Distribution of sulfakinin-like peptides in the central and sympathetic nervous system of the American cockroach, Periplaneta americana (L) and the field cricket, Teleogryllus commodus (Walker)

We describe the distribution of sulfakinin-like neuropeptides in the central and sympathetic nervous system of the American cockroach Periplaneta americana (L.) (Blattodea) and the field cricket Teleogryllus commodus (Walker) (Orthoptera), using an antisulfakinin primary antibody and confocal laser scanning microscopy. We conclude that, in the cockroach, sulfakinin-like material is produced in ten pairs of anterior cells in the pars intercerebralis, as well as two pairs of medial and one major pair of lateral posterior brain cells. This contrasts with findings in other insects, including the cricket, where only the posterior cell groups express sulfakinin-immunoreactive material. Extensive arborization of dendrites containing sulfakinin-like peptides occurs within the neuropile of both species, suggesting a neurotransmitted neuromodulator function. In the cockroach, there is clear evidence of direct distribution of sulfakinin-like peptides along axons to the foregut tissue, and a plexus of retrocerebral nerves is likely to serve as a neurohaemal release site. Neurohaemal release into the dorsal aorta is also postulated. Sulfakinin-immunoreactive axons do not innervate the hindgut in either cockroaches or crickets. Sulfakinin may function as a gut myotropin in the Blattodea, in addition to functioning as a neurotransmitter within the central nervous system. This latter function appears to be general across insect orders, while the neurohaemal distribution and myotropic activity are restricted to the Blattodea.