Cellular localization of the neural cell adhesion molecule L1 in adult rat neuroendocrine and endocrine tissues: Comparisons with NCAM

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Abstract
The tissue distribution and cellular localization of the neural cell adhesion molecule L1 was determined by immunocytochemistry at the optical and ultrastructural levels in adult rat neuroendocrine tissues and pancreatic endocrine cells. L1 was found to be abundant in the neurohypophysis but undetectable in the rest of the pituitary gland. It was barely detectable in the normal rat endocrine pancreas, but a rat pancreatic insulinoma cell line was found by immunofluorescence to express low levels of L1. In the adrenal medulla, it was present on a sub-population of chromaffin cells and its density appeared to be lower on surfaces exposed to the extracellular matrix. Double immunolabelling showed this sub-population to consist of noradrenergic chromaffin cells. Adrenergic chromaffin cells were found not to express L1. In addition, the tissue distribution and cellular localization of NCAM mRNAs was determined by in situ hybridization, extending our previous studies on the cellular expression of NCAM proteins in endocrine and neuroendocrine tissues. This confirmed that the NCAM message has a wider cellular distribution than L1 within the hypophysis and the adrenal gland. In addition to secretory cells, L1 immunoreactivity was detected in glial cells, in particular in the pituicytes of the neurohypophysis, which further distinguishes them from astrocytes, their counterparts in the central nervous system. These data are discussed in terms of the different embryological origins of the various endocrine tissues examined and also in terms of the specific design constraints imposed on these tissues during their development.