Risques nucléaires, radiologiques, biologiques et chimiques (NRBC) : la « chaîne de survie NRBC » et son acronyme « DUST DAHO », un outil cognitif destiné aux primo-intervenants non spécialistes pour la prise en charge des victimes les premières heures

Les risques terroristes nucléaires, radiologiques, biologiques et chimiques (NRBC) constituent une menace permanente. Les primo-intervenants seront probablement des personnels non spécialisés face à un événement de cette nature. À l’extérieur ou à l’accueil des hôpitaux, leur rôle sera pourtant décisif sur le plan tactique afin de mettre en œuvre les premières mesures et minimiser les effets sur la population. Acquérir et entretenir un niveau de formation suffisant pour un risque d’occurrence rare, pour agir efficacement en tenue de protection dans un contexte aussi stressant sont des défis pédagogiques et organisationnels pour nos services. En 2019, la brigade de sapeurs-pompiers de Paris conceptualise la « chaîne de survie NRBC » regroupant les cinq actions essentielles à mener par les primointervenants en cas d’événements NRBC. Ces tâches, indissociables, sont représentées sous la forme d’une chaîne constituée de cinq maillons : 1) Décontamination d’urgence pour limiter l’intoxication et la contamination ; 2) Recherche de symptômes pour identifier l’agent et alerter les secours ; 3) Administration précoce des traitements pour réduire la morbi mortalité ; 4) Décontamination approfondie pour protéger le système de santé ; 5) Évacuation vers l’hôpital. En 2020, l’acronyme « DUST DAHO » est ajouté pour optimiser la mémorisation et la restitution des cinq maillons de cette chaîne. Cet outil cognitif s’adresse à tous les acteurs, soignants ou non, à l’extérieur ou à l’accueil de l’hôpital, quel que soit l’agent NRBC en cause. Il pourrait également être un outil de communication précieux pour le grand public en cas de crise.

Evidence for a modulatory role of orexin A on the nitrergic neurotransmission in the mouse gastric fundus

The presence of orexins and their receptors in the gastrointestinal tract supports a local action of these peptides. Aim of the present study was to investigate the effects of orexin A (OXA) on the relaxant responses of the mouse gastric fundus. Mechanical responses of gastric strips were recorded via force-displacement transducers. The presence of orexin receptors (OX-1R) was also evaluated by immunocytochemistry. In carbachol precontracted strips and in the presence of guanethidine, electrical field stimulation (EFS) elicited a fast inhibitory response that may be followed, at the highest stimulation frequencies employed, by a sustained relaxation. All relaxant responses were abolished by TTX. The fast response was abolished by the nitric oxide (NO) synthesis inhibitor l-NNA (2x10(-4) M) as well as by the guanylate cyclase inhibitor ODQ (1x10(-6) M). OXA (3x10(-7) M) greatly increased the amplitude of the EFS-induced fast relaxation without affecting the sustained one. OXA also potentiated the amplitude of the relaxant responses elicited by the ganglionic stimulating agent DMPP (1x10(-5) M), but had no effects on the direct smooth muscle relaxant responses elicited by papaverine (1x10(-5) M) or VIP (1x10(-7) M). In the presence of l-NNA, the response to DMPP was reduced in amplitude and no longer influenced by OXA. The OX1 receptor antagonist SB-334867 (1x10(-5) M) reduced the amplitude of the EFS-induced fast relaxation without influencing neither the sustained responses nor those to papaverine and VIP. Immunocytochemistry showed the presence of neurons that co-express neuronal nitric oxide synthase and OX-1R. These results indicate that, in mouse gastric fundus, OXA exerts a modulatory action at the postganglionic level on the nitrergic neurotransmission.

Influence of orexin A on the mechanical activity of mouse gastric strips

The presence of orexins and orexin receptors has been revealed not only in the central nervous system but also in the gastrointestinal tract. The present study was aimed to investigate the influence of orexin A (OXA) on the mechanical activity of fundal and antral strips of the mouse stomach. In the fundus, electrical field stimulation (EFS) elicited tetrodotoxin (TTX)-sensitive, frequency-dependent contractile responses whose amplitude was markedly reduced by OXA and enhanced by the orexin-1 type receptor antagonist SB-334867. In the presence of the NO synthesis inhibitor L-N(G)-nitro arginine (L-NNA), OXA was no longer effective. Methacholine caused a sustained contracture whose amplitude was not influenced by OXA, TTX or L-NNA. In carbachol-precontracted strips, the neurally-induced relaxant responses elicited during EFS were increased in amplitude by OXA. Antral strips showed a spontaneous contractile activity that was unaffected by TTX or L-NNA and transiently depressed by EFS. OXA did not influence either the spontaneous motility or the EFS-induced effects. The results indicate that OXA exerts region-specific effects and that, in the fundus, depresses EFS-induced contractile responses by acting at the nervous level. It is likely that NO is involved in the effects of the peptide.

Reversal by relaxin of altered ileal spontaneous contractions in dystrophic (mdx) mice through a nitric oxide-mediated mechanism

Altered nitric oxide (NO) production/release is involved in gastrointestinal motor disorders occurring in dystrophic (mdx) mice. Since the hormone relaxin (RLX) can upregulate NO biosynthesis, its effects on spontaneous motility and NO synthase (NOS) expression in the ileum of dystrophic (mdx) mice were investigated. Mechanical responses of ileal preparations were recorded in vitro via force-displacement transducers. Evaluation of the expression of NOS isoforms was performed by immunohistochemistry and Western blot. Normal and mdx mice were distributed into three groups: untreated, RLX pretreated, and vehicle pretreated. Ileal preparations from the untreated animals showed spontaneous muscular contractions whose amplitude was significantly higher in mdx than in normal mice. Addition of RLX, alone or together with l-arginine, to the bath medium depressed the amplitude of the contractions in the mdx mice, thus reestablishing a motility pattern typical of the normal mice. The NOS inhibitor N(G)-nitro-L-arginine (L-NNA) or the guanylate cyclase inhibitor ODQ reversed the effects of RLX. In RLX-pretreated mdx mice, the amplitude of spontaneous motility was reduced, thus resembling that of the normal mice, and NOS II expression in the muscle coat was increased in respect to the vehicle-pretreated mdx animals. These results indicate that RLX can reverse the altered ileal motility of mdx mice to a normal pattern, likely by upregulating NOS II expression and NO biosynthesis in the ileal smooth muscle.

Relaxin restores altered ileal spontaneous contractions in dystrophic (mdx) mice

We studied the effects of relaxin on ileal contractility in normal and dystrophic (mdx) mice. Ileal preparations from male normal and mdx mice showed spontaneous myogenic contractions whose amplitude was significantly higher in the latter ones. Relaxin added to the bath medium together with l-arginine depressed the amplitude of the spontaneous contractions in the mdx mice to a level similar to that of the normal mice. The nitric oxide synthase (NOS) inhibitor L-N(G)-nitroarginine reverted this effect. In mdx mice pretreated for 18 hours with relaxin, spontaneous motility was greatly reduced in amplitude, resembling that of the normal mice. Concurrently, iNOS expression in the muscle coat was markedly increased. Therefore, in mdx mice, relaxin can restore an ileal motility pattern similar to that of the normal mice by upregulating endogenous NO biosynthesis.

Relaxin: new functions for an old peptide

The peptide relaxin (RLX) was one of the first hormones to be described with a specific function in parturition. In the past ten years, there has been a revaluation of RLX physiology and the concept that sex hormones play roles that are limited to reproductive functions is rapidly changing. In this view, growing evidence indicates that the peptide hormone RLX, structurally related to insulin and insulin-like growth factor and primarily secreted by the corpus luteum during pregnancy, besides well demonstrated actions on reproductive tissues, is involved in a variety of functions. Among them, RLX influences the brain and regulates pituitary hormone secretion, causes renal vasodilatation, increases coronary flow, exerts chronotropic action on the heart and affects gastrointestinal motor responses. Recent studies suggest that in several smooth muscles the hormone appears to act by promoting the biosynthesis of nitric oxide (NO), whose altered production may be involved in smooth muscle dysmotilities. The recent cloning of the RLX receptors and studies on their possible signal transduction mechanisms are stimulating researchers to further investigate the effects of this hormone and its mechanism of action. This may lead to the discovery of agonists and antagonists for RLX and the development of new therapeutic approaches in some human diseases. The aim of this mini-review is to summarize the most recent findings on the multiple actions of RLX hoping to bring a contribution for the future perspectives in this field.

Influence of relaxin on the neurally induced relaxant responses of the mouse gastric fundus

The peptide hormone relaxin has been reported to depress the amplitude of contractile responses in the mouse gastric fundus by upregulating nitric oxide (NO) biosynthesis at the neural level. In the present study, we investigated whether relaxin also influenced nonadrenergic, noncholinergic (NANC) gastric relaxant responses in mice. Female mice in proestrus or estrus were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Mechanical responses of gastric fundal strips were recorded via force-displacement transducers. In carbachol precontracted strips from control mice and in the presence of guanethidine, electrical field stimulation (EFS) elicited fast relaxant responses that may be followed by a sustained relaxation. All relaxant responses were abolished by tetrodotoxin. Relaxin increased the amplitude of the EFS-induced fast relaxation without affecting either the sustained one or the direct smooth muscle response to papaverine. In the presence of the NO synthesis inhibitor L-N(G)-nitro arginine (L-NNA), that abolished the EFS-induced fast relaxation without influencing the sustained one, relaxin was ineffective. In strips from relaxin-pretreated mice, EFS-induced fast relaxations were enhanced in amplitude with respect to the controls, while sustained ones as well as direct smooth muscle responses to papaverine were not changed. Further addition of relaxin to the bath medium did not influence neurally induced fast relaxant responses, whereas L-NNA did. In conclusion, in the mouse gastric fundus, relaxin enhances the neurally induced nitrergic relaxant responses acting at the neural level.

Depression by relaxin of neurally induced contractile responses in the mouse gastric fundus

The peptide hormone relaxin, which attains high circulating levels during pregnancy, has been shown to depress small-bowel motility through a nitric oxide (NO)-mediated mechanism. In the present study we investigated whether relaxin also influences gastric contractile responses in mice. Female mice in proestrus or estrus were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Mechanical responses of gastric fundal strips were recorded via force-displacement transducers. Evaluation of the expression of nitric oxide synthase (NOS) isoforms was performed by immunohistochemistry and Western blot. In control mice, neurally induced contractile responses elicited by electrical field stimulation (EFS) were reduced in amplitude by addition of relaxin to the organ bath medium. In the presence of the NO synthesis inhibitor l-NNA, relaxin was ineffective. Direct smooth muscle contractile responses were not influenced by relaxin or l-NNA. In strips from relaxin-pretreated mice, the amplitude of neurally induced contractile responses was also reduced in respect to the controls, while that of direct smooth muscle contractions was not. Further addition of relaxin to the bath medium did not influence EFS-induced responses, whereas l-NNA did. An increased expression of NOS I and NOS III was observed in gastric tissues from relaxin-pretreated mice. In conclusion, the peptide hormone relaxin depresses cholinergic contractile responses in the mouse gastric fundus by up-regulating NO biosynthesis at the neural level.

Relaxin depresses small bowel motility through a nitric oxide-mediated mechanism. Studies in mice

Gastrointestinal motility is reduced and the incidence of functional gastrointestinal disorders is increased in pregnancy, possibly due to hormonal influences. This study aims to clarify whether the hormone relaxin, which attains high circulating levels during pregnancy and has a nitric oxide-mediated relaxant action on vascular and uterine smooth muscle, also reduces bowel motility and, if it does, whether nitric oxide is involved. Female mice in proestrous or estrous were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Isolated ileal preparations from both groups were used to record contractile activity, either basal or after acute administration of relaxin (5 x 10(-8) M). Drugs inhibiting nitric oxide biosynthesis or neurotransmission were used in combination with relaxin. Expression of nitric oxide synthase isoforms by the ileum was assessed by immunocytochemistry and Western blot analysis. Relaxin caused a clear-cut decay of muscle tension and a reduction in amplitude of spontaneous contractions upon either chronic administration to mice or acute addition to isolated ileal preparations. These effects were significantly blunted by N(G)-nitro-L-arginine, but not by the neural blockers we used. Moreover, relaxin increased the expression of nitric oxide synthases II and III, but not synthase I. Relaxin markedly inhibits ileal motility in mice by exerting a direct action on smooth muscle through the activation of intrinsic nitric oxide biosynthesis.

Preliminary results on the prediction of countershock success with fibrillation power

In a study of artifact-free ventricular fibrillation episodes in 54 patients, 28 of whom experienced return of spontaneous circulation (ROSC), the power of different indicators to predict the ROSC was compared. Taking the average of sensitivity, specificity and positive and negative predictive value, the dominant frequency reaches 76%, the mean amplitude 72% and fibrillation power 71%. There is little correlation between the three indicators.

Modulation of nitrergic relaxant responses by peptides in the mouse gastric fundus

The effects of pituitary adenylate cyclase-activating peptide (PACAP-38) and vasoactive intestinal polypeptide (VIP) were investigated in the gastric fundus strips of the mouse. In carbachol (CCh) precontracted strips, in the presence of guanethidine, electrical field stimulation (EFS) elicited a fast inhibitory response that may be followed, at the highest stimulation frequencies employed, by a sustained relaxation. The fast response was abolished by the nitric oxide (NO) synthesis inhibitor L-N(G)-nitro arginine (L-NNA) or by the guanylate cyclase inhibitor (ODQ), the sustained one by alpha-chymotrypsin. alpha-Chymotrypsin also increased the amplitude of the EFS-induced fast relaxation. PACAP-38 and VIP caused tetrodotoxin-insensitive sustained relaxant responses that were both abolished by alpha-chymotrypsin. Apamin did not influence relaxant responses to EFS nor relaxation to both peptides. PACAP 6-38 abolished EFS-induced sustained relaxations, increased the amplitude of the fast ones and antagonized the smooth muscle relaxation to both PACAP-38 and VIP. VIP 10-28 and [D-p-Cl-Phe6,Leu17]-VIP did not influence the amplitude of both the fast or the sustained response to EFS nor influenced the relaxation to VIP and PACAP-38. The results indicate that in strips from mouse gastric fundus peptides, other than being responsible for EFS-induced sustained relaxation, also exerts a modulatory action on the release of the neurotransmitter responsible for the fast relaxant response, that appears to be NO.

Impaired nitrergic relaxations in the gastric fundus of dystrophic (mdx) mice

Relaxant responses to electrical field stimulation (EFS) were investigated in the gastric longitudinal fundus strips from young normal and mdx dystrophic mice, an animal model of Duchenne muscular dystrophy. In carbachol (CCh) precontracted strips from normal mice, EFS elicited brisk relaxant responses that, depending on stimulation frequency, could be followed by a sustained relaxation. In strips from mdx mice the brisk relaxation was impaired. Smooth muscle responses to direct stimulating agents did not differ in amplitude between the two groups of animals. In strips from both normal and mdx mice, N(G)-nitro-L-arginine (L-NNA) abolished the brisk phase of relaxation, without affecting the sustained response. alpha-chymotrypsin abolished, in both preparations, the sustained relaxant response to EFS as well as relaxation to vasoactive intestinal polypeptide. Results suggest that, in strips from mdx mice, a defective production/release of the neurotransmitter responsible for the brisk relaxation, likely nitric oxide, occurs.

Relaxin up-regulates the nitric oxide biosynthetic pathway in the mouse uterus: involvement in the inhibition of myometrial contractility

The uterus is a site of nitric oxide (NO) production and expresses NO synthases (NOS), which are up-regulated during pregnancy. NO induces uterine quiescence, which is deemed necessary for the maintenance of pregnancy. Relaxin is known to promote uterine quiescence. Relaxin has also been shown to stimulate NO production in several targets. In this study we investigated the effects of relaxin on the NO biosynthetic pathway of the mouse uterus. Estrogenized mice were treated with relaxin (2 microg) for 18 h, and the uterine horns were used for determination of immunoreactive endothelial-type NOS and inducible NOS. Moreover, uterine strips from estrogenized mice were placed in an organ bath, and the effect of relaxin on K+-induced contracture was evaluated in the presence or absence of the NOS inhibitor nitro-L-arginine. Relaxin increases the expression of endothelial-type NOS in surface epithelium, glands, endometrial stromal cells, and myometrium, leaving inducible NOS expression unaffected. Moreover, relaxin inhibits myometrial contractility, and this effect is blunted by nitro-L-arginine, thus indicating that the L-arginine-NO pathway is involved in the relaxant action of relaxin on the myometrium. Because relaxin is elevated during pregnancy, it is suggested that relaxin has a physiological role in the up-regulation of uterine NO biosynthesis during pregnancy.

Nitric oxide as modulator of cholinergic neurotransmission in gastric muscle of rabbits

The effects of the nitric oxide (NO) synthesis inhibitors, NG-nitro-L-arginine (L-NNA) and NG-nitro-L-arginine methyl ester (L-NAME), on the electrical field stimulation (EFS)-induced inhibitory responses were investigated. EFS caused, in strips contracted by means of substance P (SP), prostaglandin F2 alpha (PGF2 alpha), or carbachol (CCh), a fast relaxant response that, depending on stimulation frequency and strip tension, could be followed by a slower, sustained relaxation. The NO synthesis inhibitors blocked the EFS-induced fast relaxations and often reversed them into contractions; these effects were greatly counteracted in SP- or PGF2 alpha-treated strips by scopolamine or atropine. In CCh-precontracted strips, either L-NNA or L-NAME became progressively unable to block the EFS-induced fast relaxations as the CCh concentration was increased. The NO synthesis inhibitors greatly reduced the sustained relaxant responses elicited either by EFS or exogenous vasoactive intestinal polypeptide (VIP). The results indicate that the NO synthesis inhibitors abolish the neurally induced fast relaxation by interfering with the cholinergic excitatory pathway. The involvement of both VIP and NO in sustained relaxations is also suggested.

Prostaglandin E2 modulates neurally induced nonadrenergic, noncholinergic gastric relaxations in the rabbit in vivo

BACKGROUND & AIMS

Prostaglandin (PG) E2 has been shown to modulate adrenergic and cholinergic neurotransmission in the gut. This study investigated PGE2 influence on vagally induced, nonadrenergic, noncholinergic (NANC) gastric relaxations.

METHODS

Mechanical activity of the stomach was recorded in anesthetized rabbits.

RESULTS

In atropine-treated animals, electrical vagal stimulation or arterial bolus injection of the ganglion stimulant dimethyl phenylpiperazinium iodide (DMPP) evoked inhibitory responses that varied from a brisk relaxation, interrupted by a poststimulus excitatory motility (biphasic response), to a long-lasting relaxation (monophasic response). PGE2 reduced and, at the highest doses, abolished the neurally induced relaxant responses elicited either by vagal stimulation or DMPP administration but did not affect the gastric relaxation caused by adenosine triphosphate (ATP), sodium nitroprusside (SNP), or vasoactive intestinal polypeptide (VIP). ATP or 2-methylthioadenosine triphosphate (2-MeSATP) reduced and then suppressed vagally induced inhibitory motility; the relaxant responses elicited by SNP, VIP, and ATP itself were not influenced. After administration of the prostaglandin synthesis inhibitor suprofen, ATP and 2-MeSATP failed to block vagally induced inhibitory responses. Arterial infusion of adenosine at the highest rates did not influence the amplitude of the vagally induced relaxant responses. Following theophylline administration, ATP still blocked the relaxation elicited by vagal stimulation.

CONCLUSIONS

PGE2 may modulate NANC inhibitory neurotransmission in the stomach. The effects of ATP on the neurally induced NANC gastric relaxation may be caused by PGE2.

Gastric relaxation in response to chemical stimulation of the area postrema in the rabbit

Microinjections of DL-homocysteic acid into the area postrema (AP) of anesthetized rabbits provoked gastric relaxations associated with small changes in blood pressure and marked excitatory effects on respiration. Both gastric and cardiovascular effects failed to occur after bilateral vagotomy. Comparable gastric relaxations were induced before and after treatment with atropine or atropine and guanethidine. The AP appears to play a role in gastric motility via vagus nerves and nonadrenergic noncholinergic intramural inhibitory neurons.

Modulation of cholinergic transmission by nitric oxide, VIP and ATP in the gastric muscle

The influence of the putative inhibitory neurotransmitters nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and adenosine 5'-triphosphate (ATP) was examined on the contractile responses elicited, either by electrical field stimulation (EFS) or exogenous acetylcholine (Ach), in strips of the circular muscle of the rabbit gastric corpus. Muscular contractions evoked by Ach were not influenced by the NO-releasing compound sodium nitroprusside (SNP), but were depressed by VIP and scarcely affected by ATP. In contrast, the putative inhibitory neurotransmitters all depressed or even blocked the neurally induced cholinergic contractions elicited by EFS. Therefore, NO, VIP or ATP, besides causing muscular relaxation, may modulate the cholinergic transmission at the pre- and/or post-junctional level in the nerve-muscle pathway.

Effects of L-NG-nitro arginine on cholinergic transmission in the gastric muscle of the rabbit

In the circular muscle of the rabbit gastric corpus, the nitric oxide-synthesis inhibitor L-NG-nitro arginine (L-NOARG), enhanced the neurally-induced cholinergic responses evoked by electrical field stimulation (EFS) and ganglionic stimulating agents (nicotine, dimethylphenyl piperazinium iodide). The muscular contractions caused by acetylcholine (Ach) and methacholine were not influenced by the nitric oxide-synthesis inhibitor. The nitric oxide-releasing compound sodium nitroprusside (SNP) did not affect the Ach-induced muscular responses. Our results suggest that L-NOARG enhances gastric cholinergic responses by removing an inhibitory influence exerted at the prejunctional level in the nerve-muscle pathway.

The influence of the vagally induced rebound contractions on the non-adrenergic, non-cholinergic (NANC) inhibitory motility of the rabbit stomach and the role of prostaglandins

Factors influencing the vagally induced rebound contraction and its role in gastric inhibitory motility were studied in the anaesthetised rabbit. Gastric motility was assessed from measurements of gastric volume by means of an intragastric balloon. In the atropine- and guanethidine-treated animals, vagal stimulation caused biphasic motor responses: a rapid relaxation was followed by a rebound contraction. The latter, depending on experimental conditions, was able to restore and maintain gastric volume at the basal level. However, the rebound contraction was greatly influenced by the stimulation parameters and the basal gastric volume. Stimulation periods of less than 30 sec, or stimulation frequencies above 20 Hz, as well as basal gastric volumes above 70 ml could reduce the amplitude of the post-stimulus excitatory motility, and transformed the biphasic response into a triphasic one: a slow, long-lasting relaxation appeared after the rebound contraction. Prostaglandin-synthesis inhibitors of the non-steroidal anti-inflammatory group depressed the rebound contraction, and caused persistence of gastric relaxation, even after the offset of vagal stimulation. PGE2 evoked excitatory motor responses which closely mimicked the vagally induced rebound contraction. PGE2 also interrupted the rapid or slow, long-lasting relaxant responses. PGF2 alpha elicited tonic excitatory responses. These results suggest that PGE2 is involved in the mechanism underlying post-stimulus excitatory motility. They also suggest that the rebound contraction is a key factor in determining the inhibitory motility pattern of the rabbit stomach.

Vagally-induced non-adrenergic, non-cholinergic inhibitory motility in the rabbit stomach "in vivo"

In atropine-treated rabbits, electrical stimulation of vagal nerves at low frequency and low basal gastric volumes evoked a biphasic response: rapid onset relaxation followed by rebound contractions. Increase in the frequency of stimulation and/or in basal gastric volume caused a depression of the rebound contraction and a conversion of the biphasic response into a triphasic one: i.e., the post-stimulus excitatory motility was followed by a long-lasting slow relaxation. The rebound contraction, which was mimicked by arterial injections of prostaglandin E2, appears to be a key factor in the conversion of one type of response into the other.

Effects of arterial infusions of adenosine 5'-triphosphate (ATP) and vasoactive intestinal polypeptide (VIP) on vagal excitatory motor responses in the rabbit stomach 'in vivo'

In the rabbit stomach 'in vivo' adenosine and adenosine 5'-triphosphate depressed the contractile activity elicited by vagal stimulation. The order of potency was ATP greater than adenosine. Only ATP completely blocked the excitatory motor responses. Vasoactive intestinal polypeptide injected close-arterially scarcely affected the vagal contractile activity of the stomach.

Depression by fenoprofen of the rebound contractions' elicited by vagal stimulation and arterial infusion of ATP in the rabbit stomach in vivo

In the atropine-treated rabbit, vagal stimulation, arterial infusion of ATP or vasoactive intestinal peptide (VIP) caused gastric relaxation. At the end of either vagal stimulation or ATP infusion, but not after VIP, the gastric inhibitory responses were abruptly interrupted by 'rebound contractions'. Administration of fenoprofen depressed or abolished the rebound contraction, thus transforming the brisk relaxant response, elicited by vagal stimulation or ATP, into long-lasting relaxation. Indomethacin depressed the rebound contractions only at high doses and this effect was not always reproducible.

Gastric motor responses elicited by vagal stimulation and purine compounds in the atropine-treated rabbit

1. The effects of vagal inhibitory stimulation and of purine compounds were studied in the rabbit stomach. 2. Gastric motility was assessed by the balloon method. Vagal nerves were electrically stimulated at the neck. Purine compounds were injected intra-arterially. 3. In the atropine-treated rabbit, vagal stimulation caused relaxant motor responses followed by a rebound contraction. 4. Among the purine compounds, only ADP and ATP caused relaxant motor responses similar to the effects of vagal inhibitory stimulation. However, the relaxation produced by ATP was more powerful than that due to ADP, especially at lower infusion rates. 5. Vagal inhibitory responses were recorded during and after infusion of ATP. When relaxation by ATP was fully developed, vagal inhibitory stimulation was ineffective. At the highest infusion rates of ATP, a depression of the vagal inhibitory motility was also observed after cessation of the infusion. 6. Relaxant responses to ATP and vagal inhibitory stimulation were not influenced by theophylline, scarcely affected by alpha,beta-methylene ATP, but were reduced or blocked by reactive blue 2. 7. The results are consistent with ATP being an inhibitory neurotransmitter in the stomach of the rabbit.

[The presence of purinergic, quinacrine-positive neurons in the rabbit stomach]

Inhibitory non-adrenergic non-cholinergic efferent nerves are activated in the stomach of the rabbit by electrical vagal stimulation (1). Aim of the present research is to ascertain, in the rabbit stomach, by means of quinacrine fluorescence technique (6) the presence of quinacrine-positive cells and nerve fibers which are thought to be non-adrenergic non-cholinergic inhibitory nerves of gastric motility. A population of neurons showing a high affinity for quinacrine was revealed by fluorescence microscopy in the myenteric plexus of the rabbit stomach.

[Excitatory and inhibitory vagal actions on the motility of normal rabbit stomach]

Electrical vagal nerve stimulation (10-20 V, 0.2-5 msec, 1-86 Hz) was carried out at cervical level in nembutal-urethane anestetized rabbits. The aim of the research was to selectively activate (0.2 msec) "low" excitatory, and (5 msec) "high" inhibitory efferent vagal nerve fibers supplying the stomach. In the intact stomach an increasing motor effect was evoked between 1 and 16 Hz. An inhibitory motor effect became, instead, evident at higher frequencies of stimulation (16-86 Hz) In atropinized animals excitatory motor effects were blocked. The inhibitory effects were instead still present and they were not affected by guanethidine. These results suggest a non-cholinergic, non-adrenergic mechanism for the vagal inhibitory control of gastric motility in rabbit.

[Effect of motor stimulation and stretching on afferent activity of the neuromuscular spindle isolated from the frog]

The arrangement of muscle spindles in m. ext. long. dig. IV has been examined by microdissection. It is confirmed that spindle systems generally appear to consist of individual receptors. Stimulation effects of fast motor fibres (conduction velocities greater than 12 m/sec) on the spindles of the same muscle were studied. Receptors were isolated with their nerves and the appropriate spinal roots, the latter ones were used for stimulating efferent fibres and recording sensory discharges. Single shocks to the ventral root filaments caused afferent responses ranging from a single action potential to a train of impulses. During repetitive stimulation (train of stimuli at frequency of 10 to 150/sec) a marked increase in afferent activity was found. Afferent activity could be driven by the frequency of stimuli ("driving") and the stimulus/action potentials ratio varied from 1:1 to 1:3 or more. The rate of sensory discharge depended on the frequency of stimuli: the maximum effect, was attained at 30 to 50 stimuli/sec and, in the most responsive receptors, up to 80 stimuli/sec. Slight increases of the initial lengths of the receptors caused facilitation of sensory responses to motor stimulation. Moreover, impairing effects, which appear during sustained or high-frequency stimulation, possibly related to fatigue in intrafusal neuromuscular transmission, could be relieved by increasing the initial length. The repetitive stimulation of fast fusimotor fibres increased both dynamic and static responses and also raised the afferent activity after a period of stretching, when usually a depression occurs; these effects varied according to the preparation, its initial tension and the frequency of stimulation. The main feature of the examined motor fibres, when stimulated, is the constant excitatory action on muscle spindle static response. Results are discussed. It is suggested that the different characteristics of intrafusal muscle fibres, the receptor initial tension and the frequency of motor units discharges, may together affect muscle spindles static or dynamic performance.

[Effects of acetylcholine and succinylcholine on isolated frog neuromuscular spindle]

The mode of action of acetylcholine (ACh) and succinylcholine (SCh) on the isolated frog's muscle spindle has been studied. Receptor afferent nervous supply was maintained; the appropriate spinal roots were dissected for stimulating motor axons and recording from sensory fibres. Excitatory effects on the afferent activity, when the receptor was held still and during stretching, were found with ACh or SCh concentrations of 10(-8) to 10(-3); 10(-6) g/ml being usually effective. These effects are similar to those obtained by stimulating fusimotor nerve fibres. The contractile activity of intrafusal muscle fibres which occurred during these effects was observed. Seldom, and only for high concentrations of ACh and SCh, a decrease in afferent activity following the excitatory effects was found. Tubocurarine chloride (10(-5)-10(04) g/ml) in the bath prevented both motor fibres and drugs effects. Sometimes slight transient excitation occurred at very high concentrations of the two tested substances; however, this effect was prevented by stronger curarization. The observed blocking effects were always reversed by removing tubocurarine from the bath. No more excitatory effects by motor fibres stimulation and by ACh and SCh action could be found after destruction of intrafusal muscle fibres, by pinching them as close as possible to the ends of the spindle. It is suggested that ACh and SCh act indirectly by causing mechanical changes in intrafusal muscle fibres, and that a direct action on sensory nerve endings, if any, cannot, by itself, increase the afferent activity of the receptor.