Anxiety and ultrastructural consequences of chronic mild stress in rats.

Detrimental consequences following exposure to severe stress, either acute or chronic are well recognized. Chronic mild stress (CMS) is also a leading cause of emotional distress and neuropsychiatric conditions such as anxiety disorders. However, the neurobiological substrates of the latter, particularly at the ultrastructural levels have not been adequately investigated. In this study, adult male Wistar rats were subjected to 4 h daily mild restraint for 20 days and their behavior in open field and elevated plus maze (EPM) were evaluated 24 h after the last restraint. Anxiety-like behavior was evident in CMS exposed rats by increases in rearing and grooming in the open field and the avoidance of open arms in the EPM. Concomitant ultrastructural alterations such as chromatolysis, agglutination of synaptic vesicles or mitochondrial damage were also observed in the central nucleus of amygdala (CNA), an area intimately involved in emotional and fear response, in CMS exposed rats. These results while confirming detrimental consequences of CMS, also suggest that ultrastructural alterations in CNA may be a basis for CMS-induced anxiety.

Whole brain and deep gray matter structure segmentation: Quantitative comparison between MPRAGE and MP2RAGE sequences.

OBJECTIVE: T1-weighted MRI images are commonly used for volumetric assessment of brain structures. Magnetization prepared 2 rapid gradient echo (MP2RAGE) sequence offers superior gray (GM) and white matter (WM) contrast. This study aimed to quantitatively assess the agreement of whole brain tissue and deep GM (DGM) volumes obtained from MP2RAGE compared to the widely used MP-RAGE sequence. METHODS: Twenty-nine healthy participants were included in this study. All subjects underwent a 3T MRI scan acquiring high-resolution 3D MP-RAGE and MP2RAGE images. Twelve participants were re-scanned after one year. The whole brain, as well as DGM segmentation, was performed using CAT12, volBrain, and FSL-FAST automatic segmentation tools based on the acquired images. Finally, contrast-to-noise ratio between WM and GM (CNRWG), the agreement between the obtained tissue volumes, as well as scan-rescan variability of both sequences were explored. RESULTS: Significantly higher CNRWG was detected in MP2RAGE vs. MP-RAGE (Mean ± SD = 0.97 ± 0.04 vs. 0.8 ± 0.1 respectively; p<0.0001). Significantly higher total brain GM, and lower cerebrospinal fluid volumes were obtained from MP2RAGE vs. MP-RAGE based on all segmentation methods (p<0.05 in all cases). Whole-brain voxel-wise comparisons revealed higher GM tissue probability in the thalamus, putamen, caudate, lingual gyrus, and precentral gyrus based on MP2RAGE compared with MP-RAGE. Moreover, significantly higher WM probability was observed in the cerebellum, corpus callosum, and frontal-and-temporal regions in MP2RAGE vs. MP-RAGE. Finally, MP2RAGE showed a higher mean percentage of change in total brain GM compared to MP-RAGE. On the other hand, MP-RAGE demonstrated a higher overtime percentage of change in WM and DGM volumes compared to MP2RAGE. CONCLUSIONS: Due to its higher CNR, MP2RAGE resulted in reproducible brain tissue segmentation, and thus is a recommended method for volumetric imaging biomarkers for the monitoring of neurological diseases.

Age-related behavioral and ultrastructural changes in the rat amygdala.

Although the relationships between brain structure and emotions may alter across the life span, this relationship is of particular importance during aging when significant alterations in emotions may be manifested. Understanding the structural-behavioral relationship could not only provide a neurobiological basis of these changes, but could also suggest potential intervention. Since anxiety is commonly observed in aging population, we undertook this study to determine the extent of this behavioral manifestations as well as the associated ultrastructural changes in the amygdala. Rats of various age groups, adolescent, adult, and aged were tested for anxiety-like behavior and the ultrastructure/presynaptic architecture of the central nucleus of amygdala (CNA) were evaluated using transmission electron microscopy (EM). Aged rats were consistently more anxious than the other groups as evidenced by their scores in the elevated plus maze. Morphometric EM analysis of axodendritic synapses revealed that the aged rats had a lower presynaptic area as well as number of synapses, but unexpectedly a higher number of presynaptic mitochondria in CNA. Since presynaptic mitochondria are known to provide the energy for neurotransmission, it may be concluded that compensatory mechanisms are still operational during aging, and hence, may be a target for therapeutic intervention at this stage of life span.

Murine's amygdala microstructure and elevated plus maze activities following R. vomitoria root bark and G. latifolium leaf extracts administration.

R. vomitoria (RV), a plant used locally in the management of psychotic disorders, adversely affects the brain functionally and structurally. Such adverse reports, as well as the potential of G. latifolium (GL) to mitigate same warranted this investigation on the combined actions of RV and GL on the amygdala. Twenty-four male CD-1 mice weighing 22-27 g were divided into four groups (n = 6): Control (20 ml/kg body weight, b.w., distilled water); RV (200 mg/kg b.w.), GL (200 mg/kg b.w.), and RV (200 mg/kg b.w.) and GL (200 mg/kg b.w.) combination orally, and for 14 days. On day 15, the elevated-plus maze test was carried out and the animals sacrificed, and processed for histological and immunohistochemical studies. Neurobehavioural results showed significant decrease (p[Formula: see text] 0.001) in stretch-attend posture, time spent in closed arms, grooming frequency, protected head-dip, as well as significantly (p [Formula: see text] 0.01) increased time spent in the open arms and unprotected head-dips of the RV group. The combined RV and GL groups showed no such differences in these parameters. Histologically, the amygdala showed hypertrophied cells, with pyknotic and karyorrhectic nuclei, and reduced expression of Nissl substance in the RV group, while the combined RV and GL group showed less degenerative features. Glial fibrillary acidic protein expression (GFAP) was increased in the RV group, while the combined RV and GL group showed reduced expression. In conclusion, RV root bark extract has adverse effects on the microstructure of murines' amygdala and their behaviour, which may be ameliorated by GL.

Gap junctions and expression of Cx36, Cx43 and Cx45 in the posterodorsal medial amygdala of adult rats.

The posterodorsal medial amygdala (MePD) has an adapted synaptic organization that dynamically modulates reproduction and other social behaviors in rats. Discrete gap junctions between glial cells were previously reported in the MePD neuropil. Connexins (Cx) are components of gap junctions and indicative of cellular electrical coupling. Here, we report the ultrastructural occurrence of gap junctions between neurons in the MePD and demonstrate the expression and immunofluorescent labeling of Cx36, Cx43 and Cx45 in this subcortical area of adult male rats. Few neuronal gap junctions were found in the MePD and, when identified, occurred between dendrites. On the other hand, there is a diffuse presence and distribution of punctate labelling for the tested Cxs. Puncta were visualized isolated or forming clusters in the same focal plane of cell bodies or along the MePD neuropil. The Cx36 puncta were found in neurons, Cx43 in astrocytes and Cx45 in both neurons and astrocytes. Our data indicate the presence of few gap junctions and different Cxs composition in the MePD. Because Cxs can assemble, form hemichannel units and/or serve as transcriptional regulator, it is likely that additional modulation of intercellular communication can occur besides the chemical transmission in the MePD of adult rats.

PTEN Activity Defines an Axis for Plasticity at Cortico-Amygdala Synapses and Influences Social Behavior.

Phosphatase and tensin homolog on chromosome 10 (PTEN) is a tumor suppressor and autism-associated gene that exerts an important influence over neuronal structure and function during development. In addition, it participates in synaptic plasticity processes in adulthood. As an attempt to assess synaptic and developmental mechanisms by which PTEN can modulate cognitive function, we studied the consequences of 2 different genetic manipulations in mice: presence of additional genomic copies of the Pten gene (Ptentg) and knock-in of a truncated Pten gene lacking its PDZ motif (Pten-ΔPDZ), which is required for interaction with synaptic proteins. Ptentg mice exhibit substantial microcephaly, structural hypoconnectivity, enhanced synaptic depression at cortico-amygdala synapses, reduced anxiety, and intensified social interactions. In contrast, Pten-ΔPDZ mice have a much more restricted phenotype, with normal synaptic connectivity, but impaired synaptic depression at cortico-amygdala synapses and virtually abolished social interactions. These results suggest that synaptic actions of PTEN in the amygdala contribute to specific behavioral traits, such as sociability. Also, PTEN appears to function as a bidirectional rheostat in the amygdala: reduction in PTEN activity at synapses is associated with less sociability, whereas enhanced PTEN activity accompanies hypersocial behavior.

Ultrastructural localization of cannabinoid CB1 and mGluR5 receptors in the prefrontal cortex and amygdala.

Stimulation of the postsynaptic metabotropic glutamate receptor mGluR5 triggers retrograde signaling of endocannabinoids that activate presynaptic cannabinoid CB1 receptors on juxtaposing axon terminals. To better understand the synaptic structure that supports mGluR5 mediation of CB1 activation in the prefrontal cortex (PFC) and basolateral amygdala (BLA), we examined electron microscopic dual immunolabeling of these receptors in the prelimbic PFC (prPFC) and BLA of adult male rats. CB1 immunoreactivity was detected in axon terminals that were typically large, complex, and contained dense-core and clear synaptic vesicles. Of terminals forming discernible synaptic specializations, 95% were symmetric inhibitory-type in the prPFC and 90% were inhibitory in the BLA. CB1-immunoreactive terminals frequently contacted dendrites containing mGluR5 adjacent to unlabeled terminals forming excitatory-type synapses. Because most CB1-containing terminals form inhibitory-type synapses, the unlabeled axon terminals forming asymmetric synapses are the likely source of the mGluR5 ligand glutamate. In the prPFC, serial section analysis revealed that GABAergic CB1-containing axon terminals targeted dendrites adjacent to glutamatergic axon terminals, often near dendritic bifurcations. These observations provide ultrastructural evidence that cortical CB1 receptors are strategically positioned for integration of synaptic signaling in response to stimulation of postsynaptic mGluR5 receptors and facilitation of heterosynaptic communication between multiple neurons.

Midline thalamic inputs to the amygdala: Ultrastructure and synaptic targets.

One of the main subcortical inputs to the basolateral nucleus of the amygdala (BL) originates from a group of dorsal thalamic nuclei located at or near the midline, mainly from the central medial (CMT), and paraventricular (PVT) nuclei. Although similarities among the responsiveness of BL, CMT, and PVT neurons to emotionally arousing stimuli suggest that these thalamic inputs exert a significant influence over BL activity, little is known about the synaptic relationships that mediate these effects. Thus, the present study used Phaseolus vulgaris-leucoagglutinin (PHAL) anterograde tracing and electron microscopy to shed light on the ultrastructural properties and synaptic targets of CMT and PVT axon terminals in the rat BL. Virtually all PHAL-positive CMT and PVT axon terminals formed asymmetric synapses. Although CMT and PVT axon terminals generally contacted dendritic spines, a substantial number ended on dendritic shafts. To determine whether these dendritic shafts belonged to principal or local-circuit cells, calcium/calmodulin-dependent protein kinase II (CAMKIIα) immunoreactivity was used as a selective marker of principal BL neurons. In most cases, dendritic shafts postsynaptic to PHAL-labeled CMT and PVT terminals were immunopositive for CaMKIIα. Overall, these results suggest that CMT and PVT inputs mostly target principal BL neurons such that when CMT or PVT neurons fire, little feed-forward inhibition counters their excitatory influence over principal cells. These results are consistent with the possibility that CMT and PVT inputs constitute major determinants of BL activity.

Specificity of Primate Amygdalar Pathways to Hippocampus.

The amygdala projects to hippocampus in pathways through which affective or social stimuli may influence learning and memory. We investigated the still unknown amygdalar termination patterns and their postsynaptic targets in hippocampus from system to synapse in rhesus monkeys of both sexes. The amygdala robustly innervated the stratum lacunosum-moleculare layer of cornu ammonis fields and uncus anteriorly. Sparser terminations in posterior hippocampus innervated the radiatum and pyramidal layers at the prosubicular/CA1 juncture. The terminations, which were larger than other afferents in the surrounding neuropil, position the amygdala to influence hippocampal input anteriorly, and its output posteriorly. Most amygdalar boutons (76-80%) innervated spines of excitatory hippocampal neurons, and most of the remaining innervated presumed inhibitory neurons, identified by morphology and label with parvalbumin or calretinin, which distinguished nonoverlapping neurochemical classes of hippocampal inhibitory neurons. In CA1, amygdalar axons innervated some calretinin neurons, which disinhibit pyramidal neurons. By contrast, in CA3 the amygdala innervated both calretinin and parvalbumin neurons; the latter strongly inhibit nearby excitatory neurons. In CA3, amygdalar pathways also made closely spaced dual synapses on excitatory neurons. The strong excitatory synapses in CA3 may facilitate affective context representations and trigger sharp-wave ripples associated with memory consolidation. When the amygdala is excessively activated during traumatic events, the specialized innervation of excitatory neurons and the powerful parvalbumin inhibitory neurons in CA3 may allow the suppression of activity of nearby neurons that receive weaker nonamygdalar input, leading to biased passage of highly charged affective stimuli and generalized fear.SIGNIFICANCE STATEMENT Strong pathways from the amygdala targeted the anterior hippocampus, and more weakly its posterior sectors, positioned to influence a variety of emotional and cognitive functions. In hippocampal field CA1, the amygdala innervated some calretinin neurons, which disinhibit excitatory neurons. By contrast, in CA3 the amygdala innervated calretinin as well as some of the powerful parvalbumin inhibitory neurons and may help balance the activity of neural ensembles to allow social interactions, learning, and memory. These results suggest that when the amygdala is hyperactive during emotional upheaval, it strongly activates excitatory hippocampal neurons and parvalbumin inhibitory neurons in CA3, which can suppress nearby neurons that receive weaker input from other sources, biasing the passage of stimuli with high emotional import and leading to generalized fear.

Alterations in cyclin D1 and cyclin­dependent kinase 4 expression in the amygdalae of post­traumatic stress disorder rats.

The amygdalae are an important component of the human limbic system and exhibit a key role in emotional and behavioral reactions. Previous studies have demonstrated abnormal function and morphology in the amygdalae of post­traumatic stress disorder (PTSD)­like animal models, however the underlying molecular mechanisms remain elusive. The authors have previously demonstrated that PTSD induced increased apoptosis in the amygdala of PTSD­like animals. Cyclin D1 and cyclin­dependent kinase 4 (CDK4) are two important regulators of the cell cycle. The study explored the expression of cyclin D1 and CDK4 in the amygdala in PTSD. The single­prolonged stress (SPS) rat model was used as a PTSD­like model. Ultrastructural alterations of cells in the amygdala were observed using transmission electron microscopy (TEM). 4',6­Diamidino­2­phenylindole (DAPI) fluorescence was employed to detect nuclear pycnosis. Cyclin D1 and CDK4 expression in the amygdala cells was examined using immunofluorescence, Western blotting and reverse transcription­quantitative polymerase chain reaction. TEM revealed morphological alterations to the amygdala cells of the SPS rats. DAPI­stained nuclear brightness levels differed between the control and SPS groups. Expression of cyclin D1 and CDK4 in the amygdala increased gradually 1 day and 4 days following SPS stimulation, and peaked 7 days following SPS stimulation at the protein and mRNA levels, in comparison with the control rats. These findings suggest that SPS resulted in increased cyclin D1 and CDK4 expression, which may accelerate cell apoptosis. This may be associated with SPS­induced abnormal function and structure of the amygdala.

Influences of prenatal and postnatal maternal depression on amygdala volume and microstructure in young children.

Maternal depressive symptoms influence neurodevelopment in the offspring. Such effects may appear to be gender-dependent. The present study examined contributions of prenatal and postnatal maternal depressive symptoms to the volume and microstructure of the amygdala in 4.5-year-old boys and girls. Prenatal maternal depressive symptoms were measured using the Edinburgh Postnatal Depression Scale (EPDS) at 26 weeks of gestation. Postnatal maternal depression was assessed at 3 months using the EPDS and at 1, 2, 3 and 4.5 years using the Beck's Depression Inventory-II. Structural magnetic resonance imaging and diffusion tensor imaging were performed with 4.5-year-old children to extract the volume and fractional anisotropy (FA) values of the amygdala. Our results showed that greater prenatal maternal depressive symptoms were associated with larger right amygdala volume in girls, but not in boys. Increased postnatal maternal depressive symptoms were associated with higher right amygdala FA in the overall sample and girls, but not in boys. These results support the role of variation in right amygdala structure in transmission of maternal depression to the offspring, particularly to girls. The differential effects of prenatal and postnatal maternal depressive symptoms on the volume and FA of the right amygdala suggest the importance of the timing of exposure to maternal depressive symptoms in brain development of girls. This further underscores the need for intervention targeting both prenatal and postnatal maternal depression to girls in preventing adverse child outcomes.

Decrease in neuronal spine density in the postpartum period in the amygdala and bed nucleus of the stria terminalis in rat.

In pregnancy and the postpartum period, many women have emotional instability and some suffer from depression. The ovarian steroid hormone milieu is markedly changed during these periods, and this hormonal change may be an important cause of peripartum emotional instability. The amygdala is a central region of emotion, and the bed nucleus of the stria terminalis (BNST), which is considered to be the extended amygdala, is also involved in the emotional response. The amygdala and BNST are well characterized as target brain regions for ovarian steroid hormones, and this suggests that the functional response of neurons in these regions to hormonal fluctuation is affected in the peripartum period. In this study, we investigated the neuronal morphology in the central (CeA) and basolateral (BLA) nucleus of the amygdala and BNST on gestational days 15 (G15) (mid-gestation) and 20 (G20) (late gestation) and 4days after delivery (P4) (early postpartum) in rat. Golgi staining showed that the dendritic spine density, and particularly the number of mature mushroom-type spines, in the CeA, BLA and BNST was significantly decreased at P4, compared with G15 and G20 and with virgin females in the estrous phase in the normal estrous cycle (Est). Interestingly, the presence of pups after delivery influenced the spine density in the BNST. The density was significantly decreased with pup presence compared with pup absence at P4, and compared with G15, G20 and Est. These results provide fundamental insights into the neuronal basis underlying emotional instability during pregnancy and postpartum.

Activation of Supraoptic Oxytocin Neurons by Secretin Facilitates Social Recognition.

BACKGROUND: Social recognition underlies social behavior in animals, and patients with psychiatric disorders associated with social deficits show abnormalities in social recognition. Oxytocin is implicated in social behavior and has received attention as an effective treatment for sociobehavioral deficits. Secretin receptor-deficient mice show deficits in social behavior. The relationship between oxytocin and secretin concerning social behavior remains to be determined. METHODS: Expression of c-Fos in oxytocin neurons and release of oxytocin from their dendrites after secretin application were investigated. Social recognition was examined after intracerebroventricular or local injection of secretin, oxytocin, or an oxytocin receptor antagonist in rats, oxytocin receptor-deficient mice, and secretin receptor-deficient mice. Electron and light microscopic immunohistochemical analysis was also performed to determine whether oxytocin neurons extend their dendrites into the medial amygdala. RESULTS: Supraoptic oxytocin neurons expressed the secretin receptor. Secretin activated supraoptic oxytocin neurons and facilitated oxytocin release from dendrites. Secretin increased acquisition of social recognition in an oxytocin receptor-dependent manner. Local application of secretin into the supraoptic nucleus facilitated social recognition, and this facilitation was blocked by an oxytocin receptor antagonist injected into, but not outside of, the medial amygdala. In the medial amygdala, dendrite-like thick oxytocin processes were found to extend from the supraoptic nucleus. Furthermore, oxytocin treatment restored deficits of social recognition in secretin receptor-deficient mice. CONCLUSIONS: The results of our study demonstrate that secretin-induced dendritic oxytocin release from supraoptic neurons enhances social recognition. The newly defined secretin-oxytocin system may lead to a possible treatment for social deficits.

Localization of the delta opioid receptor and corticotropin-releasing factor in the amygdalar complex: role in anxiety.

It is well established that central nervous system norepinephrine (NE) and corticotropin-releasing factor (CRF) systems are important mediators of behavioral responses to stressors. More recent studies have defined a role for delta opioid receptors (DOPR) in maintaining emotional valence including anxiety. The amygdala plays an important role in processing emotional stimuli, and has been implicated in the development of anxiety disorders. Activation of DOPR or inhibition of CRF in the amygdala reduces baseline and stress-induced anxiety-like responses. It is not known whether CRF- and DOPR-containing amygdalar neurons interact or whether they are regulated by NE afferents. Therefore, this study sought to better define interactions between the CRF, DOPR and NE systems in the basolateral (BLA) and central nucleus of the amygdala (CeA) of the male rat using anatomical and functional approaches. Irrespective of the amygdalar subregion, dual immunofluorescence microscopy showed that DOPR was present in CRF-containing neurons. Immunoelectron microscopy confirmed that DOPR was localized to both dendritic processes and axon terminals in the BLA and CeA. Semi-quantitative dual immunoelectron microscopy analysis of gold-silver labeling for DOPR and immunoperoxidase labeling for CRF revealed that 55 % of the CRF neurons analyzed contained DOPR in the BLA while 67 % of the CRF neurons analyzed contained DOPR in the CeA. Furthermore, approximately 41 % of DOPR-labeled axon terminals targeted BLA neurons that expressed CRF while 29 % of DOPR-labeled axon terminals targeted CeA neurons that expressed CRF. Triple label immunofluorescence microscopy revealed that DOPR and CRF were co-localized in common cellular profiles that were in close proximity to NE-containing fibers in both subregions. These anatomical results indicate significant interactions between DOPR and CRF in this critical limbic region and reveal that NE is poised to regulate these peptidergic systems in the amygdala. Functional studies were performed to determine if activation of DOPR could inhibit the anxiety produced by elevation of NE in the amygdala using the pharmacological stressor yohimbine. Administration of the DOPR agonist, SNC80, significantly attenuated elevated anxiogenic behaviors produced by yohimbine as measured in the rat on the elevated zero maze. Taken together, results from this study demonstrate the convergence of three important systems, NE, CRF, and DOPR, in the amygdala and provide insight into their functional role in modulating stress and anxiety responses.

Selective synaptic remodeling of amygdalocortical connections associated with fear memory.

Neural circuits underlying auditory fear conditioning have been extensively studied. Here we identified a previously unexplored pathway from the lateral amygdala (LA) to the auditory cortex (ACx) and found that selective silencing of this pathway using chemo- and optogenetic approaches impaired fear memory retrieval. Dual-color in vivo two-photon imaging of mouse ACx showed pathway-specific increases in the formation of LA axon boutons, dendritic spines of ACx layer 5 pyramidal cells, and putative LA-ACx synaptic pairs after auditory fear conditioning. Furthermore, joint imaging of pre- and postsynaptic structures showed that essentially all new synaptic contacts were made by adding new partners to existing synaptic elements. Together, these findings identify an amygdalocortical projection that is important to fear memory expression and is selectively modified by associative fear learning, and unravel a distinct architectural rule for synapse formation in the adult brain.

Cranial grafting of stem cell-derived microvesicles improves cognition and reduces neuropathology in the irradiated brain.

Cancer survivors face a variety of challenges as they cope with disease recurrence and a myriad of normal tissue complications brought on by radio- and chemotherapeutic treatment regimens. For patients subjected to cranial irradiation for the control of CNS malignancy, progressive and debilitating cognitive dysfunction remains a pressing unmet medical need. Although this problem has been recognized for decades, few if any satisfactory long-term solutions exist to resolve this serious unintended side effect of radiotherapy. Past work from our laboratory has demonstrated the neurocognitive benefits of human neural stem cell (hNSC) grafting in the irradiated brain, where intrahippocampal transplantation of hNSC ameliorated radiation-induced cognitive deficits. Using a similar strategy, we now provide, to our knowledge, the first evidence that cranial grafting of microvesicles secreted from hNSC affords similar neuroprotective phenotypes after head-only irradiation. Cortical- and hippocampal-based deficits found 1 mo after irradiation were completely resolved in animals cranially grafted with microvesicles. Microvesicle treatment was found to attenuate neuroinflammation and preserve host neuronal morphology in distinct regions of the brain. These data suggest that the neuroprotective properties of microvesicles act through a trophic support mechanism that reduces inflammation and preserves the structural integrity of the irradiated microenvironment.

Hippocampal Theta Input to the Amygdala Shapes Feedforward Inhibition to Gate Heterosynaptic Plasticity.

The dynamic interactions between hippocampus and amygdala are critical for emotional memory. Theta synchrony between these structures occurs during fear memory retrieval and may facilitate synaptic plasticity, but the cellular mechanisms are unknown. We report that interneurons of the mouse basal amygdala are activated during theta network activity or optogenetic stimulation of ventral CA1 pyramidal cell axons, whereas principal neurons are inhibited. Interneurons provide feedforward inhibition that transiently hyperpolarizes principal neurons. However, synaptic inhibition attenuates during theta frequency stimulation of ventral CA1 fibers, and this broadens excitatory postsynaptic potentials. These effects are mediated by GABAB receptors and change in the Cl(-) driving force. Pairing theta frequency stimulation of ventral CA1 fibers with coincident stimuli of the lateral amygdala induces long-term potentiation of lateral-basal amygdala excitatory synapses. Hence, feedforward inhibition, known to enforce temporal fidelity of excitatory inputs, dominates hippocampus-amygdala interactions to gate heterosynaptic plasticity. VIDEO ABSTRACT.

Pathways for Emotions: Specializations in the Amygdalar, Mediodorsal Thalamic, and Posterior Orbitofrontal Network.

The primate amygdala projects to posterior orbitofrontal cortex (pOFC) directly and possibly indirectly through a pathway to the magnocellular mediodorsal thalamic nucleus (MDmc), which may convey signals about the significance of stimuli. However, because MDmc receives input from structures in addition to the amygdala and MDmc projects to areas in addition to pOFC, it is unknown whether amygdalar pathways in MDmc innervate pOFC-bound neurons. We addressed this issue using double- or triple-labeling approaches to identify pathways and key cellular and molecular features in rhesus monkeys. We found that amygdalar terminations innervated labeled neurons in MDmc that project to pOFC. Projection neurons in MDmc directed to pOFC included comparatively fewer "core" parvalbumin neurons that project focally to the middle cortical layers and more "matrix" calbindin neurons that project expansively to the upper cortical layers. In addition, a small and hitherto unknown pathway originated from MDmc calretinin neurons and projected to pOFC. Further, whereas projection neurons directed to MDmc and to pOFC were intermingled in the amygdala, none projected to both structures. Larger amygdalar neurons projected to MDmc and expressed the vesicular glutamate transporter 2 (VGLUT2), which is found in highly efficient "driver" pathways. In contrast, smaller amygdalar neurons directed to pOFC expressed VGLUT1 found in modulatory pathways. The indirect pathway from the amygdala to pOFC via MDmc may provide information about the emotional significance of events and, along with a parallel direct pathway, ensures transfer of signals to all layers of pOFC. SIGNIFICANCE STATEMENT: The amygdala-the brain's center for emotions-is strongly linked with the orbital cortex, a region associated with social interactions. This study provides evidence that a robust pathway from the amygdala reaches neurons in the thalamus that link directly with the orbital cortex, forming a tight tripartite network. The dual pathways from the amygdala to the orbital cortex and to the thalamus are distinct by morphology, neurochemistry, and function. This tightly linked network suggests the presence of fool-proof avenues for emotions to influence high-order cortical areas associated with affective reasoning. Specific nodes of this tripartite network are disrupted in psychiatric diseases, divorcing areas that integrate emotions and thoughts for decisions and flexible behavior.

Glial and axonal perikaryal coverage and somatic spines in the posterodorsal medial amygdala of male and cycling female rats.

The posterodorsal medial amygdala (MePD) is a sex-steroid-sensitive area that modulates reproductive behavior in rats. The volume of the neuronal cell body, density of dendritic spines, and glial fibrillary acidic protein immunoreactivity are sexually dimorphic or affected by gonadal hormones in the MePD. Here we add new data to this panorama and describe the ultrastructure of the glial and axonal coverage of the perikaryal membrane and the somatic spines in the MePD of males and cycling females (in diestrus, early proestrus, late proestrus, and estrus). Transmission electron microscopy data (mean values from seven to 11 neurons per rat, five or six animals per group) showed that the rat MePD has most of the perikaryal membrane covered by glial processes and a relatively large amount (up to 40%) of axonal processes contacting the neuronal cell body. No statistically significant difference was found between groups for these somatic coverages (P > 0.5). However, the density of somatic spines along the length of the perikaryal membrane was higher in the late proestrus than in estrus (P < 0.05), and somatic spines in early and late proestrus showed variable shapes with stubby/wide, thin, mushroom-like, ramified, transitional or atypical aspects. These findings add to the rapid adjustable synaptic changes in the MePD and in the integrated neural circuits that control neuroendocrine secretion and the hormonally modulated timely display of social behaviors in rats.

Running exercise delays neurodegeneration in amygdala and hippocampus of Alzheimer's disease (APP/PS1) transgenic mice.

Alzheimer's disease (AD) is an age-related neurodegenerative disease. Post-mortem examination and brain imaging studies indicate that neurodegeneration is evident in the hippocampus and amygdala of very early stage AD patients. Exercise training is known to enhance hippocampus- and amygdala-associated neuronal function. Here, we investigated the effects of exercise (running) on the neuronal structure and function of the hippocampus and amygdala in APP/PS1 transgenic (Tg) mice. At 4-months-old, an age before amyloid deposition, the amygdala-associated, but not the hippocampus-associated, long-term memory was impaired in the Tg mice. The dendritic complexities of the amygdalar basolateral neurons, but not those in the hippocampal CA1 and CA3 neurons, were reduced. Furthermore, the levels of BDNF/TrkB signaling molecules (i.e. p-TrkB, p-Akt and p-PKC) were reduced in the amygdala, but not in the hippocampus of the 4-month-old Tg mice. The concentrations of Aß40 and Aß42 in the amygdala were higher than those in the hippocampus. Ten weeks of treadmill training (from 1.5- to 4-month-old) increased the hippocampus-associated memory and dendritic arbor of the CA1 and CA3 neurons, and also restored the amygdala-associated memory and the dendritic arbor of amygdalar basolateral neurons in the Tg mice. Similarly, exercise training also increased the levels of p-TrkB, p-AKT and p-PKC in the hippocampus and amygdala. Furthermore, exercise training reduced the levels of soluble Aß in the amygdala and hippocampus. Exercise training did not change the levels of APP or RAGE, but significantly increased the levels of LRP-1 in both brain regions of the Tg mice. In conclusion, our results suggest that tests of amygdala function should be incorporated into subject selection for early prevention trials. Long-term exercise protects neurons in the amygdala and hippocampus against AD-related degeneration, probably via enhancements of BDNF signaling pathways and Aß clearance. Physical exercise may serve as a means to delay the onset of AD.