The distribution of and interactions between GABA-immunoreactive and non-immunoreactive processes presynaptic to afferents from campaniform sensilla on the trochanter of the locust leg

Summary Campaniform sensilla on the trochanter of the mesothoracic legs of the locust were backfilled with cobalt salts or horseradish peroxidase for light and electron microscopy. The distribution of the terminal branches of afferent neurones in the thoracic ganglia were described from wholemount preparations and from thick slices through the ganglia. Ultrathin sections of identified branches were processed with GABA antibodies using a post-embedding immunogold technique and examined in the electron microscope. Input synapses were observed on fine varicose branches in all regions of the terminal arborisations close to the sites of afferent output. The major branches neither make nor receive synapses. Seventy-two percent of the input synapses are made by processes immunoreactive for GABA. Immunoreactive and non-immunoreactive processes synapse onto afferent terminals in close proximity. In some instances GABA-immunoreactive processes presynaptic to an afferent are also presynaptic to a non-immunoreactive presynaptic processes strongly suggesting that different presynaptic influences can interact directly with each other.