Pathogenesis of vascular dementia in stroke-prone spontaneously hypertensive rats.

Stroke-prone spontaneously hypertensive rats (SHRSP) are the best model for essential hypertension and stroke. In this study, one investigated whether SHRSP might be a useful animal model for vascular dementia. An impairment of learning-memory function was found in SHRSP. A disturbance in circadian rhythm after stroke in SHRSP was clarified. Desynchronization of light and dark alternation cycles and abnormal rhythm were also demonstrated. These observations point to the possibility that the decreased passive avoidance response observed in SHRSP might be similar to the phenomenon of memory impairment in patients with vascular dementia. The behavioral changes in ambulation in SHRSP, including the desynchronization between light and dark alternation cycles and the abnormal rhythm before death, might correspond to the behavioral changes associated with the delirium-state observed in patients with dementia. Cerebral cortex levels of acetylcholine and choline in SHRSP decreased significantly as compared with the Wistar Kyoto rats (WKY) control group. Hippocampal levels of acetylcholine and choline in SHRSP decreased significantly as compared with those in WKY. Moreover, a correlation between passive avoidance response latency and hippocampal acetylcholine levels was observed. These findings suggest that decreased acetylcholine levels in both the cerebral cortex and the hippocampus may be related to the impairment of learning-memory function and abnormal behavior. In SHRSP, increases in blood viscosity, hematocrit and fibrinogen might produce the formation of thrombus and induce cerebral infarction. Some histopathological findings caused by cerebrovascular disorder in human brain very similar to those observed in the SHRSP brain. On the other hand, so called 'senile changes' were detected only in the human case, and not observed in the SHRSP.