Periodic components in integral spontaneous activity of sympathetic neurons

In experiments on rabbits anesthetized with urethane, we made multichannel coherent recordings of spontaneous activity and evoked activity of preganglionic sympathetic fibers in peripheral nerves of a leg and unmyelinated preganglionic fibers of the cervical sympathetic nerve trunk (CSNT). The results of a spectral analysis of the activity recorded and a correlational analysis of the activity and changes in arterial pressure allow us to conclude that preganglionic unmyelinated fibers of the CSNT are primarily vasoconstrictive and are under stronger baroreceptor control than vasoconstrictive fibers going to the skin and limb muscles. This is possibly due to differences in the functions of the innvervated organs. The latent period of the change in arterial pressure evoked by a change in the activity of vasoconstrictor fibers equals 4–10 sec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 266–273, May–June, 1991.     

Tonic sympathetic activity in the rabbit sciatic nerve

Tonic activity of sympathetic nerve fibers of the tibial and peroneal nerves was investigated in rabbits anesthetized with urethane by the multichannel coherent recording technique. Activity of stochastic character was shown to predominate in the tonic activity of these fibers. A component of activity with the frequency of the heart beat also is frequently observed, but the power of this component is never more than half the total power of activity. Activity with a frequency of 10 Hz, observed by other workers, and also modulation of tonic activity in the rhythm of respiration were not recorded in these experiments. Slow changes in the power of activity from zero to a level several times above average were observed when the blood pressure was stable.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 351–358, May–June, 1985.     

Tonic impulsation in preganglionic and postganglionic sympathetic fibers of mammals

A study of the tonic electrical activity of nerves containing preganglionic and postganglionic fibers in the superior cervical and stellate sympathetic ganglia of cats and rabbits has shown that this activity consists of groups of spikes synchronous with the pulse or respiration, and occurs on a background of irregular low-amplitude impulses. The frequency of spikes is higher (250/sec) in nerves containing preganglionic fibers than in those containing postganglionic fibers (100/sec). Groups of spikes in a nerve containing preganglionic fibers correspond in some preparations to groups of spikes of lower frequency in a nerve containing postganglionic fibers of the same ganglion; in other preparations, this correspondence was lacking, apparently due to the absence of synaptic contacts between those groups of pre- and postganglionic neurons whose activity was recorded. Neurons send axons to different nerves (cardiac and vertebral) of the stellate ganglion discharged synchronously in some preparations, and asynchronously in others. Where synchronization was observed, the neurons discharged in rhythm with cardiac contractions.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 303–308, November–December, 1969.     

Evidence for GABAergic fibers entering the superior cervical ganglion of rat from the preganglionic nerve trunk

The origin of gamma-aminobutyric acid immunoreactive (GABA-IR) nerve fibers present in the superior cervical ganglion (SCG) of rat was investigated. With immunocytochemical techniques many nerve fibers showed GABA-like positivity in the cervical sympathetic trunk, whereas similar staining could not be revealed in the internal carotid nerve or in the external carotid nerve. Ligation of the cervical sympathetic trunk for 24 h resulted a dramatic reduction in the staining density in the ganglion and in the cervical sympathetic trunk distal to the ligature. After transection of the preganglionic nerve fibers for eleven days or more, very few fibers staining for GABA were seen in the ganglion. The immunohistochemical results suggest that a major source of GABA within the SCG is a population of GABAergic axons entering from the preganglionic trunk.     

Evidence for GABAergic fibers entering the superior cervical ganglion of rat from the preganglionic nerve trunk

Summary The origin of gamma-aminobutyric acid immunoreactive (GABA-IR) nerve fibers present in the superior cervical ganglion (SCG) of rat was investigated. With immunocytochemical techniques many nerve fibers showed GABA-like positivity in the cervical sympathetic trunk, whereas similar staining could not be revealed in the internal carotid nerve or in the external carotid nerve. Ligation of the cervical sympathetic trunk for 24 h resulted a dramatic reduction in the staining density in the ganglion and in the cervical sympathetic trunk distal to the ligature. After transection of the preganglionic nerve fibers for eleven days or more, very few fibers staining for GABA were seen in the ganglion. The immunohistochemical results suggest that a major source of GABA within the SCG is a population of GABAergic axons entering from the preganglionic trunk.     

Effect of cervical sympathetic trunk transection on renal sympathetic nerve activity in rats

Stellate ganglion blockade (SGB) with a local anesthetic increases muscle sympathetic nerve activity in the tibial nerve in humans. However, whether this sympathetic excitation in the tibial nerve is due to a sympathetic blockade in the neck itself, or due to infiltration of a local anesthetic to adjacent nerves including the vagus nerve remains unknown. To rule out one mechanism, we examined the effects of cervical sympathetic trunk transection on renal sympathetic nerve activity (RSNA) in anesthetized rats. Seven rats were anesthetized with intraperitoneal urethane. RSNA together with arterial blood pressure and heart rate were recorded for 15 min before and 30 min after left cervical sympathetic trunk transection. The baroreceptor unloading RSNA obtained by decreasing arterial blood pressure with administration of sodium nitroprusside was also measured. Left cervical sympathetic trunk transection did not have any significant effects on RSNA, baroreceptor unloading RSNA, arterial blood pressure, and heart rate. These data suggest that there was no compensatory increase in RSNA when cervical sympathetic trunk was transected and that the increase in sympathetic nerve activity in the tibial nerve during SGB in humans may result from infiltration of a local anesthetic to adjacent nerves rather than a sympathetic blockade in the neck itself.     

Study of tonic and evoked electrical activity in efferent fibers of the sympathetic nerve in white rats

In anaesthetised Wistar rats, electrical sympathetic activity and a somatosympathetic reflex in the cervical sympathetic trunk elicited by a single electrical shock to forelimb or hindlimb afferent nerves, were recorded. The spontaneous activity was shown to conform with the pulse and respiratory waves of arterial pressure. Somatosympathetic reflex consists of early and late discharges evoked by somatic myelinated afferent fibres stimulation, and C-response elicited by stimulation of unmyelinated afferent fibres in spinal nerves.     

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.     

Electrical activity of the sympathetic ganglia during the depressor reflex

Tonic activity of neurons of the superior cervical sympathetic ganglion was recorded by the "sucrose gap" method and in the 4th and 5th lumbar sympathetic ganglia with the aid of focal nonpolarizing electrodes in acute experiments on anesthetized cats and rabbits. The preganglionic fibers of the ganglia were left intact. Stimulation of the depressor nerve not only sharply inhibited the tonic activity of the ganglia but also led to the appearance of electropositive potentials of 0.7 ± 0.2 mV in the superior cervical ganglion and 20–250 µV in the lumbar ganglia. The amplitude of this potential was unchanged by atropine (1 · 10^–6M). A similar effect occured without stimulation of the depressor nerve, after division of the preganglionic fibers or blocking of their conduction; it is attributed to the cessation of preganglionic tonic impulses which induce not only spikes, but also many EPSPs in neurons of the ganglion. Their frequency in the lumbar ganglia was 4/sec. Summation of these EPSPs leads to constant electronegativity of the ganglion surface relative to the postganglionic fibers, and its disappearance is recorded as a positive potential. Stimulation of the depressor nerve thus does not induce IPSPs in the ganglion; consequently, the inhibition of synaptic activity observed under these circumstances is located in the CNS and not in the ganglion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 6, No. 5, pp. 519–524, September–October, 1974.     

Electrophysiological investigation of pathways in the middle cervical sympathetic ganglion of the turtle

Single unit responses in the middle cervical sympathetic ganglion ofEmys orbicularis to stimulation of other nerves and changes in these responses during the action of sympathetic blocking agents on the ganglion were investigated. The results showed that some fibers of the cervical sympathetic trunk of the turtle are interrupted in this ganglion. Postganglionic fibers pass out of the ganglion and enter the lateral branch and the sympathetic trunk. Other fibers pass through the ganglion without interruption and, together with postganglionic fibers, leave the ganglion in the cervical sympathetic trunk in a cranial direction. The velocity of conduction of excitation along the preganglionic fibers is between 4–3 and 2–1.5 m/sec and along the postganglionic fibers between 4–2.6 and 0.7–0.5 m/sec (fibers of types B₂ and C). Synaptic delay in the fast-conducting fibers averages 6.6 msec. Preganglionic fast-conducting fibers form synaptic contacts on neurons with type B₂ axons, while preganglionic slow-conducting fibers form contacts on neurons with type C axons. Terminals of two preganglionic fibers differing very slightly in their threshold of excitability, and probably constituting the same group, converge on some neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 83–89, January–February, 1972.     

Changes in surviving nerve fibers associated with submucosal arteries following extrinsic denervation of the small intestine

Summary The neuropeptide content of nerve fibers associated with submucosal arteries in the small intestine of guinea pigs was studied in whole-mount preparations using immunohistochemical methods. Tissues were obtained from normal animals or animals in which the small intestine had been extrinsically denervated. In normal animals, submucosal arteries are innervated by extrinsic sensory nerve fibers which contain both substance P and calcitonin gene-related peptide, and by sympathetic noradrenergic nerve fibers. In preparations obtained from animals 5–9 days after denervation, nerve fibers which contained substance P without detectable calcitonin gene-related peptide were associated with a few submucosal arteries. Nerve fibers which contained vasoactive intestinal peptide were also associated with some arteries. By 42–48 days after extrinsic denervation, substance P-containing fibers (without calcitonin gene-related peptide) and vasoactive intestinal peptide-containing fibers were associated with nearly every blood vessel. The extrinsic sympathetic nerve fibers did not regenerate during the course of this study. The nerve fibers associated with submucosal arteries in denervated tissues were not sensitive to capsaicin treatment.The alteration in the innervation of submucosal arterioles that follows extrinsic denervation of the gut may reflect either an increase in the neuropeptide content of the fibers, synthesis of a new peptide, or an increase in the number of fibers as a result of axonal sprouting.     

Chronic experimental study of natural activity of the dog splanchnic nerve by the pulsed coherent component separation method

Natural electrical activity in the left greater splanchnic nerve during feeding was studied in chronic experiments on dogs. The method of separation of coherent components in pulsed form was used to analyze the discharges: Recording from the nerve was carried out at two points; activity was delayed by the time for its conduction along the nerve between the channels, in the channel which received it first, and it was then led from both channels to the coincidence unit. Spontaneous afferent impulsation was shown to spread among a group of nerve fibers with conduction velocities of between 3.7 and 20 m/sec, and with a mean velocity for the maximum of activity of 9.2±1.0 m/sec. Efferent spontaneous activity was not detected. During feeding with meat, besides spontaneous activity, activity of a group of afferent fibers with conduction velocities within the range 3.7–9.2 m/sec also was found (the mean velocity for the maximum of activity was 5.8±0.7 m/sec), and also activity of a group of efferent fibers with conduction velocities within the range 2.5–9.8 m/sec (mean value for maximum 3.5±0.5 m/sec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 636–642, November–December, 1981.     

Paradoxical Cardiac Rhythm in Rat Pups as a Possible Analog of the Sick Sinus Syndrome

Experiments with simultaneous recordings of ECG, electrogram of myocardial fibers of the right ventricle and neurogram of the right branch of vagus or sympathetic nerves were carried out on 3–18-day old rat pups. The electric activity recordings were performed under both in vivo and in situ conditions at unilateral or bilateral pneumothorax. It is established that the change in the cholinergic system activation level produced prior to pneumothorax decelerates the rhythm of cardiac contractions (CC) and induces periods of more frequent CC. After pneumothorax, this syndrome becomes more pronounced. The periods of alternation of the slow and fast rhythms may last for up to 1–2 min. The development of the pathological process leads to development of the sino-auricular and atrio-ventricular blocks. There appears a pattern of CC changes and complexes of the ventricular electric potentials that occur in decasecond and then in minute rhythms and are separated by periods of total asystole or preserved potentials of atrial excitation. When the electrograms of myocardium were recorded in rat pups under conditions of bilateral pneumothorax without any pharmacological intervention, it was possible to see a distortion of the sinus rhythm of CC developing for 2–2.5 h after respiration arrest and similar to the above-described distortion. The appearance and development of the phenomenon of the atypical cardiac rhythm is not directly related to the firing patterns of vagus and sympathetic nerves. At the same time, a correlation is clearly seen between the amplitude–frequency modulation of CC and discharges of vagus. A contraction of groups of respiratory muscles lasts for up to 30 min after pneumothorax, with occasional discharges seen in neurogram even after the complete immobilization of the animal. The development of the pathological process reveals a certain similarity with the phenomenon described in literature as the sinus node syndrome (tachy–bradycardia syndrome, TBS). Based on analysis of the cardiac rhythm transformation, it is suggested that the clinical TBS is a consequence of recapitulation, i.e., a successive release of ancient rhythms of excitation due to an impair of regulatory mechanisms.     

Conduction Properties Distinguish Unmyelinated Sympathetic Efferent Fibers and Unmyelinated Primary Afferent Fibers in the Monkey

Background

Different classes of unmyelinated nerve fibers appear to exhibit distinct conductive properties. We sought a criterion based on conduction properties for distinguishing sympathetic efferents and unmyelinated, primary afferents in peripheral nerves.

Methodology/Principal Findings

In anesthetized monkey, centrifugal or centripetal recordings were made from single unmyelinated nerve fibers in the peroneal or sural nerve, and electrical stimuli were applied to either the sciatic nerve or the cutaneous nerve endings, respectively. In centrifugal recordings, electrical stimulation at the sympathetic chain and dorsal root was used to determine the fiber''s origin. In centrifugal recordings, sympathetic fibers exhibited absolute speeding of conduction to a single pair of electrical stimuli separated by 50 ms; the second action potential was conducted faster (0.61 0.16%) than the first unconditioned action potential. This was never observed in primary afferents. Following 2 Hz stimulation (3 min), activity-dependent slowing of conduction in the sympathetics (8.6 0.5%) was greater than in one afferent group (6.7 0.5%) but substantially less than in a second afferent group (29.4 1.9%). In centripetal recordings, most mechanically-insensitive fibers also exhibited absolute speeding to twin pulse stimulation. The subset that did not show this absolute speeding was responsive to chemical stimuli (histamine, capsaicin) and likely consists of mechanically-insensitive afferents. During repetitive twin pulse stimulation, mechanosensitive afferents developed speeding, and speeding in sympathetic fibers increased.

Conclusions/Significance

The presence of absolute speeding provides a criterion by which sympathetic efferents can be differentiated from primary afferents. The differences in conduction properties between sympathetics and afferents likely reflect differential expression of voltage-sensitive ion channels.     

Opposite effects of iv amiodarone on cardiovascular vagal and sympathetic efferent activities in rats

It is unknown whether amiodarone exerts a direct central action on the cardiovascular autonomic nervous system. This study was designed to evaluate the effects of acute amiodarone administration on vagal and sympathetic efferent nerve discharges. Experiments were carried out in 25 decerebrate unanesthetized rats. In one group, vagal activity was recorded from preganglionic fibers isolated from the cervical vagus nerve. In another group, sympathetic recordings were obtained from fibers isolated from the cervical sympathetic trunk in intact conditions or after barodenervation. Recordings were performed before and for 60 min after amiodarone (50 mg/kg iv) administration. In all groups, amiodarone induced bradycardia and hypotension. Vagal activity increased immediately, reaching a significant difference after 20 min (260 +/- 131% from 16.4 +/- 3.3 spikes/s) and was unmodified by the barodenervation. At difference, sympathetic activity after an initial and short-lasting increase (150 +/- 83% from 24.8 +/- 5.7 spikes/s) began to decrease significantly after 20 min (36 +/- 17%) throughout the experiment. The initial increase in sympathetic activity was not observed in barodenervated animals. These changes in vagal and sympathetic activity could play an important role in contributing to the antiarrhythmic action of amiodarone.     

Cold stress alters characteristics of sympathetic nerve discharge bursts.

Frequency-domain analyses were used to determine the effect of cold stress on the relationships between the discharge bursts of sympathetic nerve pairs, sympathetic and aortic depressor nerve pairs, and sympathetic and phrenic nerve pairs in chloralose-anesthetized, baroreceptor-innervated rats. Sympathetic nerve discharge (SND) was recorded from the renal, lumbar, splanchnic, and adrenal nerves during decreases in core body temperature from 38 to 30 degrees C. The following observations were made. 1) Hypothermia produced nonuniform changes in the level of activity in regionally selective sympathetic nerves. Specifically, cold stress increased lumbar and decreased renal SND but did not significantly change the level of activity in splanchnic and adrenal nerves. 2) The cardiac-related pattern of renal, lumbar, and splanchnic SND bursts was transformed to a low-frequency (0-2 Hz) pattern during cooling, despite the presence of pulse-synchronous activity in arterial baroreceptor afferents. 3) Peak coherence values relating the discharges between sympathetic nerve pairs decreased at the cardiac frequency but were unchanged at low frequencies (0-2 Hz), indicating that the sources of low-frequency SND bursts remain prominently coupled during progressive reductions in core body temperature. 4) Coherence of discharge bursts in phrenic and renal sympathetic nerve pairs in the 0- to 2-Hz frequency band increased during mild hypothermia (36 degrees C) but decreased during deep hypothermia (30 degrees C). We conclude that hypothermia profoundly alters the organization of neural circuits involved in regulation of sympathetic nerve outflow to selected regional circulations.     

Effects of surgical sympathectomy on laminar nerve endings in myenteric ganglia

Extirpation of the anterior regions of the sympathetic ganglionated chain (all cervical ganglia and the four subsequent thoracic ganglia) has been carried out in the cat. Histological study of the esophagus wall has shown intraganglionic laminar endings (IGLEs) to suffer an alteration which, in time, reverts to normality. Since it is not a Wallerian degeneration as such, we conclude, contrary to what has previously been assessed by some authors, that these nerve apparatuses are not dependent either on nerve cells located in sympathetic ganglia or on nerve fibers coursing through the sympathetic trunk. Speculations are made as to why IGLEs undergo a transitory alteration after experimental destruction of nerve structures to which they are not directly related.     

Conducting pathways of the rabbit lumbar sympathetic ganglia

Conducting pathways of ganglia from the lumbar portion (L₃–L₅) of the sympathetic trunk in rabbits were studied by recording action potentials from nerves of the ganglia evoked by stimulation of other nerves of these ganglia, and by intracellular recording from single neurons. Besides the well-known system of descending preganglionic fibers, which enter the trunk through white rami communicantes and, as they pass through the ganglia, form synapses on ganglionic neurons, some preganglionic fibers were shown to enter the sympathetic chain through gray rami communicantes and to run in both ascending and descending directions, forming synaptic connections with neurons of the lumbar ganglia.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 247–254, March–April, 1984.     

Measurement of sympathetic nerve activity in the unanesthetized rat

A new system was developed in our laboratory to continuously monitor intra-arterial pressure, heart rate, and sympathetic nerve activity in unanesthetized rats. The animals were prepared 24 h before the start of the experiments. Sympathoneural traffic was measured at the level of splanchnic nerve. The amplitude of the spikes recorded at this level was utilized to express sympathetic nerve activity. The amplitude of the residual electroneurogram signal present 30 min after the rats were killed was 32 +/- 2 mV (mean +/- SE; n = 11). For analysis, these background values were subtracted from values determined in vivo. The nerve we studied contains postganglionic fibers, since electrical activity decreased in response to ganglionic blockade with pentolinium (1.25 mg/min iv for 4 min). The amplitude of spikes fell by 43 +/- 4% (n = 4). Sympathetic nerve activity was highly reproducible at a 24-h interval (104 +/- 26 vs. 111 +/- 27 mV for the amplitude of spikes; n = 11). Dose-response curves to the alpha 1-stimulant methoxamine and to bradykinin were established in four rats. The increase in blood pressure induced by methoxamine caused a dose-dependent fall in sympathetic nerve activity, whereas the blood pressure reduction resulting from bradykinin was associated with a dose-dependent activation of sympathetic drive. These data therefore indicate that it is possible with out system to accurately measure sympathetic nerve activity in the awake rat, together with intra-arterial pressure and heart rate.     

Distribution of myelinated and nonmyelinated nerve fibers of a cat cutaneous nerve in the spinal roots

The distribution of myelinated and nonmyelinated nerve fibers of the saphenous nerve of cats in the ventral and dorsal roots of the spinal cord was investigated by methods improving the signal—noise ratio in records of evoked responses from the nerve. The fibers of this nerve enter the spinal cord through roots of segments L_4–6. Nerve fibers with conduction velocities of between 80 and 0.38 m/sec were distributed in the dorsal roots of these segments. Four groups of nerve fibers with conduction velocities of 80–60, 40–30, 12.0–3.0, and 1.1–0.51 m/sec, possibly afferent in nature, were found in the ventral roots. The conditions of origin and detection of low-amplitude potentials in the roots of the spinal cord and the probable functional role of the nerve fibers in the ventral roots are discussed.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 647–654, November–December, 1975.