Genitalic autogrooming in the male cricket, Gryllus bimaculatus DeGeer

The genitalia of the male cricket, Gryllus bimaculatus, is automatically maintained. It is carried out by spontaneous undulation of the scaled membrane consisting of the genital chamber floor. To understand the mechanism of that movement, part of the membrane was cut out and examined in vitro with biogenic amines, and the spike activity of neurons innervating muscle fibers of the membrane was analyzed. The esults indicated that the fragment of the membrane, which showed spontaneous twitching in saline, increased its frequency at 5-HT application. In contrast, mianserin (5-HT antagonist) decreased its occurence. Immunocytochemical study indicated that massive 5-HT-positive branchibgs of one main axon nnervated muscle fibers of the genital membrane. Centrally, one of the motoneurons backfilled with ucifer Yellow through the cut end of the nerve 9v of the terminal abdominal ganglion was determined 5-HT positive. These results suggested that the undulatory movement of the genital membrane for genitalic autogrooming is mediated by 5-HT.