[Effect of 1,2,3,4-tetrahydroimidazo[4,5-c]pyridine and 1,2,3,4-tetrahydroisoquinoline derivatives on the behavior and the brain receptor system in rats].

Adducts obtained via the interaction of formaldehyde with histidine (1,2,3,4-tetrahydroimidazo[4, 5-c]pyridine-3-carboxylic acid (I)), tyrosine (7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (II)), and dopamine (6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (III)) influence the behavior and the state of the brain receptor system of rats upon chronic administration (10-day treatment at a daily dose of 50 mg/kg, i.p.). All the compounds studied decrease the horizontal and (to a lower extent) vertical motor activity and increase the quiescence period duration. On the other hand, the effects of compounds tested on the vegetative reactions were different: compounds I and III increased, whereas compound II decreased these reactions. Using the radioligand binding method, it was established that the treatment with compound I led to a decrease in the density of benzodiazepine receptors (B max of [3H]-flunitrazepam was 78% of the control level) and to a significant (148%) increase in the density of specific binding sites for [3H]-spiperone (reflecting the total density of dopamine (D2) and serotonin (5-HT2) receptors. The chronic administration of compound III produced a reliable decrease (76% of the control level) only in the density of benzodiazepine receptors. None of the tested compounds influenced the affinity of receptors with respect to the radioactive ligands used.