Inhibitory effect of cyclic guanosine 3',5'-monophosphate (cGMP) on the afferent resting activity in the cephalopod statocyst.

The effects of exo- and endogenous cGMP on the resting activity (RA) of afferent crista fibers were studied in isolated preparations of the statocysts of the cuttlefish Sepia officinalis and the squid Sepioteuthis lessoniana. Bath application of the membrane-permeable cGMP analogs 8-bromo-cGMP (B-cGMP) and N(2),2'-o-dibutyryl 3', 5'-cyclic guanosine monophosphate (dB-cGMP), and of the selective inhibitor of cGMP-phosphodiesterase zaprinast (ZAP), caused an inhibition of RA. The inhibitory effects of B-cGMP and dB-cGMP remained when the preparation was pre-treated with: (i) the guanylate cyclase inhibitors 1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-1-one (ODQ) or cystamine (CYS); (ii) the adenylate cyclase inhibitors nicotinic acid (NIC-A), 2',3'dideoxyadenosine (DDA), or MDL-12330A (MDL); (iii) the guanylate cyclase inhibitor methylene blue (M-BLU) and the adenylate cyclase inhibitor MDL combined; or (iv) the nitric oxide (NO) synthase inhibitors N(G)-nitric-L-arginine methyl ester HCl (L-NAME) or N(G)-nitro-L-arginine (L-NOARG). These data indicate that cGMP, as an intracellular messenger, has a tonic inhibitory effect on the RA of afferent crista fibers in cephalopod statocysts.