Distribution of Dip-allatostatin I-like immunoreactivity in the brain of the locust Schistocerca gregaria with detailed analysis of immunostaining in the central complex.

The distribution and morphology of neurons containing allatostatin-related substances in the brain of the locust Schistocerca gregaria was investigated using an antiserum against Diploptera punctata allatostatin I (Dip-allatostatin I, APSGAQRLYGFGL-amide). In each brain hemisphere, about 550 neurons in the midbrain and 500 neurons in the optic lobe exhibit Dip-allatostatin I-like immunoreactivity, including about eight lateral neurosecretory cells with processes to the retrocerebral complex. All major brain areas except the antennal lobe, the mushroom body, and large parts of the lamina, are innervated by Dip-allatostatin I-immunoreactive processes. Immunostaining in the central complex was studied in detail. The central complex is innervated by more than 260 Dip-allatostatin I-immunoreactive neurons belonging to six different cell types, four sets of tangential neurons and two sets of columnar neurons. These neurons give rise to intense immunostaining in the protocerebral bridge, in several layers of the upper division of the central body, and in the dorsalmost layer of the lower division of the central body. Double-label experiments show colocalization of Dip-allatostatin I- and serotonin-like immunoreactivities in one type of columnar and one type of tangential neurons of the central complex. The similar patterns of Dip-allatostatin I- and galanin message-associated peptide-like immunoreactivities result from cross-reactivity of the anti-galanin message-associated peptide antiserum with Dip-allatostatin I. The results provide further insight into the anatomical and neurochemical organization of the locust central complex and suggest a prominent neuroactive role for Dip-allatostatin I-related peptides in this brain area.