There is a U-curve phenomenon for phenylalanine and dopamine. The effective dose was 200mg/kg in rats, which translates to about 2.5g for a human in a single dose. More than that inhibits dopamine release. So, for the people doing the serotonin depletion protocol with BCAA a good starting dosage would be 5g BCAA and 2.5g of Phe. You can probably repeat that dose safely every 6 hours.
http://www.ncbi.nlm.nih.gov/pubmed/3211373
http://www.ncbi.nlm.nih.gov/pubmed/3211373