Molecular characterization of a functional cDNA encoding the rat substance P receptor

Fetal Undernutrition Programming, Sympathetic Nerve Activity, and Arterial Hypertension Development

A wealth of evidence showed that low birth weight is associated with environmental disruption during gestation, triggering embryotic or fetal adaptations and increasing the susceptibility of progeny to non-communicable diseases, including metabolic and cardiovascular diseases, obesity, and arterial hypertension. In addition, dietary disturbance during pregnancy in animal models has highlighted mechanisms that involve the genesis of arterial hypertension, particularly severe maternal low-protein intake (LP). Functional studies demonstrated that maternal low-protein intake leads to the renal decrease of sodium excretion and the dysfunction of the renin-angiotensin-aldosterone system signaling of LP offspring. The antinatriuretic effect is accentuated by a reduced number of nephron units and glomerulosclerosis, which are critical in establishing arterial hypertension phenotype. Also, in this way, studies have shown that the overactivity of the central and peripheral sympathetic nervous system occurs due to reduced sensory (afferent) renal nerve activity. As a result of this reciprocal and abnormal renorenal reflex, there is an enhanced tubule sodium proximal sodium reabsorption, which, at least in part, contributes directly to arterial hypertension development in some of the programmed models. A recent study has observed that significant changes in adrenal medulla secretion could be involved in the pathophysiological process of increasing blood pressure. Thus, this review aims to compile studies that link the central and peripheral sympathetic system activity mechanisms on water and salt handle and blood pressure control in the maternal protein-restricted offspring. Besides, these pathophysiological mechanisms mainly may involve the modulation of neurokinins and catecholamines pathways.

Elevated Neurokinin-1 Receptor Expression in Uterine Products of Conception Is Associated With First Trimester Miscarriages

Background

Miscarriage is a common complication of early pregnancy, mostly occurring in the first trimester. However, the etiological factors and prognostic and diagnostic biomarkers are not well known. Neurokinin-1 receptor (NK-1R) is a receptor of tachykinin peptide substance P (SP) and has a role in various pathological conditions, cancers, but its association with miscarriages and significance as a clinicopathological parameter are not studied. Accordingly, the present study aimed to clarify the localization and expression for NK-1R in human retained products of conception (POC). The role of NK-1R is not known in miscarriages.

Materials and Methods

NK-1R expression was assessed in POC and normal placental tissues by immunohistochemistry. Three- to four-micrometer-thin sections of formalin-fixed paraffin-embedded tissues were used for this purpose. Tissues were processed and then immunohistochemically stained with NK-1R antibody. Brain tissue was used as control for antibody. Protein expression was evaluated using the nuclear labeling index (%). Tissues were counterstained with 3,3'-diaminobenzidine (DAB), and microscopy was performed at 10×, 20×, and 40× magnifications.

Results

Ten human POC tissues and 10 normal placental tissues were studied by immunohistochemistry to demonstrate the localization of NK-1R. The expression of NK-1R protein was high in all the cases of both groups. NK-1R expression showed no notable differences among different cases of miscarriages as well as normal deliveries at full term regardless of the mother's age and gestational age at which the event occurred. Statistically, no difference was found in both groups, which is in agreement with our hypothesis and previous findings.

Conclusion

The expression of NK-1R was similar in all the cases, and it was intense. It shows that dysregulation of NK-1R along with its ligand SP might be involved in miscarriages and also involved in normal delivery. Our results provide fundamental data regarding this anti-NK-1R strategy. Thus, the present study recommends that SP/NK-1R system might, therefore, be considered as an emerging and promising diagnostic and therapeutic strategy against miscarriages. Hence, we report for the first time the expression and localization of NK-1R in POC. We suggest NK-1R antagonist in addition to the immunoglobulins and human chorionic gonadotropin to diagnose and treat spontaneous miscarriages.

The Neurokinin-1 Receptor Contributes to the Early Phase of Lipopolysaccharide-Induced Fever via Stimulation of Peripheral Cyclooxygenase-2 Protein Expression in Mice

Neurokinin (NK) signaling is involved in various inflammatory processes. A common manifestation of systemic inflammation is fever, which is usually induced in animal models with the administration of bacterial lipopolysaccharide (LPS). A role for the NK1 receptor was shown in LPS-induced fever, but the underlying mechanisms of how the NK1 receptor contributes to febrile response, especially in the early phase, have remained unknown. We administered LPS (120 µg/kg, intraperitoneally) to mice with the Tacr1 gene, i.e., the gene encoding the NK1 receptor, either present (Tacr1^+/+ ) or absent (Tacr1^-/- ) and measured their thermoregulatory responses, serum cytokine levels, tissue cyclooxygenase-2 (COX-2) expression, and prostaglandin (PG) E₂ concentration. We found that the LPS-induced febrile response was attenuated in Tacr1^-/- compared to their Tacr1^+/+ littermates starting from 40 min postinfusion. The febrigenic effect of intracerebroventricularly administered PGE₂ was not suppressed in the Tacr1^-/- mice. Serum concentration of pyrogenic cytokines did not differ between Tacr1^-/- and Tacr1^+/+ at 40 min post-LPS infusion. Administration of LPS resulted in amplification of COX-2 mRNA expression in the lungs, liver, and brain of the mice, which was statistically indistinguishable between the genotypes. In contrast, the LPS-induced augmentation of COX-2 protein expression was attenuated in the lungs and tended to be suppressed in the liver of Tacr1^-/- mice compared with Tacr1^+/+ mice. The Tacr1^+/+ mice responded to LPS with a significant surge of PGE₂ production in the lungs, whereas Tacr1^-/- mice did not. In conclusion, the NK1 receptor is necessary for normal fever genesis. Our results suggest that the NK1 receptor contributes to the early phase of LPS-induced fever by enhancing COX-2 protein expression in the periphery. These findings advance the understanding of the crosstalk between NK signaling and the "cytokine-COX-2-prostaglandin E₂" axis in systemic inflammation, thereby open up the possibilities for new therapeutic approaches.

Renal sodium handling and blood pressure changes in gestational protein-restricted offspring: Role of renal nerves and ganglia neurokinin expression

Background

Considering long-term changes in renal sodium handling and blood pressure in maternal protein-restricted (LP) offspring, we assumed that the development of LP hypertension results from abnormal dorsal root ganglia (DRG) neurokinin expression associated with impaired responsiveness of renal sensory receptors, promoting a reduced urinary excretion of sodium. The present study investigates whether increased blood pressure in protein-restricted offspring would be associated with changes in the DRG cells and in renal pelvic wall expression of NK1R, SP and CGRP when compared to NP offspring. In addition, we assessed the tubular sodium handling, estimated by creatinine and lithium clearances before and after bilateral renal denervation in conscious LP offspring relative to age-matched NP counterparts.

Methods

Dams received a normal (NP) or low-protein diet (LP) during their entire pregnancy period. Male NP or LP offspring underwent bilateral surgical renal denervation before the 8-week renal functional test and blood pressure measurements. Immunofluorescence staining in DRG cells was assessed in optical sections by confocal laser scanning microscope.

Results

The current data demonstrated a sustained rise in blood pressure associated with a decrease in fractional excretion of sodium (FENa) by reducing post-proximal tubule sodium rejection in 16-wk old LP rats relative to age-matched NP counterparts. According to this study, bilateral renal denervation attenuated blood pressure and increased FENa in LP offspring. Furthermore, an immunohistochemical analysis showed a reduced expression of SP and CGRP in DRGs of LP when compared with NP rats. Renal pelvis of LP rats did not show a strong CGRP expression related to NP rats, whereas there was no change in SP immunostaining.

Conclusions

These observations raise the possibility that impaired DRG and pelvic neurokinin expression associated with responsiveness of renal sensory receptors in 16-wk old LP offspring are conducive to excess renal reabsorption of sodium and development of hypertension in this programmed model.

PKCɛ mediates substance P inhibition of GABAA receptors-mediated current in rat dorsal root ganglion

The mechanism underlying the modulatory effect of substance P (SP) on GABA-activated response in rat dorsal root ganglion (DRG) neurons was investigated. In freshly dissociated rat DRG neurons, whole-cell patch-clamp technique was used to record GABA-activated current and sharp electrode intracellular recording technique was used to record GABA-induced membrane depolarization. Application of GABA (1-1000 μmol/L) induced an inward current in a concentration-dependent manner in 114 out of 127 DRG neurons (89.8 %) examined with whole-cell patch-clamp recordings. Bath application of GABA (1-1000 μmol/L) evoked a depolarizing response in 236 out of 257 (91.8%) DRG neurons examined with intracellular recordings. Application of SP (0.001-1 μmol/L) suppressed the GABA-activated inward current and membrane depolarization. The inhibitory effects were concentration-dependent and could be blocked by the selective neurokinin 1 (NK1) receptors antagonist spantide but not by L659187 and SR142801 (1 μmol/L, n=7), selective antagonists of NK2 and NK3. The inhibitory effect of SP was significantly reduced by the calcium chelator BAPTA-AM, phospholipase C (PLC) inhibitor U73122, and PKC inhibitor chelerythrine, respectively. The PKA inhibitor H-89 did not affect the SP effect. Remarkably, the inhibitory effect of SP on GABA-activated current was nearly completely removed by a selective PKCε inhibitor epilon-V1-2 but not by safingol and LY333531, selective inhibitors of PKCα and PKCβ. Our results suggest that NK1 receptor mediates SP-induced inhibition of GABA-activated current and membrane depolarization by activating intracellular PLC-Ca²⁺-PKCε cascade. SP might regulate the excitability of peripheral nociceptors through inhibition of the "pre-synaptic inhibition" evoked by GABA, which may explain its role in pain and neurogenic inflammation.

Similar effects of substance P on learning and memory function between hippocampus and striatal marginal division

Substance P is an endogenous neurokinin that is present in the central and peripheral nervous systems. The neuropeptide substance P and its high-affinity receptor neurokinin 1 receptor are known to play an important role in the central nervous system in inflammation, blood pressure, motor behavior and anxiety. The effects of substance P in the hippocampus and the marginal division of the striatum on memory remain poorly understood. Compared with the hippocampus as a control, immunofluorescence showed high expression of the substance P receptor, neurokinin 1, in the marginal division of the striatum of normal rats. Unilateral or bilateral injection of an antisense oligonucleotide against neurokinin 1 receptor mRNA in the rat hippocampus or marginal division of the striatum effectively reduced neurokinin 1 receptor expression. Independent of injection site, rats that received this antisense oligonucleotide showed obviously increased footshock times in a Y-maze test. These results indicate that the marginal division of the striatum plays a similar function in learning and memory to the hippocampus, which is a valuable addition to our mechanistic understanding of the learning and memory functions of the marginal division of the striatum.

Marked Effects of Tachykinin in Myositis Both in the Experimental Side and Contralaterally: Studies on NK-1 Receptor Expressions in an Animal Model

Muscle injury and inflammation (myositis) in a rabbit model of an unilateral muscle overuse were examined. It is unknown if the tachykinin system has a functional role in this situation. In this study, therefore, the neurokinin-1 receptor (NK-1R) expression patterns were evaluated. White blood cells, nerve fascicles, fine nerve fibers, and blood vessel walls in myositis areas showed NK-1R immunoreaction. NK-1R mRNA reactions were observable for white blood cells and blood vessel walls of these areas. NK-1R immunoreaction and NK-1R mRNA reactions were also seen for muscle fibers showing degenerative and regenerative features. There were almost no NK-1R immunoreactions in normal muscle tissue. Interestingly, marked NK-1R expressions were seen for myositis areas of both the experimental side and the contralateral nonexperimental side. EIA analyses showed that the concentration of substance P in the muscle tissue was clearly increased bilaterally at the experimental end stage, as compared to the situation for normal muscle tissue. These observations show that the tachykinin system is very much involved in the processes that occur in muscle injury/myositis. The effects can be related to proinflammatory effects and/or tissue repair. The fact that there are also marked NK-1R expressions contralaterally indicate that the tachykinin system has crossover effects.

Substance P antagonist CP-96345 blocks lung vascular leakage and inflammation more effectively than its stereoisomer CP-96344 in a mouse model of smoke inhalation and burn injury

The recently developed murine model of smoke inhalation and burn (SB) injury was used to study the effect of the substance-P antagonist CP96345. C57BL/6 mice were pre-treated with an i.v. dose of a specific NK-1 receptor antagonist, CP9635, or its inactive enantiomer, CP96344, (10 mg/Kg) 1 h prior to SB injury per protocol (n = 5). Mice were anesthetized and exposed to cooled cotton smoke, 2X 30 s, followed by a 40% total body surface area flame burn per protocol. At 48 h after SB injury Evans Blue (EB) dye and myeloperoxidase (MPO) were measured in lung after vascular perfusion. Lungs were also analyzed for hemoglobin (Hb) and wet/dry weight ratio. In the current study, CP96345 pre-treatment caused a significant decrease in wet/dry weight ratio (23%, p = 0.048), EB (31%, p = 0.047), Hb (46%, p = 0.002), and MPO (54%, p = 0.037) levels following SB injury compared to animals with SB injury alone. CP-96344 pre-treatment caused an insignificant decrease in wet/dry weight ratio (14%, p = 0.18), EB (16%, p = 0.134), Hb (9%, p = 0.39), and an insignificant increase in MPO (4%, p = 0.79) as compared to mice that received SB injury alone. As expected, levels of EB, Hb, MPO, and wet/dry weight ratios were all significantly (p < 0.05) increased 48 h following SB injury alone compared to respective sham animals. In conclusion, the current study indicates that pre-treatment with a specific NK-1R antagonist CP-96345 attenuates the lung injury and inflammation induced by SB injury in mice.

Substance P alters the in vitro LPS responsiveness of bovine monocytes and blood-derived macrophages

Neuromediators like substance P have a decisive influence on inflammatory processes via the neuroendocrine regulation circuit. The aim of the present study was therefore to evaluate the expression of the main substance P receptor NK-1R in cattle as well as the modulatory properties of substance P for bovine macrophages. The expression of NK-1R was detected in subsets of lymphocytes, granulocytes, monocytes and in vitro-generated macrophages (MdM). Stimulation of monocytes and MdM with lipopolysaccharide (LPS) for 3h did not alter the expression level of NK-1R. In vitro, the modulatory potential of substance P for monocytes and in vitro-generated blood-derived macrophages (MdM) was analysed. In MdM, generated in the presence of substance P, mRNA expression of chemokines, which are crucial for the attraction and activation of granulocytes and monocytes (CXCL8, CCL5) as well as the expression of IL-1beta, a classically pro-inflammatory cytokine were significantly elevated. After stimulation with LPS, MdM generated in the presence of substance P showed an elevated expression of CXCL8 and IL-1beta, while in SP-influenced monocytes only the expression of CCL5 was significantly upregulated after LPS stimulation. In addition, supernatants of MdM cultured in the presence of substance P induced neutrophil migration and inhibited both necrosis and apoptosis of neutrophil granulocytes. Thus, it has been shown that the modulation of the expression pattern of chemokines and cytokines in MdM by substance P has also functional relevance for the attraction and activation of other immune cells. In general, the modulation of sensor and effector functions by substance P suggests, that this neuromediator can alter the course of an inflammatory disease in cattle.

The involvement of substance P in the induction of aggressive behavior

Aggression is a complex social behavior that involves a similarly complex neurochemical background. The involvement of substance P (SP) and its potent tachykinin receptor (NK1) in the induction of both defensive rage and predatory attack appears to be a consistent finding. However, an overall understanding of the nature of the SP involvement in the induction of aggressive behavior has not yet been fully achieved. The aim of this review is to summarize and present the current knowledge with regards to the role of SP in the induction of aggressive behavior and to synopsize: (a) its biochemical profile, and (b) the exact anatomical circuits through which it mediates all types of aggressive behavior. Future studies should seriously consider the potential use of this knowledge in their quest for the treatment of mood and anxiety disorders.

Presence of substance P and the neurokinin-1 receptor in tenocytes of the human Achilles tendon

Nerve signal substances, such as the tachykinin substance P (SP), may be involved in the changes that occur in response to tendinopathy (tendinosis). It is previously known that the level of SP innervation within tendon tissue is limited, but results of experimental studies have suggested that SP may have stimulatory, angiogenetic and healing effects in injured tendons. Therefore, it would be of interest to know if there is a local SP-supply in tendon tissue. In the present study, the patterns of expression of SP and its preferred receptor, the neurokinin-1 receptor (NK-1 R), in normal and tendinosis human Achilles tendons were analyzed by use of both immunohistochemistry and in situ hybridization. We found that there was expression of SP mRNA in tenocytes, and that tenocytes showed expression of NK-1 R at protein as well as mRNA levels. The observations concerning both SP and NK-1 R were most evident for tenocytes in tendinosis tendons. Our findings suggest that SP is produced in tendinosis tendons, and furthermore that SP has marked effects on the tenocytes via the NK-1 R. It cannot be excluded that the SP effects are of importance concerning the processes of reorganization and healing that occur for tendon tissue in tendinosis. In conclusion, it appears as if SPergic autocrine/paracrine effects occur in tendon tissue during the processes of tendinosis, hitherto unknown effects for human tendons.

Pharmacological characterization of desensitization in scratching behavior induced by intrathecal administration of hemokinin-1 in the rat

Desensitization is induced by the repeated administration of high doses of substance P (SP) or hemokinin-1 (HK-1). However, little information is available about the mechanisms involved in the induction of desensitization by these peptides. Thus, to characterize this desensitization, we examined the dose-dependent effect of these peptides, the effect of pretreatment with neurokinin 1(NK1) receptor antagonists, and the effect of pretreatment with inhibitors of protein kinases such as protein kinase A (PKA), protein kinase C (PKC), calcium/calmodulin kinase II (CaMKII) and mitogen-activated protein kinase kinase (MEK). The number of scratchings induced by 10(-3)M SP or HK-1 decreased following pretreatment with 10(-11)-10(-3)M SP or HK-1 with a marked reduction at 10(-3) and 10(-6)M SP or HK-1. The effect of NK1 receptor antagonists on desensitization induced by pretreatment with 10(-6)M SP was marked, whereas there was little effect of pretreatment with these antagonists on 10(-6)M HK-1-induced desensitization. Additionally, 10(-6)M SP- and HK-1-induced desensitization was attenuated by pretreatment with PKA, PKC and MEK inhibitors, except a CaMKII inhibitor that inhibited SP-induced desensitization. These results indicate that the receptor and kinases involved in HK-1-induced desensitization are partially different from those of SP.

Tachykinin family genes and their receptors are differentially expressed in the hypothyroid ovary and pituitary

Plasma tachykinin levels are known to be altered with sexual acyclicity and loss of reproductive function. Ovulatory dysfunction, as seen in postmenopausal women, is also often encountered in hypothyroid patients. To know the involvement of different tachykinin genes in hypothyroidism-associated reproductive disorders, we performed DD-PCR with the pituitary RNA of control and hypothyroid rats to see the differentially expressed gene profile. Subsequently, we selected a few clones, tachykinin being one of them. Since its expression was up regulated in hypothyroidism as it does in the sexually acyclic females, we wanted to correlate these two phenomena with hypothyroidism associated reproductive disorders. We observed differential expression of tac2 along with other tk genes and their receptors in rat pituitary and ovary, which suggests that hypothyroidism affects the expression of these genes in these tissues. The experiments were repeated in ovarian tissue obtained at surgery from hypothyroid human patients, which showed similar expression pattern of TAC3 (equivalent to rat tac2) and their receptors as in rat ovary. Significant reduction of tac2 expression in reproductively less active rat ovary suggests the association of tac2 with reproductive senescence. Our results suggest that decline in reproductive function in hypothyroidism is associated with altered expression level of tac2 and its receptors. Further investigation in this area could elucidate the possible mechanism of tachykinins' involvement in loss of sexual cyclicity and other reproductive disorders associated with hypothyroidism.

Low-speed subcellular fractionation method for determining noxious stimulus-evoked spinal neurokinin-1 receptor internalization

Substance P release from nociceptive primary afferents activates post-synaptic neurokinin-1 (NK-1) receptors causing subsequent NK-1 receptor internalization. Fluorescent immunohistochemistry is typically used to quantify NK-1 receptor internalization, an indirect measure of substance P (SP) release. However, this technique entails several limitations that restrict its application. Using simple subcellular fractionation and immunoblotting methods, we demonstrate that intrathecal SP invokes a rapid and dose-dependent increase in dorsal horn cytoplasmic NK-1 receptors. We also show that hind paw compression and noxious thermal stimulation increase cytoplasmic NK-1 receptor, when compared to sham stimulations. Fluorescent immunohistochemistry confirmed that increases in cytoplasmic NK-1 corresponded with increased NK-1 receptor internalization. Herein, we report that low-speed centrifugation and Western immunoblotting provide NK-1 internalization results consistent with those obtained by more traditional methods. These data support previous findings demonstrating a role for spinal NK-1 receptors in nociceptive processing.

Neuropeptides as synaptic transmitters

Neuropeptides are small protein molecules (composed of 3-100 amino-acid residues) that have been localized to discrete cell populations of central and peripheral neurons. In most instances, they coexist with low-molecular-weight neurotransmitters within the same neurons. At the subcellular level, neuropeptides are selectively stored, singularly or more frequently in combinations, within large granular vesicles. Release occurs through mechanisms different from classical calcium-dependent exocytosis at the synaptic cleft, and thus they account for slow synaptic and/or non-synaptic communication in neurons. Neuropeptide co-storage and coexistence can be observed throughout the central nervous system and are responsible for a series of functional interactions that occur at both pre- and post-synaptic levels. Thus, the subcellular site(s) of storage and sorting mechanisms into different neuronal compartments are crucial to the mode of release and the function of neuropeptides as neuronal messengers.

Nuclear localization of SP, CGRP, and NK1R in a subpopulation of dorsal root ganglia subpopulation cells in rats

Signals generated by renal pelvic afferent nerves in response to stimulation are transmitted from peripheral processes of dorsal root ganglia neurons to their central terminals in the dorsal horn of the spinal cord to cause the release of neuropeptides, including SP and CGRP. All of the cellular activities of SP are considered to be mediated through interaction with NK(1)R located on the cell surface. We have investigated the colocalization and subcellular distribution of NK(1)R, SP, and CGRP in different subpopulations of neurons that innervate renal tissue. Our findings therefore provide the first evidence for the presence of NK(1)R, SP, and CGRP in the nuclei of DGR neural cells. The physiological significance of this localization remains unknown. One possibility is that pelvic sensory neurons may regulate their responses to different stimuli by modulating the ratio of CGRP and SP release and/or nuclear NK(1)R expression.

Upregulation of substance P receptor expression by calcitonin gene-related peptide, a possible cooperative action of two neuropeptides involved in airway inflammation

Airway hyperresponsiveness (AHR) is present in almost all patients with symptomatic asthma, yet its mechanism is not well understood. Airway inflammation is thought to be an important underlying mechanism involved in causing AHR. Recent studies indicate release of neuropeptides from C-fiber endings plays a pivotal role in airway inflammation. Substance P (SP) is a critical neurotransmitter of sensory C-fiber and a well-known effector of inflammatory response. However, roles of other neuropeptides and interaction among these neuropeptides in airway inflammation and AHR were largely unknown. Calcitonin gene-related peptide (CGRP), another intrapulmonary neuropeptide that functions as a potent vasodilator and neutrophils activator, is released from the same C-fiber ending as SP is released. By using an ozone-stressing animal model, previously we had demonstrated that CGRP might be involved in the development of AHR in rabbits. To extend the functional roles of SP, and to explore the possible interactive roles of SP and CGRP in airway inflammation, we examined expressions of SP, SP receptor (neurokinin 1, or NK-1R) and CGRP in vivo and ex vivo. We exposed guinea pigs at intervals to inhalation of ozone to induce airway inflammation. Animals were sacrificed at different time points; SP, SP receptor and CGRP expression were determined during the onset and progression of airway inflammation by radioimmunoassay, immunohistochemistry and in situ hybridization. Our data showed that after exposure to ozone, the concentration of SP in lung homogenate and the number of SP-immunoreactive cell bodies in lung slides increased within 24h, peaked on day 2, and then decreased slowly. Interestingly, CGRP expressions exhibited a similar temporal and spatial pattern, and there was a strong correlation between SP expression and CGRP expression, indicating a possible cooperative action of these two neuropeptides. We also noted an increased expression of SP receptor NK-1R in the development of airway inflammation. In order to test the hypothesis that CGRP as a coexisting neurotransmitter with SP can regulate the expression of NK-1R in the lung, and contribute to the SP-mediated inflammatory response, we used in vitro lung tissue culture to determine the effect of CGRP on NK-1R expression. We found that NK-1R expression was induced by CGRP incubation at both mRNA and protein levels, and the induction was attenuated by additions of the inhibitors of Protein Kinase A (PKA) pathway, Calmodulin-dependent Kinase pathway, and Tyrosine Protein Kinase pathway. In conclusion, our data provide compelling evidence that SP and CGRP are involved in the development of airway inflammation. The interaction between SP and CGRP is likely to contribute to the pathogenesis of AHR and other lung inflammatory diseases.

Relationships between neurokinin receptor-expressing interstitial cells of Cajal and tachykininergic nerves in the gut

The so-called interstitial cells of Cajal (ICC) are distributed throughout the muscle coat of the alimentary tract with characteristic intramural location and species-variations in structure and staining. Several ICC sub-types have been identified: ICC-DMP, ICC-MP, ICC-IM, ICC-SM. Gut motility is regulated by ICC and each sub-type is responsible for the electrical activities typical of each gut region and/or muscle layer. The interstitial position of the ICC between nerve endings and smooth muscle cells has been extensively considered. Some of these nerve endings contain tachykinins. Three distinct tachykinin receptors (NK1r, NK2r and NK3r) have been demonstrated by molecular biology. Each of them binds with different affinities to a series of tachykinins (SP, NKA and NKB). In the ileum, SP-immunoreactive (SP-IR) nerve fibers form a rich plexus at the deep muscular plexus (DMP), distributed around SP-negative cells, and ICC-DMP intensely express the SP-preferred receptor NK1r; conversely a faint NK1r-IR is detected on the ICC-MP and mainly after receptor internalization was induced by agonists. ICC-IM are never stained in laboratory mammals, while those of the human antrum are NK1r- IR. RT-PCR conducted on isolated ileal ICC-MP and gastric ICC-IM showed that these cells express NK1r and NK3r. Colonic ICC, except those in humans, do not express NK1r-IR, at least in resting conditions. Outside the gut, NK1r-IR cells were seen in the arterial wall and exocrine pancreas. In the mouse gut only, NK1r-IR is present in non-neuronal cells located within the intestinal villi, so-called myoid cells, which are c-kit-negative and alpha-smooth muscle actin-positive. Immunohistochemistry and functional studies confirmed that ICC receive input from SP-IR terminals, with differences between ICC sub-types. In the rat, very early after birth, NK1r is expressed by the ICC-DMP and SP by the related nerve varicosities. Studies on pathological conditions are few and those on mutant strains practically absent. It has only been reported that in the inflamed ileum of rats the NK1r-IR ICC-DMP disappear and that at the peak of inflammatory conditions ICC-MP are NK1r-IR. In the ileum of mice with a mutation in the W locus, ICC-DMP were seen to express c-kit-IR but not NK1-IR, and SP-IR innervation seems unchanged. In summary, there are distinct ICC populations, each of them under a different tachykininergic control and, likely, having different functions. Further studies are recommended at the aim of understanding ICC involvement in modulating/transmitting tachykininergic inputs.

Agents that act by different mechanisms modulate the activity of protein kinase CβII isozyme in the rat spinal cord during peripheral inflammation

Hyperalgesia following unilateral complete Freund's adjuvant-induced inflammation was characterized by paw withdrawal latency to thermal stimulus. Paw withdrawal latencies were significantly shorter on the complete Freund's adjuvant-treated paw than on the contralateral paw of the complete Freund's adjuvant- and the sham-treated rats. Total cytosolic protein kinase C activity in the lumbar enlargement was unchanged on the sides of the spinal cord ipsi- and contra-lateral to the inflamed paw. Membrane-associated activities of protein kinase Calpha, protein kinase CbetaI and protein kinase Cgamma did not change significantly on the sides of the cord ipsi- and contra-lateral to the inflammation. However, membrane-associated activity of protein kinase CbetaII was increased in the cord section ipsilateral to the inflammation, suggesting that increased translocation/activation of protein kinase CbetaII is related to thermal hyperalgesia. Dextrorphan (an N-methyl-D-aspartate receptor antagonist), L-703,606 (an NK-1 receptor antagonist) and an antisense oligodeoxynucleotide for a selective knockdown of protein kinase Cbeta, reduced complete Freund's adjuvant-induced hyperalgesia, and reversed significant changes in the membrane activity of protein kinase CbetaII on the spinal cord section ipsilateral to the inflamed paw. Dextrorphan and protein kinase Cbeta antisense oligodeoxynucleotide were effective in reversing complete Freund's adjuvant-induced increase in the activity of protein kinase CbetaII ipsilateral to the inflammation at all the doses tested, but L-703,606 was effective only at the highest dose. Furthermore, in the presence of inflammatory stimulus, dextrorphan and L-703,606 did not alter the activities of membrane-associated protein kinase Calpha, protein kinase CbetaI, and protein kinase Cgamma in the section of the spinal cord ipsi- and contra-lateral to the inflammation. Protein kinase Cbeta antisense oligodeoxynucleotide had no significant effect on the membrane-associated activities of protein kinase Calpha and protein kinase Cgamma, but decreased the activities of both protein kinase CbetaI and protein kinase CbetaII and the expression of protein kinase Cbeta isozyme in the spinal cord. The data provide evidence that a common molecular event that converges to initiate and maintain hyperalgesia may include the translocation and activation of protein kinase CbetaII in the spinal dorsal horn.

Regulation of neurokinin-1 receptor messenger RNA expression in synovial fibroblasts of patients with rheumatoid arthritis

We examined whether soluble mediators regulate the expression of tachykinin receptor mRNAs in synovial fibroblasts of patients with rheumatoid arthritis (RA). mRNAs encoding long and short isomers of neurokinin 1 receptor (NK1R), and neurokinin 2 receptor (NK2R) were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Level of long, but not the short, of NK1R mRNA was increased by treatment with 10-100 ng/ml basic fibroblast growth factor (bFGF) or 20 ng/ml tumor necrosis factor-alpha (TNF-alpha), but not with 1ng/ml interleukin 1beta (IL-1beta). TNF-alpha upregulated NK2R mRNA as well as long NK1R mRNA whereas bFGF had no effect on NK2R mRNA. Expression of neurokinin 3 receptor (NK3R) mRNA was not observed in RA fibroblasts, and its expression was not induced by bFGF and TNF-alpha. The basal and increased levels of long NK1R mRNA were inhibited by treatment with 20 microM SU5402, an inhibitor of the tyrosine kinase activity of FGF receptor 1 (FGFR1), or 10 ng/ml transforming growth factor-beta1 (TGF-beta1). SU5402 and TGF-beta1 had no effect on the basal level of short NK1R mRNA. Immunocytochemistry revealed the enhancement by bFGF of immunoreactive NK1Rs in the cells at 24 h after treatment. These results suggest that bFGF, TGF-beta1, and TNF-alpha in synovial tissue and fluid play a role in the regulation of long NK1R expression in synovial fibroblasts of RA patients. It appears that the pathway of downregulation by TGF-beta1 is more dominant in the long NK1R mRNA expression than that of upregulation by bFGF or TNF-alpha. Furthermore, the regulation of short NK1R mRNA expression seems to be performed via a different pathway from that of long isomer mRNA.

Vascular NK-1 receptor occurrence in normal and chronic painful Achilles and patellar tendons: studies on chemically unfixed as well as fixed specimens

It is not known as to whether the Achilles and patellar tendons contain neurokinin-1 (NK-1) receptors. This is a drawback when considering the fact that pain symptoms are frequent in these and as recent studies show that the pain symptoms might be cured via interference with blood vessel function. In the present study, the human Achilles and patellar tendons were examined concerning immunohistochemical expression of the NK-1 receptor. Chemically unfixed and fixed specimens, TRITC and PAP stainings and a battery of NK-1 receptor antibodies, including antibodies against the C-terminus and the N-terminal region, were utilized. NK-1 receptor immunoreaction could be detected in inner parts of the walls of large blood vessels and in the walls of small blood vessels. To some extent, NK-1 immunoreaction was also detectable in small nerve fascicles and in tenocytes. It was found to be of utmost importance to apply both chemically unfixed and fixed specimens. The use of chemically unfixed tissue was found advantageous in order to depict the immunoreactions in the blood vessel walls. The observations represent new findings and are of relevance as substance P (SP) is known to be of importance where neurogenic angiogenesis contributes to diseases and as SP on the whole has profound effects concerning blood vessel regulation.

Substance P and the neurokinin-1 receptor in relation to eosinophilia in ulcerative colitis

Substance P (SP) has been implicated in the pathophysiology of ulcerative colitis (UC) and it has been suggested that blocking of its effect would be advantageous in this disease. Eosinophils have also been implicated in the pathophysiology of UC. In the present study, specimens from the sigmoid colon of UC patients were investigated by the use of antisera against SP and the neurokinin-1 receptor (NK-1R) and staining for demonstration of eosinophils. The degrees of SP innervation and NK-1R immunoreaction, as well as the levels of eosinophil infiltration, varied between different patients. Interestingly, NK-1R immunoreaction in the epithelium was often seen to be the most marked where there were numerous eosinophils in the underlying mucosa and where the mucosa showed a marked morphologic derangement. The observations suggest that there are marked fluctuations in effects of SP and eosinophils during the disease. The infiltrating eosinophils may be involved in the destruction of the mucosal tissue. Furthermore, for the majority of cases where there is marked derangement of the mucosa, it is apparent that there is an upregulation of the NK-1 receptor in the epithelium in parallel with the infiltration of the eosinophils.

Multiple neurotransmitter receptors contribute to the spinal Fos expression

The aim of this study is to identify the receptors which could potentially mediate the activation of c-Fos. Therefore, the effects of neurotransmitter receptor agonists in the activation of c-Fos in spinal neurons were studied by intrathecal injection of excitatory amino acid (EAA) receptor agonists: N-Methyl-D-Aspartate (NMDA), (S)-alpha-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic acid (AMPA), 2-Carboxyl-3-carboxymethyl-4-isopropenylpyMidine (Kainic acid, KA), (1S-3R)-1-Aminocyclopentane-1, 3-dicarboxylacid (ACPD), and substance-P receptor (neurokinin-1) agonist, [Sar9, Met (O2)11] SP (SarMet-SP). All drugs tested activated the production of c-Fos in spinal dorsal horn neurons. AMPA was found as the most potent agonist tested producing market production of c-Fos particularly in neurons of lamina II at doses of 10 pM per 10-microl injection. At this dose, other agonists were relatively ineffective. At higher doses, AMPA significantly increased the activated cells. NMDA significantly increased c-Fos production to a marked extent only at doses above 10 nM per 10-microl injection. KA and ACPD were least potent of the excitatory amino acid agonists. Injection of SarMet-SP at doses of 1 nM activated Fos selectively in neurons of lamina I. A dose-dependent increase in number of c-Fos-positive cells was observed for AMPA, KA, ACPD, and SarMet-SP, whereas NMDA gave a very strong expression after a high dose with no dose dependency. These finding suggest that multiple neurotransmitter receptors lead to c-Fos production in spinal neurons.

Calcitonin gene-related peptide receptor activation produces PKA- and PKC-dependent mechanical hyperalgesia and central sensitization

Calcitonin gene-related peptide (CGRP), acting through CGRP receptors, produces behavioral signs of mechanical hyperalgesia in rats and sensitization of wide dynamic range (WDR) neurons in the spinal cord dorsal horn. Although involvement of CGRP receptors in central sensitization has been confirmed, the second-messenger systems activated by CGRP receptor stimulation and involved in pain transmission are not clear. This study tested whether the hyperalgesia and sensitizing effects of CGRP receptor activation on WDR neurons are mediated by protein kinase A or C (PKA or PKC) signaling. Intrathecal injection of CGRP in rats produced mechanical hyperalgesia, as shown by paw withdrawal threshold tests. CGRP-induced hyperalgesia was attenuated significantly by the CGRP1 receptor antagonist, CGRP8-37. The effect was also attenuated significantly by a PKA inhibitor (H89) or a PKC inhibitor (chelerythrine chloride). Electrophysiological experiments demonstrated that superfusion of the spinal cord with CGRP-induced sensitization of spinal dorsal horn neurons. The CGRP effect could be blocked by CGRP8-37. Either a PKA or PKC inhibitor (H89 or chelerythrine) also attenuated this effect of CGRP. These results are consistent with the hypothesis that CGRP produces hyperalgesia by a direct action on CGRP1 receptors in the spinal cord dorsal horn and suggest that the effects of CGRP are mediated by both PKA and PKC second-messenger pathways.

Morphological features, distribution and compartmental organization of the nicotinamide adenine dinucleotide phosphate reduced-diaphorase interneurons in the human striatum

Striatal nicotinamide adenine dinucleotide phosphate reduced-diaphorase (NADPH-d)-positive (+) cells are one of the major classes of striatal interneurons. The present study analyzes their somatodendritic morphology, distribution pattern, and compartmental organization in the caudate nucleus (CN) and putamen (Put) of nine normal human brains. The following striatal territories are examined: 1) the precommissural head of the CN; 2) the postcommissural head of the CN; 3) the body of the CN; 4) the gyrus of the CN; 5) the tail of the CN; 6) the precommissural Put; and 7) the postcommissural Put. Three morphologically distinct types of NADPH-d+ neurons were found in each of these territories. The two most common NADPH-d+ neurons displayed an ovoid or triangular perikaryon from which several thick primary dendrites emerged, although much less numerous, bipolar-shaped NADPH-d+ cells were also observed. The highest density of NADPH-d+ neurons was found in the gyrus of the CN, followed by the body of the CN, tail of the CN, postcommissural head of the CN, postcommissural Put, precommissural head of the CN, and precommissural Put. The matrix was the striatal compartment with the densest NADPH-d+ neuronal population. Some of these cells also occurred in the center and peripheral regions of the striosomes located in the head of the CN and in the Put. In the body and gyrus of the CN, the striosomes were largely devoid of these striatal interneurons. Knowledge of the density and distribution of these interneurons should advance our understanding of the organization of the normal human striatum and help to evaluate the effects of neurodegenerative processes on cell density.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Tissue-specific patterns of neurokinin-1 receptor (NK-1R) gene expression in mice exposed to sidestream cigarette smoke

Neurokinin-1 receptor (NK-1R), a high-affinity plasma membrane-bound receptor for neurokinin substance P, plays important roles in the onset of the pathophysiological responses. To test whether the transcript levels of gene encoding NK-1R in organs are affected by sidestream cigarette smoke (SSCS) exposure, the C57BL/6 mice were randomly assigned to five groups (six/group) in a study of the dose-effect relationship. The mice were exposed to 0 (filtered room air), 2, 4, 8 and 16 mg total particulate matter (TPM) of SSCS/exposure/day, respectively, for seven days through a nose-only exposure chamber (IN-TOX, Albuquerque, NM, USA). The levels of NK-1R mRNA in the lung, heart, liver, kidney and spleen tissues were detected by reverse transcription-polymerase chain reaction (RT-PCR) techniques and normalized against GAPDH expression. NK-1R mRNA in heart tissue showed SSCS-induced dose-dependent downregulation, with minimum expression at a dose of 8.0 mg TPM. Whereas, the levels of NK-1R mRNA in the liver were upregulated to 2.86 and 5.13-fold after exposure to 2.0 and 4.0 mg TPM of SSCS respectively, then returned to 4.19 and 3.93-fold at the exposure doses of 8.0 and 16.0 mg TPM, respectively, when compared to that of the control. In the kidney, SSCS exposure at a dose of 2.0 TPM, but not higher than that level, induced significant elevation of NK-1R mRNA expression. These findings suggest that there are the paracrine and/or autocrine signalling mechanisms through receptor-ligand interactions. No alteration of NK-1R gene expression was observed in the lungs and spleen tissues in this study. The tissue-specific patterns by which SSCS affect NK-1R gene expression in these organs may partially explain dissimilarity of NK-1R activation and the associated toxicity caused by environmental tobacco smoke.

GABAergic basal forebrain neurons that express receptor for neurokinin B and send axons to the cerebral cortex

Neurons expressing neurokinin B (NK3) receptor in the basal forebrain region of rats were characterized histochemically by combining immunocytochemistry, in situ hybridization and retrograde labeling, and electrophysiologically by whole-cell clamp recording. NK3 receptor-immunoreactive neurons were found in the basal forebrain region including the substantia innominata, where axon terminals immunoreactive for preprotachykinin B, the precursor peptide of neurokinin B (NKB), were densely distributed. More than 90% of NK3 receptor-expressing neurons in the basal forebrain region showed signals for glutamate decarboxylase mRNA, indicating that almost all NK3 receptor-expressing neurons were gamma-aminobutyric acid (GABA)ergic neurons. On the other hand, only a few NK3 receptor-immunoreactive neurons showed immunoreactivity for choline acetyltransferase or parvalbumin in the substantia innominata, ventral pallidum, and globus pallidus, although the distribution of NK3 receptor-expressing neurons overlapped with those of cholinergic neurons and parvalbumin-positive neurons. After injection of wheat germ agglutinin into the cerebral cortex, NK3 receptor immunoreactivity was detected in about 25% of retrogradely labeled basal forebrain neurons, indicating that NK3 receptor-expressing neurons send projection fibers to the cerebral cortex. In the whole-cell clamp recording study, a selective NK3 receptor agonist evoked membrane depolarization or inward currents with decrease of input impedance in 10 of 100 cortically projecting neurons recorded in the basal forebrain region. Because NKB-producing striatal neurons send axons selectively to the basal forebrain region, the present results suggest that the release of NKB by those striatal neurons induces an inhibitory effect on cortical neurons via facilitation of GABAergic basal forebrain neurons expressing NK3 receptor.

Neurokinin 1-receptors and sensory neuropeptides in tendon insertions at the medial and lateral epicondyles of the humerus. Studies on tennis elbow and medial epicondylalgia

There is no information on the sensory innervation at the flexor muscle origin at the medial epicondyle of the humerus and it is not known if substance P receptors (Neurokinin 1-receptors, NK1-R) are present in tendon insertions in general. In the present investigation, we have studied the muscle origin in patients suffering from medial epicondylalgia and tennis elbow. Immunohistochemistry and antibodies to substance P (SP) and CGRP as well as the general nerve marker PGP 9.5 were used. Specific immunoreactions were observed in nerve bundles and as free nerve fibers. The immunoreactive structures were partly seen in association with some of the blood vessels. The observations constitute a morphological correlate for the occurrence of nerve mediated effects in this region. By using immunohistochemistry and antibodies to NK1-R, the distribution of this receptor was studied at the insertion of the proximal tendon of the extensor carpi radialis brevis muscle at the lateral epicondyle. Specific immunoreactions were seen as varicose fibers occurring as single fibers or grouped into bundles, indicating that SP has effects in the nerves in this region. The results give further evidence for a possible neurogenic involvement in the pathophysiology of tennis elbow and in medial epicondylalgia.

Expression of functional neurokinin-1 receptors in regenerative glands during gastric wound healing in rodents

BACKGROUND & AIMS

Although functions of the neurokinin-1 receptor have been well explored in neurogenic inflammation and immunoinflammatory responses, little is known about neurokinin-1 receptors during gastric wound healing. The aim of this study was to assess whether neurokinin-1 receptors play a role in gastric wound healing.

METHODS

In vitro neurokinin-1 receptor autoradiography and immunohistochemistry were performed to identify, locate, and quantify neurokinin-1 receptors during wound healing in rodents with cryoulcers in the gastric corpus and antrum. Moreover, to assess the functionality of these receptors, the effect of the neurokinin-1 receptor antagonist NKP608 on gastric wound healing was quantified in vivo in wild-type and cyclooxygenase-2(-/-) mice.

RESULTS

Regenerative glands of the mucosal ulcer margin of rat cryoulcers of the gastric corpus showed strong expression of neurokinin-1 receptors in binding studies between days 3 and 22, with little expression on days 29-84. In addition, strong immunoreactivity for neurokinin-1 receptors was detected on the cell membrane of these regenerative glands. Expression of neurokinin-1 receptors in regenerative glands was confirmed in the rat antrum and the mouse gastric corpus. Moreover, in vivo functional tests during gastric ulcer healing showed that cell proliferation in the regenerative epithelia of the ulcer margin was significantly decreased by NKP608 compared with placebo; furthermore, gastric ulcer healing was significantly delayed by NKP608 both in wild-type and cyclooxygenase-2(-/-) mice.

CONCLUSIONS

This report shows the time-limited overexpression of neurokinin-1 receptors in the mucosal repair tissue of the corpus and antrum. Our in vitro and in vivo data suggest that neurokinin-1 receptors are involved in gastric wound healing.

Demonstration of the efficacy and safety of a novel substance P (NK1) receptor antagonist in major depression

The efficacy and safety of a selective NK(1) antagonist, L-759274, was investigated in outpatients with diagnosis of major depressive disorder with melancholic features, following evidence obtained with the novel compound aprepitant that Substance P (NK(1)) antagonists may provide a unique mechanism of antidepressant activity. A randomized, double-blind placebo-controlled study was carried out. Patients, male or female, aged 18-60, scoring >/=25 points on total of first 17 items of 21-item Hamilton Depression Scale (HAMD), and scoring >/=4 (moderately ill) on Clinical Global Impressions-Severity Scale were randomized to oral L-759274 40 mg daily (n=66) or placebo (n=62) for 6 weeks. For patients receiving L-759274, improvement (mean decrease from baseline) in HAMD-17 total score was 10.7 points, compared with a mean 7.8 point improvement in patients receiving placebo (p<0.009). Mean scores for item 1 of HAMD-17 (depressed mood) also improved to a greater extent in the active group compared with the placebo group (0.3 points, p<0.058). Compared with placebo, mean scores on Clinical Global Impressions-Improvement Scale improved significantly by the end of the trial (p=0.009). L-759274 was generally safe and well-tolerated. The incidence of sexual side effects was on par with that observed in patients receiving placebo, and the incidences of gastrointestinal effects were low. Antidepressant actions have now been observed with two different highly selective NK(1) antagonists (aprepitant and L-759274). NK(1) antagonism is a replicated and generally well-tolerated antidepressant mechanism.

Similarities of SP-, NKA- and NKB-induced currents in rat dorsal root ganglion neurons

Tachykinin (TK; including substance P (SP), neurokinin A (NKA) and neurokinin B (NKB))-induced currents (I(TK)s) were studied in freshly isolated rat dorsal root ganglion (DRG) neurons using whole-cell patch clamp recording and repatch techniques. All the three I(TK)s manifested features of fast activating kinetics, such as short latency and fast tau(on) and tau(off), and very slow desensitization. The concentration-response relationships for TKs show: (1). compared with the concentration-response curve for NKA, the curve for NKB shifted upwards, while that for SP shifted downwards; (2). the EC(50) values for NKB-, NKA- and SP-activated currents were very close to each other. The I-V curves for the three TKs were basically linear and arrayed in the order of NKB>NKA>SP; the reversal potentials for the three I(TK)s were all around +15 mV. Replacement of NaCl in the external solution by equimolar N-methyl-D-glucamine (NMDG) attenuated both NKA- and NKB-activated currents markedly, as it was the case with SP-activated current caused by the opening of Na(+) preferring non-selective cation channels observed in our previous work. All the three TKs proved to inhibit coexistent GABA(A) receptor-mediated current (I(GABA)); this effect was removed by intracellular dialysis of GDP-beta-S or H-7. However, these drugs did not block the SP-, NKA- and NKB-activated currents at all, which indicated that I(TK)s were G-protein independent. In short, the responses of rat DRG neurons to SP, NKA and NKB were similar in essence, although the amplitudes of currents induced by the same concentration of the three TKs were different. Taking the results of this study and our previous studies together, we hypothesized that SP, NKA and NKB may induce inward currents through undiscovered channels that are associated with tachykinins receptors (NK1R, NK2R, NK3R, which have already been cloned), but independent of G-protein coupling and remains to be further investigated.

Stress-induced increase of cortical dopamine metabolism: attenuation by a tachykinin NK1 receptor antagonist

The present study examined the potential role of tachykinin NK1 receptors in modulating immobilisation stress-induced increase of dopamine metabolism in rat medial prefrontal cortex. In agreement with previous studies, 20 min immobilisation stress significantly increased medial prefrontal cortex dopamine metabolism as reflected by the concentration of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC). Pretreatment with the high affinity, selective, tachykinin NK1 receptor antagonist (3(S)-(2-methoxy-5-(5-trifluoromethyltetrazol-1-yl)-phenylmethyl amino)-2(S)-phenylpiperidine) ((S)-GR205171, 10 mg/kg, s.c.), a dose that in ex vivo binding studies extensively occupied rat brain tachykinin NK1 receptors for approximately 60 min, significantly attenuated the stress-induced increase of mesocortical DOPAC concentration without affecting cortical DOPAC levels per se. In contrast, pretreatment of animals with the less active enantiomer (R)-GR205171 (10 mg/kg, s.c.), which demonstrated negligible tachykinin NK1 receptor occupancy ex vivo, failed to affect either basal or stress-induced DOPAC concentration in medial prefrontal cortex. Furthermore, pretreatment of animals with the benzodiazepine/GABAA receptor antagonist, flumazenil (15 mg/kg, i.p.), did not affect the ability of (S)-GR205171 to attenuate the increase of medial prefrontal cortex DOPAC concentration by acute stress. Results demonstrate that the selective tachykinin NK1 receptor antagonist, (S)-GR205171, attenuated the stress-induced activation of mesocortical dopamine neurones by a mechanism independent of the benzodiazepine modulatory site of the GABAA receptor.

Neurokinin 1 receptor and relative abundance of the short and long isoforms in the human brain

Substance P exerts its various biochemical effects mainly via interactions through neurokinin-1 receptors (NK1). Recently, the NK1 receptor has attracted considerable interest for its possible role in a variety of psychiatric disorders including depression and anxiety. However, little is known regarding the anatomical distribution of NK1 in the human central nervous system (CNS). Riboprobe in situ hybridization, quantitative PCR and in vitro autoradiography were performed. Highest NK1 mRNA levels were localized in the locus coeruleus and ventral striatum, while moderate hybridization signals were observed in the cerebral cortex (most abundant in the visual cortex), hippocampus and different amygdaloid nuclei. Very low levels of the NK1 mRNA were detected in the cerebellum and thalamus. In view of the existence of a long and short isoform of the NK1 receptor, it was of interest to assess whether there was a differential distribution of the two splice variants in the human CNS and peripheral tissues. A quantitative TaqMan PCR analysis showed that the long NK1 isoform was the most prevalent throughout the human brain, while in peripheral tissues the truncated form was the most represented. 3H-Substance P autoradiography revealed a good correlation between receptor binding sites and NK1 mRNA expression throughout the brain, with the highest levels of binding in the locus coeruleus. These results provide the anatomical evidence that the NK1 receptors have a strong association with neuronal systems relevant to mood regulation and stress in the human brain, but do not suggest a region-specific role of the two isoforms in the CNS.

Neurokinin-1 receptor antagonists CP-96,345 and L-733,060 protect mice from cytokine-mediated liver injury

Previously, we have shown that primary afferent sensory neurons are necessary for disease activity in T cell-mediated immune hepatitis in mice. In the present study, we analyzed the possible role of substance P (SP), an important proinflammatory neuropeptide of these nerve fibers, in an in vivo mouse model of liver inflammation. Liver injury was induced by bacterial lipopolysaccharide (LPS) in D-galactosamine (GalN)-sensitized mice. Depletion of primary afferent nerve fibers by neonatal capsaicin treatment down-regulated circulating levels of the proinflammatory cytokines tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) and protected mice from GalN/LPS-induced liver injury. Likewise, pretreatment of mice with antagonists of the SP-specific neurokinin-1 receptor (NK-1R), i.e., (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-azabicyclo(2.2.2.)-octan-3-amine (CP-96,345) and (2S,3S)3-([3,5-bis(trifluoromethyl)phenyl]methoxy)-2-phenylpiperidine (L-733,060), dose dependently protected mice from GalN/LPS-induced liver injury. The presence of the NK-1R in the murine liver was demonstrated by reverse transcription-polymerase chain reaction, sequence analysis, and immunocytochemistry. NK-1R blockade reduced inflammatory liver damage, i.e., edema formation, neutrophil infiltration, hepatocyte apoptosis, and necrosis. To get further insight into the mechanism by which receptor blockade attenuated GalN/LPS-induced liver damage, we analyzed plasma levels and intrahepatic expression of TNFalpha, IFNgamma, interleukin (IL)-6, and IL-10. NK-1R blockade clearly inhibited GalN/LPS-induced production of TNFalpha and IFNgamma, whereas synthesis of the hepatoprotective cytokines IL-6 and IL-10 was increased. NK-1 receptor antagonists might be potent drugs for treatment of inflammatory liver disease, most likely by inhibiting SP effects.

Intrathecal histamine induces spinally mediated behavioral responses through tachykinin NK1 receptors

Intrathecal injection of histamine elicited a behavioral response consisting of scratching, biting and licking in conscious mice. Here, we have examined the involvement of substance P (SP) by using intrathecal injection of tachykinin neurokinin (NK)(1) receptor antagonists and SP antiserum. Histamine-induced behavioral response was evoked significantly 5-10 min after intrathecal injection and reached a maximum at 10-15 min. Dose-dependency of the induced response showed a bell-shaped pattern from 200 to 3200 pmol, and maximum effect was observed at 800-1000 pmol. The H(1) receptor antagonist, d-chlorpheniramine and pyrilamine but not the H(2) receptor antagonists, ranitidine and zolantidine, inhibited histamine-induced behavioral response. The NK(1) receptor antagonists, CP-99,994, RP-67580 and sendide, inhibited histamine-induced behavioral response in a dose-dependent manner. A significant antagonistic effect of [D-Phe(7), D-His(9)]SP (6-11), a selective antagonist for SP receptors, was observed against histamine-induced response. The NK(2) receptor antagonist, MEN-10376, had no effect on the response elicited by histamine. Pretreatment with SP antiserum resulted in a significant reduction of the response to histamine. No significant reduction of histamine-induced response was detected in mice pretreated with NK A antiserum. The present results suggest that elicitation of scratching, biting and licking behavior induced by intrathecal injection of histamine may be largely mediated by NK(1) receptors via H(1) receptors in the spinal cord.

Costorage and coexistence of neuropeptides in the mammalian CNS

The term neuropeptides commonly refers to a relatively large number of biologically active molecules that have been localized to discrete cell populations of central and peripheral neurons. I review here the most important histological and functional findings on neuropeptide distribution in the central nervous system (CNS), in relation to their role in the exchange of information between the nerve cells. Under this perspective, peptide costorage (presence of two or more peptides within the same subcellular compartment) and coexistence (concurrent presence of peptides and other messenger molecules within single nerve cells) are discussed in detail. In particular, the subcellular site(s) of storage and sorting mechanisms within neurons are thoroughly examined in the view of the mode of release and action of neuropeptides as neuronal messengers. Moreover, the relationship of neuropeptides and other molecules implicated in neural transmission is discussed in functional terms, also referring to the interactions with novel unconventional transmitters and trophic factors. Finally, a brief account is given on the presence of neuropeptides in glial cells.

ERK MAP kinase activation in superficial spinal cord neurons induces prodynorphin and NK-1 upregulation and contributes to persistent inflammatory pain hypersensitivity

Activation of ERK (extracellular signal-regulated kinase) MAP (mitogen-activated protein) kinase in dorsal horn neurons of the spinal cord by peripheral noxious stimulation contributes to short-term pain hypersensitivity. We investigated ERK activation by peripheral inflammation and its involvement in regulating gene expression in the spinal cord and in contributing to inflammatory pain hypersensitivity. Injection of complete Freund's adjuvant (CFA) into a hindpaw produced a persistent inflammation and a sustained ERK activation in neurons in the superficial layers (laminae I-IIo) of the dorsal horn. CFA also induced an upregulation of prodynorphin and neurokinin-1 (NK-1) in dorsal horn neurons, which was suppressed by intrathecal delivery of the MEK (MAP kinase kinase) inhibitor U0126. CFA-induced phospho-ERK primarily colocalized with prodynorphin and NK-1 in superficial dorsal horn neurons. Although intrathecal injection of U0126 did not affect basal pain sensitivity, it did attenuate both the establishment and maintenance of persistent inflammatory heat and mechanical hypersensitivity. Activation of the ERK pathway in a subset of nociceptive spinal neurons contributes, therefore, to persistent pain hypersensitivity, possibly via transcriptional regulation of genes, such as prodynorphin and NK-1.

Possible involvement of tachykinin NK(1) and NMDA receptors in histamine-induced hyperalgesia in mice

Intrathecal (i.t.) injection of histamine elicited a significant hyperalgesic response as assayed by the tail-flick test. This hyperalgesic effect peaked at 15 min following i.t. administration of histamine (800 pmol) and returned to control level with 30 min. Hyperalgesia produced by histamine was inhibited dose-dependently by i.t. co-administration of the histamine H(1) receptor antagonist, d-chlorpheniramine, but not the histamine H(2) receptor antagonist, ranitidine. The tachykinin NK(1) receptor antagonists, (+)-[(2S,3S)-3-(2-methoxy-benzyl-amino)-2-phenylpiperidine] (CP-99,994), and [Tyr(6), D-Phe(7), D-His(9)]substance P-(6-11) (sendide), inhibited histamine-induced hyperalgesic response in a dose-dependent manner. A significant antagonistic effect of [D-Phe(7), D-His(9)]substance P-(6-11), a selective antagonist for substance P receptors, was observed against histamine-induced hyperalgesic response. The tachykinin NK(2) receptor antagonist, Asp-Tyr-D-Trp-Val-D-Trp-D-Trp-Lys-NH(2) (MEN-10,376), had no effect on hyperalgesia elicited by histamine. The competitive N-methyl-D-aspartate (NMDA) receptor antagonists, and D-(-)-2-amino-5-phosphonovaleric acid (D-APV), (+/-)-3-(2-carboxypiperazin-yl)propyl-1-phosphoric acid (CPP), the noncompetitive NMDA receptor antagonist dizocilpine (MK-801), and L-N(G)-nitro arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, markedly inhibited histamine-induced hyperalgesic response. The present results suggest that hyperalgesic response induced by i.t. injection of histamine may be mediated by tachykinin NK(1) receptors, but not NK(2) receptors in the spinal cord. In addition, spinal NMDA receptor-NO system may also contribute to elicitation of hyperalgesia following i.t. injection of histamine.

Changes in the expression of tachykinin receptors in the rat uterus during the course of pregnancy

In the mammalian female reproductive tract, tachykinin neuropeptides, such as substance P (SP), are localized to a population of sensory fibers and their precise physiological role is still unknown. The aim of the present study was to characterize the population of tachykinin receptors in the pregnant rat uterus and to assess their regulation during the course of pregnancy and after delivery. The expression of the tachykinin NK(1) receptor (NK(1)R), the tachykinin NK(2) receptor (NK(2)R), and the tachykinin NK(3) receptor (NK(3)R) in uteri from rats at different stages of pregnancy and on Day 1 postpartum was investigated by using a semiquantitative reverse transcription-polymerase chain reaction. The contractile effect of tachykinin receptor agonists acting selectively on the NK(1)R, the NK(2)R, or the NK(3)R was investigated by conventional organ bath techniques. Serum levels of estrogen and progesterone were measured by RIA. Our data show that the expression and function of NK(1)R and NK(3)R varied along the course of pregnancy and at postpartum. Uterine NK(2)R mRNA levels remain stable during the course of pregnancy and at Day 1 postpartum; and the contractions elicited by activating selectively the NK(2) receptor in the presence of the neutral endopeptidase inhibitor phosphoramidon (1 microM) were similar in early, mid, or late pregnancy. These results show that the expression and function of tachykinin receptors within the uterus vary with reproductive state and length of gestation, supporting a role for tachykinins in pregnancy and/or parturition in the rat.

Neurokinin(1) receptor antagonists as potential antidepressants

Selective, nonpeptide antagonists for tachykinin receptors first became available ten years ago. Of the three known tachykinin receptors, drug development has focused most intensively on the substance P-preferring receptor, neurokinin(1) (NK(1)). Although originally studied as potential analgesic compounds, recent evidence suggests that NK(1) receptor antagonists may possess antidepressant and anxiolytic properties. If confirmed by further controlled clinical studies, this will represent a mechanism of action distinct from all existing antidepressant agents. As reviewed in this chapter, the existing preclinical and clinical literature is suggestive of, but not conclusive, concerning a role of substance P and NK(1) receptors in the pathophysiology of depression and/or anxiety disorders. The ongoing clinical trials with NK(1) receptor antagonists have served as an impetus for much needed, basic research in this field.

Evidence for spatial proximity of two distinct receptor regions in the substance P (SP)*neurokinin-1 receptor (NK-1R) complex obtained by photolabeling the NK-1R with p-benzoylphenylalanine3-SP

Substance P (SP) belongs to the tachykinin family of bioactive peptides and exerts its many biological effects through functional interaction with its cell-surface, G protein-coupled neurokinin-1 receptor (NK-1R). Previous studies from our laboratory have shown that (125)I-Bolton-Hunter reagent-labeled p-benzoylphenylalanine(8)-SP (Bpa(8)SP) covalently attaches to Met(181), whereas (125)I-Bolton-Hunter reagent-labeled Bpa(4)SP covalently attaches to Met(174), both of which are located on the second extracellular loop (EC2) of the NK-1R. In this study, evidence has been obtained that at equilibrium, the photoreactive SP analogue (125)I-[D-Tyr(0)]Bpa(3)SP covalently labels residues in two distinct extracellular regions of the NK-1R. One site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on EC2 within a segment of the receptor extending from residues 173 to 177; a second site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on the extracellular N terminus within a segment of the receptor extending from residues 11 to 21, a sequence that contains both potential sites for N-linked glycosylation. Since competition binding data presented in this study do not suggest the existence of multiple peptide.NK-1R complexes, it is reasonable to assume that the receptor sequences within EC2 and N terminus identified by peptide mapping are in close proximity in the equilibrium complex.

Expression of tachykinin NK2 receptor mRNA in human brain

Tachykinin NK2 receptors have been suggested to play an important role in the central nervous system. This study, using reverse transcription-polymerase chain reaction revealed a detectable expression of NK2 receptor mRNA in various human brain regions, including the caudate nucleus, the putamen, the hippocampus, the substantia nigra and the cerebral cortex. The distribution of NK2 receptor expression in the cortex revealed a major expression in frontal and temporal cortex compared to occipital and parietal areas. These results provide a molecular basis for considering a role of NK2 receptors in human pathophysiology.

The common C-terminal sequences of substance P and neurokinin A contact the same region of the NK-1 receptor

Although neurokinin A (NKA), a tachykinin peptide with sequence homology to substance P (SP), is a weak competitor of radiolabeled SP binding to the NK-1 receptor (NK-1R), more recent direct binding studies using radiolabeled NKA have demonstrated an unexpected high-affinity interaction with this receptor. To document the site of interaction between NKA and the NK-1R, we have used a photoreactive analogue of NKA containing p-benzoyl-L-phenylalanine (Bpa) substituted in position 7 of the peptide. Peptide mapping studies of the receptor photolabeled by (125)I-iodohistidyl(1)-Bpa(7)NKA have established that the site of photoinsertion is located within a segment of the receptor extending from residues 178 to 190 (VVCMIEWPEHPNR). We have previously shown that (125)I-BH-Bpa(8)SP, a photoreactive analogue of SP, covalently attaches to M(181) within this same receptor sequence. Importantly, both of these peptides ((125)I-iodohistidyl(1)-Bpa(7)NKA and (125)I-BH-Bpa(8)SP) have the photoreactive amino acid in an equivalent position within the conserved tachykinin carboxyl-terminal tail. In this report, we also show that site-directed mutagenesis of M(181) to A(181) in the NK-1R results in a complete loss of photolabeling of both peptides to this receptor site, indicating that the equivalent position of SP and NKA, when bound to the NK-1R, contact the same residue.

Substance P (neurokinin-1) and neurokinin A (neurokinin-2) receptor gene and protein expression in the healthy and inflamed human intestine

Increasing evidence suggests that tachykinins are involved in the control of pathophysiological states, such as inflammation. The precise localization of tachykinin receptors is of paramount importance in the search for their possible physiological and pathological role; in this study, therefore, we attempted to define cellular sites of substance P (NK-1R) and neurokinin A (NK-2R) receptor expression in the healthy and the inflamed human intestine by in situ hybridization and immunohistochemistry. In the normal ileum and colon, NK-1R and NK-2R were localized to smooth muscle cells of the muscularis mucosae and propria and a few inflammatory cells of the lamina propria; NK-1R expression was also found in the muscular wall of submucosal blood vessels, enteric neurons and, to a lesser degree, in surface epithelial cells. Patients with Crohn's disease and ulcerative colitis showed a dramatic increase in NK-1R density relative to controls, in both the inflamed and the uninvolved mucosa. Up-regulation of NK-1R was particularly evident on epithelial cells lining the mucosal surface and crypts, as well as on endothelial cells of capillaries and venules. Also, a marked increase in NK-2R expression was found in both groups of patients on inflammatory cells of the lamina propria, especially eosinophils. Our findings demonstrate that in the normal human intestine NK-1R and NK-2R are expressed in multiple cell types, which are endowed with different physiological functions; in addition, they demonstrate that both NK-1R and NK-2R are up-regulated in patients with Crohn's disease and ulcerative colitis. Taken together, these observations may have important physiological and pathophysiological implications, and provide the rationale for the use of NK-1R and NK-2R antagonists in the treatment of inflammatory bowel disease.

Morphological change of substance P receptor immunoreactive dendrites of preganglionic sympathetic neurons

Substance P (SP)-containing terminals and SP receptors (SPRs) are found on the dendrites of preganglionic sympathetic neurons (PSNs) in the intermedio-lateral nucleus (IML) of the spinal cord. The SP-containing fibers were thought to be of supraspinal origin. However, the primary sensory nerve fibers terminated around PSNs, and some of them directly on PSNs. We observed approximately 150 SPR-immunoreactive (ir) varicosities on the dendrites of PSNs in slices of the first thoracic segment (T1) in control rats. The number of varicosities decreased to 41% 14 days after hemisection of the spinal cord at the fourth cervical segment (C4), and to 55% 14 days after sectioning the spinal dorsal roots at the C8 and T1 levels. The number of varicosities decreased by 33% in 8-week-old rats which had been administered capsaicin subcutaneously within 24 hours after birth to eradicate unmyelinated sensory fibers. However, varicosities increased by 15% 15 minutes after injection of capsaicin into the plantar surface of the front paw to stimulate somatosensory nerve fibers in adult rats. The results demonstrate that SPR-ir varicosities on the dendrites of PSNs were modulated not only by the supraspinal nervous system but also directly by the primary sensory nerve terminals.