Morphological heterogeneity of neurons in the human central amygdaloid nucleus.

The central amygdaloid nucleus (CeA) has an ancient phylogenetic development and functions relevant for animal survival. Local cells receive intrinsic amygdaloidal information that codes emotional stimuli of fear, integrate them, and send cortical and subcortical output projections that prompt rapid visceral and social behavior responses. We aimed to describe the morphology of the neurons that compose the human CeA (N = 8 adult men). Cells within CeA coronal borders were identified using the thionine staining and were further analyzed using the "single-section" Golgi method followed by open-source software procedures for two-dimensional and three-dimensional image reconstructions. Our results evidenced varied neuronal cell body features, number and thickness of primary shafts, dendritic branching patterns, and density and shape of dendritic spines. Based on these criteria, we propose the existence of 12 morphologically different spiny neurons in the human CeA and discuss the variability in the dendritic architecture within cellular types, including likely interneurons. Some dendritic shafts were long and straight, displayed few collaterals, and had planar radiation within the coronal neuropil volume. Most of the sampled neurons showed a few to moderate density of small stubby/wide spines. Long spines (thin and mushroom) were observed occasionally. These novel data address the synaptic processing and plasticity in the human CeA. Our morphological description can be combined with further transcriptomic, immunohistochemical, and electrophysiological/connectional approaches. It serves also to investigate how neurons are altered in neurological and psychiatric disorders with hindered emotional perception, in anxiety, following atrophy in schizophrenia, and along different stages of Alzheimer's disease.

Sexual dimorphism, estrous cycle and laterality determine the intrinsic and synaptic properties of medial amygdala neurons in rat.

The posterodorsal medial amygdala (MePD) is a sex steroid-sensitive area that modulates different social behavior by relaying chemosensorial information to hypothalamic nuclei. However, little is known about MePD cell type diversity and functional connectivity. Here, we have characterized neurons and synaptic inputs in the right and left MePD of adult male and cycling female (in diestrus, proestrus or estrus) rats. Based on their electrophysiological properties and morphology, we found two coexisting subpopulations of spiny neurons that are sexually dimorphic. They were classified as Class I (predominantly bitufted-shaped neurons showing irregular spikes with frequency adaptation) or Class II (predominantly stellate-shaped neurons showing full spike frequency adaptation). Furthermore, excitatory and inhibitory inputs onto MePD cells were modulated by sex, estrous cycle and hemispheric lateralization. In the left MePD, there was an overall increase in the excitatory input to neurons of males compared to cycling females. However, in proestrus, the MePD neurons received mainly inhibitory inputs. Our findings indicate the existence of hemispheric lateralization, estrous cycle and sexual dimorphism influences at cellular and synaptic levels in the adult rat MePD.

Remodeling of the number and structure of dendritic spines in the medial amygdala: From prepubertal sexual dimorphism to puberty and effect of sexual experience in male rats.

The posterodorsal medial amygdala (MePD) is a sexually dimorphic area and plays a central role in the social behavior network of rats. Dendritic spines modulate synaptic processing and plasticity. Here, we compared the number and structure of dendritic spines in the MePD of prepubertal males and females and postpubertal males with and without sexual experience. Spines were classified and measured after three-dimensional image reconstruction using DiI fluorescent labeling and confocal microscopy. Significantly differences are as follows: (a) Prepubertal males have more proximal spines, stubby/wide spines with long length and large head diameter and thin and mushroom spines with wide neck and head diameters than prepubertal females, whereas (b) prepubertal females have more mushroom spines with long neck length than age-matched males. (c) In males, the number of thin spines reduces after puberty and, compared to sexually experienced counterparts, (d) naive males have short stubby/wide spines as well as mushroom spines with reduced neck diameter. In addition, (e) sexually experienced males have an increase in the number of mushroom spines, the length of stubby/wide spines, the head diameter of thin and stubby/wide spines and the neck diameter of thin and mushroom spines. These data indicate that a sexual dimorphism in the MePD dendritic spines is evident before adulthood and a spine-specific remodeling of number and shape can be brought about by both puberty and sexual experience. These fine-tuned ontogenetic, hormonally and experience-dependent changes in the MePD are relevant for plastic synaptic processing and the reproductive behavior of adult rats.

Castration alters the number and structure of dendritic spines in the male posterodorsal medial amygdala.

The posterodorsal medial amygdala (MePD) is responsive to androgens and participates in the integration of olfactory/vomeronasal stimuli for the display of sexual behavior in rats. Adult gonadectomy (GDX) affects the MePD structural integrity at the same time that impairs male mating behavior. At the cellular level, dendritic spines modulate excitatory synaptic transmission, strength, and plasticity. Here, we describe the effect of GDX on the number and shape of dendritic spines in the right and left MePD using confocal microscopy and 3D image reconstruction. Age-matched adult rats were intact (n = 6), submitted to a sham procedure (n = 4) or castrated and studied 90 days after GDX (n = 5). The MePD neurons have a density of 1.1 spines/dendritic µm composed of thin, mushroom-like, stubby/wide, and few ramified or atypical spines. Irrespective of brain hemisphere, GDX decreased the dendritic spine density in the MePD, but induced different effects on each spine type. That is, compared to control groups, GDX reduced (i) the number (up to 50%) of thin, mushroom-like, and ramified spines, and (ii) the size and the neck length of thin spines as well as the head diameter of ramified spines. Besides, GDX increased the number of stubby/wide and atypical spines (up to 140% and 400%, respectively). These data show that GDX promotes a cellular and synaptic reorganization in a spine-specific manner in the MePD. By altering the number and shape of these connectional elements, GDX can affect the neural transmission and hinder the function of integrated brain circuitries in the male brain.

The human medial amygdala: structure, diversity, and complexity of dendritic spines.

The medial nucleus of the amygdala (Me) is a component of the neural circuit for the interpretation of multimodal sensory stimuli and the elaboration of emotions and social behaviors in primates. We studied the presence, distribution, diverse shape, and connectivity of dendritic spines in the human Me of adult postmortem men. Data were obtained from the five types of multipolar neurons found in the Me using an adapted Golgi method and light microscopy, the carbocyanine DiI fluorescent dye and confocal microscopy, and transmission electron microscopy. Three-dimensional reconstruction of spines showed a continuum of shapes and sizes, with the spines either lying isolated or forming clusters. These dendritic spines were classified as stubby/wide, thin, mushroom-like, ramified or with an atypical morphology including intermediate shapes, double spines, and thorny excrescences. Pleomorphic spines were found from proximal to distal dendritic branches suggesting potential differences for synaptic processing, strength, and plasticity in the Me neurons. Furthermore, the human Me has large and thin spines with a gemmule appearance, spinules, and filopodium. The ultrastructural data showed dendritic spines forming monosynaptic or multisynaptic contacts at the spine head and neck, and with asymmetric or symmetric characteristics. Additional findings included en passant, reciprocal, and serial synapses in the Me. Complex long-necked thin spines were observed in this subcortical area. These new data reveal the diversity of the dendritic spines in the human Me likely involved with the integration and processing of local synaptic inputs and with functional implications in physiological and various neuropathological conditions.

Morphological Features of Human Dendritic Spines.

Dendritic spine features in human neurons follow the up-to-date knowledge presented in the previous chapters of this book. Human dendrites are notable for their heterogeneity in branching patterns and spatial distribution. These data relate to circuits and specialized functions. Spines enhance neuronal connectivity, modulate and integrate synaptic inputs, and provide additional plastic functions to microcircuits and large-scale networks. Spines present a continuum of shapes and sizes, whose number and distribution along the dendritic length are diverse in neurons and different areas. Indeed, human neurons vary from aspiny or "relatively aspiny" cells to neurons covered with a high density of intermingled pleomorphic spines on very long dendrites. In this chapter, we discuss the phylogenetic and ontogenetic development of human spines and describe the heterogeneous features of human spiny neurons along the spinal cord, brainstem, cerebellum, thalamus, basal ganglia, amygdala, hippocampal regions, and neocortical areas. Three-dimensional reconstructions of Golgi-impregnated dendritic spines and data from fluorescence microscopy are reviewed with ultrastructural findings to address the complex possibilities for synaptic processing and integration in humans. Pathological changes are also presented, for example, in Alzheimer's disease and schizophrenia. Basic morphological data can be linked to current techniques, and perspectives in this research field include the characterization of spines in human neurons with specific transcriptome features, molecular classification of cellular diversity, and electrophysiological identification of coexisting subpopulations of cells. These data would enlighten how cellular attributes determine neuron type-specific connectivity and brain wiring for our diverse aptitudes and behavior.

Introduction: What Are Dendritic Spines?

Dendritic spines are cellular specializations that greatly increase the connectivity of neurons and modulate the "weight" of most postsynaptic excitatory potentials. Spines are found in very diverse animal species providing neural networks with a high integrative and computational possibility and plasticity, enabling the perception of sensorial stimuli and the elaboration of a myriad of behavioral displays, including emotional processing, memory, and learning. Humans have trillions of spines in the cerebral cortex, and these spines in a continuum of shapes and sizes can integrate the features that differ our brain from other species. In this chapter, we describe (1) the discovery of these small neuronal protrusions and the search for the biological meaning of dendritic spines; (2) the heterogeneity of shapes and sizes of spines, whose structure and composition are associated with the fine-tuning of synaptic processing in each nervous area, as well as the findings that support the role of dendritic spines in increasing the wiring of neural circuits and their functions; and (3) within the intraspine microenvironment, the integration and activation of signaling biochemical pathways, the compartmentalization of molecules or their spreading outside the spine, and the biophysical properties that can affect parent dendrites. We also provide (4) examples of plasticity involving dendritic spines and neural circuits relevant to species survival and comment on (5) current research advancements and challenges in this exciting research field.

Glial Cell Modulation of Dendritic Spine Structure and Synaptic Function.

Glia comprise a heterogeneous group of cells involved in the structure and function of the central and peripheral nervous system. Glial cells are found from invertebrates to humans with morphological specializations related to the neural circuits in which they are embedded. Glial cells modulate neuronal functions, brain wiring and myelination, and information processing. For example, astrocytes send processes to the synaptic cleft, actively participate in the metabolism of neurotransmitters, and release gliotransmitters, whose multiple effects depend on the targeting cells. Human astrocytes are larger and more complex than their mice and rats counterparts. Astrocytes and microglia participate in the development and plasticity of neural circuits by modulating dendritic spines. Spines enhance neuronal connectivity, integrate most postsynaptic excitatory potentials, and balance the strength of each input. Not all central synapses are engulfed by astrocytic processes. When that relationship occurs, a different pattern for thin and large spines reflects an activity-dependent remodeling of motile astrocytic processes around presynaptic and postsynaptic elements. Microglia are equally relevant for synaptic processing, and both glial cells modulate the switch of neuroendocrine secretion and behavioral display needed for reproduction. In this chapter, we provide an overview of the structure, function, and plasticity of glial cells and relate them to synaptic maturation and modulation, also involving neurotrophic factors. Together, neurons and glia coordinate synaptic transmission in both normal and abnormal conditions. Neglected over decades, this exciting research field can unravel the complexity of species-specific neural cytoarchitecture as well as the dynamic region-specific functional interactions between diverse neurons and glial subtypes.

Human cortical amygdala dendrites and spines morphology under open-source three-dimensional reconstruction procedures.

Visualizing nerve cells has been fundamental for the systematic description of brain structure and function in humans and other species. Different approaches aimed to unravel the morphological features of neuron types and diversity. The inherent complexity of the human nervous tissue and the need for proper histological processing have made studying human dendrites and spines challenging in postmortem samples. In this study, we used Golgi data and open-source software for 3D image reconstruction of human neurons from the cortical amygdaloid nucleus to show different dendrites and pleomorphic spines at different angles. Procedures required minimal equipment and generated high-quality images for differently shaped cells. We used the "single-section" Golgi method adapted for the human brain to engender 3D reconstructed images of the neuronal cell body and the dendritic ramification by adopting a neuronal tracing procedure. In addition, we elaborated 3D reconstructions to visualize heterogeneous dendritic spines using a supervised machine learning-based algorithm for image segmentation. These tools provided an additional upgrade and enhanced visual display of information related to the spatial orientation of dendritic branches and for dendritic spines of varied sizes and shapes in these human subcortical neurons. This same approach can be adapted for other techniques, areas of the central or peripheral nervous system, and comparative analysis between species.

Glutamate and GABA in the medial amygdala induce selective central sympathetic/parasympathetic cardiovascular responses.

Glutamate and γ-aminobutyric acid (GABA) participate in central cardiovascular control, and are found in the rat posterodorsal medial amygdala (MePD), an area of the forebrain that modulates emotional/social behaviors. Here we tested whether these neurotransmitters in the MePD could change the basal activity, chemoreflex, and baroreflex cardiovascular responses in awake rats. Power spectral analysis and symbolic analysis were used to evaluate these responses. Microinjections of saline, glutamate (2 µg), or GABA (61 ng or 100 µg; n = 5-7 rats per group) did not affect basal parameters or chemoreflex responses. However, baroreflex responses showed marked changes. Glutamate increased power spectral and symbolic sympathetic indexes related to both cardiac and vascular modulations (P < 0.05). In turn, the displacement of the baroreflex half-maximal heart rate (HR) response was associated with a GABA (61 ng) mediated decrease in the upper plateau (P < 0.05). Administration of GABA (61 ng, but not 100 µg) also increased HR variability (P < 0.05), in association with parasympathetic activation. These data add novel evidence that the MePD can promote selective responses in the central regulation of the cardiovascular system, i.e., glutamate in the MePD evoked activation of a central sympathetic reflex adjustment, whereas GABA activated a central parasympathetic one.

Spindle-Shaped Neurons in the Human Posteromedial (Precuneus) Cortex.

The human posteromedial cortex (PMC), which includes the precuneus (PC), represents a multimodal brain area implicated in emotion, conscious awareness, spatial cognition, and social behavior. Here, we describe the presence of Nissl-stained elongated spindle-shaped neurons (suggestive of von Economo neurons, VENs) in the cortical layer V of the anterior and central PC of adult humans. The adapted "single-section" Golgi method for postmortem tissue was used to study these neurons close to pyramidal ones in layer V until merging with layer VI polymorphic cells. From three-dimensional (3D) reconstructed images, we describe the cell body, two main longitudinally oriented ascending and descending dendrites as well as the occurrence of spines from proximal to distal segments. The primary dendritic shafts give rise to thin collateral branches with a radial orientation, and pleomorphic spines were observed with a sparse to moderate density along the dendritic length. Other spindle-shaped cells were observed with straight dendritic shafts and rare branches or with an axon emerging from the soma. We discuss the morphology of these cells and those considered VENs in cortical areas forming integrated brain networks for higher-order activities. The presence of spindle-shaped neurons and the current discussion on the morphology of putative VENs address the need for an in-depth neurochemical and transcriptomic characterization of the PC cytoarchitecture. These findings would include these spindle-shaped cells in the synaptic and information processing by the default mode network and for general intelligence in healthy individuals and in neuropsychiatric disorders involving the PC in the context of the PMC functioning.

The Subcortical-Allocortical- Neocortical continuum for the Emergence and Morphological Heterogeneity of Pyramidal Neurons in the Human Brain.

Human cortical and subcortical areas integrate emotion, memory, and cognition when interpreting various environmental stimuli for the elaboration of complex, evolved social behaviors. Pyramidal neurons occur in developed phylogenetic areas advancing along with the allocortex to represent 70-85% of the neocortical gray matter. Here, we illustrate and discuss morphological features of heterogeneous spiny pyramidal neurons emerging from specific amygdaloid nuclei, in CA3 and CA1 hippocampal regions, and in neocortical layers II/III and V of the anterolateral temporal lobe in humans. Three-dimensional images of Golgi-impregnated neurons were obtained using an algorithm for the visualization of the cell body, dendritic length, branching pattern, and pleomorphic dendritic spines, which are specialized plastic postsynaptic units for most excitatory inputs. We demonstrate the emergence and development of human pyramidal neurons in the cortical and basomedial (but not the medial, MeA) nuclei of the amygdala with cells showing a triangular cell body shape, basal branched dendrites, and a short apical shaft with proximal ramifications as "pyramidal-like" neurons. Basomedial neurons also have a long and distally ramified apical dendrite not oriented to the pial surface. These neurons are at the beginning of the allocortex and the limbic lobe. "Pyramidal-like" to "classic" pyramidal neurons with laminar organization advance from the CA3 to the CA1 hippocampal regions. These cells have basal and apical dendrites with specific receptive synaptic domains and several spines. Neocortical pyramidal neurons in layers II/III and V display heterogeneous dendritic branching patterns adapted to the space available and the afferent inputs of each brain area. Dendritic spines vary in their distribution, density, shapes, and sizes (classified as stubby/wide, thin, mushroom-like, ramified, transitional forms, "atypical" or complex forms, such as thorny excrescences in the MeA and CA3 hippocampal region). Spines were found isolated or intermingled, with evident particularities (e.g., an extraordinary density in long, deep CA1 pyramidal neurons), and some showing a spinule. We describe spiny pyramidal neurons considerably improving the connectional and processing complexity of the brain circuits. On the other hand, these cells have some vulnerabilities, as found in neurodegenerative Alzheimer's disease and in temporal lobe epilepsy.

Dendritic and Spine Heterogeneity of von Economo Neurons in the Human Cingulate Cortex.

The human cingulate cortex (CC), included in the paralimbic cortex, participates in emotion, visceral responses, attention, cognition, and social behaviors. The CC has spindle-shaped/fusiform cell body neurons in its layer V, the von Economo neurons (VENs). VENs have further developed in primates, and the characterization of human VENs can benefit from the detailed descriptions of the shape of dendrites and spines. Here, we advance this issue and studied VENs in the anterior and midcingulate cortex from four neurologically normal adult subjects. We used the thionin technique and the adapted "single-section" Golgi method for light microscopy. Three-dimensional (3D) reconstructions were carried out for the visualization of Golgi-impregnated VENs' cell body, ascending and descending dendrites, and collateral branches. We also looked for the presence, density, and shape of spines from proximal to distal dendrites. These neurons have a similar aspect for the soma, but features of spiny dendrites evidenced a morphological heterogeneity of CC VENs. Only for the description of this continuum of shapes, we labeled the most common feature as VEN 1, which has main dendritic shafts but few branches and sparse spines. VEN 2 shows an intermediate aspect, whereas VEN 3 displays the most profuse dendritic ramification and more spines with varied shapes from proximal to distal branches. Morphometric data exemplify the dendritic features of these cells. The heterogeneity of the dendritic architecture and spines suggests additional functional implications for the synaptic and information processing in VENs in integrated networks of normal and, possibly, neurological/psychiatric conditions involving the human CC.

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.

Neurotrophic factors in the posterodorsal medial amygdala of male and cycling female rats.

The posterodorsal medial amygdala (MePD) has a high concentration of receptors for gonadal hormones, is a sexually dimorphic region and dynamically controls the reproductive behavior of both males and females. Neurotrophic factors can promote dendritic spine remodeling and change synaptic input strength in a region-specific manner. Here, we analyzed the gene and protein expression of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-1), polysialylated neural cell adhesion molecule (PSA-NCAM) and Ephrin-A4 in the MePD of adult males and females in diestrus, proestrus and estrus using real-time qPCR and fluorescent immunohistochemistry. The first approach showed their amplification except for Igf1 and the latter revealed that BDNF, IGF-1, PSA-NCAM and Ephrin-A4 are expressed in the MePD of the adult rats. Protein expression of these neurotrophic factors showed no differences between groups. However, proestrus females displayed a higher number of labelled puncta than males for BDNF expression and diestrus females for IGF-1 expression. In conjunction, results indicate that IGF-1 might be released rather than synthetized in the MePD, and the expression of specific neurotrophic factors varies specifically during proestrus. The dynamic modulation of BDNF and IGF-1 during this cyclic phase is coincident with synaptic changes and spine density remodeling in the MePD, the disinhibition of gonadotrophin secretion for ovulation and the display of sexual behavior.

Neuroprotective effect of ACTH on collagenase-induced peri-intraventricular hemorrhage in newborn male rats.

Peri-intraventricular hemorrhage (PIVH) is a common and serious prematurity-related complication in neonates. Adrenocorticotropic hormone (ACTH) has neuroprotective actions and is a candidate to ameliorate brain damage following PIVH. Here, we tested the efficacy of ACTH1-24 on a collagenase-induced lesion of the germinal matrix (GM) in newborn male rats. Animals received microinjection of the vehicle (PBS, 2 µl) or collagenase type VII (0.3 IU) into the GM/periventricular tissue on postnatal day (PN) 2. Twelve hours later pups received microinjection of either the agonist ACTH1-24 (0.048 mg/kg), or the antagonist SHU9119 (antagonist of MCR3/MCR4 receptors, 0.01 mg/kg), or their combination. Morphological outcomes included striatal injury extension, neuronal and glial cells counting, and immunohistochemical expression of brain lesion biomarkers ipsilateral and contralateral to the hemorrhagic site. Data were evaluated on PN 8. Collagenase induced PIVH and severe ipsilateral striatal lesion. ACTH1-24 dampened the deleterious effects of collagenase-induced hemorrhage in significantly reducing the extension of the damaged area, the striatal neuronal and glial losses, and the immunoreactive expression of the GFAP, S100ß, and NG2-glia biomarkers in the affected periventricular area. SHU9119 blocked the glial density rescuing effect of ACTH1-24. ACTH1-24 could be further evaluated to determine its suitability for preclinical models of PVH in premature infants.

The prefrontal cortex conscious and unconscious response to social/emotional facial expressions involve sex, hemispheric laterality, and selective activation of the central cardiac modulation.

The human prefrontal cortex (PFC) processes complex sensory information for the elaboration of social behaviors. The non-invasive neuroimaging technique near-infrared spectroscopy (NIRS) identifies hemodynamic changes and concentration of oxygenated (HbO2) and deoxygenated (HHb) hemoglobin in the cerebral cortex. We studied the responses detected by NIRS in the right and left PFC activation of 28 participants (n = 14 adult young females and males) while processing social/emotional facial expressions, i.e., in conscious perception of different expressions (neutral, happy, sad, angry, disgust, and fearful) and in unconscious/masked perception of negative expressions (fearful and disgust overlapped by neutral). The power spectral analysis from concomitant ECG signals revealed the sympathetic and parasympathetic modulation of cardiac responses. We found higher HbO2 values in the right PFC of females than in males during, and in the left PFC after, following the conscious perception of the happy face. In males, the left PFC increased and the right PFC decreased HbO2 while viewing the happy expression. In both sexes, HHb values were higher during the masked presentation of disgust than fearful expression, and after the masked presentation of fearful expression than during it. Higher sympathetic and lower parasympathetic activity (LF/ HF components) occurred in females when consciously and unconsciously processing negative emotions (p < 0.05 in all cases). These results demonstrate that the human PFC displays a selective activation depending on sex, hemispheric laterality, attention, time for responding to conscious and unconscious emotionally loaded stimuli with simulataneous centrally modulated cardiovascular responses.

Cyclic changes and actions of progesterone and allopregnanolone on cognition and hippocampal basal (stratum oriens) dendritic spines of female rats.

Ovarian steroids modulate the neuronal structure and function during the estrous cycle, contrasting peak effects during the proestrus cycle and low effects during the metestrus cycle. An ovariectomy (OVX) decreases gonadal hormones and tests the effects of substitutive therapies. We studied female rats with a normal estrous cycle and we also studied the effects of systemic progesterone (P4, 4.0 mg/kg) or its reduced metabolite allopregnanolone (ALLO, 4.0 mg/kg, both for 10 days) in females who had had an OVX 16.5 weeks prior to the study (long-term OVX) with the novel object recognition test (NORT) for associative memory. The dendritic shape and spine density in Golgi-impregnated basal dendrites (stratum oriens) of hippocampal pyramidal neurons was also studied. Proestrus females had a better performance than metestrus or OVX females in short-term memory (tested 1 h after the acquisition phase). Proestrus and metestrus females showed better results than OVX females for long-term memory (24 h after the initial phase). Both P4 and ALLO recovered the cognitive impairment induced by long-term OVX. Also, proestrus females had a higher density of dendritic spines than metestrus females, OVX reduced the density of spines when compared to intact females, whereas both P4 and ALLO treatments increased the dendritic spine density, number of dendritic branches along the dendritic length, and branching order compared to vehicle. These data add the dendrites of the stratum oriens as an additional site for naturally occurring changes in spine density during the estrous cycle and evidence the actions of progestins in both behavioral recovery and the structural dendritic rearrangement of hippocampal pyramidal neurons in long-term OVX female rats.

Increases in dendritic spine density in BLA without metabolic changes in a rodent model of PTSD.

Imaging studies have shown abnormal amygdala function in patients with posttraumatic stress disorder (PTSD). In addition, alterations in synaptic plasticity have been associated with psychiatric disorders and previous reports have indicated alterations in the amygdala morphology, especially in basolateral (BLA) neurons, are associated with stress-related disorders. Since, some individuals exposed to a traumatic event develop PTSD, the goals of this study were to evaluate the early effects of PTSD on amygdala glucose metabolism and analyze the possible BLA dendritic spine plasticity in animals with different levels of behavioral response. We employed the inescapable footshock protocol as an experimental model of PTSD and the animals were classified according to the duration of their freezing behavior into distinct groups: "extreme behavioral response" (EBR) and "minimal behavioral response". We evaluated the amygdala glucose metabolism at baseline (before the stress protocol) and immediately after the situational reminder using the microPET and the radiopharmaceutical 18F-FDG. The BLA dendritic spines were analyzed according to their number, density, shape and morphometric parameters. Our results show the EBR animals exhibited longer freezing behavior and increased proximal dendritic spines density in the BLA neurons. Neither the amygdaloid glucose metabolism, the types of dendritic spines nor their morphometric parameters showed statistically significant differences. The extreme behavior response induced by this PTSD protocol produces an early increase in BLA spine density, which is unassociated with either additional changes in the shape of spines or metabolic changes in the whole amygdala of Wistar rats.

Dendritic branching features of posterodorsal medial amygdala neurons of adult male and female rats: further data based on the Golgi method.

The posterodorsal portion of the medial amygdalar nucleus (MePD) contains receptors for gonadal hormones and modulates the function of a social behavior network in rodents. The aims of this study were: to provide further data about the morphology of Golgi-impregnated dendrites of neurons from the MePD of adult rats; and, to compare the results obtained for dendritic branching and predominant dendritic spatial distribution in the MePD of males and diestrus females. MePD neurons were classified as bitufted or stellate, their spiny dendrites showed variable lengths, divided sparingly and decreased the number of branches with the distance from the soma. Dendritic arborization levels, number of branches in each level, distribution of the dendrites around the cell body and away from it, and the preferred spatial distribution of dendritic branches were studied according to different techniques and compared between sexes. Statistically significant differences were found in the predominant dendritic spatial distribution in the MePD, males with branches more oriented medially and dorsolaterally and females with more dorsally and ventromedially ones (p< or =0.05 in all cases). This result adds another clue to understand how information is processed and integrated in the MePD and within functionally dynamic sex steroids-responsive circuits relevant for reproduction in both sexes.