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.     

Influence of orotic acid upon post-excitatory facilitation released by stimulation of the tooth pulp]

The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred.     

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.     

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.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Response of Renshaw cells to sinusoidal stretch of hindlimb extensor muscles.

1. Renshaw cells responding disynaptically to electrically induced group I volleys in the intact gastrocnemius-soleus (GS) nerve, were submitted to small-amplitude, high-frequency vibration applied longitudinally to the deefferented GS muscle in precollicular decerebrate cats. 2. Vibration of the GS muscle at 200/sec, 180 mu peak-to-peak amplitude for 80-100 msec produced a sudden increase in the discharge rate of Renshaw cells, which gradually decreased within 25-50 msec to reach a steady level higher than that recorded in the absence of vibration. 3. Excitation of Renshaw cells appeared at a threshold amplitude of vibration (at 200-250/sec) of 5-20 mu and increased to a maximum value for amplitudes of about 70-80 mu, i.e., when all the primary endings of the spindles from the GS muscle had been driven by the stimulus. Recruitment of the secondary endings of the muscle spindles, due to large amplitude muscle vibration, did not modify the response of the Renshaw cells to the mechanically induced group Ia volleys. 4. These findings were obtained with the GS muscle pulled at 8 mm of initial extension. A threshold response of Renshaw cells to vibration appeared at 4 mm of static stretch, while maximal responses occurred at 8 mm. No further increase and actually a slight decrease in the response appeared for initial extensions of the muscle of 10-12 mm. 5. For a given vibration amplitude, the response of the Renshaw cells increased with increasing frequencies of vibration to reach the maximum at frequencies of 150-250/sec. Bursts of Renshaw cell discharges synchronous to each stroke of vibrator occurred only for low frequencies of stimulation (less than 25/sec). 6. It is concluded that vibration of the GS muscle represents a very effective method in exciting the Renshaw cells and that this response depends upon selective stimulation of homonymous motoneurons monosynaptically excited by the orthodromic volleys originating from the primary endings of the corresponding muscle spindles.     

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.     

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 350–358, July–August, 1971.     

Recording of short-latency vestibular evoked potentials induced by acceleration impulses in experimental animals: current status of the method and its applications

The short-latency vestibular evoked potential (VsEP) induced by angular acceleration impulses (maximal amplitude 30,000 deg/sec², rise time 2–3 msec) was recorded by skin electrodes in intact cats after various surgical and pharmacological procedures. The normal VsEP consists of 5–8 waves, several microvolts in amplitude, during the first 10 msec. The latency of the first wave (P1) is about 2 msec with respect to the start of head acceleration. The first and the second waves (P1 and P2) were shown to originate from the vestibular nerve and nucleus, respectively.The VsEP disappears permanently after bilateral labyrinthectomy, excision of the 8th nerves, or administration of large doses of gentamicin. Temporary disappearance is caused by anoxia induced for a brief period of time or injection of lidocaine (4%) into the vestibular nerve or into the inner ear after contralateral labyrinthectomy.The VsEPs in the intact cat are similar whether clockwise or counterclockwise stimuli are used and are not affected by changing the position of the head. Unilaterally labyrinthectomized animals, however, show asymmetric response whereby excitatory stimulation of any of the intact semicircular canals evokes prominent P1 and P2 waves which are absent with inhibitory stimulation.The rate and input-output intensity functions of the VsEP are described. The threshold of the VsEP was found to be 1000–1500 deg/sec².In addition to the neurogenic waves, 2 other potentials appear occasionally in the response: (1) large-amplitude and longer-duration waves with latencies of 8–20 msec, which are of myogenic origin, and (2) smaller waves with shorter latency which probably represent vestibular microphonics and generator potentials. Extracellular recordings of the responses of single second-order neurons in the vestibular nuclei to the same acceleration impulses confirmed that the kinetic vestibular neurons can respond to these stimuli with a latency as short as 3.5 msec.This method for inducing and recording VsEPs has proved to be a powerful tool for the evaluation of vestibular function in experimental animal models.     

Electrophysiological study of connections between the entorhinal cortex and the neocortex

In acute experiments in rabbits immobilized by d-tubocurarine, stimulation of the entorhinal area with rectangular electric impulses led to the appearance of evoked potentials (EP) with a latent period of 6–12 msec in the occipital, temporal, parietal, and cingular areas of the neocortex. The amplitude of the positive response component was 500 µV, and its duration 25–50 msec. The negative component was not always discernible. When rhythmic stimulation was used, these EPs followed stimulation frequencies not exceeding 20 per sec. Stimulation of the medial parts of the entorhinal area with a frequency of one to three per sec was accompanied by recruitment of the EP in the occipital and temporal neocortex areas. Nembutal depressed the amplitude of the neocortex EP appearing in response to stimulation of the entorhinal cortex. With the aid of double stimulation it could be established that, after conditioning stimulation of the entorhinal area, the positive component of the primary response (PR) evoked by stimulation of the contralateral sciatic nerve in the projection zone of the somatosensory cortex is strengthened during the first 50 msec, and subsequently after 80–120 msec. In these cases, the negative component was depressed. These findings are discussed with a view to the influence of limbic structures on the neocortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 73–78, January–February, 1970.     

Spontaneous and evoked activities of interpositus nucleus neurons before and after lesion of the cerebellar cortex

Spontaneous and evoked activities of nucleus interpositus neurons (IN) of the cerebellum were examined before and after cerebellar paravermal cortex lesions in cats anesthetized with alpha-chloralose. It was found that spontaneous activity increased dramatically following cortical ablation: before the lesion only 4% of cells encountered fired at a rate exceeding 80 impulses/sec., whereas up to 40% discharged at this rate postoperatively. Responses to paw stimulation were also altered: the initial excitation was lengthened from 8.5 to 15.8 msec; narrow; trough causing segmentation in this excitation, which seems to result from Purkinje cell inhibition, was absent; and the succeeding inhibitory period was reduced in duration by 50%. Also after the lesion there was a strong tendency for the neurons to discharge in bursts. It is suggested that changes in cell activity in the IN following cortical lesion unveil neural mechanisms of motor disturbances in lesioned cats.     

Luminescence of isolated photophores and supracaudal gland from myctophum punctatum: Electrical stimulation

• 1.1. Isolated photophores of the living bathypelagic fish Myctophum punctatum respond to train of weak (10–25 V) and short (2–5 msec) electrical stimuli applied at different frequencies (8–100/sec) by a luminus response.
• 2.2. This response is characterized by a short emission latency time, the peak of light develops within about 2 sec after the beginning of the electrical stimulation: afterwards the light decreases to a constant level within about 8 sec.
• 3.3. Stimuli of higher strength (60–75 V) and longer duration (8–16 msec) applied at different rates (1–100/sec) evoke brief flashes.
• 4.4. The isolated supracaudal gland emits flashes in response to electrical stimulation whatever the strength and the duration of stimuli.
• 5.5. The flash of the supracaudal gland differs from the flash of the isolated photophores in three respects: lower threshold, higher magnitude and longer duration.

     

Effect of motor stimulation and stretching on afferent activity of the neuromuscular spindle isolated from the frog]

The arrangement of muscle spindles in m. ext. long. dig. IV has been examined by microdissection. It is confirmed that spindle systems generally appear to consist of individual receptors. Stimulation effects of fast motor fibres (conduction velocities greater than 12 m/sec) on the spindles of the same muscle were studied. Receptors were isolated with their nerves and the appropriate spinal roots, the latter ones were used for stimulating efferent fibres and recording sensory discharges. Single shocks to the ventral root filaments caused afferent responses ranging from a single action potential to a train of impulses. During repetitive stimulation (train of stimuli at frequency of 10 to 150/sec) a marked increase in afferent activity was found. Afferent activity could be driven by the frequency of stimuli ("driving") and the stimulus/action potentials ratio varied from 1:1 to 1:3 or more. The rate of sensory discharge depended on the frequency of stimuli: the maximum effect, was attained at 30 to 50 stimuli/sec and, in the most responsive receptors, up to 80 stimuli/sec. Slight increases of the initial lengths of the receptors caused facilitation of sensory responses to motor stimulation. Moreover, impairing effects, which appear during sustained or high-frequency stimulation, possibly related to fatigue in intrafusal neuromuscular transmission, could be relieved by increasing the initial length. The repetitive stimulation of fast fusimotor fibres increased both dynamic and static responses and also raised the afferent activity after a period of stretching, when usually a depression occurs; these effects varied according to the preparation, its initial tension and the frequency of stimulation. The main feature of the examined motor fibres, when stimulated, is the constant excitatory action on muscle spindle static response. Results are discussed. It is suggested that the different characteristics of intrafusal muscle fibres, the receptor initial tension and the frequency of motor units discharges, may together affect muscle spindles static or dynamic performance.     

Analysis of evoked potentials of the cerebellar cortex

Evoked potentials (EP) of the cerebellar cortex in response to stimulation of peripheral nerves are characterized by a two-phase positive-negative oscillation of the potential having a latent period of 10–25 msec. The electropositive phase can contain up to three components. The latent period of component I comprises 3–9 msec. The latent period and amplitude of this component are distinguished by considerable stability, which indicates the predominant significance of presynaptic processes in its formation. The sign of component II changes at a depth of 500 µ (and more), which corresponds to the position of the granular cell layer. At this level there arises in the neurons a response with a latent period of 4–10 msec in the form of a group (3–10) of impulses with a frequency of up to 200 per sec. It is concluded that the granular cells participate in the formation of component II and partially participate in the formation of components I and III of the EP. Responses to stimulation of the nerves appear synchronously with the EP in 24% of responding Purkinje cells; they fall on the maximum electropositive deviation or component III of the EP. Microinjections of 1% strychnine into the cerebellar cortex cause an increase of EP amplitude; impulse activity of the neurons is intensified. This indicates participation of postsynaptic processes in the formation of EP. No shifts in the EP of the cerebellar cortex were observed after intracortical injection of 0.1% atropine.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 429–433, July–August, 1970.     

Unit responses of the sensomotor cortex to paired electrical stimuli

Unit responses of the sensomotor cortex to paired electrical stimulation and visual cortex, applied either simultaneously or after various delays (from 0 to 200 msec) depend on the order of application of the stimuli and on the interval between them. If stimulation of the sensomotor cortex was used in a conditioning role the response continued unchanged when the intervals between stimuli were increased to 200 msec. If, however, stimulation of the sensomotor cortex had a testing role interaction was observed between the stimuli so that responses to both first and second stimuli were blocked; this was exhibited most clearly for intervals of 40–80 msec between stimuli. The blocking effect persisted on some neurons with delays of up to 200 msec between stimuli, while the response of others to both the first and the second stimulus was restored.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 628–635, November–December, 1973.     

Interpretation of the Repetitive Firing of Nerve Cells

Eccentric cells of Limulus respond with repetitive firing to sustained depolarizing currents. Following stimulation with a step of current, latency is shorter than first interval and later intervals increase progressively. A shock of intensity twice threshold can evoke firing 25 msec. after an impulse. But in the same cell, a current step twice rheobase evokes a second impulse more than 50 msec. after the first, and current intensity must be raised to over five times rheobase to obtain a first interval of about 25 msec. Repetitive firing was evoked by means of trains of shocks. With stimuli of moderate intensity, firing was evoked by only some of the shocks and intervals between successive impulses increased with time. This is ascribed to accumulation of refractoriness with successive impulses. Higher frequencies of firing are obtained with shocks of intensity n x threshold than with constant currents of intensity n x rheobase. It is concluded that prolonged currents depress the processes leading to excitation and that (in the cells studied) repetitive firing is controlled both by the after-effects of firing (refractoriness) and by the depressant effects of sustained stimuli (accommodation). Development of subthreshold "graded activity" is an important process leading to excitation of eccentric cells, but is not the principal factor determining frequency of firing in response to constant currents.     

Serotonin-mediated cardiovascular responses to electrical stimulation of the raphe nuclei in the rat.

The dorsal and median raphe nuclei in rats were electrically stimulated and blood pressure and heart rate were recorded. Stimulation of each raphe nucleus caused an increase in blood pressure without affecting heart rate. The size of the increase in blood pressure depended upon the stimulus-intensity.Significant increases were already obtained with 5 sec. trains of 0.3 msec., 200 μA stimuli given at a frequency of 50 Hz. The increases in blood pressure could be obtained with electrodes within the raphe nuclei.Pretreating rats with para-chlorophenylalanine (pCPA, 100 mg/kg.day for 3 days) significantly diminished the increases in blood pressure obtained during electrical stimulation of the median raphe nucleus. However, similar pretreatment did not affect blood pressure rises induced by dorsal raphe stimulation.These data are discussed in relation to the role of central serotoninergic mechanisms in cardiovascular control.     

Background activity of neurones of the amygdaloid complex and its changes in response to hippocampal stimulation

The background activity of neurones of the amygdaloid complex (AC) and changes induced in it by stimulation of the fimbria and adjacent regions of the hippocampus were recorded by means of microelectrodes. Background activity of 40% of the neurones of the AC consisted of an irregular spike discharge, while that of 10% was regular. The remaining neurones showed a tendency to group discharges. High-frequency hippocampal stimulation at 200 pulses/sec inhibited activity of 37% and facilitated activity of 23% of the neurones. Responses began 20–300 msec after the onset of stimulation. Low-frequency stimulation at 0.5–8 pulses/sec facilitated discharges in 42.6% of neurones. The results obtained are discussed in relation to the influence of the hippocampus on AC activity.Institute of Physiology, Siberian Branch of the Academy of Sciences of the USSR, Novosibirsk. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 500–504, September–October, 1971.     

Electrophysiological investigation of the properties of the electroreceptors (ampullae of Lorenzini) in Black Sea rays

Responses of electroreceptors (ampullae of Lorenzini) in Black Sea rays to electrical stimuli were recorded in vivo as spike activity of single nerve fibers. Depending on their functional properties the fibers could be divided into silent, those with regular activity (10–15 spikes/sec) and those with grouped activity. Electrical stimuli evoked a tonic response with a varied degree of adaptation in the nerve fibers. The threshold currents were between 10^?10 and 10^?11 A/mm². The minimal latent period of the on-responses to pulses of current of maximal intensity was 15–40 msec, whereas that of the off-responses was 15–200 msec. The effect of intensity, duration, and polarity of the stimuli on the responses of the receptors and the adaptation of the electroreceptors during application of a steady current were investigated. The properties of the ampullae of Lorenzini were compared with those of other types of electroreceptors.     

Interaction between unit responses of the cat cerebellar cortex during paired stimulation of the forelimbs

Interaction between spike responses of 41 cerebellar cortical neurons to electrical stimulation of the two forelimbs with different intervals between stimuli were studied in cats anesthetized with chloralose and pentobarbital. The responsiveness of neurons with a phasic type of discharge to testing stimulation of the limb was reduced for 300–500 msec or longer after conditioning stimulation of the other limb. Interaction between the responses was less clear in neurons with a tonic type of response. Interaction was absent or was summating in character if the stimuli were applied at the same times. Only if the intertrial intervals were 50–150 msec was regular inhibition of the responses of tonic type to the testing stimulus observed. It is postulated that the nucleus of the inferior olive participates in the interaction between phasic unit responses during simultaneous stimulation of the two limbs or to stimulation separated by short intervals (under 30 msec). With longer intervals between stimuli, interaction between responses of either type is connected with involvement of the lateral reticular nucleus. In the process of interaction competitive relations may develop between responses caused by impulses reaching neurons of the cerebellar cortex along climbing and mossy fibers.