Neurokinin-1 receptor activation is sufficient to restore the hypercapnic ventilatory response in the Substance P-deficient naked mole-rat.

Naked mole-rats (NMRs) live in large colonies within densely populated underground burrows. Their collective respiration generates significant metabolic carbon dioxide (CO2) that diffuses slowly out of the burrow network, creating a hypercapnic environment. Currently, the physiological mechanisms that underlie the ability of NMRs to tolerate environmental hypercapnia are largely unknown. To address this, we used whole-body plethysmography and respirometry to elucidate the hypercapnic ventilatory and metabolic responses of awake, freely behaving NMRs to 0%-10% CO2. We found that NMRs have a blunted hypercapnic ventilatory response (HCVR): ventilation increased only in 10% CO2. Conversely, metabolism was unaffected by hypercapnia. NMRs are insensitive to cutaneous acid-based pain caused by modified substance P (SP)-mediated peripheral neurotransmission, and SP is also an important neuromodulator of ventilation. Therefore, we re-evaluated physiological responses to hypercapnia in NMRs after an intraperitoneal injection of exogenous substance P (2 mg/kg) or a long-lived isoform of substance P {[pGlu5-MePhe8-MeGly9]SP(5-11), DiMe-C7; 40-400 µg/kg}. We found that both drugs restored hypercapnia sensitivity and unmasked an HCVR in animals breathing 2%-10% CO2. Taken together, our findings indicate that NMRs are remarkably tolerant of hypercapnic environments and have a blunted HCVR; however, the signaling network architecture required for a "normal" HCVR is retained but endogenously inactive. This muting of chemosensitivity likely suits the ecophysiology of this species, which presumably experiences hypercapnia regularly in their underground niche.

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

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

Facilitated spinal neuropeptide signaling and upregulated inflammatory mediator expression contribute to postfracture nociceptive sensitization.

Tibia fracture induces exaggerated substance P (SP) and calcitonin gene-related peptide (CGRP) signaling and neuropeptide-dependent nociceptive and inflammatory changes in the hind limbs of rats similar to those seen in complex regional pain syndrome. Inflammatory changes in the spinal cord contribute to nociceptive sensitization in a variety of animal pain models. This study tested the hypothesis that fracture-induced exaggerated neuropeptide signaling upregulates spinal inflammatory mediator expression, leading to postfracture hind limb nociceptive sensitization. At 4 weeks after performing tibia fracture and casting in rats, we measured hind limb allodynia, unweighting, warmth, edema, and spinal cord neuropeptide and inflammatory mediator content. The antinociceptive effects of intrathecally injected neuropeptide and inflammatory mediator receptor antagonists were evaluated in fracture rats. Transgenic fracture mice lacking SP or the CGRP RAMP1 receptor were used to determine the effects of neuropeptide signaling on postfracture pain behavior and spinal inflammatory mediator expression. Hind limb allodynia, unweighting, warmth, edema, increased spinal SP and CGRP, and increased spinal inflammatory mediator expression (TNF, IL-1, IL-6, CCL2, and nerve growth factor) were observed at 4 weeks after fracture in rats. Fracture-induced increases in spinal inflammatory mediators were not observed in fracture mice lacking SP or the CGRP receptor, and these mice had attenuated postfracture nociceptive sensitization. Intrathecal injection of selective receptor antagonists for SP, CGRP, TNF, IL-1, IL-6, CCL2, or nerve growth factor each reduced pain behaviors in the fracture rats. Collectively, these data support the hypothesis that facilitated spinal neuropeptide signaling upregulates the expression of spinal inflammatory mediators contributing to nociceptive sensitization in a rodent fracture model of complex regional pain syndrome.

Absence of substance P and the sympathetic nervous system impact on bone structure and chondrocyte differentiation in an adult model of endochondral ossification.

OBJECTIVE: Sensory and sympathetic nerve fibers (SNF) innervate bone and epiphyseal growth plate. The role of neuronal signals for proper endochondral ossification during skeletal growth is mostly unknown. Here, we investigated the impact of the absence of sensory neurotransmitter substance P (SP) and the removal of SNF on callus differentiation, a model for endochondral ossification in adult animals, and on bone formation. METHODS: In order to generate callus, tibia fractures were set in the left hind leg of wild type (WT), tachykinin 1-deficient (Tac1-/-) mice (no SP) and animals without SNF. Locomotion was tested in healthy animals and touch sensibility was determined early after fracture. Callus tissue was prepared for immunofluorescence staining for SP, neurokinin1-receptor (NK1R), tyrosine-hydroxylase (TH) and adrenergic receptors α1, α2 and ß2. At the fracture site, osteoclasts were stained for TRAP, osteoblasts were stained for RUNX2, and histomorphometric analysis of callus tissue composition was performed. Primary murine bone marrow derived macrophages (BMM), osteoclasts, and osteoblasts were tested for differentiation, activity, proliferation and apoptosis in vitro. Femoral fractures were set in the left hind leg of all the three groups for mechanical testing and µCT-analysis. RESULTS: Callus cells stained positive for SP, NK1R, α1d- and α2b adrenoceptors and remained ß2-adrenoceptor and TH-negative. Absence of SP and SNF did not change the general locomotion but reduces touch sensitivity after fracture. In mice without SNF, we detected more mesenchymal callus tissue and less cartilaginous tissue 5 days after fracture. At day 13 past fracture, we observed a decrease of the area covered by hypertrophic chondrocytes in Tac1-/- mice and mice without SNF, a lower number of osteoblasts in Tac1-/- mice and an increase of osteoclasts in mineralized callus tissue in mice without SNF. Apoptosis rate and activity of osteoclasts and osteoblasts isolated from Tac1-/- and sympathectomized mice were partly altered in vitro. Mechanical testing of fractured- and contralateral legs 21 days after fracture, revealed an overall reduced mechanical bone quality in Tac1-/- mice and mice without SNF. µCT-analysis revealed clear structural alteration in contralateral and fractured legs proximal of the fracture site with respect to trabecular parameters, bone mass and connectivity density. Notably, structural parameters are altered in fractured legs when related to unfractured legs in WT but not in mice without SP and SNF. CONCLUSION: The absence of SP and SNF reduces pain sensitivity and mechanical stability of the bone in general. The micro-architecture of the bone is profoundly impaired in the absence of intact SNF with a less drastic effect in SP-deficient mice. Both sympathetic and sensory neurotransmitters are indispensable for proper callus differentiation. Importantly, the absence of SP reduces bone formation rate whereas the absence of SNF induces bone resorption rate. Notably, fracture chondrocytes produce SP and its receptor NK1 and are positive for α-adrenoceptors indicating an endogenous callus signaling loop. We propose that sensory and sympathetic neurotransmitters have crucial trophic effects which are essential for proper bone formation in addition to their classical neurological actions.

Acid mediates a prolonged antinociception via substance P signaling in acid-induced chronic widespread pain.

BACKGROUND: Substance P is an important neuropeptide released from nociceptors to mediate pain signals. We recently revealed antinociceptive signaling by substance P in acid-sensing ion channel 3 (ASIC3)-expressing muscle nociceptors in a mouse model of acid-induced chronic widespread pain. However, methods to specifically trigger the substance P antinociception were still lacking. RESULTS: Here we show that acid could induce antinociceptive signaling via substance P release in muscle. We prevented the intramuscular acid-induced hyperalgesia by pharmacological inhibition of ASIC3 and transient receptor potential V1 (TRPV1). The antinociceptive effect of non-ASIC3, non-TRPV1 acid signaling lasted for 2 days. The non-ASIC3, non-TRPV1 acid antinociception was largely abolished in mice lacking substance P. Moreover, pretreatment with substance P in muscle mimicked the acid antinociceptive effect and prevented the hyperalgesia induced by next-day acid injection. CONCLUSIONS: Acid could mediate a prolonged antinociceptive signaling via the release of substance P from muscle afferent neurons in a non-ASIC3, non-TRPV1 manner.

Role of tachykinin 1 and 4 gene-derived neuropeptides and the neurokinin 1 receptor in adjuvant-induced chronic arthritis of the mouse.

OBJECTIVE: Substance P, encoded by the Tac1 gene, is involved in neurogenic inflammation and hyperalgesia via neurokinin 1 (NK1) receptor activation. Its non-neuronal counterpart, hemokinin-1, which is derived from the Tac4 gene, is also a potent NK1 agonist. Although hemokinin-1 has been described as a tachykinin of distinct origin and function compared to SP, its role in inflammatory and pain processes has not yet been elucidated in such detail. In this study, we analysed the involvement of tachykinins derived from the Tac1 and Tac4 genes, as well as the NK1 receptor in chronic arthritis of the mouse. METHODS: Complete Freund's Adjuvant was injected intraplantarly and into the tail of Tac1(-/-), Tac4(-/-), Tacr1(-/-) (NK1 receptor deficient) and Tac1(-/-/)Tac4(-/-) mice. Paw volume was measured by plethysmometry and mechanosensitivity using dynamic plantar aesthesiometry over a time period of 21 days. Semiquantitative histopathological scoring and ELISA measurement of IL-1ß concentrations of the tibiotarsal joints were performed. RESULTS: Mechanical hyperalgesia was significantly reduced from day 11 in Tac4(-/-) and Tacr1(-/-) animals, while paw swelling was not altered in any strain. Inflammatory histopathological alterations (synovial swelling, leukocyte infiltration, cartilage destruction, bone damage) and IL-1ß concentration in the joint homogenates were significantly smaller in Tac4(-/-) and Tac1(-/-/)Tac4(-/-) mice. CONCLUSIONS: Hemokinin-1, but not substance P increases inflammation and hyperalgesia in the late phase of adjuvant-induced arthritis. While NK1 receptors mediate its antihyperalgesic actions, the involvement of another receptor in histopathological changes and IL-1ß production is suggested.

Neurokinin-1 receptor signalling impacts bone marrow repopulation efficiency.

Tachykinins are a large group of neuropeptides with both central and peripheral activity. Despite the increasing number of studies reporting a growth supportive effect of tachykinin peptides in various in vitro stem cell systems, it remains unclear whether these findings are applicable in vivo. To determine how neurokinin-1 receptor (NK-1R) deficient hematopoietic stem cells would behave in a normal in vivo environment, we tested their reconstitution efficiency using competitive bone marrow repopulation assays. We show here that bone marrow taken from NK-1R deficient mice (Tacr1(-/-)) showed lineage specific B and T cell engraftment deficits compared to wild-type competitor bone marrow cells, providing evidence for an involvement of NK-1R signalling in adult hematopoiesis. Tachykinin knockout mice lacking the peptides SP and/or HK-1 (Tac1 (-/-), Tac4 (-/-) and Tac1 (-/-)/Tac4 (-/-) mice) repopulated a lethally irradiated wild-type host with similar efficiency as competing wild-type bone marrow. The difference between peptide and receptor deficient mice indicates a paracrine and/or endocrine mechanism of action rather than autocrine signalling, as tachykinin peptides are supplied by the host environment.

Substance P induces adverse myocardial remodelling via a mechanism involving cardiac mast cells.

AIMS: Substance P and neurokinin A (NKA) are sensory nerve neuropeptides encoded by the TAC1 gene. Substance P is a mast cell secretagogue and mast cells are known to play a role in adverse myocardial remodelling. Therefore, we wondered whether substance P and/or NKA modulates myocardial remodelling via a mast cell-mediated mechanism. METHODS AND RESULTS: Volume overload was induced by aortocaval fistula in TAC1(-/-) mice and their respective wild types. Left ventricular internal diameter of wild-type (WT) fistulas increased by 31.9%; this was prevented in TAC1(-/-) mice (4.2%). Matrix metalloproteinase (MMP) activity was significantly increased in WT fistula mice and was prevented in TAC1(-/-) mice. Myocardial collagen volume fraction was decreased in WT fistula mice; this collagen degradation was not observed in the TAC1(-/-) group. There were no significant differences between any groups in tumour necrosis factor (TNF)-α or cell death. Cardiac mast cells were isolated from rat hearts and stimulated with substance P or NKA. We found that these cells degranulated only to substance P, via the neurokinin-1 receptor. To determine the effect of substance P on mast cells in vivo, volume overload was created in Sprague-Dawley rats treated with the NK-1 receptor antagonist L732138 (5 mg/kg/day) for a period of 3 days. L732138 prevented: (i) increases in cardiac mast cell density; (ii) increased myocardial TNF-α; and (iii) collagen degradation. CONCLUSIONS: Our studies suggest that substance P may be important in mediating adverse myocardial remodelling secondary to volume overload by activating cardiac mast cells, leading to increased TNF-α and MMP activation with subsequent degradation of the extracellular matrix.

TRPA1 and substance P mediate colitis in mice.

BACKGROUND & AIMS: The neuropeptides calcitonin gene-related peptide (CGRP) and substance P, and calcium channels, which control their release from extrinsic sensory neurons, have important roles in experimental colitis. We investigated the mechanisms of colitis in 2 different models, the involvement of the irritant receptor transient receptor potential of the ankyrin type-1 (TRPA1), and the effects of CGRP and substance P. METHODS: We used calcium-imaging, patch-clamp, and neuropeptide-release assays to evaluate the effects of 2,4,6-trinitrobenzene-sulfonic-acid (TNBS) and dextran-sulfate-sodium-salt on neurons. Colitis was induced in wild-type, knockout, and desensitized mice. RESULTS: TNBS induced TRPA1-dependent release of colonic substance P and CGRP, influx of Ca2+, and sustained ionic inward currents in colonic sensory neurons and transfected HEK293t cells. Analysis of mutant forms of TRPA1 revealed that TNBS bound covalently to cysteine (and lysine) residues in the cytoplasmic N-terminus. A stable sulfinic acid transformation of the cysteine-SH group, shown by mass spectrometry, might contribute to sustained sensitization of TRPA1. Mice with colitis had increased colonic neuropeptide release, mediated by TRPA1. Endogenous products of inflammatory lipid peroxidation also induced TRPA1-dependent release of colonic neuropeptides; levels of 4-hydroxy-trans-2-nonenal increased in each model of colitis. Colitis induction by TNBS or dextran-sulfate-sodium-salt was inhibited or reduced in TRPA1-/- mice and by 2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4-isopro-pylphenyl)-acetamide, a pharmacologic inhibitor of TRPA1. Substance P had a proinflammatory effect that was dominant over CGRP, based on studies of knockout mice. Ablation of extrinsic sensory neurons prevented or attenuated TNBS-induced release of neuropeptides and both forms of colitis. CONCLUSIONS: Neuroimmune interactions control intestinal inflammation. Activation and sensitization of TRPA1 and release of substance P induce and maintain colitis in mice.

Gender differences in reduced substance P (SP) in children with slow-transit constipation.

PURPOSE: Adult slow-transit constipation (STC) occurs predominantly in females and is associated with low numbers of substance P (SP)-containing nerves in colonic circular muscle. AIM: To determine if reduced SP nerves is female predominant in paediatric STC. METHODS: Children with STC were identified from records of more than 600 nuclear transit studies (NTS) and intestinal biopsies done for intractable chronic constipation between November 1998 and March 2009. Colonic seromuscular biopsies collected from hepatic and splenic flexures, and sigmoid colon were processed for immunohistochemistry. Nerve fibre density in circular muscle containing SP was measured qualitatively by a pathologist. RESULTS: Eighty-eight children with chronic constipation had both NTS and intestinal biopsies. Seventy-eight children (52 M; age 2-15.5 years; mean 7.7 years) had STC diagnosed by NTS. SP was reduced in 10/26 girls, but only 11/52 boys. CONCLUSION: In this sample, STC was more common in boys than girls. However, in girls with STC, SP deficiency occurred in 40%, when compared with 20% of boys. During puberty, the percentage of girls with reduced SP decreased, whilst the percentage of boys increased. These results suggest that STC is heterogeneous and that there are some gender differences, the implication of which requires further investigation.

Acute morphine effects on respiratory activity in mice with target deletion of the tachykinin 1 gene (Tac1-/-).

Search for physiological mechanisms which could antagonize the opioid-induced respiratory depression is of important clinical value. In this study, we investigated the acute effects of morphine on respiratory activity in genetically modified newborn (P2) mice with target deletion of the (Tac1 -/-) gene lacking substance P (SP) and neurokinin A (NKA). In vivo, as shown with whole-body flow barometric plethysmography technique, morphine induced significantly attenuated minute ventilation during intermittent hypoxia in control animals. In contrast, knockout mice revealed significant increase in minute ventilation. In vitro, in brainstem preparation, knockout mice demonstrated greater changes in burst frequency during intermittent anoxia challenge. The data suggest that hereditary deficiency in tachykinins, SP and NKA results in more robust hypoxic response in newborn Tac1-/- mice during respiratory depression induced by morphine.

Early protection from burn-induced acute lung injury by deletion of preprotachykinin-A gene.

RATIONALE: Burn-induced acute lung injury (ALI) is a common clinical disorder associated with high mortality even in the absence of inhalational injury. Identification of endogenous triggers that mediate the early onset of remote ALI after burn represents an important goal but remains poorly defined. OBJECTIVES: We investigated the role of proinflammatory neuropeptide, substance P (SP), in instigating remote ALI and its effects on respiratory function early after severe local burn injury. METHODS: A 30% total body surface area full-thickness burn was induced in wild-type (WT) mice, preprotachykinin-A (PPT-A) gene deficient mice, which encodes for SP, and PPT-A(-/-) mice challenged with exogenous SP, followed by ALI and lung function analysis. MEASUREMENTS AND MAIN RESULTS: Endogenous SP production was heightened in burn-injured WT mice, which induced significant elevation of proinflammatory cytokines, chemokines, and endothelial adhesion molecules concurrent with disruption of pulmonary permeability barrier, excessive neutrophil infiltration, and severe ALI. Additionally, decreased neutral endopeptidase and elevated matrix metalloproteinase-9 were evident. Notably, disruption of respiratory function demonstrates a critical role of SP in lungs after burn. These effects were significantly attenuated in PPT-A(-/-) mice, whereas the exogenous administration of SP to PPT-A(-/-) mice restored the inflammatory response and ALI. Furthermore, analysis of neurokinin-1-receptor (NK1R), to which SP binds preferentially, revealed that SP in conjunction with burn injury regulates NK1R expression. CONCLUSIONS: We show that the absence of a single endogenous factor, SP, significantly provides early protection against burn-induced ALI in mice with marked improvement in respiratory function. Thereby, the blockade of SP may be beneficial in preventing early inflammation and ALI in patients with critical burn injuries.

Depletion of substance P, a mechanism for inhibition of mouse scratching behavior by tacrolimus.

Itching is the most important problem in atopic dermatitis and tacrolimus has been suggested to attenuate the itching by topical application. However, the anti-itch mechanism of tacrolimus has not been well elucidated. In the present study, an allergic dermatitis accompanied by frequent scratching behaviors was induced by repeated paintings with 2,4-dinitrofluorobenzene (DNFB) acetone solution onto the mouse ear and the effects of tacrolimus and dexamethasone on the dermatitis and associated scratching behavior were comparatively examined. Repeated DNFB paintings caused a typical dermatitis accompanied by elevated serum immunoglobulin E (IgE) and frequent scratching behaviors. Both tacrolimus and dexamethasone given topically for 10 days before the final challenge significantly inhibited the ear swelling and reduced the expression of interferon-gamma mRNA. Dexamethasone inhibited the accumulation of eosinophils completely, although tacrolimus did not. Both drugs did not affect the elevation of serum IgE levels. Tacrolimus significantly inhibited the scratching behavior, whereas dexamethasone failed to affect it. Repeated DNFB challenge depleted substance P in the dermis. Treatment with tacrolimus before the final challenge completely inhibited the recovery of substance P content, whereas dexamethasone facilitated the recovery. DNFB-induced ear swelling and scratching behavior were significantly inhibited by FK888, a tachykinin NK(1) receptor antagonist. Therefore, substance P seems to participate in the induction of ear swelling and scratching behavior upon final challenge with DNFB, and depletion of substance P by tacrolimus in the dermis contributes to its inhibition of ear swelling and scratching behavior at least in part.

Slow-transit constipation in children: our experience.

Constipation is a common problem in children, with childhood prevalence estimated at between 1 and 30%. It accounts for a significant percentage of referrals to paediatricians and paediatric gastroenterologists. It commonly runs in families, suggesting either an underlying genetic predisposition or common environmental factors, such as dietary exposure. The peak age for presentation of constipation is shortly after toilet training, when passage of hard stools can cause pain on defecation, which then triggers holding-on behaviour in the child. At the time of the next call to stool the toddler may try to prevent defecation by contraction of the pelvic floor muscles and anal sphincter. Unless the holding-on behaviour is quickly corrected by interventions to soften faeces and prevent further pain, the constipation can very rapidly become severe and chronic. Until recently, this mechanism was thought to be the only significant primary cause of constipation in childhood. In this review, we will summarise recent evidence to suggest that severe chronic constipation in children may also be due to slowed colonic transit.

An association of multiple endocrine neoplasia 2B, a RET mutation; constipation; and low substance P-nerve fiber density in colonic circular muscle.

BACKGROUND: Multiple endocrine neoplasia (MEN) 2B is a rare hereditary syndrome that results from an activating mutation of the RET proto-oncogene. The RET gene is involved in the development of the enteric nervous system. Patients with MEN 2B have enlarged enteric ganglia and may be affected by gastrointestinal dysmotility. A deficiency of the neurotransmitter substance P (SP) has been identified in both pediatric and adult patients with chronic constipation. METHODS: Three patients, in whom constipation was the presenting symptom and MEN 2B had been provisionally diagnosed, underwent genetic analysis. Seromuscular colonic biopsies were taken for immunofluorescence imaging in all 3 patients. A retrospective review of the patient notes was undertaken. RESULTS: All 3 patients had constipation refractory to conservative treatment. Genetic analyses in the 3 patients confirmed an identical RET mutation (Met918Thr). Immunofluorescence imaging in all 3 patients identified grossly enlarged myenteric plexus ganglia but surprisingly a low density of SP-labeled nerve fibers in the colonic circular muscle. Nitric oxide synthase and vasoactive intestinal peptide labeling were not reduced. CONCLUSION: The results show an association between MEN 2B and its most common RET mutation, colonic dysmotility, and low density of SP in the colonic circular muscle. Larger numbers of patients need to be studied to investigate whether low SP is primarily associated with the constipation or RET mutation and if it is a common feature of MEN 2B.

Tachykinin substance P depletion by capsaicin exacerbates inflammatory response to sidestream cigarette smoke in rats.

To evaluate the role of substance P (SP)-containing C-fiber nerves in the development of the inflammatory responses to sidestream cigarette smoke (SSCS), female Fischer 344 rats were randomly assigned into vehicle and capsaicin groups, respectively. Then, half the number in each group (N = 24) was nose-only exposed to air or 0.4 mg/m3 total particulate matter of SSCS for 4 h/day for 7 days. Exposure of the vehicle rats to SSCS induced obvious pulmonary neurogenic inflammation as indicated by elevations in plasma extravasation and proinflammatory cytokine secretions [interieukin (IL)-1beta and IL-12]. In addition, except for SP release, SSCS exposure significantly induced the tachykininergic toxicities at the gene level: upregulation of beta-preprotachykinin-I (beta-PPT-I) mRNA. However, neither SSCS exposure nor capsaicin pretreatment affects the immunolabeling density of neurokinin-1 receptor (NK-1R) in airway epithelium. SSCS also significantly inactivated pulmonary neutral endopeptidase (NEP) in lung tissue. Moreover, pretreatment with capsaicin significantly exacerbated the SSCS-induced inflammatory responses mentioned above as well as the release of plasma protein. Considering that capsaicin did not affect the normal control baselines of these parameters except for a decrease in NK-1R mRNA, we conclude that the degree of SSCS-induced inflammatory response was exacerbated because of the depletion of stored SP and/or inactivation of capsaicin-sensitive C-fiber nerves. Our data suggest the loss of afferent tachykinin SP signaling may lead to dysfunction of the sensory C-fiber nerve reflexes during exposure to SSCS, suggesting that SP serves a protective role.

Functional development of neurokinin peptides substance P and neurokinin A in nociception.

It is unclear how neonates respond to noxious stimuli. This study examined the role of neurokinin peptides in 3- and 21-day-old rat pups using the preprotachykinin-A (PPTA) knockout mouse, lacking neurokinin A and substance P. We assessed pain behaviors of these mice before the neurokinin system is putatively active, 3 days after birth, and after this system is active, 21 days after birth. The lack of these peptides failed to alter behavioral responses to nociceptive stimulation in the 3-day-old mice. The 21-day-old mice lacking these peptides were less responsive to 5 microl 2% formalin and to high intensity thermal and mechanical stimuli. Thus, the neurokinins appear not to be an important mechanism in the processing of nociceptive information in the infant.

Diminished anxiety- and depression-related behaviors in mice with selective deletion of the Tac1 gene.

The tachykinin neuropeptide substance P and its receptor neurokinin 1 have been implicated in the regulation of many physiological and pathological processes, including the control of emotional behaviors. The present study examines mice with a targeted deletion of the Tac1 gene, which encodes the neuropeptides substance P and neurokinin A, in animal models relevant to depressive illness and anxiety. In depression-related paradigms, Tac1-deficient mice were more active in the Porsolt's forced-swimming test and the tail-suspension test, and they did not become hyperactive after bulbectomy. Tac1 mutant mice were also less fearful in several animal models of anxiety. They were more active and less affected by the light conditions in the central area of the open-field arena; they showed more social interactions in an aversive environment, they were more active in the open areas of an elevated zero-maze, and they had a reduced latency to feed in the Thatcher-Britton conflict paradigm. These results demonstrate that tachykinins are powerful mediators of depression-like or anxiety-related behaviors in mice. The tachykinin system therefore may play an important role in the regulation of emotional states and the development of anxiety disorders and depression.

Long-term deprivation of substance P in PPT-A mutant mice alters the anoxic response of the isolated respiratory network.

The aim of this study was to elucidate the role of the neuromodulator substance P and its related tachykinin neurokinin A (NKA) in the homeostasis of respiratory activity. Respiratory activities, in form of fictive eupneic and sigh activities, were recorded extracellularly from the preBötzinger complex (PBC) in normoxic and anoxic conditions using medullary slice preparations. The effect of a blockade of endogenous substance P was assessed by an acute pharmacological blockade of the receptors with spantide in wild-type animals and by the use of preprotachykinin-A (PPT-A) mutants. These mutants lack from birth the PPT-A gene, which codes for the precursor of substance P and NKA. Spantide treatment reduced frequency (-37%, n = 9) and regularity (twofold) of eupneic-like respiratory activity under normoxic conditions, whereas in PPT-A mutants, eupneic-like activity was under normoxic conditions not significantly different from the wild-type mice (WT). The response to short anoxic episodes (5 min) was characterized in the WT by an increase in respiratory frequencies at the onset of anoxia (ratio anoxic/control frequency = 1.9 +/- 0.2, n = 18). This anoxic ratio was unaltered in the presence of spantide (ratio = 2.3 +/- 0.4, n = 8) but increased in the mutant (ratio = 4.1, n = 15). We conclude that endogenously released substance P is important for the maintenance of regular respiratory activity. Short-term blockade of substance P receptors decreases the frequency and regularity of rhythmic activity. Long-term deficiency in substance P leads to compensatory mechanisms that result in an apparently normal respiratory activity under normoxic conditions but a significantly altered response of the respiratory network during anoxia.