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Regeneration and soma size changes following axotomy of the trochlear nerve
Author(s) -
Hazel Murphy E.,
Brown Joyce,
Iannuzzelli Pasquale G.,
Baker Robert
Publication year - 1990
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.902950411
Subject(s) - axotomy , axon , soma , anatomy , biology , nerve injury , lesion , regeneration (biology) , medicine , pathology , neuroscience , microbiology and biotechnology
The effects of CNS and PNS axotomy of the IVth nerve on cell death, soma size, axon size, and axon number were investigated. In adult cats, the IVth nerve was axotomised by using four surgical paradigms: (1) peripheral IVth nerve crush, (2) peripheral IVth nerve cut, (3) peripheral IVth nerve resection, and (4) a CNS IVth nerve cut in the velum. The extent of cell death resulting from each surgical paradigm was determined. Following axotomy distal to the decussation of the IVth nerves, cell death was least after nerve crush, intermediate after nerve cut, and maximal after resection of 5–7 mm of the nerve. Following axotomy at the decussationa CNS lesion‐most cells died but some successful regeneration was observed. Soma size measurements following a short‐term survival (3 days to 4 weeks) before the regenerating axons reached their target muscle revealed that somas of axotomised cells underwent hypotrophy within 1 week of axotomy and then gradually increased in size. They re‐attained normal size by 4 weeks postoperative when regenerating axons first reach their target. Following a long‐term survival (>2 months), somas were significantly hypertrophied, and the degree of hypertrophy was inversely related to the extent of cell survival up to a limit of 40% soma size increase. Counts and measurements of axons revealed that mean axon diameter of regenerated axons was much smaller than normal 3 months after axotomy, increased during the third to sixth postoperative months, but then showed no subsequent increase and remained below normal. In animals with cell death varying from 10% to 70%, the number of axons in the nerve was maintained constant at approximately 1,000. These data indicate that there is a mechanism for the production and maintenance of the appropriate number of regenerative axonal brabches following axotomy. In animals in which cell death exceeded 70%, the number of axons was controlled by a maximum ratio of 3 to 4 axon branches per surviving cell. The results suggest that axon number is strongly influenced by the target muscle and that hypertrophy of regenerated cells is related to the number of axonal sprouts each cell has to produce and suppot in order to re‐establish the preoperative number of axons in the regenerated trochlear nerve.