Carey D. Balaban, Ph.D. - US grants

DESCRIPTION (provided by applicant): The proposed neuroanatomical and electrophysiological studies continue investigations of the organization of pathways that mediate vestibular influences on autonomic and limbic pathways, particularly in pathways that mediate the linkage between balance disorders and anxiety disorders. Three circuitry networks appear to be critical for balance-anxiety link: a vestibulo-parabrachial nucleus (PBN) network, coeruleo-vestibular (noraderenergic) network and raphe-vestibular (serotonergic and non-serotonergic) networks. The physiology and connections of the PBN network will be studied in primates; the organization of the noradrenergic and raphe pathways will be explored in rats. Our on-going primate studies have shown that a caudal region of PBN contains neurons that receive vestibular nuclear input and are sensitive to whole body rotation. New electrophysiologic studies in alert primates are directed at elucidating the spatial organization of responses of parabrachial nucleus neurons during whole body rotation. Two main foci will be characterization of otolith-related responses and a test of the hypothesis that responses will differ for predictable and unpredictable whole body rotation in three dimensions. Anatomical studies in primates are also designed elucidate the afferent and efferent connections of this vestibulo-recipient region of PBN. Our on-going studies have shown that the dorsal raphe nucleus, nucleus raphe obscurus and nucleus raphe pallidus provide serotonergic input to the vestibular nuclei. Anatomical studies will elucidate the topography of these projections, the distribution of immunoreactive serotonin receptors in the vestibular nuclei and test specific hypotheses regarding the organization of collateralized raphe projections to the vestibular nuclei and other sites. Finally, anatomical studies in rats will test specific hypotheses regarding the organization of collateralized noradrenergic projections to the vestibular nuclei and other sites.

Abrupt dysfunction of one vestibular labyrinth or nerve produces a syndrome that includes acute vertigo, postural asymmetry and instability, nystagmus and autonomic manifestations. These signs resolve over a period of days to weeks, in a process that has been termed vestibular compensation. Although previous studies implicate a variety of neurotransmitter mechanisms in the compensatory process, the intracellular events that produce vestibular compensation remain obscure. The proposed studies are based upon initial results indicating that the expression of a particular class of intracellular signal, protein kinase C (PKC), changes in a regionally specific manner in the vestibular nuclei and flocculonodular lobe within 6 hours of unilateral labyrinthectomy. The proposed experiments will extend these findings by a detailed examination of the regional expression of enzymes involved with intracellular signalling substrates (protein kinase C (PKC), phospholipase C (PLC; inositol lipid system) and phospholipase A2 )PLA2: arachidonic acid path) in the cerebellar cortex, vestibular nuclei and inferior olive during the early stages of vestibular compensation in rats (6 hours-8 days). These studies will provide insights into early intracellular signalling events during vestibular compensation and the anatomical distribution of neurons involved in these compensatory responses. The first experiment will use immunohistochemistry, Western blots, enzyme activity assays and Northern blots to test the hypothesis that vestibular compensation is accompanied by regionally specific changes in expression of six PKC isoforms, PLA2 and PLC by inferior olive neurons, vestibular nucleus neurons and Purkinje cells in the cerebellar flocculo-nodular lobe, paramedian lobule and vermal regions of the posterior and anterior lobes. The second experiment will test the hypothesis that an intact climbing fiber pathway is essential for producing regionally specific changes in Purkinje cell PKCs, PLC and PLA2 expression after unilateral labyrinthectomy. These studies will test the prediction that destruction of the inferior olive with 3-actylpyridine or neuropeptide transmitter ablation with antisense oligonucleotide injections in the inferior olive will retard compensation and will block regionally specific changes in expression of PKC isoforms, PLA2 and PLC.

The Core consists of a 300 sq. ft. laboratory and a small dark room. Both facilities are located at the Eye and Ear Institute building where the investigators have their offices and laboratories. The Core facility will be staffed by a certified histotechnician, for whom funding is being sought.

DESCRIPTION (provided by applicant): Vomiting is a consequence of a stereotyped pattern of co-contractions of the diaphragm and abdominal muscles that generate high intragastric pressures. The goal of this application is to decipher the processing of vestibular inputs by the medullary circuitry that produces vomiting, and to determine how this signal processing is affected by other inputs that can elicit emesis. Specific Aim 1 will map the locations of neurons activated during vomiting and accompanying nausea elicited by stimulation of vestibular receptors and compare the sites to those activated during emesis triggered by gastrointestinal (GI) inputs. Specific Aim 2 will employ inactivation of subregions of the vestibular nuclei (VN) to identify the area that is essential for producing vestibular-elicited vomiting. Once the brainstem regions containing neurons that participate in generating vomiting are established, subsequent experiments will ascertain the responses of cells in these areas to natural vestibular stimulation added to activation of GI receptors. Specific Aim 3 will consider neuronal responses in nucleus tractus solitarius (NTS) and the VN, which respectively receive GI and labyrinthine inputs from the periphery that can induce emesis and nausea. Specific Aim 4A will determine the responses of neurons in a region that is a component of the vomiting pattern generator: the dorsal medullary lateral tegmental field (LTF) positioned between NTS and the retrofacial nucleus. Specific Aim 4B will consider the processing of signals by PBN, which is involved in transmitting viscerosensory signals to the forebrain, to provide insights into how integration of vestibular and visceral inputs together differs in this region critical for generating nausea and medullary elements that produce vomiting. At the conclusion of Aim 4 we will have thoroughly sampled the responses of neurons to labyrinthine stimulation in the major brainstem areas known to participate in triggering and coordinating vomiting and accompanying affective responses. We will also systematically determine how vestibular signals are transformed in the emetic circuit as they are relayed from the VN to NTS and finally to LTF and the PBN. Furthermore, we will ascertain how the presence of other emetic signals affects the processing of labyrinthine inputs, and whether this processing is profoundly altered immediately before or after an episode of vomiting. As such, the studies will provide insights into the signal integration responsible for the generation of motion sickness.

The goal of this project is to investigate the effects of blast-induced traumatic brain injury (bTBI) using advanced finite element (FE) modeling techniques. This study will focus on the posterior fossa region of the brain (brainstem, cerebellum, great vein of Galen and other vasculature). Previous studies and recent animal model experiments indicate that this important region of the brain sustains damage in bTBI cases. Further, such injuries are consistent with symptoms reported by subjects. An anatomically correct, biomechanically-based, 3-dimensional FE head model will be produced. A detailed FE submodel of the brainstem and veins will be created, which uses the stress/strain distribution from the global head model as the boundary conditions on the separate assembly model. The effects of blast strength and direction will also be studied.

This research is the direct result of the convergence of several important needs in medicine, engineering, education, industry, and the military. If successful, the research benefits will be broad and influence several areas. Early diagnosis and treatment of traumatic brain injury is critical for long term treatment success and even survival. Both can be aided by developing treatment modalities and dose/response relationships that complement the precise injury mechanisms. The work will lay the ground work for the development of better protective equipment for bomb squads, industrial firefighters, and soldiers. For example, head models can be augmented with models of protective equipment or vehicles. Other injury mechanisms (e.g. impacts, flying shrapnel) could also be incorporated into the models. Making these models available in the public domain will be a considerable contribution to the scientific and engineering community. Students and faculty will interact across traditional disciplines, a synergy highly beneficial. The research materials and procedures resulting from this project will be adapted for classroom use.

Project Summary/Abstract: For decades, it has been assumed that despite the triggering stimulus, the same brainstem areas are responsible for producing nausea and emesis. However, our recent preliminary studies suggested that nausea and vomiting are complex conditions that include a variety of physiological responses that vary between individuals, and in accordance with the triggering stimulus. This grant uses synergistic approaches to characterize the divergence, convergence, and multisensory integration by brainstem neurons of vestibular and other signals that can produce emesis. Specific Aim 1 includes the first comprehensive comparison of the brainstem pathways that participate in generating nausea and emesis following the intragastric infusion of copper sulfate or presentation of vestibular stimuli to induce motion sickness. By utilizing an innovative statistical approach that we recently developed, we will identify the neural networks that are activated by these stimuli from Fos labeling patterns. We hypothesize that different brainstem networks are engaged in animals that exhibit objective changes in stomach myoelectric activity indicative of nausea following stimulation of vestibular versus gastrointestinal receptors. Specific Aims 2 and 3 respectively use neurophysiologic techniques to characterize the integration of emetic inputs by parabrachial nucleus (PBN) neurons that transmit these signals to supratentorial brain areas, and by parasympathetic preganglionic neurons (PPGNs) in the dorsal motor nucleus of the vagus (DMV) and near-by nucleus ambiguus that transmit the signals to peripheral effectors. Aim 3 will also compare the responses of PPGNs to those of neurons in two adjacent areas that play a key role in integrating these signals: nucleus tractus solitarii (NTS) and the lateral tegmental field (LTF), which comprises the brainstem ?vomiting center.? Aim 3 incorporates the first characterization of responses to vestibular stimulation of PPGNs; although these neurons coordinate the changes in gastrointestinal activity during vomiting, virtually nothing is known about modifications in their firing rate elicited by emetic stimuli. By contrasting the integration of inputs from vestibular and gastrointestinal afferents in these key groups of brainstem neurons (PPGNs and those in PBN, NTS, and LTF), we can test our overall hypothesis that signals that elicit vomiting are processed independently in the brainstem, and only converge on neurons that directly control emetic responses. Understanding how vestibular and gastrointestinal signals are transformed in brainstem emetic pathways is key to generating insights into new treatments for nausea and vomiting. At the conclusion of the proposed studies, we will have identified brainstem networks that mediate nausea and vomiting, the influences of nausea-related and emetic signals on the activity of neurons in those networks, and their differential and/or synergistic responsiveness to vestibular and gastrointestinal signals.