NADPH-diaphorase histochemistry in the terminal abdominal ganglion of the crayfish

Nitric oxide (NO) has an important modulatory role on the processing of sen sory signals in vertebrates and invertebrates. In this investigation we stu died the potential sources of NO in the terminal abdominal ganglion of the crayfish, Pacifastacus leniusculus, using NADPH-diaphorase (NADPHd) histoch emistry, with NADPHd acting as a marker for NO synthase (NOS). In the termi nal ganglion a mean of 27 strongly labelled NADPHd-positive cell bodies wer e found, and of these 8% occurred in three regions located in antero-latera l, central and posterior parts of the ganglion. Ventral and antero-ventral commissures as well as specific dorsal and ventral areas of the dendritic n europil showed positive staining. Intense labelling was seen in the ventro- medial tract, and in the connective between the terminal ganglion and the 5 th abdominal ganglion. In addition, some motor neurones and neurones with b ranches in the sensory commissures were NADPHd positive. Our finding that N ADPHd-positive cells occur in consistent patterns in the terminal abdominal ganglion implies that NO may have a role in mechanosensory processing in t he crayfish.