Summary
Information processing in the mushroom bodies which are an important part of most invertebrate central nervous systems was analysed by extracellular electrophysiological techniques. The mushroom bodies consist of layers of parallel intrinsic neurons which make synaptic contact with extrinsic input and output neurons. The intrinsic neurons (approximately 170,000/mushroom body) have very small axon diameters (0.1–1 μm) which makes it difficult to record their activity intracellularly. In order to analyse the functional properties of this neuropil field potentials were measured extracellularly.
Series of averaged evoked potentials (AEPs) were recorded along electrode tracks at consecutive depth intervals in different parts of the mushroom bodies of the bee. These potentials were elicited by olfactory, mechanical and visual stimuli.
In order to locate the synaptic areas generating these potentials, current source-densities (CSD) were calculated using the consecutively measured evoked potentials. The conductivities of the extracellular space along the electrode tracks in the pedunculus and calyx and in part of the alpha-lobe of the mushroom bodies were found to be constant.
The CSD analysis reveals a complex pattern of source-sink distributions in the mushroom bodies. There is a high degree of correlation between current sinks and sources detected by CSD analysis and the morphological distribution of neurons.
The CSD analysis shows that the inputs and outputs of the mushroom bodies involve multimodal synaptic interactions, whereas information processing in the intrinsic Kenyon-cells is limited to sensory inputs from the antenna.
Comparison of the electrophysiological with the histological results shows that the intrinsic cells of the mushroom bodies are physiologically not a homogeneous group as is often proposed. Among the intrinsic neurons clearly defined areas of current sources and sinks can be identified and attributed to Kenyon-cells in different layers.
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Abbreviations
- AEP :
-
averaged evoked potentials
- AGT :
-
antennoglomerular tract
- CSD :
-
current source-density
- PCT :
-
antennoglomerular tract
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Kaulen, P., Erber, J. & Mobbs, P. Current source-density analysis in the mushroom bodies of the honeybee (Apis mellifera carnica). J. Comp. Physiol. 154, 569–582 (1984). https://doi.org/10.1007/BF00610170
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DOI: https://doi.org/10.1007/BF00610170