Morphological Neuron Classification Based on Dendritic Tree Hierarchy.

The shape of a neuron can reveal interesting properties about its function. Therefore, morphological neuron characterization can contribute to a better understanding of how the brain works. However, one of the great challenges of neuroanatomy is the definition of morphological properties that can be used for categorizing neurons. This paper proposes a new methodology for neuron morphological analysis by considering different hierarchies of the dendritic tree for characterizing and categorizing neuronal cells. The methodology consists in using different strategies for decomposing the dendritic tree along its hierarchies, allowing the identification of relevant parts (possibly related to specific neuronal functions) for classification tasks. A set of more than 5000 neurons corresponding to 10 classes were examined with supervised classification algorithms based on this strategy. It was found that classification accuracies similar to those obtained by using whole neurons can be achieved by considering only parts of the neurons. Branches close to the soma were found to be particularly relevant for classification.

Neuronal types of the human cortical amygdaloid nucleus.

The human cortical amygdaloid nucleus (CoA) receives exteroceptive sensory stimuli, modulates the functions coded by the intrinsic amygdaloid circuit, and constitutes the beginning of the limbic lobe continuum with direct and indirect connections toward subcortical, allocortical, and higher order neocortical areas. To provide basic data on the human CoA, we characterized and classified the neurons using the thionin and the "single-section" Golgi method adapted for postmortem brain tissue and light microscopy. We found 10 different types of neurons named according to the morphological features of the cell body, dendritic branches, and spine distribution. Most cells are multipolar spiny neurons with two or more primary dendrites, including pyramidal-like ones. Three-dimensional reconstructions evidenced the types and diversity of the dendritic spines in each neuron. The unlike density of spines along dendritic branches, from proximal to distal ones, indicate that the synaptic processing and plasticity can be different in each CoA neuron. Our study provides novel data on the neuronal composition of the human CoA indicating that the variety of cells in this region can have phylogenetic, ontogenetic, morphological, and likely functional implications for the integrated human brain function. This can reflect both a more complex subcortical synaptic processing of sensory and emotional information and an adaptation for species-specific social behavior display.

Axon terminals from the nucleus isthmi pars parvocellularis control the ascending retinotectofugal output through direct synaptic contact with tectal ganglion cell dendrites.

The optic tectum in birds and its homologue the superior colliculus in mammals both send major bilateral, nontopographic projections to the nucleus rotundus and caudal pulvinar, respectively. These projections originate from widefield tectal ganglion cells (TGCs) located in layer 13 in the avian tectum and in the lower superficial layers in the mammalian colliculus. The TGCs characteristically have monostratified arrays of brush-like dendritic terminations and respond mostly to bidimensional motion or looming features. In birds, this TGC-mediated tectofugal output is controlled by feedback signals from the nucleus isthmi pars parvocellularis (Ipc). The Ipc neurons display topographically organized axons that densely ramify in restricted columnar terminal fields overlapping various neural elements that could mediate this tectofugal control, including the retinal terminals and the TGC dendrites themselves. Whether the Ipc axons make synaptic contact with these or other tectal neural elements remains undetermined. We double labeled Ipc axons and their presumptive postsynaptic targets in the tectum of chickens (Gallus gallus) with neural tracers and performed an ultrastructural analysis. We found that the Ipc terminal boutons form glomerulus-like structures in the superficial and intermediate tectal layers, establishing asymmetric synapses with several dendritic profiles. In these glomeruli, at least two of the postsynaptic dendrites originated from TGCs. We also found synaptic contacts between retinal terminals and TGC dendrites. These findings suggest that, in birds, Ipc axons control the ascending tectal outflow of retinal signals through direct synaptic contacts with the TGCs.

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.

Purkinje cell dendritic atrophy induced by prenatal stress is mitigated by early environmental enrichment.

BACKGROUND: Prenatal stress (PS) in experimental animals causes long-lasting changes in Purkinje cell dendritic morphology. Furthermore, these structural changes are associated with an increase in anxiogenic behaviors in the elevated plus maze (EPM) and open-field (OF) test. OBJECTIVES: As environmental enrichment (EE) has significant restorative effects on brain neurons and behavior, the aim of this study was to evaluate if postweaning EE mitigates the decrease in Purkinje cell dendritic expansion and exploratory behavior induced by PS in mice. MATERIALS AND METHODS: Restraint stress was induced from gestational day 14 (G14) to G21. Approximately 50% of the PS animals were submitted to the EE paradigm between postnatal days 22 (P22) and P52. At P52 and P82, male animals were behaviorally evaluated, and then the morphology of the cerebellar vermal Purkinje cells was analyzed. RESULTS: We found that EE significantly ameliorates the Purkinje cell dendritic atrophy and anxiety-like behavior in the EPM. CONCLUSION: Our data show that long-lasting Purkinje cell dendritic impairments and anxiety-like behavior can be mitigated by postweaning EE.

Effects of monocular deprivation on the dendritic features of retinal ganglion cells / Efectos de la privación monocular sobre las características dendríticas de las células ganglionares de la retina

Monocular deprivation results in anatomical changes in the visual cortex in favor of the non-deprived eye. Although the retina forms part of the visual pathway, there is scarcity of data on the effect of monocular deprivation on its structure. The objective of this study was to describe the effects of monocular deprivation on the retinal ganglion cell dendritic features. The study design was quasi-experimental. 30 rabbits (18 experimental, 12 controls) were examined. Monocular deprivation was achieved through unilateral lid suture in the experimental animals. The rabbits were observed for three weeks. Each week, 6 experimental and 3 control animals were euthanized, their retina harvested and processed for light microscopy. Photomicrographs of the retina were taken using a digital camera then entered into FIJI software for analysis. The number of primary branches, terminal branches and dendritic field area among the non-deprived eyes increased by 66.7%(p=0.385), 400%(p=0.002), and 88.4%(p=0.523) respectively. Non-deprived eyes had 114.3% more terminal dendrites (p=0.002) compared to controls. Among deprived eyes, all variables measured had a gradual rise in the first two weeks followed by decline with further deprivation. There were no statistically significant differences noted between the deprived and control eyes. Monocular deprivation results in increase in synaptic contacts in the non-deprived eye, with reciprocal changes occurring in the deprived eye.

La privación monocular de la visión resulta en cambios anatómicos en la corteza visual en favor del ojo no privado. Aunque la retina forma parte de la vía visual, hay escasez de datos sobre el efecto de la privación monocular en su estructura. El objetivo de esta investigación fue describir los efectos de la privación monocular en las características de las dendritas de las células ganglionares de la retina. Se diseñó un estudio cuasi-experimental. Se examinaron 30 conejos (18 experimentales, 12 controles). La privación monocular se logró a través de la sutura unilateral del párpado en los animales de experimentación. Los conejos fueron observados durante tres semanas. Cada semana, 6 animales experimentales y 3 control fueron eutanasiados, donde se obtuvo la retina y fue procesada para realizar microscopía óptica. Las microfotografías de la retina fueron tomadas con una cámara digital y luego se utilizó el software FIJI para su análisis. El número de dendritas primarias, terminales y el área del campo de dendritas en los ojos no privados aumentó un 66,7% (p=0,385), 400% (p=0,002), y 88,4% (p=0,523), respectivamente. Los ojos no privados, tenían 114,3% más dendritas terminales (p=0,002) en comparación con los controles. Entre los ojos privados, todas las variables medidas tuvieron un aumento gradual en las dos primeras semanas, seguido de descenso con mayor privación. No se observaron diferencias estadísticamente significativas entre los ojos privados y el grupo control. En conclusion, la privación monocular produce un aumento de los contactos sinápticos en los ojos no privados, con cambios recíprocos que se manifiestan en los ojos privados de la visión.

Developmentally dynamic colocalization patterns of DSCAM with adhesion and synaptic proteins in the mouse retina.

PURPOSE: The Down syndrome cell adhesion molecule (Dscam) gene is required for normal dendrite arborization and lamination in the mouse retina. In this study, we characterized the developmental localization of the DSCAM protein to better understand the postnatal stages of retinal development during which laminar disorganization occur in the absence of the protein. METHODS: Immunohistochemistry and colocalization analysis software were used to assay the localization of the DSCAM protein during development of the retina. RESULTS: We found that DSCAM was initially localized diffusely throughout mouse retinal neurites but then adopted a punctate distribution. DSCAM colocalized with catenins in the adult retina but was not detected at the active zone of chemical synapses, electrical synapses, and tight junctions. Further analysis identified a wave of colocalization between DSCAM and numerous synaptic and junction proteins coinciding with synaptogenesis between bipolar and retinal ganglion cells. CONCLUSIONS: Research presented in this study expands our understanding of DSCAM function by characterizing its location during the development of the retina and identifies temporally regulated localization patterns as an important consideration in understanding the function of adhesion molecules in neural development.

Transport along the dendritic endoplasmic reticulum mediates the trafficking of GABAB receptors.

In neurons, secretory organelles within the cell body are complemented by the dendritic endoplasmic reticulum (ER) and Golgi outposts (GOPs), whose role in neurotransmitter receptor trafficking is poorly understood. γ-aminobutyric acid (GABA) type B metabotropic receptors (GABABRs) regulate the efficacy of synaptic transmission throughout the brain. Their plasma membrane availability is controlled by mechanisms involving an ER retention motif and assembly-dependent ER export. Thus, they constitute an ideal molecular model to study ER trafficking, but the extent to which the dendritic ER participates in GABABR biosynthesis has not been thoroughly explored. Here, we show that GABAB1 localizes preferentially to the ER in dendrites and moves long distances within this compartment. Not only diffusion but also microtubule and dynein-dependent mechanisms control dendritic ER transport. GABABRs insert throughout the somatodendritic plasma membrane but dendritic post-ER carriers containing GABABRs do not fuse selectively with GOPs. This study furthers our understanding of the spatial selectivity of neurotransmitter receptors for dendritic organelles.

Nicotine prevents synaptic impairment induced by amyloid-ß oligomers through α7-nicotinic acetylcholine receptor activation.

An emerging view on Alzheimer disease's (AD) pathogenesis considers amyloid-ß (Aß) oligomers as a key factor in synaptic impairment and rodent spatial memory decline. Alterations in the α7-nicotinic acetylcholine receptor (α7-nAChR) have been implicated in AD pathology. Herein, we report that nicotine, an unselective α7-nAChR agonist, protects from morphological and synaptic impairments induced by Aß oligomers. Interestingly, nicotine prevents both early postsynaptic impairment and late presynaptic damage induced by Aß oligomers through the α7-nAChR/phosphatidylinositol-3-kinase (PI3K) signaling pathway. On the other hand, a cross-talk between α7-nAChR and the Wnt/ß-catenin signaling pathway was revealed by the following facts: (1) nicotine stabilizes ß-catenin, in a concentration-dependent manner; (2) nicotine prevents Aß-induced loss of ß-catenin through the α7-nAChR; and (3) activation of canonical Wnt/ß-catenin signaling induces α7-nAChR expression. Analysis of the α7-nAChR promoter indicates that this receptor is a new Wnt target gene. Taken together, these results demonstrate that nicotine prevents memory deficits and synaptic impairment induced by Aß oligomers. In addition, nicotine improves memory in young APP/PS1 transgenic mice before extensive amyloid deposition and senile plaque development, and also in old mice where senile plaques have already formed. Activation of the α7-nAChR/PI3K signaling pathway and its cross-talk with the Wnt signaling pathway might well be therapeutic targets for potential AD treatments.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study.

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 µm, revealed that changes were more pronounced in the range 120-200 µm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

BDNF regulates Rab11-mediated recycling endosome dynamics to induce dendritic branching.

Dendritic arborization of neurons is regulated by brain-derived neurotrophic factor (BDNF) together with its receptor, TrkB. Endocytosis is required for dendritic branching and regulates TrkB signaling, but how postendocytic trafficking determines the neuronal response to BDNF is not well understood. The monomeric GTPase Rab11 regulates the dynamics of recycling endosomes and local delivery of receptors to specific dendritic compartments. We investigated whether Rab11-dependent trafficking of TrkB in dendrites regulates BDNF-induced dendritic branching in rat hippocampal neurons. We report that TrkB in dendrites is a cargo for Rab11 endosomes and that both Rab11 and its effector, MyoVb, are required for BDNF/TrkB-induced dendritic branching. In addition, BDNF induces the accumulation of Rab11-positive endosomes and GTP-bound Rab11 in dendrites and the expression of a constitutively active mutant of Rab11 is sufficient to increase dendritic branching by increasing TrkB localization in dendrites and enhancing sensitization to endogenous BDNF. We propose that Rab11-dependent dendritic recycling provides a mechanism to retain TrkB in dendrites and to increase local signaling to regulate arborization.

Cellular components of the human medial amygdaloid nucleus.

The medial nucleus (Me) is a superficial component of the amygdaloid complex. Here we assessed the density and morphology of the neurons and glial cells, the glial fibrillary acidic protein (GFAP) immunoreactivity, and the ultrastructure of the synaptic sites in the human Me. The optical fractionator method was applied. The Me presented an estimated mean neuronal density of 1.53 × 105 neurons/mm³ (greater in the left hemisphere), more glia (72% of all cells) than neurons, and a nonneuronal:neuronal ratio of 2.7. Golgi-impregnated neurons had round or ovoid, fusiform, angular, and polygonal cell bodies (10-30 µm in diameter). The length of the dendrites varied, and pleomorphic spines were found in sparsely spiny or densely spiny cells (1.5-5.2 spines/dendritic µm). The axons in the Me neuropil were fine or coarsely beaded, and fibers showed simple or notably complex collateral terminations. The protoplasmic astrocytes were either isolated or formed small clusters and showed GFAP-immunoreactive cell bodies and multiple branches. Furthermore, we identified both asymmetrical (with various small, clear, round, electron-lucent vesicles and, occasionally, large, dense-core vesicles) and symmetrical (with small, flattened vesicles) axodendritic contacts, also including multisynaptic spines. The astrocytes surround and may compose tripartite or tetrapartite synapses, the latter including the extracellular matrix between the pre- and the postsynaptic elements. Interestingly, the terminal axons exhibited a glomerular-like structure with various asymmetrical contacts. These new morphological data on the cellular population and synaptic complexity of the human Me can contribute to our knowledge of its role in health and pathological conditions.

Chronic caffeine consumption prevents cognitive decline from young to middle age in rats, and is associated with increased length, branching, and spine density of basal dendrites in CA1 hippocampal neurons.

Chronic caffeine consumption has been inversely associated with the risk of developing dementia and Alzheimer's disease. Here we assessed whether chronic caffeine treatment prevents the behavioral and cognitive decline that male Wistar rats experience from young (≈3 months) to middle age (≈10 months). When animals were young they were evaluated at weekly intervals in three tests: motor activity habituation in the open field (30-min sessions at the same time on consecutive days), continuous spontaneous alternation in the Y-maze (8 min), and elevated plus-maze (5 min). Afterward, rats from the same litter were randomly assigned either to a caffeine-treated group (n=13) or a control group (n=11), which received only tap water. Caffeine treatment (5 mg/kg/day) began when animals were ≈4 months old, and lasted for 6 months. Behavioral tests were repeated from day 14 to day 28 after caffeine withdrawal, a time period that is far in excess for the full excretion of a caffeine dose in this species. Thirty days after caffeine discontinuation brains were processed for Golgi-Cox staining. Compared with controls, we found that middle-aged rats that had chronically consumed low doses of caffeine (1) maintained their locomotor habituation during the second consecutive day exposure to the open field (an index of non-associative learning), (2) maintained their exploratory drive to complete the conventional minimum of nine arm visits required to calculate the alternation performance in the Y-maze in a greater proportion, (3) maintained their alternation percentage above chance level (an index of working memory), and (4) did not increase the anxiety indexes assessed by measuring the time spent in the open arms of the elevated plus maze. In addition, morphometric analysis of hippocampal neurons revealed that dendritic branching (90-140 µm from the soma), length of 4th and 5th order branches, total dendritic length, and spine density in distal dendritic branches were greater in the basal but not the apical dendrites of CA1 pyramidal neurons from rats chronically treated with caffeine, in comparison with their age- and littermate-matched controls. Altogether, the present findings strengthen the epidemiological observations suggesting that prolonged caffeine intake prevents the cognitive decline associated with aging, and open the possibility that this process could be mediated by promoting the growth of dendrites and spines in neurons of the adult mammalian brain.

Análisis morfométrico del proceso de diferenciación in vitro de neuronas del hipocampo / Morphometric analysis of the differentiation process of hippocampal neurons in vitro

Los cultivos neuronales del sistema nervioso central se han venido usando ampliamente para el estudio de los mecanismos que conducen el proceso de diferenciación neuronal, así como también se han empleado como modelos in vitro para evaluar drogas y desarrollar nuevas terapias, de allí la importancia profundizar en la caracterización de dicho proceso. En este estudio, se prepararon cultivos primarios de células del hipocampo para estudiar los tipos celulares desarrollados, el desarrollo de dendritas y axones, la densidad de vesículas sinápticas y el desarrollo de los conos de crecimiento. Mediante inmunofluorescencia usando anticuerpos y marcadores no inmunológicos, se observaron los cambios experimentados por las estructuras de interés durante diferentes estadios temporales (1-21 días). Observamos una mayor proporción de neuronas sobre glias, desarrollo normal de las redes neuronales (conformadas por dendritas y axones), incremento en la longitud de dendritas y el establecimiento de sinapsis. Las vesículas sinápticas también experimentaron un incremento en su densidad a medida que aumentaba el tiempo de cultivo. Finalmente, se estudiaron los cambios morfológicos de los conos de crecimiento observándose que al inicio del cultivo en su mayoría se encontraban cerrados, pero a medida que maduraban las neuronas la proporción de conos de crecimiento abiertos aumentó. Este trabajo representa un avance en la caracterización morfométrica de los cultivos neuronales puesto que recoge de manera simultánea y cuantitativa los principales aspectos que marcan el proceso de diferenciación neuronal. En este estudio, la medición de estas características morfológicas hizo posible establecer parámetros cuantitativos que ayudarán a distinguir las principales etapas de la diferenciación neuronal.

Neuronal cultures of the central nervous system are widely used to study the molecular mechanisms that rule the differentiation process. These cultures have also been used to evaluate drugs and to develop new therapies. From this we can infer the relevance of performing an extended characterization that involves the main aspects driving such process. To carry out such characterization in the present study we prepared primary cultures from hippocampal cells to study cell identity, development of neuronal processes (dendrites and axons), density of synaptic vesicles and development of growth cones. Using immunofluorescence techniques, specific antibodies and non-immunological probes, we studied the changes experienced by the structures under study during different temporal stages (1-21 days). We observed a major proportion of neurons over glia, normal development of neuronal networks (formed by dendrites and axons), increase in the length of dendrites and axons and establishment of synaptic connections. Synaptic vesicles also showed an increase in their densities as long as the time of the culture progressed. Finally, we studied the morphological changes of the growth cones and observed that those were mostly closed at the beginning of the culture period. As neurons matured we observed an increase in the proportion of open growth cones. This work represents an advance in the morphometric characterization of neuronal cultures, since it gathers the main aspects that outline the neuronal differentiation process. In this study, measurement of these morphological features made possible to establish quantitative markers that will allow establishing more precisely the different stages of neuronal differentiation.

Basal dendrites are present in newly born dentate granule cells of young but not aged pilocarpine-treated chronic epileptic rats.

Epilepsy is known to influence hippocampal dentate granule cell (DGC) layer neurogenesis. In young adult rats, status epilepticus (SE) increases the number DGC newly borne cells and basal dendrites (BD), which persist at long-term. In contrast, little is known on whether these phenomena occur in elderly epileptic animals. In the present study, we compare DGC proliferation and the incidence of BD in young and aged pilocarpine-treated rats. Three epileptic groups were considered: Young animals given pilocarpine at 3 months of age. Aged animals treated with pilocarpine at 3 months of age that were sacrificed at 17-20 months. Aged animals that had pilocarpine and developed SE at 20 months, being sacrificed 2 months later. Nine days prior to sacrifice, animals underwent swimming sessions in the Morris water maze as a protocol for the development of hippocampal neurogenesis. We found a higher incidence of newly born DGC cells in young as compared to aged epileptic animals (P<0.001). This later group however, was not homogeneous. While a significant increase in DGC neurogenesis was observed when aged animals with long lasting epilepsy were compared to non-epileptic controls (P<0.01), this has not been recorded in aged animals that had epilepsy for only 2 months (P>0.05). When the number of DGC containing BD was considered, a significantly higher incidence was observed in young as compared to aged epileptic rats (P=0.001). Animals in this later group virtually lacked BD in newly formed dentate gyrus (DG) cells. Based on these results we conclude that plastic changes during epileptogenesis and the development of a pathological substrate in young animals is associated with DGC proliferation and the emergence of BD. As aging occurs, DGC neurogenesis can still be induced in rats with a long-term history of epilepsy but the emergence of BD is markedly reduced.

Reversal of neuronal and cognitive consequences of amphetamine sensitization following chronic treatment with a D1 antagonist.

Neuroplasticity is a key factor in restoration of brain function following neuropathology associated with disease or drug exposure. Here we examined the potential for chronic treatment with the selective D1 receptor antagonist SCH39166 to reverse the profound and enduring cognitive impairment associated with amphetamine (AMPH) sensitization in the nonhuman primate and to stimulate re-growth of atrophied pyramidal dendrites in the dorsolateral prefrontal cortex of these animals. Four rhesus monkeys with sustained cognitive impairment (>1year following AMPH sensitization) were treated for up to 8months with SCH39166. Cognitive testing was performed before, during, and for up to 1(1/2) year following treatment. Significant improvement in working memory performance was observed only after cessation of the D1 antagonist treatment but then was sustained for the duration of the post-treatment testing period. Postmortem quantitative assessment of Golgi-impregnated pyramidal neurons in BA9 showed that apical dendritic length and trunk spine density were increased in D1 antagonist treated monkeys relative to AMPH-sensitized and AMPH-naïve monkeys. These findings, which suggest that the deleterious consequences of AMPH sensitization can be reversed by modulation of D1 receptor signaling, have implications for treating the underlying neural basis of cognitive deficits in both schizophrenia and substance abuse.

Effects of prenatal stress and exercise on dentate granule cells maturation and spatial memory in adolescent mice.

Exposure to prenatal stress (PS) increases the risk of developing neurobehavioral disturbances later in life. Previous work has shown that exercise can exert beneficial effects on brain damage; however, it is unknown whether voluntary wheel running (VWR) can ameliorate the neurobehavioral impairments induced by PS in adolescent offspring. Pregnant CF-1 mice were randomly assigned to control (n=5) or stressed (n=5) groups. Pregnant dams were subjected to restraint stress between gestational days 14 and 21 (G14-21), whereas controls remained undisturbed in their home cages. On postnatal day 21 (P21), male pups were randomly assigned to the following experimental groups: control (n=5), stressed (n=5), and stressed mice+daily submitted to VWR (n=4). At P52, all groups were behaviorally evaluated in the Morris water maze. Animals were then sacrificed, and Golgi-impregnated granule cells were morphometrically analyzed. The results indicate that PS produced significant behavioral and neuronal impairments in adolescent offspring and that VWR significantly offset these deleterious effects.

[Morphometric analysis of the differentiation process of hippocampal neurons in vitro]. / Análisis morfométrico del proceso de diferenciación in vitro de neuronas del hipocampo.

Neuronal cultures of the central nervous system are widely used to study the molecular mechanisms that rule the differentiation process. These cultures have also been used to evaluate drugs and to develop new therapies. From this we can infer the relevance of performing an extended characterization that involves the main aspects driving such process. To carry out such characterization in the present study we prepared primary cultures from hippocampal cells to study cell identity, development of neuronal processes (dendrites and axons), density of synaptic vesicles and development of growth cones. Using immunofluorescence techniques, specific antibodies and non-immunological probes, we studied the changes experienced by the structures under study during different temporal stages (1-21 days). We observed a major proportion of neurons over glia, normal development of neuronal networks (formed by dendrites and axons), increase in the length of dendrites and axons and establishment of synaptic connections. Synaptic vesicles also showed an increase in their densities as long as the time of the culture progressed. Finally, we studied the morphological changes of the growth cones and observed that those were mostly closed at the beginning of the culture period. As neurons matured we observed an increase in the proportion of open growth cones. This work represents an advance in the morphometric characterization of neuronal cultures, since it gathers the main aspects that outline the neuronal differentiation process. In this study, measurement of these morphological features made possible to establish quantitative markers that will allow establishing more precisely the different stages of neuronal differentiation.

Summation of excitatory postsynaptic potentials in electrically-coupled neurones.

Dendritic electrical coupling increases the number of effective synaptic inputs onto neurones by allowing the direct spread of synaptic potentials from one neurone to another. Here we studied the summation of excitatory postsynaptic potentials (EPSPs) produced locally and arriving from the coupled neurone (transjunctional) in pairs of electrically-coupled Retzius neurones of the leech. We combined paired recordings of EPSPs, the production of artificial excitatory postsynaptic potentials (APSPs) in neurone pairs with different coupling coefficients and simulations of EPSPs produced in the coupled dendrites. Summation of the EPSPs produced in the dendrites was always linear, suggesting that synchronous EPSPs are produced at two or more different pairs of coupled dendrites and not in both sides of any one gap junction. The different spatio-temporal relationships explored between pairs of EPSPs or APSPs produced three main effects. (1) Synchronous pairs of EPSPs or APSPs exhibited an elongation of their decay phase compared to single EPSPs. (2) Asymmetries in the amplitudes between the pair of EPSPs added a "hump" to the smallest EPSP. (3) Modelling the inputs near the electrical synapse or anticipating the production of the transjunctional APSP increased the amplitude of the compound EPSP. The magnitude of all these changes depended on the coupling coefficient of the neurones. We also show that the hump improves the passive conduction of EPSPs by adding low frequency components. The diverse effects of summation of local and alien EPSPs shown here endow electrically-coupled neurones with a wider repertoire of adjustable integrative possibilities.

Role of the 5-HT(1A) somatodendritic autoreceptor in the dorsal raphe nucleus on salt satiety signaling in rats.

We investigated the possible role of 5-HT(1A) somatodendritic autoreceptors in the dorsal raphe nucleus (DRN) on salt intake response during basal conditions and following natriorexigenic challenge aroused by sodium depletion in rats. Acute systemic administration (76-1520 nmol/kg s.c.) of 8-OH-DPAT, a selective 5-HT(1A) somatodendritic autoreceptor agonist, induced a clear and dose-dependent preference for salt intake through free choice between water and 0.3 M NaCl simultaneously offered under basal conditions. Acute intra-DRN microinjection (7.5 nmol/rat) of 8-OH-DPAT significantly mimicked the acute systemic protocol in sodium-replete rats. Interestingly, microinjection of 8-OH-DPAT into the DRN raised an additional long-lasting increase of 0.3 M NaCl intake in sodium-depleted rats despite a high volume ingested 30 min after central injection. Conversely, chronic systemic treatment (1520 nmol/kg s.c.) with 8-OH-DPAT for 2 and 3 weeks or repeated intra-DRN microinjection (7.5 nmol/rat) evoked a significant long-term decrease in 0.3 M NaCl intake in sodium-depleted rats given only water and a sodium-deficient diet over the course of 24 h after furosemide injection. These results show a clear-cut involvement of the DRN 5-HT(1A) somatodendritic autoreceptors in sodium satiety signaling under basal conditions and during the consummatory phase of salt intake in sodium-depleted rats.