Evidence That Agouti-Related Peptide May Directly Regulate Kisspeptin Neurons in Male Sheep

Abstract

Agouti-related peptide (AgRP) neurons, which relay information from peripheral metabolic signals, may constitute a key central regulator of reproduction. Given that AgRP inhibits luteinizing hormone (LH) secretion and that nutritional suppression of LH elicits an increase in AgRP while suppressing kisspeptin expression in the arcuate nucleus (ARC) of the hypothalamus, we sought to examine the degree to which AgRP could directly regulate ARC kisspeptin neurons. Hypothalamic tissue was collected from four castrated male sheep (10 months of age) and processed for the detection of protein (AgRP input to kisspeptin neurons) using immunohistochemistry and mRNA for melanocortin 3 and 4 receptors (MC3R; MC4R) in kisspeptin neurons using RNAscope. Immunohistochemical analysis revealed that the majority of ARC kisspeptin neurons are contacted by presumptive AgRP terminals. RNAscope analysis revealed that nearly two thirds of the ARC kisspeptin neurons express mRNA for MC3R, while a small percentage (<10%) colocalize MC4R. Taken together, this data provides neuroanatomical evidence for a direct link between orexigenic AgRP neurons and reproductively critical kisspeptin neurons in the sheep, and builds upon our current understanding of the central link between energy balance and reproduction.

Estrogenic regulation of reproduction and energy homeostasis by a triumvirate of hypothalamic arcuate neurons

“…311 Next, POMC activity firing rates rise to the higher frequencies (approximately 20 Hz) 312 necessary to elicit synaptic release of β-endorphin that inhibits AgRP neurons via activation of μ-opioid receptors. 150 When circulating E 2 levels are high, such as during proestrus, POMC and Kiss1 ARH neurons have enhanced glutamate release probability onto AgRP neurons. 80 However, simultaneously increased expression of the Group III metabotropic glutamate receptor 7 postsynaptically in AgRP neurons causes this to be a net inhibitory input.…”

“…With sufficient energy stores, AgRP neurons become less active, leading to disinhibition of POMC neurons 311 . Next, POMC activity firing rates rise to the higher frequencies (approximately 20 Hz) 312 necessary to elicit synaptic release of β‐endorphin that inhibits AgRP neurons via activation of μ‐opioid receptors 150 . When circulating E 2 levels are high, such as during proestrus, POMC and Kiss1 ARH neurons have enhanced glutamate release probability onto AgRP neurons 80 .…”

“…When circulating E 2 levels are high, such as during proestrus, POMC and Kiss1 ARH neurons have enhanced glutamate release probability onto AgRP neurons 80 . However, simultaneously increased expression of the Group III metabotropic glutamate receptor 7 postsynaptically in AgRP neurons causes this to be a net inhibitory input 80,150 . With the same enhanced glutamate release, Kiss1 ARH neurons will excite POMC neurons through Group I mGluRs 80 .…”

Caspase-4/11 exacerbates disease severity in SARS–CoV-2 infection by promoting inflammation and immunothrombosis

“…ISH was performed using RNAscope Multiplex Fluorescent Reagent Kit v2 (Advanced Cell Diagnostics, Cat. #323100) as described before ( 52 ). All incubations between 40 and 60 °C were conducted using an ACD HybEZ II Hybridization System with an EZ-Batch Slide System (Advanced Cell Diagnostics, Cat.…”

The impact of undernutrition on KNDy (kisspeptin/neurokinin B/dynorphin) neurons in female lambs

“…In addition, more recent work in sheep has revealed that ARC kisspeptin neurons also express insulin receptors, 13 although it has yet to be shown that insulin administration during undernutrition can activate kisspeptin neurons. Although direct metabolic regulation should not be ruled out, recent findings in sheep 71 and mice 72 showing that the majority of ARC kisspeptin neurons express melanocortin 3 receptors support the idea that KNDy neurons may be governed by neurons within the ARC that have classically been associated with regulating energy homeostasis (i.e., pro‐opiomelanocortin and agouti‐related peptide neurons). Furthermore, although larger litter sizes during pregnancy result in lower birth weights in sheep, 73 the data obtained in the present study are not sufficient to determine whether litter size has a long‐term impact on hypothalamic neurons during undernutrition and this warrants further investigation.…”