Erich S. Luschei - US grants

Cells in the Mesencephalic Nucleus of the fifth nerve (MES V) are the somata of afferent fibers innervating spindles in jaw closing muscles or tooth-supporting tissues. Studies of the firing patterns of these afferents, in alert, behaving animals as well as in more conventional neurophysiological preparations, strongly suggest that these afferents "encode" mandibular position, the timing and direction of mandibular movement, or the force on teeth and/or the maxilla produced by jaw muscle activity. We know, at present, almost nothing about where and how MES V afferents project within the central nervous system; the goal of our proposal is to provide this information. It will increase our understanding of how proprioception is involved in oral motor control. Besides being of interest to basic neuroscience, this subject is of interest to health-related disciplines such as communicative disorders and dentistry. Projections of MES V neurons will be studied anatomically in cats by injection of peroxidase-labeled lectin in the vicinity of MES V neurons after a previous kainic acid injection in this region has killed all but the MES V neurons (MES V neurons are reported to be insensitive to kainic acid). In another series of experiments, neurophysiological techniques with cars will be used to confirm the projection of MES V neurons to other structures, and to assess whether there is a differential projection based upon the functional properties of the afferents. Controlled natural stimuli will also be used to study the response properties of second-order and higher-order neurons in the projection pathway. In a concurrent study, we will study a projection of MES V neurons that we are sure exists, but one about which we have no detailed knowledge: to the face area of the precentral cortex of the monkey. We will study the responses of precentral neurons in unanesthetized monkeys trained to perform two different mandibular tasks. In one task, the animal will have to grade biting force, and in the other, will have to control mandibular position against a constant load. All cells studied will be tested in terms of how they respond to electrical stimulation of MES V and natural oral stimuli designed to selectively excite the three basic types of MES V afferents.

The basic goal of the research is to identify and study the anatomy and physiology of the pathways by which neurons of the Mesencephalic Nucleus of the Fifth Nerve (MES V) convey sensory information to higher neural structures and reflexly affect jaw muscle motoneurons. MES V cells are the somata of first-order afferents from jaw muscle spindles or from tooth mechanoreceptors. Research associated with this project has demonstrated the existence of cells in the Nucleus Supratrigeminalis that appear to receive selective input from jaw muscle spindle differents. The proposed research is designed to learn more about the specific projection of functionally-identified MES V cells to brainstem neurons by intracellularly injecting MES V cells with horseradish peroxidase. Another aim is to identify the projection areas of the jaw muscle spindle-driven cells in Nucleus Supratrigeminalis by attempting to antidromically excite them from electrodes placed in the cerebellum, thalamus, and trigeminal motor nucleus. Another goal is to study the morphology of trigeminal motoneurons by intracellular injection of horseradish peroxidase. A last goal is to study the synaptic distribution of MES V cells and interneurons in Nucleus Supratrigeminalis to trigeminal motoneurons. Intracellular recordings from identified trigeminal motoneurons will be averaged with respect to activity of these jaw sensory neurons. It seems possible from past research that the "monosynaptic" jaw stretch reflex includes a component that is largely dependent upon a disynaptic pathway. The proposed research should test this possibility. If evidence of a substantial disynaptic excitatory pathway is found, it would radically affect or general understanding of the synaptic control of jaw motoneurons.

There is a crucial need to increase the number, quality, and diversity of scientists who are dedicated to understanding the basis of communication disorders and improving the treatment of these conditions. In recognition of this need, a Training Program was included as part of the National Center for Voice and Speech, and during the last four years, ten predoctoral students and seven post-doctoral fellows have received support and research training as part of this Training Program. We feel it is very important to continue our Training Program, and therefore propose to fund three predoctoral and two post-doctoral positions each year. Predoctoral trainees will be doctoral students in the Department of Speech Pathology and Audiology at the University of Iowa who are strongly motivated to conduct research related to voice and speech disorders. Post-doctoral fellows will be M.D.'s and Ph.D.'s with a broad spectrum of scientific training who seek research training with NCVS faculty members at any of the four consortium sites. One post-doctoral position per year will be specifically allocated for an applicant whose previous training has been in the area of molecular biology- and who desires to carry this approach into the study of voice and speech. Recruiting efforts will be comprehensive, using both personal and institutional efforts to include individuals from underrepresented minorities in our training program.