Robert J. Butera - US grants

DESCRIPTION (provided by applicant): A major issue in neuroscience is how networks of neurons generate complex behaviors responsible for sustained health and well being;the neural control system for breathing is one such network. Evidence over the past decade suggests that the pre- Botzinger Complex (pBC), a bilaterally distributed subregion of the ventrolateral medulla, contains a region of the brainstem important for respiratory rhythm generation. The objective of this application is to develop computational models to elucidate mechanisms for rhythm generation at the level of the pBC in the transverse slice. The rationale for this particular project is that an ultimate understanding of how intrinsic and synaptic cellular properties contribute to the generation and control of respiratory rhythmogenesis is required to understand the neural control of breathing in vivo, in both physiological and pathophysiological states. Computational approaches are particularly useful for this investigation because the single cell and network dynamics are complex and difficult to analyze mechanistically by experimental approaches alone. We are particularly well prepared to undertake this proposed research, since we previously formulated minimal computational models of pBC rhythm generation, have developed and are continuing to develop more complex ion-channel based models of neurons in the transverse slice, and have an active collaborative relationship with a leading experimental laboratory in this field. The aims of this proposal are 1) Investigate multiple mechanisms for excitatory- coupling based rhythm generation that depend on both intrinsic ion channel as well as synaptic properties. 2) Development of comprehensive ion channel models of the major respiratory-related neuron types in the transverse slice, including the pBC neurons, pre- motor neurons, hypoglossal neurons, and minimal models of raphi and tonic neurons providing critical baseline modulatory input to the pBC neurons. 3) Integrate the model types from Aim 2 into a comprehensive transverse slice model that includes a complete pathway from raphi to pBC to premotor to motoneuron. Our approach is innovative in that our continuing philosophy is to pursue this approach methodically, from the bottom up, i.e. starting with the transverse. Besides the relevance to respiratory physiology, our results will also contribute in general to a growing body of knowledge on general mechanisms of stable rhythm generation from neural populations.

DESCRIPTION (provided by applicant): This is a multi-disciplinary _Bioengineering Research Grants_ (BRG) proposal in response to PA-10-009, with design-driven and discovery-driven elements. It is based on a hypothesis that is gaining in popularity, that the progression of a number of neurological disorders is rooted in homeostatic plasticity that has become maladaptive. These can be classified as de-afferentation disorders, where disruptive synchronized population bursting activity develops across days or weeks, in CNS tissue whose inputs have been greatly reduced or eliminated by white matter damage, stroke, or damage to sensory receptors or peripheral nerves. Low-frequency, high-amplitude electrical discharges from population bursting can manifest as seizures, chronic pain, dystonia, tinnitus, or other disabling symptoms, depending on which part of the nervous system has become hyper-excitable after deafferentation. Pharmacological treatments are often completely ineffective. This has lead many to propose therapies that involve direct, localized brain stimulation with implanted electrodes or transcranial magnetic stimulation. Optogenetics provides a much more localized and specific way to stimulate brain tissue, because it can render defined neural cell types sensitive to light of specific colors. Wit it, light can either activate or silence targeted neurons in an effort to normalize aberrant neural activity. Based on a successful closed-loop approach to quieting seizure-like population bursting in cultured cortical networks with multi-electrode array stimulation, this project is to develop and optimize a closed-loop optogenetic tool to gain control over homeostatic plasticity mechanisms, and to reverse the tendency of deafferented tissue to express synchronized bursting. This _Population Clamp_ will employ extracellular recording from multi-electrode array substrates as the feedback signal, to rapidly and continuously adjust pulses of colored light, selectively activating and inhibiting different neuron types, to maintain a desired activity level. Cortical networks expressing population discharges due to the deafferentation typical of in vitro preparations will be clamped to different activity set----points for days. Homeostatic responses, such as changes in synaptic strength, will be monitored with intracellular recording and extracellular measures of population activity. Combinations of optogenetic constructs, directed at excitatory pyramidal neurons or inhibitory interneurons using adeno-associated viral vectors, will be compared in terms of their ability to serve as handles by which homeostatic plasticity can be manipulated. Feedback control algorithms will be developed that enable the most effective and enduring remission of population bursting, while enhancing measures of network function, such as the mutual information between complex light input and spiking output. By providing an accessible and manipulable test bed for studying different constructs and parameters, the Optogenetic Population Clamp will pave the way for gene-therapeutic treatments of a variety of neurological disorders that employ closed-loop light stimulation via implanted fiber optics.