Effects of stimulating the central gray matter on neuronal response in the cat medial thalamic nuclei

This study was performed on the effects of stimulating the midbrain central gray matter (CGM) on neuronal response in the association medial thalamic nuclei evoked by stimulation of A-alpha and A-delta fibers of the infraorbital nerve and the caudal nucleus of the spinal trigeminal tract (CN STT) and tooth pulp stimulation using cats anesthetized by thiopental-chloralose as experimental animals. Stimulating the CGB with trains of stimuli was found to evoke an excitatory response in a percentage of the neurons tested, in which latency fluctuated between 15 and 40 msec. Applying conditioned stimuli to the CGM caused suppression of response to afferent impulses in neurons belonging to the "convergent" and "low" and "high" threshold groups. Responses induced by stimulating tooth pulp and A-delta fibers showed 100% inhibition as compared with 86% during A-alpha fiber and infraorbital nerve stimulation. The fact that stimulating the CGM produces an inhibitory effect on the response of thalamic neurons evoked by stimulation of both peripheral afferents and the CN STT would indicate that the CGM can exert a direct action on thalamic neuronal activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 660–665, September–October, 1987.     

Effects of stimulating midbrain central gray matter on neuronal response in the caudal trigeminal nucleus to peripheral nerve stimulation

Stimulating the midbrain central gray matter (CGM) with trains of 10–20 stimuli was found to inhibit response to electrical stimulation of infraorbital nerve and tooth pulp A-alpha and A-delta afferents at 100 msec intervals in 65% of the caudal trigeminal nucleus in neurons tested during experiments on cats under chloralose-Nembutal anesthesia. Response was inhibited most effectively in convergent neurons (activated by stimulating infraorbital nerve and tooth pulp A-alpha and A-delta afferents) to stimulating tooth pulp (0.76) and, to a somewhat lesser degree, to stimulation of A-alpha afferents (0.6). For high-threshold neurons (activated by stimulating infraorbital nerve and tooth pulp A-delta afferents), success rate of inhibiting response under the effects of CGM stimulating measured 0.71 and 0.48 for low-threshold cells (activated by stimulating infraorbital nerve A-alpha afferents). Stimulating CGM produced an excitatory response in 10 caudal trigeminal nucleus neurons within 7.5–20 msec; after this neurons showed no reaction to peripheral nerve stimulation for a 200–450 msec period. The possible involvement of these neurons in pressing the mouth-opening reflex produced by CGM stimulation is discussed in this article.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 729–736, November-December, 1988.     

Effects of stimulating the central gray matter on neuronal activity in the trigeminal nucleus

A comparative study was conducted on the effects of stimulating different central gray matter (CGM) areas on neuronal activity of the trigeminal nucleus during nociceptive stimulation before and after complete section of medial brainstem structures. The possible role of opiate and non-opiate systems in inhibition of nocieptive afferents is discussed. The CGM was found to be a functionally diverse structure: pain-suppressing and pain-promoting systems exist side by side at this site. The inhibitory influence of the ventromedial CGM is exerted by activation of raphe nucleus neurons; that of the dorsomedial area could well be mediated by involvement of the lateral bulbar area and/or activation of rostral brain structures.I. S. Bertiashvili Institute of Physiology, Academy of Sciences of the Georgian SSR. Tbilisi. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 381–387, May–June, 1990.     

Segmental inhibitory response in the frog spinal cord during orthodromic motoneuron activation

Different types of reflex discharges were produced in various preparations by stimulating the dorsal root of isolated frog spinal cord. These ranged from multiphasic low-amplitude waves to distinctly synchronized monosynaptic response. The discharges were followed by facilitation in the former and deep, protracted inhibition of response to test dorsal root stimulation in the latter. When interstimulus intervals measured 40–50 msec, inhibitory action was less pronounced than at shorter (15–30 msec) or longer (60–100 msec) intervals, thus indicating that at least two types of inhibition were at work, one at an earlier and the other at a later stage. Strychnine at a concentration of 10^–5 M effectively reinforced the former and blocked the latter, while 10^–4 M d-tubocurarine attenuated both types of inhibition substantially. It is concluded that inhibition of response occurs mainly as a result of recurrent activation of inhibitory systems via recurrent motoneuron axon collaterals when frog spinal cord afferents are excited. Intensity of the later (presynaptic) and earlier (postsynaptic) inhibition of reflex transmission is determined by the degree of synchrony in motoneuronal discharge in response to orthodromic stimulation.Institute of Medical Radiology, Academy of Medical Sciences of the USSR, Obninsk, Kaluga Oblast. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 343–350, May–June, 1987.     

Cholinergic modulation of the synaptic transmission in the frog spinal cord

It was found during experiments on isolated frog spinal cord involving extracellular recording from the dorsal roots (sucrose bridging) and intracellular recording from motoneurons by microelectrodes that 10 mM of the M-cholinomimetic arecoline produces motoneuronal depolarization which is matched by depolarizing electronic ventral root potentials and a rise in motoneuronal input resistance. Arecoline changes synaptic transmission by increasing the amplitude of postsynaptic potentials during intracellular recording and that of motoneuronal reflex discharges in the ventral roots but reduces the duration of dorsal root potentials. In the presence of arecoline, L-glutamate-induced motoneuronal response increases. Facilitation of synaptic transmission produced by arecoline in the spinal cord is bound up with cholinergic M₂- activation, since it is suppressed by atropine but not by low concentrations of pirenzipine; it is also coupled with a reduction in adenylcyclase activity. When motoneuronal postsynaptic response has been suppressed, as in the case of surplus calcium or theophylline, arecoline produces an inhibitory effect on the amplitude of motoneuronal monosynaptic reflex discharges which is suppressed by pirenzipine at a concentration of 1×10^–7 M. This would indicate the presence at the primary afferent terminals of presynaptic cholinergic M₁ receptors which mediate its inhibition of impulses of transmitter release. This effect is independent of changes in cyclic nucleotide concentration.A. M. Gorkii Medical Institute, Donetsk. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 399–405, May–June, 1987.     

Effects of stimulating the midbrain central gray matter on neuronal response in the cat ventroposteromedial thalamic nucleus

The effects of stimulating the midbrain central gray matter (CGM) on neuronal response in the ventroposteromedial (VPM) nucleus produced by stimulating tooth pulp, A-alpha and A-delta fibers of the intraorbital nerve and the caudal nucleus of the spinal trigeminal tract (CN STT) were investigated during experiments on cats under thiopental-chloralose anesthesia. It was found that applying trains of stimuli to the CGM produced excitatory responses in a proportion of the test neurons with latencies of up to 30 msec. Application of conditioning stimulus to the CGM led to suppression of response of efferent stimulation in neurons belonging to low-threshold, convergent, and high-threshold groups. Responses produced in 40% of neurons by stimulating tooth pulp and A-delta fibers of the suborbital nerve, as well as those evoked in 26.4% of thalamic VPM cells by stimulating A-alpha fibers of the suborbital nerve were completely suppressed. The inhibitory effect found when stimulating CGM on response in certain neurons, produced by stimulating both the peripheral nerve and the CN STT, would indicate that the CGM could exert an influence on the activity of thalamic VPM neurons directly.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 688–694, September–October, 1988.     

Effects of partial bulbar section on inhibition of jaw-opening reflexes induced by central gray matter stimulation in the cat

The effects of severing the spinal trigeminal tract and its caudal nucleus on high-threshold jaw-opening reflex elicited by tooth pulp stimulation were investigated during experiments on cats under chloralose-Nembutal anesthesia. Low-threshold jaw-opening reflex produced by stimulating the A--infraorbital nerve at an intensity 2–3 thresholds in relation to the most excitable fibers on this nerve was also observed, as well as suppression of these reflexes induced by central gray matter stimulation. It was found that spinal trigeminal tract section produces a 8–52% increase in high-threshold reflex. The amplitude of low-threshold reflex either remained unchanged or showed a slight tendency to rise or fall. Brief stimulation of the central gray matter produced a 100% decrease in high-threshold reflex in intact animals compared with a 40–60% decrease after section of the trigeminal tract. Protracted stimulation of the central gray brought about an 80% decline in high-threshold reflex in intact animals as against 25–30% after section. The degree to which brief stimulation of the central gray produced depression of low-threshold stimulation remained unchanged by trigeminal tract section. Protracted stimulation of the central gray matter brought about a 25–50% reduction in low-threshold reflex in intact animals and a reduction of 75% in three animals and 15–20% in four animals. This implied that the caudal nucleus of the spinal trigeminal tract exerts a more substantial influence on the process of high- than low-threshold reflex inhibition when the central gray matter is stimulated.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 362–368, May–June, 1987.     

Response induced in prog motoneurons by glutamate application

It was shown during experiments on isolated frog brain (fromRana ridibunda) that response to microelectrophoretically injected glutamate on to various points on the somatodendritic motoneuronal membrane (GLU response) displayed the same properties as EPSP induced in the same motoneuron by activation of three different synaptic inputs. Techniques of transmembrane polarization and current chop by means of a single microelectrode were used in this research. Mean levels of reversal potentials of GLU response and EPSP occurring as a result of stimulating the reticular formation, dorsal root, and microstimulation of presynaptic elements at the point of glutamate application equaled –16.9 ± 1.7 (n=13), –6.8 ± 1.7 (n=13), –9.8 ± 1.8 (n=6), and –15.1 ± 1.4 mV (n=13), respectively. Summation of GLU response and EPSP were quasilinear. Changes (upwards) in conductance associated with GLU response did not exceed 10%. Findings would indicate that glutamate, acting on the postsynaptic membrane receptors, induces depolarization and may serve as transmitter in all three inputs investigated.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 776–785, November–December, 1988.     

Role of the serotoninergic system in inhibition of jaw-opening reflex induced by stimulating the midbrain central gray matter

The effects were studied in waking cats of brief stimulation (20 stimuli at a rate of 400 Hz) of the central gray matter (CGM) and dorsal raphe nucleus (DRN) on high-threshold jaw-opening reflex (HJOR) evoked by tooth pulp stimulation during blockade of serotonin synthesis produced by application of 300 mg/kg parachlorophenylalanine (PCPA) i.p. Inhibitory effects of CGM and DRN stimulation had already declined in comparison with post-stimulation (but pre-PCPA) level within 24 h after PCPA application; 96 h afterwards, inhibition of HJOR induced by CGM and DRN stimulation had become only minimal: amplitude of the reflex had declined to 30–35% and duration of inhibitory effects ws 200–250 msec. It is therefore deduced that serotonin contributes to the HJOR depression induced by CGM and DRN stimulation and the possible involvement of other neuromodulators in this effect is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 45–52, January–February, 1989.     

Corticofugal influences on neurons of the main trigeminal sensory nucleus

The effects of stimulation of the ipsilateral sensomotor cortex were studied on 88 neurons in the region of the main trigeminal sensory nucleus of a cat. The cortex was stimulated via a coaxial electrode by single impulses. Stimulation of the cortex caused the appearance of EPSPs and action potentials in these neurons; a small number of these responses were monosynaptic. The polarity of the impulse applied to the cortex had a significant effect on the magnitude of the latent period of the response and the postsynaptic reaction, which is apparently caused by the stimulation of different types of cortex neurons. Apparently, corticofugal pulsation regulates the level of sensitivity of the trigeminal sensory neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 47–53, July–August, 1969.     

Mechanisms underlying inhibition of nociceptive jaw-opening reflex produced by stimulating limbic structures

The comparative effectiveness of the inhibitory influence of tetanic (100 Hz) stimulation of the hypothalamus, amygdala, and limbic cortex on electromyograph (EMG) response in m. digastricus produced by electrical stimulation of tooth pulp afferents was investigated in cats anesthetized by a mixture of chloralose and Nembutal. It was found that the most pronounced inhibition of nociceptive EMG response was produced by stimulating the medial and lateral structures of the hypothalamus, a less intense response by stimulating central and medial amygdaloid nuclei, and the least reaction by stimulation of different areas of the limbic cortex. It was shown that mechanisms underlying inhibition of the jaw-opening reflex produced by hypothalamic tetanic stimulation is unconnected with the concomitant increase in blood pressure. The inhibitory action of hypothalamic tetanic stimulation following blood pressure stabilization persists; this would suggest a primary but not baroafferent mechanism underlying inhibition of activity in trigeminal nucleus nociceptive neurons. Pronounced and protracted depression of jaw-opening reflex takes place following long-term pressor response produced by injecting noradrenaline intravenously. The same pronounced and protracted pressor response occurs under the effects of angiotensin but without any noticeable change in the amplitude of nociceptive EMG response. Hypothalamic and noradrenergic mechanisms of pain sensitivity are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 825–832, November–December, 1987.     

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.     

Synaptic processes in facial motoneurons evoked by stimulation of the caudal trigeminal nucleus

Field potentials and postsynaptic potentials of facial motoneurons evoked by stimulation of the caudal trigeminal nucleus were investigated in acute experiments on cats by extra- and intra-cellular recording. Pre- and postsynaptic components of field potentials were found. Four types of motoneuron response were distinguished: EPSP with generation of single action potentials; a gradual shift of depolarization inducing grouped action potentials; a rhythmic discharge of action potentials arising at a low level of depolarization; and EPSPs or EPSP-IPSP sequences. The monosynaptic and (chiefly) polysynaptic nature of these responses was demonstrated. The possible mechanism of afferent control over facial motoneurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 272–282, May–June, 1980.     

Synaptic potentials of digastric-muscle motoneurons

We studied the antidromic and synaptic potentials evoked from 32 digastric-muscle motoneurons by stimulation of the motor nerve to this muscle, different branches of the trigeminal nerve, and the mesencephalic trigeminal nucleus. Antidromic potentials appeared after 1.1 msec and lasted about 2.0 msec. Stimulation of the infraorbital, lingual, and inferior alveolar nerves led to development of excitatory postsynaptic potentials (EPSP) and action potentials in the motoneurons. The antidromically and synaptically evoked action potentials of the digastric-nerve motoneurons were characterized by weak after-effects. We were able to record EPSP and action potentials in two of the motoneurons investigated in response to stimulation of the mesencephalic trigeminal nucleus, the latent period being 1.3 msec. This indicates the existence of a polysynaptic connection between the mesencephalic-nucleus neurons and the digastric-muscle motoneurons. Eight digastric-muscle motoneurons exhibited inhibitory postsynaptic potentials (IPSP), which were evoked by activation of the afferent fibers of the antagonistic muscle (m. masseter). The data obtained indicate the presence of reciprocal relationships between the motoneurons of the antagonistic muscles that participate in the act of mastication.A. A. Bogomol'ts Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 52–57, January–February, 1971.     

Effect of noradrenalin and serotonin on synaptic transmission in the rat spinal cord

Experiments on superfused isolated spinal cord preparations from rats aged 8–13 days showed that noradrenal in and serotonin have only a weak effect on monosynaptic reflex discharges but a substantial effect on polysynaptic motoneuronal discharges: noradrenalin potentiates whereas serotonin inhibits them. Both amines inhibit dorsal root potentials evoked by stimulation of high-threshold afferents. Potentiation of polysynaptic motoneuronal discharges induced by noradrenalin is connected with hyperpolarization of high-threshold afferents due to inhibition of the function of neurons in the substantia gelatinosa, and with increased excitability of interneurons participating in the generation of motoneuronal discharges. Serotonin inhibits polysynaptic motoneuronal discharges through its direct depolarizing effect on terminals of high-threshold afferents and depression of interneuron activity responsible for these discharges. Adrenergic and serotonin receptors, mediating these effects of noradrenalin and serotonin, were subjected to pharmacologic analysis.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 241–247, May–June, 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.     

Spatial configuration of rabbit superior collicular evoked response to punctiform afferent stimulation

Evoked potentials arising in the rabbit superior colliculus in response to punctiform stimulation of the receptive field were studied. This response has only negative polarity at the focus of maximal activity and does not exhibit reversal of the potential which is a characteristic feature of the response to diffuse stimulation. The evoked potential was recorded at depths of between 0.1 and 0.9–1.0 mm from the collicular surface, corresponding to the stratum griseum superficiale. The response disappeared when the stimulating spot was shifted through 4–6° away from the optical position. It is suggested that evoked potentials to punctiform stimulation can give more complete information on the location of different synapses.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 441–450, September–October, 1979.     

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.     

Structural organization and connections of the cat bulbar locomotor strip

Sections of the medulla known as the locomotor strip were investigated during cat experiments using the horseradish peroxidase retrograde transport technique. The enzyme was administered under functional control (stimulating the injection site evoked locomotion). Results showed no evidence of a hypothetical column of cells either along the locomotor strip or medially to the strip. This would cast doubts on the existence of such a strip as a separate structural formation. It was shown by comparing findings from morphological research and experiments involving electrical stimulation that the bulbar locomotor strip may in fact consist of the spinal trigeminal tract and its nucleus. It is postulated that non-specific afferent activation of the brainstem reticular formation plays a crucial role in initiating locomotion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 308–315, May–June, 1987.     

Effects of vasopressin and oxytocin on evoked dorsal horn cell activity in an isolated segment of spinal cord

During experiments on an isolated segment of the spinal cord of 2- to 3-week-old rats, a study was made of the effects of vasopressin and oxytocin on the activity of dorsal horn cells produced by stimulating the afferent root. Both field and action potentials were recorded in single cells. It was established that vasopressin and oxytocin produced reversible inhibition of the postsynaptic component of field potentials. The amplitude of potentials was reduced by 33–39% by vasopressin and by 12–34% using oxytocin. The effect of the test substances depended on the concentration used and the duration of their action on the brain. Both vasopressin and oxytocin reversibly depressed discharges of single dorsal horn cells evoked by stimulating the dorsal root. These two neuropeptides prolonged latency, and reduced the number of evoked potentials or completely suppressed response. A facilitatory effect was recorded in a small number of cells. We deduced from our findings that their hypothalamospinal neurohormonal system inhibits transmission of afferent impulses at the level of interneurons of the dorsal horn.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 634–640, September–October, 1985.