RESUMO
Sparse coding can improve discrimination of sensory stimuli by reducing overlap between their representations. Two factors, however, can offset sparse coding's benefits: similar sensory stimuli have significant overlap and responses vary across trials. To elucidate the effects of these 2 factors, we analyzed odor responses in the fly and mouse olfactory regions implicated in learning and discrimination-the mushroom body (MB) and the piriform cortex (PCx). We found that neuronal responses fall along a continuum from extremely reliable across trials to extremely variable or stochastic. Computationally, we show that the observed variability arises from noise within central circuits rather than sensory noise. We propose this coding scheme to be advantageous for coarse- and fine-odor discrimination. More reliable cells enable quick discrimination between dissimilar odors. For similar odors, however, these cells overlap and do not provide distinguishing information. By contrast, more unreliable cells are decorrelated for similar odors, providing distinguishing information, though these benefits only accrue with extended training with more trials. Overall, we have uncovered a conserved, stochastic coding scheme in vertebrates and invertebrates, and we identify a candidate mechanism, based on variability in a winner-take-all (WTA) inhibitory circuit, that improves discrimination with training.
Assuntos
Dípteros , Percepção Olfatória , Animais , Camundongos , Condutos Olfatórios/fisiologia , Olfato/fisiologia , Odorantes , Aprendizagem/fisiologia , Percepção Olfatória/fisiologiaRESUMO
Anatomic and physiologic studies have suggested a model in which neurons of the piriform cortex receive convergent input from random collections of glomeruli. In this model, odor representations can only be afforded behavioral significance upon experience. We have devised an experimental strategy that permits us to ask whether the activation of an arbitrarily chosen subpopulation of neurons in piriform cortex can elicit different behavioral responses dependent upon learning. Activation of a small subpopulation of piriform neurons expressing channelrhodopsin at multiple loci in the piriform cortex, when paired with reward or shock, elicits either appetitive or aversive behavior. Moreover, we demonstrate that different subpopulations of piriform neurons expressing ChR2 can be discriminated and independently entrained to elicit distinct behaviors. These observations demonstrate that the piriform cortex is sufficient to elicit learned behavioral outputs in the absence of sensory input. These data imply that the piriform does not use spatial order to map odorant identity or behavioral output.
Assuntos
Comportamento Animal , Neurônios/fisiologia , Condutos Olfatórios/citologia , Olfato , Animais , Comportamento Apetitivo , Channelrhodopsins , Condicionamento Psicológico , Camundongos , Neurônios/citologia , Odorantes , Condutos Olfatórios/fisiologiaRESUMO
G protein-coupled receptor (GPCR) signaling is ubiquitous. As an archetype of this signaling motif, rod phototransduction has provided many fundamental, quantitative details, including a dogma that one active GPCR molecule activates a substantial number of downstream G protein/enzyme effector complexes. However, rod phototransduction is light-activated, whereas GPCR pathways are predominantly ligand-activated. Here, we report a detailed study of the ligand-triggered GPCR pathway in mammalian olfactory transduction, finding that an odorant-receptor molecule when (one-time) complexed with its most effective odorants produces on average much less than one downstream effector. Further experiments gave a nominal success probability of tentatively â¼10-4 (more conservatively, â¼10-2 to â¼10-5). This picture is potentially more generally representative of GPCR signaling than is rod phototransduction, constituting a paradigm shift.
Assuntos
Ligantes , Odorantes , Receptores Acoplados a Proteínas G , Receptores Odorantes , Transdução de Sinais , Olfato , Animais , Transdução de Sinal Luminoso , Mamíferos/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Receptores Odorantes/metabolismo , Células Fotorreceptoras Retinianas BastonetesRESUMO
Molecular biomarkers for neurodegenerative diseases are critical for advancing diagnosis and therapy. Normal pressure hydrocephalus (NPH) is a neurological disorder characterized by progressive neurodegeneration, gait impairment, urinary incontinence and cognitive decline. In contrast to most other neurodegenerative disorders, NPH symptoms can be improved by the placement of a ventricular shunt that drains excess CSF. A major challenge in NPH management is the identification of patients who benefit from shunt surgery. Here, we perform genome-wide RNA sequencing of extracellular vesicles in CSF of 42 NPH patients, and we identify genes and pathways whose expression levels correlate with gait, urinary or cognitive symptom improvement after shunt surgery. We describe a machine learning algorithm trained on these gene expression profiles to predict shunt surgery response with high accuracy. The transcriptomic signatures we identified may have important implications for improving NPH diagnosis and treatment and for understanding disease aetiology.
RESUMO
Voltage-gated CaV2.2 calcium channels are expressed in nociceptors at presynaptic terminals, soma, and axons. CaV2.2 channel inhibitors applied to the spinal cord relieve pain in humans and rodents, especially during pathologic pain, but a biological function of nociceptor CaV2.2 channels in processing of nociception, outside presynaptic terminals in the spinal cord, is underappreciated. Here, we demonstrate that functional CaV2.2 channels in peripheral axons innervating skin are required for capsaicin-induced heat hypersensitivity in male and female mice. We show that CaV2.2 channels in TRPV1-nociceptor endings are activated by capsaicin-induced depolarization and contribute to increased intracellular calcium. Capsaicin induces hypersensitivity of both thermal nociceptors and mechanoreceptors, but only heat hypersensitivity depends on peripheral CaV2.2 channel activity, and especially a cell-type-specific CaV2.2 splice isoform. CaV2.2 channels at peripheral nerve endings might be important therapeutic targets to mitigate certain forms of chronic pain.SIGNIFICANCE STATEMENT It is generally assumed that nociceptor termini in the spinal cord dorsal horn are the functionally significant sites of CaV2.2 channel in control of transmitter release and the transmission of sensory information from the periphery to central sites. We show that peripheral CaV2.2 channels are essential for the classic heat hypersensitivity response to develop in skin following capsaicin exposure. This function of CaV2.2 is highly selective for heat, but not mechanical hypersensitivity induced by capsaicin exposure, and is not a property of closely related CaV2.1 channels. Our findings suggest that interrupting CaV2.2-dependent calcium entry in skin might reduce heat hypersensitivity that develops after noxious heat exposure and may limit the degree of heat hypersensitivity associated with certain other forms of pain.
Assuntos
Canais de Cálcio Tipo N/metabolismo , Cálcio/metabolismo , Hiperalgesia/metabolismo , Neurônios/fisiologia , Nociceptores/fisiologia , Terminações Pré-Sinápticas/metabolismo , Pele/inervação , Corno Dorsal da Medula Espinal/metabolismo , Animais , Temperatura Alta , Camundongos , Nociceptividade/fisiologia , Estimulação Física , Pele/metabolismo , Transmissão Sináptica/fisiologiaRESUMO
One defining characteristic of the mammalian brain is its neuronal diversity. For a given region, substructure, layer or even cell type, variability in neuronal morphology and connectivity persists. Although it is well known that such cellular properties vary considerably according to neuronal type, the substantial biophysical diversity of neurons of the same morphological class is typically averaged out and ignored. Here we show that the amplitude of hyperpolarization-evoked sag of membrane potential recorded in olfactory bulb mitral cells is an emergent, homotypic property of local networks and sensory information processing. Simultaneous whole-cell recordings from pairs of cells show that the amount of hyperpolarization-evoked sag potential and current (Ih) is stereotypic for mitral cells belonging to the same glomerular circuit. This is corroborated by a mosaic, glomerulus-based pattern of expression of the HCN2 (hyperpolarization-activated cyclic nucleotide-gated channel 2) subunit of the Ih channel. Furthermore, inter-glomerular differences in both membrane potential sag and HCN2 protein are diminished when sensory input to glomeruli is genetically and globally altered so that only one type of odorant receptor is universally expressed. Population diversity in this intrinsic property therefore reflects differential expression between local mitral cell networks processing distinct odour-related information.
Assuntos
Rede Nervosa/fisiologia , Bulbo Olfatório/citologia , Bulbo Olfatório/fisiologia , Olfato/fisiologia , Animais , Feminino , Perfilação da Expressão Gênica , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização , Canais Iônicos/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Modelos Neurológicos , Canais de Potássio , Receptores Odorantes/metabolismoRESUMO
The odorant receptor (OR) genes constitute the largest mammalian gene family and are expressed in a monogenic and monoallelic fashion, through an unknown mechanism that likely exploits positive and negative regulation. We devised a genetic strategy in mice to examine OR selection by determining the transcriptional activity of an exogenous promoter homologously integrated into an OR locus. Using the tetracycline-dependent transactivator responsive promoter (tet(o)), we observed that the OR locus imposes spatial and temporal constraints on tet(o)-driven transcription. Conditional expression experiments reveal a developmental change in the permissiveness of the locus. Further, expression of an OR transgene that suppresses endogenous ORs similarly represses the OR-integrated tet(o). Neurons homozygous for the tet(o)-modified allele demonstrate predominantly monoallelic expression, despite their potential to express both copies. These data reveal multiple axes of regulation, and support a model of initiation of OR choice limited by nonpermissive chromatin and maintained by repression of nonselected alleles.
Assuntos
Receptores Odorantes/genética , Ativação Transcricional , Alelos , Animais , Regulação da Expressão Gênica , Genes Reporter , Camundongos , Camundongos Endogâmicos C57BL , Regiões Promotoras Genéticas , Tetraciclina , TransgenesRESUMO
As an evolutionarily ancient sense, olfaction is key to learning where to find food, shelter, mates, and important landmarks in an animal's environment. Brain circuitry linking odor and navigation appears to be a well conserved multi-region system among mammals; the anterior olfactory nucleus, piriform cortex, entorhinal cortex, and hippocampus each represent different aspects of olfactory and spatial information. We review recent advances in our understanding of the neural circuits underlying odor-place associations, highlighting key choices of behavioral task design and neural circuit manipulations for investigating learning and memory.
Assuntos
Odorantes , Animais , Condutos Olfatórios/fisiologia , Olfato/fisiologia , Humanos , Percepção Olfatória/fisiologia , Percepção Espacial/fisiologia , Encéfalo/fisiologiaRESUMO
Neuroscience research has evolved to generate increasingly large and complex experimental data sets, and advanced data science tools are taking on central roles in neuroscience research. Neurodata Without Borders (NWB), a standard language for neurophysiology data, has recently emerged as a powerful solution for data management, analysis, and sharing. We here discuss our labs' efforts to implement NWB data science pipelines. We describe general principles and specific use cases that illustrate successes, challenges, and non-trivial decisions in software engineering. We hope that our experience can provide guidance for the neuroscience community and help bridge the gap between experimental neuroscience and data science.
RESUMO
Anxiety disorders are characterized by persistent fear in the absence of immediate threat and represent the most common psychiatric diseases, with an estimated 28% lifetime prevalence worldwide (Kessler et al., 2010). While symptoms of anxiety are typically evoked by sensory stimuli, it is unknown whether sensory deficits contribute to the development of anxiety disorders. Here we examine the effect of defined genetic mutations that compromise the function of the olfactory system on the development of anxiety-like behaviors in mice. We show that the functional inactivation of the main olfactory epithelium, but not the vomeronasal organ, causes elevated levels of anxiety. Anxiety-like behaviors are also observed in mice with a monoclonal nose, that are able to detect and discriminate odors but in which the patterns of odor-evoked neural activity are perturbed. In these mice, plasma corticosterone levels are elevated, suggesting that olfactory deficits can lead to chronic stress. These results demonstrate a central role for olfactory sensory cues in modulating anxiety in mice.
Assuntos
Ansiedade/genética , Odorantes , Mucosa Olfatória/fisiologia , Olfato/genética , Órgão Vomeronasal/fisiologia , Animais , Ansiedade/sangue , Ansiedade/etiologia , Corticosterona/sangue , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos TransgênicosRESUMO
Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development. Heterochromatin assembly and genomic compartmentalization of OR alleles also vary across the axes of the olfactory epithelium and may preferentially eliminate ectopically expressed ORs with more dorsal expression destinations from this "privileged" repertoire. Our experiments identify early transcription as a potential "epigenetic" contributor to future developmental patterning and reveal how two spatially responsive probabilistic processes may act in concert to establish deterministic, precise, and reproducible territories of stochastic gene expression.
RESUMO
Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in the mouse genome in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development. Heterochromatin assembly and genomic compartmentalization of OR alleles also vary across the axes of the olfactory epithelium and may preferentially eliminate ectopically expressed ORs with more dorsal expression destinations from this 'privileged' repertoire. Our experiments identify early transcription as a potential 'epigenetic' contributor to future developmental patterning and reveal how two spatially responsive probabilistic processes may act in concert to establish deterministic, precise, and reproducible territories of stochastic gene expression.
Assuntos
Neurônios Receptores Olfatórios , Receptores Odorantes , Animais , Camundongos , Receptores Odorantes/genética , Epigenômica , Alelos , Epigênese GenéticaRESUMO
The Fos protein, a major component of the AP-1 transcription factor, is essential for osteoclast differentiation, acts as an oncogene, potentiates transforming signals, and controls invasive growth and angiogenesis during tumor progression. To investigate a potential genetic interaction between the Trp53 and Fos pathways, Trp53/Fos double knockout mice were generated. These mice develop highly proliferative and invasive rhabdomyosarcomas of the facial and orbital regions, with more than 90% penetrance at 6 months of age. Rhabdomyosarcoma cell lines established from the primary tumors express characteristic muscle-specific markers, and reexpression of Fos is associated with enhanced apoptosis in vitro. Moreover, Fos is able to repress Pax7 expression in rhabdomyosarcoma cell lines and primary myoblasts, suggesting a molecular link to genetic alterations involved in human rhabdomyosarcomas.
Assuntos
Músculo Esquelético/fisiopatologia , Mutação , Osteoclastos/metabolismo , Proteínas Proto-Oncogênicas c-fos/genética , Rabdomiossarcoma/genética , Fator de Transcrição AP-1/genética , Animais , Apoptose/fisiologia , Diferenciação Celular , Regulação Neoplásica da Expressão Gênica , Proteínas de Homeodomínio/metabolismo , Humanos , Camundongos , Camundongos Knockout , Fator de Transcrição PAX7 , Proteínas Proto-Oncogênicas c-fos/metabolismo , Rabdomiossarcoma/etiologia , Rabdomiossarcoma/metabolismo , Fator de Transcrição AP-1/metabolismo , Células Tumorais CultivadasRESUMO
Projection neurons (PNs) in the mammalian olfactory bulb (OB) receive input from the nose and project to diverse cortical and subcortical areas. Morphological and physiological studies have highlighted functional heterogeneity, yet no molecular markers have been described that delineate PN subtypes. Here, we used viral injections into olfactory cortex and fluorescent nucleus sorting to enrich PNs for high-throughput single nucleus and bulk RNA deep sequencing. Transcriptome analysis and RNA in situ hybridization identified distinct mitral and tufted cell populations with characteristic transcription factor network topology, cell adhesion, and excitability-related gene expression. Finally, we describe a new computational approach for integrating bulk and snRNA-seq data and provide evidence that different mitral cell populations preferentially project to different target regions. Together, we have identified potential molecular and gene regulatory mechanisms underlying PN diversity and provide new molecular entry points into studying the diverse functional roles of mitral and tufted cell subtypes.
Assuntos
Interneurônios/fisiologia , Neurônios/fisiologia , Bulbo Olfatório/fisiologia , Fatores de Transcrição/metabolismo , Animais , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Análise de Sequência de RNARESUMO
Odor memories are exceptionally robust and essential for animal survival. The olfactory (piriform) cortex has long been hypothesized to encode odor memories, yet the cellular substrates for olfactory learning and memory remain unknown. Here, using intersectional, cFos-based genetic manipulations ("Fos tagging"), we show that olfactory fear conditioning activates sparse and distributed ensembles of neurons in the mouse piriform cortex. We demonstrate that chemogenetic silencing of these Fos-tagged piriform ensembles selectively interferes with odor fear memory retrieval but does not compromise basic odor detection and discrimination. Furthermore, chemogenetic reactivation of piriform neurons that were Fos tagged during olfactory fear conditioning causes a decrease in exploratory behavior, mimicking odor-evoked fear memory recall. Together, our experiments identify specific ensembles of piriform neurons as critical components of an olfactory fear memory trace.
Assuntos
Medo/fisiologia , Memória/fisiologia , Rememoração Mental/fisiologia , Odorantes , Córtex Piriforme/fisiologia , Animais , Feminino , Masculino , Camundongos , Proteínas Proto-Oncogênicas c-fos/genéticaRESUMO
Olfactory perception and behaviors critically depend on the ability to identify an odor across a wide range of concentrations. Here, we use calcium imaging to determine how odor identity is encoded in olfactory cortex. We find that, despite considerable trial-to-trial variability, odor identity can accurately be decoded from ensembles of co-active neurons that are distributed across piriform cortex without any apparent spatial organization. However, piriform response patterns change substantially over a 100-fold change in odor concentration, apparently degrading the population representation of odor identity. We show that this problem can be resolved by decoding odor identity from a subpopulation of concentration-invariant piriform neurons. These concentration-invariant neurons are overrepresented in piriform cortex but not in olfactory bulb mitral and tufted cells. We therefore propose that distinct perceptual features of odors are encoded in independent subnetworks of neurons in the olfactory cortex.
Assuntos
Neurônios/fisiologia , Odorantes , Percepção Olfatória , Córtex Piriforme/fisiologia , Animais , Sinalização do Cálcio , Camundongos , Modelos Neurológicos , Imagem ÓpticaRESUMO
Odorant receptor (OR) gene choice in mammals is a paradigmatic example of monogenic and monoallelic transcriptional selection, in which each olfactory sensory neuron (OSN) chooses to express one OR allele from over 1,000 encoded in the genome [1-3]. This process, critical for generation of the circuit from nose to brain [4-6], is thought to occur in two steps: a slow initial phase that randomly activates a single OR allele, followed by a rapid feedback that halts subsequent expression [7-14]. Inherent in this model is a finite failure rate wherein multiple OR alleles may be activated prior to feedback suppression [15, 16]. Confronted with more than one receptor, the neuron would need to activate a refinement mechanism to eliminate multigenic OR expression and resolve unique neuronal identity [16], critical to the generation of the circuit from nose to olfactory bulb. Here we used a genetic approach in mice to reveal a new facet of OR regulation that corrects adventitious activation of multiple OR alleles, restoring monogenic OR expression and unique neuronal identity. Using the tetM71tg model system, in which the M71 OR is expressed in >95% of mature OSNs and potently suppresses the expression of the endogenous OR repertoire [10], we provide clear evidence of a post-selection refinement (PSR) process that winnows down the number of ORs. We further demonstrate that PSR efficiency is linked to OR expression level, suggesting an underlying competitive process and shedding light on OR gene switching and the fundamental mechanism of singular OR choice.
Assuntos
Regulação da Expressão Gênica , Bulbo Olfatório/metabolismo , Neurônios Receptores Olfatórios/metabolismo , Receptores Odorantes/genética , Alelos , Animais , Camundongos , Receptores Odorantes/metabolismoRESUMO
Perturbations in neural circuits can provide mechanistic understanding of the neural correlates of behavior. In M71 transgenic mice with a "monoclonal nose", glomerular input patterns in the olfactory bulb are massively perturbed and olfactory behaviors are altered. To gain insights into how olfactory circuits can process such degraded inputs we characterized odor-evoked responses of olfactory bulb mitral cells and interneurons. Surprisingly, calcium imaging experiments reveal that mitral cell responses in M71 transgenic mice are largely normal, highlighting a remarkable capacity of olfactory circuits to normalize sensory input. In vivo whole cell recordings suggest that feedforward inhibition from olfactory bulb periglomerular cells can mediate this signal normalization. Together, our results identify inhibitory circuits in the olfactory bulb as a mechanistic basis for many of the behavioral phenotypes of mice with a "monoclonal nose" and highlight how substantially degraded odor input can be transformed to yield meaningful olfactory bulb output.
Assuntos
Rede Nervosa/fisiologia , Rede Nervosa/fisiopatologia , Neurônios/fisiologia , Bulbo Olfatório/fisiologia , Bulbo Olfatório/fisiopatologia , Animais , Camundongos Transgênicos , Transtornos do Olfato/genéticaRESUMO
The ability to target subclasses of neurons with defined connectivity is crucial for uncovering neural circuit functions. The olfactory (piriform) cortex is thought to generate odour percepts and memories, and odour information encoded in piriform is routed to target brain areas involved in multimodal sensory integration, cognition and motor control. However, it remains unknown if piriform outputs are spatially organized, and if distinct output channels are delineated by different gene expression patterns. Here we identify genes selectively expressed in different layers of the piriform cortex. Neural tracing experiments reveal that these layer-specific piriform genes mark different subclasses of neurons, which project to distinct target areas. Interestingly, these molecular signatures of connectivity are maintained in reeler mutant mice, in which neural positioning is scrambled. These results reveal that a predictive link between a neuron's molecular identity and connectivity in this cortical circuit is determined independent of its spatial position.
Assuntos
Perfilação da Expressão Gênica , Rede Nervosa/metabolismo , Córtex Olfatório/metabolismo , Tonsila do Cerebelo/metabolismo , Animais , Masculino , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Bulbo Olfatório/metabolismo , Córtex Piriforme/metabolismo , Córtex Pré-Frontal/metabolismoRESUMO
The immediate early gene c-fos is part of the activator protein-1 transcription factor and has been postulated to participate in the molecular mechanisms of learning and memory. To test this hypothesis in vivo, we generated mice with a nervous system-specific c-fos knock-out using the Cre-loxP system. Adult mice lacking c-Fos in the CNS (c-fosDeltaCNS) showed normal general and emotional behavior but were specifically impaired in hippocampus-dependent spatial and associative learning tasks. These learning deficits correlated with a reduction of long-term potentiation (LTP) in hippocampal CA3-CA1 synapses. The magnitude of LTP was restored by a repeated tetanization procedure, suggesting impaired LTP induction in c-fosDeltaCNS mice. This rescue was blocked by a selective inhibitor of NR2B-type NMDA receptors. This blockade was compensated in wild-type mice by NR2A-type NMDA receptor-activated signaling pathways, thus indicating that these pathways are compromised in c-fosDeltaCNS mice. In summary, our data suggest a role for c-Fos in hippocampus-dependent learning and memory as well as in NMDA receptor-dependent LTP formation.