perspectives, and emotional responses.

Evaluating Functional Autocorrelation within Spatially Distributed Neural Processing Networks

Data-driven statistical approaches, such as cluster analysis or independent component analysis, applied to in vivo functional neuroimaging data help to identify neural processing networks that exhibit similar task-related or restingstate patterns of activity. Ideally, the measured brain activity for voxels within such networks should exhibit high autocorrelation. An important limitation is that the algorithms do not typically quantify or statistically test the strength or nature of the within-network relatedness between voxels. To extend the results given by such data-driven analyses, we propose the use of Moran's I statistic to measure the degree of functional autocorrelation within identified neural processing networks and to evaluate the statistical significance of the observed associations. We adapt the conventional definition of Moran's I, for applicability to neuroimaging analyses, by defining the global autocorrelation index using network-based neighborhoods. Also, we compute network-specific contributions to the overall autocorrelation. We present results from a bootstrap analysis that provide empirical support for the use of our hypothesis testing framework. We illustrate our methodology using positron emission tomography (PET) data from a study that examines the neural representation of working memory among individuals with schizophrenia and functional magnetic resonance imaging (fMRI) data from a study of depression.

The neural correlates of social anxiety disorder and response to pharmacotherapy

This study attempted to define further the neural processing events underlying social anxiety in patients with social anxiety disorder (SAD) and their response to pharmacotherapy. Social anxiety-related changes in regional cerebral blood flow were defined by [15O]H2 positron emission tomography (PET) in medication-free individuals with generalized SAD (gSAD), and age- and sex-matched comparison subjects, and analyzed using a linear mixed effects model. PET studies were again acquired in the gSAD individuals following an 8-week, flexible dose treatment trial of nefazodone. Both script-guided mental imagery of an anxiogenic social situation and a confrontational mental arithmetic task were associated with marked increases in self-rated anxiety in both subject groups. For gSAD subjects, social anxiety induced by guided mental imagery was associated with increased activity in the left postcentral gyrus and lenticulate, and the right inferior frontal and middle temporal gyri. Social anxiety induced by the mental arithmetic task was associated with activation of the medial and left dorsolateral prefrontal cortex, cerebellum, thalamus, insula, and ventral striatum. Both tasks were associated with relative decreases in activity in the right amygdala and the hippocampus. A direct group comparison indicated that comparison subjects exhibited a differing pattern of social anxiety-related neural activations. Nefazodone treatment was associated with marked clinical improvement. Comparison of social anxiety-related neural activations prior to and after nefazodone administration indicated greater activity in the precentral gyrus, insula, midbrain/hypothalamus, and middle frontal and anterior cingulate gyrus prior to treatment, and greater activity in the left middle occipital and bilateral lingual gyri, postcentral gyrus, gyrus rectus, and hippocampus after treatment. The results of an analysis relating neural activity and treatment-related changes in symptom severity indicated differential neural responses associated with states of symptom remission vs partial response. The observed social anxiety-related changes in distributed neural activity are consistent with cognitive models of SAD and adaptive decreases in amygdala activity in response to social anxiogenics, and support the association of altered frontal cortical responses with treatment response.

Effect of methylphenidate on executive functioning in adults with attention-deficit/hyperactivity disorder: normalization of behavior but not related brain activity

BACKGROUND

We examined the effect of prolonged methylphenidate (MPH) treatment on the functional neuroanatomy of executive functioning in adult men with attention-deficit/hyperactivity disorder (ADHD).

METHODS

Positron emission tomography with [(15)O] water measured alterations of regional cerebral blood flow (rCBF) during the Paced Auditory Serial Addition Task and a control task in 10 ADHD and 11 normal control men. Attention-deficit/hyperactivity disorder men were imaged unmedicated and after a clinically optimal dose of MPH for 3 weeks.

RESULTS

Methylphenidate improved ADHD task performance, reduced rCBF in the prefrontal cortex (PFC), and increased rCBF in the right thalamus and precentral gyrus. Comparisons between the ADHD and normal control groups showed that normal control participants exhibited greater anterior cingulate cortex and temporal gyrus rCBF than ADHD participants under both conditions. Executive functioning was associated with greater subcortical (basal ganglia and cerebellar vermis) activation in the ADHD than normal control group under both conditions.

CONCLUSIONS

Methylphenidate does not normalize task-related activity in ADHD. Task-related rCBF decreases in the PFC may be due to improved filtering out of task-irrelevant stimuli by way of MPH-mediated dopamine release in the PFC.

The neural correlates of cue-induced craving in cocaine-dependent women

OBJECTIVE

Drug use reminders are associated with localized changes in brain activity related to intense drug wanting or craving in cocaine-dependent men. While cocaine dependence is prevalent and disabling in women, and certain clinically relevant sex differences exist, there is an absence of knowledge related to the neural correlates of cocaine craving in cocaine-dependent women.

METHOD

The differential neural response to imagery depicting cocaine use and neutral imagery was defined by using [15O]H2O positron emission tomography (PET) imaging in eight cocaine-dependent women. Results were compared with a matched group of eight cocaine-dependent men.

RESULTS

Cocaine-related imagery was associated with relative increases in cocaine craving and increases in regional cerebral blood flow in the superior temporal gyrus, dorsal anterior and posterior cingulate cortex, nucleus accumbens area, and the central sulcus. Compared with the results of an identical PET study in matched cocaine-dependent men, conditioned cocaine craving in women was associated with less activation of the amygdala, insula, orbitofrontal cortex, and ventral cingulate cortex and greater activation of the central sulcus and widely distributed frontal cortical areas.

CONCLUSIONS

These findings suggest the presence of sex differences in the functional anatomy of cue-induced cocaine craving associated with drug dependence. Such differences may reflect sex differences in conditioned associations to cocaine use, in affective and other corollaries of cocaine craving, or in their volitional regulation and may underlie apparent sex differences in the effects of cocaine abstinence and the expectations of treatment outcome. Some support for the need for sex-specific strategies for treatment of cocaine dependence is also furnished by the findings of this study.

Synthesis and characterization of iodine-123 labeled 2beta-carbomethoxy-3beta-(4'-((Z)-2-iodoethenyl)phenyl)nortropane. A ligand for in vivo imaging of serotonin transporters by single-photon-emission tomography

2beta-Carbomethoxy-3beta-(4'-((Z)-2-iodoethenyl)phenyl)nortropane (ZIENT) (6) and 2beta-carbomethoxy-3beta-(4'-((E)-2-iodoethenyl)phenyl)nortropane (EIENT) (10) were prepared and evaluated in vitro and in vivo for serotonin transporter (SERT) selectivity and specificity. High specific activity [(123)I]ZIENT and [(123)I]EIENT were synthesized in 45% (n = 5) and 42% (n = 4) radiochemical yield (decay-corrected to end of bombardment (EOB)), respectively, by preparation of the precursor carbomethoxy-3beta-(4'-((Z)-2-trimethylstannylethenyl)phenyl)nortropane (7) and 2beta-carbomethoxy-3beta-(4'-((E)-2-tributylstannylethenyl)phenyl)nortropane (9), respectively, followed by treatment with no carrier-added sodium [(123)I]iodide and hydrogen peroxide in ethanolic HCl. Competition binding in cells stably expressing the transfected human SERT, dopamine transporter (DAT), and norepinephrine transporter (NET) using [(3)H]citalopram, [(3)H]WIN 35,428, and [(3)H]nisoxetine, respectively, demonstrated the following order of SERT affinity (K(i) in nM): ZIENT (0.05) > nor-CIT (0.12) >> EIENT (1.15) > fluvoxamine (1.46). The affinity of ZIENT and EIENT for DAT was 69 and 1.6-fold lower, respectively, than for SERT. In vivo biodistribution and blocking studies were performed in male rats and demonstrated that the brain uptake of [(123)I]ZIENT was selective and specific for SERT-rich regions (hypothalamus, striatum, pons, and prefrontal cortex). SPECT brain imaging studies in monkeys demonstrated high [(123)I]ZIENT uptake in the diencephalon, which resulted in diencephalon-to-cerebellum ratios of 2.12 at 190 min. [(123)I]ZIENT uptake in the diencephalon achieved transient equilibrium at 157 min. In a displacement experiment of [(123)I]ZIENT in a cynomolgus monkey, radioactivity was reduced by 39% in the diencephalon at 101 min following injection of citalopram. The high specific activity one-step radiolabeling preparation and high selectivity of [(123)I]ZIENT for SERT support its candidacy as a radioligand for mapping brain SERT sites.

Dissociable neural pathways are involved in the recognition of emotion in static and dynamic facial expressions

Facial expressions of emotion powerfully influence social behavior. The distributed network of brain regions thought to decode these social signals has been empirically defined using static, usually photographic, displays of such expressions. Facial emotional expressions are however highly dynamic signals that encode the emotion message in facial action patterns. This study sought to determine whether the encoding of facial expressions of emotion by static or dynamic displays is associated with different neural correlates for their decoding. We used positron emission tomography to compare patterns of brain activity in healthy men and women during the explicit judgment of emotion intensity in static and dynamic facial expressions of anger and happiness. Compared to judgments of spatial orientation for moving neutral facial expressions, the judgment of anger in dynamic expressions was associated with increased right-lateralized activity in the medial, superior, middle, and inferior frontal cortex and cerebellum, while judgments of happiness were associated with relative activation of the cuneus, temporal cortex, and the middle, medial, and superior frontal cortex. In contrast, the perception of anger or happiness in static facial expressions activated a motor, prefrontal, and parietal cortical network previously shown to be involved in motor imagery. The direct contrast of dynamic and static expressions indicated differential activation of visual area V5, superior temporal sulcus, periamygdaloid cortex, and cerebellum for dynamic angry expressions and differential activation of area V5, extrastriate cortex, brain stem, and middle temporal cortical activations for dynamic happy expressions. Thus, a distribution of neural activations is related to the analysis of emotion messages in the nearly constant biological motion of the face and differ for angry and happy expressions. Static displays of facial emotional expression may represent noncanonical stimuli that are processed for emotion content by mental strategies and neural events distinct from their more ecologically relevant dynamic counterparts.

Ecstasy and agony: activation of the human amygdala in positive and negative emotion

Considerable evidence indicates that the amygdala plays a critical role in negative, aversive human emotions. Although researchers have speculated that the amygdala plays a role in positive emotion, little relevant evidence exists. We examined the neural correlates of positive and negative emotion using positron emission tomography (PET), focusing on the amygdala. Participants viewed positive and negative photographs, as well as interesting and uninteresting neutral photographs, during PET scanning. The left amygdala and ventromedial prefrontal cortex were activated during positive emotion, and bilateral amygdala activation occurred during negative emotion. High-interest, unusual photographs also elicited left-amygdala activation, a finding consistent with suggestions that the amygdala is involved in vigilance reactions to associatively ambiguous stimuli. The current results constitute the first neuroimaging evidence for a role of the amygdala in positive emotional reactions elicited by visual stimuli. Although the amygdala appears to play a more extensive role in negative emotion, it is involved in positive emotion as well.

Neural activity related to anger in cocaine-dependent men: a possible link to violence and relapse

This study examined the neural correlates of cue-induced anger in cocaine-dependent men in an initial investigation of possible neurobiological explanations for the putative association between cocaine addiction and violence. We used positron emission tomography (PET) to localize alterations in regional cerebral blood flow (rCBF) during mental imagery of a personal anger-associated scene and of an emotionally neutral scene in ten cocaine-dependent men. Compared to the emotionally neutral imagery control condition, anger was associated with marked decreases in rCBF in multiple areas of the frontal cortex (particularly the right inferior frontal gyrus), left posterior insula, left fusiform gyrus, and midbrain. Conversely, this same inferior frontal area was activated by anger imagery in nicotine-dependent men. Anger was also associated with increases in rCBF in the right fusiform gyrus, right and left middle occipital gyri, left post-central gyrus, left medial frontal gyrus, left cuneus, and in the left anterior cingulate gyrus. The study showed that cue-induced anger in cocaine-dependent men was associated with decreased activity in frontal cortical areas involved in response monitoring and inhibition. The lack of this association in nicotine-dependent men suggests a possible deficit in anger regulation associated with cocaine dependence and a possible link between cocaine dependence, violence, and relapse.

Neural activity related to drug craving in cocaine addiction

BACKGROUND

Crack cocaine dependence and addiction is typically associated with frequent and intense drug wanting or craving triggered by internal or environmental cues associated with past drug use.

METHODS

Water O 15 positron emission tomography (PET) studies were used to localize alterations in synaptic activity related to cue-induced drug craving in 8 crack cocaine-dependent African American men. In a novel approach, script-guided imagery of autobiographical memories were used as individualized cues to internally generate a cocaine craving state and 2 control (ie, anger and neutral episodic memory recall) states during PET image acquisition.

RESULTS

The mental imagery of personalized drug use and anger-related scripts was associated with self-ratings of robust drug craving or anger, and comparable alterations in heart rate. Compared with the neutral imagery control condition, imagery-induced drug craving was associated with bilateral (right hemisphere amygdala activation greater than left) activation of the amygdala, the left insula and anterior cingulate gyrus, and the right subcallosal gyrus and nucleus accumbens area. Compared with the anger control condition, internally generated drug craving was associated with bilateral activation of the insula and subcallosal cortex, left hippocampus, and anterior cingulate cortex and brainstem. A brain-wide pixel-by-pixel search indicated significant positive and negative correlations between imagery-induced cocaine craving and regional cerebral blood flow (rCBF) in distributed sites.

CONCLUSIONS

The collected findings suggest the craving-related activation of a network of limbic, paralimbic, and striatal brain regions, including structures involved in stimulus-reward association (amygdala), incentive motivation (subcallosal gyrus/nucleus accumbens), and anticipation (anterior cingulate cortex).

18F-labeled FECNT: a selective radioligand for PET imaging of brain dopamine transporters

Fluorine-18 labeled 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(2-fluoroethyl)nort ropane (FECNT) was synthesized in the development of a dopamine transporter (DAT) imaging ligand for positron emission tomography (PET). The methods of radiolabeling and ligand synthesis of FECNT, and the results of the in vitro characterization and in vivo tissue distribution in rats and in vivo PET imaging in rhesus monkeys of [18F]FECNT are described. Fluorine-18 was introduced into 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(2-fluoroethyl)nort ropane (4) by preparation of 1-[18F]fluoro-2-tosyloxyethane (2) followed by alkylation of 2beta-carbomethoxy-3beta-(4-chlorophenyl)nortropane (3) in 21% radiochemical yield (decay corrected to end of bombardment [EOB]). Competition binding in cells stably expressing the transfected human DAT serotonin transporter (SERT) and norepinephrine transporter (NET) labeled by [3H]WIN 35428, [3H]citalopram, and [3H]nisoxetine, respectively, indicated the following order of DAT affinity: GBR 12909 > CIT >> 2beta-carbomethoxy-3beta-(4-chlorophenyl)-8-(3-fluoropropyl) nortropane (FPCT) > FECNT. The affinity of FECNT for SERT and NET was 25- and 156-fold lower, respectively, than for DAT. Blocking studies were performed in rats with a series of transporter-specific agents and demonstrated that the brain uptake of [18F]FECNT was selective and specific for DAT-rich regions. PET brain imaging studies in monkeys demonstrated high [18F]FECNT uptake in the caudate and putamen that resulted in caudate-to-cerebellum and putamen-to-cerebellum ratios of 10.5 at 60 min. [18F]FECNT uptake in the caudate/putamen peaked in less than 75 min and exhibited higher caudate- and putamen-to-cerebellum ratios at transient equilibrium than reported for 11C-WIN 35,428, [11C]CIT/RTI-55, or [18F]beta-CIT-FP. Analysis of monkey arterial plasma samples using high performance liquid chromatography determined that there was no detectable formation of lipophilic radiolabeled metabolites capable of entering the brain. In equilibrium displacement experiments with CIT in rhesus monkeys, radioactivity in the putamen was displaced with an average half-time of 10.2 min. These results indicate that [18F]FECNT is a radioligand that is superior to 11C-WIN 35,428, [11C]CIT/RTI-55, [18F]beta-CIT-FP, and [18F]FPCT for mapping brain DAT in humans using PET.

Chronic lithium treatment decreases neuronal activity in the nucleus accumbens and cingulate cortex of the rat

Although the efficacy of lithium as a mood stabilizer is well documented, the mechanism of its therapeutic effect associated with prolonged treatment remains unknown. Identifying discrete brain regions and neural pathways that are functionally altered following long-term lithium treatment is central to elucidating a psychotherapeutic mechanism. We have used a sensitive and quantitative histochemical assay for the determination of cytochrome oxidase (CO) activity, a mitochondrial marker of neuronal activity, to determine the effect of repeated lithium treatment on regional neuronal activity in the rat brain. Oral lithium treatment (21 days) selectively decreased cytochrome oxidase activity in the cingulate cortex and regions of the nucleus accumbens. These decreases were not seen after 5 days of lithium administration, although serum lithium concentrations were similar after both 5 and 21 days of treatment. The analysis of interregional correlations further suggests a role for amygdala pathways in the effects of lithium following 21 days of treatment. The implications of these data for understanding the mechanisms of action of lithium are discussed.

Amygdala activity related to enhanced memory for pleasant and aversive stimuli

Pleasant or aversive events are better remembered than neutral events. Emotional enhancement of episodic memory has been linked to the amygdala in animal and neuropsychological studies. Using positron emission tomography, we show that bilateral amygdala activity during memory encoding is correlated with enhanced episodic recognition memory for both pleasant and aversive visual stimuli relative to neutral stimuli, and that this relationship is specific to emotional stimuli. Furthermore, data suggest that the amygdala enhances episodic memory in part through modulation of hippocampal activity. The human amygdala seems to modulate the strength of conscious memory for events according to emotional importance, regardless of whether the emotion is pleasant or aversive.

Neurotensin induces Fos and Zif268 expression in limbic nuclei of the rat brain

The endogenous tridecapeptide neurotensin exerts a wide range of behavioral, electrophysiological and neurochemical effects when administered directly into the brain. These effects are thought to result from the activation of distinct populations of neurotensin receptors distributed throughout the central nervous system. We have mapped the sites of functional change in the rat brain associated with the central administration of neurotensin using the induction of the nuclear protein products of the immediate early genes c-fos and zif268 as markers of cellular activation. The administration of neurotensin into the lateral ventricle of rats produced an increase in the number of nuclei positive for Fos and Zif268 immunoreactivity in the central and basolateral nuclei of the amygdala and the paraventricular and supraoptic nuclei of the hypothalamus. Neurotensin also produced an increase in serum corticosterone concentration and decrease in body temperature. The intraperitoneal administration of SR48692, a non-peptide neurotensin receptor antagonist, blocked the neurotensin-induced corticosterone secretion and significantly reduced the number of neurotensin-induced Fos-positive and Zif268-positive neurons in the amygdaloid complex. A significant positive correlation was found between the number of Fos-positive nuclei in the central or basolateral nucleus of the amygdala and the serum corticosterone concentration. A significant positive correlation was also found between the number of Zif-positive cells in the paraventricular nucleus of the hypothalamus and change in body temperature following treatment. Our findings indicate that the central role of neurotensin in increasing serum corticosterone involves the induction of Fos in the central and basolateral nuclei of the amygdala. In contrast, the neurotensin-induced hypothermia, which was unaffected by pretreatment with SR48692, involves Zif induction in the paraventricular nucleus of the hypothalamus. These data support further the existence of central neurotensin receptor subtypes which may regulate distinct immediate early genes.

Differential Effects of Conditioned and Unconditioned Stress on the Neurotensin Content of Dopamine Cell Body Groups of the Ventral Mesencephalon

The findings of this study extend the observations of Deutch et al. who suggested that NT in the ventral mesencephalon may be involved in the environmentally elicited activation of selectively responsive populations of mesotelencephalic dopamine neurons. The unconditioned response of NT-LI to electric footshock was observed only at an intensity of 500 microA and only in the lateral subdivision of the VTA. The selective effect of footshock stress on the NT content of a specific cell body group of the ventral mesencephalon suggests that NT mechanisms in the lateral VTA may, in part, underlie the stress-induced activation of dopamine neurons that originate in the lateral VTA. However, it should be noted that populations of dopamine neurons are activated by footshock intensities less than 500 microA, while NT concentrations of mesencephalic dopamine cell body groups are not altered by these shock intensities. The disparity weakens the possibility of a role for NT in the stress-induced activation of brain dopamine neurons unless NT mechanisms may be involved in transducing the effects of higher intensity stressors versus low intensity stressors. However, it should be noted that changes in the concentration of NT-LI represent an endpoint of unknown sensitivity and functional significance and best serve as an initial approximation of the effects of a manipulation on NT-containing neurons. It is plausible that NT mechanisms in the ventral mesencephalon may act in concert with other neuropeptides such as substance P and Met-enkephalin to transduce the effects of stressors on alterations in the activity of mesotelencephalic dopamine neurons that originate in the ventral mesencephalon. An examination of the effects of footshock stress on the content of prepro-NT mRNA in the dopamine cell body groups of the ventral mesencephalon would be of interest in assessing whether stress enhances NT gene expression or alters the characteristics of release of this neuropeptide in the ventral mesencephalon. Lacking NT receptor antagonists, it would also be of interest to determine the effects of the passive immunoneutralization of NT in the ventral mesencephalon on footshock-induced increases in the biochemically estimated activity of mesotelencephalic dopamine neurons to better understand the involvement of NT as a transducer of the effects of stress on dopamine neuronal activity. The distinct topography of conditioned versus unconditioned stress on the concentration of NT-LI in the dopamine cell body groups of the ventral mesencephalon suggests that NT may be involved in the differential activation of distinct dopamine neuronal populations by these different stressors.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective activation of mesoamygdaloid dopamine neurons by conditioned stress: attenuation by diazepam

Populations of dopamine (DA) neurons in the rat brain are selectively activated by stress, and the response is attenuated by the administration of anxiolytics. Given the role of the component nuclei of the amygdaloid complex in conditioned associations, stress responses and the anxiolytic effects of benzodiazepines, we hypothesized that particular mesoamygdaloid DA projections might be especially sensitive to the effects of conditioned stress and to diazepam (DZ). We mapped the effect of a conditioned stressor on the concentration of the DA metabolite homovanillic acid (HVA) in distinct amygdaloid nuclei and other brain nuclei and areas and the effect of DZ (1 or 3 mg/kg) on the conditioned response in drug-experienced subjects. The conditioned stress paradigm resulted in significant elevations in classical indices of stress, including serum corticosterone and plasma epinephrine. Conditioned stress-induced increases in the estimated activity of DA neurons were specific for DA neurons projecting to the central, basolateral and lateral amygdaloid nuclei, and for DA projections to the dorsal septal nucleus. Conditioned stress-induced increases in the HVA concentration of responsive amygdaloid nuclei were antagonized by low, anxiolytic doses of DZ. These results indicate a role for a subset of mesoamygdaloid DA projections in transducing the impact of perceived stressors on the output of the amygdaloid complex. A role for particular amygdaloid DA projections in the formation of conditioned fear or anticipatory anxiety and its modulation by anxiolytics is also suggested.