SulfonesPurinesPiperazinesPhosphodiesterase InhibitorsPhosphodiesterase 5 Inhibitors3',5'-Cyclic-GMP PhosphodiesterasesErectile DysfunctionCyclic Nucleotide Phosphodiesterases, Type 5Penile ErectionHomosexuality, MaleMethamphetamineVasodilator AgentsCyclic GMPGeorgiaUnsafe SexRisk-TakingSexual BehaviorProchlorococcusChromosome MappingMonoiodotyrosineDiiodotyrosineCrosses, GeneticMice, CongenicChromosomes, Mammalian