Does light stimulation induce brain synaptic plasticity and potentially interplay with the hormonal system in the honey bee?
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1
University of Wuerzburg, Behavioral Physiology and Sociobiology, Germany
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2
Arizona State University, School of Life Sciences, United States
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3
Norwegian University of Life Sciences, Department of Chemistry, Biotechnology and Food Science, Norway
Honey bees live in colonies with complex social organization and display an amazing behavioral repertoire including complex learning and orientation skills. Their social organization is based on an age-related division of labor that includes a transition from inside duties (nurse bees) to foraging activities outside the hive (foragers). This behavioral transition is accompanied by remodeling of the brain. Especially the mushroom body (MB) - a prominent neuropil in the honey bee brain involved in learning and memory processes - shows marked changes in volume and in synaptic wiring during this process (Groh et al., 2012, in press). Currently it is unclear what exactly drives these changes in synaptic organization.
One major difference between nurses and foragers is their exposure to a different sensory environment. Inside the hive bees mostly rely on tactile and olfactory stimuli whereas outside visual stimuli become important for navigational tasks like for using the sun compass, recognizing landmarks or detect flowers. To test possible influences of visual input on division of labor, bees were subjected to a light treatment and subsequent changes were analyzed in the MB. Bees received 45 min of light pulses 5 times a day for 4 days to simulate light exposure during foraging trips. Synaptic complexes were visualized by immunostainings and quantified. The results show a decrease in the number of synaptic complexes after exposure to light in the visual-innervated regions of the MB, but not in the olfactory-innervated regions. Analyses of tubulin-positive dendritic profiles indicate that dendritic expansion and pruning of projection neurons boutons are involved in this process of synaptic reorganization.
Another factor known to vary with the bees' behavioral transition is juvenile hormone (JH). JH increase is associated with the shift from nursing to foraging and is regulated via the yolk precursor protein vitellogenin (vg). High vg levels result in low JH titers and vice versa. Application of JH to young bees was shown to induce premature foraging. We therefore started to ask whether there is a connection between the increased JH titer and synaptic rewiring in the MB - both occur with the onset of foraging. To induce n increased JH titer vg was downregulated in 1 day old bees using RNA interference. The bees were re-collected after 7 days and synaptic complexes in the MB were quantified. The results show that despite successful vg downregulation there was no significant change in the numbers of synaptic complexes. We conclude that synaptic changes are mainly driven by sensory stimuli (exposure to light), but appear rather unaffected by hormonal manipulations. We further hypothesize that hormonal changes may affect basal activity level of the bees and the likelihood for the start of first orientation flights leading to exposure to new sensory stimuli. This in turn triggers synaptic rewiring, may initiate positive feedback on the behavior (Stieb et al., 2012) and, potentially, may result in a feedback on the hormone levels. This process would allow flexible adaptation of the neuronal machinery in individual bees to changing demands of the colony.
Acknowledgements
Funded by GSLS, University of Würzburg
References
Stieb SM, Hellwig A, Wehner R, Rössler W (2012). Visual experience affects both behavioral and neuronal aspects in the individual life history of the desert ant Cataglyphis fortis. Dev Neurobiol. 72, 729–742.
Groh C, Lu Z, Meinertzhagen IA, Rössler W (2012). Age-related plasticty in the synaptic ultrastructure of neurons in the ushroom body calyx of the adult honeybee Apis mellifera. J Comp Neurol, in press.
Keywords:
behavioral plasticity,
division of labor,
Honey bee,
juvenile hormone,
Neuroanatomy,
synaptic plasticity
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for participant symposium and student poster award)
Topic:
Learning, Memory and Behavioral Plasticity
Citation:
Scholl
C,
Wang
Y,
Amdam
GV and
Roessler
W
(2012). Does light stimulation induce brain synaptic plasticity and potentially interplay with the hormonal system in the honey bee?.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00233
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Ms. Christina Scholl, University of Wuerzburg, Behavioral Physiology and Sociobiology, Wuerzburg, 97074, Germany, christina.scholl@uni-wuerzburg.de