The coordination of reproductive events in female locusts involves the interaction between sensory cells, reflex loops, and central pattern generators. Neurochemicals have also been identified as being important for initiating and/or modulating the activities of reproductive tissues. The present thesis investigates the association of neurochemicals with the spermatheca and the neural control of the spermatheca via a central pattern generator (CPG) that is coordinated with other reproductive events. Crustacean cardioactive peptide (CCAP)-like immunoreactivity is present in the innervation to the spermatheca of adult locusts. CCAP enhances basal tonus, spontaneous and neurally-evoked contractions and may function as a neuromodulator/neurotransmitter at the locust spermatheca. No locustatachykinin (LomTK)-like immunoreactivity is present in the innervation to the spermatheca, or on the spermatheca itself, whereas allatostatin-like immunoreactivity is present. LomTK1 is a stimulator of spermathecal contractions, but allatostatin 1 does not lead to any changes in spermathecal contractions. It is likely that LomTK acts as a neurohormone on the spermatheca, while the role of allatostatin remains unknown. Tyramine-like immunoreactivity is present in the nerves that project to the spermatheca and throughout all of its regions. Quantification of tyramine revealed that there is more tyramine than octopamine present in the spermatheca, and that tyramine can be released from the spermatheca by electrical stimulation of the ventral ovipositor nerve (VON). Physiological assays reveal that both tyramine and octopamine increase spermathecal contractions. Tyramine may be a co-transmitter with octopamine at the locust spermatheca. There is likely a central pattern generator (CPG) that controls the spermathecal muscle activity, that is regulated by descending inhibition. Extracellular nerve and electromyographic recordings demonstrate that this CPG appears to be localized within the VIIth and VIIIth abdominal ganglia and is found to integrate with the CPG that regulates oviposition digging in locusts.

The coordination of reproductive events in female locusts involves the interaction between sensory cells, reflex loops, and central pattern generators. Neurochemicals have also been identified as being important for initiating and/or modulating the activities of reproductive tissues. The present thesis investigates the association of neurochemicals with the spermatheca and the neural control of the spermatheca via a central pattern generator (CPG) that is coordinated with other reproductive events. Crustacean cardioactive peptide (CCAP)-like immunoreactivity is present in the innervation to the spermatheca of adult locusts. CCAP enhances basal tonus, spontaneous and neurally-evoked contractions and may function as a neuromodulator/neurotransmitter at the locust spermatheca. No locustatachykinin (LomTK)-like immunoreactivity is present in the innervation to the spermatheca, or on the spermatheca itself, whereas allatostatin-like immunoreactivity is present. LomTK1 is a stimulator of spermathecal contractions, but allatostatin 1 does not lead to any changes in spermathecal contractions. It is likely that LomTK acts as a neurohormone on the spermatheca, while the role of allatostatin remains unknown. Tyramine-like immunoreactivity is present in the nerves that project to the spermatheca and throughout all of its regions. Quantification of tyramine revealed that there is more tyramine than octopamine present in the spermatheca, and that tyramine can be released from the spermatheca by electrical stimulation of the ventral ovipositor nerve (VON). Physiological assays reveal that both tyramine and octopamine increase spermathecal contractions. Tyramine may be a co-transmitter with octopamine at the locust spermatheca. There is likely a central pattern generator (CPG) that controls the spermathecal muscle activity, that is regulated by descending inhibition. Extracellular nerve and electromyographic recordings demonstrate that this CPG appears to be localized within the VIIth and VIIIth abdominal ganglia and is found to integrate with the CPG that regulates oviposition digging in locusts.

Swallowing is an essential motor act that coordinates the movement of food or saliva from the mouth through the pharynx and into the esophagus while protecting the upper airways from aspiration of those materials. Disordered swallowing, or dysphagia, results when bolus movement from the oropharyngeal phase into the esophageal phase is uncoordinated. Dysphagia directly causes or increases the risk of aspiration during swallowing in many clinical pathologies including Parkinson’s disease, Alzheimer’s disease, cerebrovascular incidents (stroke) in addition to being prevalent among the elderly population. The coordination between breathing and swallowing is mediated through the interaction of the swallow and respiratory Central Pattern Generators (CPGs) located in the brainstem. In the pharyngeal phase of swallow respiratory airflow is temporarily interrupted, and then reset, when the bolus moves through the pharyngeal space. The lungs retain enough air during the swallow apnea to protect the lower airways from accidental aspiration of residual bolus material, modulate the latency to initiate the swallow, while providing sensory feedback for processing within the brainstem network. The timing of the pharyngeal phase of swallow with respiration occurs across a continuum of lung volumes. Following swallow, the latency to initiate inspiration of the subsequent respiratory cycle increases. The swallow-mediated increase in cycle duration on respiration may depend upon the central processing of pulmonary afferents that may also affect reconfiguration of the respiratory CPG to express the swallow CPG. The peripheral and central mechanisms of swallow-breathing coordination remain poorly understood. Here, the relationship between central inspiratory output and the resultant mechanical inflation of the lungs was manipulated and dissociated to test the hypothesis that a centrally- and peripherally-mediated “swallow gate” coordinates swallow initiation with central respiratory activity and vagally-mediated pulmonary feedback. We obtained data from decerebrate adult cats of either sex that fully recovered from isoflurane anesthesia prior to the decerebration procedure. Fictive swallows were elicited using electrical stimulation of the superior laryngeal nerves (SLN) or injection of water (Water) into the pharyngeal cavity. Both stimuli were presented at random during the central respiratory cycle and/or the mechanical ventilation cycle. Mechanical ventilation was either triggered in-phase with phrenic discharge activity or it was set independent of phrenic discharge activity. These two modes of mechanical ventilation facilitated our ability to analyze the collective and individual effect of lower airway feedback on swallow-breathing coordination. The efferent discharge activities were recorded from the right hypoglossal (XII), left phrenic (Phr), left lumbar iliohypogastric (Lum) and right vagus (X) or the right recurrent laryngeal (RLN) nerves using silver bipolar hooked electrodes. All nerve activity was full-wave rectified, amplified, RC integrated (τ=200-500 ms) and low-pass filtered prior to analysis for effects on swallow-breathing coordination across stimulation-ventilation conditions. We observed post-inspiratory type (Post-I) and expiratory type (Exp) swallows that produced discrete effects on central respiratory rhythm across all conditions. The Post-I type swallows disturbed the duration and amplitude of preceding central inspiratory activity, without affecting the duration of central expiratory activity. The Exp type swallows prolonged central expiration but produced no effect on central inspiratory activity. We observed that lung inflation negatively modulated swallow initiation during fixed mechanical ventilation in the absence of central respiratory output, i.e., during central apnea. Most swallow elicited during central apnea initiated during periods of low lower airway afferent feedback. Collectively, these findings extend the role for lower airway feedback beyond its role as a provider of lung afferent surveillance and identifies lower airway feedback as a modulator of swallow-breathing coordination.

Movement is necessary for the survival of most animals. The spinal cord contains neuronal networks that are capable of motor coordination and of producing different movements. In particular, a very reduced neuronal network in the spinal cord can produce simple rhythmic outputs even in the absence of descending or sensory inputs. This basic circuit was discovered by Thomas Graham Brown (reported in 1911) and is termed central pattern generator. For over a century a large number of studies have been carried out in order to identify the neuronal components that are part of these networks. In project 1 we focused on Renshaw cells, which are a population of spinal interneurons expressing the alpha-2 subunit of the nicotinic acetylcholine receptors (Chrna2). Renshaw cells are the only identified central targets for motor neuron inputs, and in turn they mediate inhibition of the motor neurons. We analyzed the activity pattern of Renshaw cells on a cell-population level in neonates when the circuit is still developing. At segment 1 of the lumbar spinal cord, Renshaw cells show significantly greater activity response to functional sensory and motor inputs from rostral compared to the caudal segments. Contrarily, the suppression of the monosynaptic stretch reflex was more pronounced when caudal roots were stimulated. Our data underline the importance of sensory input during motor circuit development and help to understand the functional organization of Renshaw cell connectivity. Several neurons that play distinct roles in locomotor central pattern generation have been identified with the help of genetics. For instance, the V0 population of spinal interneurons are identified by the expression of transcription factor developing brain homeobox 1 (Dbx1). V0 neurons are necessary for producing an alternating rhythm at all locomotor speeds. In project 2 we have looked at a population of dorsally derived ventrally projecting interneurons that express the transcription factor doublesex and mab-3 related transcription factor 3 (Dmrt3). On a behavioral level Dmrt3 neurons are involved in regulating coordination across different locomotor speeds. On a microcircuit level, we have shown that individual Dmrt3 neurons show distinct frequencies of oscillations for a constant locomotor rhythm. In addition, removal of inhibitory neurotransmission from Dmrt3 neurons results in uncoupling of rhythm in motor neurons. In project 3 the activity patterns in populations of flexor related motor neurons are characterized during fictive locomotion in neonatal mice. An interesting and intriguing finding in project 3 is the presence of multiple rhythmicities in motor neurons. Multiple rhythmicities are seen even when the locomotor output shows a constant frequency.

Networks of neurons, which form central pattern generators (CPGs), are important for controlling animal behaviors. Of special interest are configurations or CPG motifs composed of reciprocally inhibited neurons, such as half-center oscillators (HCOs). Bursting rhythms of HCOs are shown to include stable synchrony or in-phase bursting. This in-phase bursting can co-exist with anti-phase bursting, commonly expected as the single stable state in HCOs that are connected with fast non-delayed synapses. The finding contrasts with the classical view that reciprocal inhibition has to be slow or time-delayed to synchronize such bursting neurons. Phase-locked rhythms are analyzed via Lyapunov exponents estimated with variational equations, and through the convergence rates estimated with Poincar\'e return maps. A new mechanism underlying multistability is proposed that is based on the spike interactions, which confer a dual property on the fast non-delayed reciprocal inhibition; this reveals the role of spikes in generating multiple co-existing phase-locked rhythms. In particular, it demonstrates that the number and temporal characteristics of spikes determine the number and stability of the multiple phase-locked states in weakly coupled HCOs. The generality of the multistability phenomenon is demonstrated by analyzing diverse models of bursting networks with various inhibitory synapses; the individual cell models include the reduced leech heart interneuron, the Sherman model for pancreatic beta cells, the Purkinje neuron model and Fitzhugh-Rinzel phenomenological model. Finally, hypothetical and experiment-based CPGs composed of HCOs are investigated. This study is relevant for various applications that use CPGs such as robotics, prosthetics, and artificial intelligence.

A natureza é uma fonte inesgotável de soluções elegantes para os mais diversos problemas, da aparente simplicidade do formato do ovo, que garante maior segurança ao organismo em desenvolvimento, à evidente complexidade do sistema nervoso humano, que é capaz de pensar sobre problemas e encontrar soluções para eles. Neste trabalho foram aplicados modelos computacionais inspirados em estudos neurológicos para a realização da locomoção de um robô quadrúpede. O corpo do robô foi simulado, permitindo incorporar características mais semelhantes às de um animal do que seria possível com um robô de verdade, como grande quantidade de articulações e força dos motores. A arquitetura neural responsável pelo controle do robô teve como referência para seu desenvolvimento os Geradores Centrais de Padrões, que são circuitos neurais capazes de gerar a seqüência de ativações musculares envolvidas em diversos movimentos rítmicos, como respirar e caminhar, e estão em sua maioria localizados na medula espinhal. Para compor esta rede foi usado um modelo de neurônio com algumas propriedades encontradas em um neurônio real, como a capacidade de inibir a ativação de outros neurônios, e outras puramente matemáticas, tornando-o uma ferramenta versátil para incorporar a funcionalidade de outros modelos de neurônios e de redes neurais. Trabalhos futuros farão uso dos resultados desta pesquisa como base para abordar temas mais complexos, como planejamento motor e tomada de decisão. / Nature is an endless source of elegant solutions to every kind of problem, from the seeming simplicity of the egg’s shape, which assures a safer environment to the developing organism, to the evident complexity of the human nervous system, which is capable of thinking about problems and finding solutions to them. In this work some computational models inspired on neurological research were applied to achieve the locomotion of a quadruped robot. The robot’s body was simulated, allowing to have features more similar to their animal counterparts than would be possible using a real robot, such as the high amount of articulations and the motors’ strength. The neural architecture responsible for the robot’s control was developed using Central Pattern Generators as reference, which are neural circuits capable of generating the sequence of muscle activations involved in a variety of rhythmic movements, such as breathing and walking, and are mostly located in the spine. To assemble this network a neuron model was used which has some properties found on a real neuron, as the ability to inhibit other neurons’ activation, and others purely mathematical, making it a versatile tool to incorporate the functionality of other neuron and neural networks models. Future works will make use of these research’s results as a base to approach more complex problems, such as motor planning and decision making.

A natureza é uma fonte inesgotável de soluções elegantes para os mais diversos problemas, da aparente simplicidade do formato do ovo, que garante maior segurança ao organismo em desenvolvimento, à evidente complexidade do sistema nervoso humano, que é capaz de pensar sobre problemas e encontrar soluções para eles. Neste trabalho foram aplicados modelos computacionais inspirados em estudos neurológicos para a realização da locomoção de um robô quadrúpede. O corpo do robô foi simulado, permitindo incorporar características mais semelhantes às de um animal do que seria possível com um robô de verdade, como grande quantidade de articulações e força dos motores. A arquitetura neural responsável pelo controle do robô teve como referência para seu desenvolvimento os Geradores Centrais de Padrões, que são circuitos neurais capazes de gerar a seqüência de ativações musculares envolvidas em diversos movimentos rítmicos, como respirar e caminhar, e estão em sua maioria localizados na medula espinhal. Para compor esta rede foi usado um modelo de neurônio com algumas propriedades encontradas em um neurônio real, como a capacidade de inibir a ativação de outros neurônios, e outras puramente matemáticas, tornando-o uma ferramenta versátil para incorporar a funcionalidade de outros modelos de neurônios e de redes neurais. Trabalhos futuros farão uso dos resultados desta pesquisa como base para abordar temas mais complexos, como planejamento motor e tomada de decisão. / Nature is an endless source of elegant solutions to every kind of problem, from the seeming simplicity of the egg’s shape, which assures a safer environment to the developing organism, to the evident complexity of the human nervous system, which is capable of thinking about problems and finding solutions to them. In this work some computational models inspired on neurological research were applied to achieve the locomotion of a quadruped robot. The robot’s body was simulated, allowing to have features more similar to their animal counterparts than would be possible using a real robot, such as the high amount of articulations and the motors’ strength. The neural architecture responsible for the robot’s control was developed using Central Pattern Generators as reference, which are neural circuits capable of generating the sequence of muscle activations involved in a variety of rhythmic movements, such as breathing and walking, and are mostly located in the spine. To assemble this network a neuron model was used which has some properties found on a real neuron, as the ability to inhibit other neurons’ activation, and others purely mathematical, making it a versatile tool to incorporate the functionality of other neuron and neural networks models. Future works will make use of these research’s results as a base to approach more complex problems, such as motor planning and decision making.

A natureza é uma fonte inesgotável de soluções elegantes para os mais diversos problemas, da aparente simplicidade do formato do ovo, que garante maior segurança ao organismo em desenvolvimento, à evidente complexidade do sistema nervoso humano, que é capaz de pensar sobre problemas e encontrar soluções para eles. Neste trabalho foram aplicados modelos computacionais inspirados em estudos neurológicos para a realização da locomoção de um robô quadrúpede. O corpo do robô foi simulado, permitindo incorporar características mais semelhantes às de um animal do que seria possível com um robô de verdade, como grande quantidade de articulações e força dos motores. A arquitetura neural responsável pelo controle do robô teve como referência para seu desenvolvimento os Geradores Centrais de Padrões, que são circuitos neurais capazes de gerar a seqüência de ativações musculares envolvidas em diversos movimentos rítmicos, como respirar e caminhar, e estão em sua maioria localizados na medula espinhal. Para compor esta rede foi usado um modelo de neurônio com algumas propriedades encontradas em um neurônio real, como a capacidade de inibir a ativação de outros neurônios, e outras puramente matemáticas, tornando-o uma ferramenta versátil para incorporar a funcionalidade de outros modelos de neurônios e de redes neurais. Trabalhos futuros farão uso dos resultados desta pesquisa como base para abordar temas mais complexos, como planejamento motor e tomada de decisão. / Nature is an endless source of elegant solutions to every kind of problem, from the seeming simplicity of the egg’s shape, which assures a safer environment to the developing organism, to the evident complexity of the human nervous system, which is capable of thinking about problems and finding solutions to them. In this work some computational models inspired on neurological research were applied to achieve the locomotion of a quadruped robot. The robot’s body was simulated, allowing to have features more similar to their animal counterparts than would be possible using a real robot, such as the high amount of articulations and the motors’ strength. The neural architecture responsible for the robot’s control was developed using Central Pattern Generators as reference, which are neural circuits capable of generating the sequence of muscle activations involved in a variety of rhythmic movements, such as breathing and walking, and are mostly located in the spine. To assemble this network a neuron model was used which has some properties found on a real neuron, as the ability to inhibit other neurons’ activation, and others purely mathematical, making it a versatile tool to incorporate the functionality of other neuron and neural networks models. Future works will make use of these research’s results as a base to approach more complex problems, such as motor planning and decision making.

Contusion spinal cord injury (SCI) results in devastating life-long debilitation in which there are currently no effective treatments. The primary injury site presents a complex environment marked by subsequent secondary pathophysiological cascades involving excessive reactive oxygen and nitrogen species (ROS/RNS) production, glutamate-induced excitotoxicity, calcium dysregulation, and delayed neuronal apoptosis. Many of these cascades involve mitochondrial dysfunction, thus a single mitochondrial-centric therapy that targets a variety of these factors could be far reaching in its potential benefits after SCI. As such, this dissertation examines whether transplantation of exogenous mitochondria after SCI can attenuate secondary injury cascades to decrease the spread and severity of the injury. Our first experiment tested the dose-dependent effects of mitochondrial transplantation on the ability to maintain acute overall bioenergetics after SCI. We compared transplantation of mitochondria originating from two different sources-cultured PC12 cells or rat soleus leg muscle. 24 hours after injury, State III oxygen consumption rates were maintained to over 80% of sham levels when 100ug of mitochondria was transplanted, regardless of the origin of the mitochondria. Complex I enzyme activity assays corroborated our findings that the 100ug dosage gave optimal benefits compared to vehicle injection. We also analyzed the rostral-caudal distribution and cell-type colocalization of transplanted transgenically-labeled tGFP mitochondria after SCI. There were greater volumes and rostral-caudal spread of tGFP mitochondria at the 24 hour time point compared to 7 days post injection. tGFP mitochondria had the greatest propensity to colocalize with macrophages and pericytes. Colocalization was evident in endothelial cells, oligodendrocytes and astrocytes, though no such colabeling was present in neurons. Further, colocalization of tGFP was always greater at the 24 hour time compared to 48 hour or 7days post injection time points. These data indicate that there is a cell-type difference in incorporation potential of exogenous mitochondria which changes over time. Finally, we tested the effects of mitochondrial transplantation on long term functional recovery. Animals were injected with either vehicle, 100ug cell-derived mitochondria, or 100ug muscle-derived mitochondria immediately after contusion SCI. Functional analyses including BBB overground locomotor scale and von Frey mechanical sensitivity tests did not show any differences between treatment groups. Likewise, there were no differences in tissue sparing when mitochondria were transplanted compared to vehicle injections, though there were higher neuronal cell counts in tGFP mitochondria injected groups caudal of the injury site. These studies present the potential of mitochondrial transplantation for therapeutic intervention after SCI. While our acute measures do not correspond into long term recovery, we show that at 24 hours transplanted mitochondria do have an effect on bioenergetics and that they are taken into host cells. We believe that further investigation into caveats and technical refinement is necessary at this time to translate the evident acute bioenergetic recovery into long term functional recovery.

No description available.