A ganglionic intestinointestinal reflex activated by acute noxious challenge

To investigate noxious stimulation-responsive neural circuits that could influence the gut, we recorded from intestinally directed (efferent) nerve filaments dissected from mesenteric nerves close to the small intestine in anesthetized rats. These exhibited baseline multiunit activity that was almost unaffected by vagotomy (VagX) and reduced only slightly by cutting the splanchnic nerves. The activity was halved by hexamethonium (Hex) treatment. When an adjacent gut segment received an intraluminal stimulus 2,4,6-trinitrobenzenesulfonate (TNBS) in 30% ethanol, mesenteric efferent nerve activity increased for more than 1 h. The increased activity was almost unaffected by bilateral vagotomy or splanchnic nerve section, indicating a lack of central nervous involvement, but it was 60% reduced by hexamethonium. Spike sorting discriminated efferent single and predominantly single-unit spike trains that responded to TNBS, were unaffected by splachnectomy but were silenced by hexamethonium. After noxious stimulation of one segment, the adjacent segment showed no evidence of suppression of gut motility or vasoconstriction. We conclude that luminal application of a noxious stimulus to the small intestine activates an entirely peripheral, intestinointestinal reflex pathway. This pathway involves enteric intestinofugal neurons that excite postganglionic sympathetic neurons via a nicotinic synapse. We suggest that the final sympathetic efferent neurons that respond to a tissue damaging stimulus are distinct from vasoconstrictor, secretomotor, and motility inhibiting neurons.NEW & NOTEWORTHY An intraluminal noxious chemical stimulus applied to one segment of small intestine increased mesenteric efferent nerve activity to an adjacent segment. This was identified as a peripheral ganglionic reflex that did not require vagal or spinal connections. Hexamethonium blocked most, but not all, ongoing and reflex mesenteric efferent activity. The prevertebral sympathetic efferent neurons that are activated likely affect inflammatory and immune functions of other gut segments.

Effects of α2-adrenoceptor stimulation on luminal alkalinisation and net fluid flux in rat duodenum

The sympathetic nervous system is highly involved in the regulation of gastrointestinal functions such as luminal alkalinisation and fluid absorption. However, the exact mechanisms are not clear. This study aimed to delineate how α₂-adrenergic receptor stimulation reduces duodenal luminal alkalinisation and induces net fluid absorption. This was tested by perfusing the duodenum of anesthetized rats with isotonic solutions devoid of Cl^- and/or Na⁺, in the absence and presence of the α₂-adrenoceptor agonist clonidine. The clonidine was also studied in rats treated with dimethylamiloride (a Na⁺/H⁺ exchange inhibitor), vasoactive intestinal peptide, and the nicotinic receptor antagonist hexamethonium. Clonidine reduced luminal alkalinisation and induced net fluid absorption. The Cl^--free solution decreased luminal alkalinisation and abolished net fluid absorption, but did not prevent clonidine from doing so. Both the Na⁺-free solution and luminal dimethylamiloride increased luminal alkalinisation and abolished net fluid absorption, effects counteracted by clonidine. The NaCl-free solution (D-mannitol) did not affect luminal alkalinisation, but reduced net fluid absorption. Clonidine reduced luminal alkalinisation and induced net fluid absorption in rats perfused luminally with mannitol. However, clonidine did not affect the vasoactive intestinal peptide-induced increase in luminal alkalinisation or fluid secretion. Pre-treatment with hexamethonium abolished the effects of clonidine on luminal alkalinisation and net fluid flux. In summary, our in vivo experiments showed that clonidine-induced reduction in luminal alkalinisation and induction of net fluid absorption was unrelated to luminal Na⁺ and Cl^-, or to apical Na⁺/H⁺ or Cl^-/HCO₃^- exchangers. Instead, clonidine seems to exert its effects via suppression of nicotinic receptor-activated acetylcholine secretomotor neurons.

Successful induction of deep hypothermia by isoflurane anesthesia and cooling in a non-hibernator, the rat

The aim of the present study was to establish a novel method for inducing deep hypothermia in rats. Cooling rats anesthetized with isoflurane caused a time-dependent decrease in rectal temperature, but cardiac arrest occurred before their body temperature reached 20 °C when isoflurane inhalation was continued during the cooling process. Stopping inhalation of isoflurane when the rectal temperature reached 22.5 °C successfully induced deep hypothermia, although stopping the inhalation at 27.5 °C resulted in spontaneous recovery of rectal temperature. The hypothermic condition was able to be maintained for up to 6 h. A large number of c-Fos-positive cells were detected in the hypothalamus during hypothermia. Both the maintenance of and recovery from hypothermia caused organ injury, but the damage was transient and recovered within 1 week. These findings indicate that the established procedure is appropriate for inducing deep hypothermia without accompanying serious organ injury in rats.

Cholinergic-induced anion secretion in murine jejunal enteroids involves synergy between muscarinic and nicotinic pathways

Acetylcholine induces robust electrogenic anion secretion in mammalian intestine and it has long been hypothesized that it mediates the epithelial response through the M3 and, to a lesser extent, the M1 muscarinic receptors in the mouse. However, nicotinic receptors have recently been identified in intestinal enterocytes by quantitative real-time (qRT)-PCR/RNAseq, although any direct influence on intestinal transport has not been identified. We tested the hypothesis that cholinergic-induced anion secretion in the intestine is a result of both muscarinic and nicotinic pathways that are intrinsic to the intestinal epithelia. We developed a method to generate mouse jejunal enteroid monolayers which were used to measure active electrogenic anion secretion by the Ussing chamber/voltage-clamp technique. Here, we show that the cholinergic agonist carbachol (CCh) and the muscarinic agonist bethanechol (BCh) stimulate short-lived, concentration-dependent anion secretion in the epithelial cell-only enteroid monolayers. The muscarinic antagonist atropine completely inhibited CCh- and BCh-induced secretion, while the nicotinic antagonist hexamethonium reduced the CCh response by ~45%. While nicotine alone did not alter anion secretion, it increased the BCh-induced increase in short-circuit current in a concentration-dependent manner; this synergy was prevented by pretreatment with hexamethonium. In addition to being sensitive to hexamethonium, monolayers express both classes of cholinergic receptor by qRT-PCR, including 13 of 16 nicotinic receptor subunits. Our findings indicate that an interaction between muscarinic and nicotinic agonists synergistically stimulates anion secretion in mouse jejunal epithelial cells and identify a role for epithelial nicotinic receptors in anion secretion.

[THE INFLUENCE OF HISTAMINE ON THE EFFECTOR NEURONS OF INTRAMURAL GANGLIA OF THE TRACHEA AND BRONCHI]

We considered the influence of the neurons of intramural ganglia in the reaction of the smooth muscle trachea and bronchi caused by electric field stimulation, by the action of histamine. We studied the effect of neurons of intramural ganglia in the activity of the smooth muscle trachea and bronchi in the action of low doses of histamine (0,1 and 10 μg/ml), L-NAME and hexamethonium. It was shown the blockade of neuronal transmission decreased the contraction of the smooth muscles trachea and bronchi by stimulation of the afferent nerve structures. The smooth muscle relaxation under the influence of hexamethonium was also reduced. Histamine and hexamethonium increased contractile activity and increased the amplitude of the relaxation of the trachea and bronchi. The inhibition of NO- synthesis did not affect on the contraction, but reduced the relaxation of the trachea and bronchi. Histamine and L-NAME enhanced contractile activity, but not modified smooth muscle relaxation. Concluded that the neurons of intramural ganglia have an inhibitory effect on the smooth muscle of the trachea and bronchi and may have a modulating effect on contraction and dilatation of the smooth muscles of the airways.

In Vitro Evaluation of Carbachol and Endothelin on Contractility of Colonic Smooth Muscle in Hirschsprung’s Disease

BACKGROUND

The hypomotility of colon observed in Hirschsprung’s disease (HD) has been attributed to congenital aganglionosis only. So far, it is not clear whether the contractility of colonic smooth muscle in this condition is altered or not. Therefore, the present study attempted to understand the contractile status of colonic segments of HD patients by examining carbachol and endothelin (ET-1) evoked colonic smooth muscle contractions in vitro .

METHODS

Contractile responses were recorded from strips of colonic segments obtained from HD patients, using organ bath preparations. Cholinergic agonist carbachol and ET-1 along with their antagonists were used to evoke contractile responses. Thereafter, the samples were histopathologically confirmed for HD.

RESULTS

Colonic strips of HD did not show any spontaneous contractions but responded to carbachol and ET-1 to a lesser extent. In HD, response of carbachol was blocked by atropine and hexamethonium by nearly 73% and 50% respectively. ET-1 induced contractile responses were blocked by ET-A and ET-B antagonist up to 40%, signifying the possible role of ET-A and ET-B receptors in HD colon contractility.

CONCLUSION

As evidenced by lack of spontaneous contractions and impaired carbachol and ET-1-induced contractile responses, it is concluded that, in addition to aganglionosis, decreased contractility of colonic smooth muscle may contribute to hypomotility observed in patients with HD.

In vitro relaxant and spasmolytic effects of essential oil of Pistacia integerrima Stewart ex Brandis Galls

ETHNOPHARMACOLOGICAL RELEVANCE

Pistacia integerrima J.L. Stewart ex Brandis (Family: Anacardiaceae) galls are used in Indian ethnomedicine for its anti-asthmatic, sedative and spasmolytic properties, however, there are no scientific studies demonstrating its spasmolytic activity. The present investigation deals with the evaluation of relaxant and spasmolytic activities of the essential oil isolated from the galls of Pistacia integerrima J.L. Stewart ex Brandis (EOPI).

MATERIALS AND METHODS

In vitro pharmacological assays were carried out on rabbit jejunum spontaneous contractions, guinea pig ileum. The present investigation studied the relaxation of basal tone of isolated guinea pig ileum by possible involvement of NO, prostaglandins, membrane Na(+) channels, potassium channel, enteric nervous system, adrenoceptors, Ca(2+) channels. Additional studies were conducted for comparison of the relaxant effects of EOPI on CaCl2 induced contraction in calcium free tyrode solution, effect on nifedipine insensitive component of ACh-induced contraction and on the contractile machinery to intracellular [Ca(2+)] on isolated guinea pig ileum.

RESULTS

EOPI at non-relaxing dose potentiated the isoprenaline induced relaxation of rabbit jejunum. EOPI (50 µg/mL) exhibited 28% relaxation of basal tone of 60 mM K(+) induced contraction which is unaltered by preincubation with 0.5 mM hexamethonium, 0.5 µM Tetrodotoxin, 1 µM indomethacin, and 100 µM L-NG-Nitroarginine Methyl Ester (L-NAME). EOPI inhibited Ca(2+) induced contraction of isolated guinea pig ileum in Ca(2+) free medium. EOPI (10 µg/ml) potentiated the reversal of a KCl-induced tonic contraction has been observed in Ca(2+) free medium.

CONCLUSION

The present investigation reinforces the use of Pistacia integerrima Stewart ex Brandis as antispasmodic in folk medicine. Moreover, it is demonstrated the involvement of β- adrenoceptors and calcium channels in this activity, but not the participation of nicotinic receptors, Na(+) channels, prostaglandins or nitric oxide.

The ethanol-induced stimulation of rat duodenal mucosal bicarbonate secretion in vivo is critically dependent on luminal Cl-

Alcohol may induce metabolic and functional changes in gastrointestinal epithelial cells, contributing to impaired mucosal barrier function. Duodenal mucosal bicarbonate secretion (DBS) is a primary epithelial defense against gastric acid and also has an important function in maintaining the homeostasis of the juxtamucosal microenvironment. The aim in this study was to investigate the effects of the luminal perfusion of moderate concentrations of ethanol in vivo on epithelial DBS, fluid secretion and paracellular permeability. Under thiobarbiturate anesthesia, a ∼30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ in rats. The effects on DBS, duodenal transepithelial net fluid flux and the blood-to-lumen clearance of ⁵¹Cr-EDTA were investigated. Perfusing the duodenum with isotonic solutions of 10% or 15% ethanol-by-volume for 30 min increased DBS in a concentration-dependent manner, while the net fluid flux did not change. Pre-treatment with the CFTR inhibitor CFTR_inh172 (i.p. or i.v.) did not change the secretory response to ethanol, while removing Cl⁻ from the luminal perfusate abolished the ethanol-induced increase in DBS. The administration of hexamethonium (i.v.) but not capsazepine significantly reduced the basal net fluid flux and the ethanol-induced increase in DBS. Perfusing the duodenum with a combination of 1.0 mM HCl and 15% ethanol induced significantly greater increases in DBS than 15% ethanol or 1.0 mM HCl alone but did not influence fluid flux. Our data demonstrate that ethanol induces increases in DBS through a mechanism that is critically dependent on luminal Cl⁻ and partly dependent on enteric neural pathways involving nicotinic receptors. Ethanol and HCl appears to stimulate DBS via the activation of different bicarbonate transporting mechanisms.

[The role of the adreno-cholinergic interaction in the pulmonary hemodynamics changes following myocardial ischemia]

In acute experiments in anesthetized rabbits the pulmonary hemodynamics changes were studied following 60 s myocardial ischemia in the region of the descendent left coronary artery in control state and after the blockade of M- or N-cholinoreceptors and acetylcholine infusion. Following myocardial ischemia in control animals the pulmonary artery pressure and flow decreased, the pulmonary vascular resistance was not changed. Following myocardial ischemia after the blockade of M-cholinoreceptors by atropine the changes of pulmonary hemodynamics were the same as in control animals, the cardiac output decreased twice as more as in control animals. Following myocardial ischemia after the blockade of N-cholinoreceptors by hexamethonium the pulmonary hemodynamics changes were the same as in the control rabbits. Following myocardial ischemia after the acetylcholine infusion the pulmonary artery flow decreased more than the cardiac output, the pulmonary vascular resistance was diminished. The disbalance of the cardiac output and pulmonary artery flow changes has revealed the significance of the adreno-cholinergic interaction in the changes of the pulmonary vessels capacitance and resistive functions following myocardial ischemia.

Analgesic and anti-inflammatory effects of honey: the involvement of autonomic receptors

The use of honey for therapeutic purposes is on the increase and many studies have shown that honey has the ability to influence biological systems including pain transmission. Therefore, this study was designed to investigate the analgesic and anti-inflammatory effects of honey and the effects of concurrent administration of autonomic nervous system blocking drugs. Studies on analgesic activities was carried out using hotplate and formalin-induced paw licking models while the anti-inflammatory activity was by the carrageenan paw oedema method. Animals were distributed into six groups consisting of five animals each. They were administered saline, honey (600 mg/kg), indomethacin (5 mg/kg), autonomic blockers (3 μg/kg of tamsulosin, 20 mg/kg (intraperitoneally) of propranolol, 2 ml/kg of atropine or 10 mg/kg (intra muscularly) of hexamethonium) or honey (200 and 600 mg/kg) with one of the blockers. The results showed that honey reduced pain perception especially inflammatory pain and the administration of tamsulosin and propranolol spared the effect of honey. Hexamethonium also spared the effects of honey at the early and late phases of the test while atropine only inhibited the early phase of the test. However, atropine and hexamethonium spared the anti-inflammatory effects of honey but tamsulosin abolished the effects while propranolol only abolished the anti-inflammatory effects at the peak of the inflammation. The results suggest the involvement of autonomic receptors in the anti-nociceptive and anti-inflammatory effects of honey although the level of involvement depends on the different types of the receptors.

Hemodynamic actions and mechanisms of systemically administered α-MSH analogs in mice

α-Melanocyte-stimulating hormone (α-MSH) regulates important physiological functions including energy homeostasis and inflammation. Potent analogs of α-MSH, [Nle(4), D-Phe(7)]-α-MSH (NDP-α-MSH) and melanotan-II (MT-II), are widely used in pharmacological studies, but the hemodynamic effects associated with their systemic administration have not been thoroughly examined. Therefore, we investigated the hemodynamic actions of these compounds in anesthetized and conscious C57Bl/6N mice using peripheral routes of administration. NDP-α-MSH and MT-II induced mild changes in blood pressure and heart rate in anesthetized mice compared to the effects observed in conscious mice, suggesting that anesthesia distorts the hemodynamic actions of α-MSH analogs. In conscious mice, NDP-α-MSH and MT-II increased blood pressure and heart rate in a dose-dependent manner, but the tachycardic effect was more prominent than the pressor effect. Pretreatment with the melanocortin (MC) 3/4 receptor antagonist SHU9119 abolished these hemodynamic effects. Furthermore, the blockade of β(1)-adrenoceptors with metoprolol prevented the pressor effect and partly the tachycardic action of α-MSH analogs, while the ganglionic blocker hexamethonium abrogated completely the difference in heart rate between vehicle and α-MSH treatments. These findings suggest that the pressor effect is primarily caused by augmentation of cardiac sympathetic activity, but the tachycardic effect seems to involve withdrawal of vagal tone in addition to sympathetic activation. In conclusion, the present results indicate that systemic administration of α-MSH analogs elevates blood pressure and heart rate via activation of MC(3/4) receptor pathways. These effects and the consequent increase in cardiac workload should be taken into account when using α-MSH analogs via peripheral routes of administration.

Participation of cholinergic pathways in α-hederin-induced contraction of rat isolated stomach strips

The dry extract of Hedra helix leaves and its main active compounds, predominantly α-hederin and hederacoside C, has been traditionally believed to act spasmolytic. However, it has been recently proved that both, the extract of ivy and triterpenoid saponins, exhibit strong contractile effect on rat isolated stomach smooth muscle strips. It turned out that the most potent contractile agent isolated from the extract of ivy leaves is α-hederin. Thus, it seems reasonable to estimate the mechanism of the contractile effect of this saponin. The presented study was aimed at verifying the participation of cholinergic pathways (muscarinic and nicotine receptors) in α-hederin-induced contraction. The experiments were carried out on rat isolated stomach corpus and fundus strips under isotonic conditions. The preparations were preincubated with either atropine or hexamethonium and then exposed to α-hederin. All results are expressed as the percentage of the response to acetylcholine - a reference contractile agent. The obtained results revealed that the pretreatment of isolated stomach strips (corpus and fundus) with atropine neither prevented nor remarkably reduced the reaction of the preparations to α-hederin. Similarly, if the application of saponin was preceded by the administration of hexamethonium, the strength of the contraction of stomach fundus strips induced by α-hederin was not modified. Concluding, it can be assumed that the cholinergic pathways do not participate in α-hederin-evoked contraction of rat isolated stomach preparations.

Long-term blood pressure control: is there a set-point in the brain?

Mean arterial pressure fluctuates depending on physical or psychological activity, but should be stable at rest at around 100 mmHg throughout an entire life in human. The causes of hypertension and the blood pressure regulation mechanisms have been discussed for a long time, and many aspects have recently become more clear. Circulatory shock or short-term hypotension can be treated based on what is now known, but chronic hypertension is still difficult to treat thoroughly. The exact mechanisms for long-term blood pressure regulation have yet not been elucidated. Neuro–humoral interaction has been suggested as one of the mechanisms. Then, from the 1990s, paracrine hormones like nitric oxide or endothelins have been extensively researched in order to develop endothelial local control mechanisms for blood pressure, which have some relationships to long-term control. Although these new ideas and mechanisms are newly developed, no clear explanation for long-term control has yet been discussed, except for renal abnormality. Recently, a central set-point theory has begun to be discussed. This review will discuss the mechanisms for long-term blood pressure control, based on putative biological missions of circulatory function for life support.

[The adrenergic mechanisms are involved in the pulmonary hemodynamics changes following experimental myocardial ischemia in rabbits]

In acute experiments in anesthetized rabbits the changes of the pulmonary hemodynamics following myocardial ischemia in the region of the descendent left coronary artery were studied in control animals and after the blockade of alpha-adrenoreceptors by phentolamine or N-cholinoreceptors of autonomic ganglia by hexamethonium. Following myocardial ischemia in control animals the pulmonary artery pressure and flow decreased, the pulmonary vascular resistance was elevated not significantly, the cardiac output decreased more than pulmonary artery flow. Following myocardial ischemia after the blockade of alpha-adrenoreceptors the pulmonary artery flow and cardiac output decreased in the same level and the pulmonary vascular resistance was decreased. In these conditions the pulmonary artery pressure decreased more than in control animals, meanwhile the pulmonary artery flow was decreased in the same level as in the last case. Following myocardial ischemia after the blockade of N-cholinoreceptors the pulmonary hemodynamics changes were the same as they were following myocardial ischemia in the control rabbits, the cardiac output decreased more than pulmonary artery flow. The disbalance of the cardiac output and pulmonary artery flow changes in the case of myocardial ischemia was caused by the pulmonary vessel reactions following activations of the humoral adrenergic mechanisms.

Neuromodulation targets intrinsic cardiac neurons to attenuate neuronally mediated atrial arrhythmias

Our objective was to determine whether atrial fibrillation (AF) results from excessive activation of intrinsic cardiac neurons (ICNs) and, if so, whether select subpopulations of neurons therein represent therapeutic targets for suppression of this arrhythmogenic potential. Trains of five electrical stimuli (0.3-1.2 mA, 1 ms) were delivered during the atrial refractory period to mediastinal nerves (MSN) on the superior vena cava to evoke AF. Neuroanatomical studies were performed by injecting the neuronal tracer DiI into MSN sites that induced AF. Functional studies involved recording of neuronal activity in situ from the right atrial ganglionated plexus (RAGP) in response to MSN stimulation (MSNS) prior to and following neuromodulation involving either preemptive spinal cord stimulation (SCS; T(1)-T(3), 50 Hz, 200-ms duration) or ganglionic blockade (hexamethonium, 5 mg/kg). The tetramethylindocarbocyanine perchlorate (DiI) neuronal tracer labeled a subset (13.2%) of RAGP neurons, which also colocalized with cholinergic or adrenergic markers. A subset of DiI-labeled RAGP neurons were noncholinergic/nonadrenergic. MSNS evoked an ∼4-fold increase in RAGP neuronal activity from baseline, which SCS reduced by 43%. Hexamethonium blocked MSNS-evoked increases in neuronal activity. MSNS evoked AF in 78% of right-sided MSN sites, which SCS reduced to 33% and hexamethonium reduced to 7%. MSNS-induced bradycardia was maintained with SCS but was mitigated by hexamethonium. We conclude that MSNS activates subpopulations of intrinsic cardiac neurons, thereby resulting in the formation of atrial arrhythmias leading to atrial fibrillation. Stabilization of ICN local circuit neurons by SCS or the local circuit and autonomic efferent neurons with hexamethonium reduces the arrhythmogenic potential.

Unique ionotropic receptors for D-aspartate are a target for serotonin-induced synaptic plasticity in Aplysia californica

The non-L-glutamate (L-Glu) receptor component of D-aspartate (D-Asp) currents in Aplysia californica buccal S cluster (BSC) neurons was studied with whole cell voltage clamp to differentiate it from receptors activated by other well-known agonists of the Aplysia nervous system and investigate modulatory mechanisms of D-Asp currents associated with synaptic plasticity. Acetylcholine (ACh) and serotonin (5-HT) activated whole cell excitatory currents with similar current voltage relationships to D-Asp. These currents, however, were pharmacologically distinct from D-Asp. ACh currents were blocked by hexamethonium (C6) and tubocurarine (D-TC), while D-Asp currents were unaffected. 5-HT currents were blocked by granisetron and methysergide (MES), while D-Asp currents were unaffected. Conversely, while (2S,3R)-1-(Phenanthren-2-carbonyl)piperazine-2,3-dicarboxylic acid(PPDA) blocked D-Asp currents, it had no effect on ACh or 5-HT currents. Comparison of the charge area described by currents induced by ACh or 5-HT separately from, or with, D-Asp suggests activation of distinct receptors by all 3 agonists. Charge area comparisons with L-Glu, however, suggested some overlap between L-Glu and D-Asp receptors. Ten minute exposure to 5-HT induced facilitation of D-Asp-evoked responses in BSC neurons. This effect was mimicked by phorbol ester, suggesting that protein kinase C (PKC) was involved.

[Heterogeneity of the rat respiratory way responses to serotonin]

In stimulation of preganglionic and postganglionic nervous fibres of the trachea and stimulation of preganglionic nervous fibres of the bronchi, serotonin strengthened reduction of a smooth muscle to 114 %. Methysergide (1.0 mkg) reduced responses to serotonin to 74-77 % on the trachea and practically didn't influence the bronchi. Against ketanserinum (1.0 mkg) serotonin is dose-dependent and reduced trachea's amplitude of the constriction to 60-63% and bronchi's amplitude of the constriction to 75-79%. Hexamethonium (100.0 mkg) reduced the serotonin amplitude of the constriction of the trachea at stimulation of postganglionic nerve to 64% and the bronchi at all kinds of irritation to 82-84%. Atropine (1.0 mkg) reduced effect of serotonin in stimulation of postganglionic nerve and tracheal smooth muscles to 75-77%. On preparations of bronchi, atropine reduced the serotonin effects in stimulation of preganglionic nervous fibres to 83% and strengthened to 117% in smooth muscles in stimulation of preganglionic nerve. Thus, there is heterogeneity of responses of smooth muscles of different sites of the tracheal-bronchial pathways of the rat to serotonin.

Role of tachykinin receptors in the modulation of colonic peristaltic activity in mice

Tachykinins are important mediators of neuroneuronal and neuromuscular transmission in the gastrointestinal tract, however their contribution to colonic peristalsis in mice remains unclear. Therefore, our aim was to characterise the functional role of tachykinins in mediating peristalsis by evaluating the effect of selective tachykinin NK(1), NK(2) and NK(3) receptor agonists and antagonists on in vitro colonic peristaltic activity in mice. Using a modified Trendelenburg set-up, gradual distension of proximal and distal colonic segments evoked rhythmic, aborally migrating contractions. Peristaltic activity was assessed by quantifying the amplitude and interval of the corresponding pressure waves. Stimulation of NK(1) receptors showed regional differences as both the pressure amplitude and interval were enhanced in the distal colon without affecting peristalsis proximally. Blockade of NK(1) receptors reduced the peristaltic pressure amplitude in the proximal and distal colon while the interval was not significantly altered. NK(2) receptor stimulation resulted in a modest enhancement of the amplitude in proximal and distal segments and a slightly prolonged interval distally. Blockade of NK(2) receptors reduced the peristaltic pressure amplitude and interval in the distal colon. NK(3) receptor stimulation significantly augmented the amplitude in both segments and prolonged the interval distally. However, NK(3) receptor blockade had no effect on peristaltic activity. In conclusion, tachykinins contribute to colonic peristalsis in mice by acting mainly on NK(1) and NK(2) receptors and their effects show a proximal-to-distal gradient. NK(3) receptors might play a role in conditions of excess tachykinin release but appear not to be involved under the conditions of the present study.

Medicinal plants in Suriname: hypotensive effect of Gossypium barbadense

In traditional medicine Gossypium barbadense L. is used against hypertension. Looking for a scientific basis for this use, the blood-pressure-lowering effect of the decoction of the leaves was confirmed. Fraction II (frII) of the crude extract of G. barbadense showed a dose-dependent hypotensive effect in anaesthetized rats. In hexamethonium-treated rats, the blood-pressure-lowering effect of frII was almost abolished. A small decrease of the blood-pressure-lowering effect was followed by an increase in the blood pressure. Phentolamine antagonized the increase in blood pressure in hexamethoniumtreated rats. High doses of atropine (4 mg/rat) suppressed both depressor and heart effects. In-vitro experiments revealed that atropine did not antagonize the contraction of the ileum of the rat. Tripelennamine in a concentration of 100 μg could not influence the contraction either, whereas 300 μg did. In the guinea-pig ileum 10 μg tripelennamine did not reduce the contraction significantly.

In the mechanism of action of frII, acetylcholine receptors could be involved, but not histaminergic or adrenergic receptors. Although it is still not known which compound(s) in G. barbadense is (are) the active substance(s), the results obtained may explain the use of this plant in traditional medicine in Suriname.

Characteristics of phase 3-like activity and rebound excitation triggered by hexamethonium and atropine administration in the ovine small bowel

Administration of hexamethonium (Hx) and atropine inhibits myoelectric and motor activity and then evokes a stimulatory effect called rebound excitation (RE) in the ovine small bowel. RE has not been precisely characterized so far and it is possible that it is composed of different types of motility. This study was thus devoted to characterizing these excitatory changes in the myoelectric and motor activity of the small bowel, particularly in the duodenum in conscious sheep. These alterations occurred in response to different intravenous doses of Hx and atropine administered alone or in combinations during various phases of the migrating myoelectric or motor complex (MMC) in the fasted and non-fasted sheep. Initially two basic types of excitatory response to the cholinergic blockade were found. In the course of chronic experiments different doses of Hx and atropine evoked phase 3-like activity (unorganized phase 3 of the MMC or its fragments) alternating with the less regular RE and the duration of these changes was related to the drug dose. In the nonfasted sheep these changes were less pronounced than in the fasted animals. When the drug was given during phase 1 of the MMC, RE did not occur or was greatly reduced. Administration of Hx and atropine in the course of phase 2a and phase 2b of the MMC produced roughly similar effects. Hx triggered stronger phase 3-like activity and RE than atropine. Combinations of Hx and atropine induced an additive effect, more evident in the fasted animals. These actions of Hx and atropine, thus, appear to involve at least partly the same intramural pathways. It is concluded that Hx and atropine evoke phase 3-like activity alternating with RE as the secondary stimulatory response in conscious sheep and both these types of the intestinal motility represent two distinct motility patterns.

Effects of cigarette smoke extract and nicotine on bronchial tone and acetylcholine-induced airway contraction in mouse lung slices

BACKGROUND

Tobacco smoke is a key risk factor for chronic obstructive pulmonary disease, but it may also alter the pathophysiology of asthma. In the present study, we analyzed whether tobacco smoke has acute or chronic effects on bronchial tone and whether it alters bronchial reactivity in vitro.

METHODS

Airways in murine lung slices were digitally recorded and the change in cross-sectional area with time was quantified. T-bet KO mice served as a model for bronchial hyperreactivity. T-bet KO mice show a shift towards type 2 helper T lymphocytes and display histological as well as functional characteristics of asthma. Cigarette smoke extract (CSE) was obtained using commercially available cigarettes (Gauloise Blondes) by drawing cigarette smoke slowly through a water pump into a tube containing 10 mL of DMEM culture medium.

RESULTS

Acute exposure to CSE led to relaxation of the airway. Acute exposure to nicotine resulted in a minor relaxation of the airway in Balb/C mice and in nonsignificant relaxation of the airway in T-bet KO mice. The nicotinic acetylcholine-receptor hexamethonium partially inhibited CSE-induced airway relaxation. Airway contraction in response to acetylcholine was stronger in T-bet KO mice than in Balb/C mice. After exposure to CSE or nicotine for 48 hours, acetylcholine-induced airway contraction was no longer different between the 2 types of mice.

CONCLUSIONS

Our data indicate that acute exposure to CSE leads to airway relaxation, which is partially mediated by nicotine. Chronic exposure to CSE reverses bronchial hyperreactivity in the airways of T-bet KO mice; this effect can be mimicked by chronic exposure to nicotine.

Nicotine-evoked cytosolic Ca(2+) increase and cell depolarization in capillary endothelial cells of the bovine adrenal medulla

Endothelial cells are directly involved in many functions of the cardiovascular system by regulating blood flow and blood pressure through Ca(2+) dependent exocitosis of vasoactive compounds. Using the Ca(2+) indicator Fluo-3 and the patch-clamp technique, we show that bovine adrenal medulla capillary endothelial cells (B AMCECs) respond to acetylcholine (ACh) with a cytosolic Ca(2+) increase and depolarization of the membrane potential (20.3+/-0.9 mV; n=23). The increase in cytosolic Ca(2+) induced by 10microM ACh was mimicked by the same concentration of nicotine but not by muscarine and was blocked by 100 microM of hexamethonium. On the other hand, the increase in cytosolic Ca(2+) could be depressed by nifedipine (0.01 -100 microM) or withdrawal of extracellular Ca(2+). Taken together, these results give evidence for functional nicotinic receptors (nAChRs) in capillary endothelial cells of the adrenal medulla. It suggests that nAChRs in B AMCECs may be involved in the regulation of the adrenal gland's microcirculation by depolarizing the membrane potential, leading to the opening of voltage-activated Ca(2+) channels, influx of external Ca(2+) and liberation of vasoactive compounds.

Sympathoexcitation by oxidative stress in the brain mediates arterial pressure elevation in obesity-induced hypertension

BACKGROUND

Obesity is one of the major risk factors for cardiovascular disease and is often associated with increased oxidative stress and sympathoexcitation. We have already suggested that increased oxidative stress in the brain modulates the sympathetic regulation of arterial pressure in salt-sensitive hypertension, which is often associated with obesity. The present study was performed to determine whether oxidative stress could mediate central sympathoexcitation in the initial stage of obesity-induced hypertension.

METHODS AND RESULTS

Four-week-old male Sprague-Dawley rats were fed a high-fat (45% kcal as fat) or low-fat (10% kcal as fat) diet for 6 weeks. Fat loading elicited hypertension and sympathoexcitation, along with visceral obesity. In urethane-anesthetized and artificially ventilated rats, arterial pressure and renal sympathetic nerve activity decreased in a dose-dependent fashion when 53 or 105 mumol/kg tempol, a membrane-permeable superoxide dismutase mimetic, was infused into the lateral cerebral ventricle. Central tempol reduced arterial pressure and renal sympathetic nerve activity to a significantly greater extent in high-fat diet-fed hypertensive rats than in low-fat diet-fed normotensive rats. Intracerebroventricular apocynin or diphenyleneiodonium, a reduced NADPH oxidase inhibitor, also elicited markedly greater reductions in arterial pressure and renal sympathetic nerve activity in the high-fat diet-fed rats. In addition, fat loading increased NADPH oxidase activity and NADPH oxidase subunit p22(phox), p47(phox), and gp91(phox) mRNA expression in the hypothalamus.

CONCLUSIONS

In obesity-induced hypertension, increased oxidative stress in the brain, possibly via activation of NADPH oxidase, may contribute to the progression of hypertension through central sympathoexcitation.

Gastric relaxation induced by electrical and chemical stimulation of the area postrema in the rat

Area postrema (AP) is considered to be an important neural center for emesis in carnivores. However, it is also known that AP mediates motor responses induced by apomorphine in rats which do not have an emetic reflex. To shed more light on the possible role of AP in the control of gastric motility in physiological or pathophysiological conditions, we observed the effects of electrical or chemical (apomorphine) stimulation of AP neurons on intragastric pressure (IGP) or intragastric volume (IGV) in rat. We found that electrical stimulation (ES) reduces IGP, and this is sensitive to hexamethonium or L-NAME, and apomorphine also reduces IGP and increases IGV. In slice preparations, apomorphine (10 micromol/l) increased the frequency of spontaneous single unit discharges of AP neurons recorded extracellularly. We also succeeded retrograde labeling of AP neurons by DiI applied into the gastric corpus, for the first time. These observations indicate that rat stomach receives efferent neural input from AP and the excitation of AP neurons relaxes the stomach in rat, suggesting some functional roles of AP neurons in the regulation of gastric motility.

Hexamethonium sensitivity of the swim musculature of the pteropod mollusc, Clione limacina

Swimming in reduced electrophysiological preparations of the pteropod mollusc, Clione limacina, was blocked by bath application of hexamethonium even though pattern generator activity continued with this treatment. Neuromuscular recordings indicated that hexamethonium blocked synaptic input from Pd-3 and Pd-4 motoneurons to slow-twitch muscle cells, while connections from Pd-1A and Pd-2A motoneurons to fast-twitch muscle cells were variable in their response to hexamethonium-synaptic inputs were suppressed in most cases and occasionally blocked, but the latter only with high concentrations and long incubations. Acutely dissociated wing muscle cells showed a concentration-dependency in the percentage of contracted cells with bath application of acetylcholine, and this contractile activity was blocked in preparations that were first bathed in hexamethonium. Intracellular recordings from dissociated slow-twitch muscle cells showed conductance-increase depolarizations of approximately 20 mV following 1 s pressure ejections of 10(-4) M acetylcholine from micropipettes placed immediately adjacent to the muscle cells. These responses were blocked when hexamethonium was bath applied prior to the pressure-applied acetylcholine. The results suggest the Pd-3/Pd-4 motoneuron to slow-twitch muscle cell junctions are cholinergic with nicotinic-like receptors, while the Pd-1A/Pd-2A to fast-twitch muscle cell connections are likely cholinergic, but with a different receptor type.

Contractile effect of tachykinins on Suncus murinus (house musk shrew) isolated ileum

Recent studies used Suncus murinus to investigate the anti-emetic potential of NK(1) tachykinin receptor antagonists. However, the pharmacology of tachykinin receptors in this species has not been fully characterized. In the present studies, therefore, we examined a range of tachykinin receptor agonists for a capacity to induce contractions of the isolated ileum. The tachykinin NK1 receptor preferring agonists substance P, septide and [Sar9Met(O2)11] substance P, and the tachykinin NK2 preferring agonists neurokinin A and GR 64349 (Lys-Asp-Ser-Phe-Val-Gly-R-gamma-lactam-Leu-Met-NH2) caused concentration dependent contractions with EC50 values in the nanomolar range. However, the tachykinin NK3 preferring agonists neurokinin B and senktide (1nM-1microM) induced only weak contractions. The action of senktide, but not [Sar9Met(O2)11] substance P, septide, or GR 64349, was antagonized significantly by atropine (P<0.05); tetrodotoxin and hexamethonium were inactive. The tachykinin NK1 receptor antagonist CP-99,994 ((+)-[(2S,3S)-3-(2-methoxy-benzyl-amino)-2-phenylpiperidine]) (10-100nM) inhibited substance P- and septide-induced contractions non-competitively. The pA2 value estimated for CP-99,994 against septide was 7.3+/-0.1. It also non-competitively antagonized the contractile responses induced by [Sar9Met(O2)11] substance P with a pA2 of 7.4+/-0.1. CP-99,994 also had a slight inhibitory action on neurokinin A-induced contractions, but did not modify the action of GR 64349. Conversely, the tachykinin NK2 receptor antagonist, saredutant, competitively antagonized GR 64349-induced contractions with a pA2 of 7.34+/-0.02. On the other hand, the presence of both CP-99,994 and saredutant competitively antagonized substance P-induced contraction. The present studies indicate that tachykininNK1 and NK2 receptors exist in the ileum of S. murinus and are involved in mediating contractions directly on smooth muscle, whereas tachykinin NK3 receptors may play a minor role involving a release of acetylcholine.

[Non-neuronal effects of muscarinic antagonists in the prophylaxis of stress]

We have studied the stress-limiting role of the immune reaction initiated by cholinergic antagonists and the influence of these drugs on the dynamics of antibody formation in the spleen and the blood serum corticosterone level. The protective effect of immune reaction initiated by methacine (muscarinic receptor antagonist) or hexamethonium (nicotinic receptor antagonist) in prevention of stress gastric ulcer in rats (induced by water immersion stress, WIS) was estimated upon administration of the drugs for 5 days (local response) or 14 days (systemic response) prior to WIS. The pharmacological effects of drugs were estimated upon their administration 30 minutes prior to WIS. It is shown that, if cholinergic antagonists affect the systemic immune response the induction of WIS at this level of immune reaction leads to the effective prevention of stress gastric ulcer. The administration of methacine (but not hexamethonium) 14 days prior to WIS effectively reduces gastric lesions up to 1.0 +/- 0.1 arbitrary units in comparison to 3.6 + 0.2 arbitrary units in the control group. Under effective prophylaxis, the number of antibody-forming cells (AFC/10(6) of splenocytes) and corticosterone concentration are close to their basal level, while under stress conditions, these parameters significantly increase up to 870 +/- 21 and 350 +/- 4 vs. 100 +/- 17 and 107 +/- 6 in the control group, accordingly. It is established that both methacine and hexamethonium remain immunologically active for 28 days and more: the maximum amount of AFC upon administration of hexamethonium and methacine was on the 5th day and 14th day, respectively. Thus, determination of the drug influence on the systemic immune response allows one to predict the non-neuronal effects of cholinergic antagonists and, in this way, to affect the pathogenesis of stress gastric ulcer. Estimation of the AFC response and corticosterone level after WIS shows the efficacy ofprophylaxis of the gastric stress lesion.

Calcitonin gene-related peptide-evoked sustained tachycardia in calcitonin receptor-like receptor transgenic mice is mediated by sympathetic activity

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) are potent vasodilators and exert positive chronotropic and inotropic effects on the heart. Receptors for CGRP and AM are calcitonin receptor-like receptor (CLR)/receptor-activity-modifying protein (RAMP) 1 and CLR/RAMP2 heterodimers, respectively. The present study was designed to delineate distinct cardiovascular effects of CGRP and AM. Thus a V5-tagged rat CLR was expressed in transgenic mice in the vascular musculature, a recognized target of CGRP. Interestingly, basal arterial pressure and heart rate were indistinguishable in transgenic mice and in control littermates. Moreover, intravenous injection of 2 nmol/kg CGRP, unlike 2 nmol/kg AM, decreased arterial pressure equally by 18 ± 5 mmHg in transgenic and control animals. But the concomitant increase in heart rate evoked by CGRP was 3.7 times higher in transgenic mice than in control animals. The effects of CGRP in transgenic and control mice, different from a decrease in arterial pressure in response to 20 nmol/kg AM, were suppressed by 2 μmol/kg of the CGRP antagonist CGRP(8-37). Propranolol, in contrast to hexamethonium, blocked the CGRP-evoked increase in heart rate in both transgenic and control animals. This was consistent with the immunohistochemical localization of the V5-tagged CLR in the superior cervical ganglion of transgenic mice. In conclusion, hypotension evoked by CGRP in transgenic and control mice was comparable and CGRP was more potent than AM. Unexpectedly, the CLR/RAMP CGRP receptor overexpressed in postganglionic sympathetic neurons of transgenic mice enhanced the positive chronotropic action of systemic CGRP.

Urocortin I is present in the enteric nervous system and exerts an excitatory effect via cholinergic and serotonergic pathways in the rat colon

Corticotropin-releasing factor (CRF) and urocortin I (UcnI) have been shown to accelerate colonic transit after central nervous system (CNS) or peripheral administration, but the mechanism of their peripheral effect on colonic motor function has not been fully investigated. Furthermore, the localization of UcnI in the enteric nervous system (ENS) of the colon is unknown. We investigated the effect of CRF and UcnI on colonic motor function and examined the localization of CRF, UcnI, CRF receptors, choline acetyltransferase (ChAT), and 5-HT. Isometric tension of rat colonic muscle strips was measured. The effect of CRF, UcnI on phasic contractions, and electrical field stimulation (EFS)-induced off-contractions were examined. The effects of UcnI on both types of contraction were also studied in the presence of antalarmin, astressin2-B, tetrodotoxin (TTX), atropine, and 5-HT antagonists. The localizations of CRF, UcnI, CRF receptors, ChAT, and 5-HT in the colon were investigated by immunohistochemistry. CRF and UcnI increased both contractions dose dependently. UcnI exerted a more potent effect than CRF. Antalarmin, TTX, atropine, and 5-HT antagonists abolished the contractile effects of UcnI. CRF and UcnI were observed in the neuronal cells of the myenteric plexus. UcnI and ChAT, as well as UcnI and 5-HT, were colocalized in some of the neuronal cells of the myenteric plexus. This study demonstrated that CRF and UcnI act on the ENS and increase colonic contractility by enhancing cholinergic and serotonergic neurotransmission. These peptides are present in myenteric neurons. CRF and, perhaps, to a greater extent, UcnI appear to act as neuromodulators in the ENS of the rat colon.

Neonatal maternal separation of rat pups results in abnormal cholinergic regulation of epithelial permeability

Neonatal maternal separation (MS) predisposes adult rats to develop stress-induced mucosal barrier dysfunction/visceral hypersensitivity and rat pups to develop colonic epithelial dysfunction. Our aim was to examine if enhanced epithelial permeability in such pups resulted from abnormal regulation by enteric nerves. Pups were separated from the dam for 3 h/day (days 4-20); nonseparated (NS) pups served as controls. On day 20, colonic tissues were removed and mounted in Ussing chambers. Horseradish peroxidase (HRP) flux was used to measure macromolecular permeability. HRP flux was increased in MS versus NS pups. The enhanced flux was inhibited by the cholinergic muscarinic antagonist atropine and the nicotinic antagonist hexamethonium. The cholinergic component was greater in tissues from MS versus NS pups, suggesting that increased cholinergic activity was responsible for the MS elevated permeability. Western blots and immunohistochemistry of colonic tissues demonstrated increased expression of choline acetyltransferase (ChAT) in MS pups, indicating greater synthesis of acetylcholine. Since a previous study indicated that corticotrophin-releasing factor (CRF) mediates barrier dysfunction in MS pups, we examined if the two pathways were linked. In MS tissues, nonselective CRF receptor antagonism inhibited the enhanced flux, and the addition of atropine did not produce further inhibition. Using selective receptor antagonists, we identified that CRF receptor 2 was involved in mediating this effect. These findings suggest that CRF, via CRF receptor 2, acts on cholinergic nerves to induce epithelial barrier dysfunction. Our study provides evidence that MS stimulates synthesis of acetylcholine, which, together with released CRF, creates a condition conducive to the development of epithelial barrier defects.

Effect of esophageal distention on basal and stimulated gastric acid secretion in rats

BACKGROUND

It is well established that the esophageal distention (ED) leads to gastric relaxation, partly by vago-vagal reflex, but till now, the effect of ED on gastric acid secretion has not been investigated. The aim of this study was to investigate the effect of ED on basal and stimulated gastric acid secretion.

METHODS

Adult male Wistar rats (200-240 g) were deprived of food but not the water 24 h before the experiments. Under urethane anesthesia (1.2 g/kg, i.p.), animals underwent tracheostomy and laparotomy. A catheter was inserted in the stomach through duodenum for gastric distention and gastric washout and the esophagus was cannulated with a distensible balloon orally to distend esophagus (0.3 ml, 10 min). Gastric acid secretion was stimulated by gastric distention, carbachol (4 microg/kg, i.p.) or histamine (5 mg/kg, s.c.). Effects of vagotomy, NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg, i.v.) and also hexamethonium were investigated.

RESULTS

Basal and gastric distention- and carbachol, histamine-stimulated acid secretion were reduced by the ED (P<0.05, P<0.0001, P<0.01 and P<0.02, respectively). L-NAME (10 mg/kg, i.v.) elevated the acid output (P<0.002). Vagotomy reduced the inhibitory effect of the esophagus distention on gastric distention-induced acid secretion (P<0.01).

CONCLUSION

These results indicate that the vagus nerves are involved in the inhibitory effect of the ED on the basal and stimulated gastric acid secretion. Furthermore, nitric oxide could be involved.

CHRONIC SALT LOADING AND CARDIOVASCULAR-ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

1. High-sodium intake may increase blood pressure and diabetes is a salt-sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)-diabetic rats that underwent chronic salt loading. 2. We studied male Wistar rats (150-280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C-S and D-S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin-converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin-angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V(1) receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3. Glycaemia was similar between C and C-S (P = 0.612) and between D and D-S (P = 0.552), but higher in diabetic compared with non-diabetic rats (P < 0.0001). The D-S rats had an increment of 24% in mean AP compared with D (120 +/- 4 vs 97 +/- 2 mmHg, respectively; P = 0.0001), which was not seen in C-S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D-S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D-S compared with D rats (P = 0.001). 4. The main neurohumoral mechanisms of salt-induced cardiovascular changes in STZ-diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.

Key role of mucosal primary afferents in mediating the inhibitory influence of capsaicin on vagally mediated contractions in the mouse esophagus

Transient receptor potential ion channel of the vanilloid type 1 (TRPV1)-dependent pathway, consisting of capsaicin-sensitive tachykininergic primary afferent and myenteric nitrergic neurons, was suggested to mediate the inhibitory effect of capsaicin on the vagally mediated striated muscle contractions in the rat esophagus. These primary afferent neurons upon entering into the esophagus are distributed through the myenteric plexus, terminating either in the myenteric ganglia or en route to the mucosa where they branch into a delicate net of fine varicose fibers. Therefore, this study aimed to investigate whether the mucosal primary afferents are a main mediator for the capsaicin inhibitory influence on vagally mediated contractions in the mouse esophagus. For this purpose, the vagally induced contractile activity of a thoracic esophageal segment was measured in the circular direction with a force transducer. Vagal stimulation (30 microsec, 25 V, 1-50 Hz for 1 sec) produced monophasic contractile responses, whose amplitudes were frequency-dependent. These contractions were completely abolished by d-tubocurarine (5 microM) while resistant to atropine (1 microM) and hexamethonium (100 microM). Capsaicin (30 microM) significantly inhibited the vagally induced contractions in esophagi with intact mucosa while its effect on preparations without mucosa was insignificant. Additionally, immunocytochemistry revealed the presence of TRPV1-positive nerve fibers in the tunica mucosa. Taken together, we conclude that in the mouse esophagus, capsaicin inhibits the vagally mediated striated muscle contractions mainly through its action on mucosal primary afferents, which in turn activate the presumed inhibitory local reflex arc.

Sympathetic and renin-angiotensin systems contribute to increased blood pressure in sucrose-fed rats

BACKGROUND

This study evaluated the effect of chronic sucrose feeding on hemodynamic parameters and renal sympathetic nervous activity. In addition, angiotensin I, II, and 1-7 levels were determined in plasma, heart, kidney, and the epididymal adipose tissue.

METHODS

Male Wistar rats were treated for 30 days with 20% sucrose solution (n = 21) or tap water (n = 19) and food ad libitum. Blood pressure, cardiac output, and total peripheral resistance were recorded at the end of the 30-day treatment period. Sympathetic and angiotensinergic systems were evaluated by acute hexamethonium and captopril administration; plasma and tissue (heart, kidney, and epididymal adipose tissue) angiotensins were measured by high-performance liquid chromatography; and angiotensin-converting enzyme activity was determined by continuous fluorescent assay. Plasma renin activity and plasma levels of insulin and leptin were evaluated by radioimmunoassay.

RESULTS

Chronic sucrose feeding was associated with increased blood pressure (BP) (129 +/- 1 v 102 +/- 3 mm Hg) and circulating insulin (171%) and leptin (356%) levels when compared with the control group. The sucrose group also showed a 27% higher renal sympathetic nervous activity. The depressor response to hexamethonium was similar in both groups, whereas captopril caused a more pronounced decrease in BP in the sucrose group than in controls (-40 +/- 2 v -11 +/- 2 mm Hg), possibly reflecting the higher plasma renin activity and plasma content of angiotensin II and renal angiotensin II in sucrose rats.

CONCLUSIONS

These findings suggest a specific renal renin-angiotensin-sympathetic activation as a potential mechanism for the cardiovascular changes in response to chronic sucrose feeding.

Neurally released pituitary adenylate cyclase-activating polypeptide enhances guinea pig intrinsic cardiac neurone excitability

Intracellular recordings were made in vitro from guinea-pig cardiac ganglia to determine whether endogenous neuropeptides such as pituitary adenylate cyclase-activating polypeptide (PACAP) or substance P released during tetanic neural stimulation modulate cardiac neurone excitability and/or contribute to slow excitatory postsynaptic potentials (sEPSPs). When nicotinic and muscarinic receptors were blocked by hexamethonium and atropine, 20 Hz stimulation for 10 s initiated a sEPSP in all innervated neurones. In 40% of the cells, excitability was enhanced after termination of the sEPSP. This suggested that non-cholinergic receptor-mediated mechanisms contributed to the sEPSP and modulated neuronal excitability. Exogenous PACAP and substance P initiated a slow depolarization in the neurones whereas neuronal excitability was only increased by PACAP. When ganglia were treated with the PAC1 antagonist PACAP6-38 (500 nM), the sEPSP evoked by 20 Hz stimulation was reduced by approximately 50% and an enhanced excitability occurred in only 10% of the cells. These observations suggested that PACAP released from preganglionic nerve terminals during tetanic stimulation enhanced neuronal excitability and evoked sEPSPs. After addition of 1 nM PACAP to the bath, 7 of 9 neurones exhibited a tonic firing pattern whereas in untreated preparations, the neurons had a phasic firing pattern. PACAP6-38 (500 nM) diminished the increase in excitability caused by 1 nM PACAP so that only 4 of 13 neurones exhibited a tonic firing pattern and the other 9 cells retained a phasic firing pattern. These findings indicate that PACAP can be released by tetanic neural stimulation in vitro and increase the excitability of intrinsic cardiac neurones. We hypothesize that in vivo PACAP released during preganglionic firing may modulate neurotransmission within the intrinsic cardiac ganglia.

Behavioral Cross-Tolerance between Repeated Intracerebellar Nicotine and Acute Δ9-Tetrahydrocannabinol-Induced Cerebellar Ataxia: Role of Cerebellar Nitric Oxide

We have previously demonstrated that acute intracerebellar nicotine or N-methyl-4-(3-pyridinyl)-3-buten-1-amine (RJR-2403), a selective alpha(4)beta(2) nicotinic acetylcholine receptor (nAChR) agonist, dose dependently attenuates Delta(9)-tetrahydrocannabinol (Delta(9)THC)-induced ataxia. Presently, we have shown that intracerebellar nicotine (1.25, 2.5, and 5 ng; once daily for 5 days) and RJR-2403 (250, 500, and 750 ng; once daily for 5 days) significantly attenuate cerebellar Delta(9)-THC-induced ataxia dose dependently, suggesting the development of cross-tolerance between nicotine or RJR-2403 with Delta(9)-THC in male CD-1 mice. Intracerebellar RJR-2403 (750 ng) microinfused for 1, 2, 3, 5, and 7 days (once daily) significantly attenuated Delta(9)-THC-induced ataxia in the 3-, 5-, and 7-day treatment groups; optimal cross-tolerance was evident at day 5 and persisted till 36 h after the last RJR-2403 microinfusion. Intracerebellar microinfusion of hexamethonium (nAChR antagonist; 1 microg) or dihydro-beta-erythroidine hydrobromide (alpha(4)beta(2) nAChR antagonist; 500 ng) for 5 days 10 min before daily intracerebellar nicotine or RJR-2403 microinfusion virtually abolished cross-tolerance between nicotine or RJR-2403 and Delta(9)-THC, indicating nAChR participation. In addition, microinfusion of antagonists 10 min after daily intracerebellar nicotine or RJR-2403 failed to alter the cross-tolerance, suggesting possible involvement of downstream cerebellar second-messenger mechanisms. Finally, the cerebellar concentration of nitric oxide products [total sum of nitrite + nitrate (NO(x))] was increased after 5 days of intracerebellar nicotine or RJR-2403 treatment, which was decreased by acute intracerebellar Delta(9)-THC treatment. The "nicotine or RJR-2403 + Delta(9)-THC" treatments significantly increased cerebellar NO(x) levels compared with treatment with Delta(9)-THC alone, supporting a functional correlation between cerebellar nitric oxide production and cerebellar Delta(9)-THC-induced ataxia and suggesting participation of nitric oxide in the observed cross-tolerance between nicotine/RJR-2403 and Delta(9)-THC.

Effects of some beta-adrenoceptor antagonists on orthostatic hypotension in repeatedly cold- (SART-) stressed rats

Rats stressed by specific alternation of rhythm in temperature (SART) show various symptoms of disautonomia, increased pulse rates, continuous hypotension, and severe orthostatic hypotension (OH) when they are subjected to postural change. The OH symptoms are improved by muscarinic M2-receptor blockers. In the present study, effects of beta-adrenoceptor blocking agents on OH in SART-stressed rats were investigated. Anesthetized rats were restrained on a board in the supine position, and direct blood pressure and ECG were measured automatically using Fluclet Jr.2. Postural change was performed by raising the rat's head up to a 60 degrees angle for 4 min. Unstressed rats treated with hexamethonium showed large decrease in blood pressure, small reflex from the bottom of pressure and decreased tachycardia reflex, whereas isoproterenol showed little changes. In SART-stressed rats, isoproterenol alleviated the decrease in blood pressure in postural change, brought large reflex from the bottom of pressure and increased tachycardia reflex, whereas hexamethonium had little changes. Propranolol and atenolol induced the similar changes as those seen by hexamethonium. ICI-118,551, a selective beta2-adrenoceptor antagonist showed large reflex from the bottom of pressure and increased tachycardia reflex in stressed rats, whereas little changes in unstressed rats. In conclusion, it was suggested that the hypotension in OH manifestation time of rats reflects the state of peripheral blood vessels, and beta1-adrenoceptors played a role in compensatory tachycardia reflex and beta2-adrenoceptors in blood pressure reflex. The circulatory regulation in SART-stressed rats seems to be poorly functioning in nervous reflex in postural changes.

Enhancement effects of nicotine on neurogenic contractile responses in rabbit gastric fundus

Nicotine, a nicotinic acetylcholine receptor agonist, plays a role in the modulation of neurotransmitter release following nerve stimulation in both the central and the peripheral nervous system. Nitric oxide and prostaglandins modulate the release of various neurotransmitters in different tissues. We aimed to investigate the effects of nicotine on neurogenic contractile responses via nicotinic acetylcholine receptors and, if a change occurred, to investigate the effects of N(W)-nitro-L-arginine methyl ester (L-NAME) and indomethacin on this change in rabbit gastric fundus. Electrical field stimulation (EFS)-evoked contractile responses were recorded from gastric fundus strips obtained from rabbits with an isometric force displacement transducer. Nicotine was applied to preparations at varying concentrations. Then, the effects of hexamethonium, cadmium (Cd(2+)), indomethacin, and L-NAME were tested on the EFS-evoked contractions in the presence of nicotine. Nicotine-induced transient neurogenic contractions in a dose-dependent manner. Cd(2+) and hexamethonium inhibited nicotine-induced transient neurogenic contractions, but indomethacin and L-NAME produced no effect. In conclusion, nicotine increased EFS-evoked contractile responses, possibly by facilitating neurotransmitter release from nerve terminals by a mechanism dependent on the influx of Ca(2+) from voltage-gated Ca(2+) channels via activation of nicotinic acetylcholine receptors in isolated rabbit gastric fundus. Endogenous nitric oxide and prostaglandins do not play a physiological role in the regulation of this neurotransmitter release.

Effects of adiponectin on the renal sympathetic nerve activity and blood pressure in rats

Adiponectin is an adipocytokine that modulates energy homeostasis and glucose metabolism. Here, we examined the effects of acute intravenous (iv) and lateral cerebral ventricular (LCV) injections of adiponectin on the renal sympathetic nerve activity (RSNA) and blood pressure (b/p) in urethane-anesthetized rats. Both iv and LCV injections of adiponectin induced dose-dependent suppressions of RSNA and b/p. Moreover, we found that bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) abolished the effects of iv injection of adiponectin on RSNA and b/p. These findings suggest that adiponectin decreases the RSNA and b/p in a dose-dependent manner and that the SCN is implicated in mechanism of adiponectin actions on RSNA and b/p. These findings also suggest that the hypotensive-action activity of adiponectin is realized, at least partially, via changes in activities of autonomic nerves activity.

[Hexamethonium, nicotinic receptor blocker, changes the neuronal reactions on glutamate in the medial septal area in vitro]

Despite the great interest in studying the medial septal area, the interactions of its neurochemical systems are not yet clearly understood. The aim of this study was to elucidate the role of nicotinic receptors in the interaction of glutamatergic and cholinergic systems of the medial septal area. The effect of L-glutamate (1 microM) on septal neurons was studied under the application of hexamethonium, nicotinic cholinoreceptor blocker by using the method of extracellular recording of neuronal activity in brain slices of ground squirrels. The response of septal neurons to glutamate depended on the type of their initial activity and on the presence of pacemaker properties. For the first time, the ability of septal neurons to respond to glutamate with an increase in burst frequency was shown. The influence of hexamethonium on the neuronal activity was similar to that of glutamate. After a preliminary application of hexamethonium, the reactions of neurons to glutamate changed. The excitatory reactions were masked, while the inhibitory reactions became stronger. It was found that nicotinic cholinergic receptors modulated the reactions of MS-DB cells to glutamate and the expression of the oscillatory properties of the septal neuronal network.

Ischaemia-induced sympathoexcitation in spinalyzed rats

Systemic ischaemia increases sympathetic activity via both reflex and direct effects on the nervous system, which include the hypothalamus and brainstem structures that provide excitatory drive to sympathetic pre-ganglionic motoneurones. Using an arterially perfused working heart-brainstem preparation (WHBP), we evaluated the sympathoexcitatory response recorded from the thoracic sympathetic chain (tSC) in response to systemic ischaemia (produced by arresting perfusion for 30 s) before and after transecting consecutively at both the ponto-medullary and medullary-spinal cord junctions. Ischaemia produced a striking increase in tSC activity that persisted after transecting at both the ponto-medullary and medullary-spinal cord levels (intact: 70+/-3%; ponto-medullary: 77+/-7%; medullary-spinal cord: 61+/-6%; n=9). In sino-aortic denervated (SAD) rats (n=4), sympathoexcitatory responses were smaller in both intact and ponto-medullary, but not in medullary-spinal cord transected versus intact rats. Following administration of a ganglionic blocker [hexamethonium (hex), 25 mg/kg] after medullary-spinal cord transection the ischaemia-induced sympathoexcitatory response was reduced (12+/-6% increase relative to control, n=4). In medullary-spinal cord transected preparations, intrathecal injection of N2-saturated saline increased tSC discharge (22+/-3%, n=4), which was attenuated by hex (5+/-1%). We propose that neural mechanisms within the cervical-thoracic segments can make a substantial contribution to the sympathoexcitatory response during systemic ischaemia.

Antinociceptive effects of the novel spirocyclopiperazinium salt compound LXM-10 in mice

The compound LXM-10 (2,4-dimethyl-9-beta-phenylethyl-3-oxo-6, 9-diazaspiro [5.5]undecane chloride) is a new spirocyclopiperazinium salt compound. This is the first article to evaluate its antinociceptive effect in the abdominal constriction test induced by acetic acid and the hot-plate test. In the abdominal constriction test, LXM-10 had a significant dose-response effect, and the maximal inhibition ratio was 79.2%. In the hot-plate test, LXM-10 had significant dose-response and time-response effects. The antinociceptive effect began at 1.0 h, peaked at 2.0 h, and persisted 3.0 h after s.c. administration. The hot-plate latency was increased by 126.8% at the dose of 12.0 mg/kg. The antinociceptive effect of LXM-10 was blocked by mecamylamine (a central and peripheral neuronal nicotinic acetylcholine receptor antagonist, 0.25, 0.5, 1.0 mg/kg, i.p.), hexamethonium (a peripheral neuronal nicotinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.), atropine (a central and peripheral muscarinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.), and atropine methylnitrate (a peripheral muscarinic acetylcholine receptor antagonist, 0.2, 1.0, 5.0 mg/kg, i.p.) in a dose-dependent fashion. In contrast, the effect was not blocked by naloxone (a non-selective opioid receptor antagonist, 2.0 mg/kg, i.p.) or yohimbine (a alpha(2)-adrenergic receptor antagonist, 1.0, 2.5, 5.0 mg/kg, i.p.) in the hot-plate test. Therefore, the antinociceptive effects of LXM-10 involve the peripheral neuronal nicotinic and muscarinic acetylcholine receptors; they are not related to opioid receptors or alpha(2)-adrenergic receptors. LXM-10 did not affect motor coordination, spontaneous activity, or body temperature. These findings with LXM-10 suggest that spirocyclopiperazinium derivatives could provide insight on new analgesics.

Acute distal colitis impairs gastric emptying in rats via an extrinsic neuronal reflex pathway involving the pelvic nerve

BACKGROUND AND AIMS

Patients with inflammatory bowel disease often present with abnormal gut motility away from the inflammatory site. We studied remote motility disturbances and their pathophysiology in a rat model of colitis.

METHODS

Colitis was induced 72 h prior to experiments using trinitrobenzene sulphate (TNBS) instillation. Inflammation was verified using histology and myeloperoxidase (MPO) measurements. To assess gut motility, we determined gastric emptying, distal front and geometric centre (GC) of intestinal transit 30 min after intragastric administration of a semiliquid Evans blue solution. The effects of hexamethonium (20 mg/kg), capsaicin (125 mg/kg) and pelvic nerve section on colitis induced motility changes were evaluated. c-Fos expression was studied in the pelvic nerve dorsal root ganglion (DRG) S1.

RESULTS

Colitis reduced gastric emptying from 38.4 (3.6)% in controls to 22.7 (4.4)% in TNBS treated rats in the absence of local gastric inflammation. Colitis had no effect on the distal front or on the geometric centre of small intestinal transit. Hexamethonium reduced gastric emptying in controls to 26.3 (4.1)% but restored it to 35.8 (4.4)% in TNBS treated rats. Capsaicin significantly impaired gastric emptying in controls from 33.1 (5.2)% to 9.5 (3.3)% while this effect was less pronounced in TNBS treated rats (from 19.2 (2.3)% to 11.5 (3.8)%; NS). In TNBS treated rats, pelvic nerve section completely restored gastric emptying from 19.8 (5.3)% to 52.5 (6.3)% without any effect on gastric emptying in control rats. TNBS colitis induced de novo c-Fos expression in the DRG S1.

CONCLUSIONS

Experimental colitis in rats delays gastric emptying via a neuronal pathway involving pelvic afferent nerve hyperactivity.

Mucosal stimulation activates secretomotor neurons via long myenteric pathways in guinea pig ileum

This study examined whether mucosal stimulation activates long secretomotor neural reflexes and, if so, how they are organized. The submucosa of in vitro full thickness guinea pig ileal preparations was exposed in the distal portion and intracellular recordings were obtained from electrophysiologically identified secretomotor neurons. Axons in the intact mucosa of the oral segment were stimulated by a large bipolar stimulating electrode. In control preparations, a single stimulus pulse evoked a fast excitatory postsynaptic potential (EPSP) in 86% of neurons located 0.7-1.0 cm anal to the stimulus site. A stimulus train evoked multiple fast EPSPs, but slow EPSPs were not observed. To examine whether mucosal stimulation specifically activated mucosal sensory nerve terminals, the mucosa/submucosa was severed from the underlying layers and repositioned. In these preparations, fast EPSPs could not be elicited in 89% of cells. Superfusion with phorbol dibutyrate enhanced excitability of sensory neurons and pressure-pulse application of serotonin to the mucosa increased the fast EPSPs evoked by mucosal stimulation, providing further evidence that sensory neurons were involved. To determine whether these reflexes projected through the myenteric plexus, this plexus was surgically lesioned between the stimulus site and the impaled neuron. No fast EPSPs were recorded in these preparations following mucosal stimulation whereas lesioning the submucosal plexus had no effect. These results demonstrate that mucosal stimulation triggers a long myenteric pathway that activates submucosal secretomotor neurons. This pathway projects in parallel with motor and vasodilator reflexes, and this common pathway may enable coordination of intestinal secretion, blood flow, and motility.

The non-neuronal cholinergic system in peripheral blood cells: effects of nicotinic and muscarinic receptor antagonists on phagocytosis, respiratory burst and migration

Peripheral blood cells express the complete non-neuronal cholinergic system. For example synthesis of acetylcholine and nicotinic as well muscarinic receptors have been demonstrated in leucocytes isolated from human peripheral blood. In the present experiments mononuclear cells and granulocytes were isolated from the peripheral blood to investigate content and synthesis of acetylcholine as well as phenotypic functions like respiratory burst, phagocytosis and migration. Mononuclear cells (T-cells and monocytes) contained 0.36 pmol/10(6) cells acetylcholine, whereas acetylcholine content in granulocytes was 100-fold lower. Acetylcholine synthesis amounted to 23.2+/-4.7 nmol/mg protein/h and 2.90+/-0.84 in CD15+ (granulocytes) and CD3+ cells (T-lymphocytes), respectively. Neither atropine (blockade of muscarinic receptors) nor tubocurarine (blockade of nicotinic receptors) exerted an effect on the respiratory burst. Tubocurarine (30 muM), alone or in combination with atropine (1 microM), reduced phagocytosis in granulocytes by 13% and 19%, respectively (p<0.05). Spontaneous transwell migration of granulocytes was doubled by tubocurarine combined with atropine (p>0.05). Also alpha-bungarotoxin (10 microg/ml) enhanced spontaneous granulocyte migration, but hexamethonium (300 microM) was without effect. The present experiments demonstrate a cholinergic modulation of immune functions in peripheral leucocytes under in vitro conditions, i.e. in the absence of a neuronal innervation. Blockade of nicotine receptors (alpha1 muscular subtype) facilitates spontaneous migration of granulocytes.

Nicotine-induced vascular endothelial growth factor release via the EGFR-ERK pathway in rat vascular smooth muscle cells

Cigarette smoke has been firmly established as an independent risk factor for atherosclerosis and other vascular diseases. The proliferation and migration of vascular smooth muscle cells (VSMC) induced by growth factors have been proposed to play an important role in the progression of atherosclerosis. In the present study, we investigated the effects of nicotine, which is one of the important constituents of cigarette smoke, on vascular endothelial growth factor (VEGF) release, in rat VSMC. The stimulation of cells with nicotine resulted in a time- and concentration-dependent release of VEGF. Hexamethonium, an antagonist of nicotinic acetylcholine receptor (nAChR), inhibited nicotine-induced VEGF release. We next investigated the mechanisms by which nicotine induces VEGF release in the cells. The nicotine-induced VEGF release was inhibited by treatment with U0126, a selective inhibitor of MEK, which attenuated the nicotine-induced ERK phosphorylation. Nicotine induced a transient phosphorylation of ERK. Furthermore, AG1478, a selective inhibitor of epidermal growth factor receptor (EGFR) kinase, inhibited nicotine-induced ERK phosphorylation and VEGF release. These data suggest that nicotine releases VEGF through nAChR in VSMC. Moreover, VEGF release induced by nicotine is mediated by an EGFR-ERK pathway in VSMC. VEGF may contribute to the risk of cardiovascular diseases in cigarette smokers.

Nicotine Potentiates the Electrical Field Stimulation-Evoked Contraction of Non-Pregnant Rabbit Myometrium

The women who smoke have lower fertility rates which might be due to harmful effects of nicotine on tubal function and menstrual cycle. Although the uterine contractility of the non-pregnant uterus plays an important role in the human reproduction process, the influence of nicotine on the contractile responses in uterus is not known. Nicotine increases the release of neurotransmitters following nerve stimulation both in the central and peripheral nervous system through acting on nicotinic acetylcholine receptors (nAchRs). The aim of this study was to examine whether the electrical field stimulation (EFS)-evoked contraction is altered in rabbit myometrium strips in the presence of nicotine to evaluate the changes in contractility. EFS-evoked contractile responses were recorded from myometrium strips obtained from non-pregnant rabbits in the absence and presence of nicotine. Nicotine led to the increase in the amplitudes of the EFS-evoked contractile responses in a dose-dependent manner. Therefore, the effects of hexamethonium, cadmium, indomethacin, atropine, and N(omega)-Nitro-L-arginine methyl ester hydrochloride were tested on the EFS-evoked contractions in the absence or presence of nicotine to clarify the mechanisms of nicotine-induced potentiation in EFS-evoked contractile responses. Indomethacin, a non-selective cyclooxygenase inhibitor, and hexamethonium, a ganglionic blocker, inhibited nicotine-induced increase in EFS-evoked responses, whereas other chemicals produced no effect. These results suggest that nicotine-induced potentiation may be mediated by nAchRs and prostaglandins. In conclusion, failure of quiescence in the uterus due to increased contractility by nicotine might be one of the factors contributing to infertility in female smokers.

Ethanol-induced dopamine elevation in the rat — Modulatory effects by subchronic treatment with nicotinic drugs

Chronic nicotine administration is associated with increased ethanol consumption in laboratory animals and in humans. Some smokers report less sedation during acute ethanol intoxication after nicotine administration and the sedative effects from ethanol are mediated by inhibitory GABA(A)-receptors. In a series of in vivo microdialysis experiments we investigated whether subchronic pre-treatment with nicotinic drugs known to enhance ethanol consumption in the rat (nicotine or the peripheral nicotinic antagonist hexamethonium) could modulate the alterations in extracellular dopamine observed in response to administration of ethanol or the sedative GABA(A)-agonist diazepam. In the nucleus accumbens and the dorsal striatum, systemic and/or local ethanol administration resulted in transient increases in extracellular dopamine levels that returned to baseline before the local levels of ethanol started to decline. In hexamethonium pre-treated rats, however, the nucleus accumbens dopamine levels were time-locked to the ethanol levels in the same area after systemic or local ethanol administration. Perfusion of diazepam into the nucleus accumbens produced a significant reduction in nucleus accumbens dopamine in controls. Prior subchronic treatment with nicotine or hexamethonium abolished this effect. The present results suggest that subchronic treatment with the nicotinic acetylcholine receptor antagonist hexamethonium reduces a GABA(A)-R mediated counteraction of the nucleus accumbens dopamine response to ethanol. Additionally, we demonstrate that modulation of nicotinic receptors may reduce the sensitivity of GABA(A) receptors to benzodiazepines. These phenomena may offer a novel explanation to why nicotine and alcohol are often co-abused.

Bladder volume-dependent excitatory and inhibitory influence of lumbosacral dorsal and ventral roots on bladder activity in rats

This study was undertaken to examine the role of the afferent and efferent pathways of the lumbosacral spinal nerve roots in the tonic control of bladder activity. Changes of isovolumetric bladder activity were recorded in 21 sympathectomized female rats under urethane anesthesia following transection of the dorsal (DRT) and ventral (VRT) lumbosacral spinal roots, and after intraperitoneal administration of hexamethonium. DRT altered the baseline intravesical pressure in a bladder volume-dependent manner in each animal. The percent change of baseline pressure after VRT following DRT was also dependent upon bladder volume. The percent change of baseline pressure after VRT alone was similarly dependent on bladder volume, but not after VRT followed by DRT. The percent change of baseline intravesical pressure (y)(-9 to +8 cm H(2)O, -56 to +46%) after DRT and VRT depended upon bladder volume (x)(y = 44.7 x -40.4) in all rats. Hexamethonium increased the amplitude of small myogenic bladder contractions after DRT and VRT. In conclusion, the bladder is tonically excited or inhibited by a local reflex pathway and by a parasympathetic reflex pathway that depends on connections with the lumbosacral spinal cord and the pelvic nerves. Both reflex mechanisms are influenced by bladder volume.

In vitro Pharmacological Characterization of Mitemcinal (GM-611), the First Acid-Resistant Non-Peptide Motilin Receptor Agonist, in Smooth Muscle of Rabbit Small Intestine

The pharmacological properties of mitemcinal (GM-611), the first acid-resistant non-peptide motilin agonist, were investigated in the smooth muscle of the rabbit small intestine and compared with porcine motilin (pMTL), erythromycin A (EMA) and its derivatives (EM-523, EM-574 and ABT-229). Mitemcinal, pMTL, EMA, EM-523, EM-574 and ABT-229 produced concentration-dependent contractions with approximately the same maximum contractions in the isolated rabbit duodenum longitudinal strips. The contractile response to mitemcinal or pMTL was competitively inhibited by a selective motilin antagonist, GM-109. The pA(2) values for GM-109 as an antagonist of mitemcinal and pMTL showed approximately the same values. However, the concentration-dependent contractile responses to mitemcinal or pMTL were not affected by pretreatment with atropine, tetrodotoxin, hexamethonium, naloxone or tropisetron. The removal of calcium ions from the medium and pretreatment with verapamil greatly suppressed the contractions induced by mitemcinal and pMTL. The contractile response to mitemcinal was not affected by preincubation in acidic solutions, while those of EM-523, EM-574 and ABT-229 were strongly diminished in the same condition. Mitemcinal as well as other motilin agonists displaced (125)I-pMTL bound to a homogenate of the rabbit duodenum muscle tissue. The displacement curves of all these compounds were parallel. These results indicate that mitemcinal is a selective and full motilin receptor agonist in the smooth muscle of the rabbit small intestine and that this agent has an excellent acid-resistant property.