Fig. 1.

Odorant responses in the glomerular layer of the main olfactory bulb. a Schematical representation of the nose–brain preparation (left panel) and the three main glomerular clusters of the MOB (right panel). b Whole-mount olfactory bulb preparation stained with Fluo-4 dextran showing the three main clusters of the MOB (upper panel; LC red, MC blue). Application of amino acids preferentially induced an increase in Ca²⁺-dependent fluorescence in the lateral cluster (intermediate panel), whereas forskolin elicited activity predominantly in the medial cluster (lower panel). A representative example of seven separate experiments is shown. c Sequence of three pseudocolored images showing calcium transients of an individual glomerulus situated in the medial cluster upon application of amines. The images were taken before stimulus application, at the peak of the response and after return to the baseline fluorescence (from left to right). The fine glomerular structure of the activated glomerulus was visualized by a grayscale correlation map (rightmost image; see “Materials and methods” for details). The time courses of the [Ca²⁺]_i transients of the glomerulus, evoked by mucosal application of the different odorant groups are given below the images. The lower group of pictures shows an individual glomerulus, situated in the lateral cluster, responsive solely to amino acids (same explanation as above). d Histogram showing the location of odorant-responsive glomeruli (n = 80 glomeruli from 32 nose–brain preparations). e Out of 33 glomeruli tested for their responsiveness to all four odorant groups, 24 responded to one odorant group, eight responded to two odorant groups, and one glomerulus to three odorant groups (left panel). Odorant profiles of multiresponsive glomeruli are shown in the right panel. All odorants were applied at a final concentration of 200 μM, forskolin was applied at a final concentration of 50 μM. A anterior, P posterior, L lateral, M medial, OO olfactory organ, ON olfactory nerve, OB olfactory bulb, AA amino acids, AL alcohols, ketones, and aldehydes, AM amines, BA bile acids, FO forskolin, LC lateral glomerular cluster, IC intermediate glomerular cluster, MC medial glomerular cluster, V lateral ventricle, control application of bath solution