ULTRASTRUCTURAL IMMUNOGOLD LOCALIZATION OF VIMENTIN AND S-100 PROTEININ GUINEA-PIG PARS TUBERALIS

Ultrastructural features of vimentin- and S-100 protein-positive cells in guinea pig pars tuberalis were examined by immunoelectron microsco py with the postembedding immunogold method. Interstitial cells that e xhibited elongated cytoplasm and partly surrounded the specific secret ory cells were filled with intermediate filament bundles on which immu nogold particles for vimentin were densely located, Small colloid-cont aining follicles were occasionally distributed in the cranial Legion s urrounding the median eminence, The follicular cells lining the lumina l cavities contained considerable amounts of intermediate filaments im munoreactive for vimentin, Some specific secretory cells displayed var ious amounts of intermediate filaments immunoreactive for vimentin, wh ich were scattered throughout the cytoplasm or concentrated around the nucleus, The specific secretory cells in which many parallel profiles of rough endoplasmic reticulum (RER) or a large number of mitochondri a were dispersed throughout cytoplasm, i.e., being highly metabolicall y active, were devoid of intermediate filaments, The ventrocaudal regi on in continuity with the pars distalis was occupied by cells that wer e packed with vesicular inclusions, considered to be dilated cisternae of RER, and frequently formed colloid-containing follicles, Immunorea ctivity for S-100 protein was located exclusively in this novel cell t ype. Immunogold particles for S-100 protein were distributed in the cy toplasmic matrix and were also associated with the membrane of vesicul ar inclusions, Gold particles were also detected on the tight junction s, desmosomes, and fibril materials at the apical cell regions of the colloid-containing follicles. The finding of two separate populations of cells containing vimentin and S-100 protein, respectively, supports the idea of functional separation in the pars tuberalis.