RESUMO
The olfactory system is a fascinating and beguiling sensory system: olfactory sensory neurons detect odors underlying behaviors essential for mate choice, food selection, and escape from predators, among others. These sensory neurons are unique in that they have dendrites contacting the outside world, yet their first synapse lies in the central nervous system. The information entering the central nervous system is used to create odor memories that play a profound role in recognition of individuals, places, and appropriate foods. Here, the structure of the olfactory epithelium is given as an overview to discuss the origin of the olfactory placode, the plasticity of the olfactory sensory neurons, and finally the origins of the gonadotropin-releasing hormone neuroendocrine cells. For the purposes of this review, the development of the peripheral sensory system will be analyzed, incorporating recently published studies highlighting the potential novelties in development mechanisms. Specifically, an emerging model where the olfactory epithelium and olfactory bulb develop simultaneously from a continuous neurectoderm patterned at the end of gastrulation, and the multiple origins of the gonadotropin-releasing hormone neuroendocrine cells associated with the olfactory sensory system development will be presented. Advances in the understanding of the basic mechanisms underlying olfactory sensory system development allows for a more thorough understanding of the potential causes of human disease.
Assuntos
Regeneração Nervosa/fisiologia , Doenças Neurodegenerativas/patologia , Nervo Olfatório/fisiopatologia , Condutos Olfatórios/embriologia , Neurônios Receptores Olfatórios/citologia , Olfato/fisiologia , Animais , Humanos , Doenças Neurodegenerativas/etiologia , Condutos Olfatórios/citologiaRESUMO
Enormous advances have been made in the recent years in regard to the mechanisms and neural circuits by which odors are sensed and perceived. Part of this understanding has been gained from parallel studies in insects and rodents that show striking similarity in the mechanisms they use to sense, encode, and perceive odors. In this review, we provide a short introduction to the functioning of olfactory systems from transduction of odorant stimuli into electrical signals in sensory neurons to the anatomical and functional organization of the networks involved in neural representation of odors in the central nervous system. We make emphasis on the functional and anatomical architecture of the first synaptic relay of the olfactory circuit, the olfactory bulb in vertebrates and the antennal lobe in insects. We discuss how the exquisite and conserved architecture of this structure is established and how different odors are encoded in mosaic activity patterns. Finally, we discuss the validity of methods used to compare activation patterns in relation to perceptual similarity.
Assuntos
Rede Nervosa/fisiologia , Odorantes , Condutos Olfatórios/citologia , Percepção Olfatória/fisiologia , Neurônios Receptores Olfatórios/fisiologia , Olfato/fisiologia , Animais , Humanos , Transdução de Sinais/fisiologiaRESUMO
The mammalian olfactory cortex is a complex structure located along the rostro-caudal extension of the ventrolateral prosencephalon, which is divided into several anatomically and functionally distinct areas: the anterior olfactory nucleus, piriform cortex, olfactory tubercle, amygdaloid olfactory nuclei, and the more caudal entorhinal cortex. Multiple forebrain progenitor domains contribute to the cellular diversity of the olfactory cortex, which is invaded simultaneously by cells originating in distinct germinal areas in the dorsal and ventral forebrain. Using a combination of dye labeling techniques, we identified two novel areas that contribute cells to the developing olfactory cortices, the septum and the ventral pallium, from which cells migrate along a radial and then a tangential path. We characterized these cell populations by comparing their expression of calretinin, calbindin, reelin and Tbr1 with that of other olfactory cell populations.
Assuntos
Vias Neurais/fisiologia , Condutos Olfatórios/citologia , Prosencéfalo/embriologia , Prosencéfalo/fisiologia , Animais , Calbindina 2 , Calbindinas , Moléculas de Adesão Celular Neuronais/metabolismo , Movimento Celular , Corantes/farmacologia , Proteínas da Matriz Extracelular/metabolismo , Feminino , Camundongos , Camundongos Endogâmicos C57BL , Proteínas do Tecido Nervoso/metabolismo , Vias Neurais/citologia , Neurônios/metabolismo , Gravidez , Prenhez , Proteína Reelina , Proteína G de Ligação ao Cálcio S100/metabolismo , Serina Endopeptidases/metabolismo , Fatores de TempoRESUMO
Decapod crustaceans show proliferation of the nerve cells in the olfactory lobe throughout their lives. However, the regulation of this process is still poorly understood, since it may vary with endogenous and exogenous factors. The objective of the present investigation was to quantify the proliferation of nerve cells and number of nerve cells with ecdysone receptors in the clusters of the central olfactory system in Neohelice granulata, according to moult stages and in different seasons (summer and winter). Three injections of bromodeoxyuridine (BrdU) were administered to the crabs. Brains were sectioned by microtome and fixed on slides for immunohistochemistry with anti-BrdU and anti-EcR antibodies. The proliferation of nerve cells was higher in winter than in summer, probably because in winter the crabs do not breed and the premoult and postmoult periods are longer. Crabs in postmoult exhibited more BrdU-labelled cells than crabs in premoult or intermoult in winter, because of a greater number of mitoses related to an increase in body size and addition of olfactory receptor neurons. The number of EcR-labelled cells was higher in premoult than in postmoult or intermoult in winter. The proliferation of nerve cells is regulated seasonally and according to moult stages.
Assuntos
Braquiúros , Proliferação de Células , Muda/fisiologia , Neurônios/citologia , Receptores de Esteroides/metabolismo , Estações do Ano , Animais , Contagem de Células , Sistema Nervoso Central/citologia , Sistema Nervoso Central/fisiologia , Ecdisona/metabolismo , Ecdisona/fisiologia , Gânglios dos Invertebrados/citologia , Gânglios dos Invertebrados/metabolismo , Neurônios/metabolismo , Condutos Olfatórios/citologia , Condutos Olfatórios/metabolismoRESUMO
The sense organs of the vertebrate head arise predominantly from sensory placodes. The sensory placodes have traditionally been grouped as structures that share common developmental and evolutionary characteristics. In attempts to build a coherent model for development of all placodes, the fascinating differences that make placodes unique are often overlooked. Here I review olfactory placode development with special attention to the origin and cell movements that generate the olfactory placode, the derivatives of this sensory placode, and the degree to which it shows plasticity during development. Next, through comparison with adenohypophyseal, and lens placodes I suggest we revise our thinking and terminology for these anterior placodes, specifically by: (1) referring to the peripheral olfactory sensory system as neural ectoderm because it expresses the same series of genes involved in neural differentiation and differentiates in tandem with the olfactory bulb, and (2) grouping the anterior placodes with their corresponding central nervous system structures and emphasizing patterning mechanisms shared between placodes and these targets. Sensory systems did not arise independent of the central nervous system; they are part of a functional unit composed of peripheral sensory structures and their targets. By expanding our analyses of sensory system development to also include cell movements, gene expression and morphological changes observed in this functional unit, we will better understand the evolution of sensory structures.
Assuntos
Ectoderma/fisiologia , Plasticidade Neuronal/fisiologia , Condutos Olfatórios/embriologia , Olfato/fisiologia , Animais , Movimento Celular , Ectoderma/citologia , Condutos Olfatórios/citologiaRESUMO
In vitro studies support the existence of adult neural stem cells in the rostral migratory stream (RMS). The evidence supporting this possibility in vivo is scarce. We then explore this issue by taking advantage of a rat model in which a physical barrier implanted in the brain interrupted the migration of neuroblasts derived from the SVZ along the RMS at the level of its vertical limb. The presence of local stem cells and neurogenesis were then established by estimating the number of nuclei labeled with bromo-deoxyuridine (BrdU), the number of doublecortin-positive neuroblasts and the existence of cells displaying co-localization of BrdU and Sox-2 immunoreactivity along the RMS, at different time points following barrier implantation. Estimations of the number of the granular and periglomerular neurons integrated into the corresponding layers of the olfactory bulb of implanted rats established that stem cells in the RMS give rise predominantly to periglomerular neurons. Our results then support the notion that the RMS is indeed a region in which neurogenesis is taking place in the adult brain. They also support that the relative location of the neurogenic niche might imprint, at least in some degree, the identity and lineage of the neuroblasts arising from them.
Assuntos
Movimento Celular/fisiologia , Neurônios/citologia , Condutos Olfatórios/citologia , Células-Tronco/citologia , Fatores Etários , Animais , Divisão Celular/fisiologia , Ventrículos Cerebrais/citologia , Proteína Duplacortina , Masculino , Neurônios/fisiologia , Bulbo Olfatório/citologia , Ratos , Ratos Wistar , Células-Tronco/fisiologiaRESUMO
Las células de la glía envolvente olfatoria hacen parte del tejido del sistema olfatorio. Este sistema puede presentar neurogénesis durante de toda la vida, lo cual permite el crecimiento de axones de neuronas sensoriales desde la periferia y la posterior formación de sinapsis con receptores axonales olfatorios dentro del sistema nervioso central en el bulbo olfatorio. El conocimiento de las propiedades funcionales de dichas células de la glía envolvente en el sistema olfatorio ha promovido su estudio como posibles elementos para el tratamiento de lesiones del sistema nervioso central, en especial, las lesiones de médula espinal. Se han reportado resultados que muestran que las células de la glía envolvente pueden tener alguna habilidad como promotoras de crecimiento y regeneración axonal y, también, como células remielinizantes.El objetivo de esta revisión es hacer un resumen del conocimiento actual sobre las células de la glía envolvente olfatoria, haciendo énfasis en sus características biológicas y funcionales, y en los resultados de estudios publicados en el campo de la regeneración en lesiones de médula espinal.
Assuntos
Humanos , Técnicas de Cultura de Células , Condutos Olfatórios/citologia , Condutos Olfatórios/fisiologiaRESUMO
The amygdala complex is a heterogeneous group of temporal lobe brain structures involved in the processing of biologically significant sensory stimuli and in the generation of appropriate responses to them. The amygdala has also been implicated in certain forms of emotional learning and memory. While much progress has been made in understanding neural processing in the basolateral subgroup of the amygdala, physiological studies in the cortical regions of the complex, also known as olfactory amygdala, are missing. Using a rat brain slice preparation, we conducted whole-cell recordings on pyramidal neurons of the periamygdaloid cortex and the anterior cortical nucleus, two structures receiving direct connections from the olfactory bulb. Upon depolarization by current injection through the recording electrode, a fraction of periamygdaloid cortex and most anterior cortical nucleus layer II pyramidal neurons displayed an intermittent discharge pattern, where clusters of action potentials were interspersed by periods of membrane potential subthreshold oscillations. Oscillations frequency increased with membrane potential and correlated linearly with the cluster spiking frequency. Frequency ranged from 3 to 20 Hz, considering different cells and membrane potential values (up to approximately 30 mV above resting potentials of typically approximately -70 mV). Subthreshold oscillations were preserved after pharmacological inhibition of fast excitatory and inhibitory synaptic transmission, but were abolished by application of the sodium channel blocker tetrodotoxin. We conclude that pyramidal neurons of the olfactory cortical amygdala display intrinsically generated voltage-dependent membrane potential rhythmic fluctuations in the theta-low beta range, requiring the activation of a sodium conductance.
Assuntos
Tonsila do Cerebelo/citologia , Potenciais da Membrana/fisiologia , Condutos Olfatórios/citologia , Periodicidade , Células Piramidais/fisiologia , 2-Amino-5-fosfonovalerato/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Anestésicos Locais/farmacologia , Animais , Antagonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas GABAérgicos , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Técnicas de Patch-Clamp/métodos , Picrotoxina/farmacologia , Células Piramidais/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Tetrodotoxina/farmacologiaRESUMO
There are some apparently healthy male rats that fail to mate after repeated testing with receptive females. We have previously shown that these "non-copulator (NC)" males show no partner preference for a receptive female when given the opportunity to physically interact with a sexually receptive female or a sexually active male. We also demonstrated that although NC males prefer odors from estrous females to odors from anestrous females, this preference is significantly reduced in comparison to the preference displayed by copulating (C) males. The aim of the present study was to evaluate in NC males sexual incentive motivation, that is, the approach behavior of male rats to either a sexually receptive female or a sexually active male in a test where the subjects can smell, hear, and see the stimulus animal but prevents their physical interaction. In addition, we determined whether NC rats have alterations in their ability to detect odors from conspecifics or odors related to food. In the detection of odors from conspecifics, we determined if these NC males are sexually attracted toward odors from receptive females or sexually active males. For food-related odors, we quantified the time it took the subjects to locate a hidden a piece of apple. Finally, using the induction of Fos-immunoreactivity (Fos-IR) as an index of neuronal activation, we compared the response of the vomeronasal projection pathway (VN pathway) of C and NC male rats exposed to estrous bedding. Males without sexual experience (WSE) were included in all experiments to determine the importance of previous heterosexual experience in the different behavioral tests and in the activity of the VN pathway. In the sexual incentive motivation test, we found that C and WSE male rats have a clear preference for estrous females over sexually active males, whereas NC male rats showed no preference. In odor tests, our results showed that C males had a clear preference for odors from estrous females as opposed to odors from sexually active males. Although NC and WSE male rats showed a preference for estrous female odors, this preference was significantly reduced compared to that shown by C males. No differences were found between WSE, C, and NC males in the detection of stimuli associated with food-related odors. A significant increase in Fos-IR was observed in the mitral cell layer of the accessory olfactory bulb in all groups when exposed to estrous bedding. However, only the C male rats exposed to estrous female bedding showed an increase Fos-IR in all structures of the VN pathway. An increase in Fos-IR was observed in the medial preoptic area (MPOA) of WSE males exposed to estrous bedding. No increases in Fos-IR were detected along the VN pathway in NC male rats. We proposed that NC male rats do not display sexual behavior due to a reduced sexual motivation that could be caused by alterations in the neuronal activity of the VN pathway during the processing of estrous odors.
Assuntos
Motivação , Condutos Olfatórios/fisiologia , Comportamento Sexual Animal/fisiologia , Olfato/fisiologia , Órgão Vomeronasal/fisiologia , Animais , Copulação/fisiologia , Sinais (Psicologia) , Feminino , Masculino , Neurônios/metabolismo , Bulbo Olfatório/citologia , Bulbo Olfatório/fisiologia , Condutos Olfatórios/citologia , Proteínas Proto-Oncogênicas c-fos/metabolismo , Distribuição Aleatória , Ratos , Ratos Wistar , Órgão Vomeronasal/citologia , Órgão Vomeronasal/inervaçãoRESUMO
The role of Orphanin-FQ/nociceptin in synaptic plasticity was assessed by its potency in modulating kindling epileptogenesis in vivo, and feed-forward inhibition in hippocampal recordings in vitro. In addition, a specific rabbit antiserum against this peptide was obtained and the immunohistochemical distribution of nociceptin was determined in rat brain slices. After the establishment of kindling epilepsy, by daily electrical stimulation of the piriform cortex, the i.c.v. injection of nociceptin, 20 min before the kindling stimulation, was not able to block the generation of the generalized seizures, nor to alter their duration. However, the i.c.v. injection of nociceptin, 20 min before each stimulation along the kindling process, depressed its development in a dose-dependent manner. This effect was specific since the nociceptin antagonist [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2, but not the broad-spectrum opiate antagonist, naloxone, was able to completely block nociceptin actions. The inhibitory role of nociceptin was assessed by in vitro recordings from entorhinal cortex-hippocampal slices. By single pulses applied over the Schaffer collaterals, we found that synaptic transmission was facilitated onto CA1, but using a paired-pulse protocol, we found that nociceptin potentiated feed-forward inhibition. The immunohistochemical data show that nociceptin is expressed in limbic cortical regions, including the piriform cortex and the hippocampus. Our results demonstrate that nociceptin exerts a modulatory role in limbic excitability and suggest that it provides an inhibitory control in the development of epilepsy by possibly inhibiting the spread of excitation through the system, by favoring feed-forward inhibition.