Abstract
The afferents of the Johnston's organ (JO) in the honeybee brain send their axons to three distinct areas, the dorsal lobe, the dorsal subesophageal ganglion (DL-dSEG), and the posterior protocerebral lobe (PPL), suggesting that vibratory signals detected by the JO are processed differentially in these primary sensory centers. The morphological and physiological characteristics of interneurons arborizing in these areas were studied by intracellular recording and staining. DL-Int-1 and DL-Int-2 have dense arborizations in the DL-dSEG and respond to vibratory stimulation applied to the JO in either tonic excitatory, on-off-phasic excitatory, or tonic inhibitory patterns. PPL-D-1 has dense arborizations in the PPL, sends axons into the ventral nerve cord (VNC), and responds to vibratory stimulation and olfactory stimulation simultaneously applied to the antennae in long-lasting excitatory pattern. These results show that there are at least two parallel pathways for vibration processing through the DL-dSEG and the PPL. In this study, Honeybee Standard Brain was used as the common reference, and the morphology of two types of interneurons (DL-Int-1 and DL-Int-2) and JO afferents was merged into the standard brain based on the boundary of several neuropiles, greatly supporting the understanding of the spatial relationship between these identified neurons and JO afferents. The visualization of the region where the JO afferents are closely appositioned to these DL interneurons demonstrated the difference in putative synaptic regions between the JO afferents and these DL interneurons (DL-Int-1 and DL-Int-2) in the DL. The neural circuits related to the vibration-processing interneurons are discussed.
Highlights
Honeybees communicate with each other for the benefit of the whole society
We successfully identified three types of interneurons that have dense arborizations in both the dorsal lobe (DL) and the dorsal subesophageal ganglion or the posterior protocerebral lobe (PPL) and that respond to vibratory stimulation applied to the Johnston’s organ (JO) in specific patterns
CENTRAL PROJECTIONS OF JO AFFERENTS Axons originating from the JO project into the brain SEG through the sensory tracts T6I and T6II, and their projection areas are spatially segregated in the PPL and the DL and the dorsal subesophageal ganglion (dSEG) (DL-dSEG), respectively (Ai et al, 2007; Figures 2A,B)
Summary
Honeybees communicate with each other for the benefit of the whole society. One of the most intriguing forms of communication is the waggle dance: a dancing bee sends a message to other bees indicating the direction and distance from their hive to a site of nectar-bearing flowers. Karl von Frisch showed that bees are recruited by the waggle dance of their nestmates and that information encoded by the waggle dance guides them to a remote food source (Frisch, 1967). This finding was recently proved directly by following the flight paths of recruited bees using harmonic radar recording (Riley et al, 2005). The antenna and sensory neurons in the JO are specialized for detecting vibrations with frequencies in the range of 250–300 Hz, which is the normal range of the main vibration frequencies generated by the waggle dance (Tsujiuchi et al, 2007). The JO has been suggested to play a role in detecting air current during flight (Srinivasan and Zhang, 2004)
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