Cerebral sympatholysis: experiments on in vivo cerebrovascular regulation and ex vivo cerebral vasomotor control.

Whether cerebral sympathetic-mediated vasomotor control can be modulated by local brain activity remains unknown. This study tested the hypothesis that the application or removal of a cognitive task during a cold pressor test (CPT) would attenuate and restore decreases in cerebrovascular conductance (CVC), respectively. Middle cerebral artery blood velocity (transcranial Doppler) and mean arterial pressure (finger photoplethysmography) were examined in healthy adults ( = 16; 8 females and 8 males) who completed a control CPT, followed by a CPT coupled with a cognitive task administered either ) 30 s after the onset of the CPT and for the duration of the CPT or ) at the onset of the CPT and terminated 30 s before the end of the CPT (condition order was counterbalanced). The major finding was that the CPT decreased the index of CVC, and such decreases were abolished when a cognitive task was completed concurrently and restored when the cognitive task was removed. As a secondary experiment, vasomotor interactions between sympathetic transduction pathways (α-adrenergic and Y-peptidergic) and compounds implicated in cerebral blood flow control [adenosine, and adenosine triphosphate (ATP)] were explored in isolated porcine cerebral arteries (wire myography). The data reveal α-receptor agonism potentiated vasorelaxation modestly in response to adenosine, and preexposure to ATP attenuated contractile responses to α-agonism. Overall, the data suggest a cognitive task attenuates decreases in CVC during sympathoexcitation, possibly related to an interaction between purinergic and α-adrenergic signaling pathways. The present study demonstrates that the cerebrovascular conductance index decreases during sympathoexcitation and this response can be positively and negatively modulated by the application or withdrawal of a nonexercise cognitive task. Furthermore, isolated vessel experiments reveal that cerebral α-adrenergic agonism potentiates adenosine-mediated vasorelaxation and ATP attenuates α-adrenergic-mediated vasocontraction.