The nitric oxide signaling molecule produced by the neuronal Nos1 gene is widely expressed, affecting diverse systems. The knockout of this gene has been shown to affect such normal characteristics as cognition and behavior, long-term memory, cortical development, colonic motility, skeletal muscle contraction, ovarian cycle regulation, cardiac/cardiovascular function, and even sensitivity to Anthrax lethal toxin. Heterozygous mice are viable and fertile, while some lethality is seen in homozygotes due to stomach hypertrophy. Homozygotes have enlarged stomachs with hypertrophy of the pyloric sphincter and the circular muscle layer (Huang et al., 1993). Western blots of brain homogenates from homozygous mutant mice showed no detectable protein. However, splice variants are expressed and variable low levels of NOS activity are seen in the brain. Homozygous males are reported to be more aggressive than normal wildtype siblings although this has not been confirmed in The Jackson Laboratory colony.
