IMMUNOLOCALIZATION OF POLYSIALIC ACID IN THE MEDIAN-EMINENCE AND NEUROINTERMEDIATE HYPOPHYSEAL LOBE OF ADULT-RATS

Polysialic acid (PSA) is abundant on growing axons during brain develo pment and down regulated on maturation. However, high amounts of this carbohydrate polymer have been found to persist in some regions of the adult rat brain including the mediobasal hypothalamus. In this study, confocal laser scanning microscopy combined with double fluorescence immunostaining was used to characterize the cellular localization of P SA throughout the median eminence and neurointermediate hypophysial lo be of adult rats. In these regions, polysialic acid-immunoreactivity ( PSA-IR) generally appeared associated with fiber-like structures. Doub le immunostaining experiments demonstrated that, in addition to large axons of the neural lobe immunoreactive to vasopressin or oxytocin, PS A was constantly associated with fibers projecting into the intermedia te hypophysial lobe immunoreactive to either gamma-aminobutyric acid ( GABA) or tyrosine hydroxylase. Similarly, PSA-IR was detected on most, but not all the fibers immunoreactive to GABA or tyrosine hydroxylase dispersed throughout the neural lobe and the different layers of the median eminence. On the other hand, no PSA-IR was detected on axons im munoreactive to somatostatin or to corticotropin releasing hormone pro jecting throughout the median eminence, or on glial cell bodies and pr ocesses immunoreactive for glial fibrillary acidic protein (GFAP) or f or vimentin dispersed throughout the median eminence and the neural lo be.