Assessment and discrimination of odor stimuli in rat olfactory bulb by dynamic functional MRI

Dynamic blood oxygenation level-dependent functional MRI was applied at 7 T in the rat olfactory bulb (OB) with pulsed delivery of iso-amyl acetate (I AA) and limonene. Acquisition times for single-slice and whole on data were 8 and 32 s, respectively, with spatial resolution of 220 x 220 x 250 mu m. On an intrasubject basis, short IAA exposures of 0.6 min separated by 3.5- min intervals induced reproducible spatial activity patterns (SAPs) in the olfactory nerve layer, glomerular layer, and external plexiform layer. Duri ng long exposures (approximate to 10 min), the initially dominant dorsal SA Ps declined in intensity and area, whereas in some on regions, the initiall y weak ventral/lateral SAPs increased first and then decreased. The SAPs of different concentrations were topologically similar, which implies that wh ereas an odor at various concentrations activates the same subsets of recep tor cells, different concentrations are assessed and discriminated by varia ble magnitudes of laminar-specific activations. IAA and limonene reproducib ly activated different subsets of receptor cells with some overlaps. Wherea s qualitative topographical agreement was observed with results from other methods, the current dynamic blood oxygenation level-dependent functional M RI results can provide quantitative SAPs of the entire OB.