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Nerve growth factor‐induced sprouting of mature, uninjured sympathetic axons
Author(s) -
Isaacson L. G.,
Saffran B. N.,
Crutcher K. A.
Publication year - 1992
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.903260302
Subject(s) - sprouting , axon , superior cervical ganglion , biology , nerve growth factor , fascicle , anatomy , growth cone , neuroscience , receptor , biochemistry , botany
The infusion of nerve growth factor (NGF) into the lateral ventricle ofthe mature rat brain elicits a sprouting response from axons associated with the intradural segment of the internal carotid artery. Using electron microscopic techniques, we observed a three–fold increase in the total number of perivascular axons. This NGF‐elicited response is characterized by a dramatic reduction in glial cell ensheathment similar to that observed during development and by the presence of profiles devoid of organelles that may represent newly formed sprouts. In spite of the increase in axon number, no significant changes in the percentage of small, medium, or large axons wereobserved. The three‐fold increase in the total number of axons was accompanied byan increase in the number of axons/fascicle but no change in the number of fascicles. This, along with the observation that a majority of sprouted axons were associated with other axons, supports the idea that the sprouted axons tend to associate preferentially with other axons. Bilateral superior cervical ganglionectomies following cytochrome C infusion indicate that approximately 60% of the axons associated with the internal carotid artery arise from the superior cervical ganglion and that the majority of axons contacting the smooth muscle layer arise from this ganglion. Sympathectomy following NGF infusion resulted in a 79% reduction in the total number of perivascular axons, demonstrating overwhelmingly that the majority of sprouted axons are sympathetic fibers. These results demonstrate that infusion of NGF into the mature rat brain results in the preferential sprouting of sympathetic axons associated with the internal carotid artery. These findings are consistent with the hypothesis that NGF normally plays a role in the regulation of autonomic cerebrovascular innervation in the adult animal and that mature, uninjured sympathetic neurons remain responsive to NGF. © 1992 Wiley‐Liss, Inc.