Nitric oxide as a putative messenger molecule in the crayfish olfactory midbrain

NADPH-d histochemistry was used to investigate presumptive nitric oxide synthase (NOS)-containing neurons in the crayfish olfactory midbrain. Three anatomically different types of local olfactory interneurons exhibiting NADPH-d activity were observed: two pairs of large interneurons as well as positively stained globuli cells. Branches derived from the large interneurons were confined to the ipsilateral olfactory lobe and accessory lobe, but only a few branches innervated the olfactory lobe glomeruli. Local field potential recordings on the olfactory lobe showed that administration of SNP or SIN-1 (10-4 M) into the brain had reversible inhibitory effects on electrically-evoked responses of unidentified neuronal cell populations.