Diss. (sammanfattning) Umeå : Univ., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Umeå : Umeå universitet, 2006. / Härtill 4 uppsatser.

Neural representations of odors get associated with other stimuli through experience. Are action potentials the neural representation that directly gets associated with reinforcement during conditioning? In Manduca , I found that odor presentations elicited only one or two spikes at odor onset (and sometimes offset) in each of a small portion of Kenyon cells, a population of neurons known to be crucial for olfactory associative learning. By using a series of odor-taste associative conditioning paradigms with various sucrose presentation timings, I carefully controlled the temporal overlap between Kenyon cell spiking and sucrose reinforcement timing. I found that in paradigms that led to learning, spiking in Kenyon cells ended well before the reinforcement was given. Further, increasing the temporal overlap between Kenyon cell spiking and sucrose reinforcement actually reduced learning efficacy. Therefore, spikes in Kenyon cells are not the neural representation that gets directly reinforced, and Hebbian spike timing--dependent plasticity in Kenyon cells alone cannot underlie this learning. / Two important focuses in neuroscience are to study how animals process sensory stimuli, and how such stimuli get associated with other sensory modalities through experience. Often, sensory stimuli elicit the oscillatory synchronization of neurons in different parts of the brain, and thus may constitute an important stage in sensory processing. Odor-evoked oscillatory synchronization has been observed in a wide variety of animals, including mammals and insects. Despite differences in details of anatomical structure, animals from widely different phyla appear to use similar strategies to encode odors. Here, using the moth Manduca sexta, I examined the factors that cause odor-evoked oscillatory synchronization of olfactory neurons and that determine the frequency of these oscillations. I found that frequency of oscillations decreased from ∼40 Hz to ∼20 Hz during the course of a lengthy odor pulse. This decrease in oscillatory frequency appeared in parallel with a decrease in net olfactory receptor output, suggesting that the intensity of olfactory receptor neuron input to the antennal lobe, the first olfactory relay center, may determine oscillatory frequency. However, I found that changing odor concentration had little effect on oscillatory frequency. Combining the results of recordings made in vivo and computational models, I found that increasing odor concentration recruited additional, but less well-tuned olfactory receptor neurons to respond to the odor. Firing rates of these neurons were tightly constrained by adaptation and saturation. My work established that, in the periphery, odor concentration is mainly encoded by the size of the olfactory receptor neuron population that responded to the odor, whereas oscillatory frequency is determined by the adaptation and saturation of this response. / Ong, Chik Ying Rose. / Advisers: Siu Kai Kong; Mark Stopfer. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 132-147). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [115]-133).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 128-157).

No description available.

Narcolepsy is a disorder of unstable wake and sleep states caused by the lack of orexin neurons which degenerate most likely as a consequence of an autoimmune process. The state instability of narcolepsy includes rapid eye movement (REM) sleep intruding into wake in the form of dream-like hallucinations and cataplexy, muscle paralysis (atonia) much like occurs in REM sleep. In mice lacking orexin peptides, cataplexy is also observed with similar presentation as in humans of muscle paralysis during wakefulness which is often triggered by positive emotions. Prior research showed that the activation of the central amygdala is sufficient to promote cataplexy in a mouse model of narcolepsy. The central amygdala (CeA) contains a variety of neuronal types, and we hypothesize that γ-aminobutyric acid (GABA)-ergic neurons expressing the oxytocin receptor (OTR) mediate cataplexy as these neurons project to a known REM sleep atonia-regulating region, the ventrolateral periaqueductal gray (vlPAG)/lateral pontine tegmentum (LPT), and, as oxytocin (OT) sensitive neurons in the amygdala, likely participate in emotional processing and social behavior. In this study, we used fiber photometry to investigate the behavior of these neurons in response to social and rewarding stimuli, during emotion-triggered cataplexy, and across arousal states in an effort to define their potential role in emotion-triggered cataplexy. Initial recordings were conducted at too low an excitation light power to stimulate the green fluorescent calcium indicator, GCaMP6s, but were useful in optimizing MATLAB analysis and behavioral tests later done at higher LED power. The second series of recordings with higher excitation light power and better signal to noise ratio, showed increased activity in response to social interaction and reward, prior to REM transitions, and decreased activity during cataplexy confirming patterns seen in initial recordings. In recordings with higher excitation light, these responses appear to occur before interaction with stimulus mice or reward stimulus. In the future, additional recordings with a higher signal to noise ratio will be needed to confirm these results. In conclusion, responses of CeA-OTR neurons to social and rewarding stimuli, cataplexy, and at REM transitions are in support of a possible role of these neurons in emotion-triggered cataplexy which can be tested using additional methods, such as optogenetics.

No description available.

<p>Sensory neuron diversity is a common theme in the animal kingdom. It provides the cellular infrastructure that supports the accurate perception of the external world. Among all sensory systems, the olfactory system demonstrates an extreme in the extraordinarily diversified neuronal classes it holds. The system-wide cellular diversity is in sharp contrast with the individual specialization of olfactory receptor neurons (ORNs) per se. How the nervous system, particularly the olfactory system, uses limited genetic information to generate a huge variety of neurons with distinct properties remains elusive. </p><p>The adult Drosophila olfactory system is an excellent model to address this question due to its conserved organizational principles and reduced complexity. The fly olfactory appendages contain 50 ORN classes, each of which expresses a single receptor gene from a family of ~80 genes. Stereotyped clusters of 1-4 ORN classes define about 20 sensilla subtypes, belonging to 3 major morphological types. All cellular components within a sensillum are born by a single sensory organ precursor (SOP) via asymmetric divisions. The molecular mechanisms that determine SOP differentiation potentials to develop into distinct sensilla subtypes and the associated ORN classes are unknown.</p><p>From a genetic screen, we identified two mutant alleles in the rotund (rn) gene locus, which has a critical function in diversifying ORN classes. Rn is required in a subset of SOPs to confer novel sensilla subtype differentiation potentials from otherwise default ones within each sensilla type lineage. In rn mutants, ORNs in rn-positive sensilla subtypes are converted to lineage-specific default rn-negative fates, resulting in only half of the normal ORN diversity. This work is described in Chapter 2.</p><p>Based on an unbiased time-course transcriptome analysis, we discovered two critical downstream targets of Rn, Bric-à-brac (Bab) and Bar. In light of the knowledge about leg development, we found these genes, along with Apterous (Ap) and Dachshund (Dac), are part of the conserved proximal-distal (PD) gene network that play a crucial role in patterning the antennal precursor field prior to proneural gene-mediated SOP selection. Interactions between these PD genes under the influence of morphogen gradients separate the developing antennal disc into 7 concentric domains. Each ring is represented by a unique combination of the aforementioned transcription factors, coding the differentiation potentials for a limited number of sensilla subtypes. Genetic perturbations of the network lead to predictable changes in the ratios of different sensilla subtypes and corresponding ORN classes. In addition, using CRISPR/Cas9 technology, we were able to add tags to specific rn isoforms in the endogenous locus, and show positive regulation of Bab and negative regulation of Bar by the direct binding of Rn to the promoters in vivo. This work is presented in Chapter 3.</p><p>We proposed a three-step mechanism to explain ORN diversification, starting from pre-patterning of the precursor field by PD genes, followed by SOP selection by proneural genes, and ended with Notch-mediated neurogenesis. The final outcomes are greatly determined by the pre-patterning phase, which may be modified during evolution to compensate special olfactory needs by individual species. In our model, each step serves a single purpose, which displays context-dependent functions. By changing contexts, reassembly of the same logical steps may guide neuronal diversification in parallel systems with completely different identities. This step-wise mechanism seems to be a common strategy that is used by many other systems to generate neuronal diversity.</p> / Dissertation

Diese Dissertation befasst sich mit dem Einfluss von Resonanz und Synchronisation auf die Präzision und die Zuverlässigkeit von Rezeptorneuronen. Präzision von individuellen Neuronen an der Peripherie eines Nervensystems, beispielsweise in sensorischen Neuronen, ist äusserst wichtig für höhere Stufen der Verarbeitung. Verschiedene Formen von Resonanz können dazu führen, dass sich die Präzision eines Neurons erhöht. Hier wird neuronale Timing-Resonanz untersucht: diese kommt vor, wenn ein Neuron für Signale mit Frequenzen um seine Resonanzfrequenz - seiner Feuerrate - Aktionspotentiale (Spikes) mit höherer Präzision produziert, als für andere Frequenzen. Mit Hilfe von elektrophysiologischen Experimenten an auditorischen Rezeptorneuronen der Heuschrecke Locusta migratoria werden Spike-Antworten gewonnen, welche mit verschiedenen Zuverlässigkeitsmassen auf ihre Präzision untersucht werden. Verschiedene auditorische Stimulus-Typen und Stimulus-Parameter werden verwendet, um Kopplungsverhältnisse zwischen der Stimulusfrequenz und der Spike-Antwort und deren Einfluss auf Spike-Zeiten-Zuverlässigkeit, Phasen-Kopplung und Spike-Jitter zu untersuchen. Dabei werden durch Variation der Stimulusamplitude sogenannte Arnold-Zungen sichtbar. Der deutlichste Effekt ist für Stimulusfrequenzen in der Nähe der mittleren Feuerrate zu sehen, wo die Breite der Arnold-Zunge ansteigt, wenn die Stimulusamplitude erhöht wird und erhöhte Werte für die Zuverlässigkeitsmasse vorhanden sind. / This thesis deals with the effect of resonance and synchronisation on the precision and reliability of receptor neurons. Precision of individual neurons at the periphery of a nervous system, for example sensory neurons, is very important for later stages of processing. Different forms of resonance lead to an increase of precision in a neuron. Here, we examine neuronal timing resonance: a neuron produces action potentials (spikes) with greater precision around its resonance frequency - its firing rate - than at other frequencies. By using electrophysiological experiments on auditory receptor neurons of the locust Locusta migratoria, spike responses are generated whose precision is investigated using different reliability measures. Different types of auditory stimuli and stimulus parameters are used to examine locking of the spike response to the frequency of the stimulus, and the influence this locking has on spike time reliability, phase coupling and spike jitter. By varying the stimulus amplitude, so-called Arnold tongues become visible. The most prominent effect is seen for stimulus frequencies around the average firing rate, where the width of the Arnold tongue and the values of the reliability measures increases for increasing stimulus amplitudes.