title: The neuronal growth-associated protein (GAP)-43 is expressed by corticotrophs in the rat anterior pituitary after adrenalectomy.
abstract: The neuronal growth-associated protein (GAP)-43 has been localized in both long fibers and punctate clusters by immunocytochemistry within the rat anterior pituitary (AP). After adrenalectomy (ADX), GAP-43 immunoreactivity (GAP-43-ir) is greatly increased and is associated with corticotrophs at the light microscopic level. We have undertaken an electron microscopic study to determine the cellular localization of GAP-43 in the post-ADX AP. Using preembedding immunocytochemistry, we found GAP-43-ir localized exclusively to the cytoplasmic surface of the plasmalemma within a subset of endocrine cells with ultrastructure typical of degranulated corticotrophs at 4 d after ADX. We combined preembedding immunoelectron microscopy for GAP-43 with immunogold labeling for ACTH and found that GAP-43-ir was invariably present only in cells containing ACTH-positive granules. The density of GAP-43-ir was highest within extensive processes emanating from the soma, suggesting that these processes are the basis for the punctate clusters of GAP-43 staining seen surrounding corticotrophs in the light microscope. We also observed rare synaptic-like contacts between GAP-43-ir processes and distant cell bodies. GAP-43 mRNA was detected in extracts of the AP 4 d after ADX using RT-PCR, and quantitative PCR confirmed that GAP-43 mRNA was significantly up-regulated in the AP in response to ADX. We postulate that increased expression of GAP-43 may stimulate process outgrowth and intercellular communication by activated corticotrophs.
authors.affiliation: Department of Cell Biology and Neuroscience, 513 Leon Johnson Hall, Montana State University, Bozeman, 59717-3148, USA. cpaden@montana.edu
authors.forename: Charles M
authors.initials: CM
authors.lastname: Paden
authors.forename: John A
authors.initials: JA
authors.lastname: Watt
authors.forename: Tiffany H
authors.initials: TH
authors.lastname: Selong
authors.forename: Courtney L
authors.initials: CL
authors.lastname: Paterson
authors.forename: Harwood J
authors.initials: HJ
authors.lastname: Cranston
mesh_terms: D000315:Adrenalectomy; D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism*; D008297:Male; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D010903:Pituitary Gland, Anterior / Q000378:metabolism* / Q000648:ultrastructure; D010913:Pituitary-Adrenal System / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D019922:GAP-43 Protein; D012333:RNA, Messenger; D000324:Adrenocorticotropic Hormone