Corpora striata old rats (24–25 months) contain only about half as much mRNA for D2 dopamine receptors as those of young (6 months) counterparts. This reduction can be observed by in situ hybridization of brain slices as well as with Northern and dot blot analyses of striatal extracts. Decreased levels of D2 receptor mRNA as described in this study are consistent with reductions in receptor containing neurons (20%) and receptor biosynthesis (40%), as previously observed in this and other laboratories. Thus, age related changes in D2 receptor gene expression appear to be partially responsible for loss of these receptors.

The microtubule-associated protein tau, and the cytoplasmic protein ubiquitin, are constituents of pathological neurofibrillary tangles found in Alzheimer's disease. In order to see if there is any physiological relationship between these proteins in a functioning human system, human neuroblastoma (LAN-5) cells were grown in vitro and differentiated to a neuronal phenotype. Cell extracts were analyzed by SDS-PAGE, immunoblot, and immunoprecipitation techniques. The colocalization of ubiquitin and tau immunoreactivity was noted in 12- and 35-kDa bands, predominantly located in a cell membrane fraction. The bands were also isolated by immunoprecipitation with the Alz-50 antibody and then identified with a ubiquitin antiserum. These findings show a relationship between tau and ubiquitin in a human neural cell line. This interaction suggests that tau may normally be degraded by an ubiquitin-dependent mechanism and alterations in it may contribute to the formation of neuro-fibrillary pathology.