Xenobiotic shown below is a pesticide commonly used in developing countries, but is largely banned in the United States because of its potent neurotoxic effects. To mediate these neurotoxic effects, the pesticide must be able to cross the blood brain barrier. Inspection of the chemical/physiochemical properties of the pesticide suggest it would not readily diffuse across membranes and be absorbed through the skin or GI tract, much less cross the blood brain barrier. To understand how the pesticide can distribute to the brain, the following experiments were performed. Mice were fed the pesticide and then sacrificed 24 hr later. Their brain tissue is stained with an antibody that binds the toxin and gives a green color. The results of the experiment are shown in the immunostain below. Panel (a) is no pesticide administered and Panel (b) is with the pesticide. Panel [c] is the same dose of pesticide as (b) with the addition of a large concentration of the amino acid arginine.
Explain why inspection of the structure of the pesticide would suggest it would not accumulate in the brain. What does the inhibition of pesticide accumulation in the brain by the amino acid arginine suggest about the mechanism of transport of the pesticide (limit 5-6 sentences)?