Rapid and efficient escape behaviors in response to noxious sensory stimuli are essential for protection and survival. In Drosophila larvae, the class III (cIII) and class IV (cIV) dendritic arborization (da) neurons detect low-threshold mechanosensory and noxious stimuli, respectively. Their axons project to modality-specific locations in the neuropil, reminiscent of vertebrate dorsal horn organization. Despite extensive characterization of nociceptors across organisms, how noxious stimuli are transformed to the coordinated behaviors that protect animals from harm remains poorly understood. In larvae, noxious mechanical and thermal stimuli trigger an escape behavior consisting of sequential C-shape body bending followed by corkscrew-like rolling, and finally an increase in forward locomotion (escape crawl). The downstream circuitry controlling the sequential coordination of escape responses is largely unknown. This work identifies a population of interneurons in the nerve cord, Down-and-Back (DnB) neurons, that are activated by noxious heat, promote nociceptive behavior, and are required for robust escape responses to noxious stimuli. Activation of DnB neurons can trigger both rolling, and the initial C-shape body bend independent of rolling, revealing modularity in the initial nociceptive responses. Electron microscopic circuit reconstruction shows that DnBs receive direct input from nociceptive and mechanosensory neurons, are presynaptic to pre-motor circuits, and link indirectly to a population of command-like neurons (Goro) that control rolling. DnB activation promotes activity in Goro neurons, and coincident inactivation of Goro neurons prevents the rolling sequence but leaves intact body bending motor responses. Thus, activity from nociceptors to DnB interneurons coordinates modular elements of nociceptive escape behavior. The impact of DnB neurons may not be restricted to synaptic partners, as DnB presynaptic sites accumulate dense-core vesicles, suggesting aminergic or peptidergic signaling. Anatomical analyses show that DnB neurons receive spatially segregated input from cIII mechanosensory and cIV nociceptive neurons. However, DnB neurons do not seem to promote or be required for gentle-touch responses, suggesting a modulatory role for cIII input. Behavioral experiments suggest that cIII input presented prior to cIV input can enhance nociceptive behavior. Moreover, weak co-activation of DnB and cIII neurons can also enhance nociceptive responses, particularly C-shape bending. These results indicate that timing and level of cIII activation might determine its modulatory role. Taken together, these studies describe a novel nociceptive circuit, which integrates nociceptive and mechanosensory inputs, and controls modular motor pathways to promote robust escape behavior. Future work on this circuit could reveal neural mechanisms for sequence transitions, peptidergic modulation of nociception, and developmental mechanisms that control convergence of sensory afferents onto common synaptic partners.

The physical architecture of neural circuits is thought to underlie the computations that give rise to higher order feature sensitivity in the neocortex. Recent technological breakthroughs have allowed the structural and functional investigation of the basic computational units of neural circuits; individual synaptic connections. However, it remains unclear how cortical neurons sample and integrate the thousands of synaptic inputs, supplied by different brain structures, to achieve feature selectivity. Here, I first describe how visual cortical circuits transform the elementary inputs supplied by the periphery into highly diverse, but well-organized, feature representations. By combining and optimizing newly developed techniques to map the functional synaptic connections with defined sources of inputs, I show that the intersection between columnar architecture and dendritic sampling strategies can lead to the selectivity properties of individual neurons: First, in the canonical feedforward circuit, the basal dendrites of a pyramidal neuron utilize unique strategies to sample ON (light increment) and OFF (light decrement) inputs in orientation columns to create the distinctive receptive field structure that is responsible for basic sensitivity to visual spatial location, orientation, spatial frequency, and phase. Second, for long-range horizontal connections, apical dendrites unbiasedly integrate functionally specialized and spatially targeted inputs in different orientation columns, which generates specific axial surround modulation of the receptive field. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Artificial neural networks are computational paradigms which are inspired by biological neural networks (the human brain). Recurrent neural networks (RNNs) are characterized by neuron connections which include feedback paths. This dissertation uses the dynamics of RNN architectures for solving linear and certain nonlinear equations. Neural network with linear dynamics (variants of the well-known Hopfield network) are used to solve systems of linear equations, where the network structure is adapted to match properties of the linear system in question. Nonlinear equations inturn are solved using the dynamics of nonlinear RNNs, which are based on feedforward multilayer perceptrons. Neural networks are well-suited for implementation on special parallel hardware, due to their intrinsic parallelism. The RNNs developed here are implemented on a neural network processor (NNP) designed specifically for fast neural type processing, and are applied to the inverse kinematics problem in robotics, demonstrating their superior performance over alternative approaches.

Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 03/03/2010). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

Many recent studies on the segmental motor control system have employed spike-triggered-averaging (STA) and other forms of cross-correlation to either attribute CNS, reflex, or direct motor effects to the impulses of a single (reference) neuronal spike train or to explore conditions under which pairs of neural units show temporal correlations in their discharge. Our experience with these techniques suggested the need for a control procedure that tests for synchrony between the reference and other spike trains such as to: (1) either preclude that the observed effects are due to spike trains other than or in addition to the reference train; or (2) give insight into the conditions leading to correlated discharge between two units. A motor unit synchronization test based on analysis of EMG waveforms has already been described. We have modified this test for the detection of synchrony between either afferent or efferent signals by analysis of averaged muscle nerve signals rather than EMG waveforms. Our procedure involves use of a multi-unit muscle nerve recording that serves as the input to a signal averager triggered by a spike train from either: (1) a motor unit's EMG; (2) a dorsal root filament or ganglion cell; or (3) a ramdom trigger source. With appropriate delay of the muscle nerve signal input, the non-rectified average of the trigger signal's waveform is compared to the rectified average which contains this waveform together with contributions of all other active unitary events. Additionally, the rectified average is compared to a "randomly" triggered average of the same input signal. On the basis of these recordings, it can be determined, within certain boundary conditions, whether or not any other unitary events are in synchrony with the reference event. Such synchronization is expressed quantitatively in the form of a synchronization index (SI). We evaluated the efficacy of the SI by electronic simulation procedures and by comparing its use to that of a cross-correlation procedure that tests for synchrony on the basis of crosscorrelograms computed between two simultaneously recorded spindle afferent spike trains during brief stretch of a passive muscle at progressively increasing amplitudes (5 - 100um). These experiments revealed that the SI is a sensitive test of afferent synchrony in the passive muscle provided the spike trains of interest have a signal-to-noise (S/N) ratio > 0.2 in the muscle nerve recording and that it is recognized that the detectable degree of synchronization of a non-reference event is a function of its S/N ratio. For tests on the active muscle, the force levels must remain low. Otherwise increased neuronal activity in the muscle nerve recording decreases the S/N ratio of individual spike trains. Thus, despite restrictive (but predictable) boundary conditions, the SI test can contribute importantly to select conclusions drawn from cross-correlation studies.

No description available.

Hemoglobin, the oxygen-carrying component of red blood cells, is known as a nitric oxide (NO) chelating agent. For this reason, hemoglobin has been used widely in studying the role of nitric oxide in long-term potentiation (LTP) and excitotoxicity. However, the direct electrophysiological actions of hemoglobin has not been examined. In this investigation, the actions of hemoglobin on rat hippocampal CAl neurons were studied since hemoglobin may be present in hemorrhagic stroke and other head injuries. Superfusion of rat hippocampal slices with 0.1 mM of bovine hemoglobin for 15 minutes was induced a significant depolarization associated with an increase in the input resistance. In addition, hemoglobin suppressed the evoked synaptic responses and increased the depolarization-induced discharge of action potentials, of rat hippocampal CAl neurons. These hemoglobin-mediated changes usually recovered partially 30 minutes after the removal of hemoglobin. While the depolarizing action of hemoglobin was enhanced in a calcium-free medium, it was not significantly changed by 2-amino-5-phosphonovalerate (APV) and 6- cyano-7-nitroquinoxaline-2,3-dione (CNQX). These observations suggest that the depolarizing action of hemoglobin is independent of the presence of extracellular calcium and activations of the excitatory amino acid receptors. Because hemoglobin has been observed to suppress the depolarizing action of glutamate, it is possible that hemoglobin suppresses the EPSP by interfering with the actions of glutamate. Although hemoglobin has been suggested to suppress LTP and excitability by scavenging nitric oxide (Garthwaite et al., 1988; Haley et al., 1992; 0’ Dell et al., 1991; Schuman and Madison, 1991), the reported actions of hemoglobin were not removed by pre-treatment with 100 pM or 500 pM of No-nitro-L-arginine, a nitric oxide synthase inhibitor. Similar to the scavenging property of hemoglobin, the iron content of hemoglobin probably did not contribute to the actions of hemoglobin since 0.4 mM or 2.0 mM of ferric chloride did not simulate the effects of hemoglobin. Because neurons can be exposed to hemoglobin in hemorrhagic stroke and head injuries, the electrophysiological actions of hemoglobin on rat hippocampal CAl neurons may be relevant to the neurological complications associated with intracranial hemorrhage and head injuries. Further studies on mechanisms of the electrophysiological actions of hemoglobin are necessary for understanding the role of hemoglobin in neuronal damages associated with hemorrhagic stroke and other head injuries.

No description available.

5-HT powerfully affects gastrointestinal function. However, the study of these effects is complicated because 5-HT from both mucosa and a subset of enteric neurons acts on multiple receptor subtypes in enteric tissues. The role of neural 5-HT has been difficult to isolate with current techniques. This thesis aimed to elucidate the role of 5-HT neurons in motility using anatomical and functional methods. In Chapter 2, confocal microscopy was used to examine over 95% of myenteric neurons in guinea pig jejunum, categorized neurochemically, to identify neurons that received anatomically-defined input from 5-HT interneurons. The data showed that cholinergic secretomotor neurons were strongly targeted by 5-HT interneurons. In another key finding, excitatory motor neurons were surrounded by 5-HT terminals; this could provide an anatomical substrate for the descending excitation reflex. Subgroups of ascending interneurons and neurons with immunoreactivity for NOS, were also targeted by 5-HT interneurons. Thus, subtypes of these neurons might act in separate reflex pathways. Despite strong physiological evidence for 5-HT inputs to AH/Dogiel type II neurons, few contacts were identified. In Chapter 3, the confocal microscopy survey was extended to the three other interneuron classes (VIP/NOS and SOM descending interneurons; calretinin ascending interneurons) of guinea pig small intestine. A high degree of convergence between the otherwise polarized ascending and descending interneuron pathways was identified.

Thesis (M.S.)--Oregon Graduate Center, 1988.