Anti-nociceptive responses produced by human putative counterpart of nocistatin

Effects of nociceptin and nocistatin on uterine contraction

The presence and effects of nociceptin (N/OFQ) and nocistatin (NST) in the central nervous system have been reasonably well described, but less data are available on their peripheral functions. Besides their presence in several peripheral organs (white blood cells, airway, liver, skin, vascular and intestinal smooth muscles, ovary, and testis), they have been found in the pregnant myometrium in both rat and human. The level of their precursor prepronociceptin is elevated in the preterm human myometrium as compared with full-term samples, whereas it gradually increases toward term in the pregnant rat uterus. Both N/OFQ and NST inhibit myometrial contractions, an effect which can be enhanced by naloxone and blocked by Ca²⁺-dependent K⁺ channel (BK(Ca)) inhibitors. Both compounds increase the myometrial cAMP level which may be responsible for the activation of this channel and subsequent intracellular hyperpolarization. NST releases calcitonin gene-related peptide from the sensory nerve ends, which explains its cAMP-elevating effect. In contrast with the nervous system, where they behave as antagonists, N/OFQ and NST are able to potentiate the uterine-relaxing effect of each other in both rat and human tissues. Further studies are required to clarify the roles of N/OFQ and NST in the regulation of the myometrial contractions and the perception of pain during delivery.

Localization of nocistatin-binding sites in mice brain and spinal cord using a biotinylated nocistatin probe

Nocistatin and nociceptin/orphanin FQ are two neuropeptides processed from the same precursor prepronociceptin. They have opposing roles in nociception and several other biological functions. Whereas the location and structure of the nociceptin/orphanin FQ receptors has been defined, the location of the nocistatin receptors remains unknown. In the course of this study, we synthesized a novel probe for histochemistry by linking biotin to the N terminus of nocistatin, and purified this with high-pressure liquid chromatography and confirmed the structure by mass spectrometer. Using this probe, we found nocistatin-binding sites in the cerebral cortex and the dorsal horn nucleus of the spinal cord. We also found that the nocistatin-binding sites were in the cell body, whereas the nociceptin/orphanin FQ binding sites were on the fibrous processes.

Supraspinal nocistatin and its amide derivative antagonize the hyperalgesic effects of nociceptin in mice

Nocistatin (NST) and nociceptin (NCP)/orphanin FQ are new neuropeptides derived from the same precursor molecule, and which are involved in pain transmission. Nocistatin has been shown to antagonize several effects of nociceptin by acting on a different receptor. We examined the effects of supraspinal nocistatin and nocistatin amide, and their interaction with nociceptin on nociceptive behavior in mice, using hotplate response times. We found that both nocistatin and nocistatin amide did not change the response time compared to control mice, whereas increasing doses of nociceptin caused progressive shortening of response times. Nocistatin and nocistatin amide were both able to antagonize the hyperalgesic effect of nociceptin. The effect of nocistatin amide was longer lasting and more potent, suggesting that the C-terminal free carboxyl group of nocistatin is not necessary for its biological activity, and that the amide derivative may be more biologically stable.

Identification of mature nocistatin and nociceptin in human brain and cerebrospinal fluid by mass spectrometry combined with affinity chromatography and HPLC

Nocistatin (NST) and nociceptin/orphanin FQ (NCP) are two important bio-peptides derived from the precursor protein prepronociceptin (ppNCP), involved in several central nervous system (CNS) functions including pain transmission. Since the actual form of human NST in CNS is not fully characterized, we studied the structure of NST from human brain tissue and cerebrospinal fluid (CSF) samples. NST and NCP were isolated from human brain and CSF samples by affinity chromatography combined with HPLC. Mass spectrometry was used for the identification and characterization of the peptides. The total NST immunoreactivity was detected as 11.5+/-2.3 pmol/g tissue for the brain and 0.44 pmol/ml for the pooled CSF sample after the HPLC purification by radioimmunoassay. The presence of two different forms of mature nocistatin (NST-17 and NST-30) and a possible N-terminal methionine cleaved NST-29 were confirmed by both radioimmunoassay and mass spectrometry. Affinity chromatography, HPLC and mass spectrometry methods used in this study were highly sensitive and suitable for identification of actual chemical structures and quantification of very small amounts of peptides in biological samples. The present findings may help further for search for new treatment of neuropathic pain, which is often poorly managed by current therapies.

Normal sensitivity to acute pain, but increased inflammatory hyperalgesia in mice lacking the nociceptin precursor polypeptide or the nociceptin receptor

Nociceptin/orphanin FQ (N/OFQ) is the endogenous agonist of the N/OFQ peptide receptor (NOP receptor). It is released from a larger precursor polypeptide, called prepro-nociceptin (ppN/OFQ) from which, in addition to N/OFQ, other biologically active neuropeptides may be derived. Increasing evidence indicates that exogenous application of N/OFQ to the central nervous system of mice and rats induces pro- and antinociceptive effects depending on the dose and site of administration. Much less is known about a potential contribution of endogenous N/OFQ to pain control. Here, we have used a genetic approach to address this topic. Mice deficient in either the NOP receptor (NOP-R-/- mice) or the N/OFQ precursor polypeptide (ppN/OFQ-/- mice) or both (double knockout mice) were compared with wild-type littermates in animal models of acute and tonic pain. Nociceptive responses to acute noxious heat of all three types of mutant mice were indistinguishable from those of wild-type mice. Accordingly, nociceptive behaviour was very similar in the early phase of the formalin test. However, NOP-R-/-, ppN/OFQ-/- and double knockout mice showed markedly stronger nociceptive responses during prolonged nociceptive stimulation in the second phase of the formalin test and significantly lower thermal pain thresholds in inflamed tissue after zymosan A injection. These results indicate that N/OFQ contributes significantly to endogenous pain control during prolonged nociceptive stimulation but does not affect acute pain sensitivity. Among the three types of mutant mice nociceptive behaviour was nearly identical, indicating that the lack of other potential ppN/OFQ products in the ppN/OFQ-/- mice was apparently without effect on the nociceptive phenotype.

Expression and purification of a neuropeptide nocistatin using two related plant viral vectors

Both odontoglossum ringspot virus (ORSV) and tobacco mosaic virus (TMV) were investigated as expression viral vectors for the expression of a neuropeptide nocistatin. Chimeras of ORSV and TMV were constructed by fusion of 17 amino acids of mouse nocistatin (mNST) to the C-terminal of the coat protein (CP) gene via a Factor Xa cleavage linker to yield ORSV-mNST and TMV-mNST. Expression of the mNST peptide was demonstrated by immuno-transmission electron microscopy, western blot, mass spectrometry and radioimmunoassay. Serial passaging of the chimeric viruses revealed loss of mNST from TMV-mNST by the fifth passage. The mNST was maintained in ORSV-mNST throughout six passages. The mNST peptide could be effectively cleaved and purified from chimeric ORSV CP. To our knowledge, this is the first successful attempt in obtaining a complete peptide with no additional amino acid sequence after expression and purification through the use of either ORSV or TMV as vectors.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Actions of nociceptin/orphanin FQ and other prepronociceptin products on rat rostral ventromedial medulla neurons in vitro

1. Whole-cell patch clamp recordings were made from rat rostral ventromedial medulla (RVM) neurons in vitro to investigate the cellular actions of the opioid-like receptor ORL1 (NOP), ligand nociceptin/orphanin FQ and other putative prepronociceptin products. 2. Primary and secondary RVM neurons were identified as responding to the kappa-opioid receptor agonist U-69593 (300 nM to 1 microM) and the mu- and delta-opioid receptor agonist met-enkephalin (10 microM), respectively. Both primary and secondary RVM neurons responded to nociceptin (3 nM to 1 microM) with an outward current that reversed polarity at -115 mV in brain slices and with inhibition of Ca(2+) channel currents in acutely isolated cells. 3. The putative ORL1 antagonist J-113397 (1 microM) produced no change in membrane current and abolished the outward current produced by nociceptin (100 nM). In contrast, Phe(1)psi(CH(2)-NH)Gly(2)]-nociceptin-(1-13)NH(2) (300 nM to 1 microM) alone produced an outward current and partially reduced the outward current produced by nociceptin (300 nM) when co-applied. 4. In brain slices nociceptin (300 nM) reduced the amplitude of evoked GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) but not non-NMDA receptor-mediated excitatory postsynaptic currents (EPSCs). 5. Met-enkephalin (10 microM), but not nociceptin (300 nM), reduced the rate of spontaneous miniature IPSCs in normal external potassium solution (K(+) 2.5 mM). In high external potassium (K(+) 17.5 mM), nociceptin reduced the rate of miniature IPSCs in the presence (Ca(2+) 2.4 mM, Mg(2+) 1.2 mM) but not in the absence of external calcium (Ca(2+) 0 mM, Mg(2+) 10 mM, Cd(2+) 10 microM). Nociceptin and met-enkephalin had no effect on the amplitude of miniature IPSCs. 6. The putative nociceptin precursor products nocistatin (rat prepronociceptin(125-132)) and rat prepronociceptin(154-181) had no effect on membrane currents, evoked IPSCs and evoked EPSCs. 7. These results indicate that nociceptin acts via the ORL1 receptor to directly inhibit both primary and secondary RVM neurons by activating a potassium conductance and by inhibiting calcium conductances. In addition, nociceptin inhibits GABA release within the RVM via a presynaptic Ca(2+)-dependent mechanism. Thus, nociceptin has the potential to exert both disinhibitory and inhibitory effects on neuronal action potential firing within the RVM.

Recent advances in opioid pharmacology

Despite their many and sometimes life-threatening side-effects, opioids in general and morphine in particular are valuable and potent painkillers. This article describes recent developments in sex-related differences in opioid (morphine) pharmacodynamics, morphine metabolites, the nociceptin/orphanin FQ receptor system, acute opioid tolerance and opioid-induced side-effects, such as opioid-induced respiratory depression and itch, and P-glycoprotein modulation of opioid effect.

Characterization of the ORL(1) receptor on adrenergic nerves in the rat anococcygeus muscle

1. Nociceptin, the endogenous ORL(1) receptor agonist inhibited the motor response to electrical-field stimulation in the rat anococcygeus muscle. This effect was characterized using the peptide ligands acetyl-Arg-Tyr-Tyr-Arg-Trp-Lys-NH(2) (Ac-RYYRWK-NH(2)), acetyl-Arg-Tyr-Tyr-Arg-Ile-Lys-NH(2) (Ac-RYYRIK-NH(2)) and [Phe(1)psi(CH(2)-NH)Gly(2)]nociceptin(1-13)NH(2) ([F/G]NC(1-13)NH(2)), and the non-selective opioid antagonist naloxone benzoylhydrazone (NalBzOH). 2. Nociceptin produced a concentration-dependent inhibition of the adrenergic motor response to electrical-field stimulation (EC(50) 19 nM, pEC(50) 7.7+/-0.1, n=8), but the response to exogenous noradrenaline (0.2 - 1 microM) was unaffected. The inhibitory nerve response was not affected by up to 1 microM nociceptin. 3. After inhibition of nitric oxide synthase (N(omega)-nitro-L-arginine 100 microM), and in the presence of peptidase inhibitors, nociceptin produced full inhibition of the pure adrenergic motor response (EC(50) 4 nM; pEC(50) 8.4+/-0.1, E(max) 98.3+/-1.2%, n=12). Ac-RYYRWK-NH(2) was a potent partial-agonist (pEC(50) 9.0+/-0.1, E(max) 66.4+/-5.2; n=11) but the efficacy of Ac-RYYRIK-NH(2) (pEC(50) 8.0+/-0.2, E(max) 36.7+/-3.5; n=12) was lower and the peptide could be tested as an antagonist (pA(2) 9.01). 4. [F/G]NC(1-13)NH(2) and NalBzOH had little or no efficacy and were competitive antagonists with pK(B) values of 7.4 (95% c.l. 7.1, 7.7) and 6.9 (95% c.l. 6.7, 7.1) respectively. Both increased the response to field stimulation at high concentrations, suggesting the release of an endogenous agonist for the ORL(1) receptor during stimulation. 5. Rat nocistatin did not affect the response to electrical-field stimulation, nor did it modify the inhibitory action of nociceptin. 6. Our findings suggest there is a significant endowment of ORL(1) receptors on sympathetic terminals of the rat anococcygeus, where nociceptin mediates a powerful inhibitory effect on adrenergic neuromuscular transmission.

Selective suppression of inhibitory synaptic transmission by nocistatin in the rat spinal cord dorsal horn

Nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) are two recently identified neuropeptides with opposing effects on several CNS functions, including spinal nociception. The cellular mechanisms that underlie this antagonism are not known. Here, we have investigated the effects of both peptides on synaptic transmission mediated by the three fast neurotransmitters l-glutamate, glycine, and GABA in the superficial layers of the rat spinal cord horn, which constitute the first important site of integration of nociceptive information in the pain pathway. NST selectively reduced transmitter release from inhibitory interneurons via a presynaptic Bordetella pertussis toxin-sensitive mechanism but left excitatory glutamatergic transmission unaffected. In contrast, N/OFQ only inhibited excitatory transmission. In the rat formalin test, an animal model of tonic pain in which N/OFQ exerts antinociceptive activity, NST induced profound hyperalgesia after intrathecal application. Similar to glycine and GABA(A) receptor antagonists, NST had no significant effects in the rat tail-flick test, a model of acute thermal pain. Our results provide a cellular basis for the antagonism of N/OFQ and NST and suggest the existence of a so far unidentified membrane receptor for NST. In addition, they support a role of NST as an endogenous inhibitor of glycinergic and GABAergic neurotransmission in the sensory part of the spinal cord and as a mediator of spinal hyperalgesia.

The hyperphagic effect of nociceptin/orphanin FQ in rats

Nociceptin/orphanin FQ (NC), the endogenous ligand of the opioid receptor-like1 (ORL1) receptor, has been reported to stimulate feeding in rats. The present article reviews the studies so far published on the effect of NC on food intake and reports new findings concerning the sensitivity of brain regions to the hyperphagic effect of NC in rats. The results obtained indicate that the hypothalamic arcuate nucleus is the most sensitive site among the brain regions so far investigated. On the basis of these findings and of the neurochemical and electrophysiological effects of NC, possible mechanisms of action and possible interactions with other neurotransmitter systems affecting feeding are discussed.

Nocistatin: a novel neuropeptide encoded by the gene for the nociceptin/orphanin FQ precursor

We identified a novel neuropeptide and named it "nocistatin." Its presence was expected by analysis of the precursor for the neuropeptide nociceptin or orphanin FQ (Noc/OFQ), previously identified as an endogenous ligand for the orphan opioid receptor-like receptor. The precursor prepronociceptin/orphanin FQ (ppNoc/OFQ) comprises at least two bioactive peptides, nocistatin and Noc/OFQ. Noc/OFQ is involved in a broad range of pharmacological actions in various tissues from the central nervous system to the periphery. In pain transmission, Noc/OFQ is reported to have different effects including nociception, no effect, and analgesia, depending on the animal species tested, doses, route of administration, and so on. We found that intrathecal administration of Noc/OFQ induced pain responses including allodynia and hyperalgesia. Simultaneous administration of nocistatin blocked the allodynia and hyperalgesia induced by Noc/OFQ, whereas anti-nocistatin antibody decreased the threshold for the Noc/OFQ-induced allodynia. The endogenous heptadecapeptide nocistatin was isolated from bovine brains and recently identified in mouse, rat, and human brain and in human cerebrospinal fluid. Although human, rat and mouse ppNoc/OFQ produced larger respective counterparts with 30, 35, and 41 amino acid residues, all peptides showed the antinociceptive activity. This activity was ascribed to the carboxyl-terminal hexapeptide of nocistatin, Glu-Gln-Lys-Gln-Leu-Gln, which is conserved beyond species. Nocistatin also attenuated the allodynia and hyperalgesia evoked by prostaglandin E(2) and the inflammatory hyperalgesia induced by formalin or carrageenan/kaolin, and reversed the Noc/OFQ-induced inhibition of morphine analgesia at picogram doses. Furthermore, nocistatin counteracted the impairment of learning and memory induced by Noc/OFQ or scopolamine. Nocistatin is widely present in the spinal cord and brain. Although nocistatin did not bind to the Noc/OFQ receptor, it bound to the membrane of mouse brain and spinal cord with a high affinity. Nocistatin is a novel bioactive peptide produced from the same precursor as Noc/OFQ, and it plays important roles in the regulation of pain transmission and learning and memory processes in the central nervous system.

Selective suppression of inhibitory synaptic transmission by nocistatin in the rat spinal cord dorsal horn

Nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) are two recently identified neuropeptides with opposing effects on several CNS functions, including spinal nociception. The cellular mechanisms that underlie this antagonism are not known. Here, we have investigated the effects of both peptides on synaptic transmission mediated by the three fast neurotransmitters l-glutamate, glycine, and GABA in the superficial layers of the rat spinal cord horn, which constitute the first important site of integration of nociceptive information in the pain pathway. NST selectively reduced transmitter release from inhibitory interneurons via a presynaptic Bordetella pertussis toxin-sensitive mechanism but left excitatory glutamatergic transmission unaffected. In contrast, N/OFQ only inhibited excitatory transmission. In the rat formalin test, an animal model of tonic pain in which N/OFQ exerts antinociceptive activity, NST induced profound hyperalgesia after intrathecal application. Similar to glycine and GABA(A) receptor antagonists, NST had no significant effects in the rat tail-flick test, a model of acute thermal pain. Our results provide a cellular basis for the antagonism of N/OFQ and NST and suggest the existence of a so far unidentified membrane receptor for NST. In addition, they support a role of NST as an endogenous inhibitor of glycinergic and GABAergic neurotransmission in the sensory part of the spinal cord and as a mediator of spinal hyperalgesia.

Effects of supraspinal orphanin FQ/nociceptin

The first reported behavioral action of the endogenous ligand for the "orphan" opioid receptor was a seemingly paradoxical increased sensitivity to nociception (i.e. hyperalgesia) after supraspinal injection into the cerebral ventricles of mice. In the continuing absence of an appropriate in vivo receptor antagonist, studies attempting to define the role of orphanin FQ/nociceptin (OFQ/N) in pain modulation and other behaviors have also featured central injection of peptide. This article reviews the findings of such studies. There appears to be concordance around the observation of anti-opioid actions of supraspinally injected OFQ/N, whereas the observations of hyperalgesia and/or analgesia are much less clear. A portion of the discrepant data may be explained in terms of methodological issues, stress-induced analgesia accompanying experimental protocols, and genotypic variation among subjects. Clarification of OFQ/N's role in nociception, as with other putative biologic functions, will probably depend upon the availability of a selective receptor antagonist.

Pharmacology of nociceptin and its receptor: a novel therapeutic target

Nociceptin (NC), alias Orphanin FQ, has been recently identified as the endogenous ligand of the opioid receptor-like 1 receptor (OP(4)). This new NC/OP(4) receptor system belongs to the opioid family and has been characterized pharmacologically with functional and binding assays on native (mouse, rat, guinea-pig) and recombinant (human) receptors, by using specific and selective agonists (NC, NC(1 - 13)NH(2)) and a pure and competitive antagonist, [Nphe(1)]NC(1 - 13)NH(2). The similar order of potency of agonists and affinity values of the antagonist indicate that the same receptor is present in the four species. OP(4) is expressed in neurons, where it reduces activation of adenylyl cyclase and Ca(2+) channels while activating K(+) channels in a manner similar to opioids. In this way, OP(4) mediates inhibitory effects in the autonomic nervous system, but its activities in the central nervous system can be either similar or opposite to those of opioids. In vivo experiments have demonstrated that NC modulates a variety of biological functions ranging from nociception to food intake, from memory processes to cardiovascular and renal functions, from spontaneous locomotor activity to gastrointestinal motility, from anxiety to the control of neurotransmitter release at peripheral and central sites. These actions have been demonstrated using NC and various pharmacological tools, as antisense oligonucleotides targeting OP(4) or the peptide precursor genes, antibodies against NC, an OP(4) receptor selective antagonist and with data obtained from animals in which the receptor or the peptide precursor genes were knocked out. These new advances have contributed to better understanding of the pathophysiological role of the NC/OP(4) system, and ultimately will help to identify the therapeutic potential of new OP(4) receptor ligands.

Nociceptin, Phe(1)psi-nociceptin(1 - 13), nocistatin and prepronociceptin(154 - 181) effects on calcium channel currents and a potassium current in rat locus coeruleus in vitro

1. The actions of the neuropeptide nociceptin, the putative nociceptin receptor antagonist [Phe1psi(CH(2)-NH)Gly(2)]-nociceptin-(1 - 13)NH(2) (Phe(1)psi-nociceptin(1 - 13)) and the putative nociceptin precursor products nocistatin (rat prepronociceptin(125 - 132)) and rat prepronociceptin(154 - 181) were examined on membrane properties of rat locus coeruleus (LC) neurons using whole cell patch clamp techniques. 2. Nociceptin inhibited I(Ba) in all LC neurons, (pD(2) of 8.9, maximum inhibition 50%). The inhibition of I(Ba) by nociceptin was associated with slowing of the activation of I(Ba) and could be significantly reversed by a strong depolarizing prepulse. Phe(1)psi-nociceptin(1 - 13) also inhibited I(Ba) in LC neurons (notional pD(2) of 7.6, maximum inhibition 18%). Application of Phe(1)psi-nociceptin(1 - 13) (1 microM) significantly occluded the subsequent effects of a co-application of nociceptin (3 nM) on I(Ba). 3. As previously reported for nociceptin, Phe(1)psi-nociceptin(1 - 13) caused an outward current in LC neurons voltage clamped at -60 mV (pD(2) of 7.1, maximum current 50% of that of methionine enkephalin, 10 microM). The Phe(1)psi-nociceptin(1 - 13) induced current reversed polarity at -112 mV and exhibited pronounced inward rectification. Phe(1)psi-nociceptin(1 - 13) (1 microM) reversibly inhibited the current caused by nociceptin (300 nM) by 30%. 4. Neither nocistatin nor rat prepronociceptin(154 - 181) inhibited I(Ba) in LC neurons, or prevented the subsequent inhibition by nociceptin. Neither nocistatin or prepronociceptin(154 - 181) affected the membrane properties of LC neurons. 5. This study demonstrates that nociceptin modulates somatic I(Ba) in rat LC neurons. The putative ORL1 antagonist Phe(1)psi-nociceptin(1 - 13) exhibited partial agonist activity at inhibiting I(Ba) and opening K(+) channels in LC. Other putative nociceptin precursor products were without effect on LC cells.

Effects of nociceptin and nocistatin on antidromic vasodilatation in hairless skin of the rat hindlimb in vivo

1. We tested whether nociceptin (NCE), the endogenous ligand of the opioid receptor-like 1 (ORL1) receptor, and nocistatin (NST), which reverses central NCE effects when applied intrathecally (i.t.), affect small-diameter afferent fibre-mediated vasodilatation in rat hairless skin. 2. Female Wistar rats were vagotomized. Ongoing sympathetic vasoconstrictor activity was abolished by bilateral section of the lumbar sympathetic trunk between ganglia L2 and L3. Sensory axons were selectively stimulated in the dorsal root L5 by 20 electrical impulses supramaximal for activating C-fibres at 1 Hz. Blood flow was measured on the plantar skin of the left hind paw in the L5 dermatome using laser Doppler flowmetry. 3. NCE injected intravenously (i.v.) as single boluses (1, 10 and 100 nmol kg(-1) 7 - 8 min before dorsal root stimulation (n=6) dose-dependently decreased blood pressure and local vascular resistance and suppressed antidromic vasodilatation maximally by 47% (P<0.01). When NCE was injected 2 min before stimulation (n=3), antidromic vasodilatation was reduced by 64% after NCE (1 nmol kg-1) and totally, or almost totally, abolished after the two higher doses. 4. NST (1 - 100 nmol kg(-1) i.v., n=6) was without significant effect on blood pressure and cutaneous vascular resistance. Applied 5 (n=6) or 2 min (n=3) before stimulation it also did not affect antidromic vasodilatation. NST (100 nmol kg(-1) i.v.) applied shortly before an equimolar dose of NCE did not antagonize NCE effects on vascular resistance, blood pressure and antidromic vasodilatation (n=4). 5. In conclusion, NCE inhibits antidromic vasodilatation, a component of neurogenic inflammation, in rat skin while NST is without effect. NST, at the small-diameter sensory ending, is not an effective antagonist of NCE.