Antennal lobe neurons of the honey bee,Apis mellifera, express a D2-like dopamine receptor in vitro

Abstract

We have used the D2-specific dopamine receptor ligand spiperone [N-(p-aminophenethyl) spiperone; NAPS] coupled to the fluorophore 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD) to visualize dopamine receptors expressed in vitro by neurons of the primary antennosensory centers (antennal lobes) of the brain of the honey bee, Apis mellifera. Changes in the percentage of antennal lobe neurons exhibiting spiperone binding sites over time in culture and at different stages of metamorphic adult development have been investigated. Neurons obtained from animals at all stages of development exhibited spiperone binding sites, but only after 2 days or more in vitro. The percentage of antennal lobe neurons in vitro expressing spiperone binding sites increased significantly with the development of the antennal lobe neuropil. Fluorescently labelled spiperone (120 nM) could be displaced effectively by 1 mM dopamine but not by the same concentration of tyramine, octopamine, or serotonin. In addition, the D2 antagonist spiperone and the D2/D1 antagonist fluphenazine were more effective at displacing the fluorescent ligand than the D1-specific antagonist SCH23390. Our results indicate that Apis antennal lobe neurons in culture express a dopamine receptor and that this receptor is more likely to be D2-like than D1-like in nature. The receptor is expressed early in the metamorphic adult development of the antennal lobe neuropil of the brain.

Dietary dopamine causes ovary activation in queenless Apis mellifera workers

“…Studies on these receptors and their related intracellular signaling have been reviewed by Blenau and Baumann (2001). Dopamine receptors were characterized in the corpora allata of Manduca sexta (Granger et al, 2000), in the antennal lobe neurons (Kirchhof and Mercer, 1997) and in the brain (Kokay and Mercer, 1996) of the honey bee, and in the mushroom bodies of locust (Degen et al, 2000). Characterization of dopamine receptors in ovaries or fat body could clarify the observed effect of dopamine on honey bee worker ovary growth.…”

Differential expression of voltage-sensitive K+ and Ca2+ currents in neurons of the honeybee olfactory pathway

“…This, however, requires a staining technique that allows the identification of the neuron type prior to recording. Whereas cultures of mushroom bodies comprise somata of a homogeneous cell type (Kenyon cells), the dissociation of antennal lobes yields a heterogeneous mixture of projection neurons and local interneurons (Gascuel and Masson, 1991b;Devaud et al, 1994;Kirchhof and Mercer, 1997). To record from identified cell types, namely projection neurons and Kenyon cells, we have developed a labelling technique that enabled us to identify neurons in the culture dish prior to patch clamp recording.…”

“…Thus, dissection of antennal lobes yielded cultures containing neurons of different classes (cf. Kirchhof and Mercer, 1997) and projection neurons needed to be identified in vitro. Since K + and Ca 2+ currents in honeybee olfactory neurons only projection neurons were labelled by dextran-rhodamine, their somata were easily identified in the culture dish by their fluorescence.…”

“…Cultured projection neurons or Kenyon cells do not retain their in vivo morphology. This is probably not a consequence of the labelling procedure, because it has been described previously for cultures of unlabelled Kenyon cells (Kreissl and Bicker, 1992) and unidentified antennal lobe neurons (Devaud et al, 1994;Kirchhof and Mercer, 1997). Also, in the present study branching patterns of labelled and unlabelled neurons within a given culture dish were indistinguishable.…”

“…Kloppenburg and Hörner, 1998;Kloppenburg et al, 1999a;Dugladze et al, 2001) and was confirmed here. Projection neurons grew extensive neurites in culture throughout the period of observation (3-6 days), as has B. Grünewald been described for unidentified antennal lobe neuron cultures (Gascuel and Masson, 1991a;Devaud et al, 1994;Kirchhof and Mercer, 1997), which suggests that they were healthy and that the dye did not impair the viability of the cells. The applied mass staining technique is therefore a very reliable method for the identification of honeybee antennal lobe projection neurons in vitro and may be used in the future for analyses of other identified neurons of the bee brain, such as mushroom body feedback neurons.…”