Colocalisation of taurine- with transmitter-immunoreactivities in the nervous system of the migratory locust

The expression of taurine immunoreactivity (TAU-IR) by neurones immunoreactive for octopamine (OA-IR), gamma-aminobutyric acid (GABA-IR), and the C-terminal peptide sequence arginine-phenylalanine (RFamide-IR) was investigated in the migratory locust (Locusta migratoria). TAU-IR is colocalised with OA-IR in the dorsal unpaired median neurones, which are efferent neuroparacrine cells. TAU-IR is not, however, expressed by OA-IR interneurones in the thoracic ganglia and brain. The only other TAU-IR somata found with peripheral axons are the medial neurosecretory cells in abdominal ganglia that project to the neurohaemal organs. These cells exhibit RFamide-IR. The majority of TAU-IR somata in the thoracic abdominal nervous system exhibit GABA-IR. These cells correspond to populations of identified local and intersegmentally projecting inhibitory interneurones. TAU-IR is not, however, exhibited by the well-known GABAergic common inhibitor neurones, which have peripherally projecting axons. This differential distribution of TAU-IR in basically two, functionally different, neuronal subsets (efferent neurosecretory and neuroparacrine cells, inhibitory interneurones) conforms with the concept of taurine acing as a depressive agent to limit excitation during stressful conditions.