Both start with receptor cells on the animal’s antenna. In bees, receptor cell axons enter the antennal lobe forming four tracts, T1-T4, with T1 and T3 innervating approx. 70 glomeruli each, and the other two approx. 7 glomeruli each. In the antennal Selleckchem PD0332991 lobe, T1 glomeruli and T2-T4 glomeruli form two separate sublobes. From each of these two sublobes, two distinct tracts of projection neurons

leave the antennal lobe toward higher processing centers, the mushroom bodies and the lateral protocerebrum (Abel et al., 2001 and Kirschner et al., 2006). One tract travels along the midline (the medial antenno-protocerebral tract, mAPT, innervated by T2-T4), while the other tract travels laterally (lAPT, innervated by T1). The functional www.selleckchem.com/products/ly2835219.html implication of these two subsystems for olfactory processing remains unclear to date (Galizia and Rossler, 2010). Optical imaging,

and in particular calcium imaging, has increased our possibilities to record odor-evoked glomerular activity patterns (Friedrich and Korsching, 1997 and Joerges et al., 1997). Using wide-field microscopy, and a calcium-sensitive reporter such as Calcium-Green, Fura or genetically encoded probes, it is possible to simultaneously record neurons across wide areas of the brain surface. Small brains, such as those of insects, are particularly suitable because their limited size allows measuring combinatorial activity from substantial parts of their olfactory system simultaneously. The honeybee antennal lobe has a diameter of approx. 250 μm, and with a 20× objective MRIP the entire antennal lobe surface can be recorded in an in vivo preparation. In the honeybee, olfactory glomeruli are arranged in a single layer around a central coarse neuropil, so that the interference from deeper brain layers on odor-evoked signals is small. Moreover, this neural structure forms a separate lobe, and is attached to the rest of the brain on only a small fraction of its surface, potentially

allowing direct access to many glomeruli from multiple angles. However, when opening the head capsule of the animal, optical access is drastically reduced to about 30–40 glomeruli on the frontal part of the antennal lobe. Almost all the glomeruli that are directly visible in this standard brain preparation belong to the lAPT system ( Galizia et al., 1999b and Sachse et al., 1999). As a result, although the combinatorial nature of odor-coding in lAPT glomeruli has been studied in great detail, knowledge about the mAPT remains weak, deriving mostly from single cell recordings ( Krofczik et al., 2008 and Müller et al., 2002). Does the mAPT code for the same odors as the lAPT? Do the two systems differ in the dynamics of their responses, or in the combinatorial logic of odor-coding? To answer these questions, a technique that allows recording from a large number of mAPT glomeruli is necessary. In this study, we therefore developed a new technique to image concealed brain surfaces.