Serotonergic ligand binding in aging brain of experimental animals.

Although the use of aging experimental animals for studying serotonergic neuronal changes is limited because of species differences, cholinergic neuronal deterioration does appear to be a feature common to mammalian aging brains. In the present study, a recently introduced experimental animal, Suncus murinus (house musk shrew, an insectivore classified as being at the stem of the mammalian phylogenic tree) which in certain physiological characteristics is more closely related to the primate than is the rat, was used as an experimental animal model for serotonergic neuronal deterioration in aging brain. We examined the changes in binding to the membrane fraction of aging brain cortex of the experimental animals Suncus and Fischer rat of the serotonergic ligands, 5-HT, imipramine, and 8-OH-DPAT. Morphological study of the brain stem including the Nucleus raphae by immunohistochemical staining demonstrated that in Suncus all the serotonergic ligands had decreasing affinity to the membrane of aging brain; binding of 8-OH-DPAT and imipramine decreased to a greater extent than that of 5-HT. In contrast, the aging rat brain showed no appreciable change in the binding of serotonergic ligands.