Electrophysiological investigation of central neurons of the electroreceptor system of the skate

Bioelectrical responses of acoustico-lateral neurons to electrical stimulation of the ampullae of Lorenzini were investigated in acute experiments on the anesthetized Black Sea skateTrigon pastinaca. Three types of responses were found: a primary composite response, prolonged activity, and single unit activity. Excitation of the neurons corresponded to a more marked negative phase, and inhibition to a more marked positive phase of the primary response. The thresholds of the unit responses to adequate electrical stimulation were 10^–9–10^–10 A/mm² and the minimal latent period 20 msec. The spontaneous activity of some neurons clearly depended on the animal's respiration. The character of the response depended on stimulus polarity, as reflected in the appearance of on- and off-responses. A tonic type of response with features of adaptation was predominant. The dependence of some response parameters (latent period of on- and off-responses, firing rate, duration of the contrast interval, response thresholds) on those of the stimulus is analyzed. The mechanisms of these bioelectrical responses are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.1, pp.59–67, January–February, 1974.     

Unit responses of the cat lateral geniculate bodies to visceral and somatic stimulation

Acute experiments on cats anesthetized with pentobarbital and immobilized with Diplacin or Listhenon showed that electrical stimulation of the vagus, splanchnic, pelvic, and sciatic nerves and also of the mesencephalic reticular formation induces either a prolonged change in the frequency of unit activity or phasic responses of single units of the lateral geniculate body. During stimulation of the visceral nerves tonic changes in unit activity were predominant, whereas phasic responses were found more often during somatic stimulation. Most neurons tested responded to all types of stimulation used and only 15–18% responded only to the specific stimulus: photic stimulation of the receptive field. The results suggest that interaction of visceral, somatic, and sensory-specific excitation takes place on single neurons of the lateral geniculate body.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Ivano-Frankovsk Medical Institute. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 246–252, May–June, 1973.     

Functional characteristics of electroreceptors of the Turkestan catfish

Acute experiments to record spike activity from single fibers of the lateral line nerve of the Turkestan catfish revealed electroreceptor formations which, in their functional characteristics, were similar to the ampullated electroreceptors of other freshwater fish (the so-called small pit organs). The threshold intensity of the uniform electric field was 1 µV/cm. A voltage drop on the skin of the fish was shown to be an effective stimulus for the electroreceptors. A spike response to a change in the magnetic field was found for the first time in electroreceptors of freshwater fish. The threshold level of magnetic induction for a velocity of rotation of the permanent magnet of 1 m/sec was 2.9 · 10^–4 T. Temperature and mechanical sensitivity of the electroreceptors was determined. The biological significance of electroreceptors of the Turkestan catfish is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. M. I. Kalinin Andizhan Medical Institute, Ministry of Health of the Uzbek SSR. S. M. Kirov Murmansk Marine Biological Institute, Kola Branch, Academy of Sciences of the USSR, Dal'nie Zelentsy. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 508–516, September–October, 1980.     

Frequency characteristics of skate electroreceptive central neurons responding to electrical and magnetic stimulation

Responses of single neurons in the lateral lobes of the medulla to stimulation of the electroreceptive system by homogeneous sinusoidal electrical and magnetic fields were investigated in acute experiments on the skateRaja radiata. Thresholds of neuronal responses to electrical stimulation varied from 0.03 to 10 µV/cm. The optimal frequency ranges for electrical and magnetic reception were in the regions of 0.05–5 and 2–3 Hz respectively. The possible mechanisms and functional significance of frequency characteristics of central neurons are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 464–470, July–August, 1984.     

Convergence of autonomic,somatic, and vestibular afferent impulses on single units of the medullary vasomotor center of the cat

Responses of vasomotor neurons of the cat medulla to electrical stimulation of the depressor nerve and of mixed nerves of the limbs and to adequate stimulation of the vestibular apparatus were investigated. Evoked unit activity was demonstrated as groups of action potentials followed by inhibition of spontaneous activity. Three types of unit responses to stimulation of the depressor nerve and somatic afferent fibers and changes in unit activity in response to vestibular stimulation are described. The features distinguishing the convergence of afferent impulses on vasomotor neurons are discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 460–467, September–October, 1973.     

Unit responses in the cat auditory cortex to electrical stimulation of nerve fibers innervating receptor cells in different parts of the organ of corti

Responses of 200 primary auditory cortical neurons to electrical stimulation of nerve fibers in different receptor zones of the cochlea were studied in cats anesthetized with pentobarbital. Under the influence of paired stimulation, after the response to the conditioning stimulus a state of prolonged (from 4 to 200 msec) refractiveness to the second stimulus developed in all the neurons tested. This long-lasting inhibition of unit activity was due to inhibition developing in the thalamus and the auditory cortex itself. The intensity and duration of excitation and inhibition in the cortical projection focus were maximal when the center of the receptive field was stimulated and decreased when the stimulus shifted from the center to the periphery. The region of the receptor surface of the cochlea to stimulation of which the auditory cortical neurons respond by an action potential is much narrower than the region whose electrical stimulation depresses the discharge of these neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 418–425, July–August, 1982.     

Responses of upper cervical spinal neurons in cats to stimulation of the brain-stem locomotor region at different frequencies

Synaptic responses of neurons in segments C₂ and C₃ to stimulation of locomotor points in the medulla or midbrain were recorded extracellularly in mesencephalic cats. Neurons generating responses with an index of 0.4–0.6 to stimulation with a frequency of 2 Hz maintained this same index at frequencies of 20–60 Hz. The discharge index of many neurons during stimulation at 2 Hz was low, and it increased to 0.4–0.6 when high-frequency stimulation was used. More than half of the cells were excited by stimulation of both ipsilateral and contralateral locomotor points; one-quarter of the neurons responded to stimulation of locomotor points in both medulla and midbrain. The cells studied were located 1.8–4.2 mm from the dorsal surface of the spinal cord. The mean latencies of responses with an index of not less than 0.5 lay within the range 2–30 msec, with a mode of 2–8 msec. Considerable fluctuations of latent period were observed for long-latency responses. The possibility that the neurons studied may participate in the transmission of activity from the locomotor region of the brain stem to stepping generators in the spinal cord is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 355–361, July–August, 1983.     

Inhibitory influence of supplementary extraneous stimulation upon neuronal responses in the sensorimotor cortex of the cat during a conditioned reflex

Using alert rabbits trained to perform placing movements in response to a sound click, we investigated impulse responses (IR) of neurons of the somatosensory cortex preceding realization of the reflex by 50–150 msec. When a brief extraneous stimulation (light flashes, audible tone, electrical stimulation of a limb) was applied after initiation of the reflex, learned movements with the earlier behavioral parameters (latent periods and duration) were maintained. However, the IR of neurons to the presentation of a conditioned stimulus (CS) was of lesser intensity and arose 50–250 msec later. A constant extraneous stimulation (an audible tone, a forced stream of air upon the muzzle) or a decrease in the intensity of the CS administered to the threshold of hearing resulted in similar changes in the neuronal responses upon the application of the CS, but the parameters of the learned movements were maintained. We suggest that the cause of these changes in neuronal responses is increased exteroceptive attention to extraneous stimulation to additional extraneous stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 174–181, March–April, 1991.     

Effect of removal of corticofugal influences on receptive fields of lateral geniculate neurons in the cat

Unilateral division of corticogeniculate connections increases the number of spikes in unit responses of the ipsilateral lateral geniculate body to receptive field stimulation and potentiates the effects of lateral inhibition. The area of the zone of complete summation of all lateral geniculate neurons recorded on the side of operation depends on contrast of the local photic stimulus. It is concluded that cortical fibers descending to the lateral geniculate body are inhibitory in nature and that the existence of receptive fields with a variable zone of spatial summation is due to intrageniculate mechanisms.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 486–492, September–October, 1975.     

Two patterns of bulbar neuronal response to microstimulation of locomotor and inhibitory brain stem sites

Synaptic responses (postsynaptic potentials and action potentials) were evoked in mesencephalic decerebellated cats by stimulating pontine bulbar locomotor and inhibitory sites (LS and IS, respectively) with a current of not more than 20 µA in "medial" and "lateral" neurons of the medulla. Some neurons even produced a response to presentation of single (actually low — 2–5 Hz — frequency) stimuli. The remaining cells responded to stimulation at a steady rate of 30–60 Hz only. Both groups of medial neurons were more receptive to input from LS. Lateral neurons responding to even single stimuli reacted more commonly to input from LS and those responding to steady stimulation only to input from IS. Many neurons with background activity (whether lateral or medial) produced no stimulus-bound response, but rhythmic stimulation either intensified or inhibited such activity. This response occurs most commonly with LS stimulation. Partial redistribution of target neurons in step with increasing rate of presynaptic input may play a major part in control of motor activity.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 257–266, March–April, 1990.     

Responses of medullary neurons to microstimulation of the "locomotor strip" in cats

Synaptic responses of medullary neurons to stimulation of the bulbar locomotor strip with a current of about 20 µA were studied by an extracellular recording method in mesencephalic cerebellectomized cats. The mean latent period of response of 177 neurons was 3.2 msec. Neurons in which synaptic responses appeared were located in both the lateral and the medial parts of the reticular formation, but short-latency responses were recorded predominantly in the lateral part. In response to a single stimulus 32% of neurons generated a discharge of 2–4 spikes. "Respiratory" neurons were not excited by stimulation of the locomotor point. The results indicate that neurons of the locomotor strip may have an excitatory action not only on each other, but also on neurons located medially. The possible mechanisms of the spread of activity to the superior cervical segments of the spinal cord are discussed.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 275–282, May–June, 1981.     

The functional characteristics of electroreceptive central neurons of the sea catfish Plotosus anguillaris

With the use of microelectrode techniques (extracellular recordings) and the method of post-stimulus histograms, the functional characteristics of medulla oblongata neurons of sea catfish Plotosus were investigated under stimulation of electroreceptors by a homogeneous electric field of different duration, intensity, and direction. Two types of the cells possessing, accordingly, tonic or phase activity were registered among 66 neurons investigated. The mode of responses (inhibition or acceleration) of tonic neurons to the direction of the applied electric current is typical for central neurons of fresh-water catfish connected with ampullae's electroreceptors. Neurons showing a substantial response to fields of an intensity less than 1 microV/cm were registered. The reactions were most pronounced with the duration of electric stimuli in the range of 20-200 ms; however, particularly sensitive neurons showed distinct responses to stimuli of duration of 5 and even 2 ms. Thus, for the first time a high sensitivity of ampullae's electroreceptors to high-frequency stimulus was discovered, which allows one to expand the range of studying electric signals used by weakly electric fish for electrolocation and communication.     

Responses of neurons of reticular and ventral anterior nuclei of the cat thalamus to afferent stimuli of different modalities

Responses of 146 spontaneously active neurons of the reticular nucleus (R) and of 98 neurons of the ventral anterior (VA) nucleus of the thalamus to electrical stimulation of the skin of the footpads, to flashes, and to clicks were studied in experiments on cats immobilized with D-tubocurarine or myorelaxin. Stimulation of the contralateral forelimb was the most effective: 24.9% of R neurons and 31.3% of VA neurons responded to this stimulation. A response to clicks was observed in only 4.4% of R neurons and 2.4% of VA neurons. Nearly all responding neurons did so by phasic (one spike or a group of spikes) or tonic excitation. Depression of spontaneous activity was observed only in response to electrical stimulation of the skin. Depending on the site of stimulation, it was observed in 2.6–4.3% of R neurons and 1.7–2.1% of VA neurons tested. The latent period of the phasic responses of most neurons was 6–64 msec to electrical stimulation of the contralateral forelimb, 11–43 msec in response to stimulation of the hindlimb on the same side, 10–60 msec to photic and 8–60 msec to acoustic stimulation. Depending on the character of stimulation, 75.1–95.6% of R neurons and 68.7–97.6% of VA cells did not respond at all to the stimuli used. Of the total number of cells tested against the whole range of stimuli, 25% of R neurons and 47% of VA neurons responded to stimulation of different limbs, whereas 16% of R neurons and 22% of VA cells responded to stimuli of different sensory modalities. The functional role of the convergence revealed in these experiments is to inhibit (or, less frequently, to facilitate) the response of a neuron to a testing stimulus during the 40–70 msec after conditioning stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 563–571, November–December, 1975.     

Conduction of excitation in the cat visual system

Unit responses in area 17 of the visual cortex to stimulation of the lateral geniculate body and optic tract were studied in experiments on unanesthetized cats immobilized with D-tubocurarine. Of the neurons tested, 53.6% responded to stimulation of the lateral geniculate body. In 92% of these cells the responses were orthodromic with latent periods of between 2 and 12.5 msec. Most cells responded with latent periods of 2.0–2.5, 3.0–3.5, and 4.0–4.5 msec, corresponding to latent periods of the components of the electropositive wave of the primary response. Antidromic responses to stimulation of the lateral geniculate body were given by 8% of neurons. The difference between the latent periods of responses of the same visual cortical neurons to stimulation of the optic tract and lateral geniculate body was 0.1–1.8 msec, but for most neurons (55.8%) it was 0.5–1 msec. The histograms of response latencies of visual cortical neurons to stimulation of the above-mentioned formations were found to be similar. It is concluded that the optic radiation contains three principal groups of fibers with conduction velocities of 28.5–16.6, 11.7–8.9, and 7.4–6.0 m/sec, respectively.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 589–596, November–December, 1975.     

Role of interoceptive afferent excitation in sensory integration on neurons of the cat visual cortex

Experiments on cats immobilized with diplacin showed that stimulation of the vagus and splanchnic nerves had a significant effect on spontaneous unit activity in area 17 of the cortex. The unit responses most frequently observed were prolonged tonic changes in the discharge frequency. Complex phasic unit responses with stable inhibitory pauses and periods of activation occur less often. The development of phasic responses could begin either with a period of activation or with initial inhibition of activity. As a result of splanchnic nerve stimulation responses of predominantly excitatory type appeared. These also occurred more often in response to somatic stimulation. The degree of recruiting into the responses and the intensity of the responses themselves increased if a series of stimuli was applied to the nerves. The important role of the lateral hypothalamus and mesencephalic reticular formation in the mechanism of the visceral and somatic events observed on visual cortical neurons was demonstrated.Ivano-Frankovsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 361–368, July–August, 1977.     

Unit responses in the vagal lobe of the carp brain to stimulation of chemoreceptors of the skin,mouth, and gills

Experiments on curarized carp showed that neurons of the vagal lobe of the medulla respond to stimulation not only of the mouth and gills, but also of chemoreceptors of the skin of the head. The vagal lobe was shown to contain considerably fewer neurons responding selectively to stimulation of the skin than neurons responding to stimulation of the mouth or gills. Differences were found between responses of neurons to a natural food stimulus (extract from a fish food product) and to solutions of hydrochloric acid and common salt. The different roles of the vagal and facial lobes in the processing of impulsation from skin chemoreceptors is demonstrated.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 397–404, July–August, 1980.     

Unit responses of the first and second somatosensory cortical areas to peripheral,thalamic, and cortical stimulation

Unit responses of the first (SI) somatosensory area of the cortex to stimulation of the second somatosensory area (SII), the ventral posterior thalamic nucleus, and the contralateral forelimb, and also unit responses in SII evoked by stimulation of SI, the ventral posterior thalamic nucleus, and the contralateral forelimb were investigated in experiments on cats immobilized with D-tubocurarine or Myo-Relaxin (succinylcholine). The results showed a substantially higher percentage of neurons in SII than in SI which responded to an afferent stimulus by excitation brought about through two or more synaptic relays in the cortex. In response to cortical stimulation antidromic and orthodromic responses appeared in SI and SII neurons, confirming the presence of two-way cortico-cortical connections. In both SI and SII intracellular recording revealed in most cases PSPs of similar character and intensity, evoked by stimulation of the cortex and nucleus in the same neuron. Latent periods of orthodromic spike responses to stimulation of nucleus and cortex in 50.5% of SI neurons and 37.1% of SII neurons differed by less than 1.0 msec. In 19.6% of SI and 41.4% of SII neurons the latent period of response to cortical stimulation was 1.6–4.7 msec shorter than the latent period of the response evoked in the same neuron by stimulation of the nucleus. It is concluded from these results that impulses from SI play an important role in the afferent activation of SII neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 351–357, July–August, 1976.     

Unit responses in the auditory cortex to stimulation of geniculocortical fibers

Extracellular and intracellular single unit responses of neurons of the auditory cortex to electrical stimulation of geniculocortical fibers (GCF) were recorded in experiments on cats immobilized with tubocurarine. The latent period of responses of 15% of neurons to GCF stimulation was 0.3–1.5 msec. It is postulated that they were excited anti-dromically. The latent period of spikes generated by neurons responding to GCF stimulation orthodromically varied from 1.6 to 12 msec. In 28.6% of neurons the latent period was 1.6–2.5 msec. It is postulated that these neurons were excited monosynaptically. Intracellular recording revealed primary IPSPs in response to GCF stimulation in 63.3% of neurons, a brief EPSP followed by a prolonged IPSP in 17.7%, an EPSP-spike-IPSP complex in 12.3%, and subthreshold EPSPs in 7% of neurons. The latent period of the primary IPSPs varied from 1.8 to 11 msec, being 1.8–3.7 in 72%, 3.8–5.7 in 20.0%, and 5.8–11 msec in 8.0% of neurons. The latent period of responses beginning with an EPSP was 1–4 msec (mean 1.8 msec). Orthodromic responses arising 3–10 msec after the antidromic response, and consisting of 3–5 spikes, were recorded in some antidromically excited neurons. Hypotheses regarding the functional organization of the auditory cortex and mechanisms of inhibition in its neurons are put forward on the basis of the results obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 227–235, May–June, 1972.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Effect of stimulus intensity on unit responses in the cat frontal cortex

Unit activity of the frontal cortex during changes in stimulus intensity in the near-threshold range (15–16 dB above the threshold for the combined evoked potential) was investigated by an extracellular recording method in acute experiments on cats anesthetized with chloralose (70 mg/kg). Comparative analysis of unit responses in specific (SI) and nonspecific projection areas revealed basically similar changes in pattern during an increase in stimulus intensity: A decrease in the latent period, an increase in the total frequency and the phasic character of the discharge, and an increase in the probability of response. However, a relatively stable latent period and probability of response were observed in specific projection neurons for a stimulus intensity of 3–5 threshold units, whereas for the nonspecific projection neurons it was observed for a stimulus intensity of 10–15 threshold units. All sensory projections in the frontal cortex are formed by two inputs: short-latency low-threshold and long-latency high-threshold. Analysis of modality-dependent differences in the threshold of sensitivity and the latent period of response of the polysensory neurons suggests that stimuli of different modalities converge directly on cortical neurons.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 606–612, November–December, 1976.