THE DISTRIBUTION OF NEURONS IMMUNOREACTIVE FOR BETA-TYROSINE HYDROXYLASE, DOPAMINE AND SEROTONIN IN THE VENTRAL NERVE CORD OF THE CRICKET, GRYLLUS-BIMACULATUS

The cellular localization of the biogenic amines dopamine and serotoni n was investigated in the ventral nerve cord of the cricket, Gryllus b imaculatus, using antisera raised against dopamine, P-tyrosine hy drox ylase and serotonin. Dopamine- (n less than or equal to 70) and seroto nin-immunoreactive (n less than or equal to 120) neurones showed a seg mental arrangement in the ventral nerve cord. Some neuromeres, however , did not contain dopamine-immunoreactive cell bodies. The small numbe r of stained cells allowed complete identification of brain and thorac ic cells, including intersegmentally projecting axons and terminal arb orizations. Dopamine-like immunostaining was found primarily in pluris egmental interneurones with axons descending to the soma-ipsilateral h emispheres of the thoracic and abdominal ganglia. In contrast, seroton in-immunostaining occurred predominantly in interneurones projecting v ia soma-contralaterally ascending axons to the thorax and brain. In ad dition, serotonin-immunoreactivity was also present in efferent cells and afferent elements. Serotonin-immunoreactive, but no dopamine-immun oreactive, varicose fibres were observed on the surface of some periph eral nerves. Varicose endings of both dopamine- and serotonin-immunore active neurones occurred in each neuromere and showed overlapping neur opilar projections in dorsal and medial regions of the thoracic gangli a. Ventral associative neuropiles lacked dopamine-like immunostaining but were innervated by serotonin-immunoreactive elements. A colocaliza tion of the two amines was not observed. The topographic representatio n of neurone types immunoreactive for serotonin and dopamine is discus sed with respect to possible modulatory functions of these biogenic am ines in the central nervous system of the cricket.