Proceedings of The Physiological Society
Durham University (2010) Proc Physiol Soc 21, PC19
Neurokinin B suppresses gonadotrophin-releasing hormone pulse generator frequency in female rats.
P. Grachev1, J. S. Kinsey-Jones1, X. F. Li1, K. T. O'Byrne1
1. Division of Women's Health, King's College London, London, United Kingdom.
Neurokinin B (NKB) and its G protein-coupled receptor (NK3-R) are essential for physiologic gonadotrophin secretion, reproductive development and fertility. NKB/NK3-R neurones are particularly numerous in the hypothalamic arcuate (ARC) nucleus, which is known to be the site of the gonadotropin-releasing hormone (GnRH) pulse generator. The purpose of this study was to determine whether manipulation of NKB/NK3-R signalling in the ARC impacts on endocrine and electrophysiological manifestations of the GnRH pulse generator frequency. We examined the effect of a selective NK3-R agonist, Senktide - administered intra-ARC - on pulsatile luteinizing hormone (LH) secretion in the rat. Adult female rats were anaesthetised using ketamine (100 mg/kg, i.p.) and xylazine (10 mg/kg, i.p.), bilaterally ovariectomised and implanted with subcutaneous 17β-oestradiol (E2) capsules (which produce circulating concentrations of E2 within the range observed during the diestrus phase of the estrous cycle, 38.8 ± 1.2 pg/ml). These were then chronically implanted with bilateral intra-ARC cannulae and intravenous catheters. Blood samples (25 μl) for LH measurement were automatically collected from the freely moving animals every 5 min for 6 h using a custom-built automated serial blood sampling system. After 2 h of control blood sampling, Senktide (1-10 pmol in 400 nl total injected volume, bilaterally; n = 14), or artificial cerebrospinal fluid (aCSF) vehicle (n = 5) was administered via the pre-implanted cannulae. Senktide significantly (p < 0.005; 2-tailed paired Student’s T-test) abolished LH pulses immediately following intranuclear administration. The duration of Senktide-dependent LH pulse inhibition was dose-dependent (90-200 min) with subsequent recovery of normal LH pulse frequency. To confirm that this effect was due to altered firing of neurones in the ARC, the hypothesised site of the GnRH pulse generator, we used electrophysiological techniques to record multiple-unit activity (MUA) in this region of the hypothalamus. MUA volleys correlate invariably with LH pulses, and are thus a reliable electrophysiological correlate of GnRH pulse generator activity. Ovariectomised rats (n = 5) were chronically implanted with intra-ARC electrode assemblies comprising 9 electrodes and intracerebroventricular (i.c.v.) cannulae aimed at the lateral ventricle. Following the detection of a basal MUA volley frequency, a range of doses of Senktide (100-600 pmol in 4 µl aCSF) was administered via pre-implanted cannulae. Senktide caused significant (p < 0.005; 2-tailed paired Student’s T-test) suppression of MUA volleys lasting 90-130 min. MUA volley frequency gradually returned to baseline following the suppression. These data suggest that NKB might act at the level of the hypothalamic ARC nucleus to suppress GnRH pulse generator frequency.
Where applicable, experiments conform with Society ethical requirements