Cortical and subcortical spreading depression in rats produced by focused ultrasound

Steady potential shifts produced by focused ultrasond were recorded in the cerebral cortex, hippocampus, thalamus, and caudate nucleus. Impulses of 50–100 msec duration were presented at a frequency of 5 and 10 Hz. Negative steady potential shifts were produced in each of the structures investigated, which gradually increased during rhythmic electrical reaction to reach –3 to –7 mV within 10–30 sec, often succeeded by a wave of spreading depression (SD). In each structure analyzed amplitude of SD waves measured 20–30 mV, lasting 30–40 sec in the cortex, the caudate nucleus and the thalamus, and 80–120 sec in the hippocampus. In unanesthetized and lightly anesthetized animals SD waves were on occasions the precursors of convulsive discharges forming under the action of focused ultrasound. Ultrasound at threshold doses proved ineffective for 5–7 min after the occurrence of an SD wave, but again evoked repeated SD waves once the refractory period had ended. Accordingly, local effects produced by focused ultrasound can result in functional blockage of the brain structures due to cortical and subcortical spreading depression.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Institute of Brain Research, All-Union Research Center of Mental Health, Academy of Medical Sciences of the USSR, Moscow. N. N. Andreev Acoustic Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 55–61, January–February, 1986.     

Cortical spreading depression synaptically induced by brief high-frequency electrical stimulation of the rat brain

Electrical stimulation (ES) at the surface of the rat brain (10–200 Hz; brief trains of 10 pulses) was found to be most effective for evoking waves of spreading depression (SD) in the cortex. Repeated stimuli spaced at 10–15 min intervals did not produce convulsive activity and nor did mechanisms of SD inhibition set in under these conditions. A 5–6-fold reduction in SD threshold occurred when the intra-burst rate was increased from 10 to 200 Hz. Temporal summation of residual processes occurring with suprathreshold ES applied at the rate of 50 and 200 Hz resulted in significant broadening of the SD focus in the ES area and regular occurrence of additional SD foci on the side ipsilateral to stimulation and in the contralateral cortex. The protracted changes in cortical excitation lingering after ES by high-frequency currents brought about a decline in SD threshold and pointed to the active part played by synaptic processes in triggering this reaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 789–796, November–December, 1989.     

Movement of thermowaves over the cerebral cortex in the white rat

Thermal spatial distribution and temperature pattern were recorded using techniques of thermovision and digital image processing through the intact skull during acute experiments on white rats immobilized using myorelaxants or anesthetized with Nembutal. Under certain circumstances faint cortical thermowaves of 0.2-0.1°C were seen to arise and move 8–30 mm across the cortex for 2–9 sec at a speed of 2–10 mm per sec. One of the trajectories of movement detected was circular in shape; the thermowave would start off in one hemisphere, spread across it in either direction, and cross to the other hemisphere. It would then move through the second hemisphere to the opposite side and finally return to the original area. Movement of the waves also followed linear and arc-shaped trajectories, sometimes but not always crossing over to the opposite hemisphere. The mechanisms and implications of this phenomenon are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 340–346, May–June, 1986.     

Binocular interaction in the parastriatal rat cortex during a change in intensity of one monocular stimulus

Binocular interaction in symmetrical centers of the parastriatal cortex in rats was investigated by the evoked potentials method before and after callosotomy. A model was used in which one eye was always stimulated by flashes of average intensity and the other by flashes of average intensity. The presence of contralateral and ipsilateral facilitation, increasing with the strength of the stimulus, was demonstrated; contralateral facilitation was more effective than ipsilateral. Synergism in the development of the contralateral and ipsilateral effects is emphasized, distinguishing them from the corresponding processes in the striatal cortex. After callosotomy the contralateral and ipsilateral facilitatory effects are intensified.Biological Institute, Leningrad University. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 128–132, March–April, 1973.     

Binocular interaction in the striatal cortex of rats during changes in intensity of a monocular stimulus

Binocular interaction was investigated by the evoked potentials method in symmetrical centers of the rat striatal cortex before and after division of the corpus callosum. One eye was always stimulated by flashes of average intensity and the other by flashes of varied intensity. Contralateral facilitation was shown to be increased with an increase in the strength of stimulation. Ipsilateral facilitation was found to exist and to change into ipsilateral depression. In all cases contralateral effects were stronger than ipsilateral. The reciprocity of contralateral and ipsilateral influences in the striatal cortex is emphasized. Division of the corpus callosum leads to strengthening of the contralateral and ipsilateral facilitatory and depressive influences. Depressive ipsilateral influences are found after callosotomy in response to weaker stimuli than before the operation.Biological Institute, Leningrad University. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 122–127, March–April, 1973.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Visual cortical detector neurons in the Siberian chipmunkEutamias sibiricus

Three functional classes of neurons are described in the visual cortex of the Siberian chipmunk: neurons not selective for direction of movement and orientation, neurons selective for movement in a particular direction, and neurons selective for orientation. Unselective and directionally-selective neurons were activated maximally at speeds of movement of 100–500 deg/sec or more, most orientation-selective neurons at speeds of 10–50 deg/sec. For all three classes of neurons clear correlation was observed between selectivity for velocity of movement and character of responses to presentation of stimuli stationary in the receptive field. With reference to this sign the neurons were divided into two groups: phasic (fast) and tonic (slow). Phasic (fast) neurons predominate in the visual cortex ofEutamias sibiricus.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 807–814, November–December, 1984.     

Focal evoked potentials in the rabbit visual cortex: Current source density analysis

Focal evoked potentials arising in the rabbit visual cortex in response to photic stimulation from a point source were analyzed by determination of the current source density. The response to a point stimulus arises in a circumscribed area of cortex, corresponding retinotopically to the stimulated point of the visual field and it consists of two components. The first component is created by a local current sink at a depth of 0.6 to 1.0 mm (the level of layer IV) and has a latent period of 30 msec and a peak time of 50 msec. The second component is created by a more diffuse current sink at a depth of 0.2–0.3 to 1.3–1.5 mm (levels between layers III and VI); the time to the maximum was 90–100 msec. These local sinks are regarded as active, created by depolarizing synapses. Passive current sources are concentrated around zones of active sinks. The two components of the response may reflect two consecutive waves of activation of cortical neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 474–481, September–October, 1981.     

MEP Latencies Predict the Neuromodulatory Effect of cTBS Delivered to the Ipsilateral and Contralateral Sensorimotor Cortex

Background

Recently, it was shown that the highly variable after-effect of continuous theta-burst stimulation (cTBS) of the primary motor cortex (M1) can be predicted by the latency of motor-evoked potentials (MEPs) recorded before cTBS. This suggests that at least part of this inter-individual variability is driven by differences in the neuronal populations preferentially activated by transcranial magnetic stimulation (TMS).

Methods

Here, we recorded MEPs, TMS-evoked brain potentials (TEPs) and somatosensory-evoked potentials (SEPs) to investigate the effects of cTBS delivered over the primary sensorimotor cortex on both the ipsilateral and contralateral M1, and the ipsilateral and contralateral primary somatosensory cortex (S1).

Results

We confirm that the after-effects of cTBS can be predicted by the latency of MEPs recorded before cTBS. Over the hemisphere onto which cTBS was delivered, short-latency MEPs at baseline were associated with an increase of MEP magnitude (i.e. an excitatory effect of cTBS) whereas late-latency MEPs were associated with reduced MEPs (i.e. an inhibitory effect of cTBS). This relationship was reversed over the contralateral hemisphere, indicating opposite effects of cTBS on the responsiveness of the ipsilateral and contralateral M1. Baseline MEP latencies also predicted changes in the magnitude of the N100 wave of TEPs elicited by stimulation of the ipsilateral and contralateral hemisphere, indicating that this TEP component is specifically dependent on the state of M1. Finally, there was a reverse relationship between MEP latency and the effects of cTBS on the SEP waveforms (50–130 ms), indicating that after-effects of cTBS on S1 are opposite to those on M1.

Conclusion

Taken together, our results confirm that the variable after-effects of cTBS can be explained by differences in the neuronal populations activated by TMS. Furthermore, our results show that this variability also determines remote effects of cTBS in S1 and the contralateral hemisphere, compatible with inter-hemispheric and sensorimotor interactions.     

Changes in visual evoked potentials after injection of tetanus toxin into the lateral geniculate body

Changes in visual evoked potentials were studied in rats at different stages of formation of experimental photogenic epilepsy induced by injection of tetanus toxin into the lateral geniculate body. The greatest change in evoked potentials in the lateral geniculate body consisted of the appearance of an aditional component in the series of waves of the primary response. Meanwhile in the ipsilateral visual cortex the amplitude of the first negative component of the evoked potential was considerably increased. Correlation was found between the changes in the amplitude of this component in the visual cortex and the change in steepness of the additional component of the evoked potential in the geniculate body, reflecting functional reorganization of that nucleus. The results are evidence of significant disturbances of the relay function of the lateral geniculate body when a generator of pathologically enhanced excitation is formed in it.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 142–149, March–April, 1978.     

Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28–19, 14–12, and 10–9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 243–249, May–June, 1976.     

Influence of the stimulation of the dorsal hippocampus on the dorsal root potentials of the spinal cord in the cat

Rhythmic stimulation of the dorsal hippocampus causes a long-lasting (2–6 sec) depression of both the fast and the electrotonic dorsal root potentials. The depression depends on the intensity of the stimulation of the hippocampus and on the time interval between the stimulation of the hippocampus and the nerve. The sortest time interval producing the depression was within 15–20 msec. The action of afferent impulsation is depressed during both the ipsilateral and contralateral stimulation of the hippocampus. The stimulation of the fornix also exerts a depressing influence on the dorsal root potentials; however, it is not so prolonged as the stimulation of the hippocampus (500–600 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 186–193, September–October, 1969.     

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.     

Optic Flow Stimuli in and Near the Visual Field Centre: A Group fMRI Study of Motion Sensitive Regions

Motion stimuli in one visual hemifield activate human primary visual areas of the contralateral side, but suppress activity of the corresponding ipsilateral regions. While hemifield motion is rare in everyday life, motion in both hemifields occurs regularly whenever we move. Consequently, during motion primary visual regions should simultaneously receive excitatory and inhibitory inputs. A comparison of primary and higher visual cortex activations induced by bilateral and unilateral motion stimuli is missing up to now. Many motion studies focused on the MT+ complex in the parieto-occipito-temporal cortex. In single human subjects MT+ has been subdivided in area MT, which was activated by motion stimuli in the contralateral visual field, and area MST, which responded to motion in both the contra- and ipsilateral field. In this study we investigated the cortical activation when excitatory and inhibitory inputs interfere with each other in primary visual regions and we present for the first time group results of the MT+ subregions, allowing for comparisons with the group results of other motion processing studies. Using functional magnetic resonance imaging (fMRI), we investigated whole brain activations in a large group of healthy humans by applying optic flow stimuli in and near the visual field centre and performed a second level analysis. Primary visual areas were activated exclusively by motion in the contralateral field but to our surprise not by central flow fields. Inhibitory inputs to primary visual regions appear to cancel simultaneously occurring excitatory inputs during central flow field stimulation. Within MT+ we identified two subregions. Putative area MST (pMST) was activated by ipsi- and contralateral stimulation and located in the anterior part of MT+. The second subregion was located in the more posterior part of MT+ (putative area MT, pMT).     

Conduction velocity and excitability of A and C fibers of cat mesenteric nerves

The conduction velocity and excitability of fibers running from the mesenteric into the splanchnic nerves were studied in experiments on cats. Among the A fibers of these nerves there were shown to be: 1) fibers with an excitation threshold of 0.06–0.10 V (stimulus duration 0.1 msec) and a maximal conduction velocity of 48–85 m/sec; 2) fibers with an excitation threshold of 0.3–0.7 V, impulses of which form up to five waves in the composition of the action potential, with maximal conduction velocities of between 8–10 and 33–39 m/sec; 3) fibers with an excitation threshold of over 1 V and a conduction velocity of between 1.8 and 7 m/sec. The excitation threshold of the group C fibers was 6–8 V. Impulses of these fibers form a low-amplitude wave in the composition of the action potential of the mesenteric and splanchnic nerves with a conduction velocity of 1.0–1.8 m/sec, several waves of higher amplitude with a conduction velocity of 0.5–1.2 m/sec, and several low-amplitude waves with a conduction velocity of 0.35–0.55 m/sec. The results of experiments with different combinations of arrangement of the stimulating and recording electrodes on the mesenteric and splanchnic nerves indicate that sympathetic postganglionic C fibers of the mesenteric nerves occur only in the second group, whereas afferent C fibers occur in all three of the groups distinguished.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 3, pp. 272–278, May–June, 1975.     

Thermal distribution over the cortical surface of the rat brain under direct electrical stimulation

The dynamics of thermal diffusion from the dorsal brain surface were studied in white rats through the intact skull during acute experiments on immobilized or Nembutal anesthetized white rats using a new thermovisualization technique involving direct electrical stimulation of the cortex. Local cortical heating of a 1–4 mm site in the vicinity of the electrodes set in within 160 msec after presentation of a single stimulus, reaching a maximum of 0.2°C by the 2nd-5th sec and slowly decaying to the initial level by the 2nd-3rd min. At the same time, but at a somewhat slower rate, the symmetrically opposite local site in the other hemisphere heated up, followed by a small area in the ipsilateral motor cortex and a number of other zones. Depending on the dose administered, Nembutal inhibits and decelerates the development of these effects and localizes them, raises the minimum threshold of their occurrence, and prolongs their closed state. As anesthesia deepened, the primary heat focus near the stimulating electrodes persisted the longest. The mechanisms underlying local cortical thermal responses and the time parameters of these are discussed and compared with those of the dynamics of standard electrographic effects.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 216–223, March–April, 1987.     

Investigation of detector properties of neurons in the visual system of the rabbit

Responses of neurons in the superior colliculi and visual cortex of rabbits to a black and white boundary moving in different directions were investigated. Neurons responding clearly to presentation of the black and white boundary moving in one direction (movement in the opposite direction led to inhibition of spontaneous activity) and neurons giving well-defined maximal responses to movement of this boundary in 2 or 3 directions were found in the superior colliculi. Neurons with a marked maximal response to the stimulus moving in 1 or 2 directions were found in the visual cortex. Nembutal has a powerful effect on the quantitative detector properties of visual cortical neurons and sometimes may completely inhibit unit activity.V. Kapsukas Vilnius State University. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 61–67, January–February, 1972.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Formation of "caudate spindles" in the rabbit sensomotor cortex during ontogeny

Electrical activity of the sensomotor and visual areas of the neocortex during stimulation of the caudate nucleus was recorded in young rabbits aged 3–60 days and in adults. Single stimulation of the caudate nucleus was found to cause the appearance of characteristic bursts of spindle-like rhythmic activity ("caudate spindles"), described previously in cats and monkeys, in the adult rabbit cortex. The latent period of the caudate spindle was about 200 msec, its duration 1–3 sec, and the frequency of its oscillations of the order of 12 Hz. Caudate spindles were most marked in the sensomotor cortex of the ipsilateral hemisphere. In rabbits under 10 days old caudate spindles were not found even if the intensity of stimulation was increased many times. Starting from the age of 15 days bursts of rhythmic activity resembling caudate spindles, but with lower frequency (about 8 Hz), longer latent period (up to 350 msec), and also with a higher threshold, appeared in the sensomotor cortex. The definitive type of caudate spindles was established toward the end of the first month of postnatal life, corresponding to the time of formation and complication of conditioned-reflex activity in developing animals.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 11–15, March, 1985.     

Complex interrelationships among CL,preovulatory follicle,number of follicular waves,and right or left ovaries in heifers

The diameter of the dominant follicle (DF) of wave 1 was studied on Days 9 to 17 (Day 0 = ovulation) in a survey of the ipsilateral and contralateral relationships between the location of the DF and CL, and number of follicular waves per interovulatory interval (IOI). For contralateral relationships, regardless of number of waves the diameter of the DF of wave 1 decreased (P < 0.03) between Days 11 and 13 when referenced to the follicle–CL relationship of wave 1 and decreased (P < 0.008) between Days 9 and 11 when referenced to the preovulatory follicle (PF)–CL relationship. For wave 2 in two-wave IOIs, the CL ovary of ipsilateral relationships had more (P < 0.05) follicles that reached at least 6 mm than the non-CL ovary. In three-wave IOIs, frequency of IOIs with the DF in the CL ovary was greater (P < 0.02) for wave 2 than for wave 3. In wave 3, the preovulatory and the largest subordinate follicles were located more frequently (P < 0.005) in the contralateral ovary. Ovulation in two-wave IOIs occurred more frequently (P < 0.0009) from the right ovary. In three-wave IOIs with a contralateral relationship ovulation occurred more frequently (P < 0.003) from the left ovary; a negative intraovarian effect of the CL on location of the PF may account for more ovulations from the left ovary and a reported greater frequency of the contralateral relationship. The hypothesis was supported that the ipsilateral versus contralateral relationship between the PF and CL is affected by the DF–CL relationship during the previous follicular waves and by the number and identity of waves per IOI.