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The present study focused on the interactive pain regulation of endokinin A/B (EKA/B, the common C-terminal decapeptide in EKA and EKB) or endokinin C/D (EKC/D, the common C-terminal duodecapeptide in EKC and EKD) on chimeric peptide MCRT (YPFPFRTic-N[H.sub.2], based on YPFP-N[H.sub.2] and PFRTic-N[H.sub.2]) at the supraspinal level in mice. Results demonstrated that the co-injection of nanomolar EKA/B and MCRT showed moderate regulation, whereas 30 µmol EKA/B had no effect on MCRT. The combination of EKC/D and MCRT produced enhanced antinociception, which was nearly equal to the sum of the mathematical values of single EKC/D and MCRT. Mechanism studies revealed that pre-injected naloxone attenuated the combination significantly compared with the equivalent analgesic effects of EKC/D alone, suggesting that EKC/D and MCRT might act on two totally independent pathways. Moreover, based on the above results and previous reports, we made two reasonable hypotheses to explain the cocktail-induced analgesia, which may potentially pave the way to explore the respective regulatory mechanisms of EKA/B, EKC/D, and MCRT and to better understand the complicated pain regulation of [NK.sub.1] and μ opioid receptors, as follows: (1) MCRT and endomorphin-1 possibly activated different μ subtypes; and (2) picomolar EKA/B might motivate the endogenous NPFF system after [NK.sub.1] activation. Key words: endokinin A/B, endokinin C/D, MCRT, [NK.sub.1] receptor, opioid receptors, pain regulation, co-injection. L'etude presente s'est concentree sur la regulation de la douleur par l'interaction de l'endokinine A/B (EKA/B, le decapeptide C-terminal commun a EKA et EKB) ou de l'endokinine C/D (EKC/D, le duodecapeptide commun a EKC et EKD) et du peptide chimere MCRT (YPFPFRTic-N[H.sub.2], base sur YPFP-N[H.sub.2] et PFRTic-N[H.sub.2]) au niveau supra-spinal chez la souris. Les resultats ont demontre que la co-injection de quantites nanomolaires d'EKA/B et de MCRT generait une regulation moderee, alors que 30 µmol d'EKA/B n'avaient pas d'effet sur MCRT. La combinaison d'EKC/D et de MCRT produisait un effet anti-nocicepteur accru, qui etait presqu'egal a la somme des valeurs mathematiques d'EKC/D et MCRT pris individuellement. Des etudes des mecanismes sous-jacents ont revele qu'une pre-injection de naloxone attenuait l'effet de la combinaison de facon significative, avec des effets analgesiques equivalents a ceux d'EKC/D seul, suggerant que EKC/D et MCRT pourraient agir sur deux sentiers totalement independants. De plus, selon les resultats presentes ci-dessus et des rapports precedents, les auteurs ont propose deux hypotheses raisonnables afin d'expliquer l'analgesie induite par le cocktail, qui pourraient potentiellement paver la voie a l'exploration des mecanismes regulateurs respectifs d'EKA/B, EKC/D et MCRT, et mieux comprendre la regulation complexe de la douleur par les recepteurs [NK.sub.1] et opioides μ: (1) MCRT et l'endomorphine-1 ont possiblement active differents sous-types de recepteurs μ; et (2) des quantites picomolaires d'EKA/B pourraient mobiliser le systeme NPFF endogene apres l'activation de [NK.sub.1]. [Traduit par la Redaction] Mots-cles: endokinine A/B, endokinine C/D, MCRT, recepteur [NK.sub.1], recepteurs d'opioides, regulation de la douleur, co-injection., Introduction The tachykinin peptide family, which includes more than 40 isolated tachykinins, was considered as one of the largest peptide families in the animal organism (Severini et al. 2002). Their [...]

The neuropeptide substance P manifests its biological functions through ligation of a G protein-coupled receptor, the NK1R. Mice with targeted deletion of this receptor reveal a preponderance of proinflammatory properties resulting from ligand activation, demonstrating a neurogenic component to multiple forms of inflammation and injury. We hypothesized that NK1R deficiency would afford a similar protection from inflammation associated with hyperoxia. Counter to our expectations, however, NK1R-/- animals suffered significantly worse lung injury compared with wild-type mice following exposure to 90% oxygen. Median survival was shortened to 84 h for NK1R-/- mice from 120 h for wild-type animals. Infiltration of inflammatory cells into the lungs was significantly increased; NK1R-/- animals also exhibited increased pulmonary edema, hemorrhage, and bronchoalveolar lavage fluid protein levels. TdT-mediated dUTP nick end labeling (TUNEL) staining was significantly elevated in NK1R-/- animals following hyperoxia. Furthermore, induction of metallothionein and [Na.sup.+]-[K.sup.+]-ATPase was accelerated in NK1R-/- compared with wild-type mice, consistent with increased oxidative injury and edema. In cultured mouse lung epithelial cells in 95% [O.sub.2], however, addition of substance P promoted cell death, suggesting the neurogenic component of hyperoxic lung injury is mediated by additional mechanisms in vivo. Release of bioactive constituents including substance P from sensory neurons results from activation of the vanilloid receptor, TRPV1. In mice with targeted deletion of the TRPV1 gene, acute hyperoxic injury is attenuated relative to NK1R-/- animals. Our findings thus reveal a major neurogenic mechanism in acute hyperoxic lung injury and demonstrate concerted actions of sensory neurotransmitters revealing significant protection for NKIR-mediated functions. tachykinins; neurogenic inflammation; oxidative lung injury; transient receptor potential vanilloid type 1; TRPV1 doi: 10.1152/ajplung.90509.2008

The primary afferent neurotransmitter triggering the spinal micturition reflex after complete spinal cord injury (SCI) in the rat is unknown. Substance P detected immunohistochemically in the sacral parasympathetic nucleus was significantly higher in 12 SCI rats than in 12 spinally intact rats (P = 0.008), suggesting substance P as a plausible candidate for the primary afferent neurotransmitter. The effects of the tachykinin NK1 receptor antagonist L-733060 on the spinal micturition reflex were then determined by performing conscious cystometry in an additional 14 intact rats and 14 SCI rats with L-733060 (0.1-100 [micro]g) administered intrathecally at L6-S1. L-733060 was without effect in intact rats, but blocked the spinal micturition reflex in 10 of 14 SCI rats and increased the intermicturition interval in 2 of 4 others at doses ranging from 10 to 100 [micro]g. Both phasic and nonphasic voiding contractions, differentiated according to the presence of phasic external urethral sphincter (EUS) activity, were present in most SCI rats. Both types of contractions were blocked by high doses of L-733060. Interestingly, there was a relative decline in phasic voiding contractions at high doses as well as a decline in contraction amplitude in nonphasic voiding contractions. In other respects, cystometric variables were largely unaffected in either spinally intact or SCI rats. L-733060 did not affect tonic EUS activity at any dose except when the spinal micturition reflex was blocked and tonic activity was consequently lost. These experiments show that tachykinin action at spinal NK1 receptors plays a major role in the spinal micturition reflex in SCI rats. spinal cord injury; bladder; tachykinins; external urethral sphincter

The tachykinin peptide bufokinin, isolated from the cane toad intestine, is important in intestinal and cardiovascular regulation in the toad. In this study, three tachykinin N[K.sub.1]-like receptor isoforms, bN[K.sub.1]-A, bN[K.sub.1]-B, and bN[K.sub.1]-C, encoding proteins of 309, 390, and 371 amino acids, respectively, were cloned from the toad brain and intestine. These isoforms differ only at the intracellular COOH terminus. The bN[K.sub.1]-A and bN[K.sub.1]-B isoforms are similar to the truncated and full-length forms of the mammalian N[K.sub.1] receptor, whereas bN[K.sub.1]-C is unique and does not correspond to any previously described receptor. RT-PCR studies demonstrated that three isoform transcripts are widely distributed in the toad with high expression in gut, spinal cord, brain, lung, and skeletal muscle. When expressed in COS-7 cells, bufokinin showed similar high affinity (I[C.sub.50] 0.6-0.8 nM) in competing for [sup.125]I-labeled Bolton-Hunter bufokinin binding at all receptors, but the binding affinities of substance P (SP) and neurokinin A (NKA) were very different at each isoform. When expressed in Xenopus oocytes, the truncated isoform, bN[K.sub.1]-A, was inactive, whereas bN[K.sup.1]-B and bN[K.sub.1]-C produced changes in chloride current when stimulated by tachykinins (minimum concentrations: bufokinin, 0.1 nM; SP, 1 nM; and NKA, 10 nM). A marked desensitization of the response was seen to subsequent applications of tachykinins, as experienced by the mammalian N[K.sub.1] receptor. In summary, our study describing three isoforms of N[K.sub.1]-like receptor from the toad suggests that the alternative splicing of N[K.sub.1] receptor is a physiologically conserved mechanism and raises a fundamental question as to the physiological role of each isoform. bufokinin; tachykinin receptors; sequencing and cloning; Xenopus oocyte expression; amphibian

The health burden of stress-related diseases, including depression and anxiety disorders, is rapidly increasing, whereas the range of available pharmacotherapies to treat these disorders is limited and suboptimal with regard to efficacy and tolerability. Recent findings support a major role for neuropeptides in mediating the response to stress and thereby identify neuropeptide systems as potential novel therapeutic targets for the treatment of depression and anxiety disorders. In preclinical models, pharmacological and/or genetic manipulation of substance P, corticotropin-releasing factor (CRF), vasopressin, neuropeptide Y and galanin function alters anxiety- and depression-related responses. Recently, specific and highly potent small-molecule neuropeptide receptor agonists and antagonists have been developed that can readily cross the blood--brain barrier. Clinical assessment of several compounds is currently underway, with antidepressant efficacy confirmed in double-blind, placebo-controlled trials of tachykinin N[K.sub.1] (substance P) receptor antagonists, and preliminary evidence of antidepressant activity in an open-label trial of a CR[F.sub.1] receptor antagonist.

Tachykinins interact with three neurokinin receptors (NKRs) that are often coexpressed by the same cell. Cellular responses to tachykinins depend on the NKR subtype that is activated. We compared the colocalization of NK1R and NK3R with [beta]-arrestins 1 and 2, which play major roles in receptor desensitization, endocytosis, and signaling. In cells expressing NK1R, the selective agonist SarMet-substance P induced rapid translocation of [beta]-arrestins 1 and 2 from the cytosol to the plasma membrane and then endosomes, indicative of interaction with both isoforms. In contrast, the NK3R interacted transiently with only [beta]-arrestin 2 at the plasma membrane. Despite these differences, both NK1R and NK3R similarly desensitized, internalized, and activated MAP kinases. Because interactions with [beta]-arrestins can explain differences in the rate of receptor resensitization, we compared resensitization of agonist-induced [Ca.sup.2+] mobilization. The NK1R resensitized greater than two-fold more slowly than the NK3R. Replacement of intracellular loop 3 and the COOH tail of the NK1R with comparable domains of the NK3R diminished colocalization of the NK1R with [beta]-arrestin 1 and accelerated resensitization to that of the NK3R. Thus loop 3 and the COOH tail specify colocalization of the NK1R with [beta]-arrestin 1 and determine the rate of resensitization. desensitization; endocytosis; tachykinins

Research has been conducted on the 5.6-spirolactams. The conformational preference of these compounds has been investigated via the prepared Ac-{Gly-Leu}-Met-NH (sub)2 derivatives (S,S,S) and (S,R,S) with the tripeptidic C-terminal region present in tachykinins.

Research has been conducted on the potent mammalian tachykinin substance P receptor antagonist, aprepitant. The synthesis of this antagonist is described.

The role of neurokinin 1 (N[K.sub.1]) receptor and possible interaction between N[K.sub.1] and N-methyl-D-aspartic acid (NMDA) glutamatergic receptors were investigated on spinal c-fos expression after lower urinary tract irritation with acetic acid infusion in rats. At both levels of the first ([L.sub.1]) and sixth lumbar ([L.sub.6]) spinal cord, where most of hypogastric nerve and pelvic nerve afferent terminals project, respectively, the selective N[K.sub.1] receptor antagonist CP-99,994 dose dependently reduced the total number of c-fos protein (Fos)-positive cells. However, CP-100,263, the enantiomer of CP-99,994 with a very low affinity for N[K.sub.1] receptor, did not have any effect on the total number of Fos-positive cells. Coadministration of a low dose (1 mg/kg) of CP-99,994 and NMDA receptor antagonist (MK-801), either of which alone did not affect c-fos expression, significantly inhibited c-fos expression at both levels of the spinal cord. Regarding regional differences, the number of Fos-positive cells decreased significantly at all regions of the [L.sub.6] level, but only at the dorsal horn of the [L.sub.1] level. These results indicate that N[K.sub.1] receptor is involved in spinal c-fos expression after lower urinary tract irritation and that N[K.sub.1] and NMDA receptors have a synergistic interaction in the spinal processing of nociceptive input from the lower urinary tract. CP-99,994; nociception; bladder; acetic acid; spinal cord

Neurokinin-containing nerve fibers were localized to guinea pig airway parasympathetic ganglia in control tissues but not in tissues pretreated with capsaicin. The purpose of the present study was to determine whether neurokinins, released during axonal reflexes or after antidromic afferent nerve stimulation, modulate ganglionic synaptic neurotransmission. The neurokinin type 3 (N[K.sub.3]) receptor antagonists SB-223412 and SR-142801 inhibited vagally mediated cholinergic contractions of bronchi in vitro at stimulation voltages threshold for preganglionic nerve activation but had no effect on vagally mediated contractions evoked at optimal voltage or field stimulation-induced contractions. Intracellular recordings from the ganglia neurons revealed that capsaicin-sensitive nerve stimulation potentiated subsequent preganglionic nerve-evoked fast excitatory postsynaptic potentials. This effect was mimicked by the N[K.sub.3] receptor agonist senktide analog and blocked by SB-223412. In situ, senktide analog markedly increased baseline tracheal cholinergic tone, an effect that was reversed by atropine and prevented by vagotomy or SB-223412. Comparable effects of intravenous senktide analog on pulmonary insufflation pressure were .observed. These data highlight the important integrative role played by parasympathetic ganglia and indicate that activation of N[K.sub.3] receptors in airway ganglia by endogenous neurokinins facilitates synaptic neurotransmission. capsaicin; axon reflex; bronchospasm; SB-223412; SR-142801

Cells express multiple G protein-coupled receptors that are simultaneously or sequentially activated by agonists. The consequences of activating one receptor on signaling and trafficking of another receptor are unknown. We examined the effects of selective activation of the neurokinin 1 receptor (NK1R) on signaling and trafficking of the NK3R and vice versa. Selective agonists of NK1R and NK3R induced membrane translocation of [beta]-arrestins ([beta]-ARRs). Dominant negative [beta]-AR[R.sup.319-418] inhibited endocytosis of NK1R and NK3R. Whereas an NK1R agonist caused sequestration of NK1R with [beta]-ARR in the same endosomes, thereby depleting them from the cytosol, [beta]-ARRs did not prominently sequester with the activated NK3R and rapidly returned to the cytosol. In cells coexpressing both receptors, prior activation of the NK1R inhibited endocytosis and homologous desensitization of the NK3R, which was dose-dependently reversed by overexpression of [beta]-ARR1. Similar results were obtained in enteric neurons that naturally coexpress the NK1R and NK3R. In contrast, activation of the NK3R did not affect NK1R endocytosis or desensitization. Thus, the high-affinity and prolonged interaction of the NK1R with [beta]-ARRs depletes [beta]-ARRs from the cytosol and limits their role in desensitization and endocytosis of the NK3R. Because [beta]-ARRs are critical for desensitization, endocytosis, and mitogenic signaling of many receptors, this sequestration is likely to have important and widespread implications.

We previously demonstrated that the pulmonary vascular response to substance P (SP) increased in chronically hypoxic rats. This study explored the temporal increase in reactivity of the pulmonary vascular response to SP and its underlying mechanisms. First, young female Wistar rats were exposed to sea level (SL) or simulated high altitude (HA) for 15 h/day for 3 days, 1 wk, 2 wk, and 4 wk. Lungs were isolated and perfused with 4% bovine serum albumin in Krebs-Henseleit buffer solution. SP (1.5 x [10.sup.-4] M) induced significant increases in pulmonary arterial pressure ([P.sub.pa]), venous pressure ([P.sub.v]), capillary pressure ([P.sub.c]), arterial resistance ([R.sub.a]), and filtration coefficient ([K.sub.fc]) in SL lungs. Increases in [P.sub.pa] and [R.sub.a] were significantly augmented in HA lungs, with a temporal increase trend peaking at 2 wk of HA exposure. The selective neurokinin (NK) type 1 (N[K.sub.1]) receptor antagonist SR-14033 significantly attenuated SP-induced increases in [P.sub.pa], [P.sub.v], [P.sub.c], [R.sub.a], and [K.sub.fc] in SL lungs. In lungs exposed to HA for 2 wk, SR-14033 suppressed the effect of SP on [P.sub.pa]. Also, chronic hypoxia induced significant increases in N[K.sub.1] receptors and N[K.sub.1] receptor mRNA, with a temporal trend. We conclude that chronic hypoxia temporally augments SP-induced vascular responses, which are closely associated with increases in N[K.sub.1] receptors and gene expression. pulmonary hypertension; tachykinins; gene expression

Research has been conducted on the spirobicyclic neurokinin NK-1 receptor antagonist anipod. The synthesis of this antipode has been carried out and the results indicate that the resulting allylic halide bears the cyclopropoxy-substituted aryl group.

The responses of wild-type mice to synthetic neurokinin-1 (NK1) agonists in addition of the natural agonist substance P were to those of NK1 receptor knockout mice to investigate the involvement of the NK1 receptor-mediated edema responses in the mouse dorsal skin cutaneous microvasculature. Results confirmed that the NK1 receptor is the pathway for trachykinin-mediated edema formation. The edema induced by trachykinins were also found to contain a mast cell-dependent component.

The effects of the sensory neuropeptide substance P on amylase and fluid secretion in the isolated vascularly perfused rat pancreas were studied. Substance P inhibited CCK-induced amylase release and secretin-induced juice flow via the pancreatic duct in a dose-related manner. Excitation of pancreatic sensory nerves using capsaicin inhibited both amylase and pancreatic juice flow via activation of the NK1 receptor. Findings showed that substance P inhibits exocrine secretion through an indirect neural mechanism.

Functional and autoradiographic experiments were performed to describe the effects of the tachykinin neurokinin A (NKA) on the isolated guinea pig heart. A dose-dependent bradycardia attributed to the activation of cholinergic neurons in the heart was observed. Increased force of ventricular contractions was also recorded. Moreover, the findings suggest that the presence of positive inotropic responses and coronary vasoconstriction were induced by neurokinin agonists.

Research findings indicate that populations of canine intrinsic cardiac neurons possess neurokinins NK1, NK2, and/or NK3 receptors. Furthermore, some intrinsic cardiac neurons receive tonic input via NKs in situ. Tachykinin-sensitive intrinsic cardiac neurons can activate cardiac sympathetic efferent neurons and may influence cardiac augmentor responses elicited during periods of stress such as those occurring during myocardial ischemia.

A study was conducted to examine the interactions between neurokinin A (NKA), vasoactive intestinal peptide (VIP), enteric nerves and prostanoids in controlling duodenal function. The abdominal cavity of Sprague-Dawley rats were prepared by a midline incision. Results indicated that increases in musocal permeability based on NK may be limited by mucosal nerves, with VIP as one of the transmitters.

Tannic acid was investigated to find out whether it elicits neurogenic plasma exudation from the oral mucosa in vivo in hamsters. Using intravital microscopy, it was observed that suffusion of tannic acid elicits substantial concentration-dependent leaky site formation and increase in clearance of fluorescein isothiocyanate-dextran from the in situ hamster cheek pouch. Results indicated that tannic acid elicits L-arginine-NO biosynthetic pathway-dependent neurogenic plasma exudation from the in situ hamster cheek pouch.

The expression of preprotachykinin gene-I messenger RNA (mRNA) that encodes the tachykinins substance P and neurokinin A in alveolar macrophages was investigated. Adult Sprague-Dawley rats were used as experimental models to examine gene regulation during lung inflammation. Results showed that in vivo or in vitro treatment with lipopolysaccharide stimulated the expression of preprotachykinin gene-I mRNA. Neutrophils produced in the lungs after in vivo lipopolysaccharide exposure also expressed preprotachykinin gene-I mRNA.

The effects of neurokinin A on mucosal permeability, fluid flux, bicarbonate secretion and motility of the duodenum were investigated. Male Sprague-Dawley rats were used as experimental models along with the nicotinic receptor antagonist hexamethonium to identify the mechanisms governing the integrative responses to neurokinin A. Results showed that neurokinin A stimulated duodenal motility, bicarbonate secretion, mucosal permeability and fluid production in rats. The increased duodenal mucosal bicarbonate and motility were not linked to nicotinic transmission.

The mechanisms of action of endogenous tachykinins that elicit ion secretion in the intestine were investigated. Guinea pigs were used as experimental models to determine tachykinin-evoked depolarizations of submucosal neurons, tachykinin-evoked secretomotor responses and the effect of neurokinin receptor antagonists NK1 and NK3 on intrinsic and extrinsic nerve-evoked responses. Results showed that NK1 and NK3 antagonists induced mucosal enterocytes while capsaicin-sensitive nerves released endogenous tachykinins.

The characteristics and distribution of neurokinin-1 (NK1) receptors wereinvestigated. Using adult Hartley guinea pigs as experimental models, morphological and functional methods were combined to examine single neuronal cells and effector systems. Results indicated that NK1 receptors reside on the neuronal and vascular effector systems in the submucosa of the small intestine of pigs. In addition, most secretomotor neurons were either cholinergic or noncholinergic.

The role of substance P in mucosal stroking responses and intrinsic secretory reflexes was analyzed in muscle-stripped segments of distal colon isolated from male albino guinea pigs. Administration of antagonist GR-82334 in muscle-stripped segments of guinea pig distal colon reduced mucosal stroking by 69-75%. The application of neurokinin1 (NK1)- and NK3-receptor agonist caused tetrodotoxin-sensitive increase in short-circuit current indicating the role of substance P together with NK1 and NK3 receptors in mediating secretion.

The abdominal muscle contractions of rats were analyzed after the intraperitoneal injection of acetic acid to determine the role of calcitonin gene-related peptides (CGRP) in the sensory afferents on visceral pain. Acetic acid-induced gastric emptying in rats was inhibited by the administration of RP-67580 indicating the role of neurokinin 1 receptors in mediating the release of CGRP due to peritoneal irritation. Furthermore, visceral and abdominal pain was inhibited by the administration of CGRP-receptor agonists.

The regulatory role of substance P (SP) on the airway epithelial barrier function and integrity was analyzed in confluent cultures of human bronchial epithelial cells (BE) and canine BE (CBE) cells. Ozone treatment of CBE cells significantly increased transepithelial conductance without altering net ion transport. However, the permeability-enhancing effects of ozone was inhibited by SP indicating the role of the tachykinin in maintaining BE barrier integrity by direct interaction with epithelial cells.

Mechanisms that mediate the tachykinin-induced gastric mucosal resistance were analyzed by utilizing neurokinin A (NKA)-(4-10) and [Ala5,beta-Ala8]NKA-(4-10) in rat gastric mucosa. The tachykinins protected 96% of the deeper layers of rat gastric mucosa from ethanol-induced damage. Tachykinin-mediated gastric protection is characterized by the NK2 receptor-mediated stimulation of the primary afferent neurons for the activation of nitric oxide synthesis.

An investigation of airway smooth muscle contraction in the presence of tachykinins substance P and neurokinin (NK)1 receptor agonists has provided evidence for the functional role of NK1 receptors in the small bronchi. Using a human bronchial tissue preparation, it was shown that the contraction induced by SP and NK1 receptor agonists are caused by rapid receptor desensitization and that this contraction is prostanoid-dependent.

The regulation of the circulatory system in elasmobranchs was investigated by examining the effect of tackykinins on the vascular system of the spiny dogfish, Squalus acanthias. Fishes treated with elasmobranch tackykinin scyliorhinin I (SCY I) and trout tachykinin substance P showed hypotension due to general vasodilation, followed eventually by increased mesenteric and celiac blood flow. SCY II caused hypertension due to vasoconstriction, followed by a decrease in vascular resistance and in mesenteric blood flow. There were no changes in the heart rate. It was concluded that tachykinins has a vasoactive function in the vascular system of the spiny dogfish.

The relationship between substance P release and plasma leakage was investigated by examining the localization of neurokinin-1 receptors (NK1) in the rat tracheal mucosa after vagal stimulation. NK1 receptor-immunoreactive endosomes were found in the endothelial cells of venules and capillaries but not in the arterioles. Vagal stimulation increased the number of endosomes in the capillaries. The increase corresponded to the amount of plasma leakage. These effects were blocked by the NK1 receptor antagonist SR-140333.

The mechanism of tachykinin excitation of gastrointestinal smooth muscles was studied by determining the effects of substance P (SP) and neurokinin A (NKA) on circular myocytes isolated from the canine colon. The results show that SP and NKA activate a non-selective cation conductance which causes cell membrane depolarization. Depolarization in turn activates the entry of calcium ions which leads to muscle excitation.

A study was conducted to examine the effect of tachykinins on gelatinase production by guinea pig alveolar macrophages. The lungs were treated with substance P (SP), neurokinin A or the NH2-terminal fragment of SP to determine the effect of agonists on tachykinin-induced gelatinase production. Changes in gelatinase concentrations were measured by zymography and quantified by image analysis.

Experimental observations suggest the presence of a tachykinin receptor, other than those activated by substance P (SP) and neurokinin A, on canine ileum, which induces contractions of the circular muscles. SP-initiated contractions do not facilitate histamine release from mast cells, as revealed by H1 histamine receptor studies. The neurokinin receptor NK3 does not inhibit responses to SP and is not contractile agent.

The effects of endogenous tachykinins and receptor-specific tachykinin analogues were studied in circular muscles of guinea pig stomachs. The differences in the physiological effects of substance P and neurokinin A on enteric neurons suggest the involvement of complex interactions of tachykinins with excitatory NK-1 receptors on vasoactive intestinal peptides (VIP) and cholinergic neurons, with inhibitory NK-2 receptors on VIP neurons and with NK-1 and NK-2 receptors on myocytes. This confirms VIP and nitric oxide mediation in relaxation of gastric muscles.

In vitro superfusion procedures were used to examine the effects of specific agonists of NK1, NK2 and NK3 tachykinin receptors on the presynaptic regulation of dopamine (DA) release. The aim was to investigate thefunctional differences between the striosomes and matrix of the striatum due todistinct populations of mesencephalic dopaminergic neurons innervating the two anatomical compartments. The results showed marked differences in DA release between striosomes and matrix of the striatum.

The amyloid β protein is deposited in the brains of patients with Alzheimer's disease but its pathogenic role is unknown. In culture, the amyloid β protein was neurotropic to undifferentiated [...]

Effects of substance P on identified neurons of the rat dorsal motor nucleus of the vagus. Am J Physiol Gastrointest Liver Physiol 281: G164-G172, 2001.--Previous evidence suggests that substance P (SP) activates subpopulations of neurons within the dorsal motor nucleus of the vagus (DMV). In this study we aimed at identifying these subpopulations in relation to their gastrointestinal projection organs or vagal branches and characterizing pharmacologically the SP response. Using whole cell patch-clamp recordings from identified gastrointestinal-projecting vagal motoneurons, we found that SP induced an inward current in all neuronal groups except for cecum-projecting cells. The lowest percentage of SP-responding neurons was found in fundus-projecting cells, where SP also had a concentration-response curve that was shifted to the left (P [is less than] 0.05). Independently from the projections, the SP response was reduced by sendide and MEN 10,376 and mimicked by a combination of [[Sar.sup.9]-Met[([O.sub.2]).sup.11]] SP and [Alpha]-neurokinin. SP and [Alpha]-neurokinin also increased the frequency, but not the amplitude, of postsynaptic currents. In conclusion, we demonstrated that SP induces both pre- and postsynaptic effects on DMV neurons via activation of neurokinin [NK.sub.1] and [NK.sub.2] receptors. The magnitude of the SP response was correlated to the peripheral target organ. neurokinin; electrophysiology; brain stem; gastrointestinal tract

Protein kinase C-mediated desensitization of the neurokinin 1 receptor. Am J Physiol Cell Physiol 280: C1097-C1106, 2001.--An understanding of the mechanisms that regulate signaling by the substance P (SP) or neurokinin 1 receptor (NK1-R) is of interest because of their role in inflammation and pain. By using activators and inhibitors of protein kinase C (PKC) and NK1-R mutations of potential PKC phosphorylation sites, we determined the role of PKC in desensitization of responses to SP. Activation of PKC abolished SP-induced [Ca.sup.2+] mobilization in cells that express wild-type NK1-R. This did not occur in cells expressing a COOH-terminally truncated NK1-R (NK1-R[Delta]324), which may correspond to a naturally occurring variant, or a point mutant lacking eight potential PKC phosphorylation sites within the COOH tail (NK1-R Ser-338, Thr-339, Ser-352, Ser-387, Ser-388, Ser-390, Ser-392, Ser-394/Ala, NK1-RKC4). Compared with wild-type NK1-R, the [t.sub.1/2] of SP-induced [Ca.sup.2+] mobilization was seven- and twofold greater in cells expressing NK1-R[Delta]324 and NK1-RKC4, respectively. In cells expressing wild-type NK1-R, inhibition of PKC caused a 35% increase in the [t.sub.1/2] of SP-induced [Ca.sup.2+] mobilization. Neither inhibition of PKC nor receptor mutation affected desensitization of [Ca.sup.2+] mobilization to repeated challenge with SP or SP-induced endocytosis of the NK1-R. Thus PKC regulates SP-induced [Ca.sup.2+] mobilization by full-length NK1-R and does not regulate a naturally occurring truncated variant. PKC does not mediate desensitization to repeated stimulation or endocytosis of the NK1-R. substance P; tachykinins; downregulation; G protein-coupled receptors

Mutoh, T., A. C. Bonham, and J. P. Joad. Substance P in the nucleus of the solitary tract augments bronchopulmonary C fiber reflex output. Am J Physiol Regulatory Integrative Comp Physiol 279: R1215-R1223, 2000.--Bronchopulmonary C fibers defend the lungs against injury from inhaled agents by a central nervous system reflex consisting of apnea, cough, bronchoconstriction, hypotension, and bradycardia. Glutamate is the putative neurotransmitter at the first central synapses in the nucleus of the solitary tract (NTS), but substance P, also released in the NTS, may modulate the transmission. To test the hypothesis that substance P in the NTS augments bronchopulmonary C fiber input and hence reflex output, we stimulated the C fibers with left atrial capsaicin (LA CAP) injections and compared the changes in phrenic nerve discharge, tracheal pressure (TP), arterial blood pressure (ABP), and heart rate (HR) in guinea pigs before and after substance P injections (200 [micro]M, 25 nl) in the NTS. Substance P significantly augmented LA CAP-evoked increases in expiratory time by 10-fold and increases in TP and decreases in ABP and HR by threefold, effects prevented by neurokinin-1 (NK1) receptor antagonism. Thus substance P acting at NTS NK1 receptors can exaggerate bronchopulmonary C fiber reflex output. Because substance P synthesis in vagal airway C fibers may be enhanced in pathological conditions such as allergic asthma, the findings may help explain some of the associated respiratory symptoms including cough and bronchoconstriction. neuropeptide; tachykinins; guinea pigs; respiratory reflexes

Maa, John, Eileen F. Grady, Ed H. Kim, Shandra K. Yoshimi, Matthew M. Hutter, Nigel W. Bunnett, and Kimberly S. Kirkwood. NK-1 receptor desensitization and neutral endopeptidase terminate SP-induced pancreatic plasma extravasation. Am J Physiol Gastrointest Liver Physiol 279: G726-G732, 2000.--Substance P (SP) induces plasma extravasation and neutrophil infiltration by activating the neurokinin-1 receptor (NK1-R). We characterized the mechanisms regulating this response in the rat pancreas. Anesthetized rats were continuously infused with SP, and plasma extravasation was quantified using Evans blue (EB) dye. Continuous infusion of SP (8 nmol [multiplied by] [kg.sup.-1] [multiplied by] [h.sup.-1]) resulted in a threshold increase in EB at 15 rain, a peak effect at 30 min (150% increase), and a return to baseline by 60 min. The NK1-R antagonist CP-96,345 blocked SP-induced plasma extravasation. After 60 min, the NK1-R was desensitized to agonist challenge. Resensitization was first detected at 20 min and increased until full recovery was seen at 30 min. Inhibition of the cell-surface protease neutral endopeptidase (NEP) by phosphoramidon potentiated the effect of exogenous SP; therefore endogenous NEP attenuates SP-induced plasma extravasation. Thus the continuous infusion of SP stimulates plasma extravasation in the rat pancreas via activation of the NK1-R, and these effects are terminated by both desensitization of the NK1-R and the cell-surface protease NEP. neurogenic inflammation; Evans blue; phosphoramidon; resensitization; tachykinins