Immunohistochemical characterization of rat pineal dopamine beta-hydroxylase-containing structures: use of a homologous monoclonal antibody.

Previous immunohistochemical studies using a polyclonal heterologous antibody to dopamine-beta-hydroxylase (DBH) (EC 1.14.17.1) have shown that only a few of the many sympathetic nerve fibers in the rat pineal display DBH-like immunoreactivity. This is in contrast to other sympathetically innervated organs. To ascertain this observation and to rule out antibody- or method-related artifacts, in the present study a well-characterized, monospecific, homologous monoclonal antibody to DBH was used in combination with the biotin-streptavidin-fluorescein-mediated detection system. As in a previous study, immunoreactive fibers were only rarely encountered in the rat pineal gland, with an identical distribution pattern. The present findings indicate that the sympathetic nerve fibers in the rat pineal gland appear to have a low capacity for de novo synthesis of noradrenaline and that most of the noradrenaline present may be taken up from the general circulation. In addition to nerve fibers, perikarya-like cells and endbulb-like structures were seen in the pineal gland similar to those demonstrated by the polyclonal antibody. It is suggested that both structures may be part of an as yet unknown intrapineal regulatory system.