Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
The electrophysiological properties of the dorsal horn neurons in the superficial parts of the spinal dorsal horn, and actions of substance P, somatostatin and enkephalin on these cells have been investigated by intracellular recording in an immature rat spinal cord slice preparation;The ionic nature of the action potentials has been analyzed by modifying the ionic microenvironment, and by using ions or drugs known to block specific voltage-dependent conductances. We have shown that action potentials in immature rat dorsal horn neurons are generated by voltage-dependent conductance increases to sodium and calcium ions, and in particular that two distinct types of calcium spikes are probably present in these cells;Somatostatin and enkephalin hyperpolarized dorsal horn neurons and caused reduction or abolition of spontaneous firing. While the hyperpolarization produced by enkephalin was always associated with a fall in neuronal input resistance, in the case of somatostatin the similar effect was less consistently observed. These responses were brought about by both pre- and postsynaptic actions of the peptides;Bath application of substance P depolarized dorsal horn neurons and increased their excitability. The depolarization was most commonly associated with an increase in neuronal input resistance. SP-depolarization, in addition to a decrease in a voltage-dependent potassium conductance, may have been due to increases in sodium and calcium conductances. In about one-third of the cells, substance P induced a biphasic membrane response consisting of an initial hyperpolarization followed by a depolarization. The hyperpolarization was probably of presynaptic origin;Substance P modified the duration of the Ca-spike, the most consistent change being an initial decrease of the spike duration. Our data are consistent with a possibility that substance P shortens the duration of the Ca spike by decreasing a voltage sensitive inward Ca current and/or augmenting an outward potassium current.
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Murase, Kazuyuki, "Electrophysiological properties of spinal dorsal horn neurons in vitro: calcium-dependent action potentials and actions of neuroactive peptides " (1983). Retrospective Theses and Dissertations. 8945.