Serotonergic mechanisms of memory trace retrieval.

This review summarizes our research examining the role of serotonergic mechanisms in memory processes. Analysis of serotonin (5-HT) metabolism and specific binding of radioligand [(3)H]5-HT in various brain structures at different stages of a conditioned passive avoidance response in rats has demonstrated that 5-HT is involved in the processes of memory retrieval rather than in acquisition. The process of retrieving a conditioned response formed to a new conditioned stimulus is accompanied by a reduction in postsynaptic 5-HT receptor binding in the amygdala, periacqueductal gray matter, and striatum, while no changes have been seen in the hippocampus or prefrontal cortex.

[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.

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.

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.