GABA immunostaining in the central olfactory pathway of the moth brain - visualization of single neurons and neural populations.

Abstract

 -aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system of most living organisms. A large number of neurons that contain GABA has been found in the primary olfactory centers of both humans and insects. The first integration center in the insect olfactory pathway is the antennal lobe. The antennal lobe is well suited for studying the basic principles that underlie processing of olfactory information. The moth is well suited model candidate because of the relative simplicity of the olfactory system. Only four types of neurons constitute the system: Sensory neurons, projection neurons which carry signal information to higher integration centers in the protocerebrum, local interneurons who communicate within the antennal lobe, and centrifugal neurons which modulate the information stream by sending projections from the protocerebrum into the antennal lobe. Most of the antennal-lobe local interneurons is presumed to be GABAergic. The distribution of GABA was investigated through application of a GABA aniserum. Both whole brain preperations and viberatome sections were scanned with a confocal laser microscope. In addition to pure GABA stainin gs, double labelings of pre-stained single neurons and antnnocerebral tracts were carried out. The results were finally analysed and presented through imaging software. The results were largely consistent with earlier reports. In the noctuid moth Heliothis virescens and Helicoverpa assulta the antennal lobe local interneurons are all located in the lateral cellcluster. In addition a few GABAergic projection neuron somata is also located in this cellcluster. Comprehensive immune-reactivity has been found in parts of the antenno-cerebral tracts that are constituted by projection neuron axons. The possible function of GABAergic neural networks in the olfactory system is addressed in the discussion.