Optical Signature of Olfactory Activation

Abstract

Event Abstract Back to Event Optical Signature of Olfactory Activation Frederic Pain1* 1 Université Paris Sud Orsay / CNRS, France Olfactory bulb sensory activation in living rodents is a relevant model to study brain activation thanks to its well defined architecture composed of odor specific processing units, the glomeruli, which combine locally a high density of synapses, capillaries and astrocytes. Wide field optical imaging of the activated olfactory bulb using optical contrast provide with spatio-temporal maps of complementary physiological parameters with spatial resolution of 20µm and temporal resolution of 100ms. The study of complementary physiological signals such us local changes in tissues oxygenation, blood volume, blood flow or mitochondrial flavoproteins fluorescence provides with new data regarding neuro-energetics. In order to record activation maps either sequentially or simultaneously during a single activation, we have developed a multimodal wide field macroscope that encompass a high speed spectral source (450-700nm) based on digital micro-mirrors, a modulated laser diode (680nm), CCD or sCMOS cameras with high sensitivity and high frame rate, a custom built olfactometer, and a microcontroller module for hardware synchronization. Accompanying methodological issues have been solved, including chronic cranial windows implementation, photon path-lengths calculation in turbid media, and wavelengths optimization for multispectral imaging. The first flavoprotein endogenous fluorescence dynamic maps have been recorded following activation of the olfactory bulb in the anesthetized rodent. Dynamic maps of the relative changes in oxy-hemoglobin, deoxy-hemoglobin, blood volume and blood flow have been recorded for the first time in the olfactory bulb and for increasing stimuli intensity with hexanal (dilution at 5, 10 and 20%). These patterns were found to be concentration dependent and differ significantly from those observed previously following activation of the somatosensory cortex. Future work will focus on understanding such dissimilarities which could arise either from physical causes related to light absorption and diffusion in tissues or from physiological differences between the functional architectures of the olfactory bulb and the somatosensory cortex.