Neurokinin-1 Receptor Receptor Research Articles

Fluorine-19 labeling of the tryptophan residues in the G protein-coupled receptor NK1R using the 5-fluoroindole precursor in Pichia pastoris expression.

In NMR spectroscopy of biomolecular systems, the use of fluorine-19 probes benefits from a clean background and high sensitivity. Therefore, 19F-labeling procedures are of wide-spread interest. Here, we use 5-fluoroindole as a precursor for cost-effective residue-specific introduction of 5-fluorotryptophan (5F-Trp) into G protein-coupled receptors (GPCRs) expressed in Pichia pastoris. The method was successfully implemented with the neurokinin 1 receptor (NK1R). The 19F-NMR spectra of 5F-Trp-labeled NK1R showed one well-separated high field-shifted resonance, which was assigned by mutational studies to the "toggle switch tryptophan". Residue-selective labeling thus enables site-specific investigations of this functionally important residue. The method described here is inexpensive, requires minimal genetic manipulation and can be expected to be applicable for yeast expression of GPCRs at large.

Substance P promotes the progression of bronchial asthma through activating the PI3K/AKT/NF-κB pathway mediated cellular inflammation and pyroptotic cell death in bronchial epithelial cells

ABSTRACT NOD-like receptor family pyrin domain containing three (NLRP3) inflammasome-mediated pyroptotic cell death and inflammation contribute to the pathogenesis of bronchial asthma, and it is reported that Substance P (SP) plays important role in the process, however, the detailed molecular mechanisms by which SP participates in the aggravation of bronchial asthma have not been fully studied. Here, our clinical data showed that SP and its receptor Neurokinin-1 receptor (NK1R) were significantly elevated in the plasma and peripheral blood mononuclear cell (PBMC) collected from patients with bronchial asthma, and further pre-clinical experiments evidenced that SP suppressed cell viability, accelerated lactate dehydrogenase (LDH) release, and upregulated ASC, Caspase-1, NLRP3, IL-1β and IL-18 to promote pyroptotic cell death and cellular inflammation in the human bronchial epithelial cells and asthmatic mice models in vitro and in vivo. Interestingly, SP-induced pyroptotic cell death was reversed by NK1R inhibitor L732138. Then, we uncovered the underlying mechanisms, and found that SP activated the downstream PI3K/AKT/NF-κB signal pathway in a NK1R-dependent manner, and blockage of this pathway by both PI3K inhibitor (LY294002) and NF-κB inhibitor (MG132) reversed SP-induced pyroptotic cell death and recovered cell viability in bronchial epithelial cells. Collectively, we concluded that SP interacted with its receptor NK1R to activate the PI3K/AKT/NF-κB pathway, which further triggered NLRP3-mediated pyroptotic cell death in the bronchial epithelial cells, resulting in the aggravation of bronchial asthma.

Neurokinin 1 Receptor Antagonists for Pruritus.

Pruritus, commonly known as itch, is a very common symptom in numerous dermatological disorders and systemic diseases. It can manifest as acute, or when lasting longer than 6 weeks, it is considered chronic and can lead to significant distress and reduced quality-of-life of those suffering. Current therapeutics are limited and are lacking in efficacy, and the development of more effective treatments is needed. The neurokinin 1 receptor (NK1R) antagonists are a novel class of drugs that possess several properties such as antidepressant, anxiolytic and antiemetic activities. Recently, several studies have described the antipruritic activity of NK1R antagonists for treating chronic pruritus. In this review we outline the pathogenesis of chronic pruritus, the mechanism by which the neuropeptide substance P (SP) and its receptor NK1R may be targeted to inhibit pruritic activity, and the efficacy and tolerability of NK1R antagonists, which have been, or are currently being investigated for treating conditions where chronic pruritus is a major symptom. Increasing evidence from ongoing and completed studies demonstrates the importance of SP and NK1R signalling in mediating pruritic activity. Several NK1R antagonists have shown significant antipruritic activity and thus targeting the SP-NK1R pathway may provide a therapeutic option for treating chronic pruritus of certain origin/s in the foreseeable future.

The NK-1R Antagonist Aprepitant Prevents LPS-Induced Oxidative Stress and Inflammation in RAW264.7 Macrophages.

BackgroundThe macrophage is one of the most important types of immune cells that protect against harmful stimuli. Macrophage activation plays a pivotal role in the progression and development of various inflammatory diseases. The neurokinin 1 receptor (NK-1R) is a G protein-coupled receptor that plays an important role in inflammatory diseases. Aprepitant is a kind of NK-1R antagonist. The purpose of this study is to determine the protective effect of aprepitant in lipopolysaccharide (LPS)-induced inflammatory responses in macrophages.MethodsWe examined the anti-inflammatory and anti-oxidant effects of aprepitant in LPS-treated RAW264.7 macrophages by using real-time PCR, ELISA, and Western blot analysis. We also assessed cellular oxidative stress signaling by measuring the levels of cellular MDA, total ROS, and NADPH oxidase expression. Cellular NO production was measured by DAF-FM DA staining. The inhibitory effect of aprepitant against NF-κB signaling was evaluated by luciferase assay and Western blot analysis.ResultsThe expression of NK-1R is increased in LPS-induced macrophages, suggesting a potential role of the receptor in the inflammatory response. We show that aprepitant protects macrophages against oxidative stress by reducing the generation of ROS and the expression of NOX-4. Furthermore, aprepitant inhibits the secretion of pro-inflammatory cytokines and chemotactic factors by mediating the NF-κB signaling pathway.ConclusionThe NK-1R receptor antagonist aprepitant acts as an anti-inflammatory agent, indicating that the blockage of the NK-1R pathway in macrophages has the potential to suppress inflammation.

Tachykinin NK1 receptor antagonist L-733,060 and substance P deletion exert neuroprotection through inhibiting oxidative stress and cell death after traumatic brain injury in mice.

Substance P (SP) is believed to play a role in traumatic brain injury (TBI), and the inhibition of binding of SP to the tachykinin neurokinin-1 receptor (NK1R) using NK1R antagonists had made favorable effects on TBI. Our current study addresses the functional roles and underlying mechanisms of SP and NK1R antagonist L-733,060 following TBI. Adult male wild type C57BL/6 J and SP knock out (SPKO) mice received a controlled cortical impact and outcome parameters were assessed. The results showed that TBI-induced motor and spatial memory deficits, lesion volume, brain water content and blood-brain barrier disruption were alleviated both in L-733,060-treated C57BL/6 J mice and vehicle-treated SPKO mice. L-733,060 treatment and SP deletion inhibited TBI-induced the release of cytochrome c from mitochondria to cytoplasm, activation of caspase-3, oxidative stress and neuroinflammation. Higher SP levels in serum and cortex were observed in wild type mice undergoing TBI relative to wild type sham group, but very little expression of cortical SP was detected in the SP-/- mice either TBI or not. Upregulation of NK1R expression after TBI was observed, and there was no significant difference between wild type and SPKO groups. in vitro, L-733,060 and SP deletion inhibited scratch injury-induced cell death, loss of mitochondrial membrane potential and reactive oxygen species (ROS) production following TBI. Together, the results of this study implicate a functional role for NK1-R antagonist L-733,060 and deletion of SP in TBI-induced neurological outcome, oxidative damage, neuroinflammation and cell death. Upregulation of NK1R maybe a consequence of TBI, independent of the levels of substance P. This study raises the possibility that targeting SP through its receptor NK1R or genetic deletion may have therapeutic efficacy in TBI.

Truncation of neurokinin-1 receptor-Negative regulation of substance P signaling.

Substance P (SP) is a tachykinin peptide, which triggers intracellular signaling in the nervous and immune systems, as well as, other local and systemic events. The interaction between SP and its receptor, neurokinin-1 receptor (NK1R), results in major downstream cellular actions, which include changes in calcium fluxes, ERK, and p21-activated kinase phosphorylation and NFκB activation. Two naturally occurring variants of the NK1R, the full-length, 407 aa receptor (NK1R-F) and the truncated, 311 aa isoform (NK1R-T), mediate the actions of SP. Receptor truncation partially disrupts signaling motifs of the carboxyl tail, a critical site for mediating NK1R signaling, resulting in a "less-efficient" receptor. Although NK1R-F is the predominant isoform in the central and peripheral nervous systems, NK1R-T is expressed in several tissues and cells, which include monocytes, NK cells, and T-cells. The SP binding domain is not affected by truncation and this site is identical in both NK1R receptor isoforms. However, while cells expressing NK1R-F respond to nanomolar concentrations of SP, monocyte and macrophage activation, mediated through NK1R-T, requires micromolar concentrations of SP in order to elicit signaling responses. Elevated plasma levels of SP are associated with increased inflammatory responses and NK1R antagonists reduce inflammation and cytokine production in vivo. This mini review presents and discusses the novel hypothesis that the expression of NK1R-T on immune system cells prevents immune activation in a milieu, which usually contains low concentrations of SP and, thus, maintains immune homeostasis. In contrast, in the activated neuronal microenvironment, when SP levels reach the threshold at tissue sites, SP promotes immune activation and modulates monocyte/macrophage polarization.

Immunolocalization of Substance P and NK‐1 Receptor in ADIPOSE Stem Cells

Substance P (SP) is a neuropeptide belonging to the thachykinin peptide family. SP, after binding to its receptor, the neurokinin 1 receptor (NK1R), controls several transcription factors such as NF-κB, hypoxia inducible factor (HIF-1α), c-myc, c-fos, c-jun, and AP-1. SP and NK1R have a widespread distribution in both the central and peripheral nervous systems. They are also present in cells not belonging to the nervous system (immune cells, placenta, etc.). SP is located in all body fluids, that is, blood, cerebrospinal fluid, etc., making it ubiquitous throughout the human body. SP and NK1R genes are expressed in the stem cell line TF-1 and in primary stem cells derived from human placental cord blood. However, to our knowledge, the presence of SP and the NK1R receptor in adipose stem cells (ADSC) is unknown. We demonstrated by immunofluorescence the localization of SP and NK1R in human and rat ADSC. SP and NK1R are located in both the cytoplasm and the nucleus of these cells. The NK1R is higher in the nucleus than in the cytoplasm of ADSCs. By Western blot we demonstrated the presence of different isoforms of NK1R that have different subcellular locations in the ADSC. SP induces proliferation and mitogenesis through NK1R in ADSCs. These findings reported here for the first time suggest an important role for a SP/NK1R system, either as genetic and/or epigenetic factor, in both the cytoplasm and nucleus functions of the ADSCs. J. Cell. Biochem. 118: 4686-4696, 2017. © 2017 Wiley Periodicals, Inc.

Substance p regulates puberty onset and fertility in the female mouse.

Puberty is a tightly regulated process that leads to reproductive capacity. Kiss1 neurons are crucial in this process by stimulating GnRH, yet how Kiss1 neurons are regulated remains unknown. Substance P (SP), an important neuropeptide in pain perception, induces gonadotropin release in adult mice in a kisspeptin-dependent manner. Here, we assessed whether SP, through binding to its receptor NK1R (neurokinin 1 receptor), participates in the timing of puberty onset and fertility in the mouse. We observed that 1) selective NK1R agonists induce gonadotropin release in prepubertal females; 2) the expression of Tac1 (encoding SP) and Tacr1 (NK1R) in the arcuate nucleus is maximal before puberty, suggesting increased SP tone; 3) repeated exposure to NK1R agonists prepubertally advances puberty onset; and 4) female Tac1(-/-) mice display delayed puberty; moreover, 5) SP deficiency leads to subfertility in females, showing fewer corpora lutea and antral follicles and leading to decreased litter size. Thus, our findings support a role for SP in the stimulation of gonadotropins before puberty, acting via Kiss1 neurons to stimulate GnRH release, and its involvement in the attainment of full reproductive capabilities in female mice.

Anti-emetic drug maropitant induces intestinal motility disorder but not anti-inflammatory action in mice

Maropitant is a neurokinin 1 receptor (NK1R) antagonist that is clinically used as a new anti-emetic drug for dogs. Substance P (SP) and its receptor NK1R are considered to modulate gastrointestinal peristalsis. In addition, SP works as an inflammatory mediator in gastrointestinal diseases. Aim of this study is to clarify the effects of maropitant on intestinal motility and inflammation in mice. Ex vivo examination of luminal pressure-induced intestinal motility of whole intestine revealed that maropitant (0.1–10 µM) increased frequency of contraction, decreased amplitude of contraction and totally inhibited motility index in a concentration-dependent manner. We measured intestinal transit in vivo by measuring transportation of orally administered luminal content labeled with phenol red. Our results demonstrated that maropitant (10 mg/kg, SC) delayed intestinal transit. Geometric center value was significantly decreased in maropitant-treated mice. Anti-inflammatory effects of maropitant against leukocytes infiltration into the intestinal smooth muscle layer in post-operative ileus (POI) model mice were measured by immunohistochemistry. In POI model mice, a great number of CD68-positive macrophages or MPO-stained neutrophils infiltrated into the inflamed muscle region of the intestine. However, in the maropitant treated mice, the infiltration of leukocytes was not inhibited. The results indicated that maropitant has ability to induce disorder of intestinal motility in mice, but has no anti-inflammatory action in the mouse of a POI model. In conclusion, in mice, maropitant induces disorder of intestinal motility in vivo.

Visceral Hypersensitivity in Non-erosive Reflux Disease: Neurogenic Overwhelming in Esophagus?

The mechanism underlying the pathogenesis of heartburn and chest pain in gastro-esophageal reflux disease (GERD) has not been clearly established. An important advance in understanding how heartburn is experienced has been accomplished with the reporting of dilated intracellular spaces (DIS) in the esophageal mucosa of patients with erosive GERD and non-erosive reflux disease (NERD) [1]. Although the presence of DIS provides a theoretical pathway for direct entry of hydrogen ions into the mucosa [2], its relationship to esophageal barrier function is still controversial since there are no direct measurements of esophageal acid permeability in vivo to support its contribution to barrier function. Another important breakthrough is the detection of transient receptor potential vanilloid subfamily member-1 receptors (TRPV1) in the esophageal mucosa [3], which may potentially contribute to visceral hypersensitivity as one of the important mechanisms in patients with NERD [4]. This notion is supported by the observation that perception of heartburn and esophageal sensitization can be induced by TRPV1 activation after the exposure to capsaicin and related TRPV1 activators such as heat and acid [5]. TRPV1 activation has also been hypothesized to induce neurogenic inflammation by the release of substance P and calcitonin-gene-related peptide (CGRP) in primary afferent neurons [6]. These neuropeptides mediate nociception and neurogenic inflammation via neurokinin 1 receptor (NK1R) for substance P and receptor activity-modifying protein 1 (RAMP1) for CGRP [7–9]. Therefore, the upregulation of TRPV1 expression in the esophageal mucosa is likely explanation for the phenomenon of visceral sensitization in NERD. Moreover, an induction of proteinase-activated receptor-2 (PAR-2) expression was reported in the esophageal mucosa of GERD patients, which correlated well with mucosal inflammatory changes and elevated tissue interleukin (IL)-8 concentrations, providing a possible mechanism for proinflammatory changes in GERD [10]. Furthermore, PAR-2 also mediates nociception via the release of substance P [11]. Finally, although anion-sensing ion channels (ASICs) have been implicated in the chemosensitivity in primary afferent fibers [12], its clinical implication is yet unclear in GERD and is thought to be more likely referred to the mechanosensitivity of the esophagus. In this issue of Digestive Diseases and Sciences [13], Yoshida et al. test the hypothesis regarding the role of nociceptors and neuropeptides in the pathogenesis of visceral hypersensitivity of NERD by examining the expression of acid-sensitive nociceptors including TRPV1, ASIC3, PAR-2, and neuropeptides such as substance P and CGRP with their cognate receptors NK1R and RAMP1 in the esophageal mucosa of NERD patients as compared with age-matched healthy controls. Not surprisingly, increased mRNA expression for TRPV1 and PAR-2 was present in the esophageal mucosa of NERD patients accompanied by a similar increase in substance P protein level and mRNA of its receptor NK1R. They also reported the presence of substance P-positive and CGRP-positive nerves in lamina propria of the esophageal mucosa of their patients by immunohistochemistry. They reported a positive correlation between substance P protein level and acid reflux score. Their data suggest that visceral hypersensitivity in NERD patients appears to be related to nociception and neurogenic inflammation, which supports their hypothesis C.-L. Chen (&) Department of Medicine, Buddhist Tzu Chi General Hospital and Tzu Chi University, 707, Section 3, Chung-Yang Road, Hualien 970, Taiwan e-mail: harry.clchen@msa.hinet.net

Role of Nociceptors/Neuropeptides in the Pathogenesis of Visceral Hypersensitivity of Nonerosive Reflux Disease

Esophageal visceral hypersensitivity has been proposed to be a pathogenesis of heartburn in nonerosive reflux disease (NERD), but its further mechanisms are unclear. Recently, it has been suggested that nociceptors and neuropeptides control sensory and pain mechanisms. Therefore, the objective of the present study was to estimate expression of acid-sensitive nociceptors such as transient receptor potential vanilloid 1 (TRPV1) and acid-sensing ion channel 3, protease-activated receptor 2 (PAR2), neuropeptides such as substance P and calcitonin-gene-related peptide, and their receptors such as neurokinin 1 receptor (NK1R) and receptor activity-modifying protein 1 in the esophageal mucosa of NERD patients. Biopsy samples were taken from NERD patients and healthy control subjects without heartburn. The expression level of nociceptors, neuropeptides, and their receptors were assessed by real-time RT-PCR and enzyme immunoassay. Localization of substance P and CGRP in the esophageal mucosa was determined by immunohistochemical staining. Expression of mRNA for TRPV1 and PAR2 was significantly elevated in the esophageal mucosa of NERD patients. Substance P protein level and its receptor NK1R mRNA also increased in NERD patients. A positive correlation between the substance P protein level and reflux symptoms was observed. Immunohistochemical study revealed the presence of substance P-positive nerves in the lamina propria of the esophagus. These findings suggest that visceral hypersensitivity in NERD patients is involved in neurogenic inflammation showing the increase in both substance P release and NK1R expression, which may be associated with the activation of TRPV1 and PAR2.

Neurokinin-1 receptors (NK1R:s), alcohol consumption, and alcohol reward in mice

Reduced voluntary alcohol consumption was recently found in neurokinin-1 receptor (NK1R)-deficient (KO) mice. It remains unknown whether this reflects developmental effects or direct regulation of alcohol consumption by NK1R:s, and whether the reduced consumption reflects motivational effects. The objective of this study is to obtain an expanded preclinical validation of NK1R antagonism as a candidate therapeutic mechanism in alcohol use disorders. The NK1R antagonist L-703,606 and NK1R KO mice were used in models that assess alcohol-related behaviors. L-703,606 (3-10 mg/kg i.p.) dose-dependently suppressed alcohol intake in WT C57BL/6 mice under two-bottle free choice conditions but was ineffective in NK1R KO:s, demonstrating the receptor specificity of the effect. Alcohol reward, measured as conditioned place preference for alcohol, was reduced by NK1R receptor deletion in a gene dose-dependent manner. In a model where escalation of intake is induced by repeated cycles of deprivation and access, escalation was seen in WT mice, but not in KO mice. Among behavioral phenotypes previously reported for NK1R mice on a mixed background, an analgesic-like phenotype was maintained on the C57BL/6 background used here, while KO:s and WT:s did not differ in anxiety- and depression-related behaviors. Acute blockade of NK1R:s mimics the effects of NKR1 gene deletion on alcohol consumption, supporting a direct rather than developmental role of the receptor in regulation of alcohol intake. Inactivation of NK1R:s critically modulates alcohol reward and escalation, two key characteristics of addiction. These data provide critical support for NK1R antagonism as a candidate mechanism for treatment of alcoholism.

Neurokinin 1 Receptor Mediates Membrane Blebbing in HEK293 Cells through a Rho/Rho-associated Coiled-coil Kinase-dependent Mechanism

We have investigated the effect of neurokinin 1 receptor (NK1R) agonists on HEK293 cells transfected with the NK1R receptor. The NK1R receptor mediates dramatic shape changes that include contractions of the membrane cortex resulting in membrane bleb formation. We have found that the cell shape changes correlate with changes in electrical impedance measured in cellular monolayers. The shape and impedance changes were prevented after preincubation with NK1R antagonists aprepitant and L-73060. Although bleb formation usually heralds apoptotic cell death, we have found that NK1R-mediated cellular blebbing does not associate with apoptosis. Preincubation with a cell-permeable derivative of C3 transferase that blocks Rho or with the Rho-associated coiled-coil kinase inhibitor Y27632 completely prevented NK1R-induced shape and impedance changes. Blebbing was also completely inhibited by ML-9, a myosin light chain kinase inhibitor. Furthermore, the phospholipase C inhibitor U73,122 did not interfere with the effect of Substance P (SP) on cellular morphology and cellular impedance but completely blocked SP-induced intracellular calcium increase, indicating that the blebbing is a process independent of intracellular calcium elevations. Blebbing is a protein kinase C-independent process, since the nonselective protein kinase C inhibitor GF109203X did not interfere with SP-induced effects. Based on these results, we provide the first evidence that NK1R receptor-ligand interaction can cause apoptosis-independent cellular blebbing and that this process is mediated by the Rho/Rho-associated coiled-coil kinase pathway.

Differences in the length of the carboxyl terminus mediate functional properties of neurokinin-1 receptor

The neurokinin-1 receptor (NK1R) has two naturally occurring forms that differ in the length of the carboxyl terminus: a full-length receptor consisting of 407 aa and a truncated receptor consisting of 311 aa. We examined whether there are differential signaling properties attributable to the carboxyl terminus of this receptor by using stably transfected human embryonic kidney (HEK293) cell lines that express either full-length or truncated NK1R. Substance P (SP) specifically triggered intracellular calcium increase in HEK293 cells expressing full-length NK1R but had no effect in the cells expressing the truncated NK1R. In addition, in cells expressing full-length NK1R, SP activated NF-kappaB and IL-8 mRNA expression, but in cells expressing the truncated NK1R, SP did not activate NF-kappaB, and it decreased IL-8 mRNA expression. In cells expressing full-length NK1R, SP stimulated phosphorylation of PKCdelta but inhibited phosphorylation of PKCdelta in cells expressing truncated NK1R. There are also differences in the timing of SP-induced ERK activation in cells expressing the two different forms of the receptor. Full-length NK1R activation of ERK was rapid (peak within 1-2 min), whereas truncated NK1R-mediated activation was slower (peak at 20-30 min). Thus, the carboxyl terminus of NK1R is the structural basis for differences in the functional properties of the full-length and truncated NK1R. These differences may provide important information toward the design of new NK1R receptor antagonists.

This Month in Gastroenterology

This Month in Gastroenterology

The Impact of Substance P Signalling on the Development of Experimental Staphylococcal Sepsis and Arthritis

Substance P (SP), acting on the neurokinin-1 receptor (NK-1R), is a neuropeptide, involved in the inflammatory processes. It promotes vasodilatation and increases vasopermeability, thus ensuing extravasation and accumulation of leucocytes at sites of injury. The aim of this study was to assess the impact of SP signalling on the responses during staphylococcal infection and the accompanying arthritis. Three experiments were performed where NK-1R-/- mice and controls were intravenously infected with different doses of Staphylococcus aureus. Clinical assessment of arthritis was performed as well as histological analysis of bone and cartilage destruction in the joints. In addition, the impact of NK-1R mutation on bacterial load in the kidneys as well as the phagocytic capacity of blood leucocytes were studied. Mice lacking the NK-1R displayed significantly higher bacterial load in the kidneys and significantly more severe synovitis and cartilage/bone destruction than the controls when inoculated with 1.4 x 10(7) staphylococci. Infection with 3.5 x 10(8) CFU/mouse induced sepsis. Thus, 11 days after bacterial inoculation 15 of 19 mice in the NK-1R-/- group had died versus 8 of 15 in the control group. Phagocytosis test revealed that significantly fewer macrophages from NK-1R-/- mice were able to phagocytose S. aureus when compared with macrophages from congenic control mice. Blocking the biological responses to substance P via its receptor NK-1R results in a less efficient clearance of bacteria leading to more severe arthritic lesions in mice.

A role for substance P in cancer promotion and progression: a mechanism to counteract intracellular death signals following oncogene activation or DNA damage

In the present review we discuss a central role for substance P (SP) in carcinogenesis. We suggest that one mechanism to induce mitogenesis of tumor cells is the activation of neurokinin-1 receptor (NK1R) through SP, linking cancer promotion and progression to a neurokinin-mediated environment. After reviewing the role of both SP and its receptor NK1R in normal and neoplastic cells we propose the use of neurokinin-1 receptor antagonists as a novel and promising approach for treating patients with cancer.

Intrastriatal dopamine D1 receptor agonist‐mediated motor behavior is reduced by local neurokinin 1 receptor antagonism

Recent evidence suggests that striatal neurokinin receptors modulate dopamine (DA)-induced motor behaviors. To further examine this, we studied the effects of intrastriatal neurokinin 1 receptor (NK1R) antagonism on motor behaviors induced by direct infusion of the full DA D1 receptor agonist SKF 82958. Adult male Sprague-Dawley rats received bilateral intrastriatal 0.8-mul infusions of the NK1R receptor antagonist LY 306,740 (0, 27, or 54 nmol/side) followed by intrastriatal infusions of SKF 82958 (0 or 24 nmol/side) into the dorsal striatum. Following each infusion, rats were placed into automated activity monitors for the quantification of horizontal activity, total distance traveled, movement bouts, and stereotypy counts. As expected, SKF 82958 increased motor activity on all behavioral measures. More importantly, whereas 27 nmol was without effect, prior infusion of 54 nmol LY 306,740 significantly reduced most aspects of behavior. The results of this study suggest that functional NK1Rs within the striatum play a permissive role in the motor behaviors induced by D1R stimulation.

Localization of the neurokinin 1 (NK-1) receptor in the human antrum and duodenum

A newly available antibody to the neurokinin-1 receptor (NK-1r) has made it possible to determine the distribution of the NK-1r receptor in human tissue. In the present study the distribution of the NK-1r and substance P have been determined in the human antrum and duodenum by immunocytochemistry. The NK-1r was present on myenteric and submucosal neurons and nerve fibers of the gastro-enteric nervous system. In addition, the receptor was present on spindle-shaped cells in the circular muscle layer, endothelial cells and a population of mucosal cells. In the submucosal plexus NK-1r immunoreactive neurons were surrounded by substance P containing fibers. These results indicate an extensive cellular expression of the NK-1r in the human antrum and duodenum.