Convergence of a putative polarization vision pathway with PDH-immunoreactive neurons in the medulla of the honeybee (Apis mellifera)
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1
Philipps-University Marburg, Dept. of Biology/Animal Physiology, Germany
Honeybees are well known for their ability to use sky compass cues, like the position of the sun or the polarization pattern of the sky for spatial orientation. The honeybee's sky compass is time compensated, i.e. the apparent movement of the sun across the sky (solar ephemeris function) is anticipated and taken into account, when setting a heading. This requires the neuronal representation and processing of three kinds of information: (1) the azimuth of the sun relative to the animal's body axis, (2) the time of day. (3) the solar ephemeris.
While sky compass orientation in honeybees has been extensively studied at the behavioral level, virtually nothing is known about the underlying neuronal mechanisms. As a first step to find possible neuronal substrates for time compensation in the sky compass system, we aimed to morphologically identify convergence sites of neurons associated with the circadian clock and neurons carrying polarization information. Recent anatomical data from bumblebees suggest the existence of a polarization vision pathway from the dorsal rim area of the eye, via the dorsal medulla and the lower unit of the anterior optic tubercle to the lateral accessory lobe (Pfeiffer and Kinoshita 2012, J Comp Neurol 520: 212-229). Some neurons that are part of this pathway have been also reported from honeybees (Mota et al. 2012, J Neurosci 31: 11443-11456). Through dextran injections into the polarization-sensitive dorsal rim area of the honeybee eye, and the lower unit of the anterior optic tubercle, we show here that this pathway exists almost identically in the honeybee brain.
To visualize neurons associated with the circadian clock, we used an antibody against the peptide pigment-dispersing-hormone (PDH, provided by H. Dircksen). Pigment-dispersing factor, the insect homologue to PDH is an output signal of the circadian clock and involved in regulating locomotor activity.
Convergence of putative polarization-sensitive neurons and PDH-immunoreactive fibers was found in a narrow layer of the medulla. Line-tangential neurons running in this layer have a branching field in the dorsalmost part of the posterior medulla, the area, where long visual fibres from the polarization-sensitive dorsal rim area branch, and project to the lower unit of the anterior optic tubercle. PDH-immunoreactive fibres in the medulla were exclusively found in a narrow layer that overlaps with the layer in which line-tangential neurons run. PDH-immunoreactive fibres in that area had a beaded appearance suggesting output synapses. Double labeling of line-tangential neurons of the medulla and PDH-immunoreactive neurons with different fluorescent dyes showed no colabelling, but confirmed close proximity. This suggests that the two cell types are not identical but have ramifications close to each other therefore opening the possibility, that PDH-immunoreactive neurons modulate neurons of the polarization vision pathway at an early stage.
Keywords:
circadian rhythms,
PDH-immunoreactivity,
polarization vision,
sky compass orientation,
time-compensation
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Orientation and Navigation
Citation:
Zeller
M,
Homberg
U and
Pfeiffer
K
(2012). Convergence of a putative polarization vision pathway with PDH-immunoreactive neurons in the medulla of the honeybee (Apis mellifera).
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00329
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Keram Pfeiffer, Philipps-University Marburg, Dept. of Biology/Animal Physiology, Marburg, Germany, keram.pfeiffer@uni-wuerzburg.de