Nitric oxide synthase (NOS) is the enzyme that produces the gaseous neurotransmitter nitric oxide (NO). Neuronal (n)NOS is a form of NADPH diaphorase (NADPHd), so nNOS can be visualized with NADPHd histochemstry. Miao-Fang Lin Altshuller conducted this procedure on larval, juvenile and metamorphosing Tritia and discovered NADPH diaphorase activity in the neuropils of all ganglia of the larval nervous system. The ganglion in competent larvae with the highest activity was the apical ganglion (AG) (Below Left, yellow arrow), which is lost at metamorphosis. In metamorphosing larvae, NADPHd activity decreases, as demonstrated by the less intense staining in a similar region (Below Right, yellow arrow). Asterisks (*) indicate dying neurons of the AG (Lin and Leise, 1996b). This dramatic change in NADPHd activity led us to speculate that NO might play a role in the control of metamorphosis. This work led directly to pharmacological experiments conducted by Stephan Froggett.
Above Left: Transverse section through part of the central nervous system of a competent larva of Tritia obsoleta displays intense NADPHd staining (at arrow) in the neuropil of the AG. CG, cerebral ganglion.
Above Right: Enlargement of the apical ganglion in a metamorphosing larva. Arrow indicates less intense NADPHd staining of neuropil.
