Pallido-nigral spheroids in nonhuman primates: Accumulation of heat shock proteins in astroglial processes

Alpha-B crystallin, ubiquitin and heat shock protein 27 (hsp27) belong to a class of proteins that are overexpressed in response to pathological conditions associated with increased cellular stress. In the present study, brain sections of old rhesus monkeys (Macaca mulatta; n=10; mean age, 29.4 years) and baboons (Papio anubis; n=8; mean age, 18.3 years) were examined for ubiquitin, alpha-B crystallin and hsp27-immunopositive structures. In both species, immunoreactive spheroid-like bodies were found in the globus pallidus and in the substantia nigra, pars reticulata. These structures frequently were associated with abnormally swollen cellular processes. To further clarify the origin of the pallido-nigral spheroids, single-and double-immunostaining was performed for hsp27, alpha-B crystallin and the astroglial marker glial fibrillary acidic protein (GFAP) as well as for neuronal markers against neurofilament and dendritic microtubule-associated protein 2. Confocal microscopic analysis demonstrated that spheroids were localized in swollen astroglial processes, whereas they were not seen in neuronal structures. Thus, pallido-nigral spheroids can be classified as astroglial accumulations of heat shock proteins. Further investigations of these structures may provide information pertinent to our understanding of astroglial heat shock protein inclusions developing in degenerative human brain diseases.