Impaired endothelium-mediated cerebrovascular reactivity promotes anxiety and respiration disorders in mice

Carbon dioxide (CO(2)), the major product of metabolism, has a strong impact on cerebral blood vessels, a phenomenon known as cerebrovascular reactivity. Several vascular risk factors such as hypertension or diabetes dampen this response, making cerebrovascular reactivity a useful diagnostic marker for incipient vascular pathology, but its functional relevance, if any, is still unclear. Here, we found that GPR4, an endothelial H(+) receptor, and endothelial Gα(q/11) proteins mediate the CO(2)/H(+) effect on cerebrovascular reactivity in mice. CO(2)/H(+) leads to constriction of vessels in the brainstem area that controls respiration. The consequential washout of CO(2), if cerebrovascular reactivity is impaired, reduces respiration. In contrast, CO(2) dilates vessels in other brain areas such as the amygdala. Hence, an impaired cerebrovascular reactivity amplifies the CO(2) effect on anxiety. Even at atmospheric CO(2) concentrations, impaired cerebrovascular reactivity caused longer apneic episodes and more anxiety, indicating that cerebrovascular reactivity is essential for normal brain function. The site-specific reactivity of vessels to CO(2) is reflected by regional differences in their gene expression and the release of vasoactive factors from endothelial cells. Our data suggest the central nervous system (CNS) endothelium as a target to treat respiratory and affective disorders associated with vascular diseases

Behavioral, respiratory and metabolic consequences of impaired cerebrovascular reactivity

Carbon dioxide (CO2) and protons (H+) have a strong influence on cerebral perfusion, but the function of this is not clear yet. Here, we found that GPR4, a receptor for H+ in the vasculature, sensed CO2/H+ and that an endothelial Gαq/11-dependent signaling pathway mediated the CO2/H+ effect on cerebrovascular reactivity. While CO2/H+-induced Gαq/11 signaling constricted vessels in the retrotrapezoid nucleus, it had a dilative effect in other brain areas explaining why loss of cerebrovascular reactivity in mice differentially modulated CO2 effects: it reduced respiration but aggravated behavioral and metabolic responses to CO2. Even with normal CO2 concentrations mice with impaired cerebrovascular reactivity were more anxious and showed metabolic changes indicating that cerebrovascular reactivity is essential for normal physiology