Johnston's organ (JO) in insects is a multicellular mechanosensory organ stimulated by movement of the distal part of the antenna. In honeybees JO is thought to be a primary sensor detecting air-particle movements caused by the waggling dance of conspecifics. In this study projection patterns of JO afferents within the brain were investigated. About 720 somata, distributed around the periphery of the second segment of the antenna (pedicel), were divided into three subgroups based on their soma location: an anterior group, a ventral group, and a dorsal group. These groups sent axons to different branches (N2 to N4) diverged from the antennal nerve. Dye injection into individual nerve branches revealed that all three groups of afferents, having fine collaterals in the dorsal lobe, sent axons broadly through tracts T6I, T6II, and T6III to terminate ipsilaterally in the medial posterior protocerebral lobe, the dorsal region of the subesophageal ganglion, and the central posterior protocerebral lobe, respectively. Within these termination fields only axon terminals running in T6I were characterized by thick processes with large varicosities. Differential staining using fluorescent dyes revealed that the axon terminals of the three groups were spatially segregated, especially in T6I, showing some degree of somatotopy. This spatial segregation was not observed in axon terminals running in other tracts. Our results show that projection patterns of JO afferents in the honeybee brain fundamentally resemble those in the dipteran brain. The possible roles of extensive termination fields of JO afferents in parallel processings of mechanosensory signals are discussed.

Honeybees detect airborne vibration by means of Johnston's organ (JO), located in the pedicel of each antenna. In this study we identified two types of vibration-sensitive interneurons with arborizations in the primary sensory area of the JO, namely, the dorsal lobe-interneuron 1 (DL-Int-1) and dorsal lobe-interneuron 2 (DL-Int-2) using intracellular recordings combined with intracellular staining. For visualizing overlapping areas between the JO sensory terminals and the branches of these identified interneurons, the three-dimensional images of the individual neurons were registered into the standard atlas of the honeybee brain (Brandt et al. [2005] J Comp Neurol 492:1-19). Both DL-Int-1 and DL-Int-2 overlapped with the central terminal area of receptor neurons of the JO in the DL. For DL-Int-1 an on-off phasic excitation was elicited by vibrational stimuli applied to the JO when the spontaneous spike frequency was low, whereas tonic inhibition was induced when it was high. Moreover, current injection into a DL-Int-1 led to changes of the response pattern from on-off phasic excitation to tonic inhibition, in response to the vibratory stimulation. Although the vibration usually induced on-off phasic excitation in DL-Int-1, vibration applied immediately after odor stimulation induced tonic inhibition in it. DL-Int-2 responded to vibration stimuli applied to the JO by a tonic burst and were most sensitive to 265 Hz vibration, which is coincident with the strongest frequency of airborne vibrations arising during the waggle dance. These results suggest that DL-Int-1 and DL-Int-2 are related to coding of the duration of the vibration as sensed by the JO.

Female honeybees use the "waggle dance" to communicate the location of nectar sources to their hive mates. Distance information is encoded in the duration of the waggle phase (von Frisch, 1967). During the waggle phase, the dancer produces trains of vibration pulses, which are detected by the follower bees via Johnston's organ located on the antennae. To uncover the neural mechanisms underlying the encoding of distance information in the waggle dance follower, we investigated morphology, physiology, and immunohistochemistry of interneurons arborizing in the primary auditory center of the honeybee (). We identified major interneuron types, named DL-Int-1, DL-Int-2, and bilateral DL-dSEG-LP, that responded with different spiking patterns to vibration pulses applied to the antennae. Experimental and computational analyses suggest that inhibitory connection plays a role in encoding and processing the duration of vibration pulse trains in the primary auditory center of the honeybee. The waggle dance represents a form of symbolic communication used by honeybees to convey the location of food sources via species-specific sound. The brain mechanisms used to decipher this symbolic information are unknown. We examined interneurons in the honeybee primary auditory center and identified different neuron types with specific properties. The results of our computational analyses suggest that inhibitory connection plays a role in encoding waggle dance signals. Our results are critical for understanding how the honeybee deciphers information from the sound produced by the waggle dance and provide new insights regarding how common neural mechanisms are used by different species to achieve communication.

No abstract

In animals, odor qualities are represented as both spatial activity patterns of glomeruli and temporal patterns of synchronized oscillatory signals in the primary olfactory centers. By optical imaging of a voltage-sensitive dye (VSD) and intracellular recording from secondary olfactory interneurons, we examined possible neural correlates of the spatial and temporal odor representations in the primary olfactory center, the antennal lobe (AL), of the cockroach Periplaneta americana. Voltage-sensitive dye imaging revealed that all used odorants induced odor-specific temporal patterns of depolarizing potentials in specific combinations of anterior glomeruli of the AL. The depolarizing potentials evoked by different odorants were temporally synchronized across glomeruli and were termed “synchronized potentials.” These observations suggest that odor qualities are represented by spatio-temporal activity patterns of the synchronized potentials across glomeruli. We also performed intracellular recordings and stainings from secondary olfactory interneurons, namely projection neurons and local interneurons. We analyzed the temporal structures of enanthic acid-induced action potentials of secondary olfactory interneurons using simultaneous paired intracellular recording from two given neurons. Our results indicated that the multiple local interneurons synchronously fired in response to the olfactory stimulus. In addition, all stained enanthic acid-responsive projection neurons exhibited dendritic arborizations within the glomeruli where the synchronized potentials were evoked. Since multiple local interneurons are known to synapse to a projection neuron in each glomerulus in the cockroach AL, converging inputs from local interneurons to the projection neurons appear to contribute the odorant specific spatio-temporal activity patterns of the synchronized potentials.

is a modular organization to the MGC such that information from the two main branches of the antenna is segregated to different sub-regions of the MGC glomeruli.

Insects use airborne vibrations caused by their own movements to control their behaviors and produce airborne vibrations to communicate with conspecific mates. In this review, I use two examples to introduce how insects use airborne vibrations to accurately control behavior or for communication. The first example is vibration-sensitive sensilla along the wing margin that stabilize wingbeat frequency. There are two specialized sensors along the wing margin for detecting the airborne vibration caused by wingbeats. The response properties of these sensors suggest that each sensor plays a different role in the control of wingbeats. The second example is Johnston's organ that contributes to regulating flying speed and perceiving vector information about food sources to hive-mates. There are parallel vibration processing pathways in the central nervous system related with these behaviors, flight and communication. Both examples indicate that the frequency of airborne vibration are filtered on the sensory level and that on the central nervous system level, the extracted vibration signals are integrated with other sensory signals for executing quick adaptive motor response.

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.