Comprehensive morphological identification and GABA immunocytochemistry of antennal lobe local interneurons in Bombyx mori

Abstract

The insect antennal lobe (AL) is the structural and functional analog of the olfactory bulb of mammals, in which odor information is spatially and/or temporally represented by functional glomerular units. Local interneurons (LNs) play critical roles through intra- and interglomerular communication to shape the output from the AL to higher brain centers; however, the function and even the components of LNs are unclear. We have used morphological and immunocytochemical approaches to examine LNs in the silkworm moth, Bombyx mori. First, we comprehensively analyzed the morphological variation of LNs. One hundred fifty-three AL LNs were intracellularly stained, analyzed in three dimensions with a confocal microscope, and subdivided into five morphological types based on differences in the arborization region in the AL and dendritic profiles within the glomeruli. Two global multiglomerular types arborized in the macroglomerular complex (MGC) and in most ordinary glomeruli, and the other three oligoglomerular types innervated some ordinary glomeruli with or without the MGC. Second, we performed double-labeling of Lucifer Yellow staining of a single LN combined with gamma-aminobutyric acid (GABA) immunocytochemistry. The two global multiglomerular types and two of the oligoglomerular types were GABA-immunoreactive, but the third oligoglomerular type, which innervates the MGC and some ordinary glomeruli, included some GABA-immunonegative neurons, suggesting the existence of a non-GABAergic subtype. These results suggest that the complex neural circuits of the AL are composed of several morphologically different types of LNs, most of which are inhibitory.

γ-Aminobutyric acid immunostaining in the antennal lobe of the moth Heliothis virescens and its colocalization with neuropeptides

“…These neurons are suggested to act as a general enhancer to guarantee the reliable transmission of olfactory information to the Kenyon cells of the mushroom bodies. Furthermore, a subpopulation of GABA-immunonegative local neurons has been identified in the antennal lobe of the silk moth, Bombyx mori (Seki and Kanzaki 2008). Interestingly, the LomTK-IIimmunoreactive somata reported here are slightly larger than the other local neurons (Berg et al 2007), a finding that also applies to the somata of the cholinergic local neurons in the fly (Shang et al 2007).…”

Calcium Current Diversity in Physiologically Different Local Interneuron Types of the Antennal Lobe

“…Historically, LNs have been regarded mostly as GABAergic, inhibitory neurons, and GABAergic LNs have been reported in the AL of various insect species including A. mellifera (Schäfer and Bicker, 1986), Bombyx mori (Iwano and Kanzaki, 2005;Seki and Kanzaki, 2008), D. melanogaster (Wilson and Laurent, 2005), M. sexta (Hoskins et al, 1986), P. americana (Distler, 1989), and S. americana (Leitch and Laurent, 1996). Immunohistochemical, mass-spectrometric and physiological studies, however, showed that the LNs are biochemically a more heterogeneous population of neurons than previously thought.…”

Novel antennal lobe substructures revealed in the small hive beetle Aethina tumida

“…6, reviewed in Schachtner et al, 2005, Seki andKanzaki, 2008;Husch et al, 2009;Carlsson et al, 2010;Chou et al, 2010;Seki et al, 2010;Neupert et al, 2012;Binzer et al, 2014;Siju et al, 2014). Comparing the different pattern of glomerulus supply via central neurons (CNs, LNs, PNs), innervation can beoccur a) only at the surface, b) scattered throughout the whole glomerulus c) or only through parts of the glomerulus, d) up to massive dense innervation of the whole or e) a distinct area of a glomerulus, or f) as described in this study, through islet like projections, which are evenly distributed throughout the glomerulus (Fig.…”