Reduced 5-HT(2A) receptor signaling following selective bilateral amygdala damage

From histology to macroscale function in the human amygdala

The amygdala is a subcortical region in the mesiotemporal lobe that plays a key role in emotional and sensory functions. Conventional neuroimaging experiments treat this structure as a single, uniform entity, but there is ample histological evidence for subregional heterogeneity in microstructure and function. The current study characterized subregional structure-function coupling in the human amygdala, integrating post-mortem histology and in vivo MRI at ultra-high fields. Core to our work was a novel neuroinformatics approach that leveraged multiscale texture analysis as well as non-linear dimensionality reduction techniques to identify salient dimensions of microstructural variation in a 3D post-mortem histological reconstruction of the human amygdala. We observed two axes of subregional variation in this region, describing inferior-superior as well as mediolateral trends in microstructural differentiation that in part recapitulated established atlases of amygdala subnuclei. Translating our approach to in vivo MRI data acquired at 7 Tesla, we could demonstrate the generalizability of these spatial trends across 10 healthy adults. We then cross-referenced microstructural axes with functional blood-oxygen-level dependent (BOLD) signal analysis obtained during task-free conditions, and revealed a close association of structural axes with macroscale functional network embedding, notably the temporo-limbic, default mode, and sensory-motor networks. Our novel multiscale approach consolidates descriptions of amygdala anatomy and function obtained from histological and in vivo imaging techniques.

Hostility in medication-resistant major depression and comorbid generalized anxiety disorder is related to increased hippocampal-amygdala 5-HT2A receptor density

Major depressive disorder (MDD) and generalized anxiety disorder (GAD) are severe and difficult-to-treat psychiatric illnesses with high rates of comorbidity. Although both disorders are treated with serotonergic based psychotropic agents, little is known on the influence of the serotonergic neurotransmitter system on the occurrence of comorbid GAD when clinically depressed. To investigate this poorly understood clinical question, we examined the involvement of frontolimbic post-synaptic 5-HT_2A receptors in 20 medication-resistant depressed (MRD) patients with half of them diagnosed with comorbid GAD with ¹²³I-5-I-R91150 SPECT. To explore whether 5-HT_2A receptor-binding indices (BI) associated with comorbid GAD could be related to distinct psychopathological symptoms, all were assessed with the symptom Checklist-90-Revised (SCL-90-R). MRD patients with comorbid GAD displayed significantly higher 5-HT_2A receptor BI in the hippocampal-amygdala complex, compared to MRD patients without GAD. Correlation analyses revealed that the 5-HT_2A receptor BI in these areas were significantly related to the SCL-90-R subscale hostility (HOS), especially for those MRD patients with comorbid GAD. Comorbid MRD-GAD may be characterized with increased hippocampal-amygdala 5-HT_2A receptor BI which could represent enhanced levels in hostility in such kinds of patients. Adapted psychotherapeutic interventions may be warranted.

Receptor-driven, multimodal mapping of the human amygdala

The human amygdala consists of subdivisions contributing to various functions. However, principles of structural organization at the cellular and molecular level are not well understood. Thus, we re-analyzed the cytoarchitecture of the amygdala and generated cytoarchitectonic probabilistic maps of ten subdivisions in stereotaxic space based on novel workflows and mapping tools. This parcellation was then used as a basis for analyzing the receptor expression for 15 receptor types. Receptor fingerprints, i.e., the characteristic balance between densities of all receptor types, were generated in each subdivision to comprehensively visualize differences and similarities in receptor architecture between the subdivisions. Fingerprints of the central and medial nuclei and the anterior amygdaloid area were highly similar. Fingerprints of the lateral, basolateral and basomedial nuclei were also similar to each other, while those of the remaining nuclei were distinct in shape. Similarities were further investigated by a hierarchical cluster analysis: a two-cluster solution subdivided the phylogenetically older part (central, medial nuclei, anterior amygdaloid area) from the remaining parts of the amygdala. A more fine-grained three-cluster solution replicated our previous parcellation including a laterobasal, superficial and centromedial group. Furthermore, it helped to better characterize the paralaminar nucleus with a molecular organization in-between the laterobasal and the superficial group. The multimodal cyto- and receptor-architectonic analysis of the human amygdala provides new insights into its microstructural organization, intersubject variability, localization in stereotaxic space and principles of receptor-based neurochemical differences.

Hippocampal serotonin-2A receptor-immunoreactive neurons density increases after testosterone therapy in the gonadectomized male mice

The change of steroid levels may also exert different modulatory effects on the number and class of serotonin receptors present in the plasma membrane. The effects of chronic treatment of testosterone for anxiety were examined and expression of 5-HT_2A serotonergic receptor, neuron, astrocyte, and dark neuron density in the hippocampus of gonadectomized male mice was determined. Thirty-six adult male NMRI mice were randomly divided into six groups: intact-no testosterone treatment (No T), gonadectomy (GDX)-No T, GDX-Vehicle, GDX-6.25 mg/kg testosterone (T), GDX-12.5 mg/kg T, and GDX-25 mg/kg T. Anxiety-related behavior was evaluated using elevated plus maze apparatus. The animals were anesthetized after 48 hours after behavioral testing, and decapitated and micron slices were prepared for immunohistochemical as well as histopathological assessment. Subcutaneous injection of testosterone (25 mg/kg) may induce anxiogenic-like behavior in male mice. In addition, immunohistochemical data reveal reduced expression of 5-HT_2A serotonergic receptor after gonadectomy in all areas of the hippocampus. However, treatment with testosterone could increase the mean number of dark neurons as well as immunoreactive neurons in CA1 and CA3 area, dose dependently. The density of 5-HT_2A receptor-immunoreactive neurons may play a crucial role in the induction of anxiety like behavior. As reduction in such receptor expression have shown to significantly enhance anxiety behaviors. However, replacement of testosterone dose dependently enhances the number of 5-HT_2A receptor-immunoreactive neurons and interestingly also reduced anxiety like behaviors.

Emotion moderates the association between HTR2A (rs6313) genotype and antisaccade latency

The serotonin system is heavily involved in cognitive and emotional control processes. Previous work has typically investigated this system's role in control processes separately for cognitive and emotional domains, yet it has become clear the two are linked. The present study, therefore, examined whether variation in a serotonin receptor gene (HTR2A, rs6313) moderated effects of emotion on inhibitory control. An emotional antisaccade task was used in which participants looked toward (prosaccade) or away (antisaccade) from a target presented to the left or right of a happy, angry, or neutral face. Overall, antisaccade latencies were slower for rs6313 C allele homozygotes than T allele carriers, with no effect of genotype on prosaccade latencies. Thus, C allele homozygotes showed relatively weak inhibitory control but intact reflexive control. Importantly, the emotional stimulus was either present during target presentation (overlap trials) or absent (gap trials). The gap effect (slowed latency in overlap versus gap trials) in antisaccade trials was larger with angry versus neutral faces in C allele homozygotes. This impairing effect of negative valence on inhibitory control was larger in C allele homozygotes than T allele carriers, suggesting that angry faces disrupted/competed with the control processes needed to generate an antisaccade to a greater degree in these individuals. The genotype difference in the negative valence effect on antisaccade latency was attenuated when trial N-1 was an antisaccade, indicating top-down regulation of emotional influence. This effect was reduced in C/C versus T/_ individuals, suggesting a weaker capacity to downregulate emotional processing of task-irrelevant stimuli.

The Loudness Dependence of Auditory Evoked Potentials (LDAEP) in individuals at risk for developing bipolar disorders and schizophrenia

OBJECTIVES

The Loudness Dependence of Auditory Evoked Potentials (LDAEP) is considered as an indicator of central serotonergic activity. Alteration of serotonergic neurotransmission was reported in bipolar disorders and schizophrenia. In line with previous reports on clinically manifest disorders, we expected a weaker LDAEP in subjects at risk for bipolar disorders and schizophrenia compared to healthy controls.

METHODS

We analyzed LDAEP of individuals at risk for developing bipolar disorders (n=27), with high-risk status (n=74) and ultra-high-risk status for schizophrenia (n=86) and healthy controls (n=47).

RESULTS

The LDAEP did not differ between subjects at risk for schizophrenia or bipolar disorders and controls. Among subjects without medication (n=122), the at-risk-bipolar group showed a trend towards a weaker LDAEP than both the high-risk and the ultra-high-risk groups for schizophrenia.

CONCLUSIONS

The LDAEP did not appear as a vulnerability marker for schizophrenia or bipolar disorders. This suggests that an altered LDAEP may not be measurable until the onset of clinically manifest disorder. However, the hypothesis that pathogenic mechanisms leading to bipolar disorders may differ from those leading to schizophrenia is supported.

SIGNIFICANCE

This is the first study investigating LDAEP in a population at risk for bipolar disorders.

The effect of cognitive challenge on delay discounting

Recent findings suggest that the dorsolateral prefrontal cortex (DLPFC), a region consistently associated with impulse control, is vulnerable to transient suppression of its activity and attendant functions by excessive stress and/or cognitive demand. Using functional magnetic resonance imaging, we show that a capacity-exceeding cognitive challenge induced decreased DLPFC activity and correlated increases in the preference for immediately available rewards. Consistent with growing evidence of a link between working memory capacity and delay discounting, the effect was inversely proportional to baseline performance on a working memory task. Subjects who performed well on the working memory task had unchanged, or even decreased, delay discounting rates, suggesting that working memory ability may protect cognitive control from cognitive challenge.

Intrinsic connectivity in the human brain does not reveal networks for 'basic' emotions

We tested two competing models for the brain basis of emotion, the basic emotion theory and the conceptual act theory of emotion, using resting-state functional connectivity magnetic resonance imaging (rs-fcMRI). The basic emotion view hypothesizes that anger, sadness, fear, disgust and happiness each arise from a brain network that is innate, anatomically constrained and homologous in other animals. The conceptual act theory of emotion hypothesizes that an instance of emotion is a brain state constructed from the interaction of domain-general, core systems within the brain such as the salience, default mode and frontoparietal control networks. Using peak coordinates derived from a meta-analysis of task-evoked emotion fMRI studies, we generated a set of whole-brain rs-fcMRI 'discovery' maps for each emotion category and examined the spatial overlap in their conjunctions. Instead of discovering a specific network for each emotion category, variance in the discovery maps was accounted for by the known domain-general network. Furthermore, the salience network is observed as part of every emotion category. These results indicate that specific networks for each emotion do not exist within the intrinsic architecture of the human brain and instead support the conceptual act theory of emotion.

Asparagus racemosus attenuates anxiety-like behavior in experimental animal models

Asparagus racemosus Linn. (AR) is used worldwide as a medicinal plant. In the present study, the anxiolytic activity of standardized methanolic extract of root of AR (MAR) was evaluated in open-field test (OFT), hole-board, and elevated plus maze (EPM) tests. Rats received oral pretreatment of MAR in the doses of 50, 100, and 200 mg/kg daily for 7 days and then were evaluated for the anxiolytic activity in different animal models. Both MAR (100 and 200 mg/kg) and diazepam (1 mg/kg, p.o.) increased the grooming behavior, number of central squares crossed, and time spent in the central area during OFT. Further, MAR (100 and 200 mg/kg) increased the head-dip and head-dip/sniffing behavior, and decreased sniffing activity in hole-board test. Furthermore, MAR (100 and 200 mg/kg) increased the percentage entries and time spent to open arm in EPM test paradigm. The anxiolytic activity in the experimental models was similar to that of diazepam. MAR (100 and 200 mg/kg) enhanced the level of amygdalar serotonin and norepinephrine. It also increased the expression of 5-HT2A receptors in the amygdala. In another set of experiment, flumazenil attenuated the anxiolytic effect of minimum effective dose of MAR (100 mg/kg) in OFT, hole-board, and EPM tests, indicating GABAA-mediated mechanism. Moreover, the anxiolytic dose of MAR did not show sedative-like effect in OFT and EPM tests compared to diazepam (6 mg/kg, p.o.). Thus, the anxiolytic response of MAR may involve GABA and serotonergic mechanisms. These preclinical data show that AR can be a potential agent for treatment of anxiety disorders.

"The mind is its own place": amelioration of claustrophobia in semantic dementia

Phobias are among the few intensely fearful experiences we regularly have in our everyday lives, yet the brain basis of phobic responses remains incompletely understood. Here we describe the case of a 71-year-old patient with a typical clinicoanatomical syndrome of semantic dementia led by selective (predominantly right-sided) temporal lobe atrophy, who showed striking amelioration of previously disabling claustrophobia following onset of her cognitive syndrome. We interpret our patient's newfound fearlessness as an interaction of damaged limbic and autonomic responsivity with loss of the cognitive meaning of previously threatening situations. This case has implications for our understanding of brain network disintegration in semantic dementia and the neurocognitive basis of phobias more generally.

Functional anatomy of 5-HT2A receptors in the amygdala and hippocampal complex: relevance to memory functions

The amygdaloid complex and hippocampal region contribute to emotional activities, learning, and memory. Mounting evidence suggests a primary role for serotonin (5-HT) in the physiological basis of memory and its pathogenesis by modulating directly the activity of these two areas and their cross-talk. Indeed, both the amygdala and the hippocampus receive remarkably dense serotoninergic inputs from the dorsal and median raphe nuclei. Anatomical, behavioral and electrophysiological evidence indicates the 5-HT2A receptor as one of the principal postsynaptic targets mediating 5-HT effects. In fact, the 5-HT2A receptor is the most abundant 5-HT receptor expressed in these brain structures and is expressed on both amygdalar and hippocampal pyramidal glutamatergic neurons as well as on γ-aminobutyric acid (GABA)-containing interneurons. 5-HT2A receptors on GABAergic interneurons stimulate GABA release, and thereby have an important role in regulating network activity and neural oscillations in the amygdala and hippocampal region. This review will focus on the distribution and physiological functions of the 5-HT2A receptor in the amygdala and hippocampal region. Taken together the results discussed here suggest that 5-HT2A receptor may be a potential therapeutic target for those disorders related to hippocampal and amygdala dysfunction.

Potential role of cortical 5-HT(2A) receptors in the anxiolytic action of cyamemazine in benzodiazepine withdrawal

The antipsychotic cyamemazine is a potent serotonin 5-HT(2A) receptor (5-HT(2AR)) antagonist. A positron emission tomography (PET) study in human patients showed that therapeutic doses of cyamemazine produced near saturation of 5-HT(2AR) occupancy in the frontal cortex, whereas dopamine D(2) occupancy remained below the level for motor side effects observed with typical antipsychotics. Recently, numerous studies have revealed the involvement of 5-HT(2AR) in the pathophysiology of anxiety and a double-blind, randomized clinical trial showed similar efficacy of cyamemazine and bromazepam in reducing the anxiety associated with benzodiazepine withdrawal. Therefore, we reviewed the above articles about 5-HT(2AR) and anxiety in order to understand better the anxiolytic mechanisms of cyamemazine in benzodiazepine withdrawal. The 5-HT(2AR) is the most abundant serotonin receptor subtype in the cortex. Non-pharmacological studies with antisense oligodeoxynucleotides and genetically modified mice clearly showed that cortical 5-HT(2AR) signaling positively modulates anxiety-like behavior. With a few exceptions, most other studies reviewed here further support this view. Therefore, the anxiolytic efficacy of cyamemazine in benzodiazepine withdrawal can be due to a 5-HT(2AR) antagonistic activity at the cortical level.

Fear processing and social networking in the absence of a functional amygdala

BACKGROUND

The human amygdala plays a crucial role in processing social signals, such as face expressions, particularly fearful ones, and facilitates responses to them in face-sensitive cortical regions. This contributes to social competence and individual amygdala size correlates with that of social networks. While rare patients with focal bilateral amygdala lesion typically show impaired recognition of fearful faces, this deficit is variable, and an intriguing possibility is that other brain regions can compensate to support fear and social signal processing.

METHODS

To investigate the brain's functional compensation of selective bilateral amygdala damage, we performed a series of behavioral, psychophysiological, and functional magnetic resonance imaging experiments in two adult female monozygotic twins (patient 1 and patient 2) with equivalent, extensive bilateral amygdala pathology as a sequela of lipoid proteinosis due to Urbach-Wiethe disease.

RESULTS

Patient 1, but not patient 2, showed preserved recognition of fearful faces, intact modulation of acoustic startle responses by fear-eliciting scenes, and a normal-sized social network. Functional magnetic resonance imaging revealed that patient 1 showed potentiated responses to fearful faces in her left premotor cortex face area and bilaterally in the inferior parietal lobule.

CONCLUSIONS

The premotor cortex face area and inferior parietal lobule are both implicated in the cortical mirror-neuron system, which mediates learning of observed actions and may thereby promote both imitation and empathy. Taken together, our findings suggest that despite the pre-eminent role of the amygdala in processing social information, the cortical mirror-neuron system may sometimes adaptively compensate for its pathology.

Paradoxical facilitation of working memory after basolateral amygdala damage

Working memory is a vital cognitive capacity without which meaningful thinking and logical reasoning would be impossible. Working memory is integrally dependent upon prefrontal cortex and it has been suggested that voluntary control of working memory, enabling sustained emotion inhibition, was the crucial step in the evolution of modern humans. Consistent with this, recent fMRI studies suggest that working memory performance depends upon the capacity of prefrontal cortex to suppress bottom-up amygdala signals during emotional arousal. However fMRI is not well-suited to definitively resolve questions of causality. Moreover, the amygdala is neither structurally or functionally homogenous and fMRI studies do not resolve which amygdala sub-regions interfere with working memory. Lesion studies on the other hand can contribute unique causal evidence on aspects of brain-behaviour phenomena fMRI cannot "see". To address these questions we investigated working memory performance in three adult female subjects with bilateral basolateral amygdala calcification consequent to Urbach-Wiethe Disease and ten healthy controls. Amygdala lesion extent and functionality was determined by structural and functional MRI methods. Working memory performance was assessed using the Wechsler Adult Intelligence Scale-III digit span forward task. State and trait anxiety measures to control for possible emotional differences between patient and control groups were administered. Structural MRI showed bilateral selective basolateral amygdala damage in the three Urbach-Wiethe Disease subjects and fMRI confirmed intact functionality in the remaining amygdala sub-regions. The three Urbach-Wiethe Disease subjects showed significant working memory facilitation relative to controls. Control measures showed no group anxiety differences. Results are provisionally interpreted in terms of a 'cooperation through competition' networks model that may account for the observed paradoxical functional facilitation effect.

Hypervigilance for fear after basolateral amygdala damage in humans

Recent rodent research has shown that the basolateral amygdala (BLA) inhibits unconditioned, or innate, fear. It is, however, unknown whether the BLA acts in similar ways in humans. In a group of five subjects with a rare genetic syndrome, that is, Urbach-Wiethe disease (UWD), we used a combination of structural and functional neuroimaging, and established focal, bilateral BLA damage, while other amygdala sub-regions are functionally intact. We tested the translational hypothesis that these BLA-damaged UWD-subjects are hypervigilant to facial expressions of fear, which are prototypical innate threat cues in humans. Our data indeed repeatedly confirm fear hypervigilance in these UWD subjects. They show hypervigilant responses to unconsciously presented fearful faces in a modified Stroop task. They attend longer to the eyes of dynamically displayed fearful faces in an eye-tracked emotion recognition task, and in that task recognize facial fear significantly better than control subjects. These findings provide the first direct evidence in humans in support of an inhibitory function of the BLA on the brain's threat vigilance system, which has important implications for the understanding of the amygdala's role in the disorders of fear and anxiety.

Overnight deprivation from smoking disrupts amygdala responses to fear

Cigarette smoking, a major, yet avoidable, cause of disability and premature death, is the most prevalent form of nicotine addiction. An emerging theme in the neurobiology of nicotine addiction is the integrity of the amygdala. Using functional MRI, amygdala responses during a face perception task were compared between 28 chronic smokers [14 females, 14 males; age, 26.3 (2.8) years; age at onset of smoking, 15.8 (2.6) years; years smoked, 9.1 (2.1); cigarettes per day, 17.1 (3.7); Fagerström test for nicotine dependence score, 4.1 (1.9); exhaled carbon-monoxide level, 17.8 (9.5) ppm] and 28 age- and education-matched nonsmokers [14 females, 14 males; age, 26.9 (2.4) years]. Subjects underwent imaging on two separate occasions 1 week apart: smoking satiety versus overnight smoking deprivation, in a randomized counterbalanced order. Our results show no difference in amygdala responses to faces between nonsmokers and satiated smokers. However, overnight deprivation from smoking was associated with a significantly lowered amygdala response to fear, an effect that was probabilistically mapped to the basolateral amygdala. We suggest that aberrant amygdala reactivity in overnight-deprived smokers may reflect a pre-existing vulnerability to smoking and/or increase the risk of smoking relapse after a cessation attempt.

The human amygdala and the induction and experience of fear

Although clinical observations suggest that humans with amygdala damage have abnormal fear reactions and a reduced experience of fear, these impressions have not been systematically investigated. To address this gap, we conducted a new study in a rare human patient, SM, who has focal bilateral amygdala lesions. To provoke fear in SM, we exposed her to live snakes and spiders, took her on a tour of a haunted house, and showed her emotionally evocative films. On no occasion did SM exhibit fear, and she never endorsed feeling more than minimal levels of fear. Likewise, across a large battery of self-report questionnaires, 3 months of real-life experience sampling, and a life history replete with traumatic events, SM repeatedly demonstrated an absence of overt fear manifestations and an overall impoverished experience of fear. Despite her lack of fear, SM is able to exhibit other basic emotions and experience the respective feelings. The findings support the conclusion that the human amygdala plays a pivotal role in triggering a state of fear and that the absence of such a state precludes the experience of fear itself.

Oxytocin enhances amygdala-dependent, socially reinforced learning and emotional empathy in humans

Oxytocin (OT) is becoming increasingly established as a prosocial neuropeptide in humans with therapeutic potential in treatment of social, cognitive, and mood disorders. However, the potential of OT as a general facilitator of human learning and empathy is unclear. The current double-blind experiments on healthy adult male volunteers investigated first whether treatment with intranasal OT enhanced learning performance on a feedback-guided item-category association task where either social (smiling and angry faces) or nonsocial (green and red lights) reinforcers were used, and second whether it increased either cognitive or emotional empathy measured by the Multifaceted Empathy Test. Further experiments investigated whether OT-sensitive behavioral components required a normal functional amygdala. Results in control groups showed that learning performance was improved when social rather than nonsocial reinforcement was used. Intranasal OT potentiated this social reinforcement advantage and greatly increased emotional, but not cognitive, empathy in response to both positive and negative valence stimuli. Interestingly, after OT treatment, emotional empathy responses in men were raised to levels similar to those found in untreated women. Two patients with selective bilateral damage to the amygdala (monozygotic twins with congenital Urbach-Wiethe disease) were impaired on both OT-sensitive aspects of these learning and empathy tasks, but performed normally on nonsocially reinforced learning and cognitive empathy. Overall these findings provide the first demonstration that OT can facilitate amygdala-dependent, socially reinforced learning and emotional empathy in men.

Age dependency of cerebral P-gp function measured with (R)-[11C]verapamil and PET

PURPOSE

The aim of this study was to assess the influence of age on the functional activity of the multidrug efflux transporter P-glycoprotein (P-gp) at the human blood-brain barrier.

METHODS

Seven young (mean age: 27 +/- 4 years) and six elderly (mean age: 69 +/- 9 years) healthy volunteers underwent dynamic (R)-[(11)C]verapamil (VPM) positron emission tomography (PET) scans and arterial blood sampling. Parametric distribution volume (DV) images were generated using Logan linearisation, and age groups were compared with statistical parametric mapping (SPM). Brain regions that SPM analysis had shown to be most affected by age were analysed by a region of interest (ROI)-based approach using a maximum probability brain atlas, before and after partial volume correction (PVC).

RESULTS

SPM analysis revealed significant clusters of DV increases in cerebellum, temporal and frontal lobe of elderly compared to younger subjects. In the ROI-based analysis, elderly subjects showed significant DV increases in amygdala (+30%), insula (+26%) and cerebellum (+25%) before PVC, and in insula (+33%) after PVC.

CONCLUSIONS

Increased VPM DV values in the brains of elderly subjects suggest a decrease in cerebral P-gp function with increasing age.