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Counts of axons in electron microscopic sections of ventral roots in lampreys
Author(s) -
Rovainen Carl M.,
Dill Dorothy A.
Publication year - 1984
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902250308
Subject(s) - biology , petromyzon , lamprey , anatomy , axon , spinal cord , population , neuroscience , demography , fishery , sociology
Abstract The number of motoneurons in the lamprey spinal cord was estimated by counting axons in electron microscopic sections of ventral roots. Physiologically identified and marked motoneurons had one axon each in an ipsilateral ventral root. The corresponding axons in sections were unmyelinated, individually ensheathed, and 2–20 μm in diameter. Lampreys lack an organized sympathetic nervous system, but a minor and variable population of small axons with dense‐cored vesicles was also present in ventral and dorsal roots. The estimated numbers of motor axons per ventral root in adult Ichthyomyzon unicuspis and I. castaneus were 70.6 ± 9.3 (mean ± S.D), in adult landlocked Petromyzon marinus 100.1 ± 15.0, and in large ammocoetes of anadromous Petromyzon marinus 106.8 ± 14.3. The total estimated numbers of myotomal and fin motoneurons were as many as 13,000 in the spinal cord of adult Ichthyomyzon and 24,000 in adult Petromyzon .

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