Functional morphology of the tubular lattice in the crayfish, Procambarus Clarkii, medial giant axon / by Paulette C. Hahn.
| Author/creator | Hahn, Paulette C. author. |
| Other author | Kalmus, Gerhard W., degree supervisor. |
| Other author | East Carolina University. Department of Biology. |
| Format | Theses and dissertations |
| Production | 1989. |
| Description | [vii], 85 leaves, 21 unnumbered leaves of plates : illustrations ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | The periaxonal space is the extracellular environment immediately adjacent to the axon. Ionic homeostasis, in general, and potassium homeostasis, in particular, of the extracellular microenvironment is important in neuronal function and synaptic integration. Potassium accumulation in the periaxonal space, which can occur during neural excitation, can adversely affect the resting membrane potential, action potential amplitude, action potential propagation along the nerve cord, synaptic transmission, and the excitation threshold. This study of the medial giant axon of the crayfish was undertaken to investigate the functional morphology of structures that may be involved in potassium clearance from the periaxonal space, particularly, the role of the tubular lattice. As a first step, an electron microscopic study including a morphometric analysis of the neuronal structures was conducted to provide quantitative data about the structure. From the morphometric data two structurally different- glial layers were identified, the inner (adaxonal) and outer glial layers. The tubular lattice was found to be predominantly in the adaxonal glial layer. The average length of the mesaxonal intercellular pathways was calculated. It was found that the length of the intercellular pathways was reduced by 12% via tubular lattice connections. A structural model of the tubular lattice in the adaxonal glial layer was formed from morphometric data. In order to relate the morphometric data to physiological events we measured electrophysiological parameters including action potential amplitude, action potential duration, and resting membrane potential in parallel with electron microscopic studies. Lanthanum proved to be a good extracellular potassium ionic diffusion space marker. Examination of electron micrographs showed lanthanum at the axon surface and bound in the tubular lattice. Stimulation and current pulse experiments, except for an apparent osmotic effect, showed no conclusive change in lanthanum uptake into the tubular lattice. Drugs known to act on glia membrane electrophysiological properties, i.e., carbachol and forskolin, did not alter lanthanum distribution around or in the tubular lattice adjacent to the axon. The result of these studies suggest that: 1. The tubular lattice is accessible to small ions and molecules from the extracellular space and. 2. The long tortuous intercellular diffusional length may be short circuited by the presence of the tubular lattice to account for a small change in the time constant of potassium clearance. |
| General note | Submitted to the faculty of the Department of Biology. |
| General note | Advisor: Gerhard W. Kalmus |
| Dissertation note | M.S. East Carolina University 1989 |
| Bibliography note | Includes bibliographical references (leaves 81-85). |
| Genre/form | dissertations. |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
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