Ultrastructure and functional characteristics of the optic nerve of Rana temporaria L. in the norm and during degeneration

Results of electron microscopy and electrophysiological studies of the frog optic nerve are presented. The nerve contains 96% unmyelinated (about 210,000) and 4% myelinated (8700–14,800) fibers. The peripheral zone of the nerve (20–30 µm) has relatively few myelinated fibers, whereas in other zones these fibers are distributed uniformly (counting area 300–400 µm²). The curve of the distribution of the diameters of myelinated fibers has a number of peaks: a main peak at 1 µm and additional peaks at 0.6 and 1.6 µm (the latter is more prominent). Individual fibers have a diameter of 0.4–3.9 µm. The diameter of the unmyelinated fibers are 0.1–0.4 µm; 64% of these fibers have a diameter of 0.2 µm. Most fibers at a temperature of 18–20° conduct at 0.3–0.4 m/sec and a few (myelinated with a diameter of 1.0–1.6 µm) at 3 and 6 m/sec. After enucleation the myelinated fibers degenerate at first and are phagocytized by neuroglia; the ultrastructure and function of the unmyelinated fibers at 18–20° remain unchanged up to 100 days postoperation.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 627–635, November–December, 1970.     

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.     

Effect of preliminary mechanical and antidromic influences on orthodromic activity in C fibers from mechanoreceptors of the cat skin

Analysis of afferent activity in unmyelinated fibers of a cutaneous nerve was carried out by the colliding impulses method in cats. The effect of antidromic excitation of the nerve and mechanical stimulation of the receptors on subsequent orthodromic activity during stretching of the skin was investigated. Both these factors were shown to reduce subsequent orthodromic activity evoked by testing stimulation. The reduction in activity was greatest 10–15 sec after stimulation. The duration of the inhibitory effect was greater after mechanical than after antidromic stimulation. Combined mechanical stimulation and antidromic excitation resulted in a greater decrease of afferent activity and an increase in the time of its recovery. An increase in the frequency of antidromic excitation potentiated the inhibitory effect of preliminary stimulation on orthodromic activity in C fibers.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 307–312, May–June, 1977.     

Morpho-functional characteristics of the optic nerve of the steppe turtle Agrionemys horsfieldi]

The optic nerve of the tortoise Agrionemys horsfieldi contains about 400,000 fibers (90% unmyelinated and 10% myelinated ones). the diameter of unmyelinated fibers varies from 0.3 to 1.1 mu, mean value being equal to 0.5 mu; fibers with a diameter 0.4-0.7 comprise 77%. The diameter of myelinated fibers varies within 0.3-3.0 mu, average value being 0.5-0.8 nu; fibers with a diameter 0.5-0.9 mu amount to 62%. Electrogram of the optic nerve consists of two components which are equal in their amplitudes. These components presumably reflect summary firings of modal groups of unmyelinated and myelinated fibers. The velocity of propagation of excitation along the fibers producing the first component is equal to 1.3 m/sec, wheras that in fibers producing the second component - to 0.5 m/sec. The data obtained are compared with those related for the other tortoise - Emys orbicularis.     

Excitation of cat spinal cord dorsal column fibers during stimulation of different fiber groups of cutaneous and somatic nerves

The effects of electrically stimulating different groups of nerve fibers supplying the skin and muscle on evoked potentials in cat spinal cord dorsal columns were studied. Significant differences in the configuration of dorsal column potentials recorded in response to stimulation of these nerves were found. It was shown that cutaneous nerve unmyelinated fibres were connected to unmyelinated dorsal column fibers. In addition, excitation of cutaneous C-fibers lead to activation of dorsal column fibers with the maximum conduction velocity. The somatic nerve was only connected to myelinated dorsal column fibers, and excitation of its non-myelinated fibers did not cause other types of dorsal column fibers to be activated. It is suggested that the acceleration of cutaneous signal transmission in the dorsal column system may be brought about by the necessity for rapid warning of potentially harmful stimuli.Medical Institute, Russian Federation Ministry of Public Health, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 625–635, September–October, 1992.     

Activity of myelinated fibers under heat and burn influences on the skin

The dynamics of the activity of myelinated fibers of a cutaneous nerve under heat and burn influences on hair-covered skin was investigated in acute experiments on cats using the method of cross-correlation functions. Under heat influence on the skin the total activity of the nerve was reduced chiefly at the expense of the rapidly conducting myelinated fibers, whereas in the case of painful heating of the skin the A fibers were activated. The results obtained make it possible to solve the problem of the heat-information code from the standpoint of the flow "pattern" theory.S. M. Kirov Medical Institute, Ministry of Health of the Russian Federation, Nizhnii Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 567–577, September–October, 1992.     

Conduction velocities and fiber diameters in a cutaneous nerve of the pigeon

Summary The characteristics of fibers of a cutaneous nerve supplying the wing skin of the pigeon have been investigated with electrophysiological and electron microscopic techniques.Recordings of the compound action potential showed four distinct peaks with conduction velocities of about 30 m/s, 12 m/s, 4 m/s and 0.5 m/s.From electron micrographs both fiber diameters and thickness of myelin sheath were assessed and used as criteria for segregating various fiber populations. Altogether four groups could be discerned: large thickly myelinated fibers, small thickly myelinated fibers, small thinly myelinated fibers, and unmyelinated or C-fibers. The subdivision of the thickly myelinated fibers into two populations is evidenced mainly by corresponding peaks in the compound action potential. The thinly myelinated fibers with a mean diameter of 2 m contributed about 90% of all myelinated fibers in this nerve.When comparing fiber dimensions and conduction velocities of this avian nerve with those of mammalian cutaneous nerves, the lower CV's of avian nerve fibers can be explained by smaller diameters and thinner myelin sheaths.The results of this investigation are a prerequisite for latency considerations in central somatosensory pathways in birds.Abbreviations CAP compound action potential - CV conduction velocity - D fiber diameter - d axon diameter - g ratio d/D - m thickness of myelin sheath     

Functional and ultrastructural changes in the midbrain tectum of the frog after enucleation

In experiments on frogs immobilized with Diplacin at different times after unilateral enucleation, as degeneration of the optic fibers and their terminals developed, a successive disappearance of the components of evoked potential (EP) was observed; this indicates the direct dependence of the rate of degeneration on the diameters of the fibers. The nature of the ultrastructural changes also depends on the diameter of the cut axons: the terminals of all or some of the myelinated fibers of large diameter degenerated with the condensation of the endings and of all the cytoplasmatic organelles ("dark" type); the terminals of thin myelinated and unmyelinated fibers degenerated with a gradual lysis of organelles ("light" type). Unmyelinated optic fibers and their synapses survived and transmitted the excitation for more than 140 days at a temperature of 18–20°C. In the course of the survival of optic fibers and synapses, the static (latency, duration, and amplitude) as well as dynamic (lability, excitability cycle, and posttetanic changes) characteristics of the EP for electrical stimulation of the nerve changed insignificantly. Direct response of the midbrain tectum decreased in the course of the degeneration of the optic fibers, and after 280 days its amplitude was about 20% of the control value.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 180–188, March–April, 1970.     

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.     

Convergence of preganglionic fibers on vasomotor neurons of the sympathetic ganglia in cats

Convergence of different preganglionic fibers on antidromically identified vasomotor neurons was studied by intracellular recording from neurons of ganglia L3 and L4 of the sympathetic chain, isolated from their rostral and caudal commissures, white ramus communicans, and muscular and cutaneous (mixed) twigs of the ventral branch and dorsal branch of the mixed nerve, in cats. Neurons activated antidromically by stimulation of these twigs were confidently considered to be vasomotor. Preganglionic fibers of only the B₂ and C groups were shown to converge on the vasomotor neurons, by contrast with the rest. Discharges of neurons were evoked only by excitation of preganglionic fibers of the B₂-group, arising mainly from higher segments of the spinal cord and entering through the rostral commissure. Vasomotor neurons also differ from the remaining ganglion cells in the properties of their axons, which conduct excitation at a significantly slower velocity (0.95±0.05 m/sec) than axons of other neurons (1.30±0.15 m/sec).I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 592–597, November–December, 1977.     

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.     

Theoretical analysis of mechanisms of nerve impulse conduction along myelinated fiber after a functional change in the properties of individual nodes

It is shown in a mathematical model of a myelinated nerve fiber that the development of a local response in an inexcitable node plays an important role in the mechanism of the "jumping" of an action potential (AP) across the inexcitable node. In the absence of such a response (for example, in the case of a 1000-fold decrease in the maximum sodium permeability, _Na) in fibers with normal relations between the length of the internodal segment (L) and its diameter (D) (L/D>100), the conduction is blocked. It is possible only in fibers with relatively short internodal segments (L/D<90). With a decrease in the _Na in several nodes, the transmission of excitation from the first to the second altered node is of critical importance for propagation of the impulse. The conduction of an AP becomes decremental if in each of the altered nodes the AP acquires a gradual character, for example, in the case of acceleration of sodium inactivation through the rate constant _h.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 316–324, May–June, 1971.     

Mechanism for sympathetic modulation of activity of cutaneous receptors (with Aδ fibers)

The afferent flow in A fibers from cutaneous receptors was studied in acute experiments with cats. A decline in the number of fibers activated during adequate receptor stimulation was observed at 5 and 35 sec after the excitation of sympathetic efferents. Similar changes in the afferent flow were recorded in identical time intervals after the preliminary stretching and cooling of the skin. The results obtained indicate that the quantitative characteristics of afferent flow during the first 30 sec after stimulation of the sympathetic chain are primarily due to the change in the mechanical state of the tissues surrounding the receptors.N. I. Lobachevskii Institute of Mathematics and Cybernetics, Gor'kii University. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 517–521, July–August, 1985.     

Functional properties of propriospinal pathways of the dorsolateral tract of the cat spinal cord

The characteristics of conduction of the excitation wave along propriospinal fibers of the dorsolateral tract of the spinal cord were studied in cats anesthetized with pentobarbital. At a preliminary operation, 10–18 days beforehand, lateral hemisection of the spinal cord was performed, cranially in the lumbar division and caudally and cranially in the cervical division to the segments to be studied, leading to degeneration of the long descending and ascending fibers. During stimulation, the dorsolateral tract developed a composite response consisting of a positive-negative wave recorded up to 60–65 mm (4 or 5 segments) from the point of stimulation. The mean conduction velocity of this wave in the lumbar division was 37.9 m/sec compared with 44.5 m/sec in the cervical division. From its properties as a whole this wave can be regarded as the result of excitation of relatively fast-conducting propriospinal fibers of the dorsolateral tract. If the strength of stimulation was increased, late components began to appear in the response. These were evidently connected with excitation of thinner propriospinal fibers and synaptic activation of other other groups of spinal neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 54–60, January–February, 1973.     

Morpho-functional changes in the turtle midbrain tectum after enucleation

Morpho-functional changes in the tectum mesencephali during degeneration after enucleation were studied inEmys orbicularis L. Comparison of amplitude-time characteristics of evoked potentials of the visual center with degenerative changes in axon terminals and fibers of the optic nerve in the same animals revealed a "light" type of degeneration of the terminals of unmyelinated axons and a "dark" type in terminals of myelinated axons. During "dark" degeneration (4–5 months after enucleation) the low-amplitude presynaptic component of the evoked potential, reflecting excitation of large myelinated fibers, disappeared and changes occurred in the characteristics of the first high-amplitude component, the appearance of which is connected with excitation of myelinated fibers of medium diameter. The last component disappeared 7 months after the operation, along with disappearance of the "dark" degeneration. During "light" degeneration (2.5–3.5 months) changes took place in the characteristics of the second high-amplitude component of the evoked potential, which reflects excitation of thin fibers, both myelinated and unmyelinated, whose ranges of diameters overlap. This component disappeared after 6–7 months, almost simultaneously with disappearance of the first high-amplitude component, as the result of simultaneous completion of degeneration of myelinated fibers of medium and small diameter.     

Energy transfer to the reaction centres in bacterial photosynthesis

From a combined study of (1) bacteriochlorophyll fluorescence lifetimes, (2) relative yields and (3) differential absorption changes corresponding to the reaction centres photooxidation, the absolute values of fluorescence lifetimes and quantum yields for two bacteriochlorophyll fractions have been calculated. The main bacteriochlorophyll fraction (80–90%) serving as a light-gathering antenna for reaction centresP ₈₉₀ is characterized by dark values of fluorescence lifetimes of the order of 10^–11 sec and fluorescence yields of 10^–3. The remaining part of the bulk pigment, not associated withP ₈₉₀ as far as excitation energy transfer is concerned, has an approximately constant fluorescence yield of about 5–8% and lifetime of about 10^–9 sec. Basing on these results, excitation jump times and intermolecular coupling energies were estimated to be 10^–13 sec and 10^–2 ev respectively. The conclusion is made that excitation energy transfer in the main part of bacteriochlorophyll occurs by the exciton mechanism at moderate intermolecular energies.     

Investigation of the frequency distribution of natural activity in a mixed nerve trunk by the colliding impulse method

the theory of the colliding impulse method of determining the discharge frequency spectrum and the distribution of fibers by frequency in a mixed nerve trunk is examined. Using the double impulse method, a modification of the colliding impulse method, afferent A-fibers of the aortic nerve in the cat were investigated. Only 61% of these fibers were found to be activated in the initial phase of cardiac ejection when the arterial pressure was 120 mm Hg. Most of the active fibers functioned with a frequency of about 115 spikes/sec.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 6, No. 3, pp.318–327, May–June, 1974.     

Parameters of conduction via afferent nerve fibers in mice with streptozotocin-induced and genetically determined diabetes

The parameters of conduction via afferent nerve fibers were studied in mice with streptozotocin-induced and genetically determineddiabetes mellitus (9- to 12-week-old animals; streptozotocin was injected into 5-week-old mice). Recording of spinal cord dorsal surface potentials evoked by stimulation of the sciatic nerve showed that within the studied time interval the mice of the two diabetic groups were characterized by a moderate decrease (by 7.9% and 5.8%, on average) in the conduction velocity for afferent volleys (measured according to the delay of the peak of positivity of a volley) and by a considerable increase in the duration of the positive phase of these volleys (by 36% and 33%, respectively, as compared with the values in intact animals). Therefore, the population of relatively slow group A afferent fibers becomes noticeably larger in the sciatic nerve of diabetic mice even at early stages of the pathology, but at the same time a considerable amount of the fastest-conducting (about 45–60 m/sec) fibers is still preserved. The changes in mice with diabetes of different etiology were very similar, in spite of different hyperglycemia levels in these groups. Possible factors determining diabetes-induced modifications of the conduction velocity via the nerve fibers are discussed.Neirofiziologiya/Neurophysiology, Vol. 28, No. 4/5, pp. 173–178, July–October, 1996.     

Conduction velocity and excitability of A and C fibers of cat mesenteric nerves

The conduction velocity and excitability of fibers running from the mesenteric into the splanchnic nerves were studied in experiments on cats. Among the A fibers of these nerves there were shown to be: 1) fibers with an excitation threshold of 0.06–0.10 V (stimulus duration 0.1 msec) and a maximal conduction velocity of 48–85 m/sec; 2) fibers with an excitation threshold of 0.3–0.7 V, impulses of which form up to five waves in the composition of the action potential, with maximal conduction velocities of between 8–10 and 33–39 m/sec; 3) fibers with an excitation threshold of over 1 V and a conduction velocity of between 1.8 and 7 m/sec. The excitation threshold of the group C fibers was 6–8 V. Impulses of these fibers form a low-amplitude wave in the composition of the action potential of the mesenteric and splanchnic nerves with a conduction velocity of 1.0–1.8 m/sec, several waves of higher amplitude with a conduction velocity of 0.5–1.2 m/sec, and several low-amplitude waves with a conduction velocity of 0.35–0.55 m/sec. The results of experiments with different combinations of arrangement of the stimulating and recording electrodes on the mesenteric and splanchnic nerves indicate that sympathetic postganglionic C fibers of the mesenteric nerves occur only in the second group, whereas afferent C fibers occur in all three of the groups distinguished.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 3, pp. 272–278, May–June, 1975.     

Der „Kniesehnenreflex” bei Carausius morosus: Übergangsfunktion und Frequenzgang

Stretching and releasing the femoral chordotonal organ caused by a movement of the tendon of the organ gives rise to a movement of the tibia. This reaction is called Kniesehnenreflex (knee-tendon-reflex). Its step response can be described in the following manner: After a certain reaction-time (at flexion 0.02–0.06 sec, at extension 0.06–0.2 sec) the tibia moves with a maximum speed between 150°/sec and 1000°/sec at extension and between 20°/sec and 450°/sec at flexion. The amplitude of the movement and the maximum speed of tibia movement are correlated. After reaching the extreme position the tibia returnes nearly to its starting-point with half lifes of 3–58 sec after a flexion and 7–232 sec after an extension. — The frequency response shows a strong decrease of the amplitude of the tibia at about 1 Hz. Above 2 Hz the amplitude is only a few degrees. The phase shift between stimulus and reaction increases with increasing frequency. Big individual differences are observed. A step stimulus, which is given in addition to a sinoidal stimulus causes a response at all frequencies. — Slow stretching and releasing the chordotonal organ with constant speeds causes movements of the tibia even at stimulus speeds of 0.002 mm/min. — It is discussed: the significance of the results for the theory of the control mechanism at walk, the stability of the control system in connection with the rocking-movements of the animal and the control of Flexibilitas cerea.