Increase in the efficacy of synapses between parallel fibers and Purkinje cells after joint stimulation of climbing and parallel fibers in the frog

A study was made of the susceptibility of Purkinje cells to long-term plasticity changes produced by joint stimulation of two inputs: the parallel and the climbing fibers. Experiments were conducted on a preparation of isolated frog cerebellum, joined to the medulla by one peduncle. A total of 18 neurons were investigated which showed a monosynaptic response to stimulation of the parallel fibers and maintained stable background activity over a 2 h period. Curves were plotted throughout this time for the likelihood of a reaction occurring in Purkinje cells in response to stimulation of the parallel fibers. Level of current required to stimulate a Purkinje cell firing index of 0.5 (I_0.5) was calculated. Neurons in which compound response to the "climber" type had been produced by stimulating the medulla showed a I_0.5 of 0.7 (less than one unit) at the start and finish of experiments, which would suggest an increase in the efficacy of the synapses of parallel fibers in Purkinje cells when parallel and climbing fibers are stimulated simultaneously.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 156–164, March–April, 1987.     

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.     

Electrophysiological investigation of medullary neurons connected with lateral line organs of the catfish (Ictalurus nebulosus)

Unit responses in the acoustic-lateral region of the medulla to electrical and mechanical stimulation of the lateral line organs were investigated in acute experiments on curarized catfish. Of the total number of neurons 70% possessed spontaneous activity. An electrical stimulus evoked a tonic response both in spontaneously active and in "silent" cells. Three main types of firing pattern of the neurons were distinguished: fast-adapting, slow-adapting, and grouped. As regards the relation of the neurons to polarity of the stimulus they were subdivided into two groups. The thresholds of unit responses to electrical stimulation varied considerably: from 2.5·10^–9 to 5·10^–12 A/mm². The effect of intensity of the electrical stimulation on unit responses in the medulla is analyzed. The precise dependence of on- and off-responses of each neuron on stimulus intensity of any polarity was determined. The neurons were shown to be sensitive to both electrical and mechanical stimuli. It is postulated that this phenomenon is due to convergence of impulses from electrical and mechanical receptors of the lateral line on the neurons. The properties of the central neurons are compared with those of the peripheral electroreceptor system in catfish.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 156–163, March–April, 1973.     

Localization and properties of reticulospinal neurons with axons descending in the dorsolateral parts of the lateral funiculi

The localization of reticulospinal neurons responding antidromically to stimulation of fibers in the dorsolateral parts of the lateral funiculi (shown previously to be the principal collector of fibers conveying bulbar pressor influences) was determined in experiments on anesthetized and curarized cats. Most of these neurons were found to occupy the medioventral portions of the medulla, but they were concentrated in the rostral portions of the gigantocellular and ventral nuclei of the reticular formation. The velocity of conduction of excitation along axons of most reticulospinal neurons was 10–50 m/sec. Reflex responses to stimulation of the sciatic nerve with a latent period of 10–40 msec were found in 35 of 125 such cells. Stimulation of the sinus nerve did not activate them. Spontaneous activity occurred in 29 reticulospinal neurons; the mean firing rate of the various cells varied from 5 to 20/sec.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 6, No. 3, pp. 266–272, May–June, 1974.     

Effect of a polarizing current on unit activity in the respiratory center

Single unit activity in the respiratory center in the medulla was recorded in rabbits anesthetized with urethane. The neurons were polarized through the extracellular recording microelectrode by currents of different strength and polarity. In most cases a current in the positive direction (+ to the electrode tip) increased, while a negative current decreased, the firing rate. Most indices of the firing pattern of the respiratory neurons were changed by the action of the polarizing current. The coefficient of phase shift between the pneumogram and unit activity, determined by calculating the cross-correlation function between these two processes, was the most stable index. Since it takes into account the temporal and frequency characteristics of volley activity of the respiratory neurons, this coefficient can serve as a basis for their classification. The dynamics of respiratory neuronal function under subthreshold conditions was revealed by the polarization method. It was shown, in particular, that the shape of the variable component of respiratory unit activity is close to sinusoidal and differs from that suggested by the hypothesis of reciprocal interaction between two groups of neurons.Rostov State University, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 280–285, May–June, 1972.     

Modulation of neuron activity of the midbrain periaqueductal gray matter influenced by monoaminergic brainstem structures

A study was done on base activity and changes in base activity (BA) of neurons in periaqueductal gray matter (PAG) during stimulation of monoaminergic structures of the brainstem: the nucleus raphe magnus (NRM), the locus coeruleus (LC), and the substantia nigra (SN), in rats anesthetized with hexenal (200 mg/kg). Three types of PAG neurons that differed in BA structure were identified. NRM, LC and SN stimulation changed BA only in type III neurons. Stimulation of these structures evoked an increase in BA frequency in 11.0–14.5%, and inhibition in 31.0–47.5% of type III neurons. Simultaneous stimulation of two structures led to a marked drop in intensity of effects. A depressing effect on BA was always detected if stimulation of one of the structures suppressed BA. Stimulation of two structures, with one being the NRM, was most effective. The role of PAG in the organization of the brain-stem component of the antinociceptive mechanism is discussed.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 52–60, January–February, 1992.     

Interaction between central and peripheral temperature signals on temperature-sensitive hypothalamic neurons

Changes in the mean firing rate of posterior hypothalamic neurons were studied in experiments on unanesthetized cats in response to elevation of the brain temperature by 0.7–1.5°C and the skin temperature by 3–5°C separately or simultaneously. Altogether 85 neurons were studied in 14 animals: 11 responded to only one form of temperature stimulation, whereas in 16 neurons changes in the firing pattern (in most cases in the same direction) were observed in response to both forms of temperature stimulation. Different types of responses of these neurons were established. Sensitivity to the central temperature stimulus was increased in some neurons of this group when skin temperature stimulation was intensified.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 613–619, November–December, 1976.     

Modulatory Inputs on Sympathetic Neurons in the Rostral Ventrolateral Medulla in the Rat

1. The first part of this study looks at spontaneously active neurons located in the rostral ventrolateral medulla (RVLM) with projections to the thoracic spinal cord. Sixteen neurons were intracellularly recorded in vivo. Four out of 16 neurons were antidromically activated from the thoracic spinal cord (axonal conduction velocities varied from 1.8 m/s to 9.5 m/s).2. The simultaneous averages of the neuronal membrane potential and arterial blood pressure triggered by the pulsatile arterial wave or the EKG-R wave demonstrated changes in membrane potential (hyperpolarization or depolarization) locked to the cardiac cycle in four neurons in this group. These neurons (three of them bulbospinal) were further tested for barosensitivity by characterizing the responses to electrical stimulation of the aortic depressor nerve. Four neurons responded with inhibitory hyperpolarizing responses characterized as inhibitory postsynaptic potentials (IPSP) to aortic nerve stimulation (onset latency: 32.3 ± 5.0 ms; mean ± SEM).3. In two neurons in the RVLM, one of them characterized as barosensitive, electrical stimulation of the opposite RVLM (0.5 Hz, 1.0 ms pulse duration, 25–100 A) elicited excitatory postsynaptic potentials (EPSPs) with latencies of 9.07 and 10.5 ms. At resting membrane potential, the onset latency of the evoked EPSPs did not change with increasing stimulus intensities. Some of the recorded neurons were intracellularly labelled with biocytin for visualization. They were found in the RVLM.4. These experiments in vivo would support the idea of a functional commissural pathway between the RVLM of both sides.5. Anatomical data have shown that some of those commissural bundle fibers originate in the C1 adrenergic neuronal group in the RVLM. In the second part of this study, we used an intracellular recording technique in vitro to investigate the effects of the indirect adrenergic agonist tyramine on neurons in the RVLM with electrophysiological properties similar to premotor sympathetic neurons in vivo.6. Tyramine (0.5–1 mM) produced a pronounced inhibitory effect with hyperpolarization and increase in membrane input resistance on two neurons characterized as regularly firing (R), and on one neuron characterized as irregularly firing (I). This effect was preceded by a transient depolarization with increases in firing rate.7. These results would indicate that neurons in the RVLM recorded in vitro and with properties similar to premotor sympathetic neurons can be modulated by catecholamines released from terminals probably making synaptic contacts.     

Conditions and character of synchronization of the electrical activity of two neurons by means of the electrical field produced by these neurons

Isolated stretch receptors of crayfish were investigated by intracellular recording of the electrical activity from the body of the fast or slowly adapting neuron and extracellular recording from the nerve trunk. An increase of activity of one neuron during the plateau of the prolonged action potential (PAP) of another was observed both in the fast and slowly adapting neurons regardless of whether the PAP was formed under the effect of strychnine, novocain, or as a result of the body membrane, or was evoked by orthodromic or antidromic stimulation. In the case of relative equalization of the frequency of the rhythmic activity of the slowly and fast adapting neurons there is a transition from an increase in the firing rate of the fast adapting neuron during the plateau of the PAP of the slowly adapting neuron to complete synchronization of their activity; not only the PAP of one neuron and one or several impulses of another, but also the PAP of both neurons can be synchronized. It is suggested that the relation of the activity of two neurons is due to the effect of the electrical field produced during the PAP. The role of the similarity of the functional state of neurons of an epileptogenic focus in the possible synchronizing action of the electrical field produced by them is examined.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 321–328, May–June, 1970.     

Unit activity of the thalamic associative nuclei in response to peripheral stimulation of different modalities

Responses of 252 neurons of the mediodorsal nucleus (MD) and 329 cells of the pulvinar-posterolateral complex (Pulv-LP) of the thalamus to single and combined stimulation of peripheral receptor systems (visual, auditory, and somatosensory) were investigated in acute experiments on cats anesthetized with a mixture of pentobarbital and chloralose. Three types of responses of these thalamic units to peripheral stimulation were distinguished: quickening of spontaneous activity (Pulv-LP 32.0, MD 20.6%), inhibition (Pulv-LP 21.0, MD 24.2%), and mixed (Pulv-8.8, LP MD 4.0%). No response was found in 37.4% of Pulv-LP neurons and 51.2% of MD neurons. Besides definite similarity in the organization of the two structures, Pulv-LP and MD also had differences. Responses of the neurons to stimulation of peripheral receptors were divided into three groups on the basis of the duration of their latent period: short (under 20 msec), average (21–40 msec), and long (over 41 msec) latent periods. The second group was the largest.Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 469–477, September–October, 1978.     

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.     

Role of the midbrain periaqueductal gray matter in conditioned reflexes

Unit activity in the midbrain periaqueductal gray matter (PGM) during an instrumental placing reflex, its extinction, differentiation, and conditioned inhibition, was studied in chronic experiments on cats. Spike responses 1–2 sec in duration in 69 (36.7%) of 182 neurons preceded by 400–800 msec the beginning of conditioned-reflex and voluntary intertrial movements. These advanced responses appeared 200 msec before the corresponding advance responses of motor cortical neurons. Fifty-eight neurons (30.9%) responded directly to acoustic stimulation with a latent period of 10–50 msec for 2–6 sec, 19 neurons (10.1%) generated double responses, linked with both the acoustic stimulus and subsequent conditioned-reflex movement, and 42 neurons (22.3%) did not respond to acoustic stimulation, although individual neurons of this group changed the level of their spontaneous activity in response to repeated conditioned stimulation, and this change was maintained for some tens of minutes. Extinction, differentiation, and conditioned inhibition all abolished conditioned-reflex movements, but each type of internal inhibition was accompanied by its own characteristic changes in the firing pattern of PGM neurons. Functional independence of neurons of the first and second groups was demonstrated during extinction and recovery of the conditioned-reflex. The results indicate the important role of PGM not only in the mechanism of the conditioned reflex, but also in the development of its internal inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 403–419, May–June, 1984.     

Polyfunctional character of responses of single neurons of the visual cortex of wakeful rats to light flashes

The activity of single neurons of the visual cortex in the initial state and upon presentation of a certain program of stimuli, which included a series of modality-specific (light flashes, continuous light) and nonspecific (clicks, tone) stimuli used separately and in combination, was recorded extracellularly by glass electrodes in unanesthetized and uncurarized white rats restrained in a stall. The responses of the neurons to flashes and clicks were analyzed by the poststimulus histogram method. The regular shifts of neuronal activity in response to light flashes (with a frequency of one per second) in the form of an increase or decrease of firing rate were noted not only during the first 150–200 msec (short-latent responses — SLR) but also later, after 700–800 msec (long-latent responses — LLR). The LLR differed from the SLR also by greater variability (decrease or increase upon repeating the stimuli) and by pronounced interaction with the modality-nonspecific stimuli, which had a weak effect on the SLR and by themselves very rarely evoked responses of the visual cortex neurons. The neuron could demonstrate several LLR with a different latent period. The independent nature of each LLR was indicated by the relative independence of its dynamics. All these data permit the consideration that one and the same neuron in one cycle of its activity can be included in different functional systems of the brain, which evidently provide direct reception of information arriving over specific sensory conductors and its subsequent processing. Therefore, neurons, which made up more than half of those investigated, can be regarded as polyfunctional.N. I. Grashchekov Laboratory of Problems of Controlling Functions in Man and Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 242–250, May–June, 1970.     

Effect of somatostatin on neurons of the partially deafferented rabbit amygdala

Changes in spontaneous activity of 291 neurons in the rabbit amygdala were analyzed during microelectrophoretic application of somatostatin under pentobarbital anesthesia. Somatostatin was found both to enhance and to inhibit the spontaneous activity of these cells, by contrast with the exclusively inhibitory effect on spontaneous activity of hypothalamic neurons described previously. After partial chronic deafferentiation of the amygdala, 76% of 103 neurons responded to somatostatin application; 90% of the responding cells, in which the initial spontaneous firing rate was 6–20 spikes/sec, responded by more rapid firing, and only 10% of neurons (with an initial spontaneous discharge frequency of over 20 spikes/sec) showed a decrease in firing rate. Neuronal responses in the amygdala to somatostatin, glutamate, and noradrenalin are compared. Preliminary application of noradrenalin caused an increase in the number of inhibitory responses on subsequent application of somatostatin to the same cell.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 601–607, November–December, 1982.     

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.     

Effects of experimentally induced deficiency of catecholaminergic transmission on neuronal activity in the ventrolateral thalamic nucleus

Background activity was investigated in 272 neurons of the ventrolateral thalamic nucleus (VLTN) before and after systemic administration of neuroleptics (haloperidol and droperidol) at cataleptic doses by means of extracellular techniques during chronic experiments on cats. Autocorrelation and spectral analysis revealed regularly-occurring changes in the background activity rate of VLTN neurons, the periodicity of which changed by fractions of seconds (0.2–0.8 sec), seconds (1.5–10 sec), or tens of seconds (12–30 sec). While numbers of neurons with individual types of periodic activity did not exceed 6–8% in intact animals, it did increase to 18–30% after administering neuroleptics. Raised numbers of neurons with two types of regularly occurring processes within a single spike train were also noted. Experimentally-produced data were compared with findings from clinical observations. Quantities of neurons with different variations in the periodicity of their firing activity reached 19–46% in patients with parkinsonism but did not exceed 4–8% in those with torsion dystonia. The genesis of raised rhythmic firing in thalamic neurons occurring with parkinsonism is thought to be associated with impaired catecholaminergic (both dopaminergic and -adrenergic) transmission.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 359–368, May–June, 1990.     

Analysis of spike discharge and character of interconnection of identified output neurons in the rat neostriatum

Two populations of neostriatal neurons projecting into the globus pallidus and two neuron populations projecting into the substantia nigra were identified by antidromic testing in acute experiments on immobilized rats. Statistical analysis showed that the firing patterns of the identified output neurons were of either the grouped or single type. Cross-correlation analysis of the spontaneous activity of two neurons, one projecting into the substantia nigra, the other into the globus pallidus, showed that activity of the second neuron was inhibited for 300–400 msec after spike generation by the first neuron.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Computer Research Center, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 470–475, September–October, 1982.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Neocortex neuron reactions caused by stimulation of the substantia innominata in cats

We investigated neuronal impulse activity in the sensorimotor cortex after substantia innominata (SI) stimulation in cats during the execution of an instrumental conditioned response consisting of placement of a paw on a pedal coupled with alimentary reinforcement. Stimulation of the SI was initiated 1 or 3 sec prior to conditioned stimulation. Background activity of the neurons was inhibited during stimulation of the SI. Preliminary stimulation of the SI one second in advance caused an increase of reactions linked to a subsequent conditioned stimulus and a conditioned-response movement in 32% of the neurons; a 3-sec lead caused increases of such reactions in 33% of neurons. In some cells which originally did not react to the conditioned excitation, a clear reaction did manifest after stimulation. Moreover, stimulation of the SI with a 1-sec lead caused inhibition of impulse reactions in 6% of the cells; with a 3-sec lead, it caused inhibition of impulse reactions in 33% of the cells. The spread of latencies of conditioned-response actions decreased 2- to 3-fold in this case. We discuss the possibility that acetylcholine, which is released by the terminals of cholinergic neurons of the SI, has a facilitating influence on the impulse activity of neocortical neruons.Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 11–20, January–February, 1992.     

Frequency potentiation of synaptic response in medial bulbar tegmental neurons to microstimulation of the pontine inhibitory site

Synaptic response to single (2 Hz) and regular (30–50 Hz) stimuli applied to the pontine inhibitory site were recorded in decerebrate cats. A change to regular stimulation was usually accompanied by a rise in the firing index of synaptic discharges and raised amplitude of inhibitory and (to a lesser extent) excitatory postsynaptic potentials. Suppression of background spike activity was observed in some neurons. It was deduced that frequency potentiation makes a considerable contribution to the functional effect of stimulating the inhibitory site, i.e., terminating evoked locomotion.Institute for Information Transmission Studies, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 172–180, March–April, 1988.