Cerebral blood vessels of several species have been shown to receive both vasodilator and constrictor nerves. However, the respective transmitter substances have not been positively identified, nor is the functional role of these nerves in controlling brain circulation determined. Results of several recent in vivo physiological studies reveal that the sympathetic innervation, which is weak or not functional in controlling brain circulation under normal conditions, becomes functional when animals develop hypertension. On the other hand, hypertension has been considered to stand as the greatest risk factor in cerebral vascular diseases. Spontaneous brain hemorrhage is recognized as a major consequence of hypertension. Substances released from the lysed red blood cells following hemorrhage are believed to play a critical role in the pathogenesis of cerebral vascular diseases such as cerebral vasospasm. We have previously demonstrated that the erythrocyte extracts (hemolysate or hemoglobin preparations) enhance the neurogenic vasoconstriction and diminish the neurogenic vasodilation of isolated cerebral arteries. These results suggest that the vasomotor role of cerebral vessel innervation can vary under pathological states such as brain hemorrhage. However, the mechanism by which erythrocyte extracts alter the neurogenic vasomotor responses has not been examined. Several related questions regarding the transmitter mechanisms and their alteration by erythrocyte extracts will not be entirely understood unless the nature of transmitter substances is determined. The proposed study is to delineate the nature of cerebral vasodilator and constrictor nerves and effects of erythrocyte extracts on functional relationship between these nerves and the vascular smooth muscle. The in vitro tissue bath techniques and techniques of biochemical analysis and morphology (immunohistochemistry and immunoelectron microscopy) will be utilized to provide a comprehensive and multifaceted approach to this problem. We plan to (1) examine the distribution pattern and ultrastructural characteristics of cerebral vasodilator and constrictor nerves, (2) examine the coexistence of multiple transmitters in cerebral vasodilator and constrictor nerves, (3) examine postsynaptic effects of hemoglobin on cerebral vascular responses induced by potential transmitters, and (4) examine the presynaptic effect of hemoglobin on the release of potential transmitters from vasodilator and constrictor nerves. This research is a step toward our long-term goal to define the transmitter mechanisms in cerebral vasodilation and constriction, and their alterations in hypertension-related diseases.
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