Hexamethonium: a probe to assess autonomic nervous system involvement in upper gastrointestinal functions in conscious sheep

Hexamethonium, which inhibits cholinergic transmission by preventing acetylcholine release, has been considered an ideal reference drug for the blockade of autonomic ganglia, Auerbach plexus and reflex gastrointestinal secretions. The degree of inhibition of ruminant gastrointestinal functions with this reference drug were as follows: cyclical contractions of the reticulo-rumen and abomasal motility greater than gastric acid secretion and duodenal migrating myoelectrical complexes. Although reduced at high dosages, the initiation of migrating myoelectric complexes was enhanced at clinically used dosages. The duration of the inhibition of reticular contractions was dose-related varying from 0.5 to 5 h for 1.25 to 20 mg/kg subcutaneously. Abomasal motility and acid secretion were similarly reduced but exhibited strong and long-lasting rebound effects. Inhibition of the reticulum by the blockade of muscarinic receptors by atropine was also dose-related lasting from 0.5 to 3 h for 0.5 to 2 mg/kg, whereas inhibition of the abomasal motor and secretory functions lasted from 1 to 6 h. These results suggest a higher degree of impingement of the parasympathetic pathways on abomasal acid secretion and motility than on the cyclical activity of the reticulum and only a modulatory role of the extrinsic neural activity on the cyclical motor events of the duodenum.

Laterality associated with sexual dimorphism in the volume of the mouse hypogastric ganglion

The volume of the hypogastric ganglion was investigated in male, female, and prenatally androgen-exposed female newborn mice. Two milligram testosterone propionate was injected into pregnant ICR mice from days 14 to 16 of gestation. The volume of the ganglia on both sides in intact male neonates was significantly larger than that in female neonates. The volume of ganglia in testosterone-exposed females was significantly larger than those in intact females, but did not attain the male volume. In intact males, the ganglion on the left side was significantly larger than on the right. This left-right difference in the volume of the ganglia was not recognized in the intact or TP-exposed females. These results suggest that sex difference and lateralization of the volume of the hypogastric ganglion were highly dependent on the prenatal sex hormone environment.

Control of lacrimal secretion after sphenopalatine ganglion block

Tear secretion with topical anesthesia ("Basal secretion") was measured in 10 normal subjects using Schirmer's tear strips before and after a sphenopalatine ganglion block. In an additional three normal subjects, tear turnover was determined with an objective fluorophotometer both before and after sphenopalatine ganglion block. The sphenopalatine ganglion block was obtained by the injection of the lidocaine (2%) into the sphenopalatine fossa. Topical anesthesia (proparacaine 0.5%) was used prior to all measurements. Tear secretion with topical ocular anesthesia was reduced substantially by sphenopalatine block, as measured by either Schirmer's strips or objective fluorophotometry. The more exact fluorophotometric method recorded a complete cessation of tear turnover flow following ganglion block. These findings support other reports, suggesting that all tear secretion is under neurologic control and dependent on reflex stimulation.

Effect of capsaicin upon fluoride sensitive acid phosphatases in selected ganglia and spinal cord and upon neuronal size and number in dorsal root ganglion

A quantitative method for the analytical separation of the fluoride sensitive acid phosphatases of rat spinal cord and peripheral nervous tissues into tartrate-sensitive and tartrate-resistant forms (TSAP and TRAP, respectively) is described. Evidence supporting the use of L-(+)-tartrate rather than fluoride as an inhibitor is presented. The method is used for the quantitative description of the consequences of neonatal capsaicin treatment, and the results appear to justify the attribution of the TRAP activity to the capsaicin sensitive neurons. In the first experiment, rats were killed at weekly intervals after neonatal capsaicin treatment. In controls, both TRAP and TSAP activities in dorsal root ganglia (DRG) increased during the second postnatal week and remained constant thereafter. At all ages (1-4 weeks) TRAP activity was reduced 50-60% in capsaicin-treated DRG. Reduction of TSAP activity was much less. In a second experiment, rats were treated neonatally with capsaicin or vehicle (control) and allowed to grow to adulthood (4 months). TRAP activity was found to be decreased 38% in the dorsal half of the lumbar spinal cord (L3-L5), decreased 33% in nodose ganglion, and unchanged in superior cervical ganglion of the capsaicin treated animals. TSAP activity was unchanged in dorsal spinal cord and superior cervical ganglion and decreased 33% in nodose ganglion. The number of neurons in C8 DRG was found to be reduced 28% in capsaicin treated animals. The loss appeared to be among the small neurons. The number of large neurons was actually increased in ganglia from capsaicin-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-blocking and hemodynamic effects of ASL-8052

The hemodynamic and cardiac beta-blocking effects of ASL-8052 (esmolol), an ultrashort-acting beta-blocker, were examined in pentobarbital-anesthetized dogs. The compound produced dose-dependent reductions in heart rate, left ventricular dP/dt, right ventricular contractile force, and diastolic arterial blood pressure in dogs with intact autonomic function. ASL-8052 was devoid of any hemodynamic effects in ganglion-blocked animals. Responses to isoproterenol (except for diastolic blood pressure) were blocked by ASL-8052 in qualitatively similar fashion in both groups of animals. The compound reduced the rate-pressure product and decreased diastolic coronary blood flow. The reactive hyperemic response to a 10-s occlusion of the left circumflex coronary artery was not modified by ASL-8052. Heart rate and contractile force dose-response curves to isoproterenol were equally shifted to the right in a dose-dependent, parallel fashion by constant infusion of ASL-8052. During infusion of large doses in reserpinized dogs, the compound decreased heart rate, contractility, and arterial blood pressure, while left ventricular end-diastolic pressure increased. No intrinsic sympathomimetic effect was observed. Tachycardia induced by either stimulation of the right ansa subclavia or intravenous injection of isoproterenol was blocked to an equivalent degree by ASL-8052. These data indicate that ASL-8052 produces hemodynamic effects that are characteristic of and explained by beta-adrenergic receptor blockade. However, direct cardiac depression is observed at extremely high doses.

Clonidine inhibits nicotinic effects in ganglia of the cholinergic-sympathetic system

The electrodermal potential (EDP) recorded with surface electrodes between the palm and the shaven back of the forepaws of anaesthetized cats was taken as a measure of sudomotor activity in response to submaximal activation of cholinergic-sympathetic efferents with the nicotinic ganglionic stimulant DMPP. The intravenous injection of 30 micrograms/kg clonidine inhibited EDPs in despinalized cats and in vagotomized cats with chronic denervation of the stellate ganglion. In vagotomized cats clonidine (30 micrograms/kg i.v.) shifted the dose-response curve of DMPP (4-256 micrograms/kg i.v.) to the right. An inhibitory effect was also observed in despinalized cats upon topical application of 0.1 and 1 microgram clonidine to the stellate ganglion. In all preparations the inhibitory effect of clonidine could be antagonized by intravenous injection of 200 micrograms/kg yohimbine. As all substances used were also active when injected during arrest of blood flow to the foreleg by means of a tourniquet, actions at the level of the sweat gland could be excluded. The results lead to the conclusion that the activation of postsynaptic somadendritic alpha 2-adrenoceptors in sudomotor ganglia of the cholinergic-sympathetic nervous system inhibits the effects of nicotinic ganglionic stimulation. It is assumed that this action is due to the known ganglionic hyperpolarization induced by alpha 2-adrenoceptor stimulants.

Effect of ganglionic blockade on catecholamine secretion in exercised dogfish

A brief bout of vigorous exercise results in significant increases in plasma epinephrine (E) and norepinephrine (NE) in the dogfish, Squalus acanthias. Since the presence of a functioning sympathetic nervous system in dogfish is in doubt, experiments were undertaken to show whether or not exercise-induced catecholamine (CA) secretion is under autonomic neurogenic control. Changes in plasma E and NE in a control group of exercised fish were compared with changes in fish exercised while under the influence of ganglionic blockade. Ganglionic blockade was induced in dogfish by hexamethonium infusion before exercise. CA secretion in response to a subsequent bout of exercise was significantly reduced without impairment of the ability of the fish to exercise. The pattern of systemic arterial pressure response to exercise and recovery (initial decrease during exercise followed by a prompt recovery to control level) was not significantly altered by ganglionic blockade. It is concluded that in dogfish some fraction of CA secretion capacity is possibly or potentially under neurogenically related control. Apparently the fraction of CA secretion under such control is not essential for performing exercise. The pattern of CA secretion accompanying the events of exercise and recovery in dogfish suggests that CA may play a more important role in recovery from exercise than in its performance.

Prenatal exposure of male mice to androgen increases neuron number in the hypogastric ganglion

There is a sexual dimorphism in the hypogastric ganglion innervating the internal genitalia of mice. We now report that prenatal exposure of male mice to testosterone propionate brings about a significant increase of neuronal number in the hypogastric ganglion. This suggests that sexually dimorphic nature of the hypograstric ganglion depends on the prenatal hormone environment.

Substance P: a putative sensory transmitter in mammalian autonomic ganglia

Repetitive presynaptic stimulation elicited slow membrane depolarization in neurons of inferior mesenteric ganglia from guinea pigs. This response was not blocked by cholinergic antagonists but was specifically and reversibly inhibited by a substance P analog, (D-Pro2, D-Phe7, D-Trp9)-substance P, which also depressed the depolarization induced by exogenously applied substance P. The atropine-sensitive slow excitatory and slow inhibitory postsynaptic potentials evoked in neurons of rabbit superior cervical ganglia were not affected by the substance P analog. These and previous results provide strong support for the hypothesis that substance P or a closely related peptide is the transmitter mediating the slow depolarization. The latter may represent a sensory input from the gastrointestinal tract to neurons of the prevertebral ganglia.

Interactions of catecholamine uptake inhibitors and norepinephrine on autonomic ganglia

The effect of catecholamine uptake inhibitors on blockade by norepinephrine was observed in the isolated stellate ganglion of the hamster. The preganglionic nerve was stimulated, supramaximally, at 0.2 Hz and compound action potentials were recorded from the postganglionic nerve. Norepinephrine blocked ganglionic transmission. The sensitivity of the ganglion to norepinephrine was increased by the catecholamine uptake inhibitors, desipramine (3 X 10(-7) M), d-amphetamine (10(-6) and 10(-5) M) and tyramine (10(-4) M). Ouabain (10(-5) and 3 X 10(-5) M) did not change the sensitivity of the ganglion to norepinephrine. All the drugs reduced the uptake by the [3H]norepinephrine into the ganglion. The inhibition of [3H]norepinephrine uptake by the drugs could be correlated with the increase in sensitivity of the ganglion to norepinephrine. These results support the hypothesis that catecholamine uptake is important in terminating the actions of exogenously applied norepinephrine, and that inhibition of the catecholamine uptake increases the sensitivity of the ganglion to norepinephrine.

[Effect of thyroxine and methylthiouracil on the development of intramural ganglia in the chick embryo digestive tube]

The development of the vegetative muscular-gastric plexus ganglia has been studied in 17-day-old chick embryos at administration of thyroxin and the inhibitor of its production - methylthiouracil. The substances in question are injected into the air chamber of the egg on the 3d days of incubation. In histological preparations, stained after Nissl, with hematoxylin - eosin and silver impregnated, the total number of cells of the neuroblastic line and that of differentiated neurons are calculated in 50 ganglia. Under thyroxin effect the number of the differentiated neurons in the ganglia increases, while the total number of the neuroblastic cells (comparing to the control) remains constant. Under methylthiouracil effect the number of the differentiated neurons decreases and so does the total number of the neuroblastic cells. Thyroxin and methylthiouracil differently affect the differentiation rate of the neurons at various stages of this process. The effect of the drugs applied is poorly manifested in the duodenum, where (in the control) the total portion of the differentiated cells is higher than in other segments of the digestive tube, and the number of the ganglia without such cells is lower, while the portion of the ganglia with numerous differentiated neurons is more significant.

Heart rate conditioning in the pigeon immobilized with alpha-bungarotoxin

Previous in vitro studies have yielded conflicting results concerning the physiological effects of alpha-bungarotoxin (alpha-BTX) at avian autonomic ganglia. In the present study heart rate change was classically conditioned in pigeons immobilized with alpha-BTX to assess the effects of this agent on autonomic function in the intact animal. When compared with non-immobilized controls, alpha-BTX had no significant effect on basal heart rate or on the rate of acquisition, magnitude or dynamics of conditioned heart rate change. Furthermore, a significant difference in performance between groups receiving conditioning and sensitization paradigms clearly indicated the establishment of conditioned responding. It is concluded that alpha-BTX has little or no effect on the cardiac innervation at doses sufficient to block neuromuscular transmission. The irreversible blockade of neuromuscular transmission by alpha-BTX without the side-effects produced by most other paralytics makes it an ideal choice as an immobilizing agent in acute preparations.

The effects of alpha- and beta-neurotoxins from the venoms of various snakes on transmission in autonomic ganglia

We have previously shown that certain commercially available lots of alpha-bungarotoxin block transmission in ciliary and choroid neurons of both pigeon and chicken ciliary ganglia at a concentration of 10 microgram/ml (1.2 microM). The blockade is antagonized by pre-incubation with 100 microM tubocurarine. Further evidence that this blockade is produced by a postsynaptic action, as one would expect of an alpha-neurotoxin, are our findings that: (a) exposure to the toxin prevents the depolarization of ganglion cells normally seen in response to the cholinergic agonist, carbachol; and (b) the blocking activity of the toxin is removed by treatment with membranes purified from Torpedo electric organ containing an excess of alpha-neurotoxin binding sites. A high affinity binding site for [125I]alpha-bungarotoxin was characterized in the chicken ciliary ganglion. However, since it is labelled equally well by lots of alpha-bungarotoxin which block transmission and those that do not, this site does not appear to be involved in the blockade of transmission. alpha-Cobratoxin (from Naja naja siamensis), the alpha-neurotoxin L.s. III (from Laticauda semifasciata) and certain lots of alpha-bungarotoxin produce a partial blockade of transmission in ciliary neurons of the pigeon ciliary ganglion at a concentration of 10 microgram/ml (1.2 microM), but have no effect on transmission in choroid neurons. Two other alpha-neurotoxins from Laticauda semifasciata, erabutoxin a and erabutoxin b, have no effect on transmission in either cell population at this concentration. None of the alpha-neurotoxins tested had any effect on transmission in either the rat superior cervical ganglion or the rat pelvic ganglion at concentrations up to 100 microgram/ml (12 microM). Collagenase treatment of these ganglia, in an attempt to increase access of the toxins to ganglion cells, did not alter these negative results. beta-Bungarotoxin (0.5 microgram/ml, 0.02 microM) produces a complex blockade of transmission in both avian ciliary ganglia and rat superior cervical ganglia. Unlike the action of alpha-bungarotoxin, the blockade of ciliary ganglion transmission by beta-bungarotoxin is irreversible and is not prevented by pretreatment with tubocurarine.

Slow Synaptic Responses in Autonomic Ganglia and the Pursuit of a Peptidergic Transmitter

This account deals with studies of slow synaptic potentials, a new peptidergic transmitter, and integrative mechanisms at synapses in vertebrate autonomic ganglia.

In neurones of the cardiac parasympathetic ganglia of the mudpuppy (Necturus maculosus) both rapid excitatory and slow inhibitory synaptic potentials interact. The same transmitter, acetylcholine (ACh), causes in individual neurones a fast e.p.s.p. lasting up to 50 ms and a slow i.p.s.p. of about 2 s. The sequence of processes leading to these two synaptic potentials differs in important respects. Molecules of ACh released by terminals of the vagus combine with nicotinic receptors and within a fraction of 1 ms initiate the rapid e.p.s.p. which, as a rule, leads to a conducted impulse in ganglion cells. The e.p.s.p. resembles in its ionic mechanisms the rapid excitatory synaptic events seen at most neuromuscular and neuronal synapses. ACh also combines with muscarinic receptors whose activation is followed by an increased flow of K+ ions and the generation of a slow i.p.s.p. There occurs, however, an apparent delay of over 100 ms between the time ACh reaches the muscarinic receptors and the detectable activation of the inhibitory conductance. During the delay the nicotinic e.p.s.p. has declined and ACh has disappeared from the synaptic cleft. It is suggested that at least three distinct processes are involved in the activation of the inhibitory conductances.

The second part of this paper describes synaptic events in sympathetic ganglia of the frog where release of ACh initiates three different synaptic potentials: (i) a standard fast nicotinic e.p.s.p. (about 30-50 ms duration); (ii) a slow muscarinic e.p.s.p. (30–60 s); (iii) a slow i.p.s.p. (about 2 s). The fourth synaptic signal, the ‘late slow e.p.s.p.’, lasts 5–10 min and is not caused by ACh.

We have evidence that a peptide, resembling luteinizing hormone releasing hormone (LHRH), is secreted by specific axons within ganglia where it initiates the late slow e.p.s.p.s. The evidence for such a peptidergic transmitter is as follows: (1) In nerves whose stimulation leads to the late slow e.p.s.p.s one detects by radioimmunoassay a peptide with a molecular weight of about 1000 daltons, resembling LHRH. (2) The peptide is released in isotonic KCl if Ca2+ is present in the high K+ solution. (3) Five days after cutting the appropriate presynaptic nerves, about 95% of the peptide disappears from the ganglia. At the same time the content of peptide central to the cut is increased, suggesting that it is concentrated in axons and transported to the periphery from the spinal cord. (4) Application of synthetic LHRH mimics the action of the nerve-released transmitter in a specific manner. Both substances cause similar changes in the postsynaptic membrane conductance and in the excitability of neurones, and the depolarizing effect of both agents changes in parallel when neurones are hyperpolarized. (5) An analogue of LHRH which in mammals blocks the release of gonadotropins also blocks the depolarizing effect of nerve-released transmitter and of applied LHRH in ganglion cells. Similar parallel actions occur after the application of other analogues of LHRH, some of which are more potent agonists, and others which are not effective. It is suggested that the natural transmitter and LHRH and its analogues act on the same receptors.

The role of slow synaptic potentials and the way in which they influence the effectiveness of cholinergic stimulation are discussed. Since the various synaptic potentials interact in individual cells, these neurones are suitable for a study of integrative mechanisms.

The action of cAMP and catecholamines in mammalian sympathetic ganglia

Electrophysiological approaches using intracellular microelectrode techniques have failed to critically test the hypothesis that cyclic AMP (cAMP) mediates the slow inhibitory postsynpatic potential (IPSP). The slow IPSP is not readily elicited, and the resting membrane potential is relatively insensitive to application of catecholamines and adenine nucleotides. However, comprehensive studies of voltage-dependent events in postganglionic neurons reveal three Ca2+-dependent potentials that are quite sensitive to catecholamines and adenine nucleotides. The hyperpolarizing afterpotential, the action potential shoulder, and the Ca2+ spike are all inhibited by alpha-adrenergic agonists, adenosine, and cAMP. We have proposed that simulation of alpha-adrenergic and adenosine receptors on the post-synaptic membrane results in antagonism of an inward Ca2+ current. Further experimentation is necessary to determine if cAMO acts as a second messenger or only by activating an adenosine receptor. Preliminary studies suggest that catecholamines and adenine nucleotides have similar and potent actions on the terminals of preganglionic axons. Here, inhibition of Ca2+ influx results in reduced acetylcholine release but facilitates high-frequency cholinergic transmission. More quantitative biophysical and pharmacological studies are required to better characterize the synaptic mechanisms in sympathetic ganglia.

[Structuro-functional organization of the vegetative (autonomic) nervous system]

On the basis of a number of structural and functional indices, application of pharmacological analysis as well as recording of neuronal activity, the autonomic nervous system is subdivided into the sympathetic, parasympathetic and metasympathetic parts. The metasympathetic system includes the complex of microganglia situated in the walls of vosceral organs and having marked motility activity (the heart, ureters, intestine, stomach). According to the localization, separate areas of this system can be defined by its site (for example, the cardiometasympathetic area in the heart). The metasympathetic system attains the features of true autonomy. Its cells have no direct connection with the high centers: this connection is established through mono- and polysynaptic sensory and afferent units of sympathetic and parasympathetic nature. The system has a definite set of functional elements including sensory ones (mechano-, chemo- and thermosensitive those), oscillators, interneurons, tonic neurons. Neurons of the metasympathetic system are incorporated through interganglionic connections into the common functional network of the organ. A typical excitatory pattern suggests the presence of a temorary connection in the work of at least two neurons according to the "driver--follower" type. In addition to excitatory patterns there are also patterns showing inhibitory interactions. Besides well known systems of mediation including cholinergic and adrenergic ones, the metasympathetic system has its peculiar purinergic transmission.

[Effects of reserpine on the granule-containing cells in the paracervical ganglion (Frankenhäuser) in mice: electron microscopic observations (author's transl)]

Effect of reserpine on granule-containing cells in the paracervical ganglion was electron microscopically studied. Adult mice were injected intraperitoneally with 3.5 mg of reserpine per kg of body weight daily for three days, and the fine structure of the granule-containing cells was observed by electron microscopy 24 hours after the last injection. In normal mice, as reported in a previous paper, the granule-contaning cells in the ganglion are morphologically classified into three types. Type I cells contain granular vesicles, which, varying in size and shape, 80 to 400 nm in diameter, are distributed through the cytoplasm. Type II cells have relatively small granular vesicles, 80 to 150 nm in diameter, which are distributed throughout the cytoplasm. Type III cells have small granular vesicles, 80 to 150 nm in diameter, in the peripheral zone of the cytoplasm. The proportions of type I, II, and III cells are 82%, 11%, 7%, respectively. After injections of reserpine, the proportions of type I, II, and III cells are 16%, 50%, and 33%, respectively. The findings were discussed in relation to the functional significance of granule-containing cells in the paracervical ganglion.

6-Hydroxydopamine potentiates acute herpes simplex virus infection of the superior cervical ganglion in mice

Treatment of mice with 6-hydroxydopamine increased herpes simplex virus replication in the superior cervical ganglion while it decreased the subsequent prevalence of latent infection. Preganglionic neurectomy failed to block this effect. These observations suggest that intrinsic neural events modify the outcome of viral infections of the nervous system.