Analysis of GABAergic and Non-GABAergic Neuron Activity in the Optic Lobes of the Forager and Re-Orienting Worker Honeybee (Apis mellifera L.)

Taketoshi Kiya,Takeo Kubo

doi:10.1371/journal.pone.0008833

Abstract

BackgroundEuropean honeybee (Apis mellifera L.) foragers have a highly developed visual system that is used for navigation. To clarify the neural basis underlying the highly sophisticated visual ability of foragers, we investigated the neural activity pattern of the optic lobes (OLs) in pollen-foragers and re-orienting bees, using the immediate early gene kakusei as a neural activity marker.Methodology/Principal FindingsWe performed double-in situ hybridization of kakusei and Amgad, the honeybee homolog of the GABA synthesizing enzyme GAD, to assess inhibitory neural activity. kakusei-related activity in GABAergic and non-GABAergic neurons was strongly upregulated in the OLs of the foragers and re-orienting bees, suggesting that both types of neurons are involved in visual information processing. GABAergic neuron activity was significantly higher than non-GABAergic neuron activity in a part of the OLs of only the forager, suggesting that unique information processing occurs in the OLs of foragers. In contrast, GABAergic neuron activity in the antennal lobe was significantly lower than that of GABAergic neurons in the OLs in the forager and re-orienting bees, suggesting that kakusei-related visual activity is dominant in the brains of these bees.Conclusions/SignificanceThe present study provides the first evidence that GABAergic neurons are highly active in the OL neurons of free-moving honeybees and essential clue to reveal neural basis of the sophisticated visual ability that is equipped in the small and simple brain.

Highlights

European honeybee (Apis mellifera L.) workers forage for food sources using their highly developed visual sense [1,2,3]
Based on the Amgad expression pattern in the worker brain, in which the majority of GABAergic neurons were detected in the optic lobes (OLs) and antennal lobes (ALs) (Fig. 1A and B), we focused our analysis on the following four regions: cells located between the lamina and medulla (LA-ME), medulla and lobula (ME-LO), lateral side of the AL (AL), and in the ventral root of the OL (A3v) (Fig. 1A and B)
The percentage of kakuseipositive Amgad (+) or (2) cells was not significantly different between LA-ME and ME-LO (Fig. 4G and H). These results indicate that GABAergic and non-GABAergic neurons in the OLs are activated in a similar manner by the re-orienting flight, and suggest that increased kakusei-related activity of GABAergic neurons in ME-LO is specific to the foragers

Summary

Introduction

European honeybee (Apis mellifera L.) workers forage for food sources using their highly developed visual sense [1,2,3]. The honeybee brain comprises several distinct regions, including the mushroom bodies (MBs), a higher-order integration center; the optic lobes (OLs), a visual center; and the antennal lobes (ALs), the olfactory center [5,6]. European honeybee (Apis mellifera L.) foragers have a highly developed visual system that is used for navigation. To clarify the neural basis underlying the highly sophisticated visual ability of foragers, we investigated the neural activity pattern of the optic lobes (OLs) in pollen-foragers and re-orienting bees, using the immediate early gene kakusei as a neural activity marker

Methods

Results

Conclusion