Density and pattern of dopamine D2-like receptors in the cerebellar cortex of aged rats

The pharmacological properties and the anatomical localization of dopamine (DA) D2-like receptors were studied in the cerebellum of 3 months, 12 months, and 24 months male Wistar rats using combined radioligand binding and autoradiographic techniques with [3H]-spiroperidol as a ligand. The binding was consistent with the labelling of the DA D3 receptor subtype. The affinity for DA D2-like receptors was similar in the cerebellar cortex of the three animal groups investigated, whereas the density of binding sites (Bmax value) assessed using conventional radioligand binding techniques was reduced as a function of aging. Light microscope autoradiography revealed the localization of binding sites primarily in the molecular layer and to a lesser amount in Purkinje neurons layer. A loss of binding sites was noticeable with aging in the grey matter of the cerebellar cortex. It affected primarily the molecular layer. Analysis of radioligand binding data and light microscope autoradiography suggests that age-related changes of DA D2-like receptors depend in part by structural alterations of cerebellar cortex and in part by modifications in receptor expression.