Distribution of amylin-immunoreactive neurons in the monkey hypothalamus and their relationships with the histaminergic system

Amylin (AMY) is a 37 amino acid peptide of pancreatic origin that has been localized in peripheral and central nervous structures. Both peripheral and central injection of the peptide causes various effects, including anorect ic behavior in rats. Prompted by previous reports showing that the anorecti c effect of AMY is mediated by histamine release, we immunohistochemically investigated possible relationships between these two systems at the light microscopical level. Monkey (Macaca fuscata japonica) hypothalamus specimen s were submitted to immunohistochemical double staining procedures using AM Y and histidine decarboxylase (HDC) antisera. AMY-immunoreactive neurons we re found widely distributed in several nuclei of the monkey hypothalamus in cluding the supraoptic, paraventricular, perifornical, periventricular, ven tromedial, arcuate, and tuberomammillary nuclei. We detected AMY-immunoreac tive nerve fibers throughout the hypothalamus, the median eminence and hypo thalamus-neurohypophysial tract. Although AMY- and HDC-immunoreactive neuro nal cell bodies occupied distinct hypothalamic zones, many HDC-immunoreacti ve cell bodies and dendrites, particularly those in the periventricular, ar cuate, and rostral tuberomammillary regions, were surrounded by numerous AM Y-immunoreactive nerve fiber varicosities. These findings demonstrate for t he first time the presence of a discrete number of AMY- immuno reactive neu rons in the monkey hypothalamus and add morphological support to the experi mental data demonstrating that AMY probably exerts its influence on food in take via the histaminergic system.