Morphometrical and Microdensitometrical Studies on Monoaminergic and Peptidergic Neurons in the Aging Brain

Abstract

In a recent study we have characterized aging processes in transmitter-identified neurons demonstrated by immunocyto- chemistry or by radioreceptor autoradiography using computer assisted morphometry and microdensitomotry (Agnati et al. 1984). The results indicated the existence of heterogeneities in the degenerative patterns taking place in transmitter-identified nerve cells and receptors in relation to aging. It was i. a. discovered that the meso-striatal and meso-accumbens dopamine (DA) neurons underwent degeneration in the aging brain both pre- and postsynaptically, while the DA nerve terminal networks within the tuberculum olfactorium were resistant to the aging processes. Furthermore a marked and widespread disappearance of the μ- and Δ-type of opiate receptors were found in the aged brain, while the benzodiazepine binding was enhanced in several brain areas of the aging brain compared with the 3 month old rat brain. Thus, it is possible that in aging also supersensitivity development can take place in certain types of receptors such as the benzodiazepine receptors, which possibly represent co-transmitter binding sites in GABA synapses (see Guidotti et al. 1983). Instead, the GABA receptor binding sites are reduced in number in the aged brain, suggesting that some compensatory changes in aging may take place within the co-transmitter binding sites.