Summary
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1.
Motoneurons to muscles of the branchial basket were identified by physiological critera in isolated brain-gill preparations of small adult lampreys,Petromyzon marinus andIchthyomyzon castaneus. Intracellular stimulation of motoneurons produced one-to-one contractions in ipsilateral motor units; one-to-one electromyographic potentials were also observed (Fig. 2). Motoneurons were confirmed as such by antidromic stimulation (Fig. 3).
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2.
Identified respiratory motoneurons were located in the IX and X cranial motor nuclei, through which they were distributed somatotopically (Fig. 1). Cells innervating the branchial constrictor, diagonal, gill pouch, and valve muscles were intermixed. Motoneurons marked by intracellular dye injection (Fig. 4) had the same morphology as other cells of the rostral motor nucleus of the vagus.
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3.
During respiratory movements branchial motoneurons were driven by a periodic and powerful burst of excitatory postsynaptic potentials (EPSP's) (Fig. 5). Several observations indicated that these EPSP's were not due to electrical coupling of motoneurons, but rather were produced by unidentified pacemakers in the brain.
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This work was supported by USPHS grants NS09367 and NS70391. The author is grateful to Dr. Paul S. G. Stein for encouragement and helpful comments and to P. J. Manion, E. Louis King, Jr., and Paul Fishman for the sea lampreys used in the project.
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Rovainen, C.M. Respiratory motoneurons in lampreys. J. Comp. Physiol. 94, 57–68 (1974). https://doi.org/10.1007/BF00610158
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DOI: https://doi.org/10.1007/BF00610158