Peptide autoreceptors: does an autoreceptor for substance P exist?

Neuropeptides and small-molecule amine transmitters: cooperative signaling in the nervous system

Neuropeptides are expressed in cell-specific patterns throughout mammalian brain. Neuropeptide gene expression has been useful for clustering neurons by phenotype, based on single-cell transcriptomics, and for defining specific functional circuits throughout the brain. How neuropeptides function as first messengers in inter-neuronal communication, in cooperation with classical small-molecule amine transmitters (SMATs) is a current topic of systems neurobiology. Questions include how neuropeptides and SMATs cooperate in neurotransmission at the molecular, cellular and circuit levels; whether neuropeptides and SMATs always co-exist in neurons; where neuropeptides and SMATs are stored in the neuron, released from the neuron and acting, and at which receptors, after release; and how neuropeptides affect 'classical' transmitter function, both directly upon co-release, and indirectly, via long-term regulation of gene transcription and neuronal plasticity. Here, we review an extensive body of data about the distribution of neuropeptides and their receptors, their actions after neuronal release, and their function based on pharmacological and genetic loss- and gain-of-function experiments, that addresses these questions, fundamental to understanding brain function, and development of neuropeptide-based, and potentially combinatorial peptide/SMAT-based, neurotherapeutics.

Neurokinins and their receptors in the rat trigeminal system: Differential localization and release with implications for migraine pain

Substance P (SP) and calcitonin gene-related peptide (CGRP) have both been considered potential drug candidates in migraine therapy. In recent years, CGRP receptor inhibition has been established as an effective treatment, in particular as a prophylactic for chronic migraine. Curiously, inhibition of neurokinin receptor 1 (NK1R) failed to alleviate acute migraine attacks in clinical trials, and the neurokinins were consequently abandoned as potential antimigraine candidates. The reason behind this has remained enigmatic.

Utilizing immunohistochemistry and semi-quantitative cell counts the expression of neurokinins and their associated receptors was examined in the rat trigeminal ganglion.

Immunohistochemistry results revealed SP co-localization in CGRP positive neurons and C-fibres, where it mainly concentrated at boutons. Neurokinin A (NKA) was observed in a population of C-fibres and small neurons where it could co-localize with SP. In contrast, neurokinin B (NKB) did not co-localize with SP and was observed in large/medium sized neurons and Aδ-fibres. All neurokinin receptors (NK1-3R) were found to be expressed in a majority of trigeminal ganglion neurons and A-fibres.

The functional release of SP and CGRP in the trigeminovascular system was stimulated with either 60 mM K+ or 100 nM capsaicin and measured with an enzyme-linked immunosorbent assay (ELISA). ELISA results established that SP can be released locally from trigeminovascular system. The released SP was comparatively minor compared to the CGRP release from stimulated dura mater, trigeminal ganglion neurons and fibres. We hypothesize that SP and CGRP signalling pathways may work in tandem to exacerbate painful stimuli in the TGV system.

Hypoperfusion of the infrapatellar fat pad and its relationship to MRI T2* relaxation time changes in a 5/6 nephrectomy model

The purpose of present study was to longitudinally investigate the alterations in infrapatellar fat pad (IPFP) vascularity in 5/6 nephrectomized rats by using dynamic contrast enhanced (DCE) MRI and IPFP degeneration by using MRI T2* relaxation time. Twelve male Sprague–Dawley rats were assigned to a control group and a 5/6 nephrectomy CKD group. The right knees of all rats were longitudinally scanned by 4.7 T MRI, and serial changes in the IPFP were assessed at 0, 8, 16, 30, and 44 weeks by DCE-MRI (parameters A, k_el and k_ep) and MRI T2* mapping. After MRI measurements, knee specimens were obtained and evaluated histologically. The CKD group had IPFPs with lower blood volume A and lower permeability k_ep values from 16 weeks (p < 0.05), lower venous washout k_el value from 30 weeks (p < 0.001), and significantly higher T2* values reflecting adipocyte degeneration beginning at 16 weeks (p < 0.05). The histopathological results confirmed the MRI findings. Hypoperfusion and adipocytes degeneration related to CKD were demonstrated in a rodent 5/6 nephrectomy model. DCE parameters and MRI T2* can serve as imaging biomarkers of fat pad degeneration during CKD progression.

Role of infrapatellar fat pad in pathological process of knee osteoarthritis: Future applications in treatment

It has been found that obese people have a higher proportion in suffering from osteoarthritis (OA), not only in the weight-bearing joints like knee and hip joints, even in non-weight-bearing joints such as hand joints. One of the reasons is because the large amount of adipose tissue secretes some factors, which can promote the occurrence of arthritis. As an important structure of the knee joint, the infrapatellar fat pad (IPFP) is actually a piece of adipose tissue. The aim of this review is to offer a comprehensive view of the anatomy and physiological characteristics of IPFP and its relationship with the pathological process of OA, indicating the important function of IPFP in OA. At the same time, with the development of adipose derived stem cells in the treatment of OA, owing to its special advantages, the IPFP is becoming a kind of important, minimally invasive fat stem cell source, providing a new approach for the treatment of OA. We hope that this review will offer an overview of all published data regarding the IPFP and will indicate novel directions for future research.

Neurokinin-1 receptor-based bivalent drugs in pain management: The journey to nowhere?

Hybrid compounds (also known as chimeras, designed multiple ligands, bivalent compounds) are chemical units where two active components, usually possessing affinity and selectivity for distinct molecular targets, are combined as a single chemical entity. The rationale for using a chimeric approach is well documented as such novel drugs are characterized by their enhanced enzymatic stability and biological activity. This allows their use at lower concentrations, increasing their safety profile, particularly when considering undesirable side effects. In the group of synthetic bivalent compounds, drugs combining pharmacophores having affinities toward opioid and neurokinin-1 receptors have been extensively studied as potential analgesic drugs. Indeed, substance P is known as a major endogenous modulator of nociception both in the peripheral and central nervous systems. Hence, synthetic peptide fragments showing either agonism or antagonism at neurokinin 1 receptor were both assigned with analgesic properties. However, even though preclinical studies designated neurokinin-1 receptor antagonists as promising analgesics, early clinical studies revealed a lack of efficacy in human. Nevertheless, their molecular combination with enkephalin/endomorphin fragments has been considered as a valuable approach to design putatively promising ligands for the treatment of pain. This paper is aimed at summarizing a 20-year journey to the development of potent analgesic hybrid compounds involving an opioid pharmacophore and devoid of unwanted side effects. Additionally, the legitimacy of considering neurokinin-1 receptor ligands in the design of chimeric drugs is discussed.

Neuropeptidergic integration of behavior in Trichoplax adhaerens, an animal without synapses

Trichoplax adhaerens is a flat, millimeter-sized marine animal that adheres to surfaces and grazes on algae. Trichoplax displays a repertoire of different feeding behaviors despite the apparent absence of a true nervous system with electrical or chemical synapses. It glides along surfaces to find food, propelled by beating cilia on cells at its ventral surface, and pauses during feeding by arresting ciliary beating. We found that when endomorphin-like peptides are applied to an animal, ciliary beating is arrested, mimicking natural feeding pauses. Antibodies against these neuropeptides label cells that express the neurosecretory proteins and voltage-gated calcium channels implicated in regulated secretion. These cells are embedded in the ventral epithelium, where they comprise only 4% of the total, and are concentrated around the edge of the animal. Each bears a cilium likely to be chemosensory and used to detect algae. Trichoplax pausing during feeding or spontaneously in the absence of food often induce their neighbors to pause as well, even neighbors not in direct contact. Pausing behavior propagates from animal to animal across distances much greater than the signal that diffuses from just one animal, so we presume that the peptides secreted from one animal elicit secretion from nearby animals. Signal amplification by peptide-induced peptide secretion explains how a small number of sensory secretory cells lacking processes and synapses can evoke a wave of peptide secretion across the entire animal to globally arrest ciliary beating and allow pausing during feeding.

Receptor distribution studies

Receptor distribution studies have played a key role in the characterization of receptor systems (e.g. GABA_B, NMDA (GluNRs), and Neurokinin 1) and in generating hypotheses to exploit these systems as potential therapeutic targets. Distribution studies can provide important information on the potential role of candidate receptors in normal physiology/disease and alert for possible adverse effects of targeting the receptors. Moreover, they can provide valuable information relating to quantitative target engagement (e.g. % receptor occupancy) to drive mechanistic pharmacokinetic/pharmacodynamic (PK/PD) hypotheses for compounds in the Drug Discovery process. Finally, receptor distribution and quantitative target engagement studies can be used to validate truly translational technologies such as PET ligands and pharmacoEEG paradigms to facilitate bridging of the preclinical/clinical interface and thus increase probability of success.

Substance P Regulation in Epilepsy

Background:

Epilepsy is a common neurological disease characterized by abnormal temporary discharge of neurons in the central nervous system. In recent years, studies have revealed the localization and changes in the density of neuropeptides, such as substance P (SP) in the pathogenesis of epilepsy. This review is a concise overview of SP and their physiologic and pathologic functions on regulating epilepsy, and the underline mechanisms.

Methods:

We research and collect relative online content for reviewing the effects of SP in Epilepsy.

Results:

The SP/NK-1 receptor system may induce seizures and play an important role in status epilepticus and in experimental animal models of epilepsy. Newest studies show that several mechanisms may explain the excitatory effects of the SP/NK-1 receptor signaling pathway in epilepsy. By binding to the NK-1 receptor, NK-1 receptor antagonists may block the pathophysiological effects of SP, and further studies are needed to confirm the possible anti-epileptic activity of NK-1 receptor antagonists.

Conclusion:

SP plays crucial roles on through binding with NK-1 receptor during epilepsy pathologic processing, and the NK-1 receptor is receiving a great attention as a therapeutic target for treating epilepsy. Thus, the use of NK-1 receptor antagonists for the treatment of epilepsy should be investigated in further studies.

Redox-Dependent Modulation of T-Type Ca(2+) Channels in Sensory Neurons Contributes to Acute Anti-Nociceptive Effect of Substance P

AIMS

Neuropeptide substance P (SP) is produced and released by a subset of peripheral sensory neurons that respond to tissue damage (nociceptors). SP exerts excitatory effects in the central nervous system, but peripheral SP actions are still poorly understood; therefore, here, we aimed at investigating these peripheral mechanisms.

RESULTS

SP acutely inhibited T-type voltage-gated Ca(2+) channels in nociceptors. The effect was mediated by neurokinin 1 (NK1) receptor-induced stimulation of intracellular release of reactive oxygen species (ROS), as it can be prevented or reversed by the reducing agent dithiothreitol and mimicked by exogenous or endogenous ROS. This redox-mediated T-type Ca(2+) channel inhibition operated through the modulation of CaV3.2 channel sensitivity to ambient zinc, as it can be prevented or reversed by zinc chelation and mimicked by exogenous zinc. Elimination of the zinc-binding site in CaV3.2 rendered the channel insensitive to SP-mediated inhibition. Importantly, peripherally applied SP significantly reduced bradykinin-induced nociception in rats in vivo; knock-down of CaV3.2 significantly reduced this anti-nociceptive effect. This atypical signaling cascade shared the initial steps with the SP-mediated augmentation of M-type K(+) channels described earlier.

INNOVATION

Our study established a mechanism underlying the peripheral anti-nociceptive effect of SP whereby this neuropeptide produces ROS-dependent inhibition of pro-algesic T-type Ca(2+) current and concurrent enhancement of anti-algesic M-type K(+) current. These findings will lead to a better understanding of mechanisms of endogenous analgesia.

CONCLUSION

SP modulates T-type channel activity in nociceptors by a redox-dependent tuning of channel sensitivity to zinc; this novel modulatory pathway contributes to the peripheral anti-nociceptive effect of SP. Antioxid. Redox Signal. 25, 233-251.

Role of fosaprepitant, a neurokinin Type 1 receptor antagonist, in morphine-induced antinociception in rats

OBJECTIVES

Opioids such as morphine form the cornerstone in the treatment of moderate to severe pain. However, opioids also produce serious side effects such as tolerance. Fosaprepitant is a substance P (SP) receptor antagonist, which is used for treating chemotherapy-induced nausea and vomiting. SP is an important neuropeptide mediating transmission of pain at the spinal level. Thus, it was hypothesized that combining morphine with fosaprepitant would increase the antinociceptive effect of morphine. The objectives were to evaluate the effect of fosaprepitant on morphine-induced antinociception in rats and to investigate its mechanism of action.

METHODS

Sprague-Dawley rats were injected with morphine (10 mg/kg twice daily) and/or fosaprepitant (30 mg/kg once daily) for 7 days. Pain threshold was assessed by the hot plate test. Expression of SP and calcitonin gene-related peptide (CGRP) in the spinal cords of these rats was evaluated by immunohistochemistry.

RESULTS

Morphine administration resulted in an antinociceptive effect compared to the control group (day 1 and to a lesser extent on day 4). The decreased antinociception despite continued morphine treatment indicated development of tolerance. Co-administration of fosaprepitant attenuated tolerance to morphine (days 1 and 3) and increased the antinociceptive effect compared to control group (days 1-4). Expression of SP was increased in the morphine + fosaprepitant group.

CONCLUSIONS

The results show that fosaprepitant attenuates the development of tolerance to morphine and thereby, increases the antinociceptive effect. This is likely linked to decreased release of SP from presynaptic terminals.

The role of substance p in ischaemic brain injury

Stroke is a leading cause of death, disability and dementia worldwide. Despite extensive pre-clinical investigation, few therapeutic treatment options are available to patients, meaning that death, severe disability and the requirement for long-term rehabilitation are common outcomes. Cell loss and tissue injury following stroke occurs through a number of diverse secondary injury pathways, whose delayed nature provides an opportunity for pharmacological intervention. Amongst these secondary injury factors, increased blood-brain barrier permeability and cerebral oedema are well-documented complications of cerebral ischaemia, whose severity has been shown to be associated with final outcome. Whilst the mechanisms of increased blood-brain barrier permeability and cerebral oedema are largely unknown, recent evidence suggests that the neuropeptide substance P (SP) plays a central role. The aim of this review is to examine the role of SP in ischaemic stroke and report on the potential utility of NK1 tachykinin receptor antagonists as therapeutic agents.

Reactive oxygen species are second messengers of neurokinin signaling in peripheral sensory neurons

Substance P (SP) is a prominent neuromodulator, which is produced and released by peripheral damage-sensing (nociceptive) neurons; these neurons also express SP receptors. However, the mechanisms of peripheral SP signaling are poorly understood. We report a signaling pathway of SP in nociceptive neurons: Acting predominantly through NK1 receptors and G(i/o) proteins, SP stimulates increased release of reactive oxygen species from the mitochondrial electron transport chain. Reactive oxygen species, functioning as second messengers, induce oxidative modification and augment M-type potassium channels, thereby suppressing excitability. This signaling cascade requires activation of phospholipase C but is largely uncoupled from the inositol 1,4,5-trisphosphate sensitive Ca(2+) stores. In rats SP causes sensitization of TRPV1 and produces thermal hyperalgesia. However, the lack of coupling between SP signaling and inositol 1,4,5-trisphosphate sensitive Ca(2+) stores, together with the augmenting effect on M channels, renders the SP pathway ineffective to excite nociceptors acutely and produce spontaneous pain. Our study describes a mechanism for neurokinin signaling in sensory neurons and provides evidence that spontaneous pain and hyperalgesia can have distinct underlying mechanisms within a single nociceptive neuron.

Neuromodulatory function of neuropeptides in the normal CNS

Neuropeptides are small protein molecules produced and released by discrete cell populations of the central and peripheral nervous systems through the regulated secretory pathway and acting on neural substrates. Inside the nerve cells, neuropeptides are selectively stored within large granular vesicles (LGVs), and commonly coexist in neurons with low-molecular-weight neurotransmitters (acetylcholine, amino acids, and catecholamines). Storage in LGVs is responsible for a relatively slow response to secretion that requires enhanced or repeated stimulation. Coexistence (i.e. the concurrent presence of a neuropeptide with other messenger molecules in individual neurons), and co-storage (i.e. the localization of two or more neuropeptides within individual LGVs in neurons) give rise to a complicated series of pre- and post-synaptic functional interactions with low-molecular-weight neurotransmitters. The typically slow response and action of neuropeptides as compared to fast-neurotransmitters such as excitatory/inhibitory amino acids and catecholamines is also due to the type of receptors that trigger neuropeptide actions onto target cells. Almost all neuropeptides act on G-protein coupled receptors that, upon ligand binding, activate an intracellular cascade of molecular enzymatic events, eventually leading to cellular responses. The latter occur in a time span (seconds or more) considerably longer (milliseconds) than that of low-molecular-weight fast-neurotransmitters, directly operating through ion channel receptors. As reviewed here, combined immunocytochemical visualization of neuropeptides and their receptors at the ultrastructural level and electrophysiological studies, have been fundamental to better unravel the role of neuropeptides in neuron-to-neuron communication.

Inhibition of inflammatory pain by activating B-type natriuretic peptide signal pathway in nociceptive sensory neurons

B-type natriuretic peptide (BNP) has been known to be secreted from cardiac myocytes and activate its receptor, natriuretic peptide receptor-A (NPR-A), to reduce ventricular fibrosis. However, the function of BNP/NPR-A pathway in the somatic sensory system has been unknown. In the present study, we report a novel function of BNP in pain modulation. Using microarray and immunoblot analyses, we found that BNP and NPR-A were expressed in the dorsal root ganglion (DRG) of rats and upregulated after intraplantar injection of complete Freund's adjuvant (CFA). Immunohistochemistry showed that BNP was expressed in calcitonin gene-related peptide (CGRP)-containing small neurons and IB4 (isolectin B4)-positive neurons, whereas NPR-A was present in CGRP-containing neurons. Application of BNP reduced the firing frequency of small DRG neurons in the presence of glutamate through opening large-conductance Ca2+-activated K+ channels (BKCa channels). Furthermore, intrathecal injection of BNP yielded inhibitory effects on formalin-induced flinching behavior and CFA-induced thermal hyperalgesia in rats. Blockade of BNP signaling by BNP antibodies or cGMP-dependent protein kinase (PKG) inhibitor KT5823 [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester] impaired the recovery from CFA-induced thermal hyperalgesia. Thus, BNP negatively regulates nociceptive transmission through presynaptic receptor NPR-A, and activation of the BNP/NPR-A/PKG/BKCa channel pathway in nociceptive afferent neurons could be a potential strategy for inflammatory pain therapy.

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome

INTRODUCTION

An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis.

MATERIALS AND METHODS

Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell.

RESULTS

Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%.

CONCLUSION

An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.

A local circuit model of learned striatal and dopamine cell responses under probabilistic schedules of reward

Recently, dopamine (DA) neurons of the substantia nigra pars compacta (SNc) were found to exhibit sustained responses related to reward uncertainty, in addition to the phasic responses related to reward-prediction errors (RPEs). Thus, cue-dependent anticipations of the timing, magnitude, and uncertainty of rewards are learned and reflected in components of DA signals. Here we simulate a local circuit model to show how learned uncertainty responses are generated, along with phasic RPE responses, on single trials. Both types of simulated DA responses exhibit the empirically observed dependencies on conditional probability, expected value of reward, and time since onset of the reward-predicting cue. The model's three major pathways compute expected values of cues, timed predictions of reward magnitudes, and uncertainties associated with these predictions. The first two pathways' computations refine those modeled by Brown et al. (1999). The third, newly modeled, pathway involves medium spiny projection neurons (MSPNs) of the striatal matrix, whose axons corelease GABA and substance P, both at synapses with GABAergic neurons in the substantia nigra pars reticulata (SNr) and with distal dendrites (in SNr) of DA neurons whose somas are located in ventral SNc. Corelease enables efficient computation of uncertainty responses that are a nonmonotonic function of the conditional probability of reward, and variability in striatal cholinergic transmission can explain observed individual differences in the amplitudes of uncertainty responses. The involvement of matricial MSPNs and cholinergic transmission within the striatum implies a relation between uncertainty in cue-reward contingencies and action-selection functions of the basal ganglia.

Neurokinin 2 receptor-mediated activation of protein kinase C modulates capsaicin responses in DRG neurons from adult rats

Patch-clamp techniques and Ca2+ imaging were used to examine the interaction between neurokinins (NK) and the capsaicin(CAPS)-evoked transient receptor potential vanilloid receptor 1 (TRPV1) responses in rat dorsal root ganglia neurons. Substance P (SP; 0.2-0.5 microM) prevented the reduction of Ca2+ transients (tachyphylaxis) evoked by repeated brief applications of CAPS (0.5 microM). Currents elicited by CAPS were increased in amplitude and desensitized more slowly after administration of SP or a selective NK2 agonist, [Ala8]-neurokinin A (4-10) (NKA). Neither an NK1-selective agonist, [Sar9, Met11]-SP, nor an NK3-selective agonist, [MePhe7]-NKB, altered the CAPS currents. The effects of SP on CAPS currents were inhibited by a selective NK2 antagonist, MEN10,376, but were unaffected by the NK3 antagonist, SB 235,375. Phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C(PKC), also increased the amplitude and slowed the desensitization of CAPS responses. Phosphatase inhibitors, decamethrin and alpha-naphthyl acid phosphate (NAcPh), also enhanced the currents and slowed desensitization of CAPS currents. Facilitatory effects of SP, NKA and PDBu were reversed by bisindolylmaleimide, a PKC inhibitor, and gradually decreased in magnitude when the agents were administered at increasing intervals after CAPS application. The decrease was partially prevented by prior application of NAcPh. These data suggest that activation of NK2 receptors in afferent neurons leads to PKC-induced phosphorylation of TRPV1, resulting in sensitization of CAPS-evoked currents and slower desensitization. Thus, activation of NK2 autoreceptors by NKs released from the peripheral afferent terminals or by mast cells during inflammatory responses may be a mechanism that sensitizes TRPV1 channels and enhances afferent excitability.

Modulation of basal and stress-induced amygdaloid substance P release by the potent and selective NK1 receptor antagonist L-822429

It has been shown that anxiety and stress responses are modulated by substance P (SP) released within the amygdala. However, there is an important gap in our knowledge concerning the mechanisms regulating extracellular SP in this brain region. To study a possible self-regulating role of SP, we used a selective neurokinin-1 (NK1) receptor antagonist to investigate whether blockade of NK1 receptors results in altered basal and/or stress-evoked SP release in the medial amygdala (MeA), a critical brain area for a functional involvement of SP transmission in enhanced anxiety responses induced by stressor exposure. In vitro binding and functional receptor assays revealed that L-822429 represents a potent and selective rat NK1 receptor antagonist. Intra-amygdaloid administration of L-822429 via inverse microdialysis enhanced basal, but attenuated swim stress-induced SP release, while the low-affinity enantiomer of L-822429 had no effect. Using light and electron microscopy, synaptic contacts between SP-containing fibres and dendrites expressing NK1 receptors was demonstrated in the medial amygdala. Our findings suggest self-regulatory capacity of SP-mediated neurotransmission that differs in the effect on basal and stress-induced release of SP. Under basal conditions endogenous SP can serve as a signal that tonically inhibits its own release via a NK1 receptor-mediated negative feedback action, while under stress conditions SP release is further facilitated by activation of NK1 receptors, likely leading to high local levels of SP and activation of receptors to which SP binds with lower affinity.

Neurokinin 1 receptor antagonism promotes active stress coping via enhanced septal 5-HT transmission

Antagonists of the substance P (SP) preferring neurokinin 1 receptor (NK1R) represent a promising novel class of drugs for the treatment of stress-related disorders such as depression and anxiety disorders; however, the involved neuronal pathways releasing SP in response to stressors are ill defined. By using in vivo microdialysis in combination with a highly sensitive and selective radioimmunoassay we found that exposure to forced swim stress increased SP release in the rat lateral septum (LS), a key area in processing emotions and stress responses. Acute administration of the selective NK1R antagonist L-822429 injected either systemically or locally into the LS reduced passive and facilitated active stress-coping strategies in the forced swim test. This effect seems to be mediated by enhanced intraseptal serotonergic transmission via serotonin (5-HT)1A receptors since NK1R blockade reversed the swim stress-induced decrease to an increase in extracellular 5-HT efflux, and furthermore the behavioral effects of L-822429 were blocked by intraseptal 5-HT1A receptor antagonism. A direct heterosynaptic regulation by NK1R on 5-HT release from serotonergic fibers was ruled out by immunocytochemistry at the light and electron microscopic level indicating involvement of GABAergic interneuron(s) in this interaction. Taken together, our data identify the LS as a critical brain area for the involvement of SP transmission in the modulation of stress responses and demonstrate that NK1R blockade can elicit a functionally significant facilitatory effect on 5-HT transmission, which does not necessarily involve the previously proposed interaction with neuronal firing at the cell body level of raphe neurons.

Selective loss of unmyelinated nerve fibers after extracorporeal shockwave application to the musculoskeletal system

Application of extracorporeal shockwaves (ESW) to the musculoskeletal system may induce long-term analgesia in the treatment of chronic tendinopathies of the shoulder, heel and elbow. However, the molecular and cellular mechanisms behind this phenomenon are largely unknown. Here we tested the hypothesis that long-term analgesia caused by ESW is due to selective loss of nerve fibers in peripheral nerves. To test this hypothesis in vivo, high-energy ESW were applied to the ventral side of the right distal femur of rabbits. After 6 weeks, the femoral and sciatic nerves were investigated at the light and electron microscopic level. Application of ESW resulted in a selective, substantial loss of unmyelinated nerve fibers within the femoral nerve of the treated hind limb, whereas the sciatic nerve of the treated hind limb remained unaffected. These data might indicate that alleviation of chronic pain by selective partial denervation may play an important role in the effects of clinical ESW application to the musculoskeletal system.

Extracorporeal shockwave application to the distal femur of rabbits diminishes the number of neurons immunoreactive for substance P in dorsal root ganglia L5

Application of extracorporeal shockwaves to the musculoskeletal system can induce long-term analgesia in the treatment of chronic painful diseases such as calcifying tendonitis of the shoulder, tennis elbow and chronic plantar fasciitis. However, the molecular and cellular mechanisms underlying this phenomenon are largely unknown. Recently it was shown that application of extracorporeal shockwaves to the distal femur of rabbits can lead to reduced concentration of substance P in the shockwaves' focal zone. In the present study we investigated the impact of extracorporeal shockwaves on the production of substance P within dorsal root ganglia in vivo. High-energy shockwaves were applied to the ventral side of the right distal femur of rabbits. After six weeks, the dorsal root ganglia L5 to L7 were investigated with high-precision design-based stereology. The application of extracorporeal shockwaves caused a statistically significant decrease in the mean number of neurons immunoreactive for substance P within the dorsal root ganglion L5 of the treated side compared with the untreated side, without affecting the total number of neurons within this dorsal root ganglion. No effect was observed in the dorsal root ganglia L6 and L7, respectively. These data might further contribute to our understanding of the molecular and cellular mechanisms in the induction of long-term analgesia by extracorporeal shockwave application to the musculoskeletal system.

Activation of the neurokinin-1 receptor by substance P triggers the release of substance P from cultured adult rat dorsal root ganglion neurons

Background

Although substance P (SP) is an important primary afferent modulator in nociceptive processes, it is unclear whether SP regulates its own release from primary sensory neurons.

Results

Using a highly sensitive radioimmunoassay for SP, we have demonstrated that the activation of neurokinin-1 receptor by SP or GR73632 (a potent neurokinin-1 receptor agonist) triggered an increase of SP release from cultured adult rat dorsal root ganglion (DRG) neurons depending on the dose and exposure time within 60 min, and thereafter, the SP release level gradually decreased over 360 min. Accompanying the SP release, a significant reduction in the percentage of neurons expressing neurokinin-1 receptor on their membranes during exposure to SP (200 pg/dish) occurred time dependently (56 ± 5% and 32 ± 2% at 180 and 360 min, respectively). The GR73632-evoked (10 nM, 60 min) SP release was attenuated by several inhibitors for mitogen-activated protein kinase kinase, p38 mitogen-activated protein (MAP) kinase and cyclooxygenase-2 (COX-2), protein kinase C (PKC), respectively. In contrast, a c-Jun NH₂-terminal kinase inhibitor increased the GR73632-evoked SP release.

Conclusion

These results indicate that the neurokinin-1 receptor activation by its agonists regulates the SP release process involving the activation of MAP kinases, PKCs and COX-2 from cultured DRG neurons.

Neurokinin-1 receptor enhances TRPV1 activity in primary sensory neurons via PKCepsilon: a novel pathway for heat hyperalgesia

The neuropeptide substance P (SP) is expressed in unmyelinated primary sensory neurons and represents the best known "pain" neurotransmitter. It is generally believed that SP regulates pain transmission and sensitization by acting on neurokinin-1 receptor (NK-1), which is expressed in postsynaptic dorsal horn neurons. However, the expression and role of NK-1 in primary sensory neurons are not clearly characterized. Our data showed that NK-1 was expressed in both intact and dissociated dorsal root ganglion (DRG) neurons. In particular, NK-1 was mainly coexpressed with the capsaicin receptor TRPV1 (transient receptor potential vanilloid subtype 1), a critical receptor for the generation of heat hyperalgesia. NK-1 agonist [Sar(9), Met(O2)(11)]-substance P (Sar-SP) significantly potentiated capsaicin-induced currents and increase of [Ca2+]i in dissociated DRG neurons. NK-1 antagonist blocked not only the potentiation of TRPV1 currents but also heat hyperalgesia induced by intraplantar Sar-SP. NK-1 antagonist also inhibited capsaicin-induced spontaneous pain, and this inhibition was enhanced after inflammation. To analyze intracellular cross talking of NK-1 and TRPV1, we examined downstream signal pathways of G-protein-coupled NK-1 activation. Sar-SP-induced potentiation of TRPV1 was blocked by inhibition of G-protein, PLCbeta (phospholipase C-beta), or PKC but not by inhibition of PKA (protein kinase A). In particular, PKCepsilon inhibitor completely blocked both Sar-SP-induced TRPV1 potentiation and heat hyperalgesia. Sar-SP also induced membrane translocation of PKCepsilon in a portion of small DRG neurons. These results reveal a novel mechanism of NK-1 in primary sensory neurons via a possible autocrine and paracrine action of SP. Activation of NK-1 in these neurons induces heat hyperalgesia via PKCepsilon-mediated potentiation of TRPV1.

Increased plasma substance P and CGRP levels, and high ACE activity in migraineurs during headache-free periods

Substance P (SP), calcitonin gene-related peptide (CGRP), and angiotensin converting enzyme (ACE) may have roles in trigeminovascular nociceptive mechanisms. We investigated interictal levels of SP, CGRP, ACE activity, and their correlation, in a sample of migraineurs. Forty-one patients suffering from migraine with aura (MA), 54 without aura (MO), and 52 non-headache subjects (controls) participated in this study. Blood samples were collected from cubital veins. Plasma levels of SP and CGRP were measured by enzyme immunoassay. Plasma ACE activities were measured spectrophotometrically. SP levels in MA (6.6+/-3.7 pg/ml; mean+/-SD) and MO (6.6+/-3.2 pg/ml) were significantly higher than in controls (4.8+/-2.4 pg/ml) (P<0.01). CGRP levels in MA (18.8+/-8.8 pg/ml) and MO (19.1+/-9.4 pg/ml) were also significantly higher than in controls (13.4+/-4.4 pg/ml) (P<0.01). ACE activities in MA (34.6+/-19.0 U/l) were significantly higher than in MO (25.3+/-13.2 U/l) and controls (27.0+/-20.4 U/l) (P<0.05). There was a significant correlation between SP and CGRP levels (P<0.05). In MA, SP and CGRP showed a tendency toward positive correlation, which was not significant. There was a weak, but significant positive correlation between SP levels and ACE activities (P<0.01). However, a relationship between ACE activities and CGRP levels was not observed. The data suggest that SP, CGRP, and ACE are relevant to migraine pathophysiology, and that they may interact.

Beneficial effect of tachykinin NK1 receptor antagonism in the development of hapten-induced colitis in mice

The gastro-intestinal tract is highly innervated by both intrinsic and extrinsic sensory nerves and this neuronal component is thought to play a role in local inflammatory responses. This in vivo study was designed to determine the function of substance P and the tachykinin NK1 receptor in the pathogenesis of inflammatory bowel disease by the use of the specific antagonist RP 67580. The dinitrofluorobenzene (DNFB)-induced colonic hypersensitivity model is associated with increased levels of substance P in the colon. The tachykinin NK1 receptor antagonist RP 67580 was used to investigate the role of substance P on the development of diarrhea, mast cell infiltration and activation, colonic tissue damage, hypertrophy of colonic lymphoid structures and leukocyte infiltration. The formation of watery diarrhea could completely be abrogated by treatment with RP 67580 in DNFB-sensitized animals 72 h after challenge. Antagonizing the tachykinin NK1 receptor in these animals also resulted in significantly reduced colonic patch hypertrophy, leukocyte recruitment and tissue damage. Total levels of substance P in the colon of DNFB-sensitized mice treated with the inactive enantiomer of the tachykinin NK1 receptor antagonist were significantly higher compared to DNFB-sensitized mice treated with RP 67580 72 h after challenge. Although RP 67580 was capable of reducing the total number of mast cells present in the colon, mast cell activation was not affected by this treatment. In conclusion, in this chemically-induced immunological model for inflammatory bowel disease we demonstrated an important role for tachykinin NK1 receptors, and its ligand substance P, in the development of colitis downstream from mast cell activation.

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.

The role of substance P in stress and anxiety responses

Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.

The somatostatin sst1 receptor: an autoreceptor for somatostatin in brain and retina?

The sst1 receptor was the first of the 5 somatostatin receptors to be cloned by homology with the glucagon receptor 13 years ago. It is a 7-transmembrane domain G-protein-coupled receptor that is negatively coupled to adenylyl cyclase, but can also trigger other transduction pathways. The distribution of sst1 mRNA, immunolabeling, and radioligand binding are not entirely overlapping, but the recent availability of knockout (KO) mice and a (still limited) number of selective agonists/antagonists has increased our knowledge about this receptor. These new tools have helped to reveal a role for the sst1 receptor in hippocampal, hypothalamic, basal ganglia, and retinal functions. In at least the latter 3 structures, the sst1 receptor appears to act as an inhibitory autoreceptor located on somatostatin neurons, whereas in the hippocampus such a role is still based on circumstantial evidence.

Distribution of substance-P nerves inside the infrapatellar fat pad and the adjacent synovial tissue: a neurohistological approach to anterior knee pain syndrome

INTRODUCTION

The purpose of the study was to determine the distribution and number of nerves inside the infrapatellar fat pad and the adjacent synovium, in particular with regards to nociceptive substance-P nerves.

MATERIALS AND METHODS

The infrapatellar fat pad of the knee was resected from 21 patients (4 male, 17 female, mean age 69 years) during the course of standard total knee arthroplasty operations performed in our clinic. The fat pad was dissected into five standardized segments, fixed in formalin and embedded in paraffin. Immunohistochemical techniques using antibodies against S-100 protein and substance-P (SP) were employed to determine and specify the nerves.

RESULTS

Studying all the detectable nerves present in 50 observation fields (200-fold magnification), we found an average of 106 S-100 versus 25 SP nerves (24%) in the synovium and 27 S-100- versus 7 SP nerves (26%) in the interior of the fat pad. The total nerve count was significantly (P < 0.001) higher in the synovium than in the fat pad for both marker types. The number of S-100 nerves was significantly (P < 0.05) higher in the central and lateral segments of the fat pad, while SP nerves were equally distributed throughout all segments of the fat-pad. SP nerves were significantly more frequently associated with blood vessels inside the fat pad (43%, P < 0.05) than in the synovial tissue (28%).

CONCLUSION

The occurrence and distribution of SP nerves inside the infrapatellar fat pad suggest a nociceptive function and a neurohistological role in anterior knee pain syndrome. The data support the hypothesis that a neurogenous infection of the infrapatellar fat pad could contribute to anterior knee pain syndrome.

Infrapatellar fat pad pressure and volume changes of the anterior compartment during knee motion: possible clinical consequences to the anterior knee pain syndrome

This biomechanical study was performed to measure tissue pressure in the infrapatellar fat pad and the volume changes of the anterior knee compartment during knee flexion-extension motion. Knee motion from 120 degrees of flexion to full extension was simulated on ten fresh frozen human knee specimens (six from males, four from females, average age 44 years) using a hydraulic kinematic simulator (30, 40, and 50 Nm extension moment). Infrapatellar tissue pressure was measured using a closed cell sensor. Infrapatellar volume change in the anterior knee compartment was evaluated subsequent to removal of the fat pad using a water-filled bladder. We found a significant increase of the infrapatellar tissue pressure during knee flexion, at flexion angles of <20 degrees and >100 degrees . The average tissue pressure ranged from 343 (+/-223) mbar at 0 degrees to 60 (+/-64) mbar at 60 degrees of flexion. The smallest volume in the anterior knee compartment was measured at full extension and 120 degrees of flexion, whereas the maximum volume was observed at 50 degrees of flexion. In conclusion, the data suggest a biomechanical function of the infrapatellar fat pad at flexion angles of <20 degrees and >100 degrees , which suggests a role of the infrapatellar fat pad in stabilizing the patella in the extremes of knee motion.

Molekulare Grundlagen zur schmerzvermittelnden Wirkung extrakorporaler Sto�wellen

The biologic action of extracorporeal shock wave application on the musculoskeletal system is understood poorly. To prove the hypothesis that alterations of tissue concentrations of substance P and prostaglandin E(2) are involved in the biologic action of shock waves, extracorporeal shock waves with energy flux density of 0.9 mJ/mm(2 )(1500 pulses at 1/s) were applied in vivo to the distal femur of rabbits. The concentrations of substance P and prostaglandin E(2) eluated from the periosteum of the femur were measured. Compared with the untreated contralateral hindlimbs, substance P release from the periosteum from the femur was increased 6 and 24 h after extracorporeal shock wave application, but was decreased 6 weeks after extracorporeal shock wave application. By contrast, extracorporeal shock wave application did not result in altered prostaglandin E(2) release from the periosteum from the femur. Remarkably, there was a close relationship between the time course of substance P release found here, and the well-known clinical time course of initial pain occurrence and subsequent pain relief after extracorporeal shock wave application to tendon diseases. Accordingly, substance P might be involved in the biologic action of extracorporeal shock wave application on tissue of the musculoskeletal system. This is the first study providing insights into the molecular mechanisms of extracorporeal shock wave application to the musculoskeletal system.

Genetic deletion of somatostatin receptor 1 alters somatostatinergic transmission in the mouse retina

In the mammalian retina, sparse amacrine cells contain somatostatin-14 (SRIF) which acts at multiple levels of neuronal circuitry through distinct SRIF receptors (sst(1-5)). Among them, the sst1 receptor has been localised to SRIF-containing amacrine cells in the rat and rabbit retina. Little is known about sst1 receptor localisation and function in the mouse retina. We have addressed this question in the retina of mice with deletion of sst1 receptors (sst1 KO mice). In the retina of wild type (WT) mice, sst1 receptors are localised to SRIF-containing amacrine cells, whereas in the retina of sst1 KO mice, sst1 receptors are absent. sst1 receptor loss causes a significant increase in retinal levels of SRIF, whereas it does not affect SRIF messenger RNA indicating that sst1 receptors play a role in limiting retinal SRIF at the post-transcriptional level. As another consequence of sst1 receptor loss, levels of expression of sst2 receptors are significantly higher than in control retinas. Together, these findings provide the first demonstration of prominent compensatory regulation in the mouse retina as a consequence of a distinct SRIF receptor deletion. The fact that in the absence of the sst1 receptor, retinal SRIF increases in concomitance with an increase in sst2 receptors suggests that SRIF may regulate sst2 receptor expression and that this regulatory process is controlled upstream by the sst1 receptor. This finding can be important in the design of drugs affecting SRIF function, not only in the retina, but also elsewhere in the brain.

Basal and activity-induced release of substance P from primary afferent fibres in NK1 receptor knockout mice: evidence for negative feedback

The concept that NK1 receptors are located pre-junctionally on substance P (SP)-containing nerves, acting as autoreceptors to inhibit SP release, has been suggested, but remains a controversial issue. To further investigate the existence of this receptor on central and peripheral terminals of primary afferent fibres, NK1 receptor knockout mice and an NK1 receptor antagonist were used in nerve-attached tissue preparations. These were the isolated dorsal horn of the spinal cord with dorsal roots attached, and the hairy skin of the hind paw with attached saphenous nerve. The results reveal that in the dorsal horn preparation, basal release of SP is significantly higher in NK1(-/-) mice than NK1(+/+) mice (P<0.05, n=7 mice/strain). However, a difference in SP release evoked in the dorsal horn by electrical stimulation of the dorsal roots or capsaicin application was not observed. In contrast, antidromic electrical stimulation of the saphenous nerve caused a substantially greater release of SP in the skin of NK1(-/-) mice than in NK1(+/+) mice (P<0.05, n=5 to 6 mice/strain). These results provide evidence for the existence of NK1 autoreceptors on sensory nerves in skin, which may be relevant to the modulation of their peripheral pathophysiological effector functions.

Substance-P-induced protein extravasation is bilaterally increased in complex regional pain syndrome

Pain, mechanical hyperalgesia, edema, increased skin temperature, and skin reddening are characteristic symptoms of acute complex regional pain syndrome (CRPS). We have recently demonstrated facilitated neurogenic inflammation on the affected limb. To further elucidate the underlying mechanisms, exogenous substance P (SP) in ascending concentrations (10(-9), 10(-8), 10(-7), 10(-6) M) was intradermally applied to the affected and the unaffected limbs, respectively, in two groups of 11 CRPS patients each using the microdialysis technique. Fourteen healthy volunteers served as controls for SP application, and 9 volunteers and 10 patients served as controls for saline perfusion. Dialysate protein content was measured photometrically to assess plasma protein extravasation. Significant differences in dialysate protein content were found after 10(-9) M SP (affected side, 98.4 +/- 8.4% of baseline value; unaffected side, 104.4 +/- 5.6%; controls, 70.7 +/- 4.1%; P < 0.005) and after 10(-6) M SP (affected, 169.7 +/- 24.2%; unaffected, 189.4 +/- 19.1%; controls, 122.2 +/- 12.0%; P < 0.05). While 10(-9) M SP induced no protein extravasation in controls, it provoked protein extravasation in 6 of 11 patients on the affected and in 5 of 11 patients on the unaffected side (P < 0.01). We conclude that SP-induced plasma protein extravasation is increased in CRPS patients on both the affected and unaffected limbs. The underlying mechanism might be impaired SP inactivation. Thus, our results further support the hypothesis that neurogenic inflammation plays an important role in the initiation of CRPS.

Corticotropin-releasing factor receptor types 1 and 2 are differentially expressed in pre- and post-synaptic elements in the post-natal developing rat cerebellum

Corticotropin-releasing factor (CRF)-like proteins act via two G-protein-coupled receptors (CRF-R1 and CRF-R2) playing important neuromodulatory roles in stress responses and synaptic plasticity. The cerebellar expression of corticotropin-releasing factor-like ligands has been well documented, but their receptor localization has not. This is the first combination of a light microscopic and ultrastructural study to localize corticotropin-releasing factor receptors immunohistologically in the developing rat cerebellum. Both CRF-R1 and CRF-R2 were expressed in climbing fibres from early stages (post-natal day 3) to the adult, but CRF-R2 immunoreactivity was only prominent throughout the molecular layer in the posterior cerebellar lobules. CRF-R1 immunoreactivity was concentrated in apical regions of Purkinje cell somata and later in primary dendrites exhibiting a diffuse cytoplasmic appearance. In Purkinje cells, CRF-R1 immunoreactivity was never membrane bound post-synaptically in dendritic spines while CRF-R2 immunoreactivity was found on plasmic membranes of Purkinje cells from post-natal day 15 onwards. We conclude that the localization of these receptors in cerebellar afferents implies their pre-synaptic control of the release of corticotropin-releasing factor-like ligands, impacting on the sensory information being transmitted from afferents. Furthermore, the fact that CRF-R2 is membrane bound at synapses, while CRF-R1 is not, suggests that ligands couple to CRF-R2 via synaptic transmission and to CRF-R1 via volume transmission. Finally, the distinct expression profiles of receptors along structural domains of Purkinje cells suggest that the role for these receptors is to modulate afferent inputs.

Protein kinase C is involved in neurokinin receptor modulation of N- and L-type Ca2+ channels in DRG neurons of the adult rat

Whole cell patch-clamp techniques were used to examine neurokinin receptor modulation of Ca2+ channels in small to medium size dorsal root ganglia neurons (<40 pF) that express mainly N- and L-type Ca2+ currents. Low concentrations of substance P enhanced Ca2+ currents (5-40%, <0.2 microM), while higher concentrations applied cumulatively reversed these enhancements (5-28% reductions, >0.5 microM). This apparent inhibition by high concentrations of substance P was blocked by the administration of the NK3 antagonist SB 235,375 (0.2 microM). The NK1 agonist, [Sar9,Met11]-substance P (0.05 to 1.0 microM) did not alter Ca2+ currents; whereas the NK2 agonist, [betaAla8]-neurokinin A (4-10), enhanced Ca2+ currents (5-36% increase, 0.05-0.5 microM). The enhancement was reversed by the NK2 antagonist MEN 10,376 (0.2 microM) but unaffected by the NK3 antagonist SB 235,375 (0.2 microM). The NK3 agonist [MePhe7]-neurokinin B (0.5-1.0 microM) inhibited Ca2+ currents (6-24% decrease). This inhibition was not prevented by the NK2 antagonist MEN 10,376 (0.2 microM) but was blocked by the NK3 antagonist SB 235,375 (0.2 microM). Both the enhancement and inhibition of Ca2+ currents by neurokinin agonists were reversed by the protein kinase C inhibitor bisindolylmaleimide I HCl (0.2-0.5 microM). Following inhibition of Ca2+ channels by [MePhe7]-neurokinin the facilitatory effect of BayK 8644 (5 microM) was increased and the inhibitory effect of the N-type Ca2+ channel blocker w -conotoxin GVIA (1 microM) was diminished, suggesting that the NK3 agonist inhibits N-type Ca2+ channels. Similarly, block of all but N-type Ca2+ channels, revealed that [betaAla8]-neurokinin A (4-10) enhanced the currents while [MePhe7]-neurokinin B inhibited the currents. Inhibition of all but L-type Ca2+ channels, revealed that [betaAla8]-neurokinin A (4-10) enhanced the currents while [MePhe7]-neurokinin B had no effect. Activation of protein kinase C with low concentrations of phorbol-12,13-dibutyrate enhanced Ca2+ currents, but high concentrations inhibited N- and L-type Ca2+ currents. In summary, these data suggest that in adult rat dorsal root ganglia neurons, NK2 receptors enhance both L- and N-type Ca2+ channels and NK3 receptors inhibit N-type Ca2+ channels and that these effects are mediated by protein kinase C phosphorylation of Ca2+ channels.

Prostaglandin E2 increases the expression of the neurokinin1 receptor in adult sensory neurones in culture: a novel role of prostaglandins

(1) Peripheral inflammation causes an increase in the proportion of primary afferent neurones that express neurokinin(1) (NK(1)) receptors for substance P (SP). This upregulation may contribute to the neuronal mechanisms of inflammatory pain. The aim of this study was to identify endogenous mediators that stimulate upregulation of NK(1) receptors in dorsal root ganglion (DRG) neurones. Cultured DRG neurones from the adult normal rat were exposed for 2 days to media that contained specific mediators, namely potassium in high concentration, prostaglandin E(2) (PGE(2)), somatostatin (SRIF), and compounds influencing second messenger cascades. After fixation neurones were labelled with an NK(1) receptor antibody. (2) Repetitive addition of the inflammatory mediator PGE(2) or dibutyryl-cyclic adenosine 3',5' monophophate (db-cAMP) to the culture medium enhanced the proportion of neurones with NK(1) receptor-like immunoreactivity from about 12% up to 40%. PGE(2)-induced upregulation was prevented by coadministration of PGE(2) and a protein kinase A inhibitor or SRIF to the medium. High potassium concentration, protein kinase C inhibitors and omission of nerve growth factor from the medium had no effect. (3) In calcium-imaging experiments, bath application of SP evoked increases of the intracellular calcium concentration in about 20% of the neurones. This proportion increased to about 40% after PGE(2)-pretreatment, but the increase was prevented when PGE(2) and SRIF were coadministered to the medium. (4) These data show that the expression of NK(1) receptor-like immunoreactivity in DRG neurones is regulated by the inflammatory mediator PGE(2). This upregulation depends on the intracellular adenylyl cyclase-protein kinase A pathway.

Neuropeptide Y modulates a G protein-coupled inwardly rectifying potassium current in the mouse hippocampus

Neuropeptide Y (NPY) is an abundant brain peptide with endogenous antiepileptic activity. Here we examined the role played by Y1 receptors (Y1R) in the mouse hippocampus. Using whole-cell patch-clamp recordings, we show that hilar neurons in acute mouse hippocampal slices exhibit a G-protein coupled inwardly rectifying potassium (GIRK) current that is significantly enhanced during exogenous NPY application. NPY-mediated enhancement of GIRK current was observed on 47% of putative interneurons and was mimicked by application of Y1R specific agonist (Leu(31)Pro(34) NPY). Immunostaining revealed the presence of Y1R on cell somas of hilar NPY-containing interneurons. Thus, our results suggest that Y1R on hilar interneurons may act as a peptide autoreceptor.

Biologic activity of the tachykinins on lamb and sheep gallbladder

In this study, we examined the activity of the tachykinins (TKs) on lamb and sheep isolated gallbladder and whether the TKs are involved in the capsaicin-induced activity in these tissues. Substance P (SP) and physalaemin (PHYS) contracted lamb gallbladder, PHYS-induced striking tachyphylaxis. This tissue was nearly insensitive to neurokinin A (NKA), neurokinin B (NKB), septide, and capsaicin. As in lamb tissues, SP and PHYS both contracted sheep gallbladder although PHYS induced no tachyphylaxis. At doses that had no effect on lamb tissue, NKA, NKB, septide, and capsaicin contracted sheep gallbladder. Our findings indicate that TK receptors differ in adult and young ovine gallbladder. The activity of PHYS on lamb gallbladder could depend on the existence of an unusual binding site, carrying one or more residues critical for the N-terminal sequence present in PHYS but not in SP.

Effects of morphine on formalin-induced nociception in rats

This study focused on the antinociceptive action of morphine in the formalin test in rats. Formalin-induced behaviour is characterised by two phases relevant to acute and tonic pain. Morphine (1-6 mg/kg) was administered systemically before or after the early phase, and its ability to affect the late phase was investigated. Inhibitory effects of morphine (3 mg/kg) injected immediately after the early phase were significantly stronger (32+/-9%) compared to the preemptive administration (84+/-29%, relative to saline-treated controls, 5% formaldehyde). It appears that some neural and/or behavioural changes during the early phase limit effects of morphine on the late phase. Furthermore, manipulation of stimulation intensity (2% vs. 5% formaldehyde) significantly affected the ability of morphine (3 mg/kg) to suppress early (55+/-7% and 76+/-10%, respectively) but not late phase of formalin-induced behaviours. These results agree with the previous demonstrations on the effects of acute nociceptive stimulation intensity on analgesic potency of opiate drugs. Thus, the present study revealed two factors that affect the potency of morphine in formalin test: administration regimen and formalin concentration.

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.

Evidence that post-tetanic potentiation is mediated by neuropeptide release in Aplysia

Many neuromuscular and central synapses exhibit activity-dependent plasticity. The sustained high-frequency firing needed to elicit some forms of plasticity are similar to those often required to release neuropeptides. We wanted to determine if neuropeptide release could contribute to post-tetanic potentiation (PTP) and chose neuromuscular synapses in buccal muscle I3a to explore this issue. This muscle is innervated by two motor neurons (termed B3 and B38) that show PTP in response to tetanic stimulation. B3 and B38 use glutamate as their fast transmitter but express different modulatory neuropeptides. B3 expresses FMRFamide, a neuropeptide that only slightly increases its own excitatory junction potentials (EJPs). B38 expresses the small cardioactive peptide (SCP), a neuropeptide that dramatically increases its own EJPs. It was our hypothesis that SCP released from B38's terminals during tetanic stimulation mediated a component of PTP for B38. Because no antagonist to SCP currently exists, we used several indirect approaches to test this hypothesis. First, we studied the effects of increasing stimulation frequency during the tetanus or lowering temperature on PTP. Both of these changes are known to dramatically increase SCP release. We found that increasing the frequency of stimulation increased PTP for both neurons; however, the effects were larger for B38. Decreasing the temperature tended to reduce PTP for B3, while increasing PTP for B38. These results were consistent with known properties of SCP release from B38. Next we selectively superfused the neuromuscular synapses with exogenous SCP to determine if this would occlude the effects of SCP released from B38 during a tetanus. We found that exogenous SCP dramatically reduced PTP for B38 but had little effect on PTP for B3. Thus our results support the hypothesis that physiological stimulation of B38 elicits PTP that is predominantly dependent on the release of SCP from its own terminals. They also demonstrate that the mechanisms underlying PTP can be very different for two motor neurons innervating the same target muscle.

Tachykinins as modulators of the micturition reflex in the central and peripheral nervous system

In the normal urinary bladder, tachykinins (TKs) are expressed in a population of bladder nociceptors that is sensitive to the excitatory and desensitizing effects of capsaicin (i.e., capsaicin-sensitive primary afferent neurons (CSPANs)). Several endobiotics or xenobiotics excite CSPANs and release TKs and other mediators at both the peripheral and spinal cord level. The peripheral release of TKs determines a set of responses (known as neurogenic inflammation) that includes vasodilatation, plasma protein extravasation, smooth muscle contraction and stimulation of afferent nerves. Following chronic inflammation, both immune cells and capsaicin-resistant sensory neurons can de novo express TKs: whether these pools of TKs are releasable and contribute to inflammatory processes is presently unsettled. At the spinal cord level, the release of TKs contributes in determining an altered pattern of vesicourethral reflexes in response to nociceptive stimulation of the bladder by conveying: (a) the afferent transmission to supraspinal sites, and (b) descending or sensory inputs to the sacral parasympathetic nucleus (SPN). Recent evidence also attribute a synergetic role of TKs in the supraspinal modulation of the sensory arm of the micturition reflex. The overall available information suggests that TK receptor antagonists may affect bladder motility/reflexes which occur during different pathological states, while having little influence on the normal motor bladder function.

Mimicry between neurokinin-1 and fibronectin may explain the transport and stability of increased substance P immunoreactivity in patients with bone marrow fibrosis

Bone marrow (BM) fibrosis may occur in myeloproliferative diseases, lymphoma, myelodysplastic syndrome, myeloma, and infectious diseases. In this study, the role of substance P (SP), a peptide with pleiotropic functions, was examined. Some of its functions-angiogenesis, fibroblast proliferation, and stimulation of BM progenitors-are amenable to inducing BM fibrosis. Indeed, a significant increase was found in SP-immunoreactivity (SP-IR) in the sera of patients with BM fibrosis (n = 44) compared with the sera of patients with hematologic disorders and no histologic evidence of fibrosis (n = 46) (140 +/-12 vs 18 +/-3; P <.01). Immunoprecipitation of sera SP indicated that this peptide exists in the form of a complex with other molecule(s). It was, therefore, hypothesized that SP might be complexed with NK-1, its natural receptor, or with a molecule homologous to NK-1. To address this, 3 cDNA libraries were screened that were constructed from pooled BM stroma or mononuclear cells with an NK-1 cDNA probe. A partial clone (clone 1) was retrieved that was 97% homologous to the ED-A region of fibronectin (FN). Furthermore, sequence analyses indicated that clone 1 shared significant homology with exon 5 of NK-1. Immunoprecipitation and Western blot analysis indicated co-migration of SP and FN in 27 of 31 patients with BM fibrosis. Computer-assisted molecular modeling suggested that similar secondary structural features between FN and NK-1 and the relative electrostatic charge might explain a complex formed between FN (negative) and SP (positive). This study suggests that SP may be implicated in the pathophysiology of myelofibrosis, though its role would have to be substantiated in future research. (Blood. 2001;97:3025-3031)

Changes in spinal cholecystokinin release after peripheral axotomy

The gene expression of cholecystokinin (CCK), a neuropeptide with anti-opioid properties, has been reported to be upregulated in some primary sensory neurons after a peripheral nerve lesion. We have recently demonstrated that the upregulation of CCK mRNA is not accompanied by an increased potassium-evoked release CCK-like immunoreactivity (CCK-LI) 2-4 weeks after a complete transection of the sciatic nerve. The potassium-evoked release of CCK-LI at earlier and later time points has, however, not been studied. The aim of the present in vivo microdialysis study was to monitor how the basal and stimulated extracellular level of CCK in the dorsal horn of the spinal cord is affected at various time points after a complete transection of the sciatic nerve (axotomy). During the first week after transection of the sciatic nerve a tendency towards an elevation of the potassium-induced (100 mM in the perfusion fluid) release of spinal CCK-LI was observed. In contrast, no potassium-induced release of CCK-LI could be detected 2-3 weeks and 2 months after axotomy. No significant effect was observed on the basal extracellular levels of CCK-LI in the dorsal horn. The present study provides further support for the notion that the adaptive changes in the dorsal horn 2 weeks and later after a deafferentiation injury do not include an increased release of CCK.

Cooperation of NMDA and tachykinin NK(1) and NK(2) receptors in the medullary transmission of vagal afferent input from the acid-threatened rat stomach

Noxious challenge of the rat gastric mucosa by hydrochloric acid (HCl) is signaled to the nucleus tractus solitarii (NTS) and area postrema (AP). This study examined the participation of glutamate and tachykinins in the medullary transmission process. Activation of neurons was visualized by in situ hybridization autoradiography of c-fos messenger RNA (mRNA) 45 min after intragastric (IG) administration of 0.5 M HCl or saline. IG HCl caused many neurons in the NTS and some neurons in the AP to express c-fos mRNA. The NMDA glutamate receptor antagonist MK-801 (2 mg/kg), the NK(1) tachykinin receptor antagonist GR-205,171 (3 mg/kg) and the NK(2) receptor antagonist SR-144,190 (0.1 mg/kg) failed to significantly reduce the NTS response to IG HCl, whereas the triple combination of MK-801, GR-205,171 and SR-144,190 inhibited it by 45--50%. Only in rats that had been preexposed IG to HCl 48 h before the experiment was MK-801 alone able to depress the NTS response to IG HCl. In contrast, the c-fos mRNA response in the AP was significantly augmented by MK-801, an action that was prevented by coadministration of GR-205,171 plus SR-144,190. Inhibition of neuronal nitric oxide synthase with 7-nitroindazole (45 mg/kg) was without effect on the IG HCl-evoked c-fos mRNA expression in the NTS and AP. Our data show that glutamate acting via NMDA receptors and tachykinins acting via NK(1) and NK(2) receptors cooperate in the vagal afferent input from the acid-threatened stomach to the NTS and participate in the processing of afferent input to the AP in a different and complex manner. These opposing interactions in the AP and NTS and the increase in NMDA receptor function in the NTS after a gastric acid insult are likely to have a bearing on the neuropharmacology of dyspepsia.