ALTERATIONS IN GAP-43-IMMUNOREACTIVE INNERVATION IN THE AGING RAT PITUITARY

The levels and distribution of the growth-associated protein, GAP-43, were examined in the pituitary glands of young and aging Sprague-Dawle y rats, using immunohistochemical techniques on tissue sections and We stern blot analyses. GAP-43-immunoreactive innervation was observed in sections in the intermediate and neural lobes of animals aged 8-15 mo nths, while in the oldest rats studied (17 months), stained fibers wer e observed mainly in the neural, but not the intermediate lobe. Wester n blots revealed reduced levels of GAP-43 in samples from 15 month old animals, as compared to 12 month old rats, in the neurointermediate l obes. There was no immunoreactivity for GAP-43 in the anterior lobes i n the tissue sections or in the blots in any of the glands examined. A diminished level of GAP-43 in pituitary innervation in aged animals s uggests a reduced ability for nerve terminals to undergo 'plastic' cha nges in their relationship to target endocrine cells. Since GAP-43 has also been suggested to modulate neurotransmitter release, a reduction in the protein in aging nerve terminals may diminish availability of transmitters at presynaptic sites.