Abstract
Appetite or feeding motivation relies significantly on food odors. In the blowfly Phormia regina, feeding motivation for sucrose is decreased by the odor of d-limonene but increased by the odor of 1-octen-3-ol odor. These flies have antennal lobes (ALs) consisting of several tens of glomerular pairs as a primary olfactory center in the brain. Odor information from different olfactory organs—specifically, the antennae and maxillary palps—goes to the corresponding glomeruli. To investigate how odors differently affect feeding motivation, we identified the olfactory organs and glomeruli that are activated by nonappetitive and appetitive odors. We first constructed a glomerular map of the antennal lobe in P. regina. Anterograde fluorescence labeling of antennal and maxillary afferent nerves, both of which project into the contralateral and ipsilateral ALs, revealed differential staining in glomerular regions. Some of the axonal fiber bundles from the antennae and maxillary palps projected to the subesophageal ganglion (SOG). We visualized the activation of the glomeruli in response to odor stimuli by immunostaining phosphorylated extracellular signal-regulated kinase (pERK). We observed different glomerulus activation under different odor stimulations. Referring to our glomerular map, we determined that antennal exposure to d-limonene odor activated the DA13 glomeruli, while exposure of the maxillary palps to 1-octen-3-ol activated the MxB1 glomeruli. Our results indicated that a nonappetitive odor input from the antennae and an appetitive odor input from the maxillary palps activate different glomeruli in the different regions of ALs in the blowfly P. regina. Collectively, our findings suggest that compartmentalization of glomeruli in AL is essential for proper transmission of odor information.
Highlights
Many natural products serve as a means of communication between organisms
Owing to an abundance of early electrophysiological studies with the single sensillar recording method called the tip-recording procedure, the characteristic profile of four functional different gustatory receptor neurons (GRNs) in a gustatory sensillum has been revealed [5, 8, 11, 12, 14]. These GRNs, named for the stimuli to which they respond, are the sugar, salt, water, and bitter taste receptor neurons, respectively. In both P. regina and Drosophila melanogaster, it is believed that sugar receptor neurons, which can respond to a wide range of nutritious phagostimulants, and bitter taste receptor neurons, which respond to noxious compounds, directly promote positive and negative feeding motivation, respectively [14, 16,17,18,19,20,21]
Sensory projections from antennae and maxillary Palps Staining of either the antennal nerve with dextran fluorescein or the maxillary nerve with dextran tetramethylrhodamine revealed that the afferents innervated most of the antennal lobe glomeruli in the ipsilateral and contralateral hemibrains (Fig. 1a and b), even when the fluorescent dyes were introduced only from the right side
Summary
Many natural products serve as a means of communication between organisms. For example, some flowering plants provide insect pollinators with attractive sweet nectar in conjunction with floral scents, both of which help their pollinators find and consume food [1], and some have defensive chemicals to prevent herbivores from feeding [2]. Owing to an abundance of early electrophysiological studies with the single sensillar recording method called the tip-recording procedure, the characteristic profile of four functional different gustatory receptor neurons (GRNs) in a gustatory sensillum has been revealed [5, 8, 11, 12, 14]. These GRNs, named for the stimuli to which they respond, are the sugar, salt, water, and bitter taste receptor neurons, respectively. In both P. regina and Drosophila melanogaster, it is believed that sugar receptor neurons, which can respond to a wide range of nutritious phagostimulants, and bitter taste receptor neurons, which respond to noxious compounds, directly promote positive and negative feeding motivation, respectively [14, 16,17,18,19,20,21]
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