Pharmacological studies on the bungarotoxins: an analysis of the site of action of nicotinic agonists

The possibility that nicotinin agonists may exert an indirect action by releasing endogenous acetylcholine from nerve terminals has been examined by the use of nerve-free cultured muscle, and by the use of the specifically prejunctionally active β-type bungarotoxins.In cultured muscle the depolarizations produced by acetylcholine and carbachol were not greatly affected by treatment of the cultures with β-type bungarotoxins for 60 min.In the chick biventer cervicis nerve-muscle preparations dose-response curves to acetylcholine, carbachol, dimethylphenylpiperazinium and nicotine were not affected even after abolition of responses to nerve stimulation by the β-types toxins.As the responses to nicotinic agonists were obtainable in nerve-free muscle and were unimpaired in the chick biventer after elimination of nerve function by β-type bungarotoxins, we conclude that such agonists exert a direct action on the postjunctional acetylcholine receptors.     

Selective depression of synaptic excitation in cat spinal neurones by baclofen: an iontophoretic study.

1 The effects of baclofen have been examined on responses of neurones in the spinal cord of the anaesthetized cat to stimulation of appropriate synaptic pathways, acetylcholine and a range of amino acid excitants. Baclofen and excitant substances were administered by standard microiontophoretic techniques. 2 Small ejecting currents of baclofen (less than 10 nA) depressed non-cholinergic, excitatory, synaptic responses evoked by stimulation of dorsal roots or muscle or cutaneous afferents. Excitatory monosynaptic responses were particularly sensitive to the depressant action of baclofen. 3 Spontaneous firing in neurones was sometimes reduced in parallel with synaptic excitatory responses, but synaptically evoked inhibition was unaffected and ventral root evoked excitation of Renshaw cells was either unaffected or enhanced by baclofen. 4 Ejecting currents of baclofen which markedly depressed excitatory synaptic responses either had no effect or minimal depressant effects on responses induced by iontophoretically administered acetylcholine and excitant amino acids. However, relatively large currents of baclofen (e.g. 20 to 40 nA) reduced excitatory responses to exogenously administered excitants. 5 It is suggested that baclofen depresses (a) synaptic response by an action on excitatory nerve terminals and (b) responses to exogenous excitants via a postsynaptic action. 6 Comparison of baclofen with a number of other substances indicates that the depression of noncholinergic, excitatory, synaptic responses is unlikely to involve an interaction of this agent with receptors for monoamines, 5-hydroxytryptamine or the inhibitory amino acids, gamma-aminobutyric acid and glycine.     

The influence of electro-acupuncture on naloxone-induced morphine withdrawal in mice: Elevation of brain opiate-like activity

Pretreatment of carbachol (in vitro), in various doses (5.5 pM to 550 nM), produced a significant decrease in the sensitivity of the frog rectus abdominis muscle to acetylcholine (ACh), in a dose-dependent manner. This action was observed with a 60 min incubation period. Contracting induced by potassium chloride (KCl) were unaffected by carbachol. Physostigmine (10 μM) potentiated the decrease in sensitivity induced by carbachol, whereas human plasma antagonised it. Low calcium (0.27 mM) in the medium and hexamethonium (300 μM) antagonised the sensitivity decrease induced by carbachol. These results suggests that carbachol decreases the sensitivity to Ach by releasing ACh from the presynaptic nerve terminals. The results further suggest that carbachol may release ACh by depolarising the presynaptic nicotinic receptors.     

Physiological characteristics of low-threshold mechanoreceptors in joints, muscle and skin in human subjects

1. The development of microneurography, in which an insulated tungsten microelectrode is inserted into an accessible peripheral or cranial nerve in awake human subjects, has allowed detailed analyses of the signalling capacities of single mechanoreceptive afferents from the skin, muscles and joints. For example, we know much about how the two classes of rapidly adapting (Meissner and Pacinian) and two classes of slowly adapting (Merkel and Ruffini) cutaneous mechanoreceptors encode forces applied normal or tangential to the skin of the hand and the similarities and differences in glabrous versus non-glabrous skin (and receptors associated with hairs). We also know about stretch- and force-sensitive endings in muscle (the muscle spindle and Golgi tendon organ, respectively) and how they behave during passive or active movements or during isometric contractions. In addition, we have characterized the firing properties of mechanoreceptors in the joint capsules of the fingers. However, we know little about sensory nerves in the periosteum, other than that nociceptors and Pacinian corpuscles exist. 2. In addition to studies on the physiology of sensory endings in human subjects, microstimulation through the recording microelectrode has revealed how the brain deals with the sensory information conveyed by a single afferent. From this work, we know that there is specificity in the sensory channels: electrical stimulation of a single Meissner or Pacinian corpuscle generates frequency dependent illusions of 'flutter' or 'vibration', whereas microstimulation of a single Merkel afferent can produce a percept of 'pressure' and stimulation of a single joint afferent can evoke a sensation of 'joint rotation'. Interestingly, the input from a single Ruffini ending in the skin cannot be perceived and the same is true of muscle spindle afferents. So, where does this leave us with osseoperception from the mouth? Given that the periodontal receptors in the vicinity have been lost, which mechanoreceptive endings could encode forces applied to a bone-implanted prosthesis? 3. Meissner and Merkel endings have very small receptive fields and respond only to local forces. Pacinian corpuscles have an exquisite sensitivity to brisk mechanical events and could respond to such stimuli transmitted through the bone to a remote receptor, but would not be able to encode sustained forces. Ruffini endings also respond to forces applied remote to the receptive field and, unlike the Pacinian corpuscles, respond in a sustained fashion, but would their signals be perceived? Like muscle spindles, it is possible that the coactivation of many Ruffini endings could provide meaningful information. Finally, as we have seen, the input from a single joint receptor can be perceived, but they mostly respond at the limits of joint rotation, so it is unlikely that any associated with the temporomandibular joint could contribute to osseoperception.     

Evidence that endogenous catecholamines can regulate acetylcholine release in a sympathetic ganglion

The objective of this study was to test whether activation of alpha-adrenoceptors by endogenously released catecholamines alters the release of acetylcholine (ACh) from the cat superior cervical ganglion. The alpha-adrenoceptor agonists noradrenaline and clonidine depressed evoked ACh release; this effect was concentration-dependent; it was apparent during preganglionic stimulation at 20 Hz, but not so at lower frequencies of stimulation. The inhibitory effect of noradrenaline on evoked ACh release was reversed by yohimbine, by phentolamine and, to a lesser extent, by prazosin. Thus, exogenous amines can depress evoked ACh release by an action on presynaptic alpha-adrenoceptors. To determine if activation of these receptors by endogenous amines inhibits ACh release, we tested whether the alpha-adrenoreceptor antagonists enhance ACh release. Yohimbine and phentolamine increased evoked ACh release during preganglionic stimulation at 20 Hz, but not during stimulation at 5 Hz, suggesting that endogenous, like exogenous, amine can depress evoked ACh release from preganglionic nerve terminals.     

Autoregulation of acetylcholine release from vagus nerve terminals through activation of muscarinic receptors in the dog trachea.

1. The effects of pirenzepine and gallamine on the membrane and contractile properties of smooth muscle cells and on excitatory neuro-effector transmission in the dog trachea were investigated by means of microelectrode, double sucrose gap and tension recording methods. 2. Pirenzepine (10(-7) M) and gallamine (10(-5) M) had no effect on the resting membrane potential or the input resistance of the smooth muscle cells. 3. Pirenzepine (10(-10)-10(-9) M) and gallamine (10(-7) M) enhanced the amplitude of twitch contractions evoked by field stimulation in the combined presence of indomethacin (10(-5) M) and propranolol (10(-6) M). At higher concentrations pirenzepine (10(-8) M) inhibited the twitch contractions in a dose-dependent manner. Both pirenzepine and gallamine in doses over 10(-7) and 10(-5) M, respectively, reduced muscle tone. 4. Pirenzepine (10(-10)-10(-9) M) and gallamine (10(-7) M) enhanced the amplitude of excitatory junction potentials (e.j.ps) evoked by field stimulation (single or repetitive stimulation). However, a high concentration of pirenzepine (10(-8) M) reduced the amplitude of e.j.ps. In parallel with its action on e.j.ps, pirenzepine (over 10(-9) M) reduced the response of smooth muscle cells to acetylcholine (ACh), in a dose-dependent manner. Gallamine (5 X 10(-5) M) markedly enhanced the amplitude of e.j.ps but also reduced the response of muscle cells to ACh. 5. ACh (10(-10)-10(-9) M) inhibited twitch contractions evoked by field stimulation, with a slight increase of resting tension. 6. Gallamine enhanced the summation of e.j.ps during repetitive field stimulation at a high frequency (20 Hz), but was without effect on the depression phenomena of e.j.ps observed during double stimulus experiments at different time intervals (5-60 s). 7. These results indicate that both pirenzepine and gallamine have dual actions on pre- and post-junctional muscarinic receptors in dog tracheal tissue. At low concentrations both agents potentiate excitatory neuro-effector transmission, presumably due to enhancement of release of ACh from vagal nerve terminals through blockade of a negative auto-regulatory process activated by endogenous ACh. At higher concentrations, these agents inhibit the response of smooth muscle cells to ACh through post-junctional muscarinic receptors and relaxation of the muscle tissue occurs.     

Stimulating action of atropine on the release of acetylcholine by rat cerebral cortex in vitro

1. In cortical slices from rat brain incubated in a medium containing the irreversible cholinesterase inhibitor, soman (0.005 mM) and a high concentration of KCl (25 mM), atropine exerts a stimulating action on the release of acetylcholine (ACh).2. Two possible explanations for this action were examined. Atropine might expel ACh from the nerve endings by occupying its storage sites or it might prevent an inhibitory action of the released ACh on its further release by occupying muscarinic receptors at the presynaptic endings; its action would then be a kind of ;disinhibition.'3. The stimulating action of atropine on ACh release persisted during prolonged incubation (up to 3.5 h) provided choline was added to the medium. This finding would be difficult to explain if atropine acted by expelling ACh from its storage sites.4. The stimulating action of atropine on ACh release was inhibited by oxotremorine and by methacholine, added to the medium in high concentrations. This finding is readily explained if atropine acts by ;disinhibition.'     

Heterogeneous distribution of muscarinic receptors in the rabbit saphenous artery.

1. The properties of the muscarinic receptors in the rabbit saphenous artery were determined from electrical and mechanical responses of smooth muscle cells produced by acetylcholine (ACh). The inhibitory action of atropine and pirenzepine on the ACh-induced responses was also studied. 2. ACh produced a transient hyperpolarization of the membrane and inhibited the noradrenaline (NA)-induced contraction. These effects of ACh were apparent only when the endothelial cells were intact. 3. The ACh-induced transient hyperpolarization was antagonized by atropine or pirenzepine, with similar potencies (the ID50 values were about 2 x 10(-8) M for both antagonists). 4. The ACh-induced inhibition of the contraction to NA was antagonized by atropine more preferentially than by pirenzepine (the ID50 values were 2 x 10(-8) M for atropine and 10(-6) M for pirenzepine). 5. The excitatory junction potential (e.j.p.) evoked by perivascular nerve stimulation was inhibited by ACh (above 10(-8) M). The ACh-induced inhibition of the e.j.p. was antagonized by atropine more preferentially than by pirenzepine (the ID50 values were 3 x 10(-8) M for atropine and 6 x 10(-6) M for pirenzepine). 6. It is concluded that in the rabbit saphenous artery, two subtypes of muscarinic receptor (M1 and M2) are located on the endothelial cells. Stimulation of each subtype releases a different substance, i.e., a hyperpolarizing substance (M1-subtype) or a relaxant substance (M2-subtype). In prejunctional nerve terminals, the muscarinic receptors responsible for inhibiting the release of transmitter substances are of the M2-subtype.     

The Functional Role of Cholinergic Receptors in the Outlet Region of the Urinary Bladder: An in Vitvo Study in the Cat

Abstract: A method for experimental study in vitro of the outlet region (bladder base, bladder neck and proximal urethra) from the cat is described which allows simultaneous recording of resistance to flow through the region and of isometric tension in the longitudinal muscles. The results suggest that acetylcholine (ACh) may influence the smooth muscles in the outlet region by several mechanisms. Contractions in the longitudinal muscles are mediated by atropine sensitive cholinergic receptors. The resistance to flow could be either increased or decreased following ACh stimulation and in neither case could the response be blocked with atropine. If the response was an increase, however, it was blocked by phentolamine and if it was a decrease, it was blocked by propranolol. It is concluded that ACh stimulates the circular musculature in the outflow region through α- and β-adrenergic receptors. It is suggested that the effects of ACh on flow are brought about through short intramural adrenergic neurons. ACh stimulates their ganglion-cells which results in a release of nor-adrenaline at the nerve endings and in activation of adrenergic receptors in the circular muscle layer.     

Facilitation by tachykinins of neurotransmission in guinea-pig pulmonary parasympathetic nerves.

1. The effect of tachykinins on cholinergic neurotransmission was studied in an innervated tracheal tube preparation isolated from guinea-pigs anaesthetized with urethane. The tracheal tube was bathed in Krebs-Henseleit solution containing 5 microM indomethacin. 2. Neurokinin A (NKA), eledoisin (El) and substance P (SP) caused concentration-dependent increases in intraluminal pressure (ILP), with an order of potency NKA greater than El much greater than SP. 3. Low concentrations of tachykinins, that had little effect on ILP, caused an increase in the contractions elicited by stimulation of the preganglionic vagal nerve fibres and by postganglionic (transmural) stimulation. The order of potency was NKA greater than or equal to El greater than SP. Contractions induced by exogenous acetylcholine (ACh) were not increased by the tachykinins. 4. The magnitude of the tachykinin-induced augmentation of responses to nerve stimulation was inversely related to stimulation voltage and frequency. 5. These results suggest that tachykinins act on NK2 receptors, both on the trachealis muscle and on postganglionic pulmonary parasympathetic nerve terminals. Activation of the neuronal receptors may increase the probability of transmitter release from the nerve terminals.     

Characterization of the effects of cannabinoids on guinea-pig tracheal smooth muscle tone: role in the modulation of acetylcholine release from parasympathetic nerves

We investigated the ability of the cannabinoid agonists CP55,940 (CB(1)/CB(2)) and anandamide (endogenous cannabinoid) to modulate electrical field stimulation (EFS)-induced acetylcholine (ACh) release from parasympathetic nerve terminals innervating guinea-pig trachea. We assessed whether modulation of transmitter release translated to an impact on functional responses by investigating the effect of these agents on contractile responses evoked by EFS and ACh. Furthermore, we evaluated the ability of these compounds to elicit bronchodilation in pre-contracted guinea-pig tracheal strips. CP55,940 and anandamide significantly inhibited EFS-evoked ACh release (maximal inhibition of 35.1+/-2.9% and 33.4+/-6.4% at 1 microM, P<0.05, respectively). The CB(1) receptor antagonist SR 141716A (1 microM), had no effect on ACh release and failed to reverse the inhibitory effect of CP55,940 (1 microM). Paradoxically, CP55,940 had no significant effect on EFS-evoked cholinergic contractile responses. Furthermore, CP55,940 did not relax pre-contracted tracheal strips or affect contractile responses to exogenous ACh. This lack of activity on smooth muscle tone is consistent with the fact that no detectable specific binding of [(3)H] CP55,940 was found in tracheal homogenates. These data suggest that cannabinoid agonists inhibit ACh release from cholinergic nerve terminals via activation of CB(2) receptors but that this inhibitory action does not impact on functional responses such as cholinergic contraction.     

Vergleich der Wirkungen eines rasch und eines langsam depolarisierenden Muskelrelaxans auf die Muskelspindeln

Summary 1. In pentobarbital-anesthetized cats, the discharge patterns of individual hindlimb muscle spindles (of M. triceps surae) were studied after i.v. administration of succinylbischoline (SCh; 0.25–0.5 mg/kg) and of the bischoline ether of hydrochinone (M 110, Oesterreichische Stickstoffwerke, Linz; 2–5 mg/kg), respectively.2. Both depolarizing substances were found to exert principally similar excitatory effects on the muscle spindles, differing only in the degree and the duration of their action, and in the doses needed. After M 110, the steady increase in afferent spindle discharges did not reach the peak frequencies observed after SCh, but lasted for more than 60 min, as compared to about 10 min after SCh.3. Comparable differences existed in the time courses of neuromuscular blockade of the extrafusal muscle fibres. However, in contrast to SCh, M 110 was frequently found to induce incomplete abolition of intrafusal neuromuscular transmission. No signs of intrafusal twitches or fibrillations were observed in the spindle behavior. The stretch sensitivity of the receptor endings remained intact after both SCh and M 110.4. With both substances, the monosynaptic mass reflex (MMR), recorded from the central stump of an appropriate ventral root, was abolished or depressed consequent to the high-frequency spindle discharges. Only with M 110, this depression was preceded by an initial phase of reflex enhancement; the subsequent reflex depression was less marked and of longer duration than that following SCh.5. The prolonged spindle-exciting and reflex-depressing effects of M 110 beside its general muscle-relaxing action, might be useful for clinical therapeutical purposes.

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Stipendiat der Deutschen Forschungsgemeinschaft.     

Modification by lidocaine of the discharges of primary endings of muscle spindles in cat tenuissimus muscle.

The effects of lidocaine (1--20 microgram/ml) on afferent discharge patterns of primary endings of muscle spindles in cat tenuissimus muscle were investigated. Discharge from the endings, recorded in Ia afferent axons, was evoked by ramp stretch of the muscle, stimulation of single static or dynamic fusimotor axons or by a combination of stretch and fusimotor stimulation. Spontaneous discharge of the endings at the initial length of the muscles was reduced by 2--5 microgram/ml and abolished by 10--15 microgram/ml lidocaine. The static but not the dynamic discharge elicited by muscle stretch was blocked by concentrations of 10--15 microgram/ml. The same concentrations abolished static and dynamic fusimotor influences on primary ending discharge. However, in one experiment where the spindle was microscopically observed, fusimotor stimulation still resulted in contraction of the intrafusal muscle even when fusimotor stimulation failed to elicit changes in discharge response patterns of the primary endings. These findings indicate that lidocaine interferes with the encoding mechanism prior to block of impulse conduction in either the fusimotor or afferent axons.     

Vitamin B1 and autonomic drugs: a reprint

The problem of the relationship between the thiamine and autonomic system drugs was studied about 30 years ago. To the vitamin was attributed an excitatory effect upon the peripheric section of parasympathetic nervous system and a synergic action with acetylcholine. Both an acetylcholine-like substance and thiamine are liberated at the nerve terminals after a stimulation. A similar synergic action of thiamine with adrenaline was also demonstrated. The study of the relationship between these drugs and the vitamin B1 is also now interesting. We want to stimulate a new series of experiments on this subject with the reprint of this review.     

Nicotine induces glutamate release from thalamocortical terminals in prefrontal cortex.

It has been proposed that activation of nicotinic acetylcholine receptors (nAChRs) can activate the prefrontal cortex, enhancing attention and cognition. Nicotine can stimulate the release of several different neurotransmitters in many brain regions. In the present study, we found that stimulation of nAChRs by nicotine or the endogenous agonist, acetylcholine (ACh), induces a large spontaneous increase in glutamate release onto layer V pyramidal neurons of the prefrontal cortex. This release of glutamate, measured by spontaneous excitatory postsynaptic currents (sEPSCs) in the prefrontal cortical slice, depends on intact thalamocortical terminals. It can be suppressed by mu-opioids or eliminated by blocking action potentials. The increase in sEPSCs is sensitive to low concentrations of nicotine, suggesting the involvement of high-affinity (eg alpha(4)beta(2)) nAChRs. Recent work has shown alterations in prefrontal alpha(4)beta(2) nAChRs in autism and schizophrenia, two conditions that are distinguished by abnormal prefrontal cortical activation as well as difficulty in certain aspects of cognition and integrating social and emotional cues. We show that mice lacking the beta(2) nAChR subunit do not show increased sEPSCs with either nicotine or ACh, again implicating high-affinity nicotinic receptors. These findings give new insight into the mechanism by which nicotine affects excitatory neurotransmission to the output neurons of the cerebral cortex in a pathway that is critical for cognitive function and reward expectation.     

Muscarinic agonists and antagonists: effects on the urinary bladder

Voiding of the bladder is the result of a parasympathetic muscarinic receptor activation of the detrusor smooth muscle. However, the maintenance of continence and a normal bladder micturition cycle involves a complex interaction of cholinergic, adrenergic, nitrergic and peptidergic systems that is currently little understood. The cholinergic component of bladder control involves two systems, acetylcholine (ACh) released from parasympathetic nerves and ACh from non-neuronal cells within the urothelium. The actions of ACh on the bladder depend on the presence of muscarinic receptors that are located on the detrusor smooth muscle, where they cause direct (M?) and indirect (M?) contraction; pre-junctional nerve terminals where they increase (M?) or decrease (M?) the release of ACh and noradrenaline (NA); sensory nerves where they influence afferent nerve activity; umbrella cells in the urothelium where they stimulate the release of ATP and NO; suburothelial interstitial cells with unknown function; and finally, other unidentified sites in the urothelium from where prostaglandins and inhibitory/relaxatory factors are released. Thus, the actions of muscarinic receptor agonists and antagonists on the bladder may be very complex even when considering only local muscarinic actions. Clinically, muscarinic antagonists remain the mainstay of treatment for the overactive bladder (OAB), while muscarinic agonists have been used to treat hypoactive bladder. The antagonists are effective in treating OAB, but their precise mechanisms and sites of action (detrusor, urothelium, and nerves) have yet to be established. Potentially more selective agents may be developed when the cholinergic systems within the bladder are more fully understood.     

An investigation of the role of ganglia in the innervation of the rat anococcygeus muscle: an electrical and mechanical study.

1 A preparation is described which allows the rat anococcygeus muscle to be stimulated via its two extrinsic nerves. Each nerve contains both excitatory and inhibitory fibres. A ganglionated nerve plexus lies on the surface of the muscle. 2 The possibility that at least part of the excitatory pathway was interrupted as a ganglion synapse lying in one of the nodes of plexus close to the muscle was suggested by the observations that (a) the excitatory response to extrinsic nerve stimulation was reduced by the nicotinic antagonists tubocurarine (0.13 to 0.26 mM) and dihydro beta-erythroidine (0.1 to 0.14 mM). (b) Fibres from one extrinsic nerve were shown to synapse on a ganglion cell from which intracellular recordings were made while the output from this ganglion cell was traced microscopically to the muscle. 3 Intracellular recording from ganglion cells in this plexus indicated that cholinergic synaptic transmission occurred in these ganglia. Tubocurarine (0.13 mM) and hexamethonium (1.3 mM) reversibly abolished intracellularly-recorded synaptic potentials. 4 Hexamethonium (0.1 to 1 mM) initially enhanced the motor response to nerve stimulation and raised muscle tone, probably by an action involving pre- and postsynaptic sites. Subsequently, hexamethonium inhibited the response to extrinsic nerve stimulation presumably by an effect at ganglia lying along the excitatory pathway. Hexamethonium enhanced, without subsequently inhibiting, the response to exogenously added noradrenaline in both untreated and 6-hydroxydopamine-treated rats. These results suggest that the initial enhancement produced by hexamethonium involved sites at postganglionic nerve endings and on smooth muscle receptors. 5 Inhibitory responses were obtained following extrinsic nerve stimulation when the tone of the muscle was raised and the excitatory response abolished by either guanethidine (3 micron) alone or by carbachol (10 micron) followed by phentolamine (3 micron). The inhibitory response was not reduced by hexamethonium (up to 2.8 mM) tubocurarine (up to 1.3 mM) or by atropine (up to 1 micron).     

Actions of triethylcholine on neuromuscular transmission

The effects of the triethyl analogue of choline (triethyl 2-hydroxyethyl ammonium) on muscular activity have been studied in conscious rabbits, chicks, dogs and a cat. The contractions of the tibialis anticus and soleus muscles of cats under chloralose anaesthesia, and of the tibialis anticus muscle of rabbits under urethane anaesthesia and the isolated diaphragm preparation of the rat were also used. In conscious animals, triethylcholine caused a slowly developing muscular weakness which was more severe after exercise and which resembled the symptoms of myasthenia gravis. In nerve-muscle preparations triethylcholine had a selective action in reducing the contractions of muscles elicited by a high rate of nerve stimulation while leaving unaffected the contractions caused by slower rates of stimulation. During the paralysis of the tibialis muscle of the cat produced by triethylcholine, action potentials recorded from the motor nerve were unaffected and the muscle responded normally to injected acetylcholine and to direct electrical stimulation. The failure of neuromuscular transmission produced by triethylcholine was reversed by injection of choline, but anticholinesterases were ineffective. Choline reduced the toxicity of triethylcholine in mice. It is concluded that triethylcholine produces transmission failure at the neuromuscular junction by interfering with the ability of the nerve endings to synthesize acetylcholine. The possibility that triethylcholine is itself acetylated by the nerve endings and released as an inactive neurohormone is discussed. It was shown that triethylcholine was devoid of depolarizing action and curare-like blocking action. It possesses a transient ganglion blocking action of the tetraethylammonium-type as shown in experiments in which it caused a fall in blood pressure and blocked the response of the nictitating membrane to pre- but not to post-ganglionic stimulation of the cervical sympathetic nerve.     

Indirekter Nachweis parasympathischer Nervenfasern im Ventrikelmyokard des Menschen

Summary The release of endogenous acetylcholine (ACh) has been investigated in 9 human papillary muscles. In the isolated preparation, transmitter substances were released by high voltage stimulation and simultaneous application of trains of stimuli during the abolute refractory period of the myocardium.In the pharmacologically untreatet human heart muscle the negative inotropic effect of ACh was superimposed on the positive inotropic effect of simultaneously released catecholamines. After treatment with guanethidine, high voltage stimulation reduced the amplitude of isometric contraction by an average of 14%. After contractility had been increased by noradrenaline, isoprenaline, orciprenaline or theophylline high voltage stimulation reduced the amplitude of contraction by 23%. These negative inotropic effects were increased up to 47% by neostigmine, diminished by hemicholinium and prevented by atropine, Blockade of intramural nerve endings by tetrodotoxin abolished completely the positive as well as negative inotropic effects of high voltage stimuli.These findings indicate the possibility of a release of endogenous ACh from intramural nerve endings also in human ventricular myocardium. The negative inotropic effect of endogenous ACh is most pronounced during positive inotropic effects of sympathominetic agents or of theophylline.

Ein Teil der Ergebnisse wurde anläßlich der 39. Tagung der Deutschen Physiologischen Gesellschaft als vorläufige Mitteilung publiziert (Sieber et al., 1972).     

An attempt to localize the site of action of different agents within cholinergic motor neurones of the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum by the triple bath method.

The site of action of cholinergic, adrenergic, peptidergic and opioid agents was studied in myenteric plexus-longitudinal muscle strips from the guinea pig ileum. A preparation in a special triple bath was drawn through two rubber membranes, dividing the strip into three segments. Neurogenic stimulation of the oral segment, set up nerve action potentials also in the neurones projecting axons up to the aboral segment. These axons, turning into varicose nerve terminals, conducted action potentials aborally across the middle segment, that was up to 10 mm wide. Finally, the nerve terminals, extending into the aboral segment, might be also invaded triggering twitches. Agents were added, either to the oral segment, to affect the genesis and spread of action potentials in the proximal parts of cholinergic neurones (cell bodies, axon hillocks, initial segments and axon preterminals) or they were added to the middle segment to affect propagation of action potentials in varicose nerve terminals. As a result, the amplitude of aboral twitches reflected their effects at each site, quantitatively. Noradrenaline and ethylketocyclazocine were more effective at the site of varicose nerve terminals, whereas substance P, acetylcholine and oxotremorine were more effective at the proximal parts; pilocarpine and nicotine were effective at both sites. Changes in membrane polarization might be the final common effect in the mechanism of action of all the stimulatory agents used.