Axons containing the growth associated protein GAP-43 specifically target rat corticotrophs following adrenalectomy.
An extensive network of nerve fibers immunoreactive for the neuronal growth associated protein GAP-43 (GAP-43-IR) is present within the anterior pituitary (AP) of the rat, and the density of these fibers has been reported to increase 4 days after adrenalectomy (ADX). In the present study, we employed confocal dual-label immunofluorescence microscopy to determine whether GAP-43-IR fibers are specifically associated with corticotrophs at various intervals after ADX. A dramatic increase in the density of GAP-43-IR was apparent 4 days after ADX, and this increase was sustained at 7 and 14 days post-ADX. The percentage of corticotrophs in apparent contact with GAP-43-IR axons was 87% at 4 days after ADX and 92% at 14 days. In addition, fewer than 15% of GAP-43-IR terminals were associated with cells other than corticotrophs in either group. This highly specific targeting of corticotrophs during a period in which these cells are undergoing both hypertrophy and hyperplasia indicates that axonal sprouting is occurring in response to ADX. While the less intense GAP-43-IR in the AP of intact rats precluded precise quantitative analysis, the majority of corticotrophs also appeared to be selectively innervated in these animals. The observations that GAP-43-IR axons selectively contact corticotrophs, and that both the specificity and thoroughness of innervation are maintained by targeted growth of GAP-43-IR axons following ADX, strongly suggest that these fibers are of functional significance.
Paden
C M
CM
Department of Biology, Montana State University, Bozeman 59717, USA.
Babcock
C
C
Conner
K A
KA
Duong
D K
DK
Kuhl
J M
JM
D000315:Adrenalectomy; D000818:Animals; D001369:Axons / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D019922:GAP-43 Protein / Q000378:metabolism*; D008297:Male; D008856:Microscopy, Fluorescence; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000502:physiology*; D011184:Postoperative Period; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D019922:GAP-43 Protein