Changes in segmental reflex responses during stimulation of locus coeruleus and potentiation of the action of catecholamines

Repetitive stimulation of the locus coeruleus (up to 150 µA in strength) was accompanied by marked weakening of the inhibitory action of flexor reflex afferents and of the reciprocal inhibitory action on extensor motoneurons. Meanwhile stimulation of this sort had no significant effect on direct inhibition of flexor and extensor motoneurons, on the facilitatory action of flexor reflex afferents and the reciprocal inhibitory action on flexor motoneurons and also on dorsal root potentials. Intravenously injected pyrogallol had a similar action, but its effect was much weaker after spinalization of the animals or blocking of spinal cord conduction by cold. Enhancement of the monosynaptic reflex, which also was observed after injection of pyrogallol, was characterized by different temporal parameters; the intensity of this effect was unaffected both by spinalization and by cold block. These data, and also the results of experiments with partial divisions of the spinal cord, suggest that the effects of stimulation of the locus coeruleus are the result of activity of a descending coerulo-spinal tract, running in the ventral quadrant of the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 39–47, January–February, 1981.     

Neuronal organization of coeruleo-spinal connections in cats

Experiments on cats showed that electrical stimulation of the locus coeruleus leads to diminution of the inhibitory action of flexor reflex afferents (FRA) on the extensor monosynaptic reflex and to a decrease in amplitude of the IPSP evoked by FRA in extensor motoneurons. Injection of microdoses of aspartic acid and chlorpromazine into the locus coeruleus depresses the inhibitory effects of FRA, whereas injections of procaine and noradrenalin potentiate the inhibitory action of FRA. Data are given on the character of the descending influence of the locus coeruleus on different groups of spinal interneurons. It is concluded that depression of the inhibitory action of FRA is effected at the level of the final inhibitory interneurons of the "FRA system."A. A. Bogolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 362–374, May–June, 1984.     

Effect of repetitive stimulation of the locus coeruleus on spinal inhibition evoked in cats by activation of flexor reflex afferents

Repetitive stimulation of the locus coeruleus with a frequency of 40 Hz and strength of 50–150 µA in decerebellated cats anesthetized with chloralose was accompanied by a decrease in the inhibitory action of flexor reflex afferents (FRA) on the extensor monosynaptic reflex. This effect, which appeared after 600 msec, reached a maximum 1500–1700 msec after the beginning of repetitive stimulation. A minimum of 7–10 stimuli was needed to evoke the effect. After the end of stimulation the inhibitory action of FRA was not fully restored until after 2–3 sec. During application of a single stimulus or a short high-frequency series of stimuli of the same strength to the locus coeruleus no such effect was found. An increase in the strength of stimulation in that case was accompanied by activation of adjacent more rapidly conducting structures. The advantage of repetitive stimulation for detecting effects of slowly-conducting brain structures is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 187–195, March–April, 1981.     

Effect of substances potentiating or inhibiting unit activity in the locus coeruleus on some types of spinal inhibition in cats

Microinjections of aspartic acid and chlorpromazine into the region of the locus coeruleus, which strengthen spontaneous unit activity in that structure, in decerebellate cats anesthetized with chloralose, led to depression of the inhibitory influence of flexor reflex afferents on extensor discharges, but did not change the facilitatory action of these afferents on flexor monosynaptic discharges and had no effect on recurrent inhibition of extensor discharges or reduced it. Microinjection of noradrenalin into this region, which depresses spontaneous unit activity in the locus coeruleus, or of procaine, which blocks action potential generation in neurons, led to potentiation of the inhibitory action of flexor reflex afferents on extensor discharges and to strengthening of recurrent inhibition, but did not affect the facilitatory action of these afferents on flexor discharges. The role of tonic descending influences of the locus coeruleus in the control of spinal inhibition evoked by flexor reflex afferents is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 247–256, May–June, 1981.     

Effects of repetitive stimulation of the locus coeruleus on spinal inhibitory responses to suprasegmental stimulation in cats

Effects of repetitive stimulation of the locus coeruleus on spinal responses to activation of cortico-, reticulo-, and vestibulospinal tracts were studied in decerebellate cats anesthetized with chloralose. Descending influences of these structures were assessed from changes in amplitude of extensor and flexor monosynaptic discharges or from the magnitude of postsynaptic potentials recorded from the corresponding motoneurons. Stimulation of the motor cortex or modullary reticular formation as a rule evoked two-component inhibitory responses in extensor motoneurons and excitatory-inhibitory responses in flexor motoneurons. Stimulation of locus coeruleus effectively depressed the amplitude of the late component and, to a lesser degree, that of the early component of inhibition arising after stimulation of the cerebral cortex or reticular formation. During stimulation of the locus coeruleus no marked changes were found in inhibitory responses evoked by vestibulospinal influences in flexor motoneurons, and also in excitatory responses arising after stimulation of the above-mentioned descending pathways in both groups of motoneurons.     

Role of different types of fibers of the infraorbital nerve in synaptic activation of masseter and digastric motoneurons

Postsynaptic potentials of motoneurons of the masseter and digastric muscles evoked by stimulation of the infraorbital nerve with a strength of between 1 and 10 thresholds were investigated in cats anesthetized with a mixture of chloralose and pentobarbital. Depending on their ability to be activated by low-threshold afferents of this nerve, motoneurons of the masseter were divided into two groups. Stimuli with a strength of 1.2–2.5 times above threshold for the most excitable fibers of the infraorbital nerve evoked short-latency EPSPs in the motoneurons of the first group; a further increase in stimulus strength (3–9 thresholds) led to the appearance of IPSPs with latent periods of 2.8–3.5 msec. Motoneurons of the second group responded to stimulation of the infraorbital nerve with a strength of 3–9 thresholds by IPSPs whose latent periods varied from 6 to 8 msec. Stimuli below 3 thresholds in strength evoked no responses in these motoneurons. Stimulation of the infraorbital nerve with pulses of between 1 and 2 thresholds in strength evoked EPSPs in digastric motoneurons, but an increase in the strength of stimulation led to action potential generation. The presence of many excitatory and inhibitory inputs formed by afferent fibers of different types evidently provides a basis for functional diversity of jaw-opening and jaw-closing reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 596–603, November–December, 1980.     

Postsynaptic potentials of motoneurons evoked by rubrofugal impulsation in the hypoglossal nucleus of the cat

The effect of stimulation of the ipsilateral and contralateral red nuclei on motoneurons of the hypoglossal nucleus was studied in cats anesthetized with chloralose and pentobarbital. In 35 (69%) of the 51 motoneurons tested, PSPs were generated in response to stimulation of the red nuclei by series of 3 to 5 stimuli of threshold strength and with a frequency of 500–600/sec. Of this number, 33 motoneurons responded to stimulation by EPSPs, whose latent periods varied from 3.5 to 14.0 msec (mean value for the ipsilateral red nucleus 5.7±0.75, for the contralateral nucleus 6.8±0.8 msec), whereas two motoneurons responded (after 6.2 msec) by IPSPs. Of the 35 motoneurons responding to stimulation of the red nuclei, stimulation of the lingual nerve evoked EPSPs in 31 and IPSPs in 4 (two of them were inhibited by rubrofugal impulses). IPSPs were generated as a result of stimulation of the lingual nerve in 16 motoneurons which did not respond to rubrofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 62–66, January–February, 1978.     

Synaptic effects of contralateral somatic afferents on spinal motoneurons

Electrical activity of flexor and extensor alpha-motoneurons of the lumbar segments of cat's spinal cord as recorded intracellularly during electric stimulation of afferents of the contralateral posterior limb. Contralateral postsynaptic potentials (PSP) were shown to be evoked by activation of cutaneous and high-threshold muscle afferents. The high-threshold afferents of various muscle nerves participate to varying degrees in the generation of contralateral PSP. Contralateral inhibitory postsynaptic potentials (IPSP) were recorded in both flexor and extensor motoneurons along with contralateral excitatory postsynaptic potentials (EPSP). There are no fundamental differences in their distribution between flexor and extensor neurons. Inhibitory influences as a rule are predominant in both during the first 20 msec, and EPSP are predominant in the interval between 20 and 100 msec. The balance of excitatory and inhibitory pathway activity was found to be not as stable as that of the homolateral pathways.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 418–425, July–August, 1971.     

Synaptic potentials of motoneurons of the masseter muscle

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

Postsynaptic potentials of neck muscle motoneurons evoked by horizontal semicircular canal stimulation in cats

Postsynaptic potentials evoked by stimulation of ipsilateral and contralateral horizontal semicircular canals in motoneurons of muscles tilting and turning the head were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Stimulation of the ipsilateral canal evoked EPSPs with latent periods varying from 1.8 to 10.0 msec in 25 of these motoneurons and IPSPs with latent periods varying from 1.9 to 3.9 msec in 10 of them. Calculation of the impulse conduction time from the ipsilateral semicircular canal through Deiters' nucleus to the cervical motoneurons indicates that EPSPs with latent periods of under 3.8 msec may be regarded as disynaptic, and those with latent periods of over 3.8 msec as polysynaptic. Stimulation of the contralateral canal evoked EPSPs with latent periods varying from 1.8 to 6.0 msec in 19 motoneurons and IPSPs with latent periods varying from 3.2 to 3.9 msec in two cells. The possible pathways of transmission of these influences and their functional role are discussed.     

Neuronal and synaptic mechanisms of cortical inhibition

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

Postsynaptic effects evoked by activation of long propriospinal pathways in cervical spinal neurons in cats

Effects induced in motoneurons and interneurons of the cervical enlargements of the cat spinal cord by stimulation of the lateral and ventral funiculi at the lower thoracic level were studied under conditions producing degeneration of fibers of descending brain systems. Stimulation of this sort evoked PSPs (mainly of mixed character) in 57 of 90 motoneurons tested. In nine motoneurons the primary response consisted of monosynaptic EPSPs evoked by activity of fibers of the lateral funiculus, and in the rest it consisted of polysyanptic (at least disynaptic) EPSPs and IPSPs. Polysynaptic effects arising in the neuron in response to stimulation of the lateral and ventral funiculi usually differed only quantitatively. The intensity of excitatory synaptic action on motoneurons of the proximal muscle (especially thoracid) was much greater than that on motoneurons of distal muscles. Nearly all motoneurons with no synaptic action belonged to the latter group. Stimulation of the lateral and ventral funculi facilitated synaptic action induced in motoneurons by stimulation of high-threshold segmental afferents and led to excitation of interneurons located in the vectral quadrant, and had no effect on interneurons in the dorsal regions of gray matter. These effects are regarded mainly as the result of excitation of long ascending propriospinal pathways in the cervical parts of the cord; it is also postulated that some of them are evoked by the arrival of activity along collaterals of descending propiospinal pathways to the neurons in this region.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 339–347, July–August, 1979.     

Monosynaptic excitation of motoneurons of the accessory nerve nucleus by reticulofugal impulses

Acute experiments on cats anesthetized with chloralose and pentobarbital showed that excitation of fast-conducting (130 m/sec) reticulospinal fibers, arising during stimulation of the ipsilateral medullary reticular gigantocellular nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nerve nucleus. The EPSPs had latent periods of between 0.6 and 1.0 msec (mean 0.7 msec), they reached their maximal amplitude (4.0 mV) after 2.0–2.5 msec, and lasted about 10 msec. The EPSPs underwent only weak potentiation through the different types of stimulation of the gigantocellular nucleus and were not transformed into action potentials.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 62–66, January–February, 1980.     

Convergence of corticospinal and rubrospinal influences on cervical motoneurons

Synaptic responses of 121 identified cervical motoneurons to stimulation of the pyramidal tract and red nucleus were investigated by intracellular recording in cats. Responses of EPSP or EPSP-IPSP type were predominant in motoneurons of distal groups of muscles and proximal flexors, while responses of IPSP type were predominant in motoneurons of the proximal extensors. The minimal effective number of stimuli for most motoneurons was 2 or 3. The mean latent period, counted from the first stimulus in the series, was 7.86 msec for EPSPs for stimulation of the pyramidal tract and 7.91 msec for stimulation of the red nucleus, while the corresponding periods for IPSPs were 8.68 and 8.75 msec. The segmental delay of 1.3–2 msec for EPSPs and IPSPs generated in certain motoneurons in response to stimulation of both structures indicates that the shortest pathway for transmission of activity from the fibers of these tracts to the motoneurons may be disynaptic. At the same time, the possible presence of an additional neuron for most inhibitory pathways cannot be ruled out. Analysis of the results also suggests the presence of a common interneuronal apparatus for both systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.3, No.6, pp. 599–608, November–December, 1971.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Excitation of accessory motoneurons by stimulation of Deiters' nucleus in the cat

Acute experiments on cats under chloralose-pentobarbital anesthesia showed that application of single stimuli to Deiters' nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nucleus. Latent periods of EPSPs ranged from 1.3 to 2.3 msec (mean 1.8±0.3 msec), their rise time was 0.5–1.0 msec, and their duration 7–10 msec. During repetitive stimulation the EPSPs were weakly potentiated, but with an increase in the strength of stimulation applied to Deiters' nucleus they readily changed into action potentials. In some motoneurons polysynaptic EPSPs with latent periods of the order of 6.0 msec appeared on the descending phase of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 515–519, September–October, 1981.     

Synaptic effects evoked in motoneurons by stimulation of single propriospinal neurons

Experiments on cats with simultaneous extracellular recording, stimulation of single propriospinal neurons, and intracellular recording of unitary postsynaptic potentials from motoneurons, followed by computer averaging showed that direct stimulation of individual propriospinal cells receiving mono- and disynaptic influences from the medial reticular formation can evoke monosynaptic EPSPs and IPSPs in lower lumbar motoneurons. The amplitude of these EPSPs was 49.6±6.0 and of the IPSPs 28.9±2.9 µV and their synaptic delay was 0.34±0.05 msec. The same propriospinal neuron of the ventral horn of the upper lumbar segments may be connected with several motoneurons of the hind limb muscles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 300–306, May–June, 1977.     

EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

Connexions between hair-plate afferents and motoneurones in the cockroach leg.

1. The trochanteral hair-plate afferents in the metathoracic leg of the cockroach, Periplaneta americana, were stimulated electrically and at the same time intracellular recordings were made from either motoneurones, interneurones or afferent terminals within the methathoracic ganglion. 2. Activity in the hair-plate afferents evoked short latency excitatory postsynaptic potentials (EPSPs) in femur flexor motoneurones. The latency of the IPSPs was on average 1-8 ms longer than the latency ofthe EPSPs. 3. Intracellular recordings from terminal branches of the hair-plate afferents showed that the delay between the peak of the afferent terminal spike and the beginning of the EPSPs is about 0.4 ms. This finding, together with the observations that the amplitude of the EPSPs is increased by the passage of hyperpolarizing current and decreased following high-frequency stimulation, indicates that the EPpSPs are evoked via-monosynaptic chemical synaptic junctions. 4. The observations of the long latency of the IPSPs, the need for a number of afferents to be simultaneously acive for them to be evoked and the occasional variability in latency, all indicate that the IPSPs are evoked via a disynaptic pathway...     

Monosynaptic excitation of facial motoneurons during electrical stimulation of the red nucleus

Synaptic effects of the red nucleus on motoneurons of the facial nucleus were studied in cats. Impulses from the red nucleus activate motoneurons innervating the auricular, buccal, and orbicularis oculi muscles. Monosynaptic EPSPs appeared in all motoneurons which responded to stimulation. Their mean latent period was 1.5±0.04 msec, duration 12.3 ± 0.34 msec, and rise time between 1.5 and 3.2 msec. Repetitive stimulation of the red nucleus led to marked facilitation of the testing EPSP. Facilitation was maximal when the interval between stimuli was 3.5 msec; it was reduced by either a decrease or an increase in the interval. The functional role of the monosynaptic connections of neurons of the red nucleus and of the facial motoneurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 272–279, May–June, 1972.