Figure 3.

Stimulus-dependent modulation of fluorescence in neurons located under cortical surface arterioles but not venules. (a–d) Mask representations of the dorsal view of a surface arteriole (a), venule (c) and underlying neuronal soma (labeled 1–4) in the rat visual cortex, and Alexa Fluor 594 fluorescence in the indicated neurons after a visual stimulus, in the same rat (b,d; averages of 23 trials). (e) Rendering of a surface arteriole (magenta) and a neuronal soma (green) in an imaged cortical volume, illustrating the potential dependence of the neuronal imaging artifact on the relative positioning of an arteriole and a nearby neuron. The two paths of light were achieved by rotating the head of a mouse that was positioned under the two-photon microscope’s objective lens. In head angle 1, light passes through the surface arteriole. In head angle 2, light beam bypasses the arteriole. (f) Mask representation of an imaged area in mouse visual cortex (dorsal view) showing a surface arteriole (magenta) and a neuronal soma located directly below. (g) Alexa Fluor 594 fluorescence from the soma shown in f in response to visual stimuli. (h) Dorsal view of the same area as in f but after head rotation; soma is no longer under the arteriole. (i) Alexa Fluor 594 fluorescence in the soma shown in h in response to visual stimuli. Time courses in g and i are averages of 31 trials. All gray bars represent the period of visual stimulation; error bands, s.e.m.; scale bars, 50 μm.