A long-standing challenge in optical neuroimaging has been the assessment of hemodynamics and
oxygen metabolism in the awake rodent brain at the microscopic level. Here, we report first-of-a-kind head-restrained photoacoustic microscopy (PAM), which enables simultaneous imaging of the cerebrovascular anatomy, total concentration and oxygen saturation of
hemoglobin, and blood flow in awake mice. Combining these hemodynamic measurements allows us to derive two key metabolic parameters-
oxygen extraction fraction (OEF) and the cerebral metabolic rate of
oxygen (CMRO2). This enabling technology offers the first opportunity to comprehensively and quantitatively characterize the hemodynamic and
oxygen-metabolic responses of the mouse brain to
isoflurane, a
general anesthetic widely used in preclinical research and clinical practice. Side-by-side comparison of the awake and anesthetized brains reveals that
isoflurane induces diameter-dependent arterial dilation, elevated blood flow, and reduced OEF in a dose-dependent manner. As a result of the combined effects, CMRO2 is significantly reduced in the anesthetized brain under both normoxia and
hypoxia, which suggests a mechanism for
anesthetic neuroprotection. The head-restrained functional and metabolic PAM opens a new avenue for basic and translational research on neurovascular coupling without the strong influence of
anesthesia and on the
neuroprotective effects of various interventions, including but not limited to volatile
anesthetics, against
cerebral hypoxia and
ischemia.