[Influence of D1, D2 Receptor Blockade in Basolateral Amygdala on Behavior of Rats with High or Low Levels of Anxiety and Fear].

The influence of bilateral D1 or D2 receptors antagonists infusions into the rat basolateral amygdala on anxiety, as well as the expression, extinction and re-learning of conditioned fear was studied. Subjects were the male Wistar rats with high and low anxiety behavior in elevated plus maze, and also rats with low and high freezing responses during fear conditioning. The infusion of D1 receptor antagonist (SCH23390, 1 µg/0.5 µL in each side) reduced the expression of the conditioned fear to sound in rats with low freezing level, accelerated fear extinction and impaired re-learning in all animals. The injection of D2 receptor antagonist (raclopride, 1 µg/0.5 µL in each side) accelerated the extinction of conditioned fear to contextual cues in all rats and had a weak anxiolytic-like effect on behavior of high anxiety rats in elevated plus maze. These findings testify to the role of D1 receptors in the acquisition, expression and extinction of conditioned fear to stimuli, and D2 receptors in the occurrence of anxiety and fear to the contextual cues. There was discovered different sensitivity of animals with different levels of anxiety and fear to the infusion of dopamine receptors antagonists in the amygdala that suggested the inequality of dopaminergic transmission in the amygdala of animals with individual differences.

[The Manifestation of the Anxiety during Fear Conditioning in Wistar Rats].

In order to identify the correlation between anxiety and conditioned fear, the behavior of the same male Wistar rats was compared in three anxiety tests (open field, light-dark box and elevated plus-maze) and in Pavlovian auditory fear conditioning paradigm using correlation, factor and variance analyses. The correlation between anxiety/bravery and locomotion indexes in different tests was not revealed. Positive correlations between grooming, urinations and defecations, rearing in three tests were revealed. These data suggest that animals reacted to various tests differently, resulting, apparently in the emergence of different anxiety levels, specific for each test. Vegetative reactions, inclination to exploration and substituting behavior were more stable characteristics of rats. Anxiety behavior in elevated plus-maze correlated to freezing response to context after fear conditioning, while high-anxiety rats had higher level of freezing to context than low-anxiety rats. The higher freezing response to sound after fear conditioning was found in rats with middle locomotor activity in open field. Conditioned fear to the context and to the sound was associated with different forms of rat anxiety during different tests.

[Behavior of high- and low-anxiety rats after modulation of GABAergic transmission in basolateral amygdala].

The influence of GABA(A) receptor agonist (muscimol hydrobromide, 0.1 µg/0.5 µL) and antagonist (bicuculline methiodide, 0.2 µg/0.5 µL) injections into the right and the left basolateral amygdala on the behavior of the high- and low-anxiety rats was investigated in elevated plus-maze test. High- and low-anxiety rats had different sensitivities to injections of GABA receptor agents. Administration of muscimol increased open-arm time only in the high-anxiety rats, indicating anxiolytic-like effect. Injection of bicuculline increased aggression of all rats, as well as enhanced locomotion and exploration in high-anxiety rats, increased open-arm time and emotionality in the low-anxiety animals. More powerful changes in behavior of rats were revealed after injections of muscimol into the left amygdala of high-anxiety rats and bicuculline into the right amygdala of low-anxiety ones. The results evidence the existence of individual typological and interhemispheric differences in functioning of the amygdalar GABAergic system.

[Effects of intrabasolateral amygdala infusions of GABAA-receptor agonist and antagonist on expression and extinction of conditioned fear in rats with different freezing duration].

The rats were divided into two groups (little and much freezing animals) on the grounds of differences in freezing times after fear conditioning. Effects of bilateral intrabasolateral amygdale infusions of GABAA-receptors agonist (muscimol, 0.1 microg/0.5 microL in each side), antagonist (bicuculline, 0.07 microg/0.5 microL), saline (control, 0.5 microL) on expression and extinction of fear were compared in two rats groups. Muscimol infusion before retention test led to a decrease the time of freezing, it maximal biased on fear expression in little freezing rats. Bicuculline infusion increased aggressiveness of rats, decreased freezing time, induced elements of panic behavior, and evoked maximal behavioral changes in much freezing animals. Muscimol or bicuculline infusion before extinction training resulted in facilitation of extinction in much freezing rats, but not effected in little freezing animals. Received results testified to non-equivalence influences of GABA-receptors agonist and antagonist in animals with different fear levels and supposed differences in GABAergic receptors.

[Effects of intra-amygdala injection of GABA(A)-receptor agonist and antagonist on respiratory and cardiac components of conditioned fear in rabbits].

The role of GABAergic system of amygdala in vegetative and behavioral manifestations of conditioned fear was studied in groups of active and passive rabbits, selected upon testing in open field and light-dark chamber. During training, the light (4 s) was paired with electrodermal stimulation of hind limbs(1 s, 10 Hz). Conditioned fear was judged by heartbeats and respiratory rates before and in the process of conditioned and unconditioned stimuli presentation. Solutions of GABA(A)-receptor agonist (muscimol, 0.1 µg/µL) or antagonist (bicuculline methbromide, 0.5 µg/µL) were applied to the right or left basal nucleus of amygdala after conditioning. Muscimol injection evoked more powerful vegetative changes in passive rabbits than in the active ones; respiratory deceleration during freezing in response to conditioned stimuli was eliminated and the reaction to electrodermal stimulation was reduced or altered. Activation of the left amygdala by bicuculline resulted in the increased probability of active locomotor reactions in active rabbits, activation of the right amygdale, on the contrary, increased probability of freezing. The results evidence the non-equivalence of amygdalar GABAergic system in active and passive animals.

[Specific features of fear conditioning expression in active and passive rabbits].

The active and passive rabbits selected previously on the basis of their behavior in open field and light-dark test, were subjected to fear conditioning using pairing light (4 s) with footshocks (10 Hz, 0.5 s). Heart rate and respiration rate were measured during the classical fear conditioning. Heart rate and respiration rate decreased in response to light before footshock in case of passive-defensive reaction. There were no heart rate and respiration rate reduction in the course of the active defensive reaction. In active rabbits, as compared to passive ones, the frequency of active locomotors reactions and heart rate were higher, the decrease of respiration rate to light was observed at later stages of training, and the detected bradycardia was not stable. Thus, based upon vegetative characteristics, the active rabbits had lower level of fear than passive ones. The active or passive behavioral strategies of animals were preserved during fear conditioning.

[Effects of intra-amygdala injection of GABA(A)-receptor agonist and antagonist on behavior of active and passive rabbits in negative emotional situations].

The effects of right-side or left-side intra-amygdala injections of the GABA(A)-receptor agonist muscimol hydrobromide (0.1 microg/1 microl) and antagonist bicuculline methiodide (0.05, 0.1, 0.5 microg/1 microl) on the behavior of active and passive rabbits were studied in open field, light-dark test and during presentation of emotionally significant stimuli. The effect of compounds injection was differed in active and passive rabbits. The active rabbits were more sensitive to bicuculline injection and the passive rabbits to muscimol administration. Bicuculline induced anxiolytic-like effects on the active animals in open field, light-dark test and motor-activating effects during emotionally significant stimuli. Muscimol induced anxiolytic-like effects on the passive rabbits and sedative effects on the both groups of rabbits. The differences in effectiveness of right-side and left-side intra-amygdala injections on behavior of rabbits were revealed: more powerful changes were during injection of bicuculline in left and muscimol in right amygdala. Anxiolytic-like effects were revealed during injection of bicuculline into left amygdala of active rabbits and muscimol into right amygdala of passive rabbits. These findings indicate that there are individual-typological and interhemispheric differences in functioning of GABAergic system of amygdala.

[Influence of anxiolytic afobazole on amygdalar neuronal activity and behavior of rabbits in emotionally negative situations].

The influence of systemic injection of anxiolytic afobazole (1 mg/kg) on interaction between neurons of the basal and central amygdaloor nuclei and behavior of rabbits in negative emotional situations was studied in order to reveal characteristics of amygdalar neuronal network properties during unconditioned fear. An afobazole injection results in a prolongation of stay in the light compartment of dark-light chamber, in a decrease in freezing probability after exposure of emotional stimuli, in appearance of some aggressive reactions in open field. Behavioral alterations were accompanied by duration increase and latency changes of amygdalar neuronal inhibitory interactions, by increase of probability of neuronal interactions on delta-range frequency, by decrease of interactions on theta-range frequency. Under the influence of afobazole the asymmetry with right dominance in interhemispheric interaction of amygdalar neurons decreased. Changes in network properties ofamygdalar neurons during afobazole injection testify to reduction of activation level of this structure taking place at the expense of enhancement of inhibitory interactions between neurons.

[Interaction of amygdalar neurons of active and passive rabbits in negative emotional situations].

Interaction of basal and central nuclear neurons of amygdala was studied by plotting histograms of crosscorrelation in passive and active rabbits exposed to emotionally significant stimuli. The behavior of animals was studied in the open field, light-dark test and during presentation of emotionally significant stimuli. Rabbits of different typological groups applied a certain behavioral strategy in a variety of behavioral tests. Intergroup differences were revealed in the interaction of neighboring cells of amygdala. Passive rabbits (as comparied to active rabbits) demonstrated more excitatory connections and less inhibitory connections with the latency from 50 to 150 ms. Interactions with the delta1-range and theta2-range frequencies in passive animals were more rarely observed. The asymmetry of the interhemispheric neuronal interaction in amygdala with the right dominance was revealed in passive but not active animals. The results testify that amygdala is involved in the choice of behavioral strategy, and the level of its activation is higher in passive animals.

[Network activity of "interneurons" and large cells of amygdala in active and passive rabbits].

By plotting cross-correlation histograms differences were found in interaction of conjectural small "interneurons" and large principal cells of the central and basal amygdalar nuclei in negative emotional situations. The network activity of "nterneurons" was higher than in principal cells. "Interneurons" more frequently had excitatory and inhibitory input or output connections with neighbouring cells, latency of their connections with other cells was smaller than in principal neurons. Interaction of "interneurons" and principal cells differed in animals with active and passive behavioural strategy in negative emotional situations. As compared to active animals, in passive rabbits inhibitory connections to "interneurons" from other cells occurred more frequently, excitatory or inhibitory connections from "interneurons" to principal cells appeared more rare.

[Interhemisphere asymmetry of hippocampus and neocortex in correlates of active and passive behavioural strategy in negative emotional situations].

The interhemisphere interaction of neurons in bilateral derivations from parietal and sensomotor areas of neocortex and the area CA1 of hippocampus were studied in rabbits with active and passive behavioural strategy in the open field by plotting histograms of crosscorrelation. In passive animals, there was asymmetry in bilateral neuronal interaction: with right-sided dominance in the neocortex and with left-sided that--in the hippocampus. On the contrary, in active rabbits, the left-sided dominance was observed in the neocortex, and the lateralization was not revealed in the hippocampus. The brain laterality was reflected in motor asymmetry of animals in preferring left or right turns in the open field. Passive rabbits made relatively more left turns, and the active animals--right turns. Systemic administration of agonist GABA(B) receptors phenibut decreased behavioural responses to emotional stimuli and eliminated interhemisphere asymmetry observed usually in negative emotional situations. Thus the interhemisphere asymmetry of the neocortex and hippocampus is correlated with individual typological characteristics of animals and reflects the readiness to preferential forms of behavioural responses in active and passive rabbits.

[Interaction and firing pattern of rabbit amygdalar neurons in the state of unconditioned fear manifested as freezing].

In order to reveal characteristics of functioning of amygdalar neuronal network during unconditioned fear, firing patterns of basal and central nuclear neurons and their interaction were studied during freezing (fear), active unconditioned motor reactions (in the absence of fear) to emotionally significant stimuli, and during quiet wakefulness. As compared to other states, specific changes in interaction of adjacent amygdalar neurons took place during freezing. Such changes were not revealed in firing of single neurons. During freezing, the number of short-latency (to 100 ms) excitatory connections increased and the number of long-latency (250-450 ms) inhibitory connections decreased. In freezing, more frequently than in other states, delta-2 range frequencies (from 2 to 4 Hz) were observed in the interneuronal interaction. During active locomotor reactions to stimuli, the number of interacting neurons decreased, the number of long-latency (200-250 ms) excitatory and short-latency (50-200 ms) inhibitory connections decreased, and theta 1-range frequencies were frequently observed in the interaction. It was concluded that, for the development of fear, the balance between excitatory and inhibitory links of amygdalar neuronal network is essential.