Release Of Sensory Neuropeptides Research Articles

Local Motor Responses to Bradykinin and Bacterial Chemotactic Peptide Formyl-Methionyl-Leucyl-Phenylalanine (FMLP) in the Guinea-Pig Isolated Renal Pelvis and Ureter

The local motor response to bradykinin and the bacterial chemotactic peptide, formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated in the guinea-pig isolated renal pelvis and ureter in relation to possible activation of capsaicin-sensitive primary afferent nerves and release of sensory neuropeptides. Both bradykinin (1nM–10μM) and FMLP (10nM–10μM) produced a concentration-dependent positive inotropic effect in the isolated renal pelvis which was unaffected by in vitro capsaicin desensitization. The response to bradykinin was antagonized by HOE 140, a bradykinin receptor antagonist, while it was unaffected by MEN 10,376, a tachykinin receptor antagonist, hCGRP(8-37) a calcitonin gene-related peptide (CGRP) receptor antagonist and N-t-BOC-Phe-DLeu-Phe-DLeu-Phe (BPLPLP), an FMLP antagonist. The response to FMLP was blocked by BPLPLP while it was unaffected by HOE 140, MEN 10,376 or hCGRP(8-37). Indomethacin (10μM) enhanced the response to both bradykinin and FMLP.Bradykinin transiently activated rhythmic contractions in the isolated ureter. The response to bradykinin was blocked by HOE 140 and was unaffected by in vitro capsaicin desensitization, indomethacin, MEN 10,376 or BPLPLP. FMLP had no motor effect on the resting ureter but when rhythmic background contractions were evoked by the addition of 100nM endothelin 1, it produced a transient suppression of ureteral motility. This inhibitory effect was unchanged by in vitro capsaicin desensitization or HOE 140 while it was abolished by indomethacin or BPLPLP pretreatment.Both bradykinin and FMLP evoked the release of CGRP-like immunoreactivity in the renal pelvis. The effect of bradykinin but not that of FMLP was abolished by indomethacin. By contrast neither bradykinin nor FMLP did evoke a significant CGRP-LI release in the ureter.It is concluded that bradykinin and FMLP affect pyeloureteral motility through specific and independent pathways. The local motor responses produced by these chemical stimulants are independent from the release of sensory neuropeptides from capsaicin-sensitive primary afferent neurons. Direct neurochemical evidence was obtained for activation of capsaicin-sensitive primary afferents in the renal pelvis: such a mechanism could be involved in the genesis of ureteral pain whenever bradykinin or FMLP come into contact with sensory nerves in the pyeloureteral wall.

Modulation by theophylline and enprofylline of the excitatory non-cholinergic transmission in guinea-pig bronchi

The mechanism of action of xanthines in asthma remains controversial. Since sensory innervation may play a role in the pathogenesis of asthma, we investigated whether xanthines were capable of reducing the contractile response of the bronchi to nerve stimulation. In guinea-pig bronchi in vitro, electrical field stimulation (EFS: 40 V, 16 Hz, 0.2 ms during 10 s) induces a rapid cholinergic contraction followed by a long-lasting contraction due to a local release of neuropeptides from C-fibre endings. We measured isometric neuronally-mediated contractions of bronchial smooth muscle and studied the effects of increasing concentrations of two xanthine derivatives, theophylline, an antagonist of adenosine receptors, and enprofylline, which has no effect on adenosine receptors. Both enprofylline (1-50 microM) and theophylline (10-100 microM) inhibited, in a concentration-dependent manner, the peptidergic contraction, an effect which was more marked with enprofylline than theophylline (EC50 = 9.6 +/- 0.7 microM and 62.0 +/- 4.7 microM, respectively). Conversely, the cholinergic response was unaffected. Contractions induced by exogenous substance P (0.03-3 microM) were also unaffected by theophylline and enprofylline at the above mentioned EC50s. Our results suggest that concentrations of theophylline, similar to those used therapeutically, reduce the release of sensory neuropeptides from C-fibre endings. This effect is unrelated to adenosine receptor blockade, since enprofylline had a similar inhibitory effect.

Lithium inhibits substance P and vasoactive intestinal peptide-induced relaxations on isolated porcine ophthalmic artery.

Lithium is currently a major drug used as a treatment for affective disorders and cluster headache, among other conditions. Its mechanism of action remains unknown. The trigeminovascular system may be involved in the pathophysiology of cluster headache and related diseases by liberating neuropeptides such as substance P (SP) and calcitonin gene-related peptide (CGRP) in the eye-forehead region. The objective of this study was to investigate whether or not a low concentration of lithium may interfere with peptidergic neuro-transmission at this level. Vasoactive intestinal peptide (VIP), SP, CGRP, capsaicin, and SP+CGRP concentration-response relaxation curves were obtained in the presence and absence of 2 x 10(-4) M lithium in isolated porcine ophthalmic arteries. Lithium inhibited the SP and VIP, but not the CGRP responses. Capsaicin-(a neurotoxin causing release of stored sensory neuropeptides) induced relaxations were partially inhibited by lithium. It is concluded that lithium may interfere with SP- and VIP-induced relaxation. If SP and VIP are of pathogenic significance in cluster headache, lithium may possibly work by counteracting unwanted effects of such peptides.

Endogenous sensory neuropeptide release enhances nonspecific airway responsiveness in guinea pigs.

To test whether endogenous sensory neuropeptide release results in airway hyperresponsiveness to exogenous bronchoconstrictor stimuli, male Camm-Hartley guinea pigs were exposed either to capsaicin aerosol for 10 min (CAP-AER) or to saline aerosol (SAL-AER) as a control condition. The following day, animals were anesthetized, tracheostomized, and beta-adrenergically blocked with propranolol, and their bronchoconstrictor responses to intravenously administered acetylcholine (ACh), neurokinin A (NKA), or capsaicin were measured. The bronchoconstriction induced by isocapnic dry gas hyperpnea also was assessed. Compared with the SAL-AER control group, the CAP-AER-treated animals exhibited augmented bronchoconstrictor responses to ACh and NKA. In contrast, the SAL-AER and CAP-AER groups had equivalent bronchoconstrictor responses to dry gas hyperpnea and to intravenously administered capsaicin. CAP-AER treatment caused neutrophilic airway inflammation, as reflected in increased numbers of neutrophils in bronchoalveolar lavage fluid obtained from CAP-AER-treated animals. Ablation of airway c-fiber neuron function (by chronic pretreatment with capsaicin prior to capsaicin aerosol inhalation) eliminated the ACh hyperresponsiveness observed in the CAP-AER-treated animals, demonstrating that sensory nerve products play a key role in the development of this nonspecific hyperresponsiveness. Our results demonstrate that sensory nerve stimulation with capsaicin aerosol leads to nonspecific bronchoconstrictor hyperresponsiveness and cellular airway inflammation, and thus disclose another potentially important role of sensory nerves in regulating airway function.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfur dioxide-induced bronchoconstriction via ruthenium red-sensitive activation of sensory nerves.

The mechanism of sulfur dioxide-induced bronchoconstriction was studied using isolated perfused and ventilated guinea-pig lungs. They were exposed to sulfur dioxide after pretreatment with different compounds, either via the pulmonary artery or via the air passages. Neither the cyclooxygenase inhibitor indomethacin (30 microM) nor the H1-receptor antagonist diphenhydramine (15 microM), given via the perfusate, attenuated the sulfur dioxide-induced bronchoconstriction. Furthermore, sulfur dioxide exposure did not cause a release of either thromboxane or histamine into the perfusate. In experiments with atropine equivocal results were obtained with regard to protection against sulfur dioxide-evoked bronchoconstriction. Intratracheal instillation of the local anesthetic agent lidocaine (1 mg/50 microliters) markedly reduced the sulfur dioxide-induced bronchoconstriction. Also, ruthenium red (10 microM), an agent with calcium entry-blocking properties and an inhibitor of capsaicin-induced bronchoconstriction, was able to inhibit the effect of sulfur dioxide. The sulfur dioxide-induced bronchoconstriction was associated with release of calcitonin gene-related peptide, a sensory neuropeptide. The effect of sulfur dioxide was also inhibited by a Ca(2+)-free buffer plus EGTA. These results suggest that sulfur dioxide-induced bronchoconstriction in the guinea-pig lung is the result of a local effect on sensory nerves (C-fiber activation). The mechanism seems to be dependent on the Ca(2+)-dependent release of sensory neuropeptides and to be linked to opening of the cation channel, which is associated with the proposed capsaicin receptor on sensory nerves as revealed by the inhibitory effect of ruthenium red.

Release of sensory CGRP by hypertonic NaCl is not blocked by tetrodotoxin, ω-conotoxin, nifedipine and ruthenium red

Hypertonic NaCl (160 mM added to the physiological salt solution) releases CGRP in a Ca 2+-dependent manner from capsaicin-sensitive sensory nerves of the rat urinary bladder. The NaCl (160 mM)-evoked CGRP release was not affected by tetrodotoxin (0.3ωM), nifedipine (1 ωM), ω-conotoxin (0.1 ωM) and ruthenium red (10 ωM). NaCl (160 mM)-evokes release of sensory neuropeptides without the involvement of axon reflexes, and by promoting Ca 2+ influx via a dihydropyridine ω-conotoxin and ruthenium red insensitive pathway.

NON‐ADRENERGIC, NON‐CHOLINERGIC NEURAL CONTROL OF THE AIRWAYS

1. In addition to the classical cholinergic bronchoconstrictor and adrenergic bronchodilator neural mechanisms, there is a large volume of evidence to suggest the existence of neural pathways within the airways of a variety of species which are neither adrenergic nor cholinergic, the non-adrenergic, non-cholinergic (NANC) mechanisms. With respect to airway smooth muscle tone, NANC neural responses may induce either contraction (excitatory, e-NANC) or relaxation (inhibitory, i-NANC). Early investigations of NANC mechanisms in both human and other animal airways suggested a role for neuropeptides as the putative neurotransmitters. 2. Excitatory NANC (e-NANC) bronchoconstrictor responses are believed to be mediated by the release of sensory neuropeptides from a subpopulation of non-myelinated C-fibre primary afferent neurones in the airways. e-NANC nerves, which release tachykinins such as substance P (SP), neurokinin A (NKA) and the peptide calcitonin gene-related peptide (CGRP, produced as a result of alternative splicing of the calcitonin gene) are selectively degenerated by the nerve toxin capsaicin (an extract from hot peppers), with the subsequent abolition of the e-NANC responses. Tachykinin receptors have been detected by radio-ligand receptor binding studies and visualized by autoradiographic mapping, and exogenous addition of these peptides elicits a bronchoconstrictor response in both human and other animal airways. In addition to these effects on airway smooth muscle tone, tachykinins produce an increase in microvascular permeability (and associated oedema formation), mucus hypersecretion and cause an exaggerated cholinergic bronchoconstrictor response. Thus, tachykinins may play a role in the inflammatory process and contribute to the neurogenic inflammation as seen in asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Capsaicin-induced release of neurokinin A from muscle and mucosa of gastric corpus: Correlation with capsaicin-evoked release of calcitonin gene-related peptide

It has been proposed that capsaicin-sensitive nerves might participate in a gastric defence mechanism, possibly via a local release of sensory neuropeptides. In this study, it was examined whether capsaicin might induce the release of neurokinin A (NKA), substance P (SP) and calcitonin gene-related peptide (CGRP) from different regions of rat stomach. Firstly, the tissue content of NKA-, SP- and CGRP-like immunoreactivity (LI) was measured in the fundus, in the corpus, in the muscle layer and in the mucosa of corpus of control rats and rats pre-treated with systemic capsaicin, s.c. (50 mg/kg as newborn). A large depletion (about 80%) of CGRP-LI following capsaicin treatment was observed in all regions examined, while no difference was observed for NKA-LI and SP-LI, NKA-LI, SP-LI and CGRP-LI release induced by capsaicin was measured in different regions of the rat stomach. Both in the gastric fundus and in the corpus, capsaicin (10 μM) produced a remarkable release of CGRP-LI and NKA-LI, but not of SP-LI. A second administration of the drug had no longer effect, indicating desensitization. In the gastric corpus, the capsaicin-induced NKA-LI and CGRP-LI release was larger from the muscle layer than from the mucosa. The present findings provide neurochemical evidence that both NKA-LI and CGRP-LI are released from different regions of the rat stomach and both peptides should therefore be taken into account when considering the efferent function of capsaicin-sensitive primary afferents at gastric level.

The effect of thiorphan on release of sensory neuropeptides from guinea-pig cerebral venous sinuses

The effect of peptidase inhibitors on neuropeptide release from peripheral endings of capsaicin-sensitive sensory neurons was studied in cerebral superior sagittal and transverse sinuses of guinea-pig. Capsaicin (1 microM)-evoked release of substance P-like immunoreactivity (SP-LI) was increased in a concentration-dependent manner by thiorphan (0.1-10 microM). Captopril (10 microM) or a mixture of bestatin (10 microM), leupeptin (10 microM) and bacitracin (10 microM) did not affect the capsaicin-evoked SP-LI release. Thiorphan (10 microM) increased also the capsaicin-evoked release of neurokinin A-like immunoreactivity (TK-LI) and calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) by 228% and 172%, respectively, while captopril (10 microM) was without effect. Thiorphan (10 microM), but not captopril (10 microM), enhanced by 239% CGRP-LI release induced by bradykinin (10 microM). In the cerebral venous vessels neutral endopeptidase (EC 3.4.24.11, NEP)-like activity was 58.8 +/- 6.1 pmol/mg protein/min, while angiotensin converting enzyme-like activity was below the detection limit of the assay. A thiorphan-sensitive mechanism, putatively attributable to NEP, plays a major role in the inactivation of peptides released from or acting on capsaicin-sensitive sensory fibres of cerebral venous sinuses of guinea-pig.

Compartment analysis of vascular effects of neuropeptides an capsaicin in the pig nasal mucosa

The vascular effects of local infusion of capsaicin, substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) were monitored in an experimental model on the pig nasal mucosa. Arterial, venous and superficial mucosal blood flow (laser-Doppler flowmetry) as well as mucosal volume, reflecting changes in capacitance vessels were studied in parallel. All substances induced concentration dependent increases in the parameters studied with the exception of the decrease in the superficial mucosal flow induced by vasoactive intestinal polypeptide. This latter finding was interpreted as a stealing phenomenon and suggests that vasoactive intestinal polypeptide mainly exerts its vasodilatory effect in the deeper glandular layers of the nasal mucosa. The vasodilatory effect of capsaicin, except the laser-Doppler signal, was markedly reduced by pretreatment with a combination of the ganglionic blocking agent chlorisondamine and atropine implying that capsaicin evokes a central reflex with a final parasympathetic pathway and release of agents like vasoactive intestinal polypeptide. The remaining capsaicin response may depend on a local effect with axon reflexes and the release of sensory neuropeptides with actions on superficial mucosal blood flow.

The effects of calcitonin gene‐related peptide on submucosal gland secretion and epithelial albumin transport in the ferret trachea in vitro

1. We have examined the effect of calcitonin gene-related peptide (CGRP) on basal mucus volume, lysozyme and albumin outputs from the ferret whole trachea in vitro, and on the outputs produced by methacholine and substance P (SP). We have also examined the effect of inhibiting neutral enkephalinase with thiorphan on the responses to CGRP. 2. CGRP (1-100 nM) produced small concentration-dependent increases in basal mucus volume, lysozyme and albumin outputs. These effect of CGRP were enhanced by thiorphan. The increases in basal outputs with CGRP and the potentiation by thiorphan were considerably less than previously observed with SP and neurokinin A (NKA). CGRP had no significant effect on potential difference (PD) across the trachea. 3. CGRP produced a concentration-dependent inhibition of methacholine- and SP-induced lysozyme output but a concentration-dependent increase in methacholine- and SP-induced albumin output. The effects of CGRP on methacholine-induced lysozyme and albumin outputs were enhanced by thiorphan. CGRP weakly inhibited methacholine-induced mucus volume output and weakly enhanced SP-induced mucus volume output. 4. Thus, CGRP weakly stimulates basal serous cell secretion and epithelial albumin transport, but does not alter epithelial integrity. CGRP inhibits the serous cell secretion due to methacholine or SP, but potentiates the epithelial albumin transport produced by these agents. The interaction between CGRP and other sensory neuropeptides or muscarinic agonists on airway submucosal glands and epithelium may be important in the normal airway and in inflammatory airway diseases where release of sensory neuropeptides is enhanced.

The neurotransmitter role of calcitonin gene-related peptide in the rat and guinea-pig ureter: Effect of a calcitonin gene-related peptide antagonist and species-related differences in the action of omega conotoxin on calcitonin gene-related peptide release from primary afferents

In the rat and guinea-pig isolated ureter electrical field stimulation of intrinsic nerves (10 Hz for 10 s) produced transient inhibition of evoked (20 mM KCl or 0.1–1 μM neurokinin A) rhtyhmic contractions by releasing transmitter(s) from peripheral endings of capsaicin-sensitive primary afferents. The C-terminal fragments of human calcitonin gene-related peptide (8–37) blocked the inhibitory effect of electrical field stimulation as well as that produced by exogenous calcitonin gene-related peptide, while leaving unaffected the inhibitory response to isoprenaline. Human calcitonin gene-related peptide (8–37) was devoid of any inhibitory activity of its own but enhanced the amplitude and frequency of KCl-evokded rhythmic contractions in the rat ureter, probably by antagonizing the inhibitory effect of endogenous calcitonin gene-related peptide released by KCl. Omega conotoxin fraction GVIA, a peptide which possesses a potent blocking activity of N-type voltage-sensitive calcium channels, prevented the inhibitory response to electrical stimulation in the guinea-pig ureter, while leaving the response unaffected in the rat ureter. Conotoxin had no effect toward the inhibition produced by exogenous calcitonin gene-related peptide indicating its prejunctional site of action, demonstrated previously in the guinea-pig ureter [Maggi et al. (1990) Neurosci. Lett. 114, 203–206]. Dermorphin, an amphibian peptide with potent agonist activity on mu-type opioid receptors, inhibited the response to electrical stimulation in the guinea-pig ureter but had no effect in the rat ureter. Neuropeptide Y and galanin, at a concentration (0.1 μM) shown previously to inhibit sensory neuropeptide release in other guinea-pig tissue, had no effect in either the rat or guinea-pig ureter. These findings provide direct pharmacological evidence for a role of calcitonin gene-related peptide as an inhibitory transmitter in the ureter of both rats and guinea-pigs. A species difference emerges in the mechanisms of release of calcitonin gene-related peptide, conotoxin-sensitive calcium channels being important for electrically-evoked calcitonin gene-related peptide release in the guinea-pig but not in the rat ureter. Furthermore, organ-related differences in mechanisms of prejunctional modulation of sensory neuropeptide release may exist in guinea-pigs.

Neurochemical evidence of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) release from capsaicin-sensitive nerves in rat mesenteric arteries and veins

1. 1. The ability of capsaicin and antidromic stimulation of perivascular nerve fibers to release sensory neuropeptides (SP-LI and CGRP-LI) have been investigated in rat mesenteric arteries and veins. 2. 2. Both in mesenteric arteries and veins substantial SP-LI and CGRP-LI tissue levels were measured. A significant reduction in sensory neuropeptides levels was observed in tissues obtained from capsaicin-pretreated animals. 3. 3. Superfusion of isolated vessels with capsaicin (1 μM) produced a prompt and remarkable release of both SP-LI and CGRP-LI, which can be evoked only once in each preparation. 4. 4. Electrical field stimulation (EFS, 20 Hz, 50 V, 0.5 msec, trains of 10 sec every 20 sec for 15 min) of isolated vessels resulted in a significant release of CGRP-LI. This release was significantly greater in veins as compared to arteries. EFS-induced CGRP-LI release was unaffected by atropine or guanethidine and absent in preparations obtained from capsaicin-pretreated rats. 5. 5. These neurochemical findings further suggest that the local release of sensory neuropeptides from capsaicin-sensitive nerve endings might be important in the regulation of mesenteric circulation.

Capsaicin and sensory neuropeptide stimulation of goblet cell secretion in guinea‐pig trachea.

1. We studied the effect of capsaicin and sensory neuropeptides on tracheal goblet cell secretion in anaesthetized guinea-pigs using a semi-quantitative morphometric technique whereby the magnitude of discharge of stained intracellular mucus, expressed as a mucus score (MS), was related inversely to discharge. 2. Capsaicin (i.v.) induced goblet cell secretion: a decrease of 50% in MS below control (indicative of increased secretion) was maximal at 3.3 x 10(-9) mol/kg. 3. Capsaicin-induced secretion was unaffected either by prior vagus nerve section or by pre-treatment with atropine, propranolol and phentolamine which suggests that local axon reflexes with release of sensory neuropeptides are involved in the response. 4. Intravenous substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and calcitonin gene-related peptide (CGRP) produced dose-related increases in goblet cell secretion, with SP the most potent. Doses (mol/kg) causing a 50% decrease in MS from control were 3.5 x 10(-12) for SP; 72 x 10(-10) for NKA; 1.6 x 10(-9) for NKB; and 1.2 x 10(-8) for CGRP. The maximal increase in goblet cell secretion was 75% of control and occurred with SP at 10(-10) mol/kg. 5. SP-induced mucus discharge was not inhibited by atropine or the histamine receptor antagonists mepyramine or cimetidine. 6. We conclude that in guinea-pig trachea, goblet cell secretion is under the control of capsaicin-sensitive sensory nerves and release of neuropeptides from these nerves may induce mucus discharge via tachykinin receptors of the NK-1 subtype (indicated by an order of potency of SP greater than NKA greater than NKB).

5-HT3, receptor antagonists inhibit sensory neuropeptide release from the rat spinal cord

5-HT3 receptors may be present on primary afferent neurons containing substance P (SP), neurokinin A (NKA) or calcitonin gene-related peptide (CGRP). We investigated the release of SP-, NKA- and CGRP-immunoreactivities (IR) from rat spinal cord slices. Thirty mM potassium chloride caused an increased outflow of all three peptides, i.e. 140-190% of spontaneous release. This release was slightly enhanced in the presence of 3 x 10(-5) M 5-hydroxytryptamine (5-HT). In contrast, a significant inhibition of potassium-evoked, but not of basal NKA-IR and CGRP-IR release was observed when 10(-7) M BRL 43694 or ICS 205-930, two specific 5-HT3 receptor antagonists, were superfused together with 5-HT. In conclusion, 5-HT may facilitate the evoked release of peptides from central terminals of primary sensory neurons via 5-HT3 receptors.

Acrolein depletes the neuropeptides CGRP and substance P in sensory nerves in rat respiratory tract.

The mammalian respiratory tract is densely innervated by autonomic and sensory nerves around airways and blood vessels. Subsets of these nerves contain a number of putative neurotransmitter peptides, such as substance P and calcitonin gene-related peptide (CGRP) in sensory nerves and vasoactive intestinal polypeptide (VIP), possibly serving autonomic functions. CGRP is also found in endocrine cells in rat airway epithelium. These peptides are all pharmacologically potent effectors of bronchial and vascular smooth muscle and bronchial secretion. Their functions in vivo are less well established. We have therefore examined the effects of inhaled acrolein, a sensory irritant, on three pulmonary neuropeptides: CGRP, substance P, and VIP. Groups of rats (n = 3 each) were exposed for 10 min to acrolein in air (Ct = 510, 1858, and 5693 mg.min/m3) or to air alone. Fifteen minutes later they were killed (pentabarbitone IP) and their respiratory tracts were dissected and fixed in 0.4% p-benzoquinone solution. Cryostat sections were stained by indirect immunofluorescence for a general nerve marker (PGP 9.5) and neuropeptides. The acrolein-treated animals had a dose-related decrease in tracheal substance P- and CGRP-immunoreactive nerve fibers compared with controls. No change was seen in total nerve fiber distribution and number (PGP 9.5) or VIP immunoreactivity, nor in CGRP-immunoreactive epithelial endocrine cells. It is concluded that the rat tracheal peptidergic nerves are a sensitive indicator of inhaled irritant substances. Their reduced immunoreactivity may be because of a release of sensory neuropeptides that could play a role in the physiological response to irritant or toxic compounds.

Release of sensory neuropeptides from dural venous sinuses of guinea pig

Substance P- and calcitonin gene-related peptide-like immunoreactivities (SP-LI and CGRP-LI, respectively) were measured in superfusates of either superior sagittal sinus and transverse sinuses and attached dura mater dura mater alone of guinea pig. Exposure of cerebral venous sinuses to capsaicin (1 μM) evoked the release of both SP-LI and CGRP-LI, which was no longer observed upon second challenge with the drug. Neuropeptide release was induced by 80 mM K + either at the first or second administration. Bradykinin (10 μM) increased the outflow of CGRP-LI, but not of SP-LI, from cerebral venous sinuses. In vitro capsaicin pretreatment (10 μM) or incubation with 10 μM indomethacin completely abolished the bradykinin-evoked CGRP-LI release. Capsaicin (1 μM) failed to evoke release from dura mater without major intracranial venous vessels. Sensory neuropeptide released from the cerebral venous sinuses may take part in certain symptoms, such as vasodilatation and inflammation accompanying the pain of the migraine attack. Bradykinin, putatively via prostanoid generation, may participate in this event.

Effect of omega conotoxin on reflex responses mediated by activation of capsaicin-sensitive nerves of the rat urinary bladder and peptide release from the rat spinal cord

The aim of this study was to assess whether omega conotoxin fraction GVIA, a potent blocker of N- and L-type voltage-sensitive calcium channels, might interfere with reflex responses (micturition, blood pressure rise in spinal rats) produced by activation of capsaicin-sensitive sensory nerves of the rat urinary bladder. The effect of conotoxin was also investigated on reflex micturition persisting after capsaicin pretreatment. Following topical application onto the bladder, conotoxin did not affect the volume threshold to elicit micturition although it reduced the amplitude of volume-evoked bladder contractions. Likewise, topical conotoxin did not prevent the reflex rise in blood pressure elicited by sudden bladder distension or topical application of capsaicin onto the bladder. In contrast, topical lidocaine strongly prevented both reflex responses. After intrathecal administration, conotoxin produced a dose-dependent inhibition of volume-evoked bladder contractions and the cardiovascular reflex produced by mechanical or chemical stimulation of bladder nerves. Intrathecal conotoxin inhibited micturition also in rats pretreated with capsaicin (50mg/kg s.c., 4 days before). Depolarization by high potassium (80 mM) produced release of both substance P- and calcitonin gene-related peptide-like immunoreactivity from superfused slices of the dorsal half of rat spinal cord. Capsaicin (1 μM) produced a similar effect, and a previous exposure to capsaicin prevented the effect of potassium. Conotoxin (0.1μM) significantly reduced (about 50%) the potassium-induced release of neuropeptides from the dorsal half of the rat spinal cord. These findings indicate that conotoxin-sensitive calcium channels in the rat spinal cord play a role in the neurotransmission along reflex pathways activated by stimulation of capsaicin-sensitive nerves in the urinary bladder. Inhibition of sensory neuropeptide release from primary afferents in the spinal cord is a likely target for conotoxin. These findings do not support the hypothesis that conotoxin-sensitive calcium channels are implicated in the genesis of sensory impulses at the peripheral level, although clarification of this point needs further investigation.

Arachidonic acid-induced bronchomotor responses are partially mediated by release of sensory neuropeptides from capsaicin-sensitive structures.

Administration of arachidonic acid (AA) both in vitro and in vivo elicited prominent contractile responses in guinea-pig airways, which were markedly reduced after capsaicin desensitization. Furthermore, AA superfusion elicited a significant calcitonin gene-related peptide-like immunoreactivity release from isolated bronchi. It is suggested that at least part of the bronchomotor actions of AA rely upon stimulation of capsaicin-sensitive primary afferents.

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum.

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum were investigated. Capsaicin produced a contraction followed by a relaxation of the circular muscle. Both responses were easily desensitized. As the late relaxation response was not sufficiently intense to be analyzed, the inhibitory effect of capsaicin on substance P-induced contractions was explored. Capsaicin abolished the substance P-induced contractions. This inhibitory effect was not affected by tetrodotoxin, and the effect was desensitized. Therefore, all effects of capsaicin on circular muscle motility seem to be due to the release of sensory neuropeptides, similarly to those elicited in the longitudinal muscle.