Dependence of the spectrum of electrical activity of the neocortex and hippocampus in rabbits on the intensity of the stimulation of the midbrain reticular formation

Study of dominating spectral maxima in delta-, theta- and alpha-ranges of the electrical activity of rabbits' neocortex and hippocampus showed that an increase of the frequency of the mesencephalic reticular formation stimulation from 60 to 200 imp/s led in both structures to an enhancement of the theta-rhythm (up to 130% in the neocortex and 147% in the hippocampus) and suppression of delta- and alpha-activity (correspondingly up to 67 and 34% in the neocortex and 37 and 48% in the hippocampus) with subsequent weakening of this effect at frequency increase up to 1000 imp/s. In the hippocampus, the reticular stimulation was more effective with respect to the theta- and delta-rhythms, and in the neocortex--with respect to the alpha-rhythm. In both structures the theta-rhythm amplitude changed less than the amplitude of the delta- and alpha-activities. Dependence of the amplitude of dominating rhythms on intensity of reticular formation stimulation differed from the analogous frequency dependence of the same rhythms.     

Spectral characteristics of the EEG of the visual and motor cortices in the rabbit during stimulation of the reticular formation of the brain

Study of amplitude-frequency characteristics of dominating spectral maxima in the delta, theta and alpha-ranges of the rabbit visual and motor neocortical areas has shown that an increase of the midbrain reticular formation stimulation frequency from 60 to 1000 imp/s leads to an increase in both area of dominating rhythms frequencies in the theta and alpha-ranges, and to a decrease of the alpha-rhythm amplitude. The theta-rhythm amplitude in the visual area declines while in the motor area a slight increase is observed and then a decrease. Characteristics of the dominating frequency component in the delta-range are determined by three types of oscillations with different types of dependence on frequency of reticular formation stimulation. The most significant differences between areas are manifest in the spectrum amplitude characteristics. Qualitatively similar changes are also seen in correlation of power of spectral ranges in both areas but quantitatively they are more expressed in the motor area.     

Spectral correlation analysis of the potentials of the neocortex and certain subcortical structures during low-frequency electrical stimulation of nonspecific thalamic nuclei]

The spectral-correlation analysis of biopotentials in the cortex and some other brain structures (the anteroventral thalamic nucleus, dorsal hippocampus, lateral geniculate body, mid-brain reticular formation), in chronic experiments on alert rabbits, revealed that during electrical stimulation of thalamic mid-line nuclei within the ranges of 1-3, 4-7 and 8-10 c/s, there occured a rearrangement of the EEG frequencies; a dominant, narrow-band peak at the stimulation frequency, appeared. The coherence of the biopotentials of different cortical areas, of the cortex and subcortical formations increased during the stimulation at the frequency of the stimulation, reaching maximum values between the potentials of the visual and sensorimotor cortical areas.     

The dynamics of the activating and inhibitory types of cortical neuron synchronization during the realization of a defensive reflex and internal inhibition

In the visual and sensorimotor areas of the neocortex and in the hippocampus of alert nonimmobilized rabbits, in response to combinations of light flashes with electrocutaneous limb stimulation an increase was observed of synchronization in the activity of the near-by neurones by activation by inhibitory type (coincidence of the presence and absence of impulse activity). In response to flashes against the light background--conditioned inhibitor--in the visual cortex synchronization of neurones increased by inhibitory type, and in the sensorimotor cortex and hippocampus changes of synchronization appeared, similar to the action of pain reinforcement but considerably weaker. The increase of synchronization by the activation type took place mainly in the neurones pairs with unidirected increase of impulses frequency and by the inhibitory one--with its decrease. Along with this, in a considerable part of neurones pairs both changes of synchronization appeared at the impulses frequency changes of different direction.     

The structure of the background EEG of the rabbit in the high-frequency portion of the spectrum]

With the purpose of studying the character and structure of high frequency bioelectric activity of rabbits cerebral cortex in the state of calm alertness, the EEG ensembles of different areas of the cortex (sensorimotor, visual, acoustic) and dorsal hippocampus were studied with FFT method. A supposition was made about the presence of systemic organization of the background EEG in rabbits cerebral cortex, reflected, in particular, in the presence of determined components both of chaotic and rhythmic character having different degrees of manifestation. Heterogeneity was revealed in distribution of energies of spectral EEG components in the studied frequency ranges from 14.7 to 100 Hz with predominance of total specific energy value in the band of 14.7-60 Hz. In coherence functions of all the studied pairs of EEG leads rhythmic component, stable in time, was absent. Functions of the mean EEG coherence in the band of 61-100 Hz had significantly greater values in comparison with the values in the band of 14.7-40 Hz.     

Short- and long-term potentiation in afferent pathways of the neonatal rabbit hippocampus

Vocal potentials were recorded in hippocampal area CA₁ and dentate fascia in unanesthetized rabbits aged from 1 to 50 days during stimulation of Schaffer's collaterals and the perforant path, respectively, with paired (interval 15–100 msec) and repetitive (20–40 Hz for 3–5 sec) electric pulses. Short-term potentiation of focal potentials during paired stimulation and post-tetanic potentiation lasting from a few minutes to 3 h were shown to be reproduced in the hippocampus from the first days after birth, whereas in the dentate fascia, which matures later, reproduction began on the 8th–10th day, when neurons first began to respond to stimulation of the corresponding afferent pathways.     

Spatial organization of biopotentials and original features of visual images

Features of spatial organization of neocortical potentials during mental creating of the original and standard visual images were studied. Intrahemispheric and interhemispheric coherence in different EEG frequency bands and temporal relations between relative changes in the index of linear (correlation coefficient) and non-linear (multiple entropy) processes in different neocortical areas were analysed. Number of decreased coherence values in the high-frequency alpha subband between remote neocortical points during creating of an original image was significantly lower than during creating of a standard image. During creating of the original image, the number of synchronously functioning pairs of neocortical areas and the mean level of linear correlation between the areas were higher, and correlation by the non-linear index, on the contrary, was lower than during creation of the standard image. The correlation between changes in different neocortical areas for both processes during creating of the original image was only positive, and that during creating of the standard image was both positive and negative. The conclusion was made that creative and reproductive types of visual imagination were different in the spatial distribution of coordinated changes in the linear and non-linear processes, mean magnitudes of these changes, and the character of hemispheric interaction. The data on different interhemispheric relations in diagonal and central bilateral directions raise a question about the radial representation of visual imagination.     

Functional development of hippocampal mossy fiber synapses in rabbits

The course of functional maturation with age of mossy fiber synapses on pyramidal cells in areas CA_3,4 of the dorsal hippocampus was investigated by extracellular recording of focal potentials and single unit responses of the hippocampus to electrical stimulation of the dentate fascia in waking, unimmobilized rabbits aged from 1 to 14 days. After the 4th day of postnatal life focal potentials appeared in response to single stimulation, in the form of a biphasic short-latency wave, characteristic of responses of the mature hippocampus, accompanied by spike discharges with a latent period of 3 to 10 msec and inhibitory responses of the hippocampal neurons. During the next 10 days the amplitude of the focal potentials increased from several hundred millivolts, with the sharpest increase observed from the 4th through the 7th days. In early age periods global and unitary responses were shown to be capable of frequency potentiation and also of short-term after-potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 246–254, May–June, 1980.     

Content and Concentration of Taurine,Hypotaurine, and Zinc in the Retina,the Hippocampus,and the Dentate Gyrus of the Rat at Various Postnatal Days

Taurine and zinc possess neurotrophic and neuroprotective properties, and they have been demonstrated to interact in the central nervous system (CNS). The aim of this work was to determine taurine, hypotaurine, and zinc levels during postnatal development and any possible significant correlation between them in selective areas of the CNS with differential taurine level regulation and intrinsic capacity to proliferate. Taurine and hypotaurine content (nM/region) and concentration (nM/mg protein) and total zinc levels were determined in the retina, hippocampus, and dentate gyrus of the rat at postnatal days 5, 10, 15, 20, 30, and 50. Taurine and hypotaurine increased during development in the retina without significant correlation between them. In the hippocampus there was a progressive decrease, and in the dentate gyrus there was an initial increase and a posterior decrease of taurine and hypotaurine levels. Correlation between the two amino acids was observed at P10, P15, and P50 for the hippocampus and at P15, P30, and P50 for the dentate gyrus. The variations in total zinc levels followed a biphasic behavior, with an early decrease and later increase. Significant and positive correlation of zinc and taurine was only observed in the hippocampus at P30 and P50 and negative in the dentate gyrus at P30. No significant correlation was obtained for the retina. The maintenance of taurine levels in specific CNS areas does not seem to be related to the availability of the precursor, hypotaurine, which might have a role by itself. There are critical postnatal periods during which there is a preservation of taurine, hypotaurine, or zinc levels. It seems that these requirements could be related to zinc-taurine interactions.     

Alpha-Band Rhythms in Visual Task Performance: Phase-Locking by Rhythmic Sensory Stimulation

Oscillations are an important aspect of neuronal activity. Interestingly, oscillatory patterns are also observed in behaviour, such as in visual performance measures after the presentation of a brief sensory event in the visual or another modality. These oscillations in visual performance cycle at the typical frequencies of brain rhythms, suggesting that perception may be closely linked to brain oscillations. We here investigated this link for a prominent rhythm of the visual system (the alpha-rhythm, 8–12 Hz) by applying rhythmic visual stimulation at alpha-frequency (10.6 Hz), known to lead to a resonance response in visual areas, and testing its effects on subsequent visual target discrimination. Our data show that rhythmic visual stimulation at 10.6 Hz: 1) has specific behavioral consequences, relative to stimulation at control frequencies (3.9 Hz, 7.1 Hz, 14.2 Hz), and 2) leads to alpha-band oscillations in visual performance measures, that 3) correlate in precise frequency across individuals with resting alpha-rhythms recorded over parieto-occipital areas. The most parsimonious explanation for these three findings is entrainment (phase-locking) of ongoing perceptually relevant alpha-band brain oscillations by rhythmic sensory events. These findings are in line with occipital alpha-oscillations underlying periodicity in visual performance, and suggest that rhythmic stimulation at frequencies of intrinsic brain-rhythms can be used to reveal influences of these rhythms on task performance to study their functional roles.     

Distribution of biogenic amines in the hippocampal formation in the rabbit]

The hippocampal formation (the hippocampus and the dentate fascia) of the rabbit was studied by histochemical fluorescent method of Falk to determine localization of monoaminergic terminals containing biogenic amines: noradrenalin, dophamine and serotonin. It was shown that monoaminenergic terminals in the hippocampus were in two zones of afferent terminations: in the zone of ending of the perforating way (str. lacunosum-moleculare of fields CA1 and CA2; str. moleculare of the dentate fascia) and in the subgranular zone of the hilum where a part of septofimbrial way terminated on granular neurons of the dentate fascia, the main cellular elements of the hipocampus (pyramidal, granular and basket cells of the hippocampus) did not contain biogenic amines.     

The intercentral relations of the frontal cortex and limbic structures of the brain in dogs]

In 3 dogs with implanted electrodes, in conditioned experiments correlation of the bioelectrical processes was studied by coherence function calculation of the hippocampus, hypothalamus, amygdala and frontal cortex biopotentials. It was shown, that the level of maximum values of coherence function of bioelectrical oscillations, led from various pairs of the studied brain structures significantly differed both in magnitude and frequency at which the greatest synchronization of biopotentials was noticed. In one dog with a high degree of connection between the hippocampus and hypothalamus biopotentials oscillations, a low synchronization of the frontal cortex and amygdala oscillations was found; in two other animals with a higher level of coherence between the oscillations of the frontal cortex and amygdala biopotentials, a lower degree of connection between the oscillations led from the hippocampus and hypothalamus was revealed. Synchronization of the biopotentials of the hippocampus and frontal cortex and also of the hippocampus and amygdala biopotentials proved to be low in all experimental dogs, what additionally testifies to different role of these structures in organization of the behaviour.     

甲低对新生早期大鼠海马及齿状回Goα mRNA的影响

目的：研究甲状腺功能低下（甲减）对围生早期大鼠海马及齿状回Goα mRNA表达的影响。方法：采用地高辛标记寡核苷酸探针原位杂交技术,观察7d龄围生期甲减及正常Wistar大鼠海马CA1－4区及齿状回Goα mRNA的表达状况。结果：7d龄甲状腺激素对围生早期海巴及齿状回Goα 基因的表达具有负调节作用。     

Systems organization of cerebral processes in the cat during learning while undergoing electrical stimulation of the neocortex

A delayed spatial choice (DSC) was elaborated in five cats during electrical stimulation (ES) of the frontal cortical parts with a frequency of 80 imp/s. Then the task fulfillment was tested following cessation of the electrostimulation or under the action of other current frequencies (35,3 and 120 imp/s). The number of erroneous choices increased in the absence of ES or during 3 imp/s ES of the frontal parts. The effects of frequencies of 35,80 and 120 imp/s did not differ. Three cats were trained to DSC without ES. The conditioned reflexes were tested during ES of the frontal cortical parts with current frequency of 3 and 80 imp/s. Statistically significant increase of the number of erroneous responses took place in both situations. The obtained data are discussed from the point of view of the integrative activity of the cerebral structures in DSC. Its disturbance during ES of the cortical zones and dissociation (discordance) after cancellation of stimulation during which the conditioned reflex had been elaborated, point to systemic organization of brain functioning in goal-directed forms of behaviour.     

Spectral correlation parameters of neocortical potentials in the rabbit undergoing paired isorhythmic stimulation

At pairing of isorhythmic stimuli beyond the theta-rhythm frequency limits (3 and 8 Hz), in power spectra of EEGs of the sensorimotor and visual neocortical areas of rabbits, the frequencies are present both of the theta-range and of the stimulation frequency, in the background activity as well as during the stimulation. Both rhythms are in reciprocal relations. The frequency of the theta-rhythm approaches the frequency divisible by that of the stimulation. Under the action of the conditioned stimulus, crosscorrelation coefficients (CC) between the potentials of the areas under study decrease in most cases in comparison to their background values. Combination of the conditioned stimulus with the unconditioned one, leads approximately in equal number of cases to an increase or decrease of CC. After elimination of the stimuli, in most cases CC increases. CC of the background activity does not increase in the course of paired stimuli presentation though a conditioned response is being formed. At presence of stimuli frequency fluctuations simultaneously in the potentials of both areas, the rise of coherence function at this frequency does not occurs always. Thus, the above spectral-correlation parameters of rabbit's cortical potentials differ from those which arise at pairing of continuous nonrhythmic stimuli. This difference is probably due to different characteristics of the stimuli presented.     

The relative sensitivity of Renshaw cells to orthodromic group Ia volleys caused by static stretch and vibrations of extensor muscles.

1. Activity of Renshaw cells monosynaptically excited by ventral root stimulation and disynaptically excited by electric stimulation of the group Ia afferents in the gastrocnemius-soleus (GS) nerve, was recorded in precollicular decerebrate cats. The response of these units to prolonged vibration applied longitudinally to the deefferented GS muscle was then compared with that elicited by static stretch of the homonymous muscle, for comparable frequencies of discharge of the group Ia afferents. 2. Small-amplitude vibration of the GS muscle at 200/sec for one second produced a sudden increase in the discharge rate of Renshaw cells, which gradually decreased within the first 100 msec of vibration to reach steady albeit lower level than that obtained during the first part of vibration. The response of the Renshaw cells during the first 100 msec of vibration (phasic response) and that elicited during the last 500 msec of vibration (tonic response) were evaluated for different frequencies of sinusoidal stretch. The mean increase in the firing frequency per imp./sec in the Ia afferents was also calculated using the total one-second period. 3. The response of Renshaw cells to muscle vibration increased with the frequency of vibration and, over the value of 10/sec, appeared to be linearly related to the frequency of the input, at least up to the frequency of 150/sec. Since vibration was of sufficient amplitude to produce driving of all the primary endings of muscle spindles, the responses were expressed as mean increases in the discharge rate of Renshaw cells per average impulse/sec in the Ia afferents. The discharge of the Renshaw cell increased on the average by 2.90 and 1.08 imp./sec per each imp./sec in the Ia afferents during the phasic and the tonic component of the response respectively, while the response calculated during the whole period of vibration corresponded on the average to 1.45 imp./sec per each imp./sec in the Ia afferents. 4. The Renshaw cells tested above responded also with increasing frequencies of discharge to increasing levels of static extension of the GS muscle. In particular the discharge frequency of Renshaw cells was on the average linearly related to muscle extension, at least for values ranging from 0 to 8 mm. The mean increase in discharge rate as a function of the static extension corresponded on the average to 0.89 imp./sec/mm. Since the discharge rate of the primary endings of muscle spindles recorded from the deefferented GS muscle increased by 2.62 imp./sec/mm, it appears that the mean increase in the discharge rate of Renshaw cells as a function of static extension corresponded to 0.34 imp./sec per each imp./sec in the Ia afferents.     

Time course of changes in long-term potentiation of synaptic transmission following subcortical deafferentation on the rat hippocampus.

Brief tetanic stimulation potentiates synaptic transmission both in the CA1 and dentate area of slices cut from normal rats. This long-term potentiation (LTP) was assayed in slices made at various times from rats subjected to complete bilateral sectioning of all subcortical afferents which enter the hippocampus. Over about one week survival time, LTP is present in the CA1 region of all and also in the fascia dentata of about 50% of slices. We found no signs of LTP in the dentate area of slices cut over 8 weeks after deafferentation, while the responses were clearly potentiated in the CA1 area of the same slices. Four week was the longest period when a somewhat modified version of LTP could be produced in the subcortically deafferented dentate area. The results confirm previous reports that subcortical afferents mediate some unknown factors essential for maintenance of long-term plasticity of intrinsic synapses in the fascia dentata. This unidentified, perhaps trophic influence diminishes in about 4 weeks after severing the subcortical fibers. In contrast, maintenance of subcortical inputs are apparently not required for the LTP in the intrinsic CA1 synapses.     

Long-term potentiation in the dentate gyrus of the anaesthetized rat is accompanied by an increase in extracellular glutamate: real-time measurements using a novel dialysis electrode

We have used a glutamate-specific dialysis electrode to obtain real-time measurements of changes in the concentration of glutamate in the extracellular space of the hippocampus during low-frequency stimulation and following the induction of long-term potentiation (LTP). In the dentate gyrus, stimulation of the perforant path at 2 Hz for 2 min produced a transient increase in glutamate current relative to the basal value at control rates of stimulation (0.033 Hz). This activity-dependent glutamate current was significantly enhanced 35 and 90 min after the induction of LTP. The maximal 2 Hz signal was obtained during post-tetanic potentiation (PTP). There was also a more gradual increase in the basal level of extracellular glutamate following the induction of LTP. Both the basal and activity-dependent increases in glutamate current induced by tetanic stimulation were blocked by local infusion of the N-methyl-D-aspartate receptor antagonist D-APV. In areas CA1 and CA3 we were unable to detect a 2 Hz glutamate signal either before or after the induction of LTP, possibly owing to a more avid uptake of glutamate in the pyramidal cell fields. These results demonstrate that LTP in the dentate gyrus is associated with a greater concentration of extracellular glutamate following activation of potentiated synapses, either because potentiated synapses release more transmitter per impulse, or because of reduced uptake by glutamate transporters. We present arguments favouring increased release rather than decreased uptake.     

Formation of spontaneous and evoked unit activity in organotypical hippocampal tissue culture

Spontaneous and evoked single unit activity of Ammon's horn and the dentate fascia was investigated by extracellular recording in organotypical explants of neonatal mouse hippocampus during the first 2 weeks in culture. Three main types of spontaneous activity were observed: single, group, and volley. After the fifth to sixth day in culture the neurons were found to respond to stimulation of the entorhinal cortex and dentate fascia. Both short-latency (evidently monosynaptic) and long-latency responses were observed, and they usually varied if the stimulus was repeated. The appearance of evoked unit activity in the explants is considered to be due to maturation of synaptic contacts at axon endings of granule cells and perforant path, the formation of which continues during culture.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 257–266, May–June, 1977.     

Morphological and physiological study of afferent projections of the posterolateral thalamic nucleus in rats

It was shown by the method of retrograde axonal transport of horseradish peroxidase that the posterolateral thalamic nucleus (NPL) in rats receives considerable ascending projections from the superior colliculus (SC), the dorsal part of the lateral geniculate body (LGB), and the pretectal region (PT) and smaller projections from n. ventralis posterior (VP) and n. ventralis lateralis (VL) of the thalamus, the ventral part of LGB, the zona incerta, and anterior hypothalamus. The most marked descending projections run into NPL from area 18A of the cortex and the dentate fascia of the hippocampus, whereas inputs from cortical areas 18, 20, 7, 29c, 17, and 36 are less marked. In electrophysiological experiments with peripheral stimulation of visual, auditory, and somatosensory systems, polysensory convergence and interaction between signals from these systems were studied during isolated and simultaneous presentation of heterosensory stimuli. Of 229 neurons tested, 134 (58.5%) responded to at least one of the stimuli mentioned. Among monomodal neurons (53 of 134) there were some cells which responded to visual (77.4%) and somatic (22.6%) stimulation; neurons which responded only to acoustic stimulation were not found in the nucleus. As far as polymodal neurons (81 of 134) responding to two or three sensory stimuli are concerned, the most effective inputs of these units were visual and somatosensory. Interaction between stimuli acting on polymodal neurons was expressed as mutual inhibition or facilitation of responses; opposite effects could be observed on the various components of these responses.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 168–176, March–April, 1984.