Neurokinin 3 receptor-selective agonist, senktide, decreases core temperature in Japanese Black cattle.

Heat stress disrupts reproductive function in cattle. In summer, high ambient temperature and humidity elevate core body temperature, which is considered to be detrimental to reproductive abilities in cattle. Neurokinin B (NKB) is a factor that generates pulsatile GnRH and subsequent LH secretion in mammals. Recent studies have reported that NKB-neurokinin 3 receptor (NK3R) signaling is associated with heat-defense responses in rodents. The present study aimed to clarify the role of NKB-NK3R signaling in thermoregulation in cattle. We examined the effects of an NK3R-selective agonist, senktide, on vaginal temperature as an indicator of core body temperature in winter and summer. In both seasons, continuous infusion of senktide for 4 h immediately decreased vaginal temperature, and the mean temperature change in the senktide-treated group was significantly lower than that of both vehicle- and GnRH-treated groups. Administration of GnRH induced LH elevation, but there was no significant difference in vaginal temperature change between GnRH- and vehicle-treated groups. Moreover, we investigated the effects of senktide on ovarian temperature. Senktide treatment seemed to suppress the increase in ovarian temperature from 2 h after the beginning of administration, although the difference between groups was not statistically significant. Taken together, these results suggest that senktide infusion caused a decline in the vaginal temperature of cattle, in both winter and summer seasons, and this effect was not due to the gonadotropin-releasing action of senktide. These findings provide new therapeutic options for senktide to support both heat-defense responses and GnRH/LH pulse generation.

Neurokinin B and Neurokinin-3 Receptor Signaling: Promising Developments in the Management of Menopausal Hot Flushes.

Vasomotor symptoms, including hot flushes and night sweats, pose a significant symptomatic burden to women undergoing menopause, and negatively impact on both their physical and psychological well-being. Management of these symptoms can be challenging, with the use of conventional hormone replacement therapy limited by duration of treatment and clinical contraindications. Recent advances in our understanding of the neuroendocrine regulation of the reproductive axis and thermoregulation postmenopause has helped identify a promising new therapeutic target to ameliorate hot flushes. Antagonism of the neurokinin B/neurokinin-3 receptor (NK3R) signaling pathway has emerged as an efficacious treatment in managing vasomotor symptoms, with evidence of rapid and sustained reduction in hot flush frequency and severity and improvements in secondary quality-of-life measures such as sleep. Within this review, we will explore the growing body of evidence supporting the use of NK3R antagonists in the management of vasomotor symptoms, and the possible utility in managing dysfunctional sex-hormone-dependent disorders and glycolipid metabolism disorders such as polycystic ovarian syndrome.

Neurokinin-3 receptor activation selectively prolongs atrial refractoriness by inhibition of a background K+ channel.

The cardiac autonomic nervous system (ANS) controls normal atrial electrical function. The cardiac ANS produces various neuropeptides, among which the neurokinins, whose actions on atrial electrophysiology are largely unknown. We here demonstrate that the neurokinin substance-P (Sub-P) activates a neurokinin-3 receptor (NK-3R) in rabbit, prolonging action potential (AP) duration through inhibition of a background potassium current. In contrast, ventricular AP duration was unaffected by NK-3R activation. NK-3R stimulation lengthened atrial repolarization in intact rabbit hearts and consequently suppressed arrhythmia duration and occurrence in a rabbit isolated heart model of atrial fibrillation (AF). In human atrial appendages, the phenomenon of NK-3R mediated lengthening of atrial repolarization was also observed. Our findings thus uncover a pathway to selectively modulate atrial AP duration by activation of a hitherto unidentified neurokinin-3 receptor in the membrane of atrial myocytes. NK-3R stimulation may therefore represent an anti-arrhythmic concept to suppress re-entry-based atrial tachyarrhythmias, including AF.

A Comprehensive Method To Quantify Adaptations by Male and Female Mice With Hot Flashes Induced by the Neurokinin B Receptor Agonist Senktide.

Vasomotor symptoms (VMS; or hot flashes) plague millions of reproductive-aged men and women who have natural or iatrogenic loss of sex steroid production. Many affected individuals are left without treatment options because of contraindications to hormone replacement therapy and the lack of equally effective nonhormonal alternatives. Moreover, development of safer, more effective therapies has been stymied by the lack of an animal model that recapitulates the hot-flash phenomenon and enables direct testing of hypotheses regarding the pathophysiology underlying hot flashes. To address these problems, we developed a murine model for hot flashes and a comprehensive method for measuring autonomic and behavioral thermoregulation in mice. We designed and constructed an instrument called a thermocline that produces a thermal gradient along which mice behaviorally adapt to a thermal challenge to their core body temperature set point while their thermal preference over time is tracked and recorded. We tested and validated this murine model for VMS by administration of a TRPV1 agonist and a neurokinin B receptor agonist, capsaicin and senktide, respectively, to unrestrained mice and observed their autonomic and behavioral responses. Following both treatments, the mice exhibited a VMS-like response characterized by a drop in core body temperature and cold-seeking behavior on the thermocline. Senktide also caused a rise in tail skin temperature and increased Fos expression in the median preoptic area, a hypothalamic temperature control center. This dynamic model may be used to fully explore the cellular and molecular bases for VMS and to develop and test new therapeutic options.

Evidence for involvement of NK3 receptors in the anxiogenic-like effect of SP6-11(C-terminal), a metabolite of substance P, in rats evaluated in the elevated plus-maze.

INTRODUCTION: Substance P (SP) is a neuropeptide widely expressed throughout the fear-processing pathways of the brain. SP is cleaved by several proteolytic enzymes in amino (N-) and carboxy (C-) terminal sequences, which can have biological activities per se. We have previously shown that the anxiogenic-like effects elicited by SP6-11(C-terminal), a specific metabolite of SP, are mediated via NK1 and NK2 receptors. Nevertheless, there are evidences that C-terminal fragments may have a greater affinity for NK3 receptors. OBJECTIVES: The aim of the present study was to further investigate the possible involvement of NK3 receptors in the anxiogenic-like effects induced by SP6-11(C-terminal). METHODS: Adult male Wistar rats were intracerebroventricularly (i.c.v.) treated with SR142801 (NK3 receptors antagonist) or vehicle one minute to prior SP6-11(C-terminal) or vehicle. Other experimental groups received SP6-11(C-terminal) or vehicle i.c.v. one minute prior to senktide (NK3 receptors agonist) or vehicle. After five minutes, the animals were behaviorally evaluated in the elevated plus-maze test (EPM). RESULTS: SR142801 (100 pmol) or SP6-11(C-terminal) (10 pmol) reduced all the parameters of open-arms exploration and increased the number of protected stretch-attend postures in the EPM, indicating an anxiogenic-like effect. Senktide (10 pmol) promoted an opposite effect on these behavioral parameters, characterizing an anxiolytic-like profile. Pretreatment with SR142801, in an ineffective dose, potentiated the SP6-11-induced anxiety, especially in the unprotected head-dipping and protected stretch-attend postures behaviors. Moreover, the anxiolytic-like effect induced by senktide (1 pmol) was prevented by SP6-11. CONCLUSIONS: Our results give support to the involvement of NK3 receptors in the anxiogenic-like actions of SP6-11(C-terminal), where this metabolite seems to behave as an antagonist, in a way similar to SR142801.

Neurokinin 3 Receptor-Expressing Neurons in the Median Preoptic Nucleus Modulate Heat-Dissipation Effectors in the Female Rat.

KNDy neurons facilitate tail skin vasodilation and modulate the effects of estradiol on thermoregulation. We hypothesize that KNDy neurons influence cutaneous vasodilation via projections to neurons in the median preoptic nucleus (MnPO) that express the neurokinin 3 receptor (NK3R). In support of this hypothesis, focal microinjections of senktide, an NK3R agonist, into the MnPO lowers core temperature (TCORE) in the female rat. To further study the role of MnPO NK3R neurons in thermoregulation, these neurons were specifically ablated using a conjugate of a selective NK3R agonist and saporin (NK3-SAP). NK3-SAP or blank-SAP (control) was injected into the MnPO/medial septum. Tail skin temperature (TSKIN) and TCORE were measured in ovariectomized rats exposed to 3 ambient temperatures (TAMBIENT) before and after estradiol-17ß (E2) treatment. Before killing, we injected senktide (sc), monitored TCORE for 70 minutes, and harvested brains for Fos immunohistochemistry. Ablation of MnPO NK3R neurons lowered TSKIN at neutral and subneutral TAMBIENT regardless of E2 treatment. However, ablation did not prevent the effects of E2 on TCORE and TSKIN. In control rats, senktide injections induced hypothermia with numerous Fos-immunoreactive cells in the MnPO. In contrast, in NK3-SAP rats, senktide did not alter TCORE and minimal Fos-immunoreactive neurons were identified in the MnPO. These data show that NK3R neurons in the MnPO are required for the hypothermic effects of senktide but not for the E2 modulation of thermoregulation. The lower TSKIN in NK3-SAP-injected rats suggests that MnPO NK3R neurons, like KNDy neurons, facilitate cutaneous vasodilation, an important heat-dissipation effector.

Activation of the neurokinin 3 receptor promotes filopodia growth and sprouting in rat embryonic hypothalamic cells.

Members of the tachykinin family have trophic effects on developing neurons. The tachykinin neurokinin 3 receptor (NK3R) appears early in embryonic development; during the peak birthdates of hypothalamic neurons, but its involvement in neural development has not been examined. To address its possible role, immortalized embryonic hypothalamic neurons (CLU209) were treated with CellMask, a plasma membrane stain, or the membranes were imaged in CLU209 cells that were transfected with a pEGFP-NK3R expression vector. Nontransfected cells and transfected cells were then treated with senktide, a NK3R agonist, or Dulbecco's Modified Eagle's Medium (DMEM) and time-lapse confocal images were captured for the following 30 min. Compared to DMEM, senktide treatment led to filopodia initiation from the soma of both nontransfected and transfected CLU209 cells. These filopodia had diameters and lengths of approximately 200 nm and 3 µm, respectively. Pretreatment with an IP3 receptor blocker, 2-aminoethoxydiphenyl borate (2-APB), prevented the senktide-induced growth in filopodia; demonstrating that NK3R-induced outgrowth of filopodia likely involves the release of intracellular calcium. Exposure of transfected CLU209 cells to senktide for 24 h led to further growth of filopodia and processes that extended 10-20 µm. A mathematical model, composed of a linear and population model was developed to account for the dynamics of filopodia growth during a timescale of minutes. The results suggest that the ligand-induced activation of NK3R affects early developmental processes by initiating filopodia formation that are a prerequisite for neuritogenesis.

Neurokinin 3 receptor and phosphocholine transferase: missing factors for pathogenesis of C-reactive protein in preeclampsia.

C-reactive protein (CRP), an innate immune mediator, is elevated in the circulation before symptoms in patients with preeclampsia, a severe hypertensive pregnancy disorder with high mortality and morbidity. However, the specific sources underlying increased CRP and the role of elevated CRP in preeclampsia are undefined. Here, we report that circulating CRP levels are significantly increased in a large cohort of normotensive pregnant individuals when compared with nulligravid women and is further increased in patients with preeclampsia. These findings led us to discover further that placental syncytiotrophoblasts are previously unrecognized cellular sources of CRP and underlie elevated CRP in normotensive pregnant women and the additional increase in patients with preeclampsia. Next, we demonstrated that injection of CRP induces preeclampsia features, including hypertension (157 mm Hg CRP treated versus 119 mm Hg control), proteinuria (35.0 mg/µg CRP treated versus 14.1 mg/µg control), kidney, and placental damage and increased levels of sFlt-1 in pregnant mice but not in nonpregnant mice. Our study implicates that phosphocholine transferase, a placental-specific enzyme post-translationally modifying neurokinin B, is essential for the pathogenic role of CRP in preeclampsia through activation of the neurokinin 3 receptor. Overall, our studies have provided significant new insight on the pathogenic role of CRP in preeclampsia and highlighted innovative therapeutic strategies.

Evidence for tachykinin NK3 receptors-triggered peptide YY release from isolated guinea-pig distal colon.

The anorectic gut hormone, peptide YY (PYY), is released from colonic mucosal endocrine cells, but little is known about the role for tachykinin NK3 receptor in the control of PYY release from the colonic mucosa. We investigated the functional role for NK3 receptors in the control of PYY release from isolated guinea-pig distal colon, and the role for NK3 receptors-triggered PYY release in the control of colonic motility. Isolated colonic preparations were mounted in organ baths for measurement of PYY release and mechanical activity. The release of PYY from these preparations was determined by enzyme immunoassays. The NK3 receptor agonist senktide produced a tetrodotoxin/atropine-sensitive sustained increase in the release of PYY from the colonic preparations. Basal PYY release was transiently inhibited by the NK3 receptor antagonist SB222200. The neuropeptide Y1 receptor antagonist BIBO3304 produced a leftward shift of the concentration-response curves for senktide-evoked neurogenic contraction, but neither the neuropeptide Y2 receptor antagonist BIIE0246 nor the neuropeptide Y5 receptor antagonist CGP71683 affected the senktide concentration-response curves. NK3 receptors appear to play an important role in the control of PYY release from colonic mucosa, and NK3 receptor-triggered PYY release can exert Y1 receptor-mediated inhibition of tachykinergic neuromuscular transmission. This indicates a pathophysiological role for the NK3 receptor-triggered PYY release in the control of colonic motility.

Neurokinin B receptor antagonism decreases luteinising hormone pulse frequency and amplitude and delays puberty onset in the female rat.

The neural mechanisms controlling puberty onset remain enigmatic. Humans with loss of function mutations in TAC3 or TACR3, the genes encoding neurokinin B (NKB) or its receptor, neurokinin-3 receptor (NK3R), respectively, present with severe congenital gonadotrophin deficiency and pubertal failure. Animal studies have shown ambiguous actions of NKB-NK3R signalling with respect to controlling puberty onset. The present study aimed to determine the role of endogenous NKB-NK3R signalling in the control of pulsatile luteinising hormone (LH) secretion and the timing of puberty onset, and also whether precocious pubertal onset as a result of an obesogenic diet is similarly regulated by this neuropeptide system. Prepubertal female rats, chronically implanted with i.c.v. cannulae, were administered SB222200, a NK3R antagonist, or artificial cerebrospinal fluid via an osmotic mini-pump for 14 days. SB222200 significantly delayed the onset of vaginal opening and first oestrus (as markers of puberty) compared to controls in both normal and high-fat diet fed animals. Additionally, serial blood sampling, via chronic indwelling cardiac catheters, revealed that the increase in LH pulse frequency was delayed and that the LH pulse amplitude was reduced in response to NK3R antagonism, regardless of dietary status. These data suggest that endogenous NKB-NK3R signalling plays a role in controlling the timing of puberty and the associated acceleration of gonadotrophin-releasing hormone pulse generator frequency in the female rat.

Neurokinin3 receptor as a target to predict and improve learning and memory in the aged organism.

Impaired learning and memory performance is often found in aging as an early sign of dementia. It is associated with neuronal loss and reduced functioning of cholinergic networks. Here we present evidence that the neurokinin3 receptors (NK3-R) and their influence on acetylcholine (ACh) release may represent a crucial mechanism that underlies age-related deficits in learning and memory. Repeated pharmacological stimulation of NK3-R in aged rats was found to improve learning in the water maze and in object-place recognition. This treatment also enhanced in vivo acetylcholinergic activity in the frontal cortex, hippocampus, and amygdala but reduced NK3-R mRNA expression in the hippocampus. Furthermore, NK3-R agonism incurred a significantly higher increase in ACh levels in aged animals that showed superior learning than in those that were most deficient in learning. Our findings suggest that the induced activation of ACh, rather than basal ACh activity, is associated with superior learning in the aged. To test whether natural variation in NK3-R function also determines learning and memory performance in aged humans, we investigated 209 elderly patients with cognitive impairments. We found that of the 15 analyzed single single-nucleotide ploymorphism (SNPs) of the NK3-R-coding gene, TACR3, the rs2765 SNP predicted the degree of impairment of learning and memory in these patients. This relationship could be partially explained by a reduced right hippocampus volume in a subsample of 111 tested dementia patients. These data indicate the NK3-R as an important target to predict and improve learning and memory performance in the aged organism.

Neurokinin receptor 3 peptide exacerbates 6-hydroxydopamine-induced dopaminergic degeneration in rats through JNK pathway.

Neurokinin 3 (NK3) receptor is predominantly expressed in striatum and substantia nigra (SN). Evidences have indicated the roles of NK3 receptor in the pathogenesis of Parkinson's disease. By administrating NK3 receptor agonist senktide into 6-hydroxydopamine (6-OHDA)-lesioned rats, exacerbation of dopaminergic degeneration was found in striatum and substantia nigra pars compacta. From apomorphine rotation test, significant increase of contralateral rotation number was detected in 6-OHDA-lesioned rats with senktide injection. Furthermore, tyrosine hydroxylase expression in striatum and substantia nigra pars compacta were examined by immunohistochemistry and Western blotting. Further reduction of tyrosine hydroxylase immunoreactivities was found in 6-OHDA-lesioned rats that received senktide treatment. Also, phosphorylation of N-methyl-D-aspartate receptor 1 subunit was investigated in SN region and significant up-regulation was revealed in senktide-treated 6-OHDA-lesioned rats. Finally, phosphorylation of mitogen-activated protein kinase c-Jun N-terminal kinase (JNK) and c-Jun were examined in nigral region. Up-regulation of phosphorylated JNK molecules was shown in SN region after senktide injection. In line with this evidence, phosphorylation of c-Jun at Ser 63 and Ser 73 was also up-regulated by senktide treatment, thus presenting new aspects that NK3 peptide could exacerbate 6-OHDA toxicity in in vivo models and the possible mechanism may be contributed by the modulation of N-methyl-D-aspartate receptor 1 subunit and JNK pathway activities.

[Neurokinkin B and it's function on reproductive endocrine].

Neurokinkin B (NKB) is a member of tachykinin family and plays a role mainly through its receptor NK3R. NKB and NK3R are wide spread through the neural system. Studies revealed that NKB has kinds of biological functions such as constringing the smooth muscle of hollow viscus, relaxing blood vessels, reducing mean arterial pressure, slowing heart rate, exciting in vitro spinal cord neurons of rats and astringing sphincter pupillae. For the past few years, people pay more and more attentions to the regulating action of NKB on reproductive endocrine and a lot of research are made to discuss the function of NKB in HPGA. This article summarizes the distribution and physiological function of NKB and NK3R, discusses their functions in reproductive endocrine. Future studies will be needed to determine the precise mechanism of NKB.

Neurokinin Bs and neurokinin B receptors in zebrafish-potential role in controlling fish reproduction.

The endocrine regulation of vertebrate reproduction is achieved by the coordinated actions of several peptide neurohormones, tachykinin among them. To study the evolutionary conservation and physiological functions of neurokinin B (NKB), we identified tachykinin (tac) and tac receptor (NKBR) genes from many fish species, and cloned two cDNA forms from zebrafish. Phylogenetic analysis showed that piscine Tac3s and mammalian neurokinin genes arise from one lineage. High identity was found among different fish species in the region encoding the NKB; all shared the common C-terminal sequence. Although the piscine Tac3 gene encodes for two putative tachykinin peptides, the mammalian ortholog encodes for only one. The second fish putative peptide, referred to as neurokinin F (NKF), is unique and found to be conserved among the fish species when tested in silico. tac3a was expressed asymmetrically in the habenula of embryos, whereas in adults zebrafish tac3a-expressing neurons were localized in specific brain nuclei that are known to be involved in reproduction. Zebrafish tac3a mRNA levels gradually increased during the first few weeks of life and peaked at pubescence. Estrogen treatment of prepubertal fish elicited increases in tac3a, kiss1, kiss2, and kiss1ra expression. The synthetic zebrafish peptides (NKBa, NKBb, and NKF) activated Tac3 receptors via both PKC/Ca(2+) and PKA/cAMP signal-transduction pathways in vitro. Moreover, a single intraperitoneal injection of NKBa and NKF significantly increased leuteinizing hormone levels in mature female zebrafish. These results suggest that the NKB/NKBR system may participate in neuroendocrine control of fish reproduction.

Role of neurokinin B in the control of female puberty and its modulation by metabolic status.

Human genetic studies have revealed that neurokinin B (NKB) and its receptor, neurokinin-3 receptor (NK3R), are essential elements for normal reproduction; however, the precise role of NKB-NK3R signaling in the initiation of puberty remains unknown. We investigated here the regulation of Tac2 and Tacr3 mRNAs (encoding NKB and NK3R, respectively) in female rats and demonstrated that their hypothalamic expression is increased along postnatal maturation. At puberty, both genes were widely expressed throughout the brain, including the lateral hypothalamic area and the arcuate nucleus (ARC)/medial basal hypothalamus, where the expression of Tacr3 increased across pubertal transition. We showed that central administration of senktide (NK3R agonist) induced luteinizing hormone (LH) secretion in prepubertal and peripubertal females. Conversely, chronic infusion of an NK3R antagonist during puberty moderately delayed the timing of vaginal opening (VO) and tended to decrease LH levels. The expression of NKB and its receptor was sensitive to changes in metabolic status during puberty, as reflected by a reduction in Tacr3 (and, to a lesser extent, Tac2) expression in the ARC after a 48 h fast. Yet, acute LH responses to senktide in pubertal females were preserved, if not augmented, under fasting conditions, suggesting sensitization of the NKB-NK3R-gonadotropin-releasing hormone signaling pathway under metabolic distress. Moreover, repeated administration of senktide to female rats with pubertal arrest due to chronic undernutrition rescued VO (in ∼50% of animals) and potently elicited LH release. Altogether, our observations suggest that NKB-NK3R signaling plays a role in pubertal maturation and that its alterations may contribute to pubertal disorders linked to metabolic stress and negative energy balance.

The inhibitory effects of neurokinin B on GnRH pulse generator frequency in the female rat.

Neurokinin B (NKB) and its receptor (neurokinin-3 receptor) are coexpressed with kisspeptin and dynorphin A (Dyn) within neurons of the hypothalamic arcuate nucleus, the suggested site of the GnRH pulse generator. It is thought that these neuropeptides interact to regulate gonadotropin secretion. Using the ovariectomized (OVX) and OVX 17ß-estradiol-replaced rat models, we have carried out a series of in vivo neuropharmacological and electrophysiological experiments to elucidate the hierarchy between the kisspeptin, NKB, and Dyn signaling systems. Rats were implanted with intracerebroventricular cannulae and cardiac catheters for frequent (every 5 min) automated serial blood sampling. Freely moving rats were bled for 6 h, with intracerebroventricular injections taking place after a 2-h control bleeding period. A further group of OVX rats was implanted with intra-arcuate electrodes for the recording of multiunit activity volleys, which coincide invariably with LH pulses. Intracerebroventricular administration of the selective neurokinin-3 receptor agonist, senktide (100-600 pmol), caused a dose-dependent suppression of LH pulses and multiunit activity volleys. The effects of senktide did not differ between OVX and 17ß-estradiol-replaced OVX animals. Pretreatment with a selective Dyn receptor (κ opioid receptor) antagonist, norbinaltorphimine (6.8 nmol), blocked the senktide-induced inhibition of pulsatile LH secretion. Intracerebroventricular injection of senktide did not affect the rise in LH concentrations after administration of kisspeptin (1 nmol), and neither did kisspeptin preclude the senktide-induced suppression of LH pulses. These data show that NKB suppresses the frequency of the GnRH pulse generator in a Dyn/κ opioid receptor-dependent fashion.

Bidirectional regulation of human colonic smooth muscle contractility by tachykinin NK(2) receptors.

In this study, we attempted to clarify the mechanism of tachykinin-induced motor response in isolated smooth muscle preparations of the human colon. Fresh specimens of normal colon were obtained from patients suffering from colonic cancer. Using mucosa-free smooth muscle strips, smooth muscle tension with circular direction was monitored isometrically. Substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) produced marked contraction. All of these contractions were inhibited by saredutant, a selective NK(2)-R antagonist, but not by CP122721, a selective NK(1)-R antagonist or talnetant, a selective NK(3)-R antagonist. ßAla(8)-NKA(4-10) induced concentration-dependent contraction similar to NKA, but Sar(9)-Met(11)-SP and Met-Phe(7)-NKB did not cause marked contraction. Colonic contraction induced by ßAla(8)-NKA(4-10) was completely blocked by saredutant, but not by atropine. Tetrodotoxin or N(G)-nitro-L-arginine methyl ester pretreatment significantly enhanced ßAla(8)-NKA(4-10)-induced contraction. Immunohistochemical analysis showed that the NK(2)-R was expressed on the smooth muscle layers and myenteric plexus where it was also co-expressed with neuronal nitric oxide synthase in the myenteric plexus. These results suggest that the NK(2)-R is a major contributor to tachykinin-induced smooth muscle contraction in human colon and that the NK(2)-R-mediated response consists of an excitatory component via direct action on the smooth muscle and an inhibitory component possibly via nitric oxide neurons.

Characterization of nuclear neurokinin 3 receptor expression in rat brain.

Ligand-induced translocation of the G-protein-coupled receptor, neurokinin 3 (NK3-R), to the nucleus of hypothalamic neurons was reported using antibodies (ABs) raised against the C-terminal region of NK3-R. The current work was undertaken to substantiate the ability of NK3-R to enter the nucleus and identify which portion of the NK3-R molecule enters the nucleus. ABs directed at epitopes in the N-terminal and second extracellular loop of the rat NK3-R molecule were used to evaluate western blots of whole tissue homogenates and nuclear fractions from multiple brain areas. Specificity of the protein bands recognized by these ABs was demonstrated using Chinese hamster ovary (CHO) cells transfected with rat or human NK3-R. Both ABs prominently recognized a diffuse protein band of ∼56-65 kDa (56 kDa=predicted size) and distinct ∼70-kDa and 95-kDa proteins in homogenates of multiple brain areas. The ∼95-kDa protein recognized by the extracellular loop AB was enriched in nuclear fractions. Recognition of these proteins by ABs directed at different regions of the NK3-R supports their identification as NK3-R. The size differences reflect variable glycosylation and possibly linkage to different cytosolic and nuclear proteins. Recognition of protein bands by both ABs in nuclear fractions is consistent with the full-length NK3-R entering the nucleus. Hypotension increased the density of the ∼95-kDa band in nuclear fractions from the supraoptic nucleus indicating activity-induced nuclear translocation. Since NK3-R is widely distributed in the CNS, the presence of NK3-R in nuclei from multiple brain regions suggests that it may broadly influence CNS gene expression in a ligand-dependent manner.