Immunohistochemical characterization of the arcuate kisspeptin/neurokinin B/dynorphin (KNDy) and preoptic kisspeptin neuronal populations in the hypothalamus during the estrous cycle in heifers

Abstract

Elucidating the physiological mechanisms that control reproduction is an obvious strategy for improving the fertility of cattle and developing new agents to control reproductive functions. The present study aimed to identify kisspeptin neurons in the bovine hypothalamus, clarifying that a central mechanism is also present in the cattle brain, as kisspeptin is known to play an important role in the stimulation of gonadotropin-releasing hormone (GnRH)/gonadotropin secretion in other mammals. To characterize kisspeptin neurons in the bovine hypothalamus, the co-localizations of kisspeptin and neurokinin B (NKB) or kisspeptin and dynorphin A (Dyn) were examined. Hypothalamic tissue was collected from Japanese Black or Japanese Black × Holstein crossbred cows during the follicular and luteal phases. Brain sections, including the arcuate nucleus (ARC) and the preoptic area (POA), were dual immunostained with kisspeptin and either NKB or Dyn. In the ARC, both NKB and Dyn were co-localized in kisspeptin neurons during both the follicular and luteal phases, demonstrating the presence of kisspeptin/NKB/Dyn-containing neurons, referred to as KNDy neurons, in cows. In the POA, no co-localization of kisspeptin with either NKB or Dyn was detected. Kisspeptin expression in the follicular phase was higher than that in the luteal phase, suggesting that kisspeptin expression in the POA is positively controlled by estrogen in cows. The kisspeptin neuronal populations in the ARC and POA likely play important roles in regulating the GnRH pulse and surge, respectively, in cows.

Role of kisspeptin neurons as a GnRH surge generator: Comparative aspects in rodents and non‐rodent mammals

“…The administration of kisspeptin resulted in strong stimulation of GnRH and gonadotropin releases in rodents, ruminants and primates . Further, existence of kisspeptin neurons in hypothalamus are reported in wide variety of mammalian species . All these results implicate that kisspeptin is a common factor between mammals that primarily controls gonadotropin release including feedback regulation by estrogen.…”

“…Even though sheep and goats are closely related species, these GnRH/LH surge generation mechanisms may have some differences. LH surge‐generating mechanisms in cattle, also a ruminant, are still unclarified, though POA kisspeptin neurons and ARC kisspeptin (KNDy) neurons found are similar to other species . The number of KISS1 ‐expressing cells in the PeN but not in the ARC was significantly upregulated by estradiol treatment in OVX pigs, suggesting that the anterior population of kisspeptin neurons is involved in LH surge generation in pigs as well.…”

“…Kisspeptin neurons are mainly located in two regions of the hypothalamus, arcuate nucleus (ARC) in the caudal hypothalamus and rostral hypothalamic regions, such as POA in primates (humans and monkeys), ruminants (sheep, goats and cattle) and musk shrew, the hypothalamic periventricular nucleus (PeN) in pigs or anteroventral periventricular nucleus (AVPV) in rodents . Now accumulating evidence suggests that the anterior population of kisspeptin neurons regulates ovulation by controlling surge‐mode GnRH/LH secretion, and ARC kisspeptin neurons regulates follicular growth by controlling pulse‐mode GnRH/gonadotropin secretion and this model is accepted in many mammalian species …”

Novel Biology of Tachykinins in Gonadotropin-Releasing Hormone Secretion

“…Indeed, GnRH neurons are found scattered around the preoptic area with axonal projections to the ME 23 but without documented synaptic contacts with other GnRH neurons to synchronize their activity. In this context, NKB forms a dense plexus of fibers in the ARC 41,69,[83][84][85][86] that facilitates the synchronization of the neuronal activity between KNDy neurons. Supporting this contention, recent studies have demonstrated that the photostimulation of KNDy neurons induces their synchronized firing, leading to a robust pulse of GnRH.…”

Colocalization of GPR120 and anterior pituitary hormone-producing cells in female Japanese Black cattle

“…Brain samples for gene expression analysis were collected from female Japanese Black cattle at a slaughterhouse. The hypothalamus, cerebral cortex, and hindbrain were collected, and hypothalamic tissues were divided into anterior and posterior parts, including the preoptic area (POA) and the arcuate nucleus (ARC), respectively, because GnRH and kisspeptin neurons that are responsible for reproductive function are located in the POA and the ARC in cattle [17,18]. Brainstem sample included area postrema containing ependymocytes of the wall of forth cerebral ventricle that play a role for sensing nutrition condition [19,20].…”