Fig. 2

Olfactory organ of the Caribbean spiny lobster Panulirus argus, and calcium imaging of odorant-activated responses from olfactory sensory neurons. a. Location of aesthetasc sensilla mediating olfaction (blue) and bimodal chemo-mechanosensory sensilla mediating distributed chemoreception (yellow) on different body parts and appendages (1 - lateral flagellum of antennule, 2 - medial flagellum of antennule, 3 - second antenna, 4 - mouthparts, 5 - walking legs, 6 - gill chamber, 7 - tail fan, 8 - pleopods). b. Location of aesthetasc sensilla and bimodal chemo-mechanosensory sensilla on the antennules. Aesthetascs (blue) are restricted to a tuft of sensilla on the distal one-third of the lateral flagellum. Bimodal chemo-mechanosensory sensilla (yellow) among them guard sensilla (GS) are associated with the aesthetascs but also occur on the proximal part of the lateral flagellum and on the entire medial flagellum.  a. and b. are modified from [2]. c. Transmitted light microscopic image of antennule slice preparation used for calcium imaging of odorant-evoked responses. The preparation consists of an annulus bearing aesthetasc sensilla (AE), and their olfactory sensory neurons (OSNs), and guard sensilla (GS). d. Schematic drawing of a single aesthetasc of P. argus (modified from [5]). The aesthetasc is innervated by ~ 300 bipolar olfactory sensory neurons (OSNs) whose somata form a cluster below the cuticle (C). Each soma gives rise to 1) a dendrite projecting into the cuticular seta where it branches into many ciliated outer segments and 2) an axon projecting to the brain. e. Image showing the method of collecting odorant-activated OSNs using the calcium imaging preparation. An antennule slice (shown in panel c) was prepared for calcium imaging (described in Methods). The dye-filled OSNs, situated in cell clusters that are outlined, are shown with an electrode positioned near a target OSN that responded to an 800-msec pulse of the food odorant 500 mg/l TetraMarine. A video showing odorant-activated responses of OSNs in this preparation is shown in Additional file 1