Potentiation by cocaine of relaxations of the guinea-pig colon caused by noradrenaline and by stimulation of adrenergic nerves.

The distal colon of the guinea-pig is relaxed by noradrenaline, by isoprenaline and by the stimulation of fibres running with the colonic nerves or intramurally. The relaxations in response to stimulation of the colonic nerves have a guanethidine-sensitive (adrenergic) and a guanethidine-insensitive (non-adrenergic) component. Cocaine causes a three-fold sensitization of the muscle to noradrenaline but no sensitization to isoprenaline. Cocaine increases the duration, but does not affect the amplitude, of the relaxation observed when adrenergic nerves are stimulated, and affects neither duration nor amplitude of the non-adrenergic response. The adrenergic nerve terminals lie in Auerbach's plexus, not in the longitudinal muscle. It is concluded that the sensitization to noradrenaline and the increases in durations of responses to adrenergic nerve stimulation are due to inhibition of catecholamine uptake into adrenergic nerves by cocaine. It appears that, even where the neuromuscular separation is large as it is in the colon, the concentration of exogenous noradrenaline at the receptors can be decreased by neuronal uptake, and the uptake mechanism can modify responses to nerve stimulation in vitro.     

Contraction of bovine coronary vascular smooth muscle induced by cocaine is not mediated by norepinephrine

This study was designed to assess the effects of cocaine on coronary arterial smooth muscle and to determine whether previously reported cocaine-induced coronary vasospasm is mediated by substances released from the endothelium or by increased adrenergic receptor stimulation. Concentration-response relationships for cocaine (0.1-300 microM) and norepinephrine (0.1-300 microM) were studied in vitro using 2 mm segments of bovine proximal left anterior descending coronary artery. Each segmental ring was mounted in a 70 ml tissue bath for the measurement of isometric tension. Cocaine (3-300 microM) caused significant, concentration-dependent, increases in developed tension (p less than 0.05). Removal of the endothelium or pretreatment with prazosin (0.1 microM) or propranolol (1 microM) did not significantly alter this action of cocaine. In contrast to cocaine, norepinephrine (10-300 microM) caused significant decreases in developed tension (p less than 0.01). These findings suggest that cocaine-induced contraction of bovine coronary vascular smooth muscle is not mediated by endothelium derived contracting substances or norepinephrine.     

Acceleratory nervous regulation of juvenile myogenic hearts in the isopod crustacean Ligia exotica

We examined regulation of the myogenic heart by two identified cardioacceleratory neurons (CA1, CA2) in early juveniles of the isopod Ligia exotica. Repetitive stimulation of either the CA1 or CA2 axon increased the frequency and plateau amplitude of the action potential and decreased the maximum hyperpolarization of the cardiac muscle. These effects were larger with increasing stimulus frequency. The rate of increase in the frequency caused by CA1 stimulation was significantly larger than that by CA2. No impulse activity of the cardiac ganglion was induced by acceleratory nerve stimulation. The frequency of the muscle activity was decreased by injection of a hyperpolarizing current into the muscle during stimulation of the acceleratory nerve. In a quiescent heart, acceleratory nerve stimulation caused an overall depolarization in the muscle membrane and the amplitude of the depolarization induced by CA1 stimulation was significantly larger than that by CA2. These results suggest that CA1 and CA2 neurons regulate the myogenic heart affecting directly the cardiac muscle; the CA1 neuron produces more potent effects than does the CA2 neuron.     

Characteristics of cocaine block of purified cardiac sarcoplasmic reticulum calcium release channels.

We have examined the effects of cocaine on the SR Ca2+ release channel purified from canine cardiac muscle. Cocaine induced a flicker block of the channel from the cytoplasmic side, which resulted in an apparent reduction in the single-channel current amplitude without a marked reduction in the single-channel open probability. This block was evident only at positive holding potentials. Analysis of the block revealed that cocaine binds to a single site with an effective valence of 0.93 and an apparent dissociation constant at 0 mV (Kd(0)) of 38 mM. The kinetics of cocaine block were analyzed by amplitude distribution analysis and showed that the voltage and concentration dependence lay exclusively in the blocking reaction, whereas the unblocking reaction was independent of both voltage and concentration. Modification of the channel by ryanodine dramatically attenuated the voltage and concentration dependence of the on rates of cocaine block while diminishing the off rates to a lesser extent. In addition, ryanodine modification changed the effective valence of cocaine block to 0.52 and the Kd(0) to 110 mM, suggesting that modification of the channel results in an alteration in the binding site and its affinity for cocaine. These results suggest that cocaine block of the SR Ca2+ release channel is due to the binding at a single site within the channel pore and that modification of the channel by ryanodine leads to profound changes in the kinetics of cocaine block.     

Inspiratory rhythm in airway smooth muscle tone

In anesthetized paralyzed open-chested cats ventilated with low tidal volumes at high frequency, we recorded phrenic nerve activity, transpulmonary pressure (TPP), and either the tension in an upper tracheal segment or the impulse activity in a pulmonary branch of the vagus nerve. The TPP and upper tracheal segment tension fluctuated with respiration, with peak pressure and tension paralleling phrenic nerve activity. Increased end-tidal CO2 or stimulation of the carotid chemoreceptors with sodium cyanide increased both TPP and tracheal segment tension during the increased activity of the phrenic nerve. Lowering end-tidal CO2 or hyperinflating the lungs to achieve neural apnea (lack of phrenic activity) caused a decrease in TPP and tracheal segment tension and abolished the inspiratory fluctuations. During neural apnea produced by lowering end-tidal CO2, lung inflation caused no further decrease in tracheal segment tension and TPP. Likewise, stimulation of the cervical sympathetics, which caused a reduction in TPP and tracheal segment tension during normal breathing, caused no further reduction in these parameters when the stimulation occurred during neural apnea. During neural apnea the tracheal segment tension and TPP were the same as those following the transection of the vagi or the administration of atropine (0.5 mg/kg). Numerous fibers in the pulmonary branch of the vagus nerve fired in synchrony with the phrenic nerve. Only these fibers had activity which paralleled changes in TPP and tracheal tension. We propose that the major excitatory input to airway smooth muscle arises from cholinergic nerves that fire during inspiration, which have preganglionic cell bodies in the ventral respiratory group in the region of the nucleus ambiguus and are driven by the same pattern generators that drive the phrenic and inspiratory intercostal motoneurons.     

Characteristics of the functional state of rat tracheal and bronchial smooth muscle at different stages of alveolitis

In isolated tracheal smooth muscle preparations in normal rats and in rats with experimental fibrotic alveolitis, responses to electrical field stimulation of nervous and muscle fibers were studied. At stimulation of muscles or nerves of tracheal preparations without intramural ganglia in rats with acute alveolitis, parameters of smooth muscle contractions did not practically differ from those in normal rats. In rats with fibrotic alveolitis the amplitude and rate of muscle contraction decreased, while the response latent period (LP) increased. At stimulation of preganglionic nerve fibers of the tracheal preparations with intramural ganglia in rats with acute alveolitis, the value and rate of smooth muscle contraction decreased, while the response LP increased. After transition into chronic phase of the disease (fibrotic alveolitis), a partial restoration of the response parameters took place. In rats with acute alveolitis, the repeated stimulation of the nerve fibers led to an increase of amplitude and a decrease of rate of tracheal smooth muscle contractions. In rats with fibrotic alveolitis, the repeated stimulation caused a decrease of amplitude and rate of contractions and an increase of the response LP.     

Inhibition by VIP and atriopeptin II on the field stimulation evoked release of [3H]noradrenaline in the rat portal vein.

The modulatory effects of vasodilatory peptides on noradrenaline release from sympathetic nerve terminals have been studied in the rat portal vein model. Transmural field stimulation of the longitudinally mounted vein preparation evoked concomitant increases in the [3H]noradrenaline overflow and the integrated tension. Both responses were abolished by guanethidine or tetrodotoxin, whereas only the tension response was blocked by phentolamine. CGRP and VIP, both being present in intramural nerve fibers in the rat portal vein, were compared with atriopeptin II for modulatory effects. CGRP (100 nM) had no effect on the overflow of [3H]noradrenaline or the integrated tension response to transmural stimulation. VIP (30 nM) and atriopeptin II (30 nM) both caused significant reductions of both [3H]noradrenaline overflow and the integrated tension. These results indicate that the decreased tension response to transmural stimulation in the presence of VIP or AP II reflects the sum of both pre- and postsynaptic inhibitions.     

Mediator liberation at the myoneural junctions of the frog sartorius muscle when axoplasmic transport has been disrupted with colchicine]

Colchicine application to the nerve innervating the frog sartorius muscle leads to reduction of the differences in functional condition of the myoneural synapses of this muscle by the signs of quantum content of the end plate potential (EPP) and by the changes of the EPP amplitudes in high frequency stimulation. Along with this there occurs a rarefaction of the frequency of miniature potential of the end plate, and reduction of its amplitude. Apparently, the latter is caused by reduction of effective resistance of the postsynaptic membrane. Changes of the induced and spontaneous secretion of the mediator are connected with disturbances of the axoplasmic transport just in the somatic nerve fibers.     

Nerves containing substance P,vasoactive intestinal polypeptide,enkephalin or somatostatin in the guinea-pig taenia coli

Summary The guinea-pig taenia coli is rich in peptide-containing nerves. Nerve fibres containing substance P (SP), vasoactive intestinal peptide (VIP), or enkephalin, were numerous in the smooth muscle while somatostatin fibres were very few. Nerve fibres displaying SP or VIP immunoreactivity were numerous in the myenteric plexus. Enkephalin nerve fibres were fairly numerous in the plexus while somatostatin nerve fibres were sparse. Nerve cell bodies containing immunoreactive SP or VIP were regularly seen in the plexus. Delicate varicose elements of the different types of nerve fibres were found to ramify around nerve cell bodies in a manner suggestive of innervation.In the electron microscope the various peptide-storing nerve fibres (i.e., elements containing SP, VIP or enkephalin) were found to contain a varying number of fairly large, electron-opaque vesicles in the varicose swellings. These vesicles represent the storage site of the neuropeptides.The isolated taenia coli responded to electrical nerve stimulation with a contraction. After cholinergic and adrenergic blockade the contractile response was replaced by a relaxation followed by a contraction upon cessation of stimulation. SP contracted the taenia while VIP caused a relaxation. The enkephalins raised the resting tension slightly while somatostatin had no effect. These observations are compatible with a role for SP as an excitatory neurotransmitter and for VIP as an inhibitory one, and with the view that both SP neurones and VIP neurones act as motor neurones. In preparations contracted by SP the electrically induced contractions were reduced in amplitude while the electrically induced relaxations seen after adrenergic and cholinergic blockade were enhanced in amplitude. In preparations relaxed by VIP there was an increased contractile response to electrical stimulation, while in the atropine + guanethidine-treated preparation the electrically induce relaxations were reduced in amplitude. The enkephalins reduced the contractile response to electrical stimulation, while somatostatin induced a very small reduction in the amplitude of such responses. These observations suggest that SP neurones and VIP neurones may play additional roles as interneurones. Somatostatin neurones probably act as interneurones. Enkephalin-containing fibres may serve to modify the release of transmitter from other nerves in the smooth muscle, perhaps through axo-axonal arrangements. Alternatively, the enkephalin nerve fibres in the smooth muscle are afferent elements involved in mediating sensory impulses to the myenteric plexus.     

Contractile responses of canine isolated pulmonary lobar arteries and veins to norepinephrine, serotonin, and tyramine.

Isolated helical strips of canine intrapulmonary lobar arteries and veins (about 4 mm in diameter) undergo dose-related tension development when exposed to increasing concentrations (10(-8) - 10(-3) M) of norepinephrine (NE), serotonin or 5-hydroxytryptamine (5-HT) and tyramine (Tyr). Venous segments were generally more sensitive while the maximum tension development was greater in the arterial strips, probably owing to their greater thickness. Both strips were more sensitive to 5-HT than NE and only responded to Tyr at high concentrations. Norepinephrine and 5-HT were nearly equally efficacious, whereas Tyr was less so. Responses to the latter were slow to develop, exhibited tachyphylaxis, and were greatly inhibited by phentolamine (10(-8) M), an alpha-adrenergic blocker. Exposure to cocaine (10(-5) M) enhanced submaximal NE responses, inhibited Tyr contractions and had no consistent effect on 5-HT responses. Phentolamine (10(-8) M) was also found to inhibit NE responses without altering 5-HT probably acts on other receptors. Tyramine may, in part, act directly on alpha-adrenergic receptors but may also release NE from surviving adrenergic nerve terminals in the preparation. Cocaine inhibits this effect and potentiates responses to lower levels of NE, presumably by blocking NE uptake into nerve terminals although a post-junctional action cannot be excluded.     

Heart rate as a determinant of the decay rate of the cardiac inotropic response to sympathetic nervous activity

The cardiac responses to sympathetic nerve stimulation were measured in a series of open-chest, anesthetized dogs. In half the animals, the hearts were in a sinus rhythm; in the remaining animals, the hearts were in an atrioventricular (AV) junctional rhythm. Cocaine markedly prolonged the decay times of the chronotropic responses after cessation of sympathetic stimulation, regardless of the type of rhythm. The decay times of the inotropic responses were only slightly prolonged by cocaine in animals with a sinus rhythm, but the prolongations were pronounced in animals with an AV junctional rhythm. The lower basal heart rate appeared to be more responsible for the greater decay times of the inotropic responses in the animals with an AV junctional rhythm than in those with a sinus rhythm. In a second series of dogs, complete heart block was produced, cocaine was given, AND the hearts were paced at four different frequencies. The mean decay time of the inotropic response to sympathetic stimulation varied inversely AND substantially with the pacing frequency. The change in contraction frequency probably affects the rate of neurotransmitter dissipation from the ventricular myocardium, by altering either the coronary blood flow or the massaging action of the cardiac contractions.     

Effect of prednisolon on trachea smooth muscle of normal rats and rats with fibrosing alveolitis

Effect of prednisolone on isolated preparations of trachea of normal rats and rats with fibrosing alveolitis was studied. Prednisolone at a concentration of 0.4 microg/l decreased responses of smooth muscle on stimulation of preganglionar nerve fibers at trachea areas with intramural ganglia in rats with acute alveolitis by 48%, while in normal rats--by 19% of control. In trachea preparations without ganglia, prednisolone at a dose of 10 microg/l decreased responses of muscle to the nerve fiber stimulation by 21.3%. The higher prednisolone doses were less efficient: 0.1-10 microg/l glucocorticoid practically did not affect the smooth muscle responses produced by stimulation of muscle cells. In rats with fibrosing alveolitis, 10 microg/l prednisolone restored the smooth muscle responses to control values in preparations of trachea with intramural ganglia. After the prednisolone treatment, amplitude of the rat trachea muscle contraction in response to the nerve fiber electric stimulation did not differ statistically significantly from control and 0.1-10 microg/l prednisolone did not change the response value. The conclusion is made that prednisolone affected the diseased rats more efficiently than the healthy animals. The character of the glucocorticoid effect depends on the presence of intramural ganglia in the trachea wall.     

Modulation of tension production by proctolin in the dorsal longitudinal muscles of the cricket,Teleogryllus oceanicus

High-frequency electrical stimulation (～20 Hz) of the lateral nerve in abdominal segments of the cricket, Teleogryllus oceanicus, caused an increase in tonus of the abdominal dorsal longitudinal muscle (DLM). This effect persisted for 1–5 min following stimulation. Application of the pentapeptide proctolin (threshold 1–10 nM) mimicked the increase in muscle tonus produced by electrical stimulation. Individual twitches were unaffected or slightly reduced by proctolin. Low-frequency electrical stimulation (<7 Hz) of the lateral nerve counteracted a previously induced increase in muscle tonus, apparently by activation of an inhibitory motoneuron. γ-Aminobutyric acid (GABA) mimicked the effect of low-frequency stimulation and reduced muscle tonus. Octopamine, in concentrations of ≤0.1 mM, was inactive on the abdominal DLM when stimulated at low frequencies (0.5–2 Hz). Application of proctolin to the metathoracic DLM caused an increase in twitch amplitude but had little effect on basal tonus. In conjunction with the previously described responses of the metathoracic DLM to octopamine, these results show that the serially homologous abdominal and metathoracic DLMs have dissimilar responses to the modulators proctolin and octopamine.     

Control of the alary muscles of locust dorsal diaphragm

ABSTRACT. The heartbeat in whole, intact, adult Locusta migratoria R.F. was characterized by a regular rate but apparently irregular amplitude. Cutting segmental nerves often eliminated apparent amplitude fluctuations, and electrically shocking a segmental nerve in the whole animal evoked apparent amplitude changes corresponding to the shocks. Saline-perfused tissue preparations showed that the apparent amplitude fluctuations could be duplicated by segmental nerve stimulation, and that the fluctuations were due largely to contractions of the alary muscles of the dorsal diaphragm which shifted the position of the heart chamber without a change in volume. The alary muscles are each multi-terminally innervated by one motor axon. Neurally-evoked postsynaptic potentials facilitated and summated, and the diaphragm muscles began visibly contracting at stimulation rates as low as 2 Hz. Stimulation at higher frequencies caused greater depolarization of the muscle fibres with no indication of electrically-excited responses. The alary muscles were insensitive to perfusion with acetylcholine, l -glutamate, l -aspartate, dopamine, octopamine, noradrenaline, proctolin, 5-hydroxytryptamine, or gamma aminobutyric-acid in saline at concentrations up to 10^-3M. Larval or adult brain extracts of Locusta at 10 μg/μl and diluted 1:5 in saline caused uniform contractions of the alary muscle preparation, while perfusion of skeletal muscle extracts produced no response.     

Effect of prednisolone on trachea smooth muscle of normal rats and rats with fibrosing alveolitis

Effect of prednisolone on isolated preparations of trachea of normal rats and rats with fibrosing alveolitis was studied. Prednisolone at a concentration of 0.4 μg/l decreased responses of smooth muscle on stimulation of preganglionic nerve fibers at trachea areas with intramural ganglia in rats with acute alveolitis by 48%, while in normal rats—by 19% of control. In trachea preparations without ganglia, prednisolone at a dose of 10 μg/l decreased responses of muscle to the nerve fiber stimulation by 21.3%. The higher prednisolone doses were less efficient: 0.1–10 μg/l glucocorticoid practically did not affect the smooth muscle responses produced by stimulation of muscle cells. In rats with fibrosing alveolitis, 10 μg/l prednisolone restored the smooth muscle responses to control values in preparations of trachea with intramural ganglia. After the prednisolone treatment, amplitude of the rat trachea muscle contraction in response to the nerve fiber electric stimulation did not differ statistically significantly from control and 0.1–10 μg/l prednisolone did not change the response value. The conclusion is made that prednisolone affected the diseased rats more efficiently than the healthy animals. The character of the glucocorticoid effect depends on the presence of intramural ganglia in the trachea wall.     

Physiological properties of the penis retractor muscle of Aplysia

The properties of the penis retractor muscle of Aplysia have been studied using intracellular, sucrose gap and tension recording. The fibers are of the invertebrate smooth muscle type and exhibit slow contractions which occur spontaneously or in response to stretch in isolated preparations. Individual muscle fibers are innervated by excitatory and inhibitory axons. A variety of sizes of excitatory and inhibitory junctional potentials can be recorded from them. The innervation is probably diffuse and functionally polyneuronal. The fibers are electrically coupled, permeable to potassium and chloride at rest, and exhibit no overshooting active responses. The muscle shows graded responses of depolarization and contraction proportional to strength of nerve stimulation. Facilitation and depression of junctional potentials are seen with various frequencies of nerve stimulation. Post-tetanic potentiation occurs with nerve stimulation at frequencies from 2 to 50 Hz and is suppressed in the presence of increased extracellular calcium concentrations.     

The electrical and mechanical properties of the proleg retractor muscle of the Chinese oak silkmoth larva

ABSTRACT. The main proleg retractor muscle (y) of Antheraea pernyi Guer. (Lepidoptera, Saturniidae) larvae consists of three layers of fibres. The innermost layer of fibres is dually innervated. Cobalt backfills of the two motor neurones, in nerve 2d, showed the somata to be situated ventrally and anteriorly in the same segmental ganglion, ipsilateral to the filled nerve. Intramuscular microelectrode recordings showed excitatory junction potentials (EJPs) of two distinct amplitudes, both of which were relatively slow. However, 26% of the larger amplitude EJPs had an active membrane response. The EJPs and mechanical responses both summated at low stimulation frequencies. Large EJPs resulted in a much greater development of tension than small ones. Extracellular stimulation of nerve lbiii modulated peak tension and peak rate of relaxation.     

Altered breathing pattern elicited by stimulation of abdominal visceral afferents

The effect of stimulation of afferent mesenteric nerves on tidal volume (VT), phrenic nerve, and external intercostal muscle activities was studied in anesthetized spontaneously breathing cats. Both mechanical distension of the small intestine and electrical stimulation of the mesenteric nerves resulted in an initial inspiratory inhibition of VT followed by a gradual recovery above the prestimulus controls. Changes in VT were accompanied by a depression of phrenic nerve activity and an excitation of external intercostal muscle activity. During the recovery phase of VT, the amplitude of phrenic nerve activity returned only partially, whereas the activity of the external intercostal muscle was greater than the prestimulus controls. In a second group of experiments, brief tetanic stimulation at the beginning of inspiration led to a complete and maintained inhibition of phrenic nerve activity but with a simultaneous excitation of external intercostal muscle activity and without any change in VT; whereas expiratory stimulation caused a decrease in expiratory abdominal muscle activity, without changing the peak amplitude of phrenic nerve activity. The respiratory changes observed with distension of the small intestine were abolished after denervation of the mesenteric plexus. It is concluded that activation of the visceral afferents of the mesenteric region reflexly changes diaphragmatic breathing to intercostal breathing. It is assumed that such a type of breathing pattern may occur in pregnancy and in pathophysiological situations involving splanchnic viscera.     

Direct evidence that stomatogastric (Panulirus interruptus) muscle passive responses are not due to background actomyosin cross-bridges

Muscles respond to imposed length changes with rapid, large force changes followed by slow relaxations to new steady-state forces. These responses were originally believed to arise from background levels of actomyosin binding. Discovery of giant sarcomere-spanning proteins suggested muscle passive responses could arise from length changes of elastic domains present in these proteins. However, direct evidence that actomyosin plays little role in passive muscle force responses to imposed length changes has not been provided. We show here that a poison of actomyosin interaction, thiourea, does not alter initial force changes or subsequent relaxations of lobster stomatogastric muscles. These data provide direct evidence that background actomyosin cross-bridge formation likely plays, at most, a small role in muscle passive responses to length changes. Thiourea does not alter lobster muscle electrical responses to motor nerve stimulation, although in this species it does cause tonic motor nerve firing. This firing limits the utility of thiourea to study lobster muscle electrical responses to motor nerve stimulation. However, it is unclear whether thiourea induces such motor nerve firing in other animals. Thiourea may therefore provide a convenient technique to measure muscle electrical responses to motor nerve input without the confounding difficulties caused by muscle contraction.     

Maturation of respiratory reflex responses in the piglet

Stimulation of chemo-, irritant, and pulmonary C-fiber receptors reflexly constricts airway smooth muscle and alters ventilation in mature animals. These reflex responses of airway smooth muscle have, however, not been clearly characterized during early development. In this study we compared the maturation of reflex pathways regulating airway smooth muscle tone and ventilation in anesthetized, paralyzed, and artificially ventilated 2- to 3- and 10-wk-old piglets. Tracheal smooth muscle tension was measured from an open tracheal segment by use of a force transducer, and phrenic nerve activity was measured from a proximal cut end of the phrenic nerve. Inhalation of 7% CO2 caused a transient increase in tracheal tension in both age groups, whereas hypoxia caused no airway smooth muscle response in either group. The phrenic responses to 7% CO2 and 12% O2 were comparable in both age groups. Lung deflation and capsaicin (20 micrograms/kg iv) administration did not alter tracheal tension in the younger piglets but caused tracheal tension to increase by 87 +/- 28 and 31 +/- 10%, respectively, in the older animals (both P less than 0.05). In contrast, phrenic response to both stimuli was comparable between ages: deflation increased phrenic activity while capsaicin induced neural apnea. Laryngeal stimulation did not increase tracheal tension but induced neural apnea in both age groups. These data demonstrate that between 2 and 10 wk of life, piglets exhibit developmental changes in the reflex responses of airway smooth muscle situated in the larger airways in response to irritant and C-fiber but not chemoreceptor stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)