Differential expression of ubiquitin within the rat brain: discretely localized increases following salt-loading

Ubiquitin is thought to be a universal component of all eukaryotic cells. The recent finding of ubiquitin as a component of abnormal neuronal filaments in various neurodegenerative diseases has prompted the need for knowledge of its distribution within the normal nervous system. To determine this distribution, the rat brain was examined immunocytochemically. Ubiquitin immunoreactivity was found within many regions of the rat brain, although to strikingly different degrees. Staining was most intense in the hypothalamic suprachiasmatic and supraoptic nuclei, as well as the anterodorsal nucleus of the thalamus, medial and lateral habenular nuclei and associated fibre tracts. Following salt-loading, ubiquitin immunoreactivity increased dramatically in axons of the hypothalamo-neurohypophysial tract and its site of termination, the posterior pituitary. In colchicine-treated rats the ubiquitin staining became more prominent in many areas of the brain including the supraoptic nucleus, the habenular nuclei, anterodorsal thalamic nucleus, the hypothalamic arcuate nucleus and cells within the ventral pallidum/substantia innominata region showing a distribution similar to nucleus basalis of Meynert. Partial anterior hypothalamic deafferentation indicated ubiquitin to be axonally-transported at a considerably slower rate than neuropeptides. The differential distribution of ubiquitin within the brain suggests an involvement in processes not heretofore considered.