GABAergic synaptic connections in mushroom bodies of insect brains

Distribution and synaptic connections of GABA fibres in neuropil parts of the mushroom bodies in brains of crickets (Gryllus bimaculatus) and bees (Apis mellifera) were investigated by immuno-light and electron microscopy. In the inner calyx neuropil of cricket mushroom bodies, GABA fibres are pre- and post-synaptically connected with proximal Kenyon cell dendrites, indicating synaptic contacts differing from those of the Kenyon cell dendritic tips in the peripheral microglomeruli of the calyces. A more complex interaction of GABAergic fibres and Kenyon cell dendrites than assumed before is shown. In the mushroom bodies of bees, dendritic like strata of GABA fibre projections contribute to the subcompartmental layers of the vertical lobe. The GABA-immunostained fibre profiles exhibit pre- and postsynaptic sites as well and can therefore not be considered purely postsynaptic dendritic neuron parts. The micromorphology and synaptic contacts of the dendrites and dendritic like arborizations are seen as parts of local circuits within mushroom bodies.