Local cerebral blood flow responses in rats to hypercapnia and hypoxia in the rostral ventrolateral medulla and in the cortex

Abstract

The effects of hypercapnia and hypoxia on two local cerebral blood flows in the parietal cortex (PC-BF) and rostral ventrolateral medulla (RVLM-BF) were examined using laser Doppler flowmetry in anesthetized rats. Hypercapnia for 45 s duration at the end-tidal CO 2 between 5% and 10%, induced by increasing inspiratory CO 2, increased both cerebral blood flows and systemic blood pressure in a degree-dependent manner. The response of RVLM-BF was significantly stronger than that of PC-BF. Both cerebral blood flow responses to hypercapnia were not influenced by cutting peripheral chemoreceptor afferent nerves. Hypoxia for 45 s duration at the end-tidal O 2 between 12% and 6%, induced by decreasing inspiratory O 2, produced an increase of similar magnitude in both RVLM and PC local blood flows in a degree-dependent manner and a decrease in systemic blood pressure. The responses of both PC-BF and RVLM-BF to hypoxia were significantly diminished after cutting peripheral chemoreceptor afferent nerves. It is concluded that: (1) the RVLM-BF is much more sensitive to hypercapnia than the PC-BF; and (2) activation of peripheral arterial chemoreceptors possibly contributes to hypoxia-induced increase in the RVLM-BF and PC-BF.