Transcranial flavoprotein fluorescence imaging of mouse cortical activity and plasticity

Abstract

Endogenous fluorescence signals derived from mitochondria reflect activity-dependent changes in brain metabolism and may be exploited in functional brain imaging. Endogenous flavoprotein fluorescence imaging in mice is especially important because many genetically manipulated strains of mice are available and the transparent skull of mice allows transcranial fluorescence imaging of cortical activities. In the primary sensory areas of mice, cortical activities and experience-dependent plasticity have been investigated using transcranial fluorescence imaging. Furthermore, differential imaging, based on stimulus specificity of cortical areas, distinguished activities in higher visual areas around the primary visual cortex from those in primary visual cortex. The combination of transcranial fluorescence imaging with the suppression of cortical activities using photobleaching of flavoproteins is expected to aid in elucidating the roles of sensory cortices including higher areas in mice.

Synaptic Plasticity Defect Following Visual Deprivation in Alzheimer's Disease Model Transgenic Mice

“…To confirm this result and to compare responses to stimulation of each eye before and after MD in individual animals, OD plasticity was next examined in vivo using widefield imaging of intrinsic signals during localized visual stimulation. Optical intrinsic signal imaging is a well-established method for assessing retinotopic organization, the relative strength of cortical responses to stimulation of ipsilateral and contralateral eyes, as well as changes in response strength that occur following MD (Grinvald et al, 1986; Schuett et al, 2002; Cang et al, 2005; Hofer et al, 2009; Tohmi et al, 2009). The measured intrinsic signal is thought to be a result of neuronal activity and hemodynamic responses, both of which may be reduced by anesthesia and the behavioral state of the animal (Berwick et al, 2002; Niell and Stryker, 2010), prompting us to perform our analysis in awake mice that were habituated to head fixation.…”

“…To map visual cortical responses, we used in vivo epifluorescence imaging (Husson et al, 2007; Tohmi et al, 2009) to measure changes in autofluorescence signal. Autofluorescence produced by blue excitation (470 nm center, 40 nm band, Chroma) was measured through a green/red emission filter (longpass, 500 nm cutoff).…”

“…Visual responses consist of a small increase in the autofluorescence signal (corresponding to flavoprotein oxidization during increased metabolism; Tohmi et al, 2009) followed by a stronger negative signal (due to increased light absorption due to delayed increase in blood volume and deoxyhemoglobin concentration; Schuett et al, 2002). Thus, the response to a stimulus was computed as the percent change in fluorescence (% dF/F) between the average of 6 frames recorded during the first 3 seconds following stimulus onset and the average of all 20 frames recorded from 9 seconds to 19 seconds following stimulus onset.…”

A mouse model of higher visual cortical function

“…While these stimuli may not be ideal for driving the higher visual areas, they have the advantage of allowing direct comparison with the properties of V1 neurons and precise measurement of tuning features that have classically distinguished the dorsal and ventral pathways such as spatial and temporal frequency. Each of the higher visual areas has distinct preferences for these features[•22–•24,29]. For instance, neurons in anterolateral area (AL) are preferentially driven by stimuli at high temporal and low spatial frequencies while neurons in posteromedial area (PM) are driven by stimuli at low temporal and high spatial frequencies.…”

Autofluorescent Flavoprotein Imaging of Spinal Nociceptive Activity

“…Second, the signal intensity is high compared with nicotinamide adenine dinucleotide (NADH) imaging (Reinert et al, 2004) and intrinsic hemodynamic optical imaging (Sasaki et al, 2002). Third, AFI is a direct measure of neuronal metabolic demand and thus neuronal activity, in contrast to hemodynamic optical imaging and functional magnetic resonance imaging (fMRI) (Weber et al, 2004;Reinert et al, 2007;Tohmi et al, 2009). So far, AFI has never been applied to the spinal cord.…”