An immunohistochemical study on the expressional dynamics of kisspeptin neurons relevant to GnRH neurons using a newly developed anti-kisspeptin antibody.

To investigate the reported discrepancy regarding the immunohistochemical expression of kisspeptin neurons, we produced a new antibody against synthetic peptide containing the same amino acid residual sequence as rat kisspeptin10. Although the antibody showed cross-reactivities against neurons other than kisspeptin neurons, these cross-reactivities were excluded by preabsorption with neuropeptide FF (NPFF). Immunohistochemistry using the antibody preabsorbed with NPFF showed specific kisspeptin immunoreactivities (IRs) in the arcuate nucleus (Arc), the inner layer of the median eminence, and the infundibulum in the rat hypothalamus. IRs were more intense in the adult female rats than in the males. This sexual dimorphism became observable at the 7th day after birth. These IRs intensified with age. Ovariectomy enhanced the IRs in the Arc in the female rats. In contrast, regarding IRs in the anteroventral periventricular nucleus (AVPV), only a few immunoreactive fibers were detected in the adult rats. We applied this antibody for the investigation of the interaction between kisspeptin fibers and gonadotropin-releasing hormone (GnRH) neurons. No direct morphological interaction between the cell bodies of GnRH neurons and kisspeptin fibers was observed in the medial preoptic area. Many projections of kisspeptin fibers were found close to the GnRH fibers in the lateral part of the median eminence. However, we did not observe any direct contact between kisspeptin fibers and the GnRH fibers. These results suggest that kisspeptin neurons regulate GnRH neurons not via the synaptic contact but via another information transmission process that is not synapse-dependent, such as volume transmission.