Ultrastructural changes in synapses of cortical neurons following combined applications of glutamate and noradrenaline

The dimensions of postsynaptic densities (PSD) of axodendritic synapses in the sensorimotor region of the rat neocortex were determined following multiple paired microiontophoretic applications of L-glutamate (Gl) and noradrenaline (NA) using electron microscopy. It was established that combined applications of Gl and NA induce a statistically significant increase in the thickness of the PSD. In this case, the intensity of the structural changes depends on the delay time (within the range of 0–5 sec) of NA action in relation to Gl. The strongest modification in PSD was observed whenever the second neurochemical signal was received at the amount of cessation of the neuronal response to the action of the first transmitter.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 5–10, January–February, 1993.     

Pharmacological study of inhibited frog olfactory bulb glomerular input produced by a puff of air on the olfactory mucosa

The effects of applying 4-aminopyridine (10^–2 M), aminooxyacetic acid (AOAA — 10^–4–10^–3 M), -alanine (10^–3–10^–2 M), and bicuculline (10^–5, 10^–4 M) to the intact frog olfactory bulb were investigated. Having measured inhibition of orthodromic potential postsynaptic components produced either by a puff of air on the olfactory mucosa (OB input inhibition) or by single electrical stimulation of the olfactory nerve (postsynaptic inhibition) or by single electrical stimulation of the olfactory nerve (postsynaptic inhibition), it was found that 4-aminopyridine greatly intensified postsynaptic inhibition but strongly reduced that of OB input; inhibition of the latter was raised by AOAA or bicuculline and decreased by -alanine. These substances failed to exert any consistent, clear-cut effects on postsynaptic inhibition. Findings would support the hypothesis that OB input inhibition produced by a puff of air on the olfactory mucosa could occur as a result of GABA release from glial cells and subsequent binding of GABA to presynaptic GABA_B-receptors in glomeruli.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 12–20, January–February, 1987.     

Action of thiamine on different synapses

Thiamine at a concentration of 1×10^–14 to 1×10^–4 M facilitated neuromuscular transmission at the glutaminergic synapse of the crayfish adapter, manifesting as increased amplitude and quantal content of excitatory postsynaptic potentials and raised frequency of miniature excitatory postsynaptic potentials. Thiamine augmented spontaneous electrical activity and the amplitude of synaptic potentials in the longitudinal muscle of guinea pig taenia coli. It was found from studying the effects of thiamine on the membrane potential of rat brain synaptosomes that its presynaptic action is brought about by depolarization of the nerve terminal membrane. Interaction between thiamine and the nerve endings was described by a Hill coefficient of 0.22–0.30, indicating that it has several binding sites within the structure of the receptor concerned.A. V. Palladin Institute of Biochemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 621–629, September–October, 1986.     

Desensitization of choline receptors of somatic membrane command neurons in the snail

Desensitization of somatic membrane receptors to rhythmic application of acetylcholine was studied in command neurons PPa2, PPa3, LPa2, and LPa3 of the snail. The results indicate that desensitization of choline receptors is a relatively simple, short-term phenomenon usually not accompanied by more complex, long-term intracellular reorganizations. With short intervals between applications, however, densensitization may lead to a significant decrease in the reaction of the postsynaptic neuron and display certain properties characteristic also for depression of the synaptic reaction. On this basis we assume that in habituation, postsynaptic receptors participate in the processes of short-term decrease in synaptic efficiency.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 530–538, July–August, 1985.     

Response of the neurons of the snail (Helix pomatia) to orthodromic stimulation and microapplication of acetylcholine

In the case of intracellular recording in the ganglia of the apple snail, neurons giving responses of similar dynamics, both in response to orthodromic stimulation and in the case of a single microionophoresis of acetylcholine (AC) to their soma, were detected. Multiple repeated applications of AC lead to extinction of the response, similar to the habituation of these neurons to orthodromic rhythmic stimulation. This extinction is associated with desensitization of the receptors of the membrane. An artificial change in the resting potential (RP) of certain neurons within definite limits in response to the application of AC induces a prolonged exciting-inhibitory response. This may be evidence of the simultaneous existence of exciting and inhibitory receptors in the postsynaptic membrane, the activity of which is regulated by the level of the RP of the nerve cell.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 543–549, September–October, 1971.     

Postsynaptic effects of substance P in frog neuromuscular junction

We have studied the effect of substance P on the end-plate currents (EPC) and the miniature EPC (MEPC) after acetylcholine esterase (ACE) inhibition in the cut neuromuscular preparation of the frog sartorius muscle using the voltage-clamp technique. At concentrations of 5·10^–7–1·10^–6 moles/liter substance P had no effect on the amplitude and the time characteristics of single EPC and MEPC but promoted prolongation of EPC decay on repetitive stimulation of the nerve with a frequency of 10/sec, indicating intensification of postsynaptic potentiation. Elevation of the concentration of the given peptide to 5·10^–6 moles/liter led to the shortening of the decay of single EPC and a more marked depression of the EPC amplitude in the trains as compared to the control, reflecting a decrease in the sensitivity of the postsynaptic membrane to the mediator, i.e., development of desensitization.S. V. Kurashov State Medical Institute, Kazan. I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 436–441, July–August, 1991.     

Norepinephrine Drives Persistent Activity in Prefrontal Cortex via Synergistic α1 and α2 Adrenoceptors

Optimal norepinephrine levels in the prefrontal cortex (PFC) increase delay-related firing and enhance working memory, whereas stress-related or pathologically high levels of norepinephrine are believed to inhibit working memory via α1 adrenoceptors. However, it has been shown that activation of Gq-coupled and phospholipase C-linked receptors can induce persistent firing, a cellular correlate of working memory, in cortical pyramidal neurons. Therefore, despite its importance in stress and cognition, the exact role of norepinephrine in modulating PFC activity remains elusive. Using electrophysiology and optogenetics, we report here that norepinephrine induces persistent firing in pyramidal neurons of the PFC independent of recurrent fast synaptic excitation. This persistent excitatory effect involves presynaptic α1 adrenoceptors facilitating glutamate release and subsequent activation of postsynaptic mGluR5 receptors, and is enhanced by postsynaptic α2 adrenoceptors inhibiting HCN channel activity. Activation of α2 adrenoceptors or inhibition of HCN channels also enhances cholinergic persistent responses in pyramidal neurons, providing a mechanism of crosstalk between noradrenergic and cholinergic inputs. The present study describes a novel cellular basis for the noradrenergic control of cortical information processing and supports a synergistic combination of intrinsic and network mechanisms for the expression of mnemonic properties in pyramidal neurons.     

Effects of vinblastine and colchicine on the postsynaptic membrane at the frog neuromuscular junction

The possible effects of the alkaloids vinblastine and colchicine on the postsynaptic membrane of the frog neuromuscular junction were investigated using voltage-clamp techniques. Concentrations of vinblastine and colchicine which had been shown to exert no effect on the amplitude and duration of miniature endplate currents (MEPC) and the current-voltage relationship of low-quantal endplate currents (EPC) together with the coefficient of voltage-dependent EPC decay did produce a considerable rise in the amplitude of response to iontophoretically applied acetylcholine (ACh). In addition, vinblastine and colchicine accelerate MEPC and EPC during acetylcholine esterase inhibition while further depressing the amplitude of multi-quantal EPC succeeding at the rate of 10 Hz as well as response to regular (5–10 Hz) application of ACh from a micropipet. The dosage-frequency effects of vinblastine and colchicine on the postsynaptic membrane (as described) are presumed to be unconnected with the action of these agents on muscle fiber cytoskeleton but the results of accelerated desensitization of cholinoreceptors.S. V. Kurashov Medical Institute, Kazan. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 75–81, January–February, 1988.     

Modelling action of ionic channel blockers on postsynaptic currents

A mathematical model of the effects of open (ionic) channel blockers on generation of postsynaptic current at the neuromuscular junction is described. Quantitative aspects of simple blocking action are analyzed as well as criteria by which blockade of ionic channels may be discriminated from modification of their activation kinetics. Results of simulation are compared with experimental data. Some effects of channel-blocking substances following cholinesterase inhibition are examined.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry. Leningrad. S. V. Kurashov State Medical Institute, Kazan'. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 476–484, July–August, 1989.     

Connections of the corticospinal and rubrospinal tracts with neurons of the cervical spinal cord in cats

The distribution of focal potentials over the cross section of the 7th cervical segment of the spinal cord was studied during stimulation of the pyramids, the red nucleus, and a peripheral nerve (ulnar) in adult cats anesthetized with chloralose and Nembutal. The earliest focal potentials in the fasciculus dorsolateralis were recorded 1.4–1.5 msec after stimulation of the pyramids and 0.8–0.9 msec after stimulation of the red nucleus. These times correspond to maximal condution velocities of 56–68 and 105–124 m/sec respectively. The earliest post-synaptic activity in response to pyramidal stimulation was found in the lateral areas of laminae V and VI, and in response to stimulation of the red nucleus in laminae VI and VII in Rexed's classification. The pyramidal wave also evoked considerable postsynaptic activity in medial areas of the dorsal horn. In response to stimulation of peripheral afferents activity was evoked in neurons in the central and medial parts of laminae V and VI. It is postulated on the basis of these results that corticospinal and rubrospinal fibers may be connected monosynaptically with specialized interneurons, free from peripheral influences, in the lateral areas of laminae V and VII respectively; in the lateral part of lamina VI convergence of both types of influences on the same cells is possible. Interaction between descending and afferent influences possibly takes place on more medially located neurons.A.A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 158–167, March–April, 1972.     

Peculiarities of orthodromic inhibition in pacemaker neurons in Helix pomatia

We used the intracellular recording method to study the effect of a group of nerves in the visceral complex on the activity of a pacemaking giantneuron located in the peripheral part of the visceral ganglion in a mollusk. Single excitations of the left and right pallial, the intestinal, and the anal nerves with electrical stimuli evoked similar responses, consisting of phases of rapid depolarization (duration 100 msec, amplitude 3–5 mV) and slower hyperpolarization (duration 400 msec, amplitude 5–8 mV). The excitation also had an aftereffect, which was expressed in inhibition of the background activity of the pacemaker for several seconds. The most interesting of the functional characteristics of that response was the effects of summation. With rhythmic excitation by stimuli of low frequency (0.5–1 c/sec) the result of summation was general hyperpolarization of the neuron and the appearance of giant inhibitory postsynaptic potentials (IPSP's) with an amplitude of 12–16 mV. With higher frequency of excitation (2–3 c/sec and upward) we observed depolarization replacing the hyperpolarization of the neuron, but IPSP's of large amplitude were absent. At the end of rhythmic excitation prolonged inhibition of the pacemaker's activity, lasting some minutes, occurred in all cases. This article discusses the possible mechanisms of that type of prolonged inhibition of the pacemaker's activity, the origin of the phases in biphasic responses, and the reasons for differences in the course of summation of biphasic postsynaptic potentials.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 426–433, July–August, 1971.     

Effects of ethimizol on frog neuromuscular junction

The effects were studied of ethimizol, a substance activating memory processes, on features of synaptic transmission during experiments on frog cutaneous pectoris muscle. It was found that the presynaptic action of ethimizol consists of raising the frequency of miniature potentials, when used at a concentration of 0.5–10 mM, and modulating quantal content of synaptic transmission due to changes in binomial quantal release parameters p and n when 0.5–2 mM ethimizol was used. This substance facilitated transmission at synapses with a low initial level of transmitter release. This substance facilitated transmission at synapses with a low initial level of transmitter release. Ethimizol was also found to have a postsynaptic action, consisting of reducing amplitude at a concentration of 5–10 mM and prolonging synaptic currents and potentials when concentrations of 0.5–10 mM were used. The latter effect produced a considerable increase in the time integral of endplate potentials. The postsynaptic action of ethimizol is perhaps seen in its effects on features of postsynaptic ionic channels. The effects of ethimizol are discussed with a view to how it may act within the central nervous system as a nonspecific modulator.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 757–763, November–December, 1985.     

Effect of carbachol on miniature end-plate potentials and currents of rat skeletal muscle

Experiments on rats showed that carbachol (10 µM) appreciably quickens miniature end-plate potentials in the soleus muscle kept in medium with potassium chloride concentration increased to 13 mM. Potentiation of spontaneous mediator release also took place when the membrane potential of the muscle fibers was clamped at the level of the potassium equilibrium potential. It is concluded that the presynaptic action of carbachol on synaptic liberation of acetylcholine from motor nerve endings is unconnected with depolarization of the postsynaptic membrane but takes place as a result of the direct effect of the mimetic on motor nerve endings.S. V. Kurashov Medical Institute, Ministry of Health of the RSFSR, Kazan'. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 185–189, March–April, 1982.     

Statistical methods of quantal analysis in computerized compared with physiological experiments

Amplitude distributions of postsynaptic potentials subject to binomial distribution were simulated in computer-based experiments. Effects of sample size (N) and standard deviation of noise (S_n) on accuracy of determining mean quantal content (m) and quantal value (v) were investigated using four quantal analysis techniques (histograms, variation coefficient, failure and combined techniques). It was found that m and v may be determined fairly accurately (to within 10%) at S_n<2v using the last three techniques mentioned and at S_nv (where N=500–1000). It is possible to obtain similar results for N=50–200 if the experiment is repeated ten times. The possibility of applying such techniques to actual physiological results was confirmed by analyzing an extensive trace (N=1333) of inhibitory postsynaptic potentials in sensorimotor cortex units of unanesthetized rabbits.Brain Research Institute, National Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 206–215, March–April, 1990.     

Habituation of postsynaptic unit responses of the cat motor cortex to stimuli of different modalities

Habituation (extinction) of postsynaptic unit responses of the cat motor cortex to repetitive electrodermal, photic, acoustic, and combined bimodal stimulation was investigated by intracellular recording. Habituation was shown by a decrease in the number of spikes per grouped discharge and a decrease in the amplitude and duration of the EPSPs, and sometimes IPSPs, on repetition of the stimulus. The way in which the course of habituation depends on the modality and duration of stimulation (at a constant frequency of 1/sec) is examined. Habituation of postsynaptic responses to sensory stimuli is observed with neurons of different functional groups, namely identified neurons of pyramidal tract and unidentified neurons, some of which were evidently pyramidal neurons and interneurons. The hypothesis is put forward that the habituation of PSPs of the cortical neurons is based on processes taking place mainly at the subcortical level.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 545–553, September–October, 1972.     

Effect of nerve compression on the morphogenesis of the cholinesterase containing structures of the rat myoneural junction

Summary The sciatic nerve of the newborn rat was unilaterally compressed to cause temporary denervation and subsequent re-innervation of immature myoneural junctions prior to the development of postsynaptic infoldings in the rat tibialis anterior muscle. Subsequent changes in the postsynaptic structure were followed by histochemical demonstration of acetylcholinesterase activity.It was found that postsynaptic infoldings into the myoneural junctions appeared between 16–21 days of age on the temporarily denervated side but already at 5 days of age on the contralateral unoperated side. Also further development on the operated side was delayed by 10–15 days as compared to the control side.The observations indicate that the nerve-ending exerts a stimulating influence on the development of the postsynaptic structures and, in addition, that this action is long-lasting, as compared to the more transitory induction of myoneural acetylcholinesterase activity shown earlier to take place in the rat embryo at the 18-day stage.     

Relationship between the amplitudes of initial potentials of primary responses on the surface and in the depth of the cortex

There is a definite relationship between the amplitudes of the first positive phase of primary surface responses and the first negative phase of responses by the V layer of the cortex at the same point of the cortex [4, 5]. In this article we present the results of verification of the suggestion that hyperpolarizing and depolarizing postsynaptic potentials of the surface dendrites of the cortex have an electrotonically modulating effect on the manifestation of postsynaptic potentials by the membranes of the bodies of pyramidal neurons [4, 5]. Our findings have confirmed the existence of a relationship between the first positive phase of primary surface responses and the first negative phase of responses by the V layer of the cortex, have discovered its nature (a rectilinear positive correlation, the coefficient of which is 0.65), and also have reliably (B>0.999) demonstrated the existence of a modulating effect of the above-mentioned positive phase on the development of the negative phase and the possible proportion of that effect (up to 88%) in the total of effects on the latter produced by all the factors that induce fluctuations in the amplitude of that phase in certain experimental conditions.Chair of Normal Physiology, P. Lumumba University of International Friendship, Moscow. Translated from Neirofiziologiya, Vol.3, No.5, pp. 520–525, September–October, 1971.     

Identification of transmitter release sites in the motor nerve terminal

A model was produced of generation of postsynaptic current following release of a quantum of neurotransmitter from the nerve ending, whereby the law of current density attenuation is defined as j=I/r^b (A), where I is current density at the generation site and j stands at distance r from that site. Coefficient b was shown experimentally to be close to 1 using extracellular techniques of signal recording. Assuming that sites of signal generation and transmitter release are spatially identical, a new technique for determining the coordinates of the transmitter release site in the motor nerve terminal is suggested. This consists of measuring uniquantal signal amplitude by means of three extracellular microelectrodes spaced 5–10 µm apart. We were able to establish, by producing "spatial pictures" of transmitter release based on analysis of several hundred signals in the frog cutaneous pectoris muscle, that release sites are arranged in groups running diagonally to the nerve ending. These groups are thought to reflect transmitter release in active zones of the nerve ending. Advantages, disadvantages, and inaccuracies of the method are identified.S. V. Kurashov Medical Institute, Ministry of Public Health of the RSFSR, Moscow. V. I. Ulyanov-Lenin University, Kazan'. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 309–318, May–June, 1990.     

Electrical characteristics of granule cells of the carp olfactory bulb

Intracellular responses of granule cells and secondary neurons of the carp olfactory bulb to electrical stimulation of the olfactory nerve and olfactory tract were investigated. Synaptic responses of granule cells to both types of stimuli consisted of an early and late EPSP and IPSP. Comparison of responses of the secondary and granule neurons indicated that the granule cells are interneurons of postsynaptic inhibition of secondary neurons. The results suggest that dendro-dendritic and recurrent collateral pathways exist for the activation of granule cells and that inhibitory synapses are located on those dendrites of the secondary neurons that are in contact with endings of olfactory nerve fibers.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 597–602, November–December, 1975.     

Time course of miniature end-plate currents at different sites on the frog neuromuscular junction

Miniature end-plate currents (MEPC) were recorded from proximal and distal sections of the frog sartorius and cutaneo-pectoral synapses by means of glass microelectrodes using extracellular techniques. Higher MEPC amplitudes and half-decay times were found in the proximal than the distal sections. These differences disappeared under the effects of tubocurarine and augmented under the action of armine. A significant positive correlation was noted between amplitude and duration of MEPC half decay time in approximately 80% of experiments — an indication of repeated binding between acetylcholine molecules and cholinoreceptors. This correlation was observed in practically all the proximal sites investigated, but only in half of distal sites tested. Findings obtained using electronmicroscopy showed that synaptic contact is about twice as extensive at proximal as at distal sites, while postsynaptic folds are poor in arborization. It is deduced that the high amplitude and longer time course of MEPC at proximal synaptic sites are due to more pronounced repeated binding between acetylcholine molecules and cholinergic receptors of the postsynaptic membrane, which could be put down to the density of the receptor population and geometrical aspects of the synaptic cleft.S. V. Kurashov Medical Institute, Ministry of Public Health of the RSFSR, Kazan'. A. A. Zhdanov State University, Leningrad. Institute of Biophysics, Academy of Sciences of the USSR, Puschino-on-Oka. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 779–788, November–December, 1987.