Possible involvement of substance P immunoreactive nerves in the mediation of nicotine-induced contractile responses in isolated guinea pig bronchus

Cholinergic vasoregulation in normal and adjuvant monoarthritic rat knee joints

The role of cholinergic nerves in joint vasomotor control was investigated in normal and chronically inflamed rat knees. Joint inflammation was induced by unilateral intraarticular injection of Freund's complete adjuvant and experiments were performed on both the ipsilateral and contralateral joints one and three weeks after treatment. Blood flow measurements of the exposed joints were obtained using a laser Doppler perfusion imager which provides relative changes in tissue perfusion. One week after adjuvant induction, basal perfusion in both ipsilateral and contralateral joints was significantly reduced compared to normal. At three weeks, ipsilateral knee perfusion had returned to normal, however, contralateral blood flow showed no such sign of recovery. Topical application of the muscarinic receptor antagonist atropine caused a fall in knee joint basal perfusion suggesting that cholinergic nerves are inherently involved in the physiological control of rat knee blood vessels. Acetylcholine chloride (10(-13)-10(-8) mol) in normal rats produced a dose-dependent vasodilatation of the articular microvasculature with the highest dose causing blood flow to increase by about 85%. This dilator response was attenuated in the ipsilateral monoarthritic joint at both one and three weeks post-injection while contralateral joints showed a normal response to acetylcholine at both of the time points tested. This study implicates cholinergic nerves in rat knee joint vasoregulation, however, the impairment of this mechanism by chronic inflammation could exacerbate the disease process by starving the joint of much needed vascular nourishment. Furthermore, the preservation of cholinergic responses in the contralateral knee despite a fall in basal perfusion suggests that alternative non-cholinergic mechanisms may be responsible for the hypoaemia in this joint.

Role of tachykinins in airway narrowing induced by cigarette smoke in guinea pigs

To investigate the mechanism of the airway narrowing induced by cigarette smoke, anaesthetized guinea pigs were exposed to 200 puffs of smoke for 10 min. Airway narrowing was assessed by monitoring the total pulmonary resistance (R(L)). Plasma extravasation was determined by measuring the amount of Evans blue dye extravasated into the trachea and main bronchi. Exposure to cigarette smoke caused a marked airway narrowing and plasma extravasation. Pretreatment with the dual NK(1) and NK(2) receptor antagonist, FK224, abolished such airway narrowing and significantly inhibited the extravasation. While the NK(1) receptor antagonist, FK888, inhibited the extravasation, it had no effect on airway narrowing. Atropine partially inhibited airway narrowing without affecting extravasation. Results suggest that the airway narrowing induced by cigarette smoke is caused by tachykinins, and that a cholinergic pathway is involved. Thickening of the airway walls induced by NK(1) receptor-mediated extravasation may not be involved in such airway narrowing.

Effect of omega-conotoxin GVIA on tetrodotoxin-insensitive acetylcholine release by nicotine in guinea-pig bladder

1. Contractile responses and acetylcholine release evoked by nicotine and electrical field stimulation (EFS) were determined by isotonic transducer and radioimmunoassay, respectively. 2. Nicotine-induced contraction was reduced to 30% by nicotinic receptor antagonist, hexamethonium but was insensitive to tetrodotoxin. EFS-induced contraction was abolished by tetrodotoxin but was insensitive to hexamethonium. Replacement of external Na by choline completely abolished the contractile responses evoked by nicotine and EFS. 3. Both contractions evoked by nicotine and EFS were inhibited by omega-conotoxin GVIA, and inhibitory effects of the toxin were greater in low Ca concentrations. 4. In the condition that external Na or Ca is omitted from physiological solution, acetylcholine release evoked by nicotine was not observed. Nicotine-induced acetylcholine release was partially inhibited by omega-conotoxin but was insensitive to tetrodotoxin. 5. In conclusion, nicotine interacts with nicotinic receptors located on nerve terminals and produces transmitter release which depends on external Na through tetrodotoxin-insensitive mechanisms. It is suggested that voltage-dependent omega-conotoxin sensitive Ca channels are partially involved in the nicotine-induced transmitter release.

Nicotine-induced airway smooth muscle contraction: neural mechanisms involving the airway epithelium. Functional and histologic studies in vitro

To assess the mechanism of and the role of the epithelium in nicotine-induced bronchoconstriction in vitro, we performed a combined functional and histologic study. Functional study: We suspended tracheal strips or rings from 16 ferrets (1124 +/- 561 g, mean +/- SD) in organ baths. Alternate tracheal strips had their epithelium removed. Dose-response curves to acetylcholine (ACh) and nicotine were established for pairs of tissues with and without epithelium, each pair receiving only one dose of nicotine. Nicotine induced brief muscle contractions not exceeding 25% of the ACh-induced maximum. Contractions were blocked by hexamethonium and 10(-7) M atropine and were abolished or inhibited strongly by tetrodotoxin (TTX), suggesting the involvement of nicotinic neuronal and muscarinic smooth muscle receptors. Removal of the epithelium strongly inhibited contractions at concentrations of nicotine greater than 3 x 10(-5) M which completely removed any dose-response effect. ACh-induced contractions were unchanged, demonstrating smooth muscle integrity. We suggest that the removal of the epithelium attenuates nicotine-induced bronchoconstriction through the removal of nerves running in or close to the epithelium. Histologic study: In tracheae from 15 ferrets (8 male, 7 female), mean weight (+/- SD) 1288 (+/- 470) g, we examined 4 techniques of epithelium removal: (1) gentle scraping with a scalpel blade moved backwards (away from the cutting edge), (2) moving a Q-tip through the unopened tracheal tube without lateral pressure, and (3, 4) stroking the mucosa of opened tracheal segments with a Q-tip, exerting (3) light or (4) moderate pressure. All methods were equally (97%-100%) efficient in removing the epithelium but differed in the amount of damage caused to the basement membrane and/or submucosal tissue. Method (2) caused less damage to the basement membrane than the other methods but still removed almost one-third of it. The study showed that complete removal of the epithelium is at the expense of the submucosa and that a given result of "epithelium removal" is also attributable to removal of the neighboring subepithelial structures.

Different ion channel mechanisms between low concentrations of capsaicin and high concentrations of capsaicin and nicotine regarding peptide release from pulmonary afferents

Vagal nerve stimulation (1 Hz for 1 min), capsaicin (10(-8) M and 10(-6) M), resiniferatoxin (3 x 10(-10) M) and nicotine (10(-4) M) evoked a non-cholinergic bronchoconstriction in the isolated perfused guinea-pig lung preparation. Simultaneously there was an increase in the perfusate levels of calcitonin gene-related peptide-like immunoreactivity, suggesting release from sensory nerves. Both the bronchoconstriction and peptide release evoked by a low concentration of capsaicin (10(-8) M) and that evoked by nerve stimulation were depressed by tetrodotoxin, suggesting involvement of Na+ channel dependent depolarization. Since the effects of capsaicin (10(-8) M) and vagal nerve stimulation were inhibited by omega-conotoxin but not influenced by nifedipine, the Ca(2+)-channel dependent is probably of N-type. Furthermore, the capsaicin analogue resiniferatoxin also evoked omega-conotoxin sensitive peptide release and bronchoconstriction. At the higher capsaicin concentration (10(-6) M), the functional response was only slightly inhibited by omega-conotoxin or tetrodotoxin indicating that capsaicin at this concentration evoked peptide release and functional effects through other mechanisms, probably involving Ca2+ fluxes in the non-selective cation channel associated with the proposed capsaicin receptor. The nicotine (10(-4) M) evoked peptide release and bronchoconstriction were only marginally influenced by omega-conotoxin or tetrodotoxin. It is concluded that the ion-channel mechanisms underlying the peptide releasing properties of antidromic nerve stimulation and low concentrations of capsaicin are similar and depend on action potential propagation, whereas capsaicin in high, toxic concentration and nicotine mainly act via receptor operated channels.

Effects of selective tachykinin receptor antagonists on capsaicin- and tachykinin-induced bronchospasm in anaesthetized guinea-pigs

Bronchospasm induced by i.v. injection of equieffective doses of acetylcholine, capsaicin or selective tachykinin receptor agonists ([Sar9]SP sulfone or [beta-Ala8]neurokinin A (NKA-4-10)) (for NK1 and NK2 receptors, respectively) was studied in anaesthetized guinea-pigs. The NK1 and NK2 receptor antagonists, (+/-)-CP96,345 (3 mumol/kg i.v.) and MEN 10,376 (3 mumol/kg i.v.), selectively abolished the bronchoconstriction induced by the respective agonist, showing that both NK1 and NK2 receptors mediate bronchoconstriction in guinea-pig airways and that they are activated independently. Capsaicin-induced bronchospasm was inhibited by atropine (1.5 mumol/kg i.v.) and MEN 10,376 (3 mumol/kg i.v.), but unaffected by (+/-)-CP96,345 (3 mumol/kg i.v.). Hexamethonium (79 mumol/kg i.v.), propranolol (17 mumol/kg i.v.) and physostigmine (0.9 mumol/kg i.v.) enhanced the airway constriction induced by acetylcholine, capsaicin, [Sar9]SP sulfone or [beta-Ala8]NKA-(4-10) while guanethidine (67 mumol/kg s.c. for two days) increased only bronchoconstriction induced by capsaicin or the selective NK2 receptor agonist. In hexamethonium-treated animals, MEN 10,376 still abolished the increase in insufflation pressure induced by [beta-Ala8]NKA-(4-10) and reduced the increase elicited by capsaicin. In summary, in anaesthetized guinea pig i.v. capsaicin-induced bronchospasm through activation of postjunctional NK2 (but not NK1) receptors along with activation of cholinergic pathways. This motor response is moderated by the simultaneous stimulation of a sympathetic bronchodilating mechanism(s), possibly through activation of NK2 receptors localized in sympathetic ganglia.

Variable α2-adrenoceptor-mediated inhibition of bronchoconstriction and peptide release upon activation of pulmonary afferents

In the present study, we evaluated the possible regulation by alpha 2-receptor agonists (SKF 35886 and UK 14304) of peptide release and functional responses upon sensory nerve activation in the guinea-pig lung. The peptide release and bronchoconstriction caused by antidromic vagal nerve stimulation (low frequency, 1 Hz), and a low concentration of capsaicin (10(-8) M) and resiniferatoxin (3 x 10(-10) M) were attenuated by alpha 2-adrenoceptor agonists. The effects of capsaicin and nicotine in high concentrations and high frequency nerve stimulation (10 Hz) were influenced to a much smaller extent by alpha 2-adrenoceptor stimulation. The calcitonin gene-related peptide release evoked by bradykinin but not the functional effects was inhibited by alpha 2-adrenoceptor activation. It is concluded that alpha 2-adrenoceptor stimulation mainly inhibits the release of mediator and/or the bronchoconstriction caused by moderate activation of sensory nerves. It is necessary to measure mediator release directly to reveal prejunctional effects and not to rely only on indirect functional evidence.

Bronchoconstriction and delayed rapid shallow breathing induced by cigarette smoke inhalation in anesthetized rats

Bronchomotor and ventilatory responses to inhalation of cigarette smoke (50% concentration, 6 ml) were studied in anesthetized and vagotomized Sprague-Dawley rats. Low-nicotine cigarette smoke did not cause any detectable delayed response, whereas high-nicotine cigarette smoke induced rapid, shallow breathing, and a marked increase in airway resistance (RL). The increase in f reached a peak (delta f = 43 +/- 8%) at the 5th breath after the onset of smoke inhalation, preceding both the decrease in VT (delta VT = -27 +/- 4%) and the increase in RL (delta RL = 89 +/- 19%); the latter 2 reached their peaks at approximately the 10th breath, displaying a similar temporal pattern of responses between them. The bronchomotor response to high-nicotine cigarette smoke was slightly attenuated but not prevented by prior administration of isoproterenol (0.2 mg/kg, intravenously [iv]), nor was the smoke-induced rapid, shallow breathing. In contrast, prior administration of mecamylamine (0.9 mg/kg, iv) completely abolished both the bronchomotor and ventilatory responses to smoke inhalation, indicating that nicotine is the primary causative agent responsible for these changes.

Effects of ageing on nicotine-induced contraction and substance P-like materials release in guinea-pig bronchus

1. Effects of ageing on nicotine-induced contraction and release of substance P-like materials in the bronchial preparations from guinea-pigs of different ages were studied. 2. The pD2 value (potency) of nicotine decreased with age from 10 to 100 weeks. The pD2 value of substance P did not change with age suggesting that substance P receptor mechanisms do not alter with age. 3. The amount of substance P-like materials released by nicotine (10(-4) M) decreased with age from 10 to 100 weeks, supporting our previous findings that nicotine contracts the guinea-pig bronchus through the release of substance P-like materials. 4. These results suggest that the age-related decrease in the pD2 value (potency) of nicotine is due to the reduction in the amount of substance P-like materials released by nicotine.

Effect of ageing on response to nicotine in rabbit bronchial preparation

1. Effect of ageing on the response to nicotine was tested in the bronchial muscle preparations from 5, 13, 100 and 125 week-old rabbits. The pD2 value (potency) of nicotine significantly increased in the preparation from the 125 week-old rabbits. No age-related change was found in the pD2 value of carbamylcholine or pA2 value of atropine. 2. No age-related change in characteristics of nicotine receptors. Choline acetyltransferase activity, the amount of acetylcholine released by nicotine and acetylcholineesterase activity decreased in the preparations from the 125 week-old rabbits. 3. Decrease in the pD2 value of nicotine in the preparation from the older rabbit is due to a decline in choline acetyltransferase activity followed by a reduction in the acetylcholine released, and not to a change in characteristics of nicotine receptors. 4. These results also suggest that enzymes may be influenced more easily with age than drug receptors.

Cholinergic regulation of hamster pulmonary neuroendocrine cell calcitonin

The lung content of the peptide hormone calcitonin (iCT) has been localized to discrete and clustered pulmonary neuroendocrine cells. We have undertaken a study of the effect of the autonomic ganglionic agent nicotine on the iCT of hamster lung. The acute subcutaneous administration of nicotine raised serum iCT, while lung tissue concentration of the hormone changed reciprocally to that of the serum. One week following right-sided vagotomy, total (left plus right side) iCT levels decreased following nicotine; the concentration of iCT on the denervated right lung was more markedly decreased than that from the left lung. Hamster serum levels of iCT were significantly reduced following thyroid ablation. As in the intact animals, the subsequent subcutaneous injection of nicotine to these animals raised serum iCT. Further pharmacological evaluations revealed that subcutaneously administered nicotinic cholinergic antagonists, but not muscarinic cholinergic antagonists, prevented the nicotine-evoked increase in serum iCT. Furthermore, the subcutaneous injection of acetylcholine was found to mimic the effect noted for nicotine; this was also abolished by prior administration of a nicotinic antagonist, but not by a muscarinic antagonist. The present study suggests that the nicotinic effect on pulmonary iCT secretion is ganglionically mediated, presumably via vagal innervation of the pulmonary neuroendocrine cells.

Effect of ageing on nicotine-induced contraction of guinea-pig bronchial preparation

1. Nicotine-induced contraction of bronchial preparations isolated from 3, 6, 10, 50 and 100 week old guinea-pigs were studied. 2. Contractile responses to nicotine were inhibited by hexamethonium and a substance P antagonist but not by atropine or tetrodotoxin, suggesting that the nicotine-contraction was mediated through a release of substance P-like material(s). 3. The pD2 value (potency) of nicotine did not change with age from 3 to 10 weeks but decreased thereafter to 100 weeks, while no age-related change was found in the pD2 value of substance P. The pA2 value of hexamethonium did not change with age, suggesting that the affinity of drugs to nicotine receptors does not change with age. 4. These results suggest that possibility that age-related change in the pD2 value of nicotine is due to a change in the amount of nicotine receptors but not to a change in the affinity of nicotine to its receptors.

Characterization of the substance P receptor in guinea pig lung tissues

The biologic activity of substance P has been demonstrated to be limited both in in vivo and in vitro by a membrane-bound protease, neutral endopeptidase (EC 3.4.24.11). The interaction of substance P with its receptor on guinea pig lung tissues was studied in the presence of an inhibitor of neutral endopeptidase under conditions that protect the peptide from degradation. Uptake of 0.1 nM [125I]-BH-substance P in lung membrane preparations was rapid at 4 degrees C, reaching equilibrium in 30 to 40 min, and binding was stable for at least 30 min thereafter. Binding was reversible and saturable. Scatchard analyses of saturation binding data are consistent with a single class of receptor molecules in both lung parenchymal and airway membranes, with a Kd of 2 to 3 nM and a receptor density of 4,000 to 5,000 fmol/g wet wt of tissue. In competitive binding experiments, neurokinin A and substance P methyl ester were equipotent and required approximately 100-fold higher concentrations to effect equivalent displacement than unlabeled substance P. Eledoisin also competed for [125I]-BH-substance P binding, but was less effective than the other analogs. The spasmogenically inactive derivative, substance P 1-9, did not compete for substance P binding at concentrations as high as 1 microM. Binding of [125I]-BH-substance P was rapidly and completely reversed by addition of 0.1 mM GTP, suggesting that association with a GTP binding protein is required for high affinity binding of substance P to its receptor in lung. The substance P receptor molecule was further characterized by covalently crosslinking [125I]-BH-substance P to membrane preparations followed by SDS-PAGE of the solubilized material.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional studies on the cholinergic and sympathetic innervation of the rat proximal urethra: effect of pelvic ganglionectomy or experimental diabetes

1. Isolated rings of rat proximal urethra contracted in response to acetylcholine, noradrenaline, phenylephrine, tachykinins or field stimulation. In the presence of field stimulation-induced contractions, isoprenaline or CGRP produced an inhibitory effect on evoked contractions. 2. Electrical field stimulation produced frequency-related contractions which, when using trains of stimuli, consisted of a phasic and a tonic response. These contractions were abolished by tetrodotoxin (1 microM) but unaffected by hexamethonium (10 microM). 3. Atropine (3 microM) produced a partial inhibition of these nerve-mediated contractions, slightly more evident on the tonic than the phasic response. In the presence of atropine (3 microM), phentolamine (3 microM) or prazosin (1-10 nM) produced an almost complete inhibition of the response to field stimulation. 4. After bilateral removal of the pelvic ganglia, electrical field stimulation was still able to induce tetrodotoxin-sensitive contractions of the rat proximal urethra. However, the inhibitory effect of atropine was much reduced as compared to controls, while the phentolamine-sensitive portion of the response was increased. 5. DMPP (0.1 mM) a nicotinic receptor agonist, produced a contraction (phasic and tonic components) which was strongly inhibited by hexamethonium (10 microM), abolished by prazosin (1 microM) and reduced by tetrodotoxin (3 microM). 6. In urethral rings from diabetic rats (i.v. streptozotocin 7-9 weeks before) the contractile response to acetylcholine or noradrenaline as well as the response to field stimulation were unchanged as compared to controls. 7. Capsaicin (1 microM) produced an inhibitory effect on the nerve-mediated contractions of the rat proximal urethra. This response was abolished by pelvic ganglionectomy but was unaffected in streptozotocin-treated rats. 8. These findings provide functional evidence that both cholinergic and noradrenergic nerves mediate the contractions of the rat proximal urethra. In addition, capsaicin-sensitive sensory nerves can produce certain local motor responses through release of endogenous neuropeptides. In vivo studies are needed to examine the interplay between these differents sets of motor nerves in the regulation of proximal urethra motility.

Possible non-muscarinic miotic action of echothiophate iodide in humans

The proposed non-muscarinic pupillary action of echothiophate iodide (EI) was investigated in humans. In 10 healthy volunteers the variations of the pupillary area, induced by EI eye drops, were evaluated by using an electronic pupillometer. When instilled alone, as well as after homatropine, EI caused pupillary constriction. The reduction of the homatropine-induced mydriasis by EI was not accompanied by any increase in the almost abolished pupillary response to light, thus excluding that an enhancement of the parasympathetic activity contributes to pupillary constriction. These findings suggest a non-muscarinic component in the EI-induced miosis, the nature of which remains to be elucidated.

Differential release of calcitonin gene-related peptide and neuropeptide Y from the isolated heart by capsaicin, ischaemia, nicotine, bradykinin and ouabain

The influence of various drugs as well as total ischaemia on the outflow of calcitonin gene-related peptide (CGRP), which is present in sensory nerves, and neuropeptide Y (NPY), which is co-stored with noradrenaline (NA), from the isolated guinea-pig heart, was studied in vitro. Capsaicin exposure and total ischaemia for 5-30 min induced a Ca2+-dependent increase in the outflow, suggesting release, of CGRP- but not NPY-like immunoreactivity (LI) from the heart. When characterized by high performance liquid chromatography (HPLC), the CGRP-LI present in heart extracts and the released CGRP-LI by capsaicin eluted in a major peak corresponding to synthetic CGRP. Incubation with morphine, indomethacin or reserpine pretreatment did not influence the capsaicin-evoked release of CGRP-LI. Capsaicin pretreatment depleted the cardiac content of CGRP-LI but not NPY-LI. The increase in perfusate volume observed after 30 min ischaemia in controls was reduced after capsaicin pretreatment. Nicotine exposure induced release of CGRP- as well as NPY-LI in a concentration- and Ca2+-dependent manner. The increased outflow of NPY-LI was not influenced by capsaicin pretreatment. Among other agents tested, bradykinin and ouabain caused increased outflow of CGRP but not of NPY-LI. Noradrenaline, tyramine, histamine, vasopressin, alpha,beta methylene ATP, ATP or adenosine induced changes in cardiac contractility or flow but did not evoke any detectable release of CGRP- or NPY-LI. In conclusion, the release of multiple neuropeptides can be studied in combination with contractile recordings using the isolated perfused guinea-pig whole heart preparation. Activation of cardiac sensory nerves by capsaicin, nicotine, bradykinin and ouabain, as well as ischaemia, induced release of CGRP while nicotine also evoked NPY release.

Mechanism of action of nicotine in isolated iris sphincter preparations of rabbit

1. Nicotine produced a transient contraction of rabbit isolated iris sphincter muscle, a parasympathetic ganglion-free tissue. The response to nicotine was antagonized by hexamethonium, but was insensitive to tetrodotoxin (TTX). While single treatments with atropine, capsaicin or [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-substance P (rpwwL-SP) partially blocked the response, combined treatment abolished it. 2. Chronic treatment of animals with nicotine added to the drinking water (about 12 mg kg-1 per day) had no effect on the responsiveness to nicotine or the pharmacological properties of nicotine-induced contraction. 3. These results suggest that acetylcholine and tachykinin(s) released via sodium channel-independent mechanisms from nerve terminals of parasympathetic and primary sensory nerves, respectively, are involved in the nicotine-induced contractile response.

Characterization of nicotine-induced contraction in the canine bronchus

1. The modes of action of nicotine on the dog bronchial smooth muscle preparation was investigated, in order to compare with those on the bronchial preparations from the guinea-pig, rabbit and monkey. 2. Nicotine induced a contraction in the dog bronchial preparation, and this response was abolished by hexamethonium and atropine and potentiated by physostigmine. 3. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and due to the release of acetylcholine. 4. Tetrodotoxin did not inhibit the contractile response to nicotine in the dog bronchial preparation, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 5. The present observations in the dog bronchial preparations coincided with those in the rabbit and monkey bronchi but not with the findings in the guinea-pig bronchus.

Substance P-containing nerves mediate nicotine-induced contractions of rabbit bronchial smooth muscle

1. A possible role of substance P-containing nerves in the contractile response to nicotine was investigated in isolated rabbit bronchial smooth muscle preparation. 2. Nicotine caused a contraction which was attributed to the release of acetylcholine in the rabbit bronchus. The response was reduced by capsaicin (10(-5) M) and a substance P antagonist, [D-Arg1, D-Pro2, D-Trp7.9, Leu11] substance P (10(-5) M). 3. Substance P (10(-7) M)-induced contraction was reduced by atropine (10(-6) M) and potentiated by physostigmine (10(-6) M). Furthermore, substance P (10-7 M) enhanced the release of tritium or acetylcholine from the [3H]choline labelled bronchi. 4. Results suggest that substance P-like tachykinin accelerates the nicotine-evoked prejunctional endogenous neural release of acetylcholine on the nervous cells in the rabbit bronchial preparation.

Role of primary sensory neurons in the central effects of nicotine

Utilizing single unit recording techniques the nicotine-induced excitation of noradrenaline (NA)-containing neurons in the locus coeruleus (LC) was analyzed. Low doses of nicotine (40-160 micrograms, IV) were found to dose-dependently increase the LC firing rate. The effect was antagonized by pretreatment with the quaternary ganglionic blockers hexamethonium (12 mg/kg, IP) and chlorisondamine (0.3 mg/kg, IV). Also, neonatal treatment with capsaicin, a procedure that is associated with a selective degeneration of primary sensory C-fibre afferents, clearly antagonized the effect of nicotine on LC neurons. The typical effect of nicotine on LC discharge was, in all essentials, mimicked by the quaternary nicotinic agonist tetramethylammonium (TMA). We here propose that the action of nicotine on central NA neurons is primarily executed peripherally via activation of primary sensory C-fibre afferents.

Pharmacological action of nicotine in the isolated urinary bladder from rabbit: special reference to the chronic nicotine treatment

1. A mode of action of nicotine and a change of the responsiveness to nicotine following chronic nicotine treatment in the urinary bladder of rabbit were investigated. 2. Nicotine induced only a contraction in the urinary bladder of rabbit, and the response to nicotine was reduced by hexamethonium, atropine and capsaicin. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and partially due to the release of acetylcholine and tachykinins. 3. Tetrodotoxin did not inhibit the contractile response to nicotine in the rabbit detrusor muscle, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 4. Nicotine-induced contraction was reduced following the chronic nicotine treatment without a change of its pharmacological properties. These findings suggest that chronic nicotine treatment might cause a decrease of the amounts of nicotinic receptors and also receptors for mediators released by nicotine.