Neurokinin B Gene Expression Is Increased in the Arcuate Nucleus of Ovariectomized Rats

Abstract

Hypertrophy and increased gene expression of tachykinin neurons occur in the infundibular (arcuate) nucleus of postmenopausal women. We have hypothesized that the alterations in tachykinin gene expression in the hypothalami of postmenopausal women are secondary to ovarian failure and not due to age per se. In this study, in situ hybridization and computer-assisted microscopy were used to determine whether ovariectomy modulates neurokinin B (NKB), substance P (SP) or proopiomelanocortin (POMC) gene expression in the rat arcuate nucleus. Four groups were examined: proestrus; diestrous day 1; ovariectomized, and constant estrus induced by a single injection of 20 mg/kg estradiol valerate. Rats were sacrificed 2 months after treatment. Computer-assisted microscopy was used to determine the number of tachykinin neurons, cell areas, and the autoradiographic grain density of labeled neurons. We report marked changes in NKB gene expression in ovariectomized rats. The number of neurons containing NKB gene transcripts was significantly greater in ovariectomized rats (16.9 ± 1.0 neurons/arcuate section) than all other groups. There was also a significant difference in the number of NKB neurons/arcuate section between proestrous (8.9 ± 1.8 neurons) and diestrous (4.8 ± 1.0 neurons) rats. The lowest number of neurons was detected in the estradiol valerate-injected rats (2.9 ± 0.6 NKB neurons/ arcuate section). Furthermore, the autoradiographic grain density of NKB neurons was doubled in the ovariectomized group compared to all other groups. In contrast, few SP neurons were identified in the rat arcuate nucleus and no changes were detected during the estrous cycle or in response to ovariectomy. However, the mean cell area of SP neurons was decreased in the estradiol valerate rats. The only change detected in POMC arcuate neurons was a decreased number of cells in the estradiol valerate rat. These data indicate that NKB neurons in the rat arcuate nucleus are modulated by ovarian hormones and support the hypothesis that increased NKB gene expression in the hypothalamus of postmenopausal women is due to ovarian failure.

Expanding the role of tachykinins in the neuroendocrine control of reproduction

“…www.reproduction-online.org and the ventromedial nucleus (VMN), in keeping with previous reports of SP immunoreactivity in rats, monkeys and humans (Ronnekleiv et al 1984, Yamano et al 1986, Harlan et al 1989, Rance & Young 1991, Tsuruo et al 1991, Rance & Bruce 1994, Borsay et al 2014. Studies using immunohistochemical detection of SP also report a plethora of fibers that innervate the entire length of the ARC and the median eminence (ME) (Hrabovszky et al 2013, Kalil et al 2015, Fergani et al 2016, which appear to surround the capillaries of the hypophyseal portal system indicating that SP may have the ability to act directly on the anterior pituitary (Kalil et al 2015).…”

“…This is supported by the anatomical findings that virtually all KNDy neurons express NK3R (Navarro et al 2009, 2011b, Amstalden et al 2010) and >90% express kappa-opioid receptor (KOR; (Weems et al 2016)). Furthermore, KNDy cells are interconnected with NKB fibers within the ARC forming a tightly regulated network (Rance & Bruce 1994, Krajewski et al 2010. Indeed, a growing number of studies in multiple species from our lab and others support the ability of NKB, or the NKB receptor (NK3R) agonist senktide, to increase LH pulses (Grachev et al 2012, Navarro 2013, Goodman et al 2014 (Arisawa et al 1990, Kalra et al 1992, Sahu & Kalra 1992, Noritake et al 2011, de Croft et al 2013 including men (Coiro et al 1992).…”

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

“…Because the decrease in the number of kisspeptin neurons during the non-breeding season is considered to be mainly due to the reduced expression of kisspeptin rather than to apoptosis [30], the very similar ratio of colocalization of kisspeptin and NKB between the breeding [13] and non-breeding seasons suggests that the expression of NKB in the ARC is also suppressed during the non-breeding season and that photoperiodic regulation of the expression occurs in a similar direction and extent between kisspeptin and NKB. In monkeys [30], rodents [9,31] and sheep [32], it has been shown that ovariectomy increases while E2 decreases the expression of NKB in the ARC, as is the case with kisspeptin [5,28]. Moreover, the number of kisspeptin- [33,34] and NKB-positive [34] neurons in the ARC are reduced in a similar manner during lactation in rats.…”

Role for kisspeptin/neurokinin B/dynorphin (KNDy) neurons in cutaneous vasodilatation and the estrogen modulation of body temperature

“…Secretion of GnRH into portal capillaries stimulates LH secretion from the anterior pituitary gland, which stimulates the secretion of E 2 from the ovaries. E 2 negative feedback reduces serum LH and decreases NKB and kisspeptin mRNA in KNDy neurons (57,58). ERα, the isoform required for estrogen negative feedback (59), is expressed in arcuate KNDy neurons (60) but not GnRH neurons (61).…”

“…The MnPO receives information from warm-sensitive, cutaneous thermoreceptors and projects to CNS centers to modulate heatdissipation effectors (24,42). (B) Effects of ovariectomy on serum LH and tail skin vasodilatation: Loss of E 2 after ovariectomy markedly increases NKB and kisspeptin gene expression in KNDy neurons (57,58), increases GnRH secretion into the portal capillaries (63) and LH secretion from the anterior pituitary gland. In the MnPO, at neutral T AMBIENT , Fos is increased in OVX rats, compared with OVX + E 2 rats (37).…”