The origin of slow potentials on the tongue surface induced by frog glossopharyngeal efferent fiber stimulation

When the glossopharyngeal (GP) nerve of the frog was stimulated electrically, electropositive slow potentials were recorded from the tongue surface and depolarizing slow potentials from taste cells in the fungiform papillae. The amplitude of the slow potentials was stimulus strength- and the frequency-dependent. Generation of the slow potentials was not related to antidromic activity of myelinated afferent fibers in the GP nerve, but to orthodromic activity of autonomic post-ganglionic C fibers in the GP nerve. Intravenous injection of atropine abolished the positive and depolarizing slow potentials evoked by GP nerve stimulation, suggesting that the slow potentials were induced by the activity of parasympathetic post-ganglionic fibers. The amplitude and polarity of the slow potentials depended on the concentration of adapting NaCl solutions applied to the tongue surface. These results suggest that the slow potentials recorded from the tongue surface and taste cells are due to the liquid junction potential generated between saliva secreted from the lingual glands by GP nerve stimulation and the adapting solution on the tongue surface.     

Electrophysiologic, morphometric and histocytochemical characteristics of frog sartorius muscle fibers]

Three groups of muscle fibers (dark, light, and intermediate) were revealed in the fibers of the frog sartorius muscle in examination of the succinate dehydrogenase (SDH) activity. There was revealed a reverse relationship between the diameter of the muscle fibers an the SDH activity in them. The external surface of sartorius muscle is chiefly represented by dark muscle fibers, whereas the internal one--by light ones. Microelectrode study demonstrated that the fibers of the external surface were characterized, in comparison with those of the internal one, by lesser action potentials, prolonged trace negative potential, low quant composition of the end plate potentials, high amplitude and low frequency of the end plate miniature potentials. Analysis of the data obtained demonstrated definite interrelationship between the histochemical profile of the muscle fibers of the frog sartorius muscle and their electrophysiological characteristics.     

Morphologic and histochemical characteristics of frog skeletal muscle following application of colchicine to a motor nerve]

Experiments with application of colchicine to the muscle motor nerve carried out; this was done for the purpose of disturbance of rapid axoplasmic transport. A reduction of the areas of transverse sections of the muscle fibers, an increase in the number of fibers with a low succinic dehydrogenase (SDH) activity a greater homogeneity of the muscle fibers by the degree of optic density in staining for detection of the SDH activity was noted. Analogous changes were revealed under conditions of section of the motor nerve. However, denervation was accompanied by the block of conductivity and by degenerative changes in the nerve endings. As to the preparations treated with colchicine, transmission of excitation in the nerve and through the synapse was retained and was recorded by the end plate miniature potentials, end plate potentials and the action potentials of the muscle fibers. A conclusion was drawn that rapid axoplasmic transport brought substances maintaining differentiated state of the muscle fibers.     

Penis-retractor muscle of Aplysia: excitatory motor neurons

Cobalt axonal iontophoresis and intracellular recordings were used to identify a cluster of several motor neurons innervating the penis-retractor muscle of Aplysia. Intracellularly recorded motor neuron action potentials elicited direct, one-for-one, constant latency excitatory junctional potentials (ejps) in individual muscle fibers. The axons of motor neurons could be recorded extracellularly in the penis-retractor nerve and stimulation of the nerve backfired the motor neurons. Perfusion of the ganglion, the muscle, or both with solutions of either increased Mg++/decreased Ca++ or increased Ca++ sea water indicated that the presumed motor neuron impaled was not a sensory cell and that interneurons were not intercalated in the pathway. Innervation of muscle fibers was found to be functionally polyneuronal and diffuse. The ejps were found to undergo marked facilitation with repetitive motor-neuron stimulation. The motor neurons were isolated in a distinct cluster in the right pedal ganglion. Their electrical activity was characterized by spontaneous irregular action potentials and a moderate input of postsynaptic potentials.     

Changes in the electrical activity of myocardial fibers following heart transplantation to under the skin of the ear in mice]

Intracellular rest and action potentials (RP and AP, respectively) of mouse heart graft were reduced on the 3rd--4th days after the transplantation as compared with the intracellular potentials of newborn mice. Beginning from the 5th--6th days there occurred a gradual increase of the intracellular potentials of amplitude. The firt 7--8 days, both in the case of allograft and heterograft, the changes in the intracellular activity were the same. Then in heterograft there occurred a repeated reduction of the RP and AP amplitude of the graft myocardial fibers, this apparently being connected with the development of the rejection reaction. In the allograft samples the amplitude of the intracellular potentials approached by the end of the first month after the graft with RP and AP values of the recipient's myocardial fibers.     

Neuromuscular transmission of pectoral fin muscles of the goldfish Carassius auratus

The electrical properties and neuromuscular transmission of white and red fibers of pectoral fin muscles of the goldfish Carassius auratus were studied using an intracellular recording technique. The pectoral fin muscles consist mainly of white and red fibers. Almost all of white fibers elicited action potentials with overshoot by direct stimulation, but graded responses appeared in the red fibers. However, overshooting action potentials were often recorded from the red fibers in saline containing 20 microM tetraethylammonium (TEA) chloride. In response to single nerve stimulations, excitatory (EJPs) and inhibitory junction potentials (IJPs) were obtained from both white and red fibers in common. Both EJPs and IJPs were blocked completely or partially by d-tubocurarine, a nicotinic acetylcholine (ACh) receptor antagonist. Nicotine, a nicotinic ACh receptor agonist, and oxotremorine, a muscarinic ACh receptor agonist, depolarized both fiber types. The results suggest that white and red fibers receive double innervation from excitatory and inhibitory nerves, and have nicotinic and muscarinic ACh receptors. In the resting muscle, miniature excitatory junction potentials were generated spontaneously in both white and red fibers. Occasionally, miniature inhibitory junction potentials were recorded from the red fibers. The results indicate that the release of both excitatory and inhibitory transmitters is quantal in nature.     

Mechanism of the Schultz-Dale Reaction in the Denervated Diaphragmatic Muscle of the Guinea Pig

The mechanism of the contractions elicited by specific antigens in immunologically sensitized muscle tissue (Schultz-Dale responses) has been investigated on single fibers of denervated guinea pig hemidiaphragms. This preparation can be either actively or passively allergized, showing Schultz-Dale responses similar to those of visceral muscle. Specific antigens were applied with an electrically operated microtap to discrete areas of the cell surface while recording the electrical activity with intracellular microelectrodes. In this manner, a depolarizing action of the antigens on the muscle membrane was demonstrated. Brief applications of antigen gave rise to phasic potential changes (antigen potentials) similar to those elicited in the same fibers with acetylcholine-filled microtaps. However, antigen potentials occur only in denervated fibers sensitized to the specific antigen or closely related proteins; they are not seen in either innervated fibers of allergized animals or in denervated, nonallergized fibers. Repeated antigen application to the same area of the fiber causes a local irreversible desensitization. The antigen potentials are associated with a reduction in the resistance of the muscle membrane, similar to that caused by acetylcholine. It is concluded that besides causing the liberation of biogenic amines from the mast cells, antigens exert a direct action on the permeability of the muscle membrane; the molecules of antibody adsorbed to the cells appear to act as specific chemoreceptors for the antigen.     

Changes in the electrical activity of the rabbit proximal colon in vivo by stimulation of the vagus and splanchnic nerves]

1. Using extracellular electrodes placed on the serosa, we recorded the modifications of the electrical activity of the colonic muslce fibers caused by the stimulation of vagal and splanchnic nerve fibers. 2. Vagal stimulation produces two types of junction potentials: excitatory junction potentials (EJPs) and inhibitory junction potentials (IJPs). The IJPs are elicited by stimulation of vagal fibers which innervate intramural non-adrenergic inhibitory neurons. 3. The conduction velocity of the nerve impulse along the vagal pre-ganglionic fibers is 1.01 m/sec for excitatory fibers and 0.5. m/sec for inhibitory fibers. 4. Splanchnic fiber stimulation causes EJP disappearance, blocking transmission between preganglionic fibers and intramural excitatory neurons, and a decrease in IJP amplitude that most likely indicates a previous hyperpolarization of the smooth muscle. 5. IJP persistence during splanchnic stimulation proves that sympathetic inhibition does not modify the transmission of the vagal influx onto the non-adrenergic inhibitory neurons of the intramural plexuses. 6. Through a comparative study of proximal and distal colonic innervation, we are able to show that there is a similar organization of both regions, that is a double inhibitory innervation: an adrenergic one of a sympathetic origin, and a non adrenergic one of a parasympathetic origin.     

Visceral muscles and myogenic activity in the hindgut of the cockroach,Leucophaea maderae

Summary The hindgut of the Madeira cockroach contains an intricate network of longitudinal and circular muscles that are distinctive for each region. In the rectum, the longitudinal muscles are symmetrically arranged in 6 distinct bands, while the circular muscles appear as a uniform layer over the rectal pads. In the colon, the muscle fibers are arranged in an irregular lattice with the longitudinal fibers generally superimposed on the circular ones but with an evident weaving between the layers. In addition to these muscle layers, a delicate, superficial network of muscle-like fibers covers many portions of the colon and rectum.In spite of the bewilderingly complex motile activity of deganglionated hindguts, all activity could be classified under 4 basic types after cinematographic analysis: segmentation, compression, peristalsis, or reverse peristalsis or a combination thereof. Although much of the activity that occurred was seemingly random, there was an evident rhythmicity that spontaneously arose and ended in several types of motility during the course of observations. The defined modes of activity seemed to be completely myogenic in nature, as all 4 categories were readily observed in hindguts 30 min after treatment with tetrodotoxin (10^–6 g/ml). Each region of the hindgut seemed to have its own particular rhythm.Action potentials were recorded both intracellularly and extracellularly from all regions of the hindgut; amplitude usually ranged between 10 and 20 mV for intracellular recordings, and such spike potentials were often preceded by a slow depolarizing pre-potential. Generally, however, the depolarization was abrupt. Transmembrane potentials from the visceral muscle fibers were never truly at rest. Slow, continuous fluctuations (3–8 mV) were common. At times, plateau-type action potentials were recorded, but generally the repolarization contour was almost linear with time. Contractions were evoked by action potentials but not by the slow, rhythmic fluctuations in the membrane potential.No particular region or structure in the hindgut showed an exclusive pacemaker function. However, there was an evident gradient of increased excitability progressing in an caudal direction from the ileum.In a sodium-free saline, the amplitude of action potentials was remarkable enhanced from 5 to 10 min after the initial change. Even after a 20 min exposure, action potentials were still often present although their frequency and amplitude dropped. Tetrodotoxin (10^–6g/ml) had no. pronounced effect on frequency or amplitude of action potentials. However, spike potentials ceased within 1.5 min after exposure to a sodium and calcium-free saline. When such preparations were re-exposed to a sodium-free saline containing normal calcium, the action potentials reappeared, suggesting that calcium might be a current-carrying ion. Although action potentials in a calcium-free medium showed variability, we generally saw a marked reduction in amplitude of potentials within 5 min. We further observed that 2 mM manganous ion completely abolished action potentials within 2 min. Thus, it seems likely that sodium is not the sole current-carrying ion in cockroach hindgut muscle.The authors express their indebtedness to Ms. Susan Swann, Mr. Gerald Holt, Mr. David Owens, and Ms. Mary Strand for their competent technical assistance.     

Stimulating effect of focused ultrasound on auditory fibers of the acoustic nerve in the frog Rana temporaria

After mechanical destruction of the receptor apparatus, application of focused ultrasound (frequency 2.34 mHz) to the auditory fibers of the frog elicited the electrical activity in the auditory midbrain centers (torus semicircularis). Action potentials evoked by focused ultrasound were similar to those evoked by activation of the intact contralateral labyrinth. After introduction of horseradish peroxidase into the destroyed auditory capsule, fibers activated by ultrasound were detected. Therefore electrophysiological and histochemical experiments reveal stimulating effect of focused ultrasound on the auditory fibers of the VIIIth nerve.     

Differences in the Charge Distribution of Glycerol-Extracted Muscle Fibers in Rigor, Relaxation, and Contraction

Glycerol-extracted rabbit psoas muscle fibers were impaled with KCl-filled glass microelectrodes. For fibers at rest-length, the potentials were significantly more negative in solutions producing relaxation than in solutions producing either rigor or contraction; further the potentials in the latter two cases were not significantly different. For stretched fibers, with no overlap between thick and thin filaments, the potentials did not differ in the rigor, the relaxation, or the contraction solutions. The potentials measured from fibers in rigor did not vary significantly with the sarcomere length. For relaxed fibers, however, the potential magnitude decreased with increasing sarcomere length. The difference between the potentials measured for rigor and relaxed fibers exhibited a nonlinear relationship with sarcomere length. The potentials from calcium-insensitive fibers were less negative in both the rigor and the relaxation solutions than those from normal fibers. When calcium-insensitive fibers had been incubated in Hasselbach and Schneider's solution plus MgCl₂ or Guba-Straub's solution plus MgATP the potentials recorded upon impalement were similar in the rigor and the relaxation solution to those obtained from normal fibers in the relaxed state. It is concluded that the increase in the negative potential as the glycerinated fiber goes from rigor to relaxation may be due to an alteration in the conformation of the contractile proteins in the relaxed state.     

Physiological features of the wing muscle fibers of Locusta migratoria locusts

In bifunctional dorsoventral muscle M-120 of the locust Locusta migratoria migratorioides three groups of fibers have been found which differ with respect to their electrophysiological properties. The evoked fast potentials in the fibers of caudal portion differed from fast potentials observed in the fibers of rostral and intermediate portions of the muscle. In the fibers of the caudal and intermediate portions of muscle, not only fast, but other depolarization potentials were also recorded which differ in the amplitude and duration, as well as the inhibitory postsynaptic potentials. It was shown that fibers in these three parts of the muscle differ in their voltage-current properties. It is concluded that different types of potentials are due to peculiarities of innervation and to structural heterogeneity of muscle fibers.     

Analysis of postinspiratory activity of phrenic motoneurons with chemical and vagal reflexes

We examined the effects of chemical and reflex drives on the postinspiratory inspiratory activity (PIIA) of phrenic motoneurons using a single-fiber technique. Action potentials from "single" fibers were recorded from the C5 phrenic root together with contralateral mass phrenic activity (also from C5) in anesthetized, paralyzed, and artificially ventilated cats with intact vagus and carotid sinus nerves. Nerve fibers were classified as "early" or "late" based on their onset of discharge in relation to mass phrenic activity during hyperoxic ventilation. Only the early fibers displayed PIIA but not the late fibers, even when their activity began earlier in inspiration with increased chemical drives. Isocapnic hypoxia increased, whereas hyperoxic hypercapnia shortened the duration of PIIA. Pulmonary stretch and "irritant" receptors inhibited PIIA. Hypercapnia and stimulation of peripheral chemoreceptors by lobeline excited both early and late units to the same extent, but hypoxic ventilation had a less marked excitatory effect on late fiber activity. Irritant receptor activation increased the activity of early more than late fibers. Hyperoxic hyperventilation eliminated late phrenic fiber activity, whereas early fibers became tonically active. Bilateral vagotomy abolished this sustained discharge in eight of nine early units, suggesting the importance of vagal afferents in producing tonic firing during hyperventilation. These results suggest that early and late phrenic fibers have different responses to chemical stimuli and to vagally mediated reflexes; late units do not discharge in postinspiratory period, whereas early fibers do; the PIIA is not affected in the same way by various chemical and vagal inputs; and early units that exhibit PIIA display tonic activity with hyperoxic hypocapnia.     

Further Study of the Electrical and Mechanical Responses of Slow Fibers in Cat Extraocular Muscles

Electrical and mechanical responses have been obtained in situ and in vitro from the superior oblique muscle stimulated by single and repetitive electrical pulses, applied to the trochlear nerve. Two different types of muscle fibers are described, the twitch and the slow. The slow type is characterized electrically by the presence of junctional potentials, which have reversal potentials between -10 and -20 mv, and do not show propagated responses or spikes, during nerve stimulation. When the slow muscle fibers are repetitively stimulated in situ, a prolonged contraction is maintained during stimulation. At the time, the recorded electrical activity is produced locally, at the level of the neuromuscular junctions of the slow fibers. These results indicate that the contractile mechanism of the slow muscle fibers is activated locally and segmentally.     

Synaptic transmission in thoracic autonomic ganglia of the dog

Afferent stimulation of one canine thoracic cardiopulmonary nerve can generate compound action potentials in another ipsilateral cardiopulmonary nerve. These compound action potentials persist after acute decentralization of the middle cervical ganglion, indicating that they result from neural activity in the middle cervical ganglion and thoracic nerves. Changing the frequency of stimulation can alter the compound action potentials, suggesting that temporal facilitation or inhibition occurs in this middle cervical ganglion preparation. The compound action potentials can be modified by stimulation of sympathetic preganglionic fibers and by hexamethonium, atropine, phentolamine, propranolol, and (or) manganese. It thus appears that afferent cardiopulmonary nerves can activate efferent cardiopulmonary nerves via synaptic mechanisms in the stellate and middle cervical ganglia. It also appears that these mechanisms involve adrenergic and cholinergic receptors and are influenced by preganglionic sympathetic fibers arising from the cord.     

Click-evoked responses from the exposed intracranial portion of the eight nerve during vestibular nerve section: bipolar and monopolar recordings

We compare the click-evoked compound action potentials from the exposed intracranial portion of the eight nerve using bipolar and monopolar recording electrodes in patients undergoing vestibular nerve section. It is assumed that a bipolar recording electrode will only record propagated neural activity in the auditory nerve, whereas a monopolar recording electrode may in addition record electrical activity that is conducted passively to the recording site. The results of the present study confirm that the earliest detectable propagated neural activity in the intracranial portion of the auditory nerve occurs with a latency that is close to that of peak II of the brain-stem auditory evoked potentials, and the results also confirm that the late components in the click-evoked compound action potentials that have been demonstrated previously using the monopolar recording technique represent propagated neural activity in the auditory nerve. The results also indicate that the responses that are recorded by a bipolar recording electrode, when the small tips of which are placed on the eight nerve when it is relatively dry, represent only small populations of nerve fibers. Even when an attempt is made to align the two tips of a bipolar electrode with the course of the auditory nerve, this type of electrode may record from different populations of nerve fibers.     

Electrophysiological investigation of the conduction of excitation in the pterygopalatine ganglion of the cat

When responses in some nerves of the pterygopalatine ganglion of the cat in situ to stimulation of its other nerves were recorded it was found that most fibers passing through the ganglion are continuous sympathetic postganglionic fibers (at least three groups). Most of the parasympathetic preganglionic fibers forming synapses on neurons of the ganglion constitute a group of fibers with the same threshold of excitation. Intracellular recording from single neurons of the pterygopalatine ganglion showed that stimulation of the Vidian nerve evokes orthodromic spike potentials in some neurons of the ganglion with a short latent period, and in others with a long latent period (2.5–6.0 and 10–44 msec, respectively). Evidently only fast-conducting fibers terminate synaptically on most neurons of the ganglion and only slow-conducting fibers on some of them. Recording from intact nerves of the pterygopalatine ganglion revealed no tonic activity in them. Microelectrode recording from single neurons of the ganglion showed that either the frequency of generation of spike potentials is relatively low (1–3/sec) or such potentials are absent altogether.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 514–520, September–October, 1976.     

A new method for excitation-contraction uncoupling in frog skeletal muscle

The mechanical activity of frog sartorius muscle fibers can be uncoupled from the electrical activity of their surface membranes by immersing the preparation in Ringer solution containing either 1.5 or 2.0 M of formamide for 15--20 min. This uncoupling is not reversed when the muscle is transferred to normal frog Ringer solution. Formamide does not affect the electrical activity of the sciatic nerve branch, and both endplate potentials and miniature endplate potentials may be recorded from the uncoupled muscles. Prolonged exposure to formamide, beyond the time needed to paralyze, causes neuromuscular block.     

Characteristics of postsynaptic potentials and ionic currents in synapses of fast and slow rat muscle fibers

Miniature end-plate currents and potentials (MEPPs and MEPCs, respectively) were recorded in fast and slow rat muscle fibers by extracellular focal recording and voltage clamp techniques. The rise time and the half-decay time of these potentials and currents were 1.3–1.4 times greater in slow fibers than in fast. A similar difference, but lesser in degree, also was observed after inhibition of acetylcholinesterase. Decline of the end-plate currents remained, generally speaking, exponential and its rate depended on the clamped voltage. The percentage distribution of fibers of different types by duration of MEPP and MEPC in fast and slow muscles correlated with the percentage distribution of fibers identified in these muscles on the basis of other parameters. Factors determining the time course of the responses (acetylcholinesterase activity, length of diffusion pathways, differences in passive electrical properties of the membrane), and their importance for synapses of different types, are discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 627–636, November–December, 1980.