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.     

Some characteristics of the afferent flow during noxious stimulation of the skin

Quantitative characteristics of the afferent impulse flow in a cat cutaneous nerve during stimulation of the skin with acid, needles, and pins were studied by a cross-correlation method. The appearance of a nociceptive response served as the test of noxious stimulation. Mechanical and chemical noxious stimuli, acting directly on the nerve fiber, activate the same peripheral channels as weak tactile stimuli exciting receptors. Spike trains under these circumstances differed in the absolute and relative numbers of active A and C fibers and the duration of activity in them. The nociceptive response is brought about through marked predominance of activity in C fibers compared with A fibers and through its long duration in both types of fibers but, in particular, in C fibers. An optical correlometer can be used to investigate activity of a whole nerve.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 168–176, March–April, 1976.     

Afferent flow patterns in a cat cutaneous nerve during painful and painless mechanical stimulation of the skin

Quantitative characteristics of afferent flows coding information from a number of receptors were obtained by the gliding impulses method. The frequency spectrum of activity in a cutaneous nerve, the relative numbers of active A, A, and C fibers and their distribution by impulse transition frequency during stimulation of the cat's skin with pins and needles were determined. The afferent flow recorded in the nerve during pricking of the skin is characterized by high density, due to the number of excited fibers and the frequency of activity in them. The higher density of the afferent flow during the application of a painful than of a painless stimulus is mainly due to activity in C fibers. Unmyelinated fibers subjected to the action of the same stimulus and of chemically active substances liberated from the cells during tissue injury are excited directly and generate high-frequency spikes which increase the flow density in the nerve. The number of active myelinated fibers and the spike frequency during the action of a painful stimulus are only a little greater than the corresponding characteristics of the afferent discharge during painless stimulation.Scientific-Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 391–399, July–August, 1976.     

Slow electrical potentials arising after the primary response in the somatosensory region of the cerebral cortex in the cat as a result of stimulation of the ventroposterolateral nucleus of the thalamus

In experiments conducted on cats anesthetized with Nembutal, it was shown that a primary response, a delayed negative response, and afterwards, a slow negative potential ariseing. sigmoideus posterior following the application of a single stimulus to the ventroposterolateral nucleus of the thalamus. The generation of these potentials is accompanied by the appearance of three spike-like deflections in the subcortical white matter. These deflections reflect arrivals of afferent impulses to the cortex. It is suggested that the delayed negative wave chiefly reflects the activity of stellate cells, while the slow negative potential mainly reflects the activity of glial cells. It is concluded that the appearances of the three enumerated reactions are connected with the successive arrivals of impulses from the thalamus to the cortex along three different systems of afferent fibers, differing from one another with respect to velocities of impulse conduction and characteristic distributions of endings in the cortex.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 435–441, July–August, 1985.     

Inhibition in the neurons of the somatosensory cortex and the possibility of intracortical propagation of excitation

Extra- and intracellular leads were used to study the reactions of neurons in the pyramidal tract (PT) of the cat brain to antidromic and afferent effects. It was shown that afferent activation of PT neurons proceeds heterogeneously. Three types of PT neurons were identified, successively involved in the impulse response to afferent stimulation. By means of paired stimuli we determined the heterogeneous changes in sensitivity of late reacting PT neurons. It was found that, under certain conditions, the different IPSP evoked by afferent stimulation or PT stimulation do not prevent the appearance of impulse responses to secondary synaptic activation. A conclusion was drawn from these experiments on the localization of the excitatory intracortical terminals on the somas of the PT neurons and on the limited effect of inhibitory processes upon intracortical propagation of the afferent signal reaching the cortex. A functional scheme of intracortical PT neuron links is presented.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 465–473, September–October, 1971.     

Mechanism of sympathetic efferent control of c-receptor responses to skin cooling in cats

The effect of sympathetic efferents on the afferent flow in C fibers was studied in acute experiments on cats. The number of C fibers active during skin cooling was found to be increased 5–7 sec but reduced 30–40 sec after stimulation of the sympathetic chain. The increase in activity in C-afferents can be explained by a change in the mechanical state of the skin during contraction of its contractile elements. The decrease in activity in C afferents, on the other hand, is evidently due to the effect of sympathetic nervous system mediators on C receptors or directly on afferent C fibers.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii Gor'kii State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 373–378, July–August, 1982.     

Conducting pathways of the dog solar plexus

Conducting pathways of the dog solar plexus were studied by recording action potentials from its nerves. The splanchnic nerves are composed of two groups of fast-conducting afferent A fibers (with conduction velocities of 12–15 and 25–56 m/sec), slowly conducting afferent C fibers (0.4–2.0 m/sec), and preganglionic B and C fibers (1.0–12.0 m/sec). Afferent A and C fibers from peripheral nerves run without interruption through the ganglia of the solar plexus, splanchnic nerves, and sympathetic chain and they enter the spinal cord in the composition of the dorsal roots. Cell bodies of A fibers are located in the spinal ganglia, those of the C fibers below the ganglia of the solar plexus, evidently in the walls of the internal organs. Peripheral nerves contain A fibers only with very low conduction velocities (13–20 m/sec) and no fast-conducting A fibers (25–56 m/sec) were found. Preganglionic fibers terminate synaptically on neurons of the ganglia of the solar plexus whose axons run in the peripheral nerves to the internal organs. Synaptic pathways run from some peripheral nerves of the solar plexus into others through its ganglia; in all probability these pathways participate in peripheral reflex arcs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 76–83, January–February, 1976.     

Characteristics of thermo-mechanosensitive receptors in human and animal skin

With local thermal and mechanical stimulation in precise experiments on cats, a study was made of changes in impulse activity of afferent fibers of spinal dorsal roots connected with skin thermoreceptors in the extremities. Psychophysiological studies were done on the characteristics of thermosensitive points of the skin of the upper extremities of man. According to changes in average frequency of impulse activity, dynamic sensitivity, latent period of reaction, and thresholds of temperature and mechanical sensitivity, three groups of heat receptors and two of cold receptors were identified in the skin of the cat. All heat and cold receptors are mechanosensitive. According to quality and intensity of perceptions elicited by thermal stimulation and thresholds of sensitivity to mechanical and temperature effects, thermosensitive points in human skin can also be divided into three groups of heat receptors and two groups of cold receptors. All heat and cold points are mechanosensitive. An analogy between the skin thermoreceptors of animals and man is suggested.Institute of Physiology, Kazakhstan, Academy of Sciences. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 314–322, May–June, 1992.     

Localization of sources of thalamic inputs into the sensorimotor cortex in the rabbit using retrograde axonal transport technique

It was shown that the rabbit sensorimotor cortex received afferent fibers from neurons located in the specific, nonspecific, and association thalamic nuclei using the retrograde axonal transport technique. The distribution, dimensions, and shape of the somata of relay neurons spread through the thalamic nuclei were analyzed. The total number of neurons sending out thalamo-sensorimotor-cortical fibers was calculated and the coordinates of loci with the highest density of these cells in each thalamic nucleus were identified. Multipolar and stellate cells with somata measuring 12–20 µm and 10–15 µm in diameter, respectively, prevailed amongst relay neurons. Amongst the specific nuclei, the majority of afferent fibers are sent out by the ventrolateral, ventral anterior, and anterior ventral nuclei. A comparable number of afferent fibers are sent out by the mediodorsal and paracentral nuclei; these split up among the association nuclei and paracentral nuclei, respectively. It is suggested that afferents from many different groups of thalamic nuclei are essential for the sensorimotor cortex to participate in thalamocortical interaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 87–94, January–February, 1987.     

Action of ammonium acetate on central primary afferent depolarization

Experiments on anesthetized spinal cats showed that ammonium acetate, injected intravenously (2–4 mmoles/kg) inhibits the depolarization of the central endings of primary afferent fibers activated by stimulation of afferent nerves. Inhibition of primary afferent depolarization is transient in character and develops parallel with depression of postsynaptic inhibition of monosynaptic reflexes. The depression produced by the action of ammonium was not due to blocking of negative postsynaptic potentials of the dorsal surface of the spinal cord or blocking of reflex electrical discharges in the ventral spinal roots. It is suggested that depression of primary afferent depolarization is due to a decrease in the emf for synaptic ion currents producing depolarization.Allergologic Research Laboratory, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 52–60, January–February, 1977.     

Effects of aspartic acid on skate electroreceptors

The effects of L-aspartic acid (L-ASP) on spontaneous and evoked activity in afferent nerve fibers were investigated by perfusing the basal membrane of sea skate electroreceptors (the ampullae of Lorenzini) with this substance. It was found that perfusion with physiological saline containing L-ASP exerted a primarily excitatory effect on afferent activity (threshold concentration: 10^–7 M). When synaptic transmission was blocked by magnesium ions, activity was restored in the afferent fibers if L-ASP was added to the solution and spike activity persisted for longer; this would imply the presence of desensitizing processes in the postsynaptic receptors of the ampullae. Finding would lead to the conclusion that L-ASP and L-glutamate fulfill a set of criteria for likely neurotransmitters in the ampullae of Lorenzini.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 61–67, January–February, 1987.     

Neuronal and synaptic mechanisms of cortical inhibition

The latent periods, amplitude, and duration of IPSPs arising in neurons in different parts of the cat cortex in response to afferent stimuli, stimulation of thalamocortical fibers, and intracortical microstimulation are described. The duration of IPSPs evoked in cortical neurons in response to single afferent stimuli varied from 20 to 250 msec (most common frequency 30–60 msec). During intracortical microstimulation of the auditory cortex, IPSPs with a duration of 5–10 msec also appeared. Barbiturates and chloralose increased the duration of the IPSPs to 300–500 msec. The latent period of 73% of IPSPs arising in auditory cortical neurons in response to stimulation of thalamocortical fibers was 1.2 msec longer than the latent period of monosynaptic EPSPs evoked in the same way. It is concluded from these data that inhibition arising in most neurons of cortical projection areas as a result of the arrival of corresponding afferent impulsation is direct afferent inhibition involving the participation of cortical inhibitory interneurons. A mechanism of recurrent inhibition takes part in the development of inhibition in a certain proportion of neurons. IPSPs arise monosynaptically in 2% of cells. A study of responses of cortical neurons to intracortical microstimulation showed that synaptic delay of IPSPs in these cells is 0.3–0.4 msec. The length of axons of inhibitory neurons in layer IV of the auditory cortex reaches 1.5 mm. The velocity of spread of excitation along these axons is 1.6–2.8 msec (mean 2.2 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 394–403, May–June, 1984.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

Electron-microscopic analysis of synapses of the inferior mesenteric sympathetic ganglion in the afferent chain of sympathetic reflexes

There are axodendritic, axosomatic, dendrodendritic, and axoaxonic synapses in the inferior sympathetic ganglia. Preliminary transectioning of the preganglionic fibers, degeneration of these fibers, and circumferential preliminary cutting of all connections of the ganglion do not give rise to structural disturbances in all of the synapses: some of them remain intact. Preliminary cutting of the hypogastric nerves — which leads to degeneration of the central ends of peripheral afferent neuron axons, above all those of Dogel' type II cells — causes structural changes of a degenerative nature in a number of ganglionic synapses, although no changes are observed in most of them. Intact and structurally changed synapses are analyzed as synapses between afferent and efferent sympathetic neurons on the one hand, and between afferent neurons of different levels of the vegetative nervous system forming visceral afferent pathways that are interrupted in the ganglion on the other.Preliminary results were published in Dokl. Akad. Nauk BSSR,2, 934–937 (1967), and presented at the First All-Union Conference on Electron Microscopy, Leningrad, 1968.Institute of Physiology, Academy of Sciences of the Belorussian SSR, Minsk. Translated from Neirofiziologiya, Vol.3, No. 1, pp. 84–88, January–February, 1971.     

Inhibition of spinal reflex responses in the last period of embryogenesis

Some characteristics of spinal reflex reaction inhibition were studied in cat fetuses during the last three weeks of antenatal development. The experiments were conducted on fetuses with intact placental circulation. Restoration of the excitability of the spinal reflex arcs was very slow after stimulation of the dorsal root by a single stimulus. In embryos studied 20 days before birth the full inhibition of reflex responses lasted about 500 msec. Even 2–3 sec after a single stimulation of the afferent fibers the amplitude of the reflex response to the second stimulus was only 30–40% of the control value. It was determined that such long postactivation depression is unrelated to refractoriness or antidromic inhibition. The presence of a prolonged intense depolarization of afferent terminal fibers at these stages suggests a presynaptic inhibition as one of the most probable reasons for the prolonged postactivation depression. Another important factor in the appearance of postactivation depression is probably the morphologic and functional immaturity of synaptic structures. A reciprocal inhibition was observed in cat fetuses on the 10–12th antenatal day. On the basis of these data it is suggested that in embryogenesis presynaptic inhibition considerably precedes that of postsynaptic fibers.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 68–75, January–February, 1971.     

Changes in antidromic discharges in peripheral nerves during polarization of the cat spinal cord by a steady current

The effect of a steady current passed through the spinal cord on antidromic discharges in primary afferent groups of Agb cutaneous nerves of the hind limb, evoked by single and paired stimulation of the terminals of these fibers, was investigated by Wall's technique in acute experiments on spinal and anesthetized cats. A current of up to 50–100 µA, flowing in the dorso-ventral direction, led to an increase in amplitude of antidromic dischanges evoked by single stimulation of afferent terminals; if the current flowed in the opposite direction, the opposite effect was observed. The relative degree of facilitation of antidromic discharges caused by conditioning stimulation of these same fibers was reduced by a polarizing current in either direction. It is suggested that the effects of the action of a steady current flowing through the spinal cord observed in these experiments are due mainly to shifts of membrane potential in primary afferent terminals.Dnepropetrovskii State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 386–391, July–August, 1982.     

Classification of lumbosacral neurons by their discharge pattern during evoked locomotion

Unit activity was recorded in the lumbosacral division of the spinal cord during evoked locomotion in mesencephalic cats with the afferent fibers from their hind limbs intact or divided. If the afferent fibers were intact, all neurons recorded showed modulation of activity during locomotion in the rhythm of stepping movements. In experiments on cats with afferent fibers from the hind limbs divided modulation was absent in 30% of neurons, while in the modulated neurons, the frequencies in the excitation phase were approximately the same as when the limb innervation was intact. Modulation of activity in some neurons occurred in response to stimulation of the locomotor region even before stepping movements began. The tuning of the spinal generator of stepping movements is discussed.M. V. Lomonosov Moscow State University. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 410–417, July–August, 1972.     

Electrophysiological studies of pyridine-sensitive units on the crayfish walking leg

Summary Pyridine-sensitive units located on the walking legs of the crayfishAustropotamobius torrentium were studied by extracellular recording of the action potentials of single afferent fibers. To characterize the sensitivity and specificity of the pyridine receptor, 79 pyridine analogs and other related substances were tested on 70 neurons. The maximum impulse frequency of the response was used to construct dose-response curves. The effectiveness of stimulatory substances was characterized at the half-maximal-response frequency, K_M. The effectiveness rank order of the substances was found to be the same for all units tested. The most effective substances were: pyrazinecarboxamide > 3-acetylpyridine > nicotinamide > pyridine-3-aldoxime, with K_M values of 1.5×10^–6, 4× 10^–6, 10^–5 and 4 x 10^–5 mol/1, respectively. The inferred structural requirements for an optimal stimulatory molecule are that it have a N-containing aromatic ring system with a specific substituent in them position.     

Investigation of synaptic connections between primary afferents and motoneurons in the frog spinal cord by intracellular injection of horseradish peroxidase

Parallel recordings of potentials from primary afferent fibers and motoneurons connected monosynaptically with them were obtained in experiments on the isolated, perfused frog spinal cord and this was followed by intra-axonal and intracellular injection of horseradish peroxidase. Terminals of the primary afferent fibers were shown to reach the motor nuclei of the ventral horn, and one fiber could form contacts with several motoneurons. Synapses formed by afferent terminals were found not only on distal, but also on proximal segments of dendrites and also on motoneuron bodies. Synapses were most numerous on the proximal segments of the dendrites and branches of the second-third orders. Recurrent axon collaterals of motoneurons forming synapses with dendrites were found.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 60–68, January–February, 1982.     

Depolarization of different groups of lumbar afferent terminals during fictitious scratching

The kinetics of primary afferent depolarization (PAD) in the lumbar spinal cord was studied in immobilized decerebrate and decapitated cats during fictitious scratching. Fictitious scratching was accompanied by tonic and periodic PAD. Periodic PAD was cophased in different segments of the lumbosacral enlargement. Tonic depolarization was observed in terminals of all groups of afferent fibers studied (low-threshold cutaneous and of groups Ia and Ib). Periodic changes were observed only in endings of low-threshold cutaneous fibers and group Ib fibers. The physiological role of modulation of PAD by the spinal scratch generator is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 569–577, November–December, 1979.