[Different roles of dopamine and serotonin in conditioned passive avoidance response of rats].

Deamination of dopamine and serotonin by monoamine oxidase was studied in the prefrontal cortex, striatum, hippocampus and amygdaloid complex of the brain of rats during retrieval of conditioned passive avoidance response. Changes in the dopamine and serotonin metabolism were observed in different brain structures. A decrease in dopamine-deaminating activity of monoamine oxidase was found in the hippocampus, striatum and prefrontal cortex. At the same time, serotonin-deaminating activity of the enzyme was decreased in the striatum and increased in the amygdaloid complex, whereas it did not change in the prefrontal cortex and hippocampus. The observed changes in dopamine metabolism in the prefrontal cortex and hippocampus and serotonin metabolism in the amygdaloid complex indicate that dopamine and serotonin are involved in the regulation of two different processes mediating the memory trace retrieval. Dopamine is involved in neuronal mechanisms of information processes providing the strategy of behavior, whereas serotonin is related to emotional mechanisms of memory.

Changes in serotonin metabolism in the rat brain on presentation of a habituated stimulus.

The levels of serotonin and the serotonin metabolite 5-hydroxyindoleacetic acid, monoamine oxidase activity, and the kinetic parameters of the oxidative deamination of serotonin were studied in various brain structures in rats after repeated presentation of a contextual stimulus. These experiments showed that presentation of the habituated stimulus was accompanied by increases in serotonin metabolism and the active transport of its metabolite in the amygdaloid complex, striatum, and midbrain, with no significant changes in the hippocampus or prefrontal cortex. Increases in monoamine oxidase activity in various brain areas resulted from different catalytic mechanisms: an increase in the rate of formation of the enzyme-substrate complex (a decrease in the Michaelis constant) in the amygdaloid complex, and faster conversion of the enzyme-substrate complex (increases in the maximum reaction rate) in the striatum and midbrain. It is concluded that activation of the presynaptic mechanism of serotonin transmission in the amygdaloid complex and striatum may be involved in the process of suppressing the biological significance of and attention to a repeatedly presented stimulus.

Metabolism and receptor binding of serotonin in brain structures during performance of a conditioned passive avoidance response.

The levels of serotonin and its metabolite 5-hydroxyindoleacetic acid, monoamine oxidase activity, and the specific binding of the radioligand [3H]serotonin were measured in the prefrontal cortex, striatum, amygdaloid complex, hippocampus, and periacqueductal gray matter of the midbrain in rats at different time points after training to a conditioned passive avoidance reaction. Changes in serotoninergic activity were found to be characteristic only for the process of reproducing the conditioned reaction. The metabolism and serotonin receptor binding in these brain structures did not change immediately after the training period or one day after this, or in conditions of failure to reproduce the reaction because of amnesia, or in untrained animals. The involvement of the brain serotoninergic system in the process of performing the conditioned reaction was found to demonstrate a spatial-structural selectivity: the metabolism and receptor binding of serotonin changed in the amygdaloid complex, periacqueductal gray matter, and the striatum, while no changes were seen in the hippocampus or prefrontal cortex. All three brain structures showed decreases in [3H]serotonin receptor binding of. Serotonin levels did not change, though the amygdaloid complex and periacqueductal gray matter showed increases in oxidative deamination of serotonin and increases in the active transport of the metabolite, while the striatum showed decreases in serotonin catabolism. The differences in the catabolism of this neurotransmitter suggest that the decrease in serotonin receptor binding in these brain structures depends on different synaptic processes--presynaptic in the striatum and postsynaptic in the amygdaloid complex and periacqueductal gray matter. It is concluded that the decrease in the functional activity of serotoninergic transmission in the amygdaloid complex and periacqueductal gray matter is one of the mechanisms involved in activation of the emotiogenic system triggering the process of reproduction of the memory trace.

[Changes in brain serotonin metabolism and [3H]-serotonin receptor binding during recall of conditioned passive avoidance in rats]. / Metabolizm i retseptornoe sviazyvanie serotonina v strukturakh mozga pri vosproizvedenii uslvnoi reaktsii passivnogo izbeganiia.

The content of serotonin and its metabolite 5-hydroxyindoleacetic acid, monoamine oxidase activity, and [3H]-serotonin radioligand receptor binding were examined in the prefrontal cortex, striatum, amygdala, hippocampus and periaqueductal gray matter at different time after one-trial passive avoidance training of rats. Changes in the serotonergic activity were observed only in rats, which showed retrieval of conditioned passive avoidance response. No serotonergic changes were found immediately and one day after training. Also, there were no changes in trained rats without retrieval of conditioned passive avoidance response or rats with experimental amnesia. The pattern of the involvement of brain structures in the retrieval process was also revealed. [3H]-serotonin binding was decreased in the amygdala, periaqueductal gray matter and striatum, whereas it did not change in the prefrontal cortex and hippocampus. At the same time, the serotonin content in these structures did not differ from that of intact rats. Deamination of serotonin by monoamine oxidase and active transport of 5-hydroxyindoleacetic acid from nerve terminals were increased in the amygdala and periaqueductal gray matter, whereas in the striatum serotonin catabolism was decreased. The obtained differences in serotonin catabo- lism suggest that the decrease in receptor binding of serotonin in these brain structures is provided by different synaptic processes: presynaptic changes in the striatum and postsynaptic receptor changes in the amygdala and periaqueductal gray matter. It is concluded that the decrease in the serotonergic activity in the amygdala and periaqueductal gray matter represents one of the mechanisms activating the emotiogenic system mediating the memory trace retrieval in inhibitory avoidance learning.

[Change in serotonin metabolism in the rat brain in response to the repeated stimulus presentation]. / Izmenenie metabolizma serotonina v mozgu krys pri pred''iavlenii privychnogo stimula.

The content of serotonin (5-HT), its metabolite 5-hydroxyindoleacetic acid (5-HIAA), monoamine oxidase (MAO) activity and kinetic parameters (K(m) and Vmax) for the reaction of 5-HT deamination, were examined in various regions of the rat brain after repeated presentation of a contextual stimulus. Habituation to the stimulus was accompanied by an increase of 5-HT metabolism and active transport of 5-HIAA in the amygdala, striatum and midbrain, while these changes were not found in the prefrontal cortex and hippocampus. Kinetic studies have revealed that the enhancement of 5-HT deamination by MAO in the brain structures was mediated by different catalytic mechanisms. A significant decrease in K(m) value for 5-HT deamination in the amygdala indicated an increase in the affinity of enzyme towards 5-HT. In the striatum the enhanced MAO activity was provided by increasing maximal rate of 5-HT deamination. It is concluded that an activation of presynaptic mechanisms of the serotonergic transmission in the amygdala and striatum is involved in the inhibition of biological significance and attention to repeated presentation of stimulus.

Differences in serotonin and dopamine metabolism in the rat brain in latent inhibition.

Monoamine oxidase activity during deamination of serotonin and dopamine in the amygdaloid complex, hippocampus, striatum and prefrontal cortex of the brain was studied at different stages in the formation of latent inhibition, acquired by rats on the basis of a conditioned passive avoidance reaction. Latent inhibition is a behavioral phenomenon consisting of a worsening in learning using a stimulus when attention to this stimulus is quenched before acquisition of the conditioned response. At the stage of preliminary repeated presentation of the conditioned stimulus, serotonin metabolism was seen to change in the amygdaloid complex and striatum, while dopamine metabolism changed in the amygdaloid complex and hippocampus. Metabolic shifts in transmitter handling during quenching of attention to the stimulus occured in the opposite directions: the serotonin-deaminating activity of monoamine oxidase increased, while the dopamine-deaminating activity of the enzyme decreased. Unlike the reaction to the quenched stimulus, the latent inhibition effect, seen on testing the conditioned response after conditioning of the pre-exposed stimulus with unconditioned reinforcement, was accompanied by changes in serotoninergic activity only. High levels of serotonin deamination by monoamine oxidase were seen in the amygdaloid complex and striatum. In addition, there was a reduction in serotonin deamination in the prefrontal cortex specific for the stage of testing latent inhibition. At the same time, dopamine metabolism did not change in any of the brain structures studied in latent inhibition. These data lead to the conclusion that the latent inhibition effect may be based on increases in serotoninergic activity in subcortical brain structures--the amygdaloid complex and the striatum--induced by reactions to presentation of the quenched stimulus.

[Distinctions in metabolism of serotonin and dopamine in rat brain during latent inhibition]. / Razlichiia v metabolizme serotonina i dofamina v mozge krys pri latentnom tormozhenii.

Latent inhibition (LI) is a behavioral phenomenon, in which repeated presenting of a non-reinforced stimulus retards conditioning to this stimulus when it is coupled with a reinforcer. In order to find specific serotonin (5-HT- and dopamine (DA) changes mediating the LI, the 5-HT and DA metabolism was investigated in certain brain regions. Oxidative deamination of 5-HT and DA by monoamine oxidase (MAO) was determined in the prefrontal cortex, striatim, amygdala, and hippocampus at preexposure and testing stages of the LI using the passive avoidance procedure in rats. Preexposed animals demonstrated high MAO activity for 5-HT deamination in the amygdala and striatum and lower MAO activity for DA deamination in the amygdala and hippocampus. After testing the LI, a high level of 5-HT deamination by MAO was revealed in the amygdala, white the lower level of 5-HT deamination by MAO was shown in the prefrontal cortex. At the same time, no changes in DA metabolism were found in all the brain regions studied. Thus, the role of dopaminergic system in the LI effect may be limited by the preexposure stage. The obtained evidence suggests that the enhanced 5-HT activity in the amygdala and striatum induced by the preexposed stimulus is a principal biochemical mechanism underlying the LI.

[Effects of sex factors and hemispheric localization on the involvement of serotonin from the frontal cortex, striatum, and nucleus accumbens into the processing of novel and repeatedly presented information in rats]. / Vliianie faktorov pola i polusharnoi lokalizatsii na vovlechenie serotonina frontal'noi kory, striatuma i prilezhashchego iadra na obrabotku novoi i povtorno pred''iavliaemoi informatsii u krys.

The effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex, striatum, and nucleus accumbens in the left and right hemispheres were studied in male and female rats. It was found that 5-HT and 5-HIAA contents in the frontal cortex changed in response to neither relevant nor irrelevant stimuli. However, there were hemispheric difference in 5-HT and 5-HIAA in the frontal cortex of intact animals. The level of 5-HT in males and the level of 5-HIAA in females were higher in the left frontal cortex. In females, the level of 5-HIAA in the left striatum decreased in response to the novel stimulus. Sex differences in: a) 5-HT metabolism (increase in the level of 5-HIAA in males and increase in 5-HT in females) and b) lateralization (the striatal 5-HT metabolism in males changed bilaterally and only in the left hemisphere in females) were observed in reactions to irrelevant stimuli. Both in male and female rats, serotonin content in the nucleus accumbens changed only in response to the irrelevant stimuli. The 5-HT level increased in the left and right hemispheres independently of sex, but hemispheric difference was revealed only in females, in which the serotonin level was higher in the left nucleus accumbens. It is concluded that serotonergic neurotransmitter mechanisms are involved in hemispheric and sex differences in selective attention.

Pre- and postsynaptic mechanisms of the involvement of amygdaloid complex serotonin in the reproduction of a conditioned passive avoidance response in rats.

Serotonin metabolism and [3H]-serotonin radioligand receptor binding were studied in the amygdaloid complex of the rat brain at different stages of a conditioned passive avoidance response. Serotoninergic changes were specific for the process of reproduction of the conditioned response. The involvement of serotonin in the amygaloid complex during reproduction of memory traces consisted of a reduction in its postsynaptic receptor binding. The serotonin level in the amygaloid complex did not change, while changes in serotonin metabolism detected during reproduction of the conditioned avoidance response were associated with an increase in its deamination by monoamine oxidase and an increase in the active transport of 5-hydroxyindoleacetic acid from nerve terminals.

[Sexual and interhemispheric differences in the involvement of serotonin from the hippocampus and amygdaloid body in the processing of new and repeatedly presented information in rats]. / Polovye i mezhpolusharnye razlichiia v vovlechenii serotonina gippokampa i mindalevidnogo kompleksa v obrabotku novoi i povtorno pred''iavlemoi informatsii u krys.

Effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the left and right hippocamp and amygdala were studied in male and female rats. It was found that hemispheric specificity of 5-HT metabolism in hippocampus and amygdala depended on sex and novelty of information. In male rats, the hippocampal level of 5-HT in response to the novel stimulus increased in the left hemisphere, and the 5-HIAA hippocampal level increased bilaterally in response to irrelevant stimulus. In females, an increase in 5-HT and/or 5-HIAA levels was observed only in the left hippocampus in response both to relevant and irrelevant stimuli. In the amygdala, a hemispheric asymmetry of the 5-HT involvement, due to right-hemispheric changes in 5-HT metabolism, was observed only in male rats. In females, an increase in 5-HT level was found in the left and right amygdalas in response to irrelevant stimulus. These data suggest that serotonergic neurotransmitter mechanisms are an important factor which determines hemispheric and sex differences in selective attention.

[The pre- and postsynaptic mechanisms of the involvement of the serotonin of the amygdaloid body in the reproduction of the conditioned passive avoidance reaction in rats]. / Pre- i postsinapticheskie mekhanizmy vovlecheniia serotonina mindalevidnogo kompleksa v vosproizvedenie uslovnoi reaktsii passivnogo izbeganiia u krys.

Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content, MAO activity, and [3H]-5-HT specific binding were examined in rat amygdala at different stages of one-trial passive avoidance training. Serotonergic changes were revealed only at the stage of the avoidance recall. The [3H]-5-HT specific binding was decreased, MAO activity was increased and accompanied by enhanced 5-HIAA transport from serotonergic terminals. No changes were revealed in 5-HT content. It is suggested that the retrieval processes in passive avoidance learning are mediated by serotonergic system of the amygdala.

[Monoaminoxidase activity and serotonin metabolism in the brain of rats during latent inhibition]. / Aktivnost' monoaminoksidazy i obmen serotonin v mozge krys pri latentnom tormozhenii.

The monoamine oxidase (MAO) activities and the concentrations of 5-HT and 5-hydroxyindoleacetic acid were investigated in four brain regions in rats during the acquisition of latent inhibition in one-trial passive avoidance task. 5-HT metabolism was not altered in the hippocampus. Changes of 5-HT metabolism were found in the frontal cortex during testing of latent inhibition and were accompanied by lowering of MAO activity. No change of 5-HT metabolism was observed in this structure at the stage of pre-exposition to conditioned stimulus. 5-HT metabolism was activated at the stage of pre-exposition to conditioned stimulus in the amygdala and striatum and was maintained on high level, in these structures during testing of latent inhibition. The data presented here indicate that serotoninergic system in various brains regions is specifically involved in the formation of different stages of latent inhibition.

[Changes in brain monoamine oxidase activity in conditioned passive avoidance reaction in rats]. / Izmenenie aktivnosti monoaminoksidazy mozga pri vosproizvedenii uslovnoi reaktsii passivnogo izbeganiia u krys.

Activity of the enzyme monoamine oxidase (MAO) and kinetic parameters (Km, Vmax) for the 5-hydroxytryptamine (5-HT) and dopamine deamination were examined in the brain of rats with conditioned passive avoidance recall. Changes of the 5-HT and dopamine deamination were found in amygdala, striatum and frontal cortex. MAO activity was not changed in hippocampus. In amygdala the rate of 5-HT deamination was significantly increased and kinetic studies revealed increased affinity of the enzyme for 5-HT. The metabolism of dopamine in amygdala was unchanged. In frontal cortex the deamination of 5-HT was not changed, but the dopamine deamination significantly decreased. This decrease was due to lowering of MAO affinity for dopamine. In striatum the metabolism of both 5-HT and dopamine was reduced, and kinetic studies showed the lowering of Vmax for 5-HT and dopamine deamination.

[Role of serotonin receptors in the amygdaloid complex and central gray substance in conditioned passive avoidance reaction in rats]. / Uchastie serotoninovykh retseptorov mindalevidnogo kompleksa i tsentral'nogo serogo veshchestva v vosproizvedenii uslovnoi reaktsii passivnogo izbeganiia u krys.

The functional role of 5-HT1 receptors in the memory trace retrieval was investigated in amygdala (AM), central gray substance of midbrain (CGS) and frontal cortex. There is used the passive avoidance response in the rat. The decrease of 5-HT1 binding sites in AM and CGS was revealed for the rats with retention of the passive avoidance response. The binding of 3H-5-HT in AM was found two sets of binding sites. It was concluded, that 5-HT1 receptors of AM and CGS are involved in learning processes either in the moment of the memory trace retrieval or immediately after it.

[Monoamine oxidase in the rat brain in short-term exposure to high temperature]. / Monoaminoksidaza mozga krys pri kratkovremennom vysokotemperaturnom vozdeistvii.

Influence of short-term hyperthermia on the activity of mitochondrial monoamine oxidase in rat brain stem and kinetic parameters of serotonin deamination were studied. A decrease of the MAO activity at low concentrations of serotonin was found.

[Trace effects of short-term temperature action in monoamine oxidase activity]. / Sledovye éffekty kratkovremennykh temperaturnykh vozdeistvii v aktivnosti monoaminoksidazy.

The influence of short-term hypothermia and hyperthermia on the activity and catalytic properties of rat brain MAO was studied. It was found that short-term action of low and high environmental temperatures had considerable trace effects which differed in direction and duration. MAO activity increased after hypothermia and was maintained at a high level during 4 days. The lowering of serotonin deamination after hyperthermia was observed for 7 days.