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Activity of enzymes catalyzing synthesis and degradation of serotonin and dopamine in brain structures of Wistar and August rats was measured biochemically under normal conditions and after short-term exposure to delta-sleep-inducing peptide. The effects of the test peptide manifested in activation of the serotoninergic system and inhibition of the dopaminergic system, particularly in the caudate nucleus. These changes were most pronounced in the brain of Wistar rats.

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Dysfunction of the dopamine system was modeled in Wistar rats by injection of 50 mg/kg L-dopa over 4 weeks. Experimental rats demonstrated considerably decreased locomotor activity and increased emotional strain compared to the control group. Structural changes consisted in a significant decrease in the size of neuronal bodies in the sensorimotor cortex (layers III and V) and caudate nucleus together with changed variability of these parameters compared to the corresponding values in the control. The neuroglial index increased by 22% in layer V, tended to decrease in layer III, and remained unchanged in the caudate nucleus. L-Dopa changed specific activity of enzymes: tyrosine hydroxylase activity in the sensorimotor cortex decreased by 25%, while monoamine oxidase B activity in the caudate nucleus increased by 33%. Thus, dysfunction of the dopamine system resulting in changes in dopamine metabolism not only leads to structural and functional rearrangements reducing functional capacities of the cell systems, but is also associated with compensatory and repair reactions in the brain.