We recently demonstrated that three arcuate nucleus-derived peptides, neuropeptide Y (NPY), agouti-related protein (AGRP), and αMSH, are contained in axon terminals that heavily innervate hypophysiotropic TRH neurons in the rat brain and may contribute to the altered set-point of the hypothalamo-pituitary-thyroid axis during fasting. To determine whether a similar regulatory system exists in human brain, we performed a series of immunohistochemical studies using antisera against NPY, AGRP, αMSH, and TRH in adult hypothalami obtained within 15 h of death. Numerous small to medium-sized, fusiform and multipolar NPY-, AGRP-, and αMSH-immunoreactive (-IR) cells were widely distributed throughout the rostro-caudal extent of the infundibular (arcuate) nucleus. A similar distribution pattern was found for NPY- and AGRP-IR neurons in the arcuate nucleus, whereas αMSH-IR cells appeared to form a separate cell population. By double labeling fluorescent immunohistochemistry, 82% of NPY neurons cocontained AGRP, and 87% of AGRP neurons coexpressed NPY. No colocalization was found between αMSH-and AGRP-IR neurons. NPY-, AGRP-, and αMSH-containing axons densely innervated the hypothalamic paraventricular nucleus and were found in close juxtaposition to TRH-synthesizing cell bodies and dendrites. These studies demonstrate that in man, the NPY-, AGRP-, and αMSH-IR neuronal systems in the infundibular and paraventricular nuclei are highly reminiscent of that observed in the rat and may similarly be involved in regulating the hypothalamo-pituitary-thyroid axis in the human brain.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical