Diagram showing the basic cellular elements of an adult antennal lobe in <i>Manduca sexta</i>.

<p><b>A:</b> Olfactory receptor neurons (ORNs) located in the antennae extend axons (green) to the antennal lobes of the brain where they end in structures called glomeruli and synapse with antennal lobe neurons. Two classes of AL neurons, local interneurons (ln) and projection neurons (pn), have their cell bodies in clusters called the lateral and medial groups (LG & MG), which reside outside of the antennal lobe neuropil. <b>B:</b> Labeling of an untreated female antennal lobe (AL) at stage 7 with an antibody to <i>M. sexta</i> Fasciclin II (orange) and a nucleic acid dye (Syto 13, blue) makes clear the major changes in ORN axon fasciculation and direction a short distance into the sorting zone (SZ), with axons exiting the sorting zone in large MFas II-positive bundles. Projection depth = 15 µm. <b>C:</b> A single glomerulus, showing the relationship of ORN axon terminals and AL neuron dendrites. ORN axons form a nerve layer around the outside of the antennal lobe neuropil, then turn sharply and extend through the glial layer and branch in the outer portion of a glomerulus in the glomerular layer. The cell bodies and processes of neuropil (NP) glial cells form a nearly complete envelope around each glomerulus. Panels A and C adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033828#pone.0033828-Gibson3" target="_blank">[33]</a>.