The intralaminar nuclei assigned to the medial pain system and other components of this system are early and progressively affected by the Alzheimer's disease-related cytoskeletal pathology

Abstract

The intralaminar nuclei of the human thalamus are integrated into the ascending reticular activating system and into limbic, oculomotor and somatomotor loops. In addition, some of them also represent important components of the medial pain system. We examined the occurrence and severity of the Alzheimer's disease (AD)-related cytoskeletal pathology and β-amyloidosis in the seven intralaminar nuclei (central lateral nucleus, CL; central medial nucleus, CEM; centromedian nucleus, CM; cucullar nucleus, CU; paracentral nucleus, PC; parafascicular nucleus, PF; subparafascicular nucleus, SPF) in 27 autopsy cases at different stages of the cortical neurofibrillary pathology (cortical NFT/NT-stages I–VI) and β-amyloidosis (cortical phases 1–4). The CEM, CL, PF, and SPF are slightly affected at stage II (corresponding to preclinical AD). They are markedly involved at stages III and IV (i.e. incipient AD) and severely affected at stages V and VI (i.e. clinical AD). In the PC and CU, the cytoskeletal pathology is mild at stage III, marked at stage IV, and severe at stages V–VI, whereas the CM is only mildly affected at stages IV–VI. In all of the intralaminar nuclei, deposits of the protein β-amyloid occur for the first time during the final phase of cortical β-amyloidosis. Functionally, the cytoskeletal pathology encountered in the intralaminar nuclei may contribute to the memory and affective symptoms, attention deficits, and dysfunctions related to horizontal saccades and smooth pursuits seen in AD patients. Equally important, however, are the findings that the cytoskeletal pathology developing within the intralaminar nuclei assigned to the medial pain system (CEM, CL, CU, PC, PF) as well as within other components of this system begins already during the preclinical or incipient phases of AD. Given this fact, the question arises as to whether non-discriminative aspects mediated by the medial pain system could be employed to identify individuals in the very earliest stages of AD.