Abstract
Octopamine plays an important role in many behaviors in invertebrates. It acts via binding to G protein coupled receptors located on the plasma membrane of responsive cells. Several distinct subtypes of octopamine receptors have been found in invertebrates, yet little is known about the expression pattern of these different receptor subtypes and how each subtype may contribute to different behaviors. One honey bee (Apis mellifera) octopamine receptor, AmOA1, was recently cloned and characterized. Here we continue to characterize the AmOA1 receptor by investigating its distribution in the honey bee brain. We used two independent antibodies produced against two distinct peptides in the carboxyl-terminus to study the distribution of the AmOA1 receptor in the honey bee brain. We found that both anti-AmOA1 antibodies revealed labeling of cell body clusters throughout the brain and within the following brain neuropils: the antennal lobes; the calyces, pedunculus, vertical (alpha, gamma) and medial (beta) lobes of the mushroom body; the optic lobes; the subesophageal ganglion; and the central complex. Double immunofluorescence staining using anti-GABA and anti-AmOA1 receptor antibodies revealed that a population of inhibitory GABAergic local interneurons in the antennal lobes express the AmOA1 receptor in the cell bodies, axons and their endings in the glomeruli. In the mushroom bodies, AmOA1 receptors are expressed in a subpopulation of inhibitory GABAergic feedback neurons that ends in the visual (outer half of basal ring and collar regions) and olfactory (lip and inner basal ring region) calyx neuropils, as well as in the collar and lip zones of the vertical and medial lobes. The data suggest that one effect of octopamine via AmOA1 in the antennal lobe and mushroom body is to modulate inhibitory neurons.
Highlights
The biogenic amine octopamine acts as a neurotransmitter, neuromodulator and neurohormone in the nervous system of invertebrates [1,2]
Specificity of the anti-AmOA1 antibodies Two different polyclonal antibodies were used in our studies, one raised in rabbit (Ranti-AmOA1) and another raised in goat (Ganti-AmOA1) against two different peptides corresponding to different regions in the cytoplasmic carboxyl terminus of the AmOA1 receptor
Double labeling experiments revealed that these antibodies labeled the same cells and processes in the neuropil of the bee brain
Summary
The biogenic amine octopamine acts as a neurotransmitter, neuromodulator and neurohormone in the nervous system of invertebrates [1,2]. Many areas receive input from the octopaminergic ventral unpaired median neurons (central VUM neurons) identified in part by cell bodies that lie on the median (midline) ventral part of the subesophageal ganglion [30,32,34,35] Two of these neurons, VUMmx and VUMmd, have a primary neurite that projects through the midline tract of the subesophageal ganglion and gives rise to two symmetrical secondary axons that project collaterals to the antennal lobes, lateral horn, lateral protocerebrum and to the lip and basal ring of the mushroom body calyces [34,35]. These neuropils process many of the different types of sensory stimuli that honey bees are capable of associating with reinforcement
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