Abstract
Metastin neurons are located in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) with their fibers found in the median eminence (ME) and medial preoptic area. The present study aims to determine the neuronal projection of the two metastin neuronal populations in female rats in order to provide the morphological basis for the action site to stimulate GnRH release. Female rats were injected i.v. with FluoroGold (FG), a retrograde tracer and the others were stereotaxically injected with FG into the ARC. Colchicine was then injected into the lateral cerebroventricle. Some animals were ovariectomized and the others were primed with high dose of estrogen to enhance metastin immunoractivities in the ARC and AVPV, respectively. Coronal sections of the brain were made on a cryostat and dualstained with anti-FG and -metastin. Dual fluorescent immunohistochemistry revealed that 75% of metastin-immunopositive neurons in the ARC, but 5% of AVPV metastin-immunopositive neurons showed FG-immunoreactivities in animal with i.v. FG injection. This indicates that most metastin neurons projecting to the ARC-ME region originate in the ARC. Approximately 50% of metastin neurons in the AVPV had FG-immunoreactivities in animals with ARC FG injection, indicating that half of AVPV metastin neurons project to the ARC-ME region. Taken together, AVPV metastin neurons might have their neuronal terminals projecting to the ARC. In addition, most of the ARC metastin neurons might be neuroendocrine neurons projecting to the ME. In conclusion, both AVPV and ARC metastin neurons may control GnRH release at their terminals in the ARC-ME region.
