Yoshiya Tominaga

Antennal hygroreceptors of the honey bee, Apis mellifera L.

SummaryAntennal hygroreceptors of the honey bee, Apis mellifera L., have been investigated electrophysiologically and the sensillum containing these receptors with SEM. Moist and dry hygroreceptors have been identified along with a thermal receptor in a specialized coeloconic sensillum. This sensillum comprises a cuticular, shallow depression (diameter; 4 μ) having a central opening (1.4–1.5 μm) and a mushroom-shaped protrusion (1.4–1.5 μm) from the opening. The head of the protrusion is irregular in shape and is not perforated. This sensillum has been thus far referred to as a “sensillum campaniformium” (Dietz and Humphreys 1971), henceforth, it is referred to as a coelocapitular sensillum.The responses of both moist and dry hygroreceptors are of a phasic-tonic manner. Both receptors are antagonistic with respect to their responses to humidity; one responds with an increase in impulse frequency to rising humidity, the other to falling humidity. The humidity-response relationship is independent of stimulus flux.

Identificaton of UV, green and red receptors, and their projection to lamina in the cabbage butterfly, Pieris rapae

SummaryThe photoreceptors in the compound eye of a cabbage butterfly, Pieris rapae, were examined by conventional and intracellular-labeling electron microscopy by the use of the cobalt(III)-lysine complex as an ionized marker. Five types of spectral sensitivity were recorded intracellularly in electrophysiological experiments. They peaked at about 340, 380, 480, 560 and 620 nm, respectively. One of the distal retinula cells (R2) was a UV receptor, whereas the R4 distal retinula cell was a green receptor. The basal retinula cell, R9, was found to be a red receptor; it was localized near the basement membrane, having a bilobed cell body with an individual nucleus in each lobe. A small number of rhabdomere microvilli were present in a narrow cytoplasmic bridge connecting the two lobes. The axons of six retinula cells (R3–R8) in each ommatidium terminated at the cartridge in the lamina (short visual fiber), whereas those of the other three retinula cells, R1, R2 and R9, extended to the medulla (long visual fiber). The information from the UV and red receptors is therefore probably delivered directly to the medulla neurons, independent of that from the other spectral receptor types.

External structure of the sensillum capitulum, a hygro- and thermoreceptive sensillum of the cockroach, Periplaneta americana

SummaryThe antennal hygro- and thermoreceptive sensillum (sensillum capitulum) of the cockraoch, Periplaneta americana, has been identified electrophysiologically and examined by scanning electron microscopy. It appears basiconic and has a characteristic cuticular apparatus; a mushroom-shaped inner stem and a non-perforated outer wall. The head of the inner stem, which is a cap of about 0.5 μm diameter, protrudes from the distal margin of the outer wall. The inner stem is not perforated, though in some cases a tiny hollow is observed in the apex of the cap. This kind of cuticular apparatus is not found in other sensilla and may be modality-specific to hygro- and/or thermoreception. The sensillum capitulum occurs singly on the distal part of each alternating segment of the flagellum and on each segment of some distal meristal segments.

A circadian neuropeptide, pigment-dispersing factor-PDF, in the last-summer cicada Meimuna opalifera: cDNA cloning and immunocytochemistry

Abstract Pigment-dispersing factor (PDF), an 18-amino acid neuropeptide, is a principal circadian neuromodulator functioning downstream of the insect brains circadian clock, modulating daily rhythms of locomotor activity. Recently, we found that PDF precursors of the cricket Gryllus bimaculatus comprise a nuclear localization signal (NLS). Moreover, the nuclear localization of PDF immunoreactivity and the trans-location of GFP-fused PDF precursor into the nucleus have both been demonstrated. These suggest a fundamental role for PDF peptide in the circadian clock system within the nucleus, in addition to its role in downstream neural events. In the present study, we carried out the cDNA cloning of PDF from adult brains of the last-summer cicada Meimuna opalifera, and found that an isolated clone (545 bp) encodes an ordinary PDF precursor protein. PDF peptide itself shows a high sequence identity (78–94%) and similarity (89–100%) to insect PDFs and also to the crustacean β-PDH peptides. The computer-assisted sequence analysis of PDF precursor revealed a possible translocation into the nucleus, despite the lack of a definite NLS-like sequence. Using immunocytochemistry, the optic lobes of M. opalifera revealed PDF-immunore-active neurons in both the medulla and lamina neuropiles. All these PDF cells exhibited prominent immunolabeling of both their perikarya and axons, but not their nuclei. Our results provide the first structural and immunocytochemical identification of PDF neurons in Hemiptera.

Topographically distinct visual and olfactory inputs to the mushroom body in the Swallowtail butterfly, Papilio xuthus

Papilio butterflies depend highly on visual information in their flower‐foraging behavior. The retina of Papilio xuthus has been studied well, whereas the visual system in the brain is poorly understood. By investigating outputs from the optic lobe to the central brain, we found that the mushroom body of P. xuthus receives prominent direct inputs from the optic lobe in addition to olfactory inputs. The mushroom body consists of three components: the calyx, the pedunculus, and the lobes. The calyx is further subdivided into two cup‐shaped primary calyces and an accessory calyx. Each primary calyx consists of three concentric subareas, the inner zone, the outer zone, and the rim of the outer zone. Dextran injections into the optic lobe, the calyx, or the antennal lobe revealed three visual inputs and one olfactory input into the calyx. The visual inputs originate from the medulla, the lobula, and a newly identified neuropil, the ventral lobe of the lobula. All visual inputs first innervate the accessory calyx, and the two lobula inputs further spread their processes through the inner zone and the rim of the outer zone of the primary calyces. Visual inputs from the medulla and the ventral lobe of the lobula collect light information from ventral eye regions, suggesting a role in visual target detection rather than sky compass orientation. In contrast to visual inputs, olfactory inputs innervate only the calycal outer zone. The multisensory inputs to the mushroom bodies in P. xuthus are probably related to their flower‐foraging behavior. J. Comp. Neurol. 523:162–182, 2015.

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.

Molecular Cogs of the Insect Circadian Clock

Abstract During the last five years, enormous progress has been made in understanding the molecular basis of circadian systems, mainly by molecular genetic studies using the mouse and fly. Extensive evidence has revealed that the core clock machinery involves “clock genes” and “clock proteins” functioning as molecular cogs. These participate in transcriptional/translational feedback loops and many homologous clock-components in the fruit fly Drosophila are also expressed in mammalian clock tissues with circadian rhythms. Thus, the mechanisms of the central clock seem to be conserved across animal kingdom. However, some recent studies imply that the present widely accepted molecular models of circadian clocks may not always be supported by the experimental evidence.

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.

The compound eye of Parnara guttata (Insecta, Lepidoptera, Hesperiidae): Fine structure of the ommatidium

SummaryThe fine structure of an ommatidium of a skipper butterfly, Parnara guttata, has been studied using the electron microscope. Each ommatidium has nine retinula cells, which were classified into three groups: two distal, six medial and one basal retinula cells. The rhabdomeres of the distal retinula cells are localized in the distal part of the rhabdom, while those of the six medial retinula cells appear throughout most of the rhabdom. The rhabdomere of the basal retinula cell occupies only the basal part of the rhabdom. The rhabdomeres of four medial cells are constructed of parallel microvilli, while fan-like microvilli form the rhabdomeres of other two medial retinula cells. The distal and basal retinula cells have rhabdomeres consisting of both parallel and fan-like microvilli. This is the first time the construction of the rhabdomeres of the distal and basal retinula cells has been described in such fine detail for a skipper butterfly. Nine retinula cell axons of each ommatidium extend to the first neuropile of the optic lobe, the lamina ganglionaris. No difference was found in the number of retinula cells of an ommatidium or the shape of the rhabdom between the dorsal and ventral regions of the compound eye.