Changes in the 5-HT-binding sites in the cerebral cortex, striatum and hypothalamus of rats during ageing and under the effect of dopaminergic agents.

The changes in the 5-HT1-binding sites, developing during ageing and under the effect of 10-day administration of L-DOPA and haloperidol, were studied in the cerebral cortex, striatum and hypothalamus of 2-, 10- and 22-month-old rats. The values of Bmax of the 5-HT1-binding sites decreased in all three brain structures studied with the ageing of the experimental animals. Both L-DOPA and haloperidol did not change the general character of the changes in the number of 5-HT1-receptors, developing during ageing, but at the same time L-DOPA reduced their density in the three age periods and in the three cerebral areas studied, while haloperidol increased their number in the 2- and 10-month-old rats. The Kd-values of the 5-HT1-receptors manifested very varied changes, determined both by ageing and by the administration of L-DOPA and haloperidol. The generalized interpretation of these results with the results obtained in earlier studies on the age-determined changes in DA2 and the enkephalin receptors, as well as of the content of biogenic monoamines and MAO-activities, made it possible to see new elements in the adaptive possibilities of the cerebral receptors. On the other hand, the results obtained in the present and earlier studies show that ageing is paralleled by deviations in the equilibrium of the cerebral transmitter systems which seem to play an important role for the development of the behavioural changes connected with ageing.