Cerebrovascular Reactivity Remains Intact after Cortical Depolarization in Newborn Piglets

Abstract

Cerebrovascular reactivity is severely affected by ischemia, and changes in vascular responses have been reported after cortical spreading depression and head trauma as well. Cortical depolarization (CD) occurs during ischemia, cortical spreading depression, and head trauma, but its effects on cerebrovascular reactivity are unclear. We tested the hypothesis that CD induced by KCl diminishes the vascular responsiveness to various vasodilatory stimuli in piglets. Responses of pial arterioles were determined by changes in vascular diameter by use of a closed cranial window and intravital microscopy. Baseline arteriolar diameters were 105 ± 3 µm (mean ± SEM, n = 27). CD was elicited by topical administration of 1 mol/L KCl for 3 min. Vascular responses were measured before and 1 h after CD. KCl elicited CD and constricted arterioles by 54 ± 4% (n = 27). N-methyl-D-aspartate induced dose-dependent vasodilation that was unaffected by CD; the percent changes were 9 ± 1 versus 8 ± 1 (before and after CD) at 10-5 mol/L, 19 ± 2 versus 18 ± 3 at 5 × 10-5 mol/L, and 29 ± 2 versus 26 ± 3 at 10-4 mol/L (n = 9). Hypercapnic vasodilation was not diminished by CD; the percent changes were 15 ± 2 versus 16 ± 4 at 5%, and 27 ± 5 versus 27 ± 6 at 10% inspired CO2 (n = 8). Aprikalim and forskolin caused dilation that was also resistant to prior CD; the percent change values were 21 ± 4 versus 18 ± 3 and 16 ± 2 versus 16 ± 4 at 10-6 mol/L, 36 ± 5 versus 34 ± 5 and 34 ± 7 versus 37 ± 7 at 10-5 mol/L (n = 8), respectively. Finally, calcitonin gene-related peptide-induced vasodilation was unaffected by CD; percent changes were 15 ± 3 versus 16 ± 2 at 10-7 mol/L and 26 ± 4 versus 22 ± 3 at 10-6 mol/L (n = 8). The intact vascular responses after CD suggest that this component is not responsible for decreased cerebrovascular reactivity after ischemia, head trauma, or cortical spreading depression.