According to social psychology models of adult attachment, a fundamental dimension of attachment is anxiety. Individuals who are high in attachment anxiety are motivated to achieve intimacy in relationships, but are mistrustful of others and their availability. Behavioral research has shown that anxiously attached persons are vigilant for emotional facial expression, but the neural substrates underlying this perceptual sensitivity remain largely unknown. In the present study functional magnetic resonance imaging was used to examine automatic brain reactivity to approach-related facial emotions as a function of attachment anxiety in a sample of 109 healthy adults. Pictures of sad and happy faces were presented masked by neutral faces. The Relationship Scales Questionnaire (RSQ) was used to assess attachment style. Attachment anxiety was correlated with depressivity, trait anxiety, and attachment avoidance. Controlling for these variables, attachment-related anxiety was positively related to responses in left inferior, middle, and medial prefrontal areas, globus pallidus, claustrum, and right cerebellum to masked happy facial expression. Attachment anxiety was not found to be associated with brain activation due to masked sad faces. Our findings suggest that anxiously attached adults are automatically more responsive to positive approach-related facial expression in brain areas that are involved in the perception of facial emotion, facial mimicry, or the assessment of affective value and social distance.

Although the recognition of facial expressions seems automatic and effortless, discrimination of expressions can still be error prone. Common errors are often due to visual similarities between some expressions (e.g., fear and surprise). However, little is known about the neural mechanisms underlying such a confusion effect. To address this question, we recorded the magnetoencephalography (MEG) while participants judged facial expressions that were either easily confused with or easily distinguished from other expressions. The results showed that the fusiform face area (FFA), rather than the posterior superior temporal sulcus (pSTS), played a preponderant role in discriminating confusable facial expressions. No difference between high confusion and low confusion conditions was observed on the M170 component in either the FFA or the pSTS, whilst a difference between two conditions started to emerge in the late positive potential (LPP), with the low confusion condition eliciting a larger LPP amplitude in the FFA. In addition, the power of delta was stronger in the time window of LPP component. This confusion effect was reflected in the FFA, which might be associated with the perceptual-to-conceptual shift.

Biases in facial expression recognition can be reduced successfully using feedback-based training tasks. Here we investigate with event-related potentials (ERPs) at which stages of stimulus processing emotion-related modulations are influenced by training. Categorization of subtle facial expressions (morphed from neutral to happy, sad or surprise) was trained with correct-response feedback on each trial. ERPs were recorded before and after training while participants categorized facial expressions without response feedback. Behavioral data demonstrated large improvements in categorization of subtle facial expression which transferred to new face models not used during training. ERPs were modulated by training from 450 ms post-stimulus onward, characterized by a more gradual increase in P3b/Late Positive Potential (LPP) amplitude as expression intensity increased. This effect was indistinguishable for faces used for training and for new faces. It was proposed that training elicited a more fine-grained analysis of facial information for all subtle expressions, resulting in improved recognition and enhanced emotional motivational salience (reflected in P3b/LPP amplitude) of faces previously categorized as expressing no emotion.

Recent studies have suggested that both configural information, such as face shape, and surface information is important for face perception. In particular, facial color is sufficiently suggestive of emotional states, as in the phrases: "flushed with anger" and "pale with fear." However, few studies have examined the relationship between facial color and emotional expression. On the other hand, event-related potential (ERP) studies have shown that emotional expressions, such as fear, are processed unconsciously. In this study, we examined how facial color modulated the supraliminal and subliminal processing of fearful faces. We recorded electroencephalograms while participants performed a facial emotion identification task involving masked target faces exhibiting facial expressions (fearful or neutral) and colors (natural or bluish). The results indicated that there was a significant interaction between facial expression and color for the latency of the N170 component. Subsequent analyses revealed that the bluish-colored faces increased the latency effect of facial expressions compared to the natural-colored faces, indicating that the bluish color modulated the processing of fearful expressions. We conclude that the unconscious processing of fearful faces is affected by facial color.

Trait anxiety, the disposition to experience anxiety, is known to facilitate perception of threats. Trait anxious individuals seem to identify threatening stimuli such as fearful facial expressions more accurately, especially when presented under temporal constraints. In past studies on anxiety and emotion face recognition, only self-report or explicit measures of anxiety have been administered. Implicit measures represent indirect tests allowing to circumvent problems associated with self-report. In our study, we made use of implicit in addition to explicit measures to investigate the relationships of trait anxiety with recognition of and brain response to emotional faces. 75 healthy young volunteers had to identify briefly presented (67 ms) fearful, angry, happy, and neutral facial expressions masked by neutral faces while undergoing functional magnetic resonance imaging. The Implicit Association Test, the State-Trait Anxiety Inventory and the Beck Anxiety Inventory were applied as implicit and explicit measures of trait anxiety. After corrections for multiple testing, neither implicitly nor explicitly measured anxiety correlated with recognition of emotional facial expressions. Moreover, implicitly and explicitly assessed anxiety was not linked to brain response to emotional faces. Our data suggest links between discrimination accuracy and brain response to facial emotions. Activation of the caudate nucleus seems be of particular importance for recognizing fear and happiness from facial expressions. Processes of somatosensory resonance appear to be involved in identifying fear from facial expressions. The present data indicate that, regardless of assessment method, trait anxiety does not affect the recognition of fear or other emotions as has been proposed previously.

Extraversion/introversion is a basic dimension of personality that describes individual differences in social behavior and sensory sensitivity. Previous neuroimaging research exclusively relied on self reports for assessing personality traits. In recent years, implicit measures of personality have been developed that aim at assessing the implicit self-concept of personality and complement self report instruments which are thought to measure aspects of the explicit self-concept of personality. In the present study functional magnetic resonance imaging was used to examine automatic brain reactivity to facial expression as a function of both implicitly and explicitly measured extraversion in 30 healthy women. Sad, happy, and neutral faces were presented for 33 ms masked by neutral faces beside a no face control condition. Subjects evaluated the briefly shown neutral mask faces. The Implicit Association Test (IAT) and the NEO Five-Factor Inventory (NEO-FFI) were applied as measures of extraversion which were not correlated in our sample. IAT extraversion was negatively correlated with automatic reactivity of the caudate head, thalamus, and inferior frontal cortex to sad faces. NEO-FFI extraversion was negatively correlated with response of the inferior frontal cortex and putamen to sad faces. For masked happy faces, an inverse correlation of the IAT effect for extraversion with activation of the caudate head and superior parietal lobule was observed. NEO-FFI extraversion was inversely correlated with the response of the thalamus to happy faces. Neither NEO-FFI extraversion nor IAT effect were significantly related to brain response to masked neutral faces (compared to the no face condition). Taken together, a specific heightened responsivity of the fronto-striatal-thalamic circuit to facial emotions which are arousing stimuli might underlie introverts' preference for avoiding social interactions. Research on the neurobiology of extraversion could benefit from the application of implicit in addition to explicit measurement instruments when automatic neural responses are investigated.

Extraversion-introversion is a personality dimension referring to individual differences in social behavior. In the past, neurobiological research on extraversion was almost entirely based upon questionnaires which inform about the explicit self-concept. Today, indirect measures are available that tap into the implicit self-concept of extraversion which is assumed to result from automatic processing functions. In our study, brain activation while viewing facial expression of affiliation relevant (i.e., happiness, and disgust) and irrelevant (i.e., fear) emotions was examined as a function of the implicit and explicit self-concept of extraversion and processing mode (automatic vs. controlled). 40 healthy volunteers watched blocks of masked and unmasked emotional faces while undergoing functional magnetic resonance imaging. The Implicit Association Test and the NEO Five-Factor Inventory were applied as implicit and explicit measures of extraversion which were uncorrelated in our sample. Implicit extraversion was found to be positively associated with neural response to masked happy faces in the thalamus and temporo-parietal regions and to masked disgust faces in cerebellar areas. Moreover, it was positively correlated with brain response to unmasked disgust faces in the amygdala and cortical areas. Explicit extraversion was not related to brain response to facial emotions when controlling trait anxiety. The implicit compared to the explicit self-concept of extraversion seems to be more strongly associated with brain activation not only during automatic but also during controlled processing of affiliation relevant facial emotions. Enhanced neural response to facial disgust could reflect high sensitivity to signals of interpersonal rejection in extraverts (i.e., individuals with affiliative tendencies).

We previously reported that electrical stimulation of the reticular formation dorsal to the facial nucleus (RdVII) elicited excitatory masseter responses at short latencies and that RdVII neurons were antidromically activated by stimulation of the trigeminal motor nucleus (MoV), suggesting that excitatory premotor neurons targeting the MoV are likely located in the RdVII. We thus examined the properties of synaptic transmission from the RdVII to jaw-closing and jaw-opening motoneurons in horizontal brainstem preparations from developing rats using voltage-sensitive dye, patch-clamp recordings and laser photostimulation. Electrical stimulation of the RdVII evoked optical responses in the MoV. Combined bath application of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and the NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid (APV) reduced these optical responses, and addition of the glycine receptor antagonist strychnine and the GABA(A) receptor antagonist bicuculline further reduced the remaining responses. Electrical stimulation of the RdVII evoked postsynaptic currents (PSCs) in all 19 masseter motoneurons tested in postnatal day (P)1-4 rats, and application of CNQX and the NMDA receptor antagonist (+/-)-3(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) reduced the PSC amplitudes by more than 50%. In the presence of CNQX and CPP, the GABA(A) receptor antagonist SR95531 further reduced PSC amplitude, and addition of strychnine abolished the remaining PSCs. Photostimulation of the RdVII with caged glutamate also evoked PSCs in masseter motoneurons of P3-4 rats. In P8-11 rats, electrical stimulation of the RdVII also evoked PSCs in all 14 masseter motoneurons tested, and the effects of the antagonists on the PSCs were similar to those in P1-4 rats. On the other hand, RdVII stimulation evoked PSCs in only three of 16 digastric motoneurons tested. These results suggest that both neonatal and juvenile jaw-closing motoneurons receive strong synaptic inputs from the RdVII through activation of glutamate, glycine and GABA(A) receptors, whereas inputs from the RdVII to jaw-opening motoneurons seem to be weak.

Clusterin (or apolipoprotein J) is a widely distributed multifunctional glycoprotein involved in CNS plasticity and post-traumatic remodeling. Using biochemical and morphological approaches, we investigated the clusterin ontogeny in the CNS of wild-type (WT) mice and explored developmental consequences of clusterin gene knock-out in clusterin null (Clu-/-) mice. A punctiform expression of clusterin mRNA was detected through the hypothalamic region, neocortex and hippocampus at embryonic stages E14/E15. From embryonic stage E16 to the first week of the postnatal life, the vast majority of CNS neurons expressed low levels of clusterin mRNA. In contrast, a very strong hybridizing signal mainly localized in pontobulbar and spinal cord motor nuclei was observed from the end of the first postnatal week to adulthood. Astrocytes expressing clusterin mRNA were often detected through the hippocampus and neocortex in neonatal mice. Real-time polymerase chain amplification and clusterin-immunoreactivity dot-blot analyses indicated that clusterin levels paralleled mRNA expression. Comparative analyses between WT and Clu-/- mice during postnatal development showed no significant differences in brain weight, neuronal, synaptic and astrocyte markers as well myelin basic protein expression. However, quantitative estimation of large motor neuron populations in the facial nucleus revealed a significant deficit in motor cells (-16%) in Clu-/- compared with WT mice. Our data suggest that clusterin expression is already present in fetal life mainly in subcortical structures. Although the lack of this protein does not significantly alter basic aspects of the CNS development, it may have a negative impact on neuronal development in certain motor nuclei.

Reading the facial expression of other people is a fundamental skill for social interaction. Human facial expressions of emotions are readily recognized but may also evoke the same experiential emotional state in the observer. We used event-related functional magnetic resonance imaging and multi-channel electroencephalography to determine in 14 right-handed healthy volunteers (29+/-6 years) which brain structures mediate the perception of such a shared experiential emotional state. Statistical parametric mapping showed that an area in the dorsal medial frontal cortex was specifically activated during the perception of emotions that reflected the seen happy and sad emotional face expressions. This area mapped to the pre-supplementary motor area which plays a central role in control of behavior. Low resolution brain electromagnetic tomography-based analysis of the encephalographic data revealed that the activation was detected 100 ms after face presentation onset lasting until 740 ms. Our observation substantiates recently emerging evidence suggesting that the subjective perception of an experiential emotional state-empathy-is mediated by the involvement of the dorsal medial frontal cortex.

Peripherin is a type III intermediate filament which, in contrast to the neurofilaments, is strongly up-regulated after nerve injury. Although peripherin expression is stimulated in vitro by neurotrophins and cytokines, little is known about its in vivo regulation. In this report, we show that the in vivo down-regulation of peripherin expression to normal levels during regeneration closely correlates with target reconnection in rat facial motoneurons. Prevention of reconnection, by transection and suture, results in the persistence of strong peripherin expression for prolonged periods of up to 11months. This contrasts with the modulation of the p75 low-affinity neurotrophin receptor, whose expression returns to normal even in the absence of reconnection. We further demonstrate that blockade of the axonal transport in non-injured motoneurons increases the expression of peripherin. Blockade of the axonal transport simultaneously to, or after injury of, facial motoneurons does not abolish the axotomy-induced peripherin up-regulation. These data demonstrate that the in vivo expression of peripherin is normally restrained by a distal retrogradely transported inhibitory signal. Thus, peripherin up-regulation results primarily from a lack of supply in this factor. Our results show that stimulatory factors released at the injury site are not required for the initial up-regulation and maintenance of high peripherin expression. However, they appear to enhance this increase during the acute post-lesion phase. Peripherin expression is thus finely tuned by both glial cell-derived stimulatory and distal inhibitory signals that reflect neuron-target interactions.

The nucleus of the solitary tract is the site of termination of primary afferent fibers running in the facial, glossopharyngeal and vagus nerves. The present study was performed to map the distribution of glutamatergic axons terminals in the rat nucleus of the solitary tract using immunodetection of vesicular glutamate transporter 1 and vesicular glutamate transporter 2. The two vesicular glutamate transporters were differentially distributed among nucleus of the solitary tract subdivisions. Vesicular glutamate transporter 1 immunoreactivity was mostly found in the lateral part of the nucleus (ventrolateral, interstitial and intermediate subdivisions) whereas vesicular glutamate transporter 2 labeling was distributed throughout the nucleus of the solitary tract. Electron microscope examination indicated that vesicular glutamate transporter immunoreactivity was localized in axon terminals filled with round synaptic vesicles. After injection of cholera toxin B subunit in sensory ganglia, anterograde labeling was found in vesicular glutamate transporter 1, as well as vesicular glutamate transporter 2-immunoreactive boutons. Double immunolabeling experiments allowed distinctions between terminals expressing either vesicular glutamate transporter 1 or vesicular glutamate transporter 2 or both vesicular glutamate transporter 1 and vesicular glutamate transporter 2 immunoreactivities. The latter population, expressing both transporters immunolabeling, completely disappeared after deafferentation induced by removal of sensory ganglia. This study indicates that vesicular glutamate transporter content identifies three different subpopulations of glutamatergic boutons in the nucleus of the solitary tract and provides definitive evidence that primary afferent neurons contribute glutamatergic terminals to the nucleus of the solitary tract.

Peripheral nerve injury models are used to investigate processes that can potentially be exploited in CNS injury. A consistent change that occurs in injured peripheral neurons is an induction in expression of pituitary adenylyl cyclase activating peptide (PACAP), a neuropeptide with putative neuroprotective and neuritogenic actions. PACAP-deficient mice were used here to investigate actions of endogenous PACAP after facial nerve injury. Although motor neuron survival after axotomy was not significantly different in PACAP deficient vs. wild type mice, recovery of axon regeneration after crush injury was significantly delayed. The impaired regeneration was associated with 8- to 12-fold increases in gene expression of proinflammatory cytokines tumor necrosis factor-alpha, interferon-gamma, interleukin (IL) -6, and a 90% decrease in the anti-inflammatory cytokine IL-4 at the injury site. Similar cytokine changes and an increased microglial response were observed in the brainstem facial motor nucleus. Because immunocompromised animals such as SCID mice are known to exhibit peripheral nerve regeneration defects, the observations raise the novel hypothesis that PACAP is critically involved in a carefully controlled immune response that is necessary for proper nerve regeneration after injury.

Pain is a common complication of herpes zoster (HZ) infection which results from reactivation of a latent varicella zoster virus (VZV). A third of HZ patients' progress to a chronic pain state known as post herpetic neuralgia (PHN), and about a quarter of these patients' have orofacial pain. The mechanisms controlling the pain responses are not understood. Studies suggest central pathways involving the thalamus could control pain related to HZ, and studies in our lab suggest (VGAT) in the lateral thalamus influences orofacial pain. We hypothesized that thalamic VGAT functions, in part, to reduce pain, particularly orofacial pain, associated with VZV. To address this hypothesis VZV was injected into the whisker pad. Affective and motivational aspects of pain were measured using the Place Escape/Avoidance Paradigm. Thalamic neuronal activity was modulated after injecting an adeno-associated virus (AAV) expressing an engineered acetylcholine Gi-protein-coupled receptor. This receptor inhibits neuronal firing when bound by clozapine-n-oxide (CNO). VGAT expression was attenuated in the thalamus by injecting an AAV construct that expressed a VGAT silencing shRNA. VZV-induced nociception was significantly decreased after administering CNO in male rats. Nociception significantly increased concomitant with increased thalamic c-fos expression after attenuating thalamic VGAT expression. These data establish that the lateral thalamus (posterior, ventral posteromedial, ventral posterolateral and/or reticular thalamic nucleus) controls VZV-induced nociception in the orofacial region, and that GABA in this region appears to reduce the response to VZV-induced nociception possibly by gating facial pain input.

Nurr1 and Nur77 (NGFI-B) are orphan nuclear receptors, belonging to the steroid/thyroid hormone receptor gene superfamily. They have conserved amino acid sequence in the zinc-finger DNA binding domains and similar COOH-terminal regions, but have no known ligands. However, different expression patterns during brain development and tissue distributions of these messenger RNAs imply that they might reflect a different transcriptional role in the brain. In this study, the regional and cellular expression of messenger RNAs encoding these two proteins in rat brain has been determined by in situ hybridization. Nurr1 messenger RNA is highly expressed in the piriform and entorhinal cortices, hippocampus, medial habenular and paraventricular thalamic nuclei. Moderate labeling was detected in layers II-V of most of the cerebral cortex, and in the dorsal lateral geniculate nucleus, substantia nigra (pars compacta and reticularis) and interpeduncular nucleus. No Nurr1 hybridization signal was seen in the rhombencephalon. In the cerebellum, Nurr1 messenger RNA is present in the internal granular cell layer and Purkinje cell layer. In contrast, Nur77 has a widespread distribution, with the highest level of expression in the cerebral cortex. Moderate hybridization signals were detected in the hippocampus, the lateral dorsal and posterior nuclei, reuniens thalamic nuclei, and paraventricular and supraoptic hypothalamic nuclei. In the rhombencephalon, higher signals were present in the medial and lateral vestibular, dorsal cochlear and facial, and raphe magnus nuclei. Nur77 signal was also detected in the nucleus of the spinal tract of the trigeminal nerve. In the cerebellum, Nur77 messenger RNA is highly expressed in the Purkinje cell layer and lateral deep nucleus of the cerebellum. Our results show that Nurr1 and Nur77 messenger RNAs have both overlapping and different distribution patterns within the brain, suggesting that they might regulate different sets of responsive genes.

The prefrontal cortex is essential for executive functions such as decision-making and planning. There is also accumulating evidence that it is important for the modulation of pain. In this study, we investigated a possible role of prefrontal cortical calcium-independent phospholipase A2 (iPLA2) in antinociception induced by the norepinephrine reuptake inhibitor (NRI) and tetracyclic (tricyclic) antidepressant, maprotiline. Intraperitoneal injections of maprotiline increased iPLA2 mRNA and protein expression in the prefrontal cortex. This treatment also reduced grooming responses to von-Frey hair stimulation of the face after facial carrageenan injection, indicating decreased sensitivity to pain. The antinociceptive effect of maprotiline was abrogated by iPLA2 antisense oligonucleotide injection to the prefrontal cortex, indicating a role of this enzyme in antinociception. In contrast, injection of iPLA2 antisense oligonucleotide to the somatosensory cortex did not reduce the antinociceptive effect of maprotiline. Lipidomic analysis of the prefrontal cortex showed decrease in phosphatidylcholine species, but increase in lysophosphatidylcholine species, indicating increased PLA2 activity, and release of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) after maprotiline treatment. Differences in sphingomyelin/ceramide were also detected. These changes were not observed in maprotiline-treated mice that received iPLA2 antisense oligonucleotide to the prefrontal cortex. Metabolites of DHA and EPA may help to strengthen a known supraspinal antinociceptive pathway from the prefrontal cortex to the periaqueductal gray. Together, results indicate a role of prefrontal cortical iPLA2 and its enzymatic products in the antinociceptive effect of maprotiline.

How obesity exacerbates migraine and other pain disorders remains unknown. Trigeminal nociceptive processing, crucial in migraine pathophysiology, is abnormal in mice with diet induced obesity. However, it is not known if this is also true in genetic models of obesity. We hypothesized that obese mice, regardless of the model, have trigeminal hyperalgesia. To test this, we first evaluated trigeminal thermal nociception in leptin deficient (ob/ob) and control mice using an operant thermal assay. Unexpectedly, we found significant hypoalgesia in ob/ob mice. Because thermal hypoalgesia also occurs in mice lacking the transient receptor potential vanilloid 1 channel (TRPV1), we tested capsaicin-evoked trigeminal nociception. Ob/ob and control mice had similar capsaicin-evoked nocifensive behaviors, but ob/ob mice were significantly less active after a facial injection of capsaicin than were diet-induced obese mice or lean controls. Conditioned place aversion in response to trigeminal stimulation with capsaicin was similar in both genotypes, indicating normal negative affect and pain avoidance. Supporting this, we found no difference in TRPV1 expression in the trigeminal ganglia of ob/ob and control mice. Finally, we assessed the possible contribution of hyperphagia, a hallmark of leptin deficiency, to the behavior observed in the operant assay. Ob/ob and lean control mice had similar reduction of intake when quinine or capsaicin was added to the sweetened milk, excluding a significant contribution of hyperphagia. In summary, ob/ob mice, unlike mice with diet-induced obesity, have trigeminal thermal hypoalgesia but normal responses to capsaicin, suggesting specificity in the mechanisms by which leptin acts in pain processing.