Tsunao Itoh

Topographic organization of sensory afferents of Johnston's organ in the honeybee brain.

Johnstons 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. J. Comp. Neurol. 502:1030–1046, 2007.

External morphology of sensilla in the sacculus of an antennal flagellum of the fruit fly Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Abstract Sensilla in the sacculus of an antennal 3rd segment, a funiculus, of the fruit fly, Drosophila melanogaster (Diptera : Drosophilidae) have been examined by scanning electron microscopy. The sacculus was divided into 3 cavities in its interior. A morphologically distinct group of sensilla was present in each cavity. Grooved sensillum (GS), found in the largest cavity, was further subclassified on the basis of the side wall sculpture into 3 subgroups: GS Ia, GS Ib and GS II. GS Ia was 4 μm long and had 10–12 grooves (0.25 μm wide) and GS Ib was 3.8 μm long and had 6–9 grooves (0.25-0.4 μm wide). GS 1a and GS Ib were inferred to be olfactory and thermoreceptive, and olfactory, respectively. GS II was 3.2 μm long, and had 4–5 grooves. Basiconic sensillum (BS), found in the smallest cavity, was 4.5 μm long and had an irregularly sculptured side wall, suggesting the presence of numerous irregular-shaped olfactory pores. Blunt-tipped sensillum (BTS), found in the middle-sized cavity, was 1.9 μm long and had a smooth-surfaced side wall and a button-like structure on its apex. These features suggested that BTS was hygro- and thermoreceptive.

Response characteristics of vibration-sensitive interneurons related to Johnston's organ in the honeybee, Apis mellifera.

Honeybees detect airborne vibration by means of Johnstons 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. J. Comp. Neurol. 515:145–160, 2009.

Identification of Antennal Hygroreceptive Sensillum and Other Sensilla of the Firefly, Luciola cruciata

Abstract We have identified and characterized the hygroreceptive sensilla on the antenna of the adult male firefly, Luciola cruciata, by coupling extracellular electrophysiological recordings from single sensilla with observation of morphology of the sensilla using a field emission scanning electron microscope (FE-SEM). Seven morphologically different types of sensilla were present on the antenna: pored chaetic, poreless chaetic, basiconic, trichoid, capitular and campaniform sensilla and a new type of sensillum. To determine which is the hygroreceptive sensillum, responses to humidity changes were electrophysiologically recorded from each type of these sensilla. Impulses from moist and dry receptor cells could be obtained from only the capitular sensillum along with impulses from a cold receptor cell. The results clearly showed that the capitular sensillum is hygro- and thermoreceptive. The capitular sensillum had a cuticular apparatus that extends about 8 μm above the antennal surface and is externally composed of three parts: an inner stem, an outer wall and a basal dome. This cuticular apparatus was not perforated in any region. About 30 capitular sensilla per antenna were distributed only on the lateral surface of flagellar segments. A new type of sensillum, ‘sensillum gemmiformium’ was found. The cuticular apparatus of the gemmiform sensillum consists of a main spheroidal body and one to five protrusions. We discuss the common external features of the hygro- and thermoreceptive sensilla, the role of hygroreception in the behavior of fireflies and possible functions of the other types of sensilla.

Response to humidity change of deutocerebral interneurons of the honeybee,Apis mellifera L.

food quality, or predation pressure, as well as physiological differences, e.g., in age and reproductive status, may also contribute to the quantitative variation in chemical defence among populations o f Oreina gloriosa. We thank Prof. H .F . Rowell and Dr. N. Rank for their critical comments on the manuscript. We also thank Prof. J .M. Pasteels for his stimulating advice. This study was supported by the Swiss National Science Foundation.

A Circadian Neuropeptide PDF in the Honeybee, Apis mellifera: cDNA Cloning and Expression of mRNA

Pigment-dispersing factor (PDF) is a pacemaker hormone regulating the locomotor rhythm in insects. In the present study, we cloned the cDNAs encoding the Apis PDF precursor protein, and found that there are at least seven different pdf mRNAs yielded by an alternative splicing site and five alternative polyadenylation sites in the 5′UTR and 3′UTR regions. The amino acid sequence of Apis PDF peptide has a characteristic novel amino acid residue, aspargine (Asn), at position 17. Quantitative real-time PCR of total and 5′UTR insertion-type pdf mRNAs revealed, for the first time, that the expression levels change in a circadian manner with a distinct trough at the beginning of night in LD conditions, and at the subjective night under DD conditions. In contrast, the expression level of 5′UTR deletion-type pdf mRNAs was about half of that of the insertion type, and the expression profile failed to show a circadian rhythm. As the expression profile of the total pdf mRNA exhibited a circadian rhythm, transcription regulated at the promoter region was supposed to be controlled by some of the clock components. Whole mount in situ hybridization revealed that 14 lateral neurons at the frontal margin of the optic lobe express these mRNA isoforms. PDF expressing cells examined with a newly produced antibody raised against Apis PDF were also found to have a dense supply of axon terminals in the optic lobes and the central brain.

The Auditory System of the Honey Bee

The auditory organ of honey bee is the “Johnston’s organ (JO)” on the antennae which detects airborne vibration during waggle dance communication and also detects air current during flight. The sensory afferents of the JO send their axons to two distinct areas of the bee brain, the Antennal mechanosensory centers (AMMC) and the Superior posterior slope (SPS). Within these termination fields sensory axons in the ventro-medial SPS are characterized by both thick processes with large varicosities and somatotopy, while those in the AMMC by both thin processes with small varicosities and no somatotopy, suggesting that vibratory signals detected by the JO are processed in dual parallel pathways in these primary sensory centers. In order to clarify the characteristics of auditory processing, the response properties of the interneurons to the vibration stimuli, arborizing in these primary sensory centers have been investigated. AMMC-Int-1 and AMMC-Int-2 densely arborize in AMMC and respond stimulus-phase-dependently to the vibratory stimulation on the ipsilateral antenna with high sensitivity in the range of 250–300 Hz, which is the main airborne vibration frequencies generated by the waggle dance. While SPS-D-1 has dense arborizations in the SPS and sends axons into the ventral nerve cord, with blebby terminals in the contralateral dSEG and SPS, and respond to the vibratory stimulation on the ipsilateral antenna with long-lasting excitation during olfactory stimulation on the contralateral antenna. The possible roles of the parallel systems in the primary auditory centers are discussed.