Ontogenetic niche shifts generally coincide with changes in size, morphology, behavior, and/or feeding preferences during development, resulting in a shift in preferred habitat. In aquatic species, these ontogenetic niche shifts are often associated with habitat-dependent changes in competition and/or predation dynamics, expressed as a size-depth relationship where the larger-bodied adults occupy deeper habitats while the smaller-bodied juveniles primarily reside in shallower regions. While the influence of interspecific interactions on size-structured habitat occupancy has been well studied, few have examined the potential role of intraspecific agonistic interactions between size classes in ontogenetic niche shifts. A simulation model was developed to test whether the size-specific habitat occupancy observed in signal crayfish can be explained by the size-structured individual responses to agonistic interaction, where the smaller-bodied juvenile responds to the interaction with an escape movement, to avoid engagement and the risk of mortality or injury from the adult. The simulated movements of signal crayfish resulted in higher juvenile occupancy of riffles relative to pools reflecting a greater rate of escape from adults into riffles, away from the higher densities of adults in their preferred habitat (i.e. pools). This provides evidence that the juvenile escape response to size-structured, intraspecific, agonistic interactions may contribute to ontogenetic niche shifts.

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O desequilíbrio da homeostase emocional tem sido considerado como um mecanismo subjacente aos transtornos de ansiedade e humor. Em fêmeas, as alterações na secreção hormonal durante as diferentes fases do ciclo estral podem ser a base das alterações na reatividade emocional a eventos estressantes. Estudos comportamentais sobre diferenças sexuais no processamento das emoções mostram resultados conflitantes em fêmeas devido às dificuldades na seleção dos melhores modelos animais para testar as diferenças associadas ao ciclo estral. Uma vez que os testes comportamentais foram desenvolvidos em animais do sexo masculino, eles podem não ser apropriados para fêmeas. O presente estudo foi desenvolvido para contribuir nessa linha de pesquisa usando diferentes modelos de animais de medo incondicionado e condicionado, considerando as diferentes fases do ciclo estral das ratas. Comparou-se o desempenho de machos e fêmeas nas quatro fases do ciclo estral em dois testes de medo incondicionado: o switch-off, em que ratos cruzam uma caixa vai-e-vem para desligar uma luz aversiva, e o registro de vocalizações ultrassônicas (VUSs) a 22 kHz emitidos por animais sob o estresse agudo de restrição. Nos testes de medo condicionado, registrou-se o sobressalto potencializado pelo medo e a resposta decongelamento a um contexto aversivo. Em ambos os testes de medo condicionado, a reatividade emocional não se mostrou diferente entre os sexos. No entanto, no que diz respeito ao medo incondicionado, ratas em diestro tardio apresentaram maior reatividade emocional em desligar a luz intensa e maior emissão de VUSs em resposta à restrição em relação a outras fases do ciclo. Estes achados sugerem que o perfil hormonal durante a fase do diestro 2 pode aumentar a reatividade emocional de ratas frente a estímulos inatos, porém não àqueles aprendidos. / Dysfunctional emotional regulation has been implicated as a potential mechanism underlying anxiety and mood disorders. Changes in hormonal secretion during the different phases of the estrous cycle may underlie changes in emotional reactivity to stressful events in female animals. Previous behavioral studies of sex differences in emotion processing in females have yielded conflicting results. This may be due to the range of different behavioral tests used and difficulties in selecting the best animal models to test for estrous cycle-linked differences in responsiveness. Furthermore, the commonly used behavioral tests were developed in male animals and it may not be appropriate to translate directly the protocols from males to females. In the present study we have attempted to address these problems by using different animal models of anxiety based on tests for unconditioned or conditioned fear. We compared the performance of male rats and female rats at four stages of the estrous cycle defined by differences in vaginal cytology. To test for unconditioned fear, we used two tests: a light switch- off test, in which rats escape to the other compartment of a shuttle-box to turn off an aversive light and recordings of 22 kHz ultrasound vocalizations (USVs) during acute restraint stress. For the conditioned fear paradigm, we used fear potentiated startle in an aversive context and conditioned freezing using an aversive context as the conditioned stimulus. In both tests of conditioned fear there were no gender or estrous cycle-linked differences in emotional reactivity. However, with respect to unconditioned fear, female rats in late diestrus showed greater emotional reactivity expressed as switch-off responses to a light environment and USVs in response to restraint compared to other phases of the cycle. These findings suggest that the hormonal profile during the late diestrous phase may predispose to up-regulated emotional reactivity in rats facing emotional challenges to unconditioned, but not conditioned fear- inducing stimuli.

O desequilíbrio da homeostase emocional tem sido considerado como um mecanismo subjacente aos transtornos de ansiedade e humor. Em fêmeas, as alterações na secreção hormonal durante as diferentes fases do ciclo estral podem ser a base das alterações na reatividade emocional a eventos estressantes. Estudos comportamentais sobre diferenças sexuais no processamento das emoções mostram resultados conflitantes em fêmeas devido às dificuldades na seleção dos melhores modelos animais para testar as diferenças associadas ao ciclo estral. Uma vez que os testes comportamentais foram desenvolvidos em animais do sexo masculino, eles podem não ser apropriados para fêmeas. O presente estudo foi desenvolvido para contribuir nessa linha de pesquisa usando diferentes modelos de animais de medo incondicionado e condicionado, considerando as diferentes fases do ciclo estral das ratas. Comparou-se o desempenho de machos e fêmeas nas quatro fases do ciclo estral em dois testes de medo incondicionado: o switch-off, em que ratos cruzam uma caixa vai-e-vem para desligar uma luz aversiva, e o registro de vocalizações ultrassônicas (VUSs) a 22 kHz emitidos por animais sob o estresse agudo de restrição. Nos testes de medo condicionado, registrou-se o sobressalto potencializado pelo medo e a resposta decongelamento a um contexto aversivo. Em ambos os testes de medo condicionado, a reatividade emocional não se mostrou diferente entre os sexos. No entanto, no que diz respeito ao medo incondicionado, ratas em diestro tardio apresentaram maior reatividade emocional em desligar a luz intensa e maior emissão de VUSs em resposta à restrição em relação a outras fases do ciclo. Estes achados sugerem que o perfil hormonal durante a fase do diestro 2 pode aumentar a reatividade emocional de ratas frente a estímulos inatos, porém não àqueles aprendidos. / Dysfunctional emotional regulation has been implicated as a potential mechanism underlying anxiety and mood disorders. Changes in hormonal secretion during the different phases of the estrous cycle may underlie changes in emotional reactivity to stressful events in female animals. Previous behavioral studies of sex differences in emotion processing in females have yielded conflicting results. This may be due to the range of different behavioral tests used and difficulties in selecting the best animal models to test for estrous cycle-linked differences in responsiveness. Furthermore, the commonly used behavioral tests were developed in male animals and it may not be appropriate to translate directly the protocols from males to females. In the present study we have attempted to address these problems by using different animal models of anxiety based on tests for unconditioned or conditioned fear. We compared the performance of male rats and female rats at four stages of the estrous cycle defined by differences in vaginal cytology. To test for unconditioned fear, we used two tests: a light switch- off test, in which rats escape to the other compartment of a shuttle-box to turn off an aversive light and recordings of 22 kHz ultrasound vocalizations (USVs) during acute restraint stress. For the conditioned fear paradigm, we used fear potentiated startle in an aversive context and conditioned freezing using an aversive context as the conditioned stimulus. In both tests of conditioned fear there were no gender or estrous cycle-linked differences in emotional reactivity. However, with respect to unconditioned fear, female rats in late diestrus showed greater emotional reactivity expressed as switch-off responses to a light environment and USVs in response to restraint compared to other phases of the cycle. These findings suggest that the hormonal profile during the late diestrous phase may predispose to up-regulated emotional reactivity in rats facing emotional challenges to unconditioned, but not conditioned fear- inducing stimuli.

京都大学 / 新制・課程博士 / 博士(生命科学) / 甲第24943号 / 生博第505号 / 新制||生||67(附属図書館) / 京都大学大学院生命科学研究科統合生命科学専攻 / (主査)教授 上村 匡, 教授 今吉 格, 教授 鈴木 淳 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

Despite the current understanding that sensorimotor circuits function through the action of transmitters and modulators, we have a limited understanding of how the nervous system directs the flow of information necessary to orchestrate complex behaviors. In this dissertation, I aimed to uncover how the nervous system coordinates these behaviors using the escape response of the soil nematode, Caenorhabditis elegans, as a paradigm. C. elegans exhibits a robust escape behavior in response to touch. The worm typically moves forward in a sinusoidal pattern, which is accompanied by exploratory head movements. During escape, the worm quickly retreats by moving backward from the point of stimulus while suppressing its head movements. It was previously shown that the biogenic amine tyramine played an important role in modulating the suppression of these head movmemetns in response to touch. We identified a novel tyramine-gated chloride channel, LGC-55, whose activation by tyramine coordinates motor programs essential for escape. Furthermore, we found that changing the electrical nature of a synapse within the neural circuit for escape behavior can reverse its behavioral output, indicating that the C. elegans connectome is established independent of the nature of synaptic activity or behavioral output. Finally, we characterized a unique mutant, zf35 , which is hyperactive in reversal behavior. This mutant was identified as a gain of function allele of the C. elegans P/Q/N-type voltage-gated calcium channel, UNC-2. Taken together, this work defines tyramine as a genuine neurotransmitter and completes the neural circuit that controls the initial phases of the C. elegans escape response. Additionally, this research further advances the understanding of how the interactions between transmitters and ion channels can precisely regulate neural circuit activity in the execution of a complex behavior.