Neurovascular coupling investigated with two-dimensional optical imaging spectroscopy in rat whisker barrel cortex.
Optical imaging slit spectroscopy is a powerful method for estimating quantitative changes in cerebral haemodynamics, such as deoxyhaemoglobin, oxyhaemoglobin and blood volume (Hbr, HbO2 and Hbt, respectively). Its disadvantage is that there is a large loss of spatial data as one image dimension is used to encode spectral wavelength information. Single wavelength optical imaging, on the other hand, produces high-resolution spatiotemporal maps of brain activity, but yields only indirect measures of Hbr, HbO2 and Hbt. In this study we perform two-dimensional optical imaging spectroscopy (2D-OIS) in rat barrel cortex during contralateral whisker stimulation to obtain two-dimensional maps over time of Hbr, HbO2 and Hbt. The 2D-OIS was performed by illuminating the cortex with four wavelengths of light (575, 559, 495 and 587 nm), which were presented sequentially at a high frame rate (32 Hz). The contralateral whisker pad was stimulated using two different durations: 1 and 16 s (5 Hz, 1.2 mA). Control experiments used a hypercapnic (5% CO2) challenge to manipulate baseline blood flow and volume in the absence of corresponding neural activation. The 2D-OIS method allowed separation of artery, vein and parenchyma regions. The magnitude of the haemodynamic response elicited varied considerably between different vascular compartments; the largest responses in Hbt were in the arteries and the smallest in the veins. Phase lags in the HbO2 response between arteries and veins suggest that a process of upstream signalling maybe responsible for dilating the arteries. There was also a consistent increase in Hbr from arterial regions after whisker stimulation.
Berwick
J
J
Department of Psychology, University of Sheffield, Western Bank, Sheffield S10 2TP, UK. j.berwick@sheffield.ac.uk
Johnston
D
D
Jones
M
M
Martindale
J
J
Redgrave
P
P
McLoughlin
N
N
Schiessl
I
I
Mayhew
J E W
JE
D000465:Algorithms; D000818:Animals; D001808:Blood Vessels / Q000502:physiology; D001810:Blood Volume / Q000502:physiology / Q000528:radiation effects; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology / Q000528:radiation effects; D007839:Functional Laterality / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D007091:Image Processing, Computer-Assisted / Q000379:methods; D066298:In Vitro Techniques; D046032:Microscopy, Energy-Filtering Transmission Electron; D051381:Rats; D012039:Regional Blood Flow / Q000502:physiology* / Q000528:radiation effects; D013003:Somatosensory Cortex / Q000502:physiology*; D013997:Time Factors; D014738:Vibrissae / Q000294:innervation*
D006454:Hemoglobins