1-naphthol-pyronin B as a novel substrate for silver intensification: application to light and electron microscopic immunocytochemistry of neuroendocrine systems.

We describe a modification of silver intensification of immunoperoxidase end-product using 1-naphthol (1N) and 1N enhanced by pyronin B after suppressing nonspecific tissue argyrophilia with a solution of penicillamine and merthiolate buffered near neutral pH. This approach facilitates the preservation of a second antigen sequentially labeled in the same tissue section for light microscopic double immunolabeling experiments and also allows retention of ultrastructural detail. Using this protocol, we obtained rapid and uniform silver intensification of somatostatin (SRIF)-immunoreactive (IR) neuronal perikarya and processes in the rat hypothalamic paraventricular nucleus (PVN). Ultrastructurally, 1N- and 1N-pyronin B-silver intensified reaction product was clearly recognized by the presence of a coarse intracellular precipitate of high electron density. Light microscopic double-immunolabeling studies demonstrated the association between SRIF- and thyrotropin-releasing hormone (TRH)-IR neuronal systems in the PVN. We propose that silver intensification of 1N and 1N-pyronin B is a useful alternative to standard methods of silver intensification of immunoperoxidase reaction product at both light and ultrastructural levels and may be particularly amenable for double-immunolabeling studies.