Monosynaptic inhibitory postsynaptic potentials of cortical neurons

Monopolar intracortical stimulation of the auditory cortex was carried out in cats immobilized with D-tubocurarine. A macroelectrode (tip diameter 100 µ) or a microelectrode (tip diameter 10–15 µ) was used for stimulation. In both cases, besides excitatory responses, primary IPSPs with latent periods of 0.4–1.2 and 1.4–6.0 msec were recorded in cortical neurons close to the point of stimulation. The first group of IPSPs are considered to be generated in response to direct stimulation of bodies or axons of inhibitory cortical neurons, i.e., monosynaptically. The amplitude of these IPSPs varied in different neurons from 3 to 15 mV, and their duration from 4 to 150 msec. Additional later inhibitory responses were superposed on many of them. Of the IPSPs generated in auditory cortical neurons in response to stimulation of geniculocortical fibers 1.5% had a latency of 0.8–1.3 msec. They also are assumed to be monosynaptic. It is concluded that the duration of synaptic delay of IPSPs in cortical neurons and spinal motoneurons is the same, namely 0.3–0.4 msec. Axons of auditory cortical inhibitory neurons may be 1.5 mm long. The velocity of impulse conduction along these axons is 1.6–2.8 m/sec. The genesis of some special features of IPSPs of cortical neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 458–467, September–October, 1975.     

Potentiation of postsynaptic potentials in motoneurons of the frog,Rana ridibunda, by gallamine

The potentiating effect of gallamine on postsynaptic potentials was studied intracellularly on the preparation of the isolated spinal cord of the frog,Rana ridibunda. The amplitude both of afferentPSP (stimulation of DR) and of descendingPSP (stimulation of LC and VC) increased to 200–600% of the initial value. The responses reached 20 mV, and a convulsive effect developed. Both early (mono- and disynaptic) and late components were considerably potentiated. New components, absent prior to the gallamine application, appeared. Responses to a shortterm application of glutamate were potentiated much less than PSP in the same cell. NMDAresponses were not potentiated. Brain treatment with EAA blockers showed that potentiation and convulsive effect might appear under conditions of blockage of NMDA receptors but not under conditions of blockage of non-NMDA receptors. Gallamine eliminated inhibition evoked by the agents that block EAA. After gallamine application the duration of antidromic and orthodromic AP did not change substantially, while after-depolarization increased considerably, which resulted in generation of 2-3 AP in response to a single stimulus. A competitive blocker of cholinergic transmission, d-tubocurarine, did not potentiate PSP but increased synaptic noise. Mechanisms of gallamine action are discussed.     

Effect of inhibitory amino acid antagonists on postsynaptic potentials of motoneurons of the frog Rana ridibunda

On preparations of the isolated spinal cord of the frog Rana ridibunda at intracellular recording from lumbar motoneurons, it is shown that response to the 10 mM GABA application decreased selectively by 40.7 ± 23.7% (n = 6) as a result of the spinal cord treatment with bicuculline (100–150 μM), while response to the Gly application decreased selectively by 50.7 ± 17.8% (n = 10) after the spinal cord treatment with strychnine (5–10 μM). Both strychnine and bicuculline produced potentiation of EPSP by amplitude and duration as well as paroxysmal depolarizational shifts (PDS). Strychnine produced more effectively the potentiation, while bicuculline—PDS. The inhibitory Gly effect decreased significantly the DR and RF EPSP (a decrease of amplitude and duration) as a result of the spinal cord treatment with strychnine (5–10 μM), but not with bicuculline. The inhibitory GABA effect on the DR and RF EPSP decreased as a result of the spinal cord treatment with bicuculline only in a half of the studied motoneurons and to the lesser degree than the inhibitory Gly effect on the same EPSP at the strychnine treatment. Based of the obtained data, it is suggested that the inhibitory effects on the excitatory inputs of the motoneuron in the frog are expressed weaker than in mammals and are related predominantly to the GABA and Gly effects on receptors of interneurons. It is suggested that GABA specifically acts mostly on GABA_A receptors, whereas Gly—on Gly receptors, although there is some part of cross-inhibition. Original Russian Text ? G. G. Kurchavyi, N. I. Kalinina, and N. P. Vesselkin, 2006, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2006, Vol. 42, No. 5, pp. 463–471. The present work is a continuation of the work [1].     

Rubrofugal influences on unit activity in the medial reticulospinal tract

Neurophysiology - The influence of the red nucleus on activity in various groups of fibers of the medial reticulospinal tract was investigated in cats anesthetized with chloralose and...     

猫中·间脑结合部神经元与眼球下斜肌运动神经元的直接突触联系

本文应用神经元自发放电触发的迭加平均法,研究了猫中·间脑结合部内侧区神经元与眼球下斜肌运动神经元（inferiorobliquemotoneurons,IOMNs）之间的突触联系。电刺激同侧或对侧中·间脑结合部的Forel'sfieldeH（FFH）的内侧区（A7～Ag）,在IOMN池内记录到兴奋性单突触电场电位。应用FFH神经元的自发放电作为触发信号,将此放电引起的IOMNs的电位变化进行迭加平均,结果亦获得一兴奋性单突触电场电位。这些结果表明,中·间脑结合部内侧区神经元与IOMNs之间存在兴奋性单突触联系,其作用为启动眼球的垂直运动。     

Inhibitory miniature synaptic potentials in rat motoneurons

In the newborn rat spinal cord, spontaneous potentials were recorded, with KCl electrodes, from motoneurons in the presence of tetrodotoxin (10(-6) g ml-1) to abolish nerve impulses. These potentials occurred at low frequencies (less than 2 Hz), and their mean amplitude was a fraction of 1 mV. An increase of osmolarity with sucrose or an increase of extracellular K+, increased the frequency of miniature synaptic potentials. The amplitude of the spontaneous potentials was increased by intracellular injection of Cl-. Strychnine (2-25 microM) completely abolished the spontaneous potentials. It is suggested that these potentials are produced by the spontaneous release of packages of inhibitory transmitter at synapses on motoneurons.     

Corticofugal influences on reticulospinal neurons of the gigantocellular nucleus in cats

It was shown by intracellular recording that stimulation of the motor cortex evokes E PS Ps and I PS Ps in reticulospinal neurons of the gigantocellular nucleus of the cat medulla. The E PS Ps appeared in 94.3% and the I PS Ps in 5.7% of neurons tested. Analysis of the presynaptic pathway showed that 77.4% of E PS Ps studied arose through monosynaptic, and 22.6% through polysynaptic corticoreticular connections. By their latent period, duration, and rise time up to a maximum the monosynaptic E PS Ps were divided into two groups: "fast" and "slow." It is postulated that "fast" E PS Ps are generated in reticulospinal neurons which are activated by fast-conducting fibers and "slow" E PS Ps by slowly conducting corticobulbar fibers. I PS Ps were recorded from reticulospinal neurons that also were inhibited by stimulation of the ventral columns of the spinal cord. The hypothesis is put forward that cortical motor signals in cats can be transmitted to the spinal cord via monosynaptic and polysynaptic connections of "fast" and "slow" pyramidal neurons with reticulospinal neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 250–257, May–June, 1976.     

Analysis of the processes of summation of postsynaptic potentials on the membrane of motoneurons upon realization of the stretch reflex

Stretching of the m. triceps surae (TS) of decerebrated cats evokes reflex shifts of the membrane potential (MP) in spinal motoneurons resulting from summation of EPSPs. We carried out model analysis of summation of a great number of EPSPs and compared the respective results with changes in the MP observed in real experiments using intrasomatic microelectrode recording. Simulation was based on the supposition of the proximity of the time course of an excitatory postsynaptic current to the positive part of the EPSP derivative. Transformation of EPSPs was performed using low-frequency filtration with two values of the time constant, 7 and 20 msec, (models M1 and M2, respectively). The models obtained provided sufficiently adequate reflection of the ascending phase of the real EPSP but inadequately reflected the rate of its decline and slow components of the MP changes. The disagreement of simulations with the real MP shifts shows that, most probably, final postsynaptic effects are to a considerable extent provided by summation of a great number of EPSPs generated in distal dendrites, and EPSPs immediately recorded in trasomatically cannot provide one with adequate information on the entire pattern of natural synaptic activation of the neuron. In addition, simulation analysis demonstrated a high probability of the contribution of active inhibitory processes to the formation of resulting MP changes under conditions of the stretch reflex. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 260–263, May–June, 2008.     

Synaptic processes in thoracic motoneurons evoked by visceral impulses

Synaptic processes in various functional groups of thoracic motoneurons (segments T9–T11) were investigated in anesthetized (chloralose and Nembutal), decerebrate, and spinal cats. Visceral stimulation in animals with an intact CNS during artificial respiration evokes the development of primary (latent period under 12 msec) and secondary (latent period over 30 msec) PSPs in the motoneurons. The primary PSPs consist of early and principal components. The early component is due to excitation of group A₂ and A visceral afferents, the principal PSP to excitation of the A group. The principal component in motoneurons of the internal and external intercostal muscles and abdominal muscles is excitatory, while in motoneurons innervating the spinal muscles it is excitatory—inhibitory or inhibitory. The secondary PSPs as a rule are excitatory and are due to activation of fibers of the A group. During natural respiration the primary PSPs of motoneurons of the intercostal muscles and abdominal muscles are predominantly inhibitory. In spinal animals no secondary responses are present and the primary becomes entirely excitatory regardless of the functional class of the motoneurons. The mechanisms of reciprocal activation of thoracic motoneurons by visceral impulses in animals during artificial and natural respiration are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 286–295, May–June, 1972.     

Reticulospinal and propriospinal monosynaptic influences on motoneurons in frogs

Monosynaptic effects evoked by electrical stimulation of suprasegmental structures and the ventral and lateral columns were recorded intracellularly from motoneurons of the lumbar and cervical enlargements after isolation of the spinal cord and medulla in frogs. Reticulospinal fibers arising from cells of the medial reticular formation of the medulla and running in the ventro-lateral columns evoke monosynaptic excitation of cervical and lumbar motoneurons. The reticulo-motoneuronal E PSPs do not exceed 2–3 mV in amplitude and do not reach the threshold for action potential generation. Division of the spinal cord and interaction between all synaptic inputs tested in chronic experiments showed that monosynaptic E PSPs evoked by direct stimulation of the ventral and lateral columns are due to activation of the descending system of propriospinal fibers. By transmembrane polarization experiments the equilibrium potentials of the reticulo-motoneuronal and propriospinal monosynaptic E PSPs could be determined.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 164–173, March–April, 1973.     

Cortico-pyramidal and cortico-extrapyramidal synaptic influences on lumbar motoneurons in monkeys

Postsynaptic potentials evoked by stimulation of the motor cortex or pyramids before and after acute pyramidotomy were investigated in the lumbar motoneurons of monkeys. In response to activation of fibers of the pyramidal tract monosynaptic EPSPs predominated in motoneurons innervating the distal muscles of the hind limbs. Monosynaptic EPSPs in the motoneurons of the distal muscles had a significantly higher amplitude and could be evoked by weaker stimuli than EPSPs in the motoneurons of the proximal muscles. Cortico-motoneuronal EPSPs in the motoneurons of the distal muscles had a less marked frequency potentiation than EPSPs with monosynaptic segmental delay in the motoneurons of the proximal muscles. Cortico-extrapyramidal synaptic responses appeared in the pyramidotomized monkeys during intensive repetitive stimulation of the motor cortex in motoneurons of both distal and proximal muscles. These effects, transmitted by descending projections of the brain stem, may be responsible for the partial preservation of cortical motor control after pyramidotomy.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 587–596, November–December, 1972.     

Changes in postsynaptic responses in spinal motoneurons during repetitive stimulation of the locus coeruleus

Experiments on cats anesthetized with chloralose showed that repetitive stimulation of the locus coeruleus is accompanied by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons. The effect appeared 600 msec after the beginning of stimulation and reached its maximum after 1500–2000 msec. Repetitive stimulation of the locus coeruleus did not change the membrane potential and did not affect EPSPs or IPSPs evoked by stimulation of low-threshold muscle afferents; EPSPs due to activation of high-threshold cutaneous and muscle afferents likewise remained unchanged. Repetitive stimulation of more central regions of the brain stem was accompanied not only by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons, but also by a decrease in amplitude of EPSPs arising in response to stimulation of these same afferents in flexor motoneurons. These effects were not connected with activation of monoaminergic structures, for unlike effects arising during stimulation of the locus coeruleus, they were also found in previously reserpinized animals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 51–59, January–February, 1982.     

Effectiveness of ascending synaptic influences from various spinal funiculi on reticulospinal neurons in cats

Activity of reticulospinal neurons evoked by stimulation of the ventral, ventrolateral, dorsolateral, and dorsal funiculi of the spinal cord was recorded extracellularly in cats anesthetized with chloralose. Responses of 57 reticulospinal neurons, of which 22 projected into the ventral funiculus, 20 into the ventrolateral, and 15 into the dorsolateral, were studied. The functional properties (conduction velocity and refractory period) and the location of the neurons of the above-mentioned groups in the medulla did not differ appreciably. The most effective synaptic activation of all neurons was observed during stimulation of the dorsal and dorsolateral funiculi. Responses to stimulation of the dorsal funiculus had the lowest threshold. These responses arose in reticulospinal neurons of the ventral and ventrolateral funiculi after the shortest latent period. The effectiveness of synaptic influences from the dorsal and dorsolateral funiculi was identical in the group of neurons of the dorsolateral funiculus. Correlation between activity evoked by stimulation of the dorsal funiculus in reticulospinal neurons and peripheral nerves indicated that the responses appeared in these cells to stimulation of muscular (groups I and II) and cutaneous (group II) afferent fibers. The results indicate that impulses from low-threshold muscular and cutaneous afferents, which effectively activate reticulospinal neurons, are transmitted along ascending pathways of the dorsal funiculi.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 254–263, May–June, 1979.     

Antidromic action potentials in spinal motoneurons of the chick embryo

Antidromic action potentials of hind-limb motoneurons were studied in a preparation of the isolated perfused spinal cord of a chick embryo by a microelectrode recording technique. Most cells suffered appreciable damage when the microelectrode was introduced into them, but their functional characteristics recovered to some extent. From the 11th through the 18th day of embryonic development the amplitude and rise time of action potentials and the presence of components in them reflecting activation of the initial segment of the axon and the soma-dendritic membrane, and also values of resting potential of motoneurons after recovery revealed no age-dependent changes and were similar to the corresponding characteristics of motoneurons in adult birds and mammals. Meanwhile the conduction velocity along motor axons increased from 0.3–0.5 m/sec on the 10th day to 2–4 m/sec on the 18th day of embryonic development. Contrary to the view that mechanisms of action potential generation arise late in the course of ontogenetic development of warm-blooded animals, in the postnatal period, the results indicate that in fact they are formed quite early, in agreement with the concept of phylogenetic antiquity of this mechanism and also with data obtained on various preparations of the developing CNSin vitro.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 70–77, January–February, 1985.     

Suppression of postsynaptic response in trigeminal motoneurons by stimulating the midbrain central gray matter

The effects of stimulating the midbrain central gray matter (CGM) on motoneuronal response in trigeminal nerves were investigated in anesthetized cat. It was found that stimulating the CGM did not induce postsynaptic response in these motoneurones. Conditioning stimulation of the CGM brought about suppression of motoneuronal postsynaptic response to stimulation of tooth pulp and high threshold infraorbital nerve afferents without affecting motoneuronal antidromic response and jaw-opening reflex as induced by stimulating the caudal nucleus of the spinal trigeminal tract. It was thus concluded that stimulating the CGM exerts no direct effect on motoneurons but does have an influence on postsynaptic response — a result of modulation of the afferent spike flow at interneuronal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 543–549, July–August, 1990.     

Thyrotropin-releasing hormone mimics descending slow synaptic potentials in rat spinal motoneurons

Thyrotropin-releasing hormone (TRH) produced a depolarization in lumbar motoneurons of neonatal rats. The depolarization by TRH persisted after extracellular Ca2+ was replaced by Mg2+ or Mn2+, indicating its direct action upon motoneurons. Stimulation of the ventral descending tract at the lower thoracic segment evoked slow excitatory postsynaptic potentials (e.p.s.ps) lasting 20-30 s in every motoneuron. Both the TRH-induced depolarization and descending slow e.p.s.p. were accompanied by a decrease in input conductance of motoneurons. When the membrane potential of the motoneuron was shifted, both the TRH-induced depolarization and slow e.p.s.p. became larger in amplitude during depolarization and smaller during hyperpolarization. However, they could not be reversed in polarity by hyperpolarization. During the depolarization of motoneuron produced by TRH application, the slow e.p.s.p. was markedly reduced in amplitude, suggesting the involvement of identical ionic mechanisms in the two responses. After incubation of the isolated spinal cord with antisera to TRH, the depolarizing response produced by TRH as well as the descending slow e.p.s.p. was greatly diminished. In contrast, monosynaptic reflexes evoked by dorsal root stimulation remained unchanged under this condition. These results suggest that TRH serves as a neurotransmitter mediating the descending slow e.p.s.p. in motoneurons.     

Inhibitory postsynaptic potentials carry synchronized frequency information in active cortical networks

Temporal precision in spike timing is important in cortical function, interactions, and plasticity. We found that, during periods of recurrent network activity (UP states), cortical pyramidal cells in vivo and in vitro receive strong barrages of both excitatory and inhibitory postsynaptic potentials, with the inhibitory potentials showing much higher power at all frequencies above approximately 10 Hz and more synchrony between nearby neurons. Fast-spiking inhibitory interneurons discharged strongly in relation to higher-frequency oscillations in the field potential in vivo and possess membrane, synaptic, and action potential properties that are advantageous for transmission of higher-frequency activity. Intracellular injection of synaptic conductances having the characteristics of the recorded EPSPs and IPSPs reveal that IPSPs are important in controlling the timing and probability of action potential generation in pyramidal cells. Our results support the hypothesis that inhibitory networks are largely responsible for the dissemination of higher-frequency activity in cortex.