Alterations of the cerebral capillary bed in the senile dementia of Alzheimer

Brain tissue specimens from 15 patients dying with neuropathologically confirmed clinical diagnoses of senile dementia, Alzheimer type, and 10 approximately age and sex matched elderly patients without signs of senile change, were compared using a group of neurohistological techniques including scanning electron microscopy. In addition to previously described changes in structure of neurons and neuropil, dramatic changes were noted in the capillary bed. Normal cerebral vessels are characterized by smooth contours, the presence of occasional pericytes, and a plexus of pericapillary nerve fibers bearing many varicosities which have been shown to be strongly positive for norepinephrine, acetylcholine, dopamine and several other putative neurotransmitters or neuromodulators. In our series of Alzheimer patients the cerebral vessels were highly irregular in appearance, covered with rounded or conical extrusions (lumps and bumps), and totally lacking in the perivascular plexus of nerve fibers. In about three quarters of the cases studied the vessel walls were perforated by multiple openings of varying sizes, most of which appeared to run through the complete thickness of the thickened basement membrane but did not perforate the endothelial lining of the capillary lumen. The origin and pathogenesis of these changes is still unknown although some of the materials infiltrating the vascular walls appear to contain amyloid. On the basis of presently available evidence, it is suggested that widespread microvascular pathology may be caused by loss of the perivascular neural plexus (denervating microangiopathy) and that this may result in breakdown of the blood brain barrier. It is conceivable that the widespread degeneration characteristic of senile domentia, Alzheimer type, develops secondarily to these structuro-functional alterations in the microvasculature and that the primary target of the Alzheimer process may be located in subcortical nuclei, e.g. locus ceruleus and nucleus basalis of Meynert, which normally supply innervation to the cerebral vessels.