The brain melanocortin system regulates numerous physiological functions and kinds of behavior. The agouti protein inhibits melanocortin receptors in melanocytes. The (A ) mutation puts the gene under the control of the gene promotor and causes the agouti protein expression in the brain. In the present article, we investigated the effects of the A mutation on brain mRNA levels of , , and melanocortin-related genes such as , and their relationship to behavior. The experiment was performed on 6-month-old males and females of A /a and a/a (control) mice. Anxiety and obsessive-compulsive behavior were studied in elevated plus-maze and marble- burying tests. The mRNA levels were quantified by qPCR. A mutation caused anxiety in males and obsessive-compulsive behavior in females. Positive correlation between and genes mRNA levels were shown in the hypothalamus, hippocampus, and frontal cortex in A /a mice. Reduced RNA concentrations of and genes were found respectively in the hypothalamus and frontal cortex in A /a males. The gene expression positively correlates with mRNA concentrations of the gene in the hypothalamus and the gene in the hypothalamus and frontal cortex. Possible association of obsessive-compulsive behavior with reduced , or gene expression is suggested.