Neurokinin 3 Receptor Immunoreactivity in the Septal Region, Preoptic Area and Hypothalamus of the Female Sheep: Colocalisation in Neurokinin B Cells of the Arcuate Nucleus but not in Gonadotrophin‐Releasing Hormone Neurones

Abstract

Recent evidence has implicated neurokinin B (NKB) in the complex neuronal network mediating the effects of gonadal steroids on the regulation of gonadotrophin-releasing hormone (GnRH) secretion. Since the neurokinin 3 receptor (NK3R) is thought to mediate the effects of NKB at the cellular level, we determined the distribution of immunoreactive NK3R in the septal region, preoptic area (POA) and hypothalamus of the ewe. NK3R cells and/or fibres were found in areas including the bed nucleus of the stria terminalis, POA, anterior hypothalamic and perifornical areas, dopaminergic A15 region, dorsomedial and lateral hypothalamus, arcuate nucleus (ARC) and the ventral premammillary nucleus. We also used dual-label immunocytochemistry to determine whether a neuroanatomical basis for direct modulation of GnRH neurones by NKB was evident. No GnRH neurones at any rostral-caudal level were observed to contain NK3R immunoreactivity, although GnRH neurones and fibres were in proximity to NK3R-containing fibres. Because NKB fibres formed close contacts with NKB neurones in the ARC, we determined whether these NKB neurones also contained immunoreactive NK3R. In luteal-phase ewes, 64% ± 11 of NKB neurones colocalised NK3R. In summary, NK3R is distributed in areas of the sheep preoptic area and hypothalamus known to be involved in the control of reproductive neuroendocrine function. Colocalization of NK3R in NKB neurones of the ARC suggests a potential mechanism of autoregulation of this subpopulation; however, the lack of NK3R in GnRH neurones suggests that the actions of NKB on GnRH neurosecretory activity in the ewe are mediated indirectly via other neurones and/or neuropeptides.

Central Administration of Neurokinin B Activates Kisspeptin/NKB Neurons in the Arcuate Nucleus and Stimulates Luteinizing Hormone Secretion in Ewes During the Non-Breeding Season

“…However, the possibility that other neurons might also mediate the NKB action cannot be ruled out by this study. It has been demonstrated in sheep that neurons in the RCh contain NK3R [12] and that local administrations of crystalline senktide directly into the RCh in anestrous ewes produced a dramatic increase in LH secretion comparable with a preovulatory LH surge [20]. These studies suggest that a group of RCh neurons also participates in the NKB action on GnRH secretion.…”

“…On the other hand, the site responsible for the NKB action on GnRH/ LH secretion remains unclear. Unlike rodents, GnRH neurons do not contain NK3R in sheep [12]. Therefore, other neurons might mediate the action of NKB on GnRH neurons, at least in this species.…”

“…However, it seems plausible to propose that the stimulatory action of NKB on GnRH secretion is mediated by kisspeptin signaling in ARC kisspeptin/NKB neurons, based on several lines of reasoning. First, ARC kisspeptin/NKB neurons contain NK3R in rats [14], mice [9] and sheep [12], and central administration of NKB activates ARC kisspeptin/NKB neurons (Fig. 3).…”

Current and future applications of GnRH, kisspeptin and neurokinin B analogues

“…Since GnRH neurons express GPR54 but apparently not TACR3 132,137,138 , while KNDY do express TACR3, it was further postulated that NKB secreted from KNDY neurons acts in an autocrine or paracrine manner to enhance KP secretion and that NKB actions were upstream of KP 134 . This notion was supported by the demonstration that continuous infusion of KP at a GPR54-saturating concentration in patients with NKB and TACR3 inactivating mutations restored LH pulsatility 134 .…”

GENOMICS SYMPOSIUM: Using genomic approaches to uncover sources of variation in age at puberty and reproductive longevity in sows

“…Frozen coronal sections (250 μm) were cut using a cryostat (CM1950; Leica Biosystems, Inc., Buffalo Grove, IL) and mounted onto charged microscope slides (Premier; Life Science Products Inc., Manassas, VA). Sections containing the ARC were identified based on anatomical references (Kineman et al, 1988(Kineman et al, , 1989Amstalden et al, 2010). A 2-mm biopsy punch (Miltex Inc., York, PA) was used to bilaterally microisolate the ARC from each section.…”