Celecoxib after the onset of reperfusion reduces apoptosis in the amygdala

Reperfused myocardial infarction induces an inflammatory response that is responsible for local and systemic alterations. Among these, apoptosis observed in the amygdala following myocardial infarction has been pointed out as a consequence of such an inflammatory process. We hypothesized that inhibition of the inducible inflammatory enzyme Cox-2 during the reperfusion period may attenuate the apoptotic process in the amygdala. Anaesthetized rats were subjected to left anterior descending coronary artery occlusion for 40 min, followed by reperfusion. The Cox-2 antagonist Celecoxib (3 mg/kg i.p.) was administered 10 min after the onset of the reperfusion period. After 72 h of reperfusion, infarct size was determined and the lateral and medial amygdala were dissected from the brain. Infarct size was similar between untreated and Celecoxib-treated animals (40–45% of the area at risk). Cox-2 expression was significantly reduced in both parts of the amygdala in the Celecoxib group. Apoptosis regression was observed in the amygdala of the Celecoxib group as shown by decreased number of TUNEL positive cells and by decreased of caspase-3 activation. Bax/Bcl-2 ratio was not significantly altered by Celecoxib while Akt activation was increased in the lateral amygdala but not in the medial amygdala. This data indicates that inhibition of Cox-2 by Celecoxib is associated with regression of apoptosis in the amygdala following myocardial infarction.     

Involvement of amygdala central nucleus in the regulation of cardiovascular functions

Effects of high frequency stimulation of the amygdala central nucleus involved a selective decrease in the activity: an increase in the activity of the inferior cardiac nerve and a simultaneous decrease in the activity of the vertebral nerve, as well as an obvious BP increase. Bilateral electrolytic lesions of the same amygdala structure accompanied with an overload of the higher nervous activity induced no hypertensions. The role of the amygdala central nucleus in control of cardiovascular functions is discussed.     

Effect of lesions of the medial and lateral portions of the amygdala on motor activity in rats

In four groups of rats: with medial amygdala lesions, AMe, sham operated medial, AMe-C, with lateral amygdala lesions, LA, and sham operated lateral, LA-C,--motor activity was tested in small electro-magnetic cages before and after ablations. The obtained data showed an increase of motor activity only in AMe rats. Possible functional differentiation of modulatory mechanisms of the amygdala is discussed.     

Comparative study of the epileptogenic effect of kainic acid injected into the cerebral cortex, hippocampus and amygdala in adult cats chronically implanted

Intracerebral injection of kainic acid in cerebral cortex, hippocampus or amygdala in cats chronically implanted showed that: 1) Hippocampus and amygdala presented a greater sensitivity than the cerebral cortex, while hippocampus presented a greater sensitivity than the amygdala to the generation of an epileptic focus. 2) Comparison of latency, mean duration of afterdischarges, and the mean time period to obtain the peak intensity of the afterdischarge in the three cited structures, showed that mean latency of the first afterdischarge was significantly shorter in hippocampus and amygdala compared with the cerebral cortex. Moreover the mean time period to reach the peak intensity of the afterdischarge was again shorter in the subcortical structures. 3) The epileptic foci both in hippocampus and amygdala were blocked by CNQX and muscimol. 4) The behavioral changes depended on the intensity of the epileptic process. Tonic-clonic convulsions appeared only when the motor cerebral cortex was involved. Finally, 5) kainic acid injections in hippocampus and amygdala elicited an intense neuronal destruction and gliosis of these structures. We conclude that intracerebral injection of low doses of kainic acid in cats represent a good model to study focal epileptic thresholds in the CNS.     

Synaptic transmission and plasticity in the amygdala

Numerous studies in both rats and humans indicate the importance of the amygdala in the acquisition and expression of learned fear. The identification of the amygdala as an essential neural substrate for fear conditioning has permitted neurophysiological examinations of synaptic processes in the amygdala that may mediate fear conditioning. One candidate cellular mechanism for fear conditioning is long-term potentiation (LTP), an enduring increase in synaptic transmission induced by high-frequency stimulation of excitatory afferents. At present, the mechanisms underlying the induction and expression of amygdaloid LTP are only beginning to be understood, and probably involve both theN-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) subclasses of glutamate receptors. This article will examine recent studies of synaptic transmission and plasticity in the amygdala in an effort to understand the relationships of these processes to aversive learning and memory.     

Can't learn without you: predictive value coding in orbitofrontal cortex requires the basolateral amygdala

Basolateral amygdala and orbitofrontal cortex are implicated in cue-outcome learning. In this issue of Neuron, Schoenbaum et al. show that, following basolateral amygdala lesions, cue-selective neurons in orbitofrontal cortex are more sensory driven and less sensitive to the motivational value of an outcome, suggesting that predictive value coding in orbitofrontal cortex is dependent on input from basolateral amygdala.     

Dopaminergic innervation of the amygdala is highly responsive to stress

The amygdala has been implicated in the neuronal sequelae of stress, although little is known about the neurochemical mechanisms underlying amygdala transmission. In vivo microdialysis was employed to measure extracellular levels of dopamine in the basolateral nucleus of the amygdala in awake rats. Once it was established that impulse-dependent release of dopamine could be measured reliably in the amygdala, the effect of stress, induced by mild handling, on amygdala dopamine release was compared with that in three other dopamine-innervated regions, the medial prefrontal cortex, nucleus accumbens, and caudate nucleus. The magnitude of increase in dopamine in response to the handling stimulus was significantly greater in the amygdala than in the nucleus accumbens and prefrontal cortex. This increase was maximal during the application of stress and diminished after the cessation of stress. In contrast, the increases in extracellular dopamine levels in other regions, in particular the nucleus accumbens, were prolonged, reaching maximal values after the cessation of stress. These results suggest that dopaminergic innervation of the amygdala may be more responsive to stress than that of other dopamine-innervated regions of the limbic system, including the prefrontal cortex, and implicate amygdalar dopamine in normal and pathophysiological processes subserving an organism's response to stress.     

Directional Influence between the Human Amygdala and Orbitofrontal Cortex at the Time of Decision-Making

There is a growing consensus that the brain makes simple choices, such as choosing between an apple and an orange, by assigning value to the options under consideration, and comparing those values to make a choice. There is also a consensus that value signals computed in orbitofrontal cortex (OFC) and amygdala play a critical role in the choice process. However, the nature of the flow of information between OFC and amygdala at the time of decision is still unknown. In order to study this question, simultaneous local field potentials were recorded from OFC and amygdala in human patients while they performed a simple food choice task. Although the interaction of these circuits has been studied in animals, this study examines the effective connectivity directly in the human brain on a moment-by-moment basis. A spectral conditional Granger causality analysis was performed in order to test if the modulation of activity goes mainly from OFC-to-amygdala, from amygdala-to-OFC, or if it is bi-directional. Influence from amygdala-to-OFC was dominant prior to the revealed choice, with a small but significant OFC influence on the amygdala earlier in the trial. Alpha oscillation amplitudes analyzed with the Hilbert-Huang transform revealed differences in choice valence coincident with temporally specific amygdala influence on the OFC.     

Altered effective connectivity network of the amygdala in social anxiety disorder: a resting-state FMRI study

The amygdala is often found to be abnormally recruited in social anxiety disorder (SAD) patients. The question whether amygdala activation is primarily abnormal and affects other brain systems or whether it responds "normally" to an abnormal pattern of information conveyed by other brain structures remained unanswered. To address this question, we investigated a network of effective connectivity associated with the amygdala using Granger causality analysis on resting-state functional MRI data of 22 SAD patients and 21 healthy controls (HC). Implications of abnormal effective connectivity and clinical severity were investigated using the Liebowitz Social Anxiety Scale (LSAS). Decreased influence from inferior temporal gyrus (ITG) to amygdala was found in SAD, while bidirectional influences between amygdala and visual cortices were increased compared to HCs. Clinical relevance of decreased effective connectivity from ITG to amygdala was suggested by a negative correlation of LSAS avoidance scores and the value of Granger causality. Our study is the first to reveal a network of abnormal effective connectivity of core structures in SAD. This is in support of a disregulation in predescribed modules involved in affect control. The amygdala is placed in a central position of dysfunction characterized both by decreased regulatory influence of orbitofrontal cortex and increased crosstalk with visual cortex. The model which is proposed based on our results lends neurobiological support towards cognitive models considering disinhibition and an attentional bias towards negative stimuli as a core feature of the disorder.     

Maternal Separation Enhances Conditioned Fear and Decreases the mRNA Levels of the Neurotensin Receptor 1 Gene with Hypermethylation of This Gene in the Rat Amygdala

Stress during postnatal development is associated with an increased risk for depression, anxiety disorders, and substance abuse later in life, almost as if mental illness is able to be programed by early life stressors. Recent studies suggest that such “programmed” effects can be caused by epigenetic regulation. With respect to conditioned fear, previous studies have indicated that early life stress influences its development in adulthood, whereas no potential role of epigenetic regulation has been reported. Neurotensin (NTS) is an endogenous neuropeptide that has receptors densely located in the amygdala and hippocampus. Recently, NTS systems have constituted an emerging target for the treatment of anxiety. The aim of the present work is to clarify whether the NTS system is involved in the disturbance of conditioned fear in rats stressed by maternal separation (MS). The results showed that MS enhanced freezing behaviors in fear-conditioned stress and reduced the gene expression of NTS receptor (NTSR) 1 but not of NTS or NTSR2 in the amygdalas of adult rats. The microinjection of a NTSR1 antagonist into the amygdala increased the percentage of freezing in conditioned fear, whereas the microinjection of NTSR1 agonist decreased freezing. These results suggest that NTSR1 in the amygdala may play a role in the effects of MS on conditioned fear stress in adult rats. Moreover, MS increased DNA methylation in the promoter region of NTSR1 in the amygdala. Taken together, MS may leave epigenetic marks in the NTSR1 gene in the amygdala, which may enhance conditioned fear in adulthood. The MS-induced alternations of DNA methylation in the promoter region of NTSR1 in the amygdala may be associated with vulnerability to the development of anxiety disorders and depression in adulthood.     

Newly proliferated cells in the adult male amygdala are affected by gonadal steroid hormones

Gonadal steroid hormones play an important role in the proliferation, survival, and activation of neurons. The present study was performed to examine the effects of testosterone and its metabolites on newly proliferated cells in the amygdala of adult male meadow voles (Microtus pennsylvanicus). Treatment with testosterone propionate (TP) in castrated males resulted in plasma testosterone levels similar to males following mating. TP-treated males displayed a significant increase in the density of cells labeled with a cell proliferation marker (BrdU) in the amygdala. Treatment with estradiol benzoate (EB) exerted a similar effect as TP on the density of BrdU-labeled cells, whereas 5alpha-dihydrotestosterone (DHT) was ineffective. A larger proportion (approximately 44%) of the BrdU-labeled cells in the amygdala displayed a neuronal phenotype, and a lesser percentage (approximately 35%) displayed a glial progenitor phenotype; however, treatment effects were not found in either population of cells. Hormonal effects appeared to be site-specific as no group differences were found in the dentate gyrus of the hippocampus or ventromedial hypothalamus. Finally, a time course study indicated that BrdU-labeled cells in the amygdala are present as early as 30 min following an acute injection of BrdU. Together, these data suggest that gonadal steroid hormones influence the number of newly proliferated cells in the amygdala, most likely by acting through an estrogenic mechanism, and these effects may be exerted on locally proliferating progenitors within the amygdala.     

The amygdala and autism: implications from non-human primate studies

Brothers (1990 ) has proposed that the amygdala is an important component of the neural network that underlies social behavior. Kemper and Bauman (1993 ) identified neuropathology in the amygdala of the postmortem autistic brain. These findings, along with recent functional neuroimaging data, have led Baron-Cohen et al. (2000 ) to propose that dysfunction of the amygdala may be responsible, in part, for the impairment of social behavior that is a hallmark feature of autism. Recent data from studies in our laboratory on the effects of amygdala lesions in the adult and infant macaque monkey do not support a fundamental role for the amygdala in social behavior. If the amygdala is not essential for the component processes of social behavior, as seems to be case in both non-human primates and selected patients with bilateral amygdala damage, then it is unlikely to be the primary substrate for the impaired social behavior of autism. However, damage to the amygdala does have an effect on a monkey's response to normally fear-inducing stimuli, such as snakes, and removes a natural reluctance to engage novel conspecifics in social interactions. These findings lead to the conclusion that an important role for the amygdala is in the detection of threats and mobilizing an appropriate behavioral response, part of which is fear. Interestingly, an important comorbid feature of autism is anxiety ( Muris et al. 1998 ). If the amygdala is pathological in subjects with autism, it may contribute to their abnormal fears and increased anxiety rather than their abnormal social behavior.     

Increased sensitivity to the stimulant effects of morphine conferred by anti-adhesive glycoprotein SPARC in amygdala

Repeated administration of morphine substantially increases its locomotor-enhancing activity, a phenomenon termed locomotor sensitization. Here we show that secreted protein acidic and rich in cysteine (SPARC), an anti-adhesive glycoprotein present in the basolateral amygdala, contributes to the establishment of locomotor sensitization. The morphine-induced increase in SPARC levels in the basolateral amygdala persisted after morphine withdrawal and coincided with the duration of locomotor sensitization. Moreover, a single injection of morphine after SPARC infusion into the basolateral amygdala of previously uninjected mice substantially enhanced locomotor activity. Thus, SPARC may be an important element for establishing locomotor sensitization to morphine.     

Involvement of Putrescine in the Development of Kindled Seizure in Rats

During the development of kindling by daily electrical stimulations applied to the left amygdala of rats, concentrations of the polyamines putrescine, spermidine, and spermine were measured in the left amygdala and the remainder of the cerebrum. A significant increase of putrescine concentration appeared first at the left amygdala in prekindled rats and then propagated to the remainder of the cerebrum with the development of kindling. This increase in putrescine concentration in the left amygdala was higher in prekindled rats than in fully kindled rats and lasted for at least 24 h after the final kindling stimulation. The concentrations of spermidine and spermine were slightly increased in a fully kindled state. To clarify the role of putrescine in kindling, the development of amygdaloid kindling was examined in rats after microinjections of alpha-difluoromethylornithine, a specific inhibitor of polyamine synthesis, and putrescine into the ipsilateral amygdala. Pretreatment with alpha-difluoromethylornithine (50 nmol) for 10 days accelerated both the development of behavioral kindling and the propagation of the afterdischarge from the left amygdala to the frontal cortex. In contrast, pretreatment with putrescine (200 nmol) for 10 days retarded the development of kindling. These results suggest that the increase in putrescine concentration in the kindled brain has an inhibitory effect on the development of kindling.     

Bilateral MR volumetry of the amygdala in chronic PTSD patients

Posttraumatic stress disorder (PTSD) patients experience symptoms which implicate dysfunction of emotional memory circuits, and possible damage of the amygdala. Laterality differences in activity of the amygdala have been reported in PTSD patients, with presumed adaptive plasticity in the hippocampus and the amygdala. The aim of this study was to investigate possible interhemispheric differences of amygdalar volume in chronic PTSD patients, with calculation of right-to-left volume ratios. Bilateral magnetic resonance (MR) volumetry was applied in 11 chronic PTSD patients. The mean right amygdalar volume of our patients was significantly smaller than the left one (p = 0.031), with the right-to-left volume ratio of 0.96 +/- 0.06. This tendency towards smaller right amygdala may be an acquired effect as a result of stress-induced plasticity, however we can not exclude the possibility of a predisposing condition.     

The role of NCAM in auditory fear conditioning and its modulation by stress: a focus on the amygdala

Chronic stress in rodents was shown to induce structural shrinkage and functional alterations in the hippocampus that were linked to spatial memory impairments. Effects of chronic stress on the amygdala have been linked to a facilitation of fear conditioning. Although the underlying molecular mechanisms are still poorly understood, increasing evidence highlights the neural cell adhesion molecule (NCAM) as an important molecular mediator of stress‐induced structural and functional alterations. In this study, we investigated whether altered NCAM expression levels in the amygdala might be related to stress‐induced enhancement of auditory fear conditioning and anxiety‐like behavior. In adult C57BL/6J wild‐type mice, chronic unpredictable stress resulted in an isoform‐specific increase of NCAM expression (NCAM‐140 and NCAM‐180) in the amygdala, as well as enhanced auditory fear conditioning and anxiety‐like behavior. Strikingly, forebrain‐specific conditional NCAM‐deficient mice (NCAM‐floxed mice that express the cre‐recombinase under the control of the promoter of the α‐subunit of the calcium‐calmodulin‐dependent protein kinase II), whose amygdala NCAM expression levels are reduced, displayed impaired auditory fear conditioning which was not altered following chronic stress exposure. Likewise, chronic stress in these conditional NCAM‐deficient mice did not modify NCAM expression levels in the amygdala or hippocampus, while they showed enhanced anxiety‐like behavior, questioning the involvement of NCAM in this type of behavior. Together, our results strongly support the involvement of NCAM in the amygdala in the consolidation of auditory fear conditioning and highlight increased NCAM expression in the amygdala among the mechanisms whereby stress facilitates fear conditioning processes.     

Effects of PKA modulation on the expression of neuropeptide Y in rat amygdaloid structures during ethanol withdrawal

We recently reported that neuropeptide Y (NPY) protein levels and cAMP responsive element binding (CREB) protein phosphorylation are lower in amygdaloid structures during ethanol withdrawal after chronic exposure. Furthermore, we reported that normalization of CREB phosphorylation by infusing protein kinase A (PKA) activator into the central amygdala prevents anxiety-like effects in rats during ethanol withdrawal. Here we investigated whether normalization of CREB phosphorylation by infusing PKA activator (Sp-cAMP) into the central amygdala also normalizes the expression of NPY during ethanol withdrawal. Sprague-Dawley male rats were cannulated targeting the central amygdala and then treated either with Lieber-DeCarli ethanol diet or control diet for 15 days. Subsequently ethanol-fed rats were withdrawn for 0 and 24h. The control-diet fed and ethanol-withdrawn rats were infused twice with PKA activator or inhibitor (Rp-cAMP). The protein and mRNA levels of NPY were determined in amygdaloid structures using gold-immunolabeling and the in situ RT-PCR procedure. It was found that chronic ethanol treatment has no effect on mRNA and protein levels of NPY in the central, medial, or basolateral amygdala. On the other hand, ethanol withdrawal produced significant reductions in mRNA and protein levels of NPY in the central and medial but not in the basolateral amygdala. The reductions in mRNA and protein levels of NPY were normalized in the central amygdala by infusion with PKA activator in ethanol-withdrawn rats. On the other hand, PKA-inhibitor infusion does not have any effect on mRNA and protein levels of NPY in the central amygdala of ethanol-withdrawn rats, but significantly decreased the expression of NPY in the central amygdala of control-diet fed rats. These results suggest that the decreased cellular expression of NPY in the central amygdala may play an important role in the CREB-mediated regulation of anxiety-like behaviors during ethanol withdrawal.     

Increased anxiety-like behavior and enhanced synaptic efficacy in the amygdala of GluR5 knockout mice

GABAergic transmission in the amygdala modulates the expression of anxiety. Understanding the interplay between GABAergic transmission and excitatory circuits in the amygdala is, therefore, critical for understanding the neurobiological basis of anxiety. Here, we used a multi-disciplinary approach to demonstrate that GluR5-containing kainate receptors regulate local inhibitory circuits, modulate the excitatory transmission from the basolateral amygdala to the central amygdala, and control behavioral anxiety. Genetic deletion of GluR5 or local injection of a GluR5 antagonist into the basolateral amygdala increases anxiety-like behavior. Activation of GluR5 selectively depolarized inhibitory neurons, thereby increasing GABA release and contributing to tonic GABA current in the basolateral amygdala. The enhanced GABAergic transmission leads to reduced excitatory inputs in the central amygdala. Our results suggest that GluR5 is a key regulator of inhibitory circuits in the amygdala and highlight the potential use of GluR5-specific drugs in the treatment of pathological anxiety.     

Intralimbic evoked potentials in the formation of an instrumental food conditioned reflex to hippocampal electrostimulation in dogs]

In dogs with the electrodes implanted in the hippocampus, amygdala, septum and hypothalamus an instrumental alimentary conditioned reflex (CR) was elaborated to electrostimulation of the hippocampus. Intralimbic evoked potentials (EPs) were studied during the elaboration and extinction of this reflex and during stimulations of limbic structures conducted with the purpose of CR generalization checking. Late EP components in the lateral hypothalamus and central nucleus of the amygdala changed during CR elaboration and extinction and in the hippocampus during amygdala testing. In both cases the amplitude of trace positivity and of slow negative wave was less, when during stimulation of the structure an instrumental movement was initiated than at its absence.     

Sex-dependent correlations between the personality dimension of harm avoidance and the resting-state functional connectivity of amygdala subregions

Harm avoidance (HA) is a personality dimension involving the tendency to respond intensely to signals of aversive stimuli. Many previous neuroimaging studies have associated HA scores with the structural and functional organization of the amygdala, but none of these studies have evaluated the correlation between HA score and amygdala resting-state functional connectivity (rsFC). Moreover, the amygdala is not a homogeneous structure, and it has been divided into several structurally and functionally distinct subregions. Investigating the associations between HA score and properties of subregions of the amygdala could greatly improve our understanding of HA. In the present study, using a large sample of 291 healthy young adults, we aimed to uncover correlations between HA scores and the rsFCs of each amygdala subregion and to uncover possible sex-based differences in these correlations. We found that subregions of the amygdala showed different rsFC patterns, which contributed differently to individual HA scores. More specifically, HA scores were correlated with rsFCs between the laterobasal amygdala subregion and temporal and occipital cortices related to emotional information input, between the centromedial subregion and the frontal cortices associated with emotional output control, and between the superficial subregion and the frontal and temporal areas involved in both functions. Moreover, significant gender-based differences were uncovered in these correlations. Our findings provide a more detailed model of association between HA scores and amygdala rsFC, extend our understanding of the connectivity of subregions of the amygdala, and confirm sex-based differences in HA associations.