Fig. 1.

A time line of brain development in Homarus, emphasizing the developmental sequence in the olfactory pathway. Numbers indicate percentage development, from fertilization (0%) to hatching (100% development); juvenile and adult stages complete the range. Three assays related to the nitric oxide (NO) pathway were used: immunocytochemical localization of nitric oxide synthase (NOS) and cGMP (A); immunocytochemical labeling for synapsin and serotonin to monitor morphogenic changes (B); 5-bromo-2′-deoxyuridine (BrdU) labeling to assess the numbers of cells in S phase (C). To accomplish these studies, NO and cyclic 3,5 guanosine monophosphate (cGMP) levels also were manipulated using pharmacological agents (sodium nitroprusside [SNP], S-Nitroso-N-acetyl-D,L-penicillamine [SNAP], NG-Nitro-L-arginine [L-NAA], isobutylmethylxanthine [IBMX]) and by antennular ablations. The timing of the immunocytochemical and pharmacological experiments are noted below the timeline at the developmental stage when they were performed.