Interhemispheric relations of prefrontal cortical neurons in rats during emotional stimulation of increasing intensity

Unit activity of the prefrontal cortex of the right and left brain hemispheres of rats was recorded during intracranial stimulation of emotionally positive and negative brain structures. The neurons were divided according to their reaction to a change in food motivation: cells that decrease (M-neurons) and cells that increase their firing frequencies (R-neurons) after feeding. Three levels of stimulation current intensity were used. When stimuli of subthreshold intensity (evoking the behavioral reaction of smelling) were applied, the recorded neuronal activity was higher in the left hemisphere. During threshold emotionally positive or negative stimulation (producing approach behavior or freezing, respectively), activity of M-neurons was higher in the right hemisphere, whereas the left-side R-neurons were more active than the right-side ones. During strong emotionally positive stimulation producing self-stimulation, the firing frequency of both groups of neurons was higher in the left hemisphere. Strong emotionally negative stimulation that evoked behavioral avoidance to a greater extent activated the right hemisphere.     

Neuronal activity in the prefrontal cortex in rats with various typological features during emotional affect

Unit activity in the right and left prefrontal cortex was recorded in male Wistar rats after testing by the emotional resonance technique. Rats were divided in two groups by their reaction to the suffering cry of a partner. Rats from the group A ("altruists") escaped partner's crying, and those from the group E ("egoists") did not. Activity of neurons was analyzed in hungry rats, after feeding, during intracranial emotionally positive and negative stimulation, and during crying of the rat partner. Some differences in neural activity between A and E groups were revealed. In the hungry state the rate of neuronal discharges was higher in the A group. In both groups of animals the positive emotional stimulation was accompanied by more intensive neuronal reaction that the negative stimulation, but in the E group increase in the rate of neuronal discharges in both hemispheres was significantly more pronounced. Negative stimulation produced in both groups a significantly greater activation in the left hemisphere than in the right one while during the positive stimulation the neural activity was more intensive in the left hemisphere. The neuronal reaction to partner's crying was significantly higher in the A group in both hemispheres, while the neuronal activity in E group did not significantly change.     

Impulse activity in the CA1 field in animals of various typological groups exposed to emotional stimuli

Hippocampal unit activity in the right and left CA1 fields was studied in rats divided in two groups by the method of "emotional resonance": the animals that did (A) and did not stop (E) crying of rat-partner. The rate of neuron firing was studied in the state of hunger, satiation, and under exposure to intracranial electrical stimulation of the emotional positive and negative structures of the brain. It was shown that the intracranial stimulation, especially positive, increased the rate of firing. Under exposure to emotional stimuli, the neural activity was asymmetric only in the A rats. The activity at the left was more intensive than the right-sided activity and did not depend on the sigh of emotion.     

Hippocampal neurons of the CA3 field in animals of different typological groups exposed to emotional stimuli

Hippocampal unit activity in of the right and left CA3 fields was studied in rats which were divided in two groups by the method of "emotional resonance": the animals that did ("A") and did not stop ("E") crying of rat-partner. The rate of neuron firing was studied in the state of hunger, satiation, and under exposure to intracranial electrical stimulation of the emotional positive and negative structures of the brain. It was shown that the intracranial stimulation, especially positive, increased the rate of firing. Under exposure to emotional stimuli, the neural activity was asymmetric only in E rats. The activity at the left was more intensive then the right-side activity and did not depend on the sigh of emotion.     

Comparative analysis of neuronal impulse activity in the CA1 and CA3 hippocampal fields in various typological groups of rats under exposure to emotional stimuli

Hippocampal unit activity in the right and left CA1 and CA3 fields was studied in rats divided in two groups by the method of "emotional resonance": the animals which did ("A") and did not stop ("E") crying of a partner rat. The rate of neuronal firing was studied in the state of hunger, satiation, and under exposure to intracranial electrical stimulation of the emotional positive and negative structures of the brain. It was shown that units increasing their activity after satiation prevailed in the CA1 field, whereas, in the CA3 field, the majority of neurons decreased the firing rate under these conditions. Intracranial stimulation, especially positive, increased the rate of firing in both hippocampal fields. Under exposure to emotional stimuli, "A" rats displayed asymmetric unit activity only in the CA1 field, whereas in "E" rats, activity was asymmetric only in the CA3 field. Under these conditions in both groups of animals, the left-side activity was more intense than the right-side activity independently of the emotion sign.     

The structure of dependent relationship between neurons in the sensorimotor cortex of the left and right hemisphere in rabbits during immobilizing catatonia

Relations between activities of neurons simultaneously recorded in the left and right sensorimotor brain cortices of rabbits were analyzed in a series of experiments before the induction of the immobilization state ("animal hypnosis"), in the state of immobilization, and after its termination. The total baseline percent of significant correlations between activities of neighboring (within 50 microns) neurons in the left hemisphere was significantly lower than in the right hemisphere. This characteristic of the left hemisphere changed neither in the immobilization state nor after its termination. In the right-hemisphere cortex, the total percent of correlations between neighboring neurons significantly decreased during immobilization and returned to the baseline level after the termination of this state. In contrast, percent of correlations between the activities of remote (within 500 microns) neurons in the right-hemisphere did not change during immobilization, whereas in the left cortex it changed significantly and reached its baseline level after the normalization of rabbit's state. Further analysis showed that the revealed cortical interhemispheric asymmetry is underlain by asymmetric activities of individual neurons and small neuronal populations. Thus, for example, changes in the structure of interneuronal correlations in cortical microareas of the left and macroareas of the right hemispheres could be of different directions, whereas correlated activities in microareas of the right and macroareas of the left-hemispheres could change synergetically. In other words, asymmetry was revealed at different levels of neuronal integration (neuronal pairs, micro- or macrogroups of neurons). This finding testifies to a mosaic character of neuronal activity, which finally results in the general functional asymmetry during the "animal hypnosis". Certain changes in the structure of functional relations between neurons of the sensorimotor cortex that developed in the state of "animal hypnosis" persisted and even augmented after the termination of this state.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Hemispheric asymmetry of the space-motion component of a food-conditioned motor reflex

The preference of movement direction in the process of motor food conditioned reaction has been investigated in rats with intact brain and after unilateral cortical inactivation. It was shown that the degree of motorspatial preference diminished with the maturation of reaction. At the high level of differentiation the valid preference was shown only in 38% of animals investigated but it was absent in the rest of animals. After inactivation of right hemisphere cortex left-side preference occurred in the presence as well as in the absence of the original preference. Inactivation of the left hemisphere cortex is less significant; it influences the original preference of movement direction permanently affecting those animals which normally had evident preference. It is concluded that the right hemisphere cortex plays dominant part in both sensor and motorspatial components of motor food conditioned reaction. It is supposed that the definite relationship exists between the degree of preference of movement direction and the functional asymmetry of cerebral hemispheres.     

Hemispheric asymmetry of the nigrostriatal system of the brain in rats genetically predisposed to catalepsy]

Hemispheric asymmetry of nigro-striate system in a strain of rats GC bred from Wistar for a predisposition to cataleptic reaction was studied by means of biochemical and morphological methods. Hemispheric asymmetry was found in GC and Wistar rats with respect to aminopeptidase activity in neurons of caudate nucleus, with a more pronounced left-side increase in GC rats, the asymmetry index being 13.7%. Acetylcholine esterase activity in subcellular particles of caudate nucleus showed an inversion of asymmetry with higher activity in the left hemisphere of Wistar and right hemisphere of GC rats, and asymmetry index of 15.5%. With respect to the number of astroglia cells in S. nigra, and astroglia and oligodendroglia in N. accumbens there was also an inversion of asymmetry in GC rats who had more cells in the structures of the left hemisphere, whereas Wistar rats had more in the right hemisphere. The asymmetry index was high and equal to 29.8% for astroglia in S. nigra, and 17% for astroglia and 21.4% for oligodendroglia in N. accumbens. However, in S. nigra the number of neurons and oligodendroglia cells was equally increased in the right hemisphere in GC and Wistar rats. The data suggest that the mechanism of hereditary pathology of brain nigro-striate system involves both enhancement and inversion of the hemispheric asymmetry.     

Sex dimorphism of the interhemispheric asymmetry in the control of pain vocalizations in rats

First impulses were studied of pain vocalizations, elicited by electrostimulation of the tail root of semirigidly fixed 105 male and 95 female white rats of Wistar line. The rats were divided into three groups: with intact brain, with inactivated cortex of the left hemisphere and with inactivated cortex of the right one. It is shown, that as a result of unilateral decortication both in males and females changes take place in the character of durations distribution and probability of manifestation, as well as a reduction of the latency and an increase of peak amplitude of the recorded impulses. It is important that both in male and female rats the consequences of the left and right hemispheres inactivation differ by the influence on the character of durations distribution, probability of manifestation and the latency of pain vocalizations. At the same time, in males functional interhemispheric asymmetry of the control of probability of pain cries manifestation and latencies of pain squeals is more expressed than in females.     

EEG dynamics during conditioning in symmetrical neocortical regions in dogs

Changes in the frequency of the EEG recorded in symmetrical areas of the frontal and auditory cortices were studied during food conditioning in four dogs. Spectral-correlation analysis was applied. EEG frequency changes depended on individual features of the animals, frequency band, and stage of conditioning. In the beta-2-range, the EEG frequency increased in comparison to the initial values in all the dogs. In three dogs, the EEG frequency in the beta range decreased in the frontal and increased in the auditory cortex. Heterodirectional frequency changes led to the development of the functional interhemispheric EEG asymmetry that was partial and dynamic. At the initial stages of conditioning higher activity was in the left hemisphere, later on asymmetry was absent (or activity of the right hemisphere predominated).     

Functional asymmetry of electric processes in the rabbit brain cortex at formation of the hunger dominant

The motivational condition of hunger and formation of the hunger dominant after daily food deprivation was studied in the conditions of chronic experiments on rabbits. It was shown, that the hunger condition was accompanied by left sided interhemispher asymmetry on indicators of spectral capacity of EEG frontal and right-hand asymmetry sensorimotor areas of the cortex. A hunger dominant was accompanied by falling of spectral capacity of EEG of areas of both hemispheres. The condition of hunger and a hunger dominant were characterized by right-hand asymmetry on average level of EEG coherence of frontal and sensorimotor areas. At transition of a condition of hunger in a hunger dominant there was an average level of EEG coherence decrease in areas of the right hemisphere. Electric processes of the cortex of the brain at a motivational condition of hunger and a hunger dominant were different.     

Correlated activity of neurons in the sensorimotor cortex of rabbits in the state of defensive dominanta and "animal hypnosis"

A hidden excitation focus (dominanta focus) was produced in the rabbit's CNS by threshold electrical stimulation of the left forelimb with the frequency of 0.5 Hz. As a rule, after the formation of the focus, pairs of neurons with prevailing two-second rhythm in their correlated activity were revealed both in the left and right sensorimotor cortices (with equal probabilities 29.3 and 32.4%, respectively). After "animal hypnosis" induction, the total percent of neuronal pairs with the prevalent dominanta-induced rhythm decreased significantly only in the right hemisphere (21%). After the termination of the "animal hypnosis" state, percent of neuronal pairs in the right cortex with prevailing two-second rhythm significantly increasead if the neurons in a pair were neighboring and decreased if they were remote from each other. Similar changes after the hypnotization were not found in the left cortex. Analysis of correlated activity of neuronal pairs with regard to amplitude characteristics showed that for both the right and left hemispheres, the prevalence of the two-second rhythm was more frequently observed in crosscorrelation histograms constructed regarding discharges of neurons with the lowest spike amplitude (in the right hemisphere) or the lowest and mean amplitudes (in the left hemisphere) selected from multiunit records.     

Asymmetry of the transcallosal responses in the parietal cortex of kittens in the 1st month of life

In acute experiments on kittens the process of formation of asymmetry of transcallosal responses (TCR) was studied in multiple leads from symmetrical points of the parietal cortex. By the early positive-negative TCR complex, vanishing as a result of callosotomy, predominance of positive components in the right hemisphere was found in 2-7 days kittens, whereas in 8-24 days animals the left hemisphere dominated by both phases of responses. By the late TCR component preserved after section of the callosal body, left-hemispheric asymmetry was found in the elder group of kittens; it was absent in the younger animals. TCR asymmetry in the parietal cortex depended on the sex of the animals. With their age its inversion and enhancement took place. This process is based on the increase of TCR amplitude in the left hemisphere, with no increase in the right hemisphere.     

Effect of progesterone on the expression of GABAA receptor subunits in the prefrontal cortex of rats: implications of sex differences and brain hemisphere

Progesterone is a neuroactive hormone with non‐genomic effects on GABA_A receptors (GABA_AR). Changes in the expression of GABA_AR subunits are related to depressive‐like behaviors in rats. Moreover, sex differences and depressive behaviors have been associated with prefrontal brain asymmetry in rodents and humans. Thus, our objective was to investigate the effect of progesterone on the GABA_AR α1 and γ2 subunits mRNA expression in the right and left prefrontal cortex of diestrus female and male rats exposed to the forced swimming test (FST). Male and female rats (n = 8/group) were randomly selected to receive a daily dose of progesterone (0·4 mg·kg^–1) or vehicle, during two complete female estrous cycles (8–10 days). On the experiment day, male rats or diestrus female rats were euthanized 30 min after the FST. Our results showed that progesterone significantly increased the α1 subunit mRNA in both hemispheres of male and female rats. Moreover, there was an inverse correlation between depressive‐like behaviors and GABA_AR α1 subunit mRNA expression in the right hemisphere in female rats. Progesterone decreased the GABA_AR γ2 mRNA expression only in the left hemisphere of male rats. Therefore, we conclude that the GABA_A system displays an asymmetric distribution according to sex and that progesterone, at lower doses, presents an antidepressant effect after increasing the GABA_AR α1 subunit expression in the right prefrontal cortex of female rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparative analysis of discharge frequency of right and left sensorimotor cortical neurons in rabbits during tonic immobility

Multiunit activity was recorded in left and right sensorimotor cortex of rabbits in the state of tonic immobility. After the first immobilization session, the discharge frequency changed in 47% cells in the right hemisphere: 30% decreased their frequency, and 17% increased. In the left hemisphere, only 18% cells changed their discharge frequency (13% decreased and 5% increased). Reciprocal changes in discharge frequency could be observed in the neighboring neurons (recorded by the same electrode). Several days later, after the second immobilization session, the interhemispheric difference in the number of neurons, whose activity changed, almost disappeared (21% neurons in the right and 24% neurons in the left hemispheres). The relationship between the number of cortical neurons, which increased and decreased their activities in the state of "hypnosis" also became similar in the right and left hemispheres. A suggestion about the involvement of cortical neurons in organization of the state of "animal hypnosis" was made.     

Sexual differences in the interhemispheric asymmetry of the transcallosal responses of the associative areas in the cat neocortex

Sex differences of hemisphere asymmetry of homo- and heterotopic transcallosal responses in association cortex of 48 cats (24 male and 24 female) immobilized by tubocurarine have been studied by means of topographic EPs recordings in both hemispheres. In males left hemisphere dominates by the amplitude of homotopic and positive wave of heterotopic EPs and right hemisphere dominates by the amplitude of negative wave of heterotopic sensorimotor cortex EPs. The individual asymmetry of EPs has been observed in sensomotor cortex of females and in parietal cortex of animals of both sex. The interhemispheric asymmetry is expressed distinctly in females than in males. It is concluded that sex dimorphism is present in functional organization of associative system of (callosal and intracortical) connections in cat's neocortex projection and association areas which means its more expressed hemisphere lateralization in males with more expressed interhemispheric asymmetry of functional transcallosal connections in females.     

褪黑色素对缰核痛神经元单位放电的影响及可能机制

目的通过观察褪黑色素对缰核痛神经元单位放电的影响,进一步证明褪黑色素的中枢镇痛作用及可能机制。方法：应用细胞外神经元单位放电记录方法,记录缰核神经元痛相关神经元放电,并观察外侧缰核痛神经元在褪黑色素作用下电活动的改变,及对伤害性刺激痛敏感性的改变,在此基础上观察纳洛酮的翻转作用。结果：褪黑色素影响外侧缰核痛神经元的电活动,并使外侧缰核痛神经元对伤害性刺激敏感性降低,此种作用可被纳洛酮翻转。结论：褪黑色素可通过作用于外侧缰核的阿片受体而影响其痛相关神经元对痛刺激的反应,这可能是褪黑色素中枢镇痛机制之一。     

Rearrangement of the Prefrontal Cortex Neural Activity in Both Hemispheres during Learning

Neuronal activity of both right and left hemispheres of the rat prefrontal brain cortex was recorded in the two-ring maze during animal learning to operate in response to signals. At the beginning of learning, pairwise comparison of neural activity that accompanied correct and incorrect choice of the right and left sides showed significant differences in the left hemisphere and the lack of differences in the right one. With increasing percentage of correct choices during a session of learning, the differences in neuronal responses appeared in the right hemispheres and were reduced in the left one. The opposite trends in rearrangement of the total impulse activity are believed to be related to different roles of hemispheres in the construction of the internal behavioral model.     

高频刺激丘脑底核对帕金森病大鼠模型纹状体神经元放电的影响

目的:观察高频刺激丘脑底核(STN)对帕金森病(PD)大鼠模型纹状体 (STR)神经元自发放电的影响.方法:应用6-羟基多巴胺(6-OHDA)制备偏侧PD大鼠模型,丘脑底核区插入刺激电极进行高频刺激,采用细胞外单位记录的方法观察STR神经元自发放电频率的改变.结果:正常大鼠刺激后STR神经元反应主要以兴奋型反应为主, PD大鼠STR神经元反应主要以兴奋抑制型为主,且随着刺激时间的延长,抑制持续时间逐渐增加,持续时间与刺激时间密切相关(r=0.94).结论:刺激STN可使PD大鼠纹状体的异常放电得到改善,提示高频电刺激STN可作为一种有效的治疗PD的方法.